Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining

Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining Amit Dodmani, Sathyan Subbiah, A. Senthil Kumar This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3878526/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 14 Jul, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted 5 You are reading this latest preprint version Abstract Achieving a smooth surface finish in optical components by machining requires wear resistant sharp cutting tools. Single crystal diamond as a cutting tool material has met this requirement so far, but at a cost disadvantage. An economical alternative, such as alumina single crystal(sapphire), with sufficient hardness, wear resistance, and chemical inertness, is explored in this work. A sapphire cutting tool with a zero rake, seven-degree clearance, and edge radius of about 430 nm is fabricated using lapping, polishing, and chemical mechanical polishing processes. The performance of the tool was evaluated via orthogonal cutting of OFHC copper, free-cutting brass, Al6061, and Stavax ESR steel. The influence of parameters, such as cutting speed and uncut chip thickness, on surface finish, cutting force, thrust force, friction coefficient, and chip morphology are analyzed. It was observed that the sapphire tool generates surfaces with average roughness ranging from 10–40 nm on copper and aluminum alloys. However, minimal tool wear observed in the machining of copper alloys and excessive in the aluminum alloy and Stavax. Furthermore, built-up edge was significant in Al6061, and edge chipping was dominant in Stavax during machining. Sapphire is a suitable alternative cutting tool material for machining copper alloys. Sapphire orthogonal cutting ultra-precision machining OFHC Copper Free cutting brass Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 Figure 20 Figure 21 Figure 22 Figure 23 Figure 24 Figure 25 Figure 26 1 Introduction Ultra-precision machining generates optical components with smooth surfaces and precise tolerances using single-crystal diamond (SCD) tools[ 1 ]. To attain an optical quality surface finish, a smooth shearing/cutting action minimizing surface defects such as feed marks, undulations, and chatter marks is needed. This requires small uncut chip thickness with even smaller cutting-edge radius ranging from tens of nanometers to a few hundred nanometers. To achieve such a sharp edge radius, materials that are available in single crystal form and in large sizes are the ideal choice for the cutting tool. Diamond is one such material which due to its mechanical properties can also retain its sharp cutting-edge radius over longer periods of machining. However, SCD material and its processing into cutting tools with the desired geometry and edge sharpness are expensive. Hence, an alternative single crystal cutting tool material would be desirable from an economic point of view. There are several materials that are available in bulk form as single crystals and although not as hard as diamond but are several times harder than the workpiece materials subjected to ultra-precision machining[ 2 ]. Sapphire, or single crystal alumina, is one such crystal with a hardness of 22 GPa available in bulk sizes, and costs 40 times less than diamond[ 3 ]. Sapphire has exceptional properties, such as optical transparency, high wear resistance, hardness, refractoriness, and chemical inertness, and hence is widely used in various industries, including optics, semiconductors, watchmaking, and medical industries, and so is readily available. Hence, sapphire can be explored as an alternate cutting tool material in ultra-precision machining. Sapphire, being transparent, has been used as a cutting tool to better observe and visualize the mechanics of machining. Madhavan et al.[ 4 ] used sapphire’s optical transparent property to observe the tool-chip interface in-situ while machining copper, aluminium and lead with sapphire tool. Hunag et al.[ 5 ] reported on an in-situ cutting fluid film measurement method during machining using sapphire tool. Using sapphire’s stress birefringent property Bagchi et al.[ 6 ] studied the stress distribution at the tool-chip interface while machining brass and steel with a sapphire cutting tool. Sapphire's transparency has also been exploited to allow laser energy to reach the tool-chip contact zone. Park et al.[ 7 ] performed direct laser assisted machining of bulk metallic glass using sapphire cutting tool. There is one study reported on the use of sapphire for optical component machining. Oishi[ 8 ] used sapphire cutting tool for mirror cutting of the A2014 aluminium but reported occurrence of built-up edge formation due to affinity of aluminium present in both materials. In all the above studies involving sapphire as a cutting tool, there is no mention of how the sapphire cutting edge was fabricated and what cutting edge sharpness can be achieved in sapphire tools. Fabricating cutting tool from sapphire involves creating smooth planar and non-planar surface regions (rake, flank) and cutting edges where the surfaces meet. While there are many reports of polishing bulk surface regions of sapphire wafers, none that report formation of controlled geometry sharp edges formed by two smooth meeting surfaces. Presently sapphire wafers are subjected to lapping, polishing, and chemical mechanically planarization (CMP) to achieve a surface finish up to a few angstroms for growing high-quality gallium nitride (GaN) thin film. Parks et al.[ 9 ] reported lapping of sapphire wafers with #400 boron carbide (BC) abrasives on a cast-iron plate, observed a high material removal rate of 5–10 µm/min and achieved a surface roughness of 400–600 nm. Taekyung et al.[ 10 ] used Kemet copper lap having grooves to hold the diamond slurry for longer durations, reported a low material removal rate of 0.5–1 µm/min, this improved the surface roughness of the wafer and obtained 10–20 nm Ra. Aida et al.[ 11 ] reported chemical mechanical polishing of sapphire using poly urethane pad and colloidal silica as the slurry, achieved an excellent surface finish of 10–20 Å Ra and the material removal rate was very low 50 nm/hr. These series of steps can be used to form the rake and flank faces of a sapphire tool. It is however not clear how sharp and smooth will be the edge that forms from the meeting of these two surfaces. This study aims to form a sharp cutting edge on a sapphire single crystal tool and evaluate its potential as a cutting tool for ultra-precision machining. We developed a setup to fabricate a sharp single crystal sapphire tool with zero rake angle, a seven-degree clearance angle, and a straight cutting edge of 6 mm. The flank face, with a seven-degree clearance angle, is carved out using lapping by BC slurry on a cast iron plate. Subsequently, diamond slurry on a copper lap is employed to remove lay marks from the previous step. Finally, the CMP process is employed to enhance the sharpness of the cutting edge further. The edge sharpness was characterized using an edge reversal method using split block method[ 12 ]. Orthogonal cutting experiments were performed using these sharp sapphire tools in an ultra-precision machining lathe. The workpiece materials selected were oxygen-free high conductivity (OFHC) copper, free-cutting brass, Al 6061 and Stavax ESR because these are commonly used materials for metal optics. We investigated the effect of cutting parameters, such as cutting speed and uncut chip thickness, on surface finish, cutting force, thrust force, friction coefficient, and chip morphology while using sapphire tools. 2 Methodology and experimental setup 2.1 Fabrication of the sapphire cutting tool A sapphire cutting tool with 0° rake angle, 7° clearance angle and straight cutting edge of width 5 mm is carved out from the cylindrical sapphire crystal having 12 mm diameter and 6 mm thickness as shown in Fig. 1 a. The top flat surface of the cylindrical crystal has a surface finish of 5Å, this surface is chosen as rake face and the curved surface is lapped to create the flank face. This conversion from a sapphire crystal to a sapphire tool involves lapping the cylindrical face until a straight cutting edge of 5 mm width is achieved. During the lapping process, material removal occurs as abrasive particles in a slurry traverse and scratch the crystal's surface in the presence of relative rotational motion between the sapphire crystal and the platen, all while pressure is applied to the crystal. The sapphire tool is secured in a copper block as depicted in Fig. 1 c. This fixture serves the dual purpose of maintaining the crystal's stability without causing any positional disturbance during the lapping and since copper being a soft material, applying minimal pressure to prevent the initiation or propagation of cracks that could lead to the breakage of the sapphire crystal. The copper block is oriented at a 7° to the vertical plane, to generate a flat face with a clearance angle of 7°. This assembly is further held in a custom-made aluminum adapter, which is subsequently affixed to the CMP head as illustrated in Fig. 1 b. When the load is applied through the CMP head onto the crystal against the lapping material, material removal occurs, resulting in the generation of a sharp cutting edge with a clearance angle of 7° as shown in Fig. 1 e. The fabrication of the sapphire tool involves a three-step process comprising lapping, polishing, and chemical mechanical polishing (CMP) as shown in Fig. 2 . Initially, lapping is performed using boron carbide abrasives on a cast iron lap as illustrated in Fig. 2 a. This step prioritizes high material removal, utilizing larger abrasive particles to achieve an elevated material removal rate. Given the goal of transforming the cylindrical sapphire crystal into a sapphire tool with a straight cutting edge of 5 mm width, high material removal rate is essential. However, this lapping process results in increased surface roughness due to its aggressive material removal, causing fracturing and chipping which leads to poor edge sharpness. To address this, in the second step of the process, diamond slurry is applied using a spiral groove copper lap for polishing as shown in Fig. 2 b. A lapping platen made of resin-copper, created by sintering copper powder and resin, is utilized. This Cu-resin plate demonstrates a higher material removal rate (MRR) compared to other metal-resin plates. The grooves in the plate play a crucial role by spontaneously refreshing the slurry, clearing debris generated during the process, and increasing the surface area of the platen. While this step has a lower material removal rate, i.e., a few microns per minute, it effectively reduces surface roughness on the flank face and eliminates lay marks from the previous process. This contributes to an enhancement in edge quality and overall sharpness of the sapphire tool. To further enhance the surface finish on the flank face and cutting-edge sharpness chemical mechanical polishing (CMP) process is employed in the final step as depicted in Fig. 2 c. CMP serves as the final treatment, ensuring atomic-level surface flatness by eliminating damage on or near the surface caused during mechanical polishing. The polishing of sapphire using colloidal silica is thought to involve a chemical reaction that results in aluminum silicate dihydrate formation. Simultaneously, the continually forming hydrated surface layer is removed by the spherical colloidal silica particles, contributing to the desired surface quality and overall sharpness of the sapphire tool. The Bruker TriboLab CMP machine was employed in the fabrication of sharp sapphire tool as illustrated in Fig. 3 . The machine is specifically designed for chemical mechanical polishing of silicon wafers, which are commonly utilized in semiconductor devices. The machine has a servo-controlled precision loading stage, integrated high-speed/high-torque upper and lower rotational drive motors with adjustable platen and wafer head rotation speed ranging from 1 to 500 RPM, and a wafer head load range of 4 to 400 N. Incorporates a programmable peristaltic pump to regulate the slurry flow rate. Renowned for its robustness, high repeatability, and minimal vibration, the TriboLab CMP machine offers the flexibility to formulate custom recipes by adjusting polishing load, lap wheel rotational speed and slurry rate. These capabilities make the TriboLab CMP machine highly effective for the fabrication of sharp sapphire tools. Table 1 Sapphire tool fabrication process parameters Steps Lap wheel Slurry Slurry rate Load Velocity Head Oscillation Total time 1 Cast iron 300 gm BC + 150 ml Suspension + 3L DI water 30 ml/min 12 N 50 cm/s 0 25 min 2 Spiral groove copper 3 µm diamond slurry 8 ml/min 10 N 50 cm/s 0 15 min 3 Polyurethane Pad Colloidal silica 20 ml/min 8 N 50 cm/s X-axis 1 mm 20 cycles/min 60 min Table 1 contains the process parameters used for fabrication sapphire tool fabrication. The initial stage involves lapping the sapphire using boron carbide slurry on a cast iron lap with a lapping load of 12 N. The boron carbide slurry is created by mixing 250 grams of #400 boron carbide with 3 liters of de-ionized water and 150 ml of suspension. The slurry rate is consistently maintained at 30 ml/min, resulting in the formation of a sapphire tool with a 6mm width cutting edge and a 7° clearance angle. In the second step, polishing is carried out using 3µm diamond slurry on a spiral-grooved copper lap with a 10N load for 15 minutes. Due to the grooves facilitating the replenishment of abrasive particles in the slurry, the slurry rate is intentionally kept low at 8 ml/min. The final step, chemical mechanical polishing (CMP), is executed using colloidal silica on a polyurethane pad with a 10 N load. Given the very low MRR in this process, the duration is extended to 60 minutes. The slurry rate is maintained at a constant 20 ml/min, and the pH of the slurry is set at 10.5. To eliminate any polishing marks, the CMP head undergoes oscillation of traverse at 1 mm in the X direction with 20 cycles per minute. 2.2 Edge radius measurement of Sapphire tool The indentation experiments were conducted in an ultraprecision CNC machining center (KERN Microtechnik- Evo), having a positioning resolution of 100 nm. Two 99.9.% pure copper blocks of size 10 mm x 5 mm x 6 mm were prepared from grinding and polishing the surfaces. The mating surfaces have a surface roughness of 40 nm Ra. The flatness of the copper side surface is 3.7 µm on a 10 mm x 7 mm surface. The surfaces of the copper samples were cleaned with acetone and held together in the precision vise. Figure 4 displays the experimental setup. The precision vise was mounted on the Kistler Minidyn dynamometer. The edge radius of the sapphire tool was measured using the edge reversal technique, as reported by Dodmani et al.[ 12 ] Cutting edge of the tool was indented onto the surface of a split copper block. The two blocks were then separated, and the cross section of the cutting-edge profile was observed in a scanning electron microscope (SEM) to measure the edge radius of the sapphire tool. 2.3 Orthogonal cutting setup Orthogonal cutting (tube end turning) is performed in Toshiba ULG-100C (H³) an ultra-precision aspheric grinder. The machine has positioning resolution of 1 nm in the X, Y and Z-axes and is equipped with aerostatic bearing for work spindle with vacuum chuck. A cylindrical workpiece is fabricated, having three concentric channels with a width of 0.5 mm, located at diameters of 42 mm, 28 mm, and 14 mm as shown in Fig. 5 . Table 3 displays the materials selected for the workpiece and their respective chemical compositions. The workpiece is secured on to a 100 mm diameter flat disc held by vacuum chuck. Figure 5 displays the experimental setup of orthogonal cutting in the machine. Rough cutting passes are performed using CBN tool to make the surface flat and set zero reference. The sapphire cutting tool is rigidly held in a copper block which is mounted on EN8 Tool holder that is attached directly to the Kistler Type 9256 three-component piezoelectric force dynamometer as illustrated in Fig. 5 . The tool’s cutting edge is positioned 500 µm away from the zero reference prior to machining to ensure the gradual engagement of tool’s cutting edge with workpiece. The orthogonal cutting parameters like cutting speeds and uncut chip thickness are shown in Table 2 . The experiments are performed by maintaining a constant uncut chip thickness while varying the cutting speed, and alternatively keeping the cutting speed constant while varying the uncut chip thickness. The effect of cutting parameters on surface finish, cutting force, thrust force, friction coefficient and chips are studied. Table 2 Orthogonal cutting conditions Workpiece Material OFHC Copper, Free cutting brass, Al 6061, and Stavax ESR Cutting tool Single crystal alumina (Sapphire) Rake angle 0° Clearance angle 7° Edge radius 432 nm Uncut chip thickness 0.1 µm, 0.5 µm, 1 µm, 2 µm, 3 µm Cutting velocity 1 m/s, 1.5 m/s, 2 m/s, 3 m/s Table 3 Chemical composition of workpiece materials Workpiece Material Chemical Composition OFHC Copper – C10200 99.9% Cu Free Cutting Brass -C38500 59% Cu, 37% Zn, 3.5% Pb Al 6061 97.9% Al, 0.6% Si, 1.0% Mg, 0.2% Cr, 0.28% Cu Stavax ESR steel 84.47% Fe, 13.6% Cr, 0.75% Si, 0.5% Mn, 0.38% C, 0.3% V 3 Result and discussions 3.1 Sapphire tool fabrication and edge radius measurement Figure 6 presents the schematic and SEM images of the flank face, cutting edge, and the indentation profile of the sapphire tool after each stage of lapping, polishing, and CMP. Initially, the sapphire tool underwent lapping using #400 boron carbide abrasives on a cast iron lap, resulting in a material removal rate of 10 µm/min. After this step, a sapphire tool featuring a 6mm width cutting edge and a 7° clearance angle was successfully fabricated. Figure 6(step1-b) illustrates the SEM image of the cutting edge that appears blunt. This is evident from the Fig. 6(step1-c) that depicts the SEM image of the indentation profile of sapphire tool, the edge radius measured was 13.5 µm. Hence, the need for further refinement in the polishing process to fabricate the sharp sapphire tool with lesser cutting-edge radius. Subsequently, following the initial lapping process, the tool underwent polishing using a 3 µm diamond slurry applied on a spiral groove copper. The material removal rate in this process was 0.5 µm/min. The flank surface finish experienced a significant improvement, observed a decrease in surface roughness from 170 nm R a to 13.2 nm R a and the same is evident from Fig. 6(step2-a). The sharpness of the cutting tool is dependent on the edge chipping[ 13 ]. Higher MRR tends to cause increased chipping, consequently reducing sharpness and vice versa. The lapping process has high MRR compared to polishing process therefore, the sharpness of cutting edge improved in the polishing process as observed in Fig. 6(step2-b). From the sapphire tool’s indentation profile as shown in Fig. 6(step2-c), the edge radius measured was 2.8 µm. To further eliminate polishing marks on the flank face of the sapphire tool and improve the sharpness the CMP process was employed. The flank face’s surface finish enhanced from 13.2 nm R a to 2 nm R a as shown in Fig. 6(step3-a). The MRR of the CMP process is in few nanometers per minute which is least among polishing and lapping. Hence, least edge chipping was observed in this process which resulted in a sharp cutting edge as depicted in Fig. 6(step3-b). From the sapphire tool’s indentation profile as shown in Fig. 6(step3-c), the cutting-edge radius measured was 430nm. 3.2 Performance of sapphire tool while machining OFHC copper Thrust forces and cutting forces during the orthogonal cutting are measured from Kistler Type 9256 three-component piezoelectric force dynamometer. Figure 7 a displays the plot of cutting and thrust force against cutting speed, at a constant UCT of 1 µm. Cutting force is greater than the thrust force indicating material removal is taking place in shear mode as UCT 1 µm. However, it is observed that the cutting force increases with an increase in cutting speed. Due to its high ductility and low yield strength, OFHC copper displays a greater effect of strain rate hardening with an increase in cutting speed[ 14 ], rather than thermal softening. Figure 7 b displays the plot of cutting and thrust force against UCT, at a constant cutting speed of 1 m/s. As the UCT is increased from 0.1 µm to 3 µm, both the cutting force and thrust force increase due to higher material removal rate. Ploughing material removal mode is predominant when UCT is less than 0.5 µm, as the thrust force is greater than the cutting force. However, at UCT greater than 0.5 µm, shear material mode dominates, as the cutting force becomes greater than the thrust force[ 15 ]. Consequently, increasing UCT results in improved surface finish. The apparent coefficient friction (µ) between the rake face of the tool and chip is obtained from the Eq. 1 [ 16 ]. Where, \({F}_{c }\) is cutting force, \({F}_{t }\) is thrust force and α is the effective rake angle. $$\mu = \frac{{F}_{t}+ {F}_{c }\text{tan}\alpha }{{F}_{c}- {F}_{t }\text{tan}\alpha }$$ 1 The effective rake angle (α) is the angle between the vertical axis and the tangent to the contact point between the cutting tool and the UCT as depicted in Fig. 8 . When the uncut chip thickness is less than the edge radius, the effective rake angle is obtained from Eq. 2 . Where, α is the effective rake angle, t is the uncut chip thickness and \({r}_{e}\) is the cutting-edge radius of the Sapphire tool. $$\alpha ={\text{sin}}^{-1}\frac{({r}_{e}-t)}{{r}_{e}}$$ 2 When the UCT is 100 nm, which is below the cutting-edge radius of 432 nm, the application of Eq. 2 results in an effective rake angle of 50°. In all other cases where UCT exceeds the edge radius i.e., 432 nm the effective rake angle (α) becomes zero degree because the rake angle of the Sapphire tool is also zero. The values of α are substituted in the Eq. 1 accordingly to determine the apparent coefficient of friction (µ). Figure 9 a displays the relationship between coefficient of friction and cutting speed (m/s), plotted for a UCT of 1 µm. It is observed that the friction coefficient decreases from 0.88 at 1 m/s cutting speed to 0.815 at 2 m/s cutting speed and further increases to 0.822 at 3 m/s. The average surface roughness R a on the machined surface across the cutting direction is measured using Olympus confocal microscope. Figure 9 b displays the relationship between average surface roughness R a (nm) and cutting speed (m/s), plotted for a UCT of 1 µm. It is observed that the surface roughness tends to decrease from 43 nm to 12 nm as the cutting speed is increased from 1 m/s to 2 m/s. This is due to the decrease in the friction coefficient from 0.88 at 1 m/s cutting speed to 0.815 at 2 m/s as displayed in Fig. 9 a. The reduction in the coefficient of friction causes less adhesion between the tool rake face and the chip thus improving the chip separation and achieving better surface finish on the surface. Subsequently, there is a slight increase in average surface roughness to 14 nm at a cutting speed of 3 m/s. This can be attributed to an increase in the friction coefficient from 0.8148 at 2 m/s to 0.822 at 3 m/s as shown in Fig. 9 a. As the adhesion between tool and chip increases it deteriorates the chip separation hence increase in the surface roughness. Figure 10 a illustrates the plot of the apparent coefficient of friction plotted against UCT (µm) for a constant cutting speed of 1 m/s. It is observed that the friction coefficient decreases from 3.14 at 0.1 µm UCT to 0.78 at 2 µm UCT and further increases to 0.805 at 3 µm UCT. Figure 10 b displays the relationship between average surface roughness R a (nm) and UCT (µm), plotted for a constant cutting speed of 1 m/s. The surface roughness R a decreased from 69 nm to 9 nm with increase in UCT from 0.1 µm to 2 µm. This is due to the decrease in the apparent friction coefficient from 3.14 at 0.1 µm UCT to 0.78 at 2 µm because the material removal mode changes from ploughing at 0.1 µm to shearing at 2 µm. Consequently, the average surface roughness increased to 36 nm at 3 µm UCT as friction coefficient increased to 0.805. As, the increase in depth of cut caused increased the tool-chip contact length increasing the adhesion as result of which poor surface finish on workpiece surface[ 17 ]. After machining OFHC copper the chips are collected and observed under a scanning electron microscope. The use of sapphire tool used for machining OFHC copper produced small, discontinuous, and straight chips which indicates the material removal is occurred through fracture. Figure 11 displays the chip morphology at cutting speeds of 1m/s and 3m/s. It is observed that at the higher speed of 3m/s, the edges of the chips are torn, suggesting that brittle fracture is the dominant mechanism due to strain rate hardening. Figure 12 displays the chip morphology at UCT of 0.1 µm and 3 µm. It is seen that at UCT 0.1 µm chips produced are long and continuous implies that material removal is through plastic deformation than fracture, because the UCT is less than the cutting-edge radius. On contrary at UCT 3 µm chips are short, thick, and discontinuous because fracture material removal mode is dominant as UCT is much greater than cutting-edge radius. Figure 13 displays the sapphire tool’s cutting edge after machining OFHC copper with cutting distance of 10 m. From the image it is clear that tool wear is negligible because the sapphire being many times harder than the copper. Hence, sapphire can be considered as tool material for ultraprecision turning of the OFHC copper. To summarize the performance of sapphire tool while machining OFHC copper. It was observed that increasing the cutting speed from 1 m/s to 3 m/s resulted in an overall increase in both the cutting and thrust forces. This can be attributed to the strain rate hardening behaviour of OFHC copper due to its high ductility and low yield strength. Evidently the chips generated at 3 m/s had more torn edges compared to those produced at 1 m/s indicating presence of brittle fracture due to the strain hardening. The cutting force value increased significantly than the thrust force as the cutting speed increased from 1 m/s to 3 m/s indicating shear mode of fracture being dominant. Therefore, a corresponding reduction in surface roughness was observed, decreasing from 43 nm to 14 nm. As the UCT increased from 0.1 µm to 3 µm, there was a raise in both the cutting force and thrust force due to the greater amount of material being removed during the machining process. Initially, up to a UCT of 0.5 µm, the thrust force exceeded the cutting force as the UCT value approached the edge radius. However, once the UCT exceeded 0.5 µm, the cutting force surpassed the thrust force. Consequently, at a UCT of 0.1 µm, the chips produced exhibited a straight and continuous morphology, indicating that plastic deformation was the dominant mechanism of material removal. On the other hand, at a UCT of 3 µm, the chips were shorter, thicker, and discontinuous, indicating that fracture was the predominant mode of material removal. This was reflected the surface roughness, where an increase in UCT from 0.1 µm to 3 µm resulted in a decrease in average surface roughness (R a ) from 69 nm to 36 nm. 3.3 Performance of sapphire tool while machining of free cutting brass The cutting and thrust forces (N) against cutting speed (m/s) for a constant UCT (uncut chip thickness) of 1 µm are shown in Fig. 14 a. It is notable that the thrust force exceeds the cutting force, which is attributed to the high ductility and severe plastic deformation exhibited by brass during machining. Subsequently, a decrease in both thrust and cutting forces is observed as the cutting speed is increased from 1 m/s to 3 m/s. This decrease can be attributed to the effect of thermal softening, which is more prominent in free cutting brass due to its high ductility and plasticity[ 19 ]. Figure 14 b displays the plot of cutting and thrust force (N) against UCT (µm), at a constant cutting speed of 2 m/s. It can be observed that the cutting force continuously increases as the UCT is increased from 0.1 µm to 3 µm, due to the corresponding increase in material removal rate. Additionally, it is noted that until a UCT of 2 µm, the thrust force exceeds the cutting force, suggesting that ploughing material removal mode is dominant during this range. However, after the 2 µm UCT mark, the cutting force becomes greater than the thrust force, indicating the dominance of the shear material removal mode. Consequently, an increase in UCT leads to an improvement in surface finish. Figure 15 a illustrates the plot of apparent coefficient of friction against cutting speed for constant uncut chip thickness of 1 µm. The friction coefficient declines from 2.18 at 1 m/s cutting speed to 1.28 at 3 m/s cutting speed. The average surface roughness R a on the machined surface across the cutting direction is measured. Figure 15 b displays the relationship between average surface roughness R a (nm) and cutting speed (m/s), plotted for a UCT of 1 µm. It is observed that the surface roughness tends to decrease from 91 nm to 38 nm as the cutting speed is increased from 1 m/s to 3 m/s. The decline in the roughness is due to the decrease in the friction coefficient from 2.18 at 1 m/s cutting speed to 1.28 at 3 m/s as displayed in Fig. 15 a. Thermal softening is more prominent in the machining of free cutting brass with an increase in the cutting speed that leads to decrease in apparent coefficient of friction. The chip separation becomes easy at higher cutting speeds as a result we achieved better surface finish. Figure 16 a displays the plot of apparent coefficient of friction plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s. The friction coefficient declines from 4.35 at 0.1 µm UCT to 0.59 at 3 µm UCT. Figure 16 b displays the relationship between average surface roughness R a and UCT, plotted for a constant cutting speed of 2 m/s. The surface roughness R a decreased from 71 nm to 34 nm as UCT increases from 0.1 µm to 3 µm. This reduction in roughness is due to the decrease in the apparent friction coefficient from 4.35 at 0.1 µm UCT to 0.59 at 3 µm as shown in Fig. 16 a. The change in friction coefficient is a result of shift in material removal mode ploughing at 0.1 µm to shearing at 3 µm. The interaction between the tool and chip changes from sticking to sliding. After machining free cutting brass, the chips are collected and observed under a scanning electron microscope (SEM). The use of sapphire as a tool material in machining free cutting brass results in the production of continuous, and ribbon-like chips, which suggests that material removal occurs primarily through plastic deformation. Figure 17 shows the chip morphology at cutting speeds of 1m/s and 3m/s. It is noted that the curl of the chip increases at the higher speed of 3m/s. Additionally, the chip surface in contact with the cutting tool has fewer scratches and pits (is smoother) and appears shiny in the case of a 3 m/s cutting speed compared to that produced with a 1 m/s cutting speed. This suggests that thermal softening occurs at high cutting speeds. The morphology of chips produced at UCT of 0.1 µm and 3 µm is presented in Fig. 18 . It can be observed that when the UCT is 0.1 µm, the chips produced are long, straight, and exhibit torn edges, indicating that brass behaves as a brittle material. This phenomenon occurs when the UCT is less than the cutting-edge radius. Conversely, at UCT of 3 µm, the chips are continuous and ribbon-like. This condition favors a ductile mode of machining in brass, as the UCT is greater than the edge radius. Figure 19 displays the sapphire tool’s cutting edge after machining free cutting brass with cutting distance of 10 m. From the image it is clear that tool wear is negligible because the sapphire being many times harder than the copper. Hence, Sapphire is a suitable material for cutting tool in ultraprecision turning of the Free cutting brass. To sum up the performance of the sapphire tool in machining of free cutting brass. It was observed that the cutting and thrust forces decreased as the cutting speed was increased from 1 m/s to 3 m/s. The higher ductility and significant plastic deformation exhibited by brass resulted in a thrust force higher than the cutting force. This was evident from the chip morphology, which showed continuous and ribbon-like chips, indicating that material removal predominantly occurred through plastic deformation. Additionally, both cutting forces exhibited a decrease as the cutting speed increased due to the occurrence of thermal softening. Furthermore, an increase in chip curling and a smoother contact surface of the chip were observed as the cutting speed increased, indicating the influence of thermal softening. Therefore, the surface finish improved from 91 nm to 38 nm as the cutting speed was increased from 1 m/s to 3 m/s. The increase in UCT from 0.1 µm to 3 µm led to an increase in cutting force due to higher material removal, while thrust force decreased. The dominance of ploughing mode of material removal was indicated by the higher thrust force until a UCT of 2 µm, after which shear mode material removal prevailed. Chip morphology also reflected this behavior, with long and straight chips with torn edges at 0.1 µm UCT, indicating the brittle behavior of the brass during ploughing. In contrast, at 3 µm UCT, continuous and ribbon-like chips were observed, signifying shear mode material removal. As a result, the average surface roughness decreased from 71 nm at 0.1 µm UCT to 34 nm at 3 µm UCT. 3.4 Performance of Sapphire tool while machining of Al 6061 Figure 20 a illustrates the relationship between cutting speed (m/s) and the cutting and thrust forces (N) at a constant UCT of 2 µm. The cutting force surpasses the thrust force, indicating the predominant material removal mechanism in shear mode. Moreover, as the cutting speed rises from 1 m/s to 3 m/s, both the thrust and cutting forces demonstrate a decrease. This reduction can be attributed to the decline in tool-chip contact area and the decrease in shear strength within the flow zone, which occurs as the cutting speed increases, resulting in elevated temperatures[ 20 ]. Figure 20 b exhibits the plot of cutting and thrust forces (N) against UCT (µm) at a constant cutting speed of 2 m/s. It can be observed that the thrust and cutting forces continuously increase as the UCT is increased from 0.5 µm to 3 µm, due to the corresponding increase in material removal rate. Figure 21 a displays the plot of apparent coefficient of friction against cutting speed for constant uncut chip thickness of 2 µm. The friction coefficient decreases from 0.842 at 1 m/s cutting speed to 0.802 at 3 m/s cutting speed. The average surface roughness R a on the machined surface across the cutting direction is measured. Figure 21 b displays the relationship between average surface roughness R a (nm) and cutting speed (m/s), plotted for a UCT of 2 µm. It is observed that the surface roughness tends to decrease from 50 nm to 14 nm as the cutting speed is increased from 1 m/s to 3 m/s. The reduction in the surface roughness is caused due to a decline in the friction coefficient from 0.842 at 1 m/s to 0.802 at 3 m/s as depicted in Fig. 21 a. The thermal softening at higher cutting speed causes the reduction apparent friction coefficient. Figure 22 a illustrates the plot of apparent coefficient of friction plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s. The friction coefficient declines from 0.936 at 0.5 µm UCT to 0.827 at 3 µm UCT. Figure 22 b displays the relationship between average surface roughness R a and UCT, plotted for a constant cutting speed of 2 m/s. The surface roughness R a decreased from 90 nm to 34 nm as UCT increases from 0.5 µm to 3 µm. This reduction in roughness is due to the decrease in the apparent friction coefficient from 0.936 at 0.5 µm UCT to 0.827 at 3 µm. The change in friction coefficient is attributed to change in material removal mechanism from ploughing at 0.5 µm to shearing at 3 µm. Additionally, built-up edge (BUE) formation is more prominent at lower UCT like causing the increase in the apparent coefficient of friction. The adhesion between the chip and tool rake face increases the BUE formation resulting in poor surface finish. Therefore, surface finish improved from 90 nm at 0.5 µm UCT to 34 nm at 3 µm UCT. After machining Al 6061, the chips are collected and observed under a SEM. Figure 23 illustrates the chip morphology at cutting speeds of 1m/s and 3m/s. It is observed that as the cutting speed increases, the chip thickness decreases. Machining of Al 6061 with sapphire tool results in the production of continuous chips, no curling of chips is observed. The chip formed where of continuous shape, with a relatively uniform thickness and smooth surface. The formation of such continuous chips can be attributed to the more ductile behavior exhibited by Al 6061. At lower cutting speeds, the rate of deformation and strain on the material being machined is reduced. This slower cutting speed provides more time for the material to undergo plastic deformation and flow smoothly along the shear plane. Consequently, the chip formed during machining exhibits a continuous shape with a relatively uniform thickness and smooth surface. The lower cutting speeds result in lower forces acting on the material, creating a more stable and predictable chip formation process. The material can undergo substantial plastic deformation before reaching its failure point, leading to the formation of a continuous chip rather than fragmentation or serration. The chip morphology at different UCT of 0.5 µm and 3 µm is depicted in Fig. 24 . When the UCT is 0.5 µm, the chips formed are discontinuous due to inadequate tool-workpiece contact length. However, as the UCT is increased from 0.5 µm to 3 µm, the chips transition to a continuous form with regular lamella formation. This transformation is attributed to the higher UCT, which causes the material ahead of the tool to be moved in the cutting direction, leading to the creation of a shear band. As a result, the work material is removed through a conventional shearing mechanism, resulting in the generation of long continuous chips. Moreover, the increased UCT reduces the surface fragmentation of microchips by expanding the layer of material removal. Figure 25 showcases the cutting edge of the sapphire tool after machining Al 6061 with a cutting distance of 10 m. The presence of significant wear on the rake surface and the absence of wear on the flank surface indicate the formation of a built-up edge. Oishi[ 8 ] observed similar phenomena during machining of Aluminium 2014 T6 alloy with alumina tool. The built-up edge occurs due to the affinity of the alumina towards the aluminum in Al 6061. During the machining process, increase in temperature at tool-chip interface causes welding between alumina at cutting and Al6061 this results in built-up edge formation[ 21 ]. Furthermore, Al 6061 contains precipitation hardening Mg-Si alloys which are hard and brittle cause irregular machining conditions[ 22 ]. This leads to high tool wear and poor surface roughness. To summarize the machining of Al 6061 using Sapphire tool. It was observed that the cutting and thrust forces decreased as the cutting speed increased from 1 m/s to 3 m/s. This reduction was attributed to a smaller tool-chip contact area and a decrease in shear strength within the flow zone at elevated temperatures. Evidently, the chip morphology exhibited a decrease in thickness as the cutting speed increased from 1 m/s to 3 m/s. The chips generated during the machining process displayed a continuous and uniform thickness, which can be attributed to the ductile behavior of Al 6061. Consequently, an improvement in surface finish was observed, with the surface roughness (Ra) decreasing from 50 nm to 14 nm as the cutting speed increased from 1 m/s to 3 m/s. As the UCT increased from 0.5 µm to 3 µm, there was a raise in both the cutting force and thrust force due to the greater amount of material being removed during the machining process. The cutting force was higher than the thrust force indicating shear mode material removal. Consequently, at a UCT of 0.5 µm, the chips formed are discontinuous due to inadequate tool-workpiece contact length. However, at 3 µm the chips were continuous with regular lamella formation, and thicker. Furthermore, the surface finish improved from 90 nm at 0.5 µm UCT to 34 nm at 3 µm UCT. However, during the machining of Al 6061 using the Sapphire tool, the presence of built-up edge formation was observed. This was evident from the examination of the cutting edge, where significant wear was observed on the rake face, while the flank surface showed no signs of wear. 3.5 Performance of sapphire tool while machining Stavax ESR steel. Stavax ESR, known for its high hardness, toughness, and yield strength, posed challenges when machined with a sapphire tool. During the machining observed chatter and severe tool wear. As depicted in Fig. 26 edge chipping was observed on both the rake and flank faces of the tool. Consequently, the surface finish of the workpiece was poor, and didn’t have the desired optical quality finish. Consequently, we were unable to conduct an in-depth analysis of the impact of process parameters such as uncut chip thickness and cutting speed on critical factors like cutting thrust forces, surface roughness, and chip morphology. As a result, it can be concluded that sapphire cutting tool is unsuitable for ultra-precision machining of Stavax ESR steel. 4 Conclusion Sapphire, a single crystal alumina, possesses exceptional properties such as a hardness of 22 GPa, chemical inertness, and the ability to be grown in bulk sizes. These qualities position it as a promising candidate for cutting tool materials in ultra-precision machining. This study focuses on the fabrication technique of a sharp sapphire tool, the measurement of its cutting-edge radius, and its performance in ultra-precision machining of non-ferrous alloys. Sapphire as an alternative to single crystal diamond tool for ultra-precision machining has been tested in this study. The sapphire tool with uniform sharp cutting edge is fabricated with a specialized setup employing a series of operations such as lapping, polishing, and chemical mechanical polishing. The performance of the fabricated sapphire tool is evaluated via orthogonal cutting of OFHC copper, free-cutting brass, Al 6061 and Stavax ESR steel using an ultra-precision lathe. The study revealed the following observations: While machining OFHC copper, with increase in cutting speed, the cutting and thrust force increase due to the strain rate hardening effect. However, the friction coefficient decreases resulting in improvement of surface finish from 43nm Ra at 1m/s to 12nm Ra at 3m/s for constant UCT 1µm. Also, roughness decreased from 69nm Ra at 1µm to 36nm Ra at 3µm for constant speed 1m/s because of shear mode of material removal as evident from chip morphology. Furthermore, the sapphire tool cutting-edge retained its geometry with very little wear after machining OFHC copper. Machining of free-cutting brass showed that with the increase in cutting speed, the cutting and thrust force decrease due to thermal softening. The friction coefficient decreases, resulting in improved surface finish from 91nm Ra at 1m/s to 38nm Ra at 3m/s for constant UCT 1µm. An increase in uncut chip thickness (UCT) resulted in a rise in cutting force, while thrust force decreased as the material removal mode shifted from ploughing to shearing. The surface finish is enhanced from 71nm Ra at 1µm to 34nm Ra at 3µm for constant speed 1m/s because of the shearing mode of material removal at elevated uncut chip thickness (UCT). Furthermore, the sapphire tool cutting-edge suffered very less wear after machining free-cutting brass. During the machining of Al 6061, as the cutting speed increases, both cutting and thrust forces decrease because of the effect of thermal softening. Furthermore, surface finish improved from 50nm Ra at 1m/s to 14nm Ra at 3m/s for constant UCT 1µm. Increase in uncut chip thickness (UCT), both cutting and thrust raises due to high material removal. The surface roughness decreased from 90nm Ra at 1µm to 34nm Ra at 3µm for constant speed 1m/s because of shear mode of material removal at high UCT. However, a built-up edge (BUE) was observed on the rake face at the sapphire tool's cutting edge during the machining of Al 6061 due to the affinity of alumina towards the aluminum in the workpiece. During machining of Stavax-ESR, known for its high hardness and toughness, edge chipping occurred at the cutting edge of the sapphire tool, resulting in a poor surface finish on the machined surface. In summary, sapphire tools have good potential to machine OFHC copper and free-cutting brass with very less tool wear and achieve optical quality surface finish with surface roughness in the range of 10–40 nm. However, the sapphire cutting tool may not be suitable for machining Al6061 and Stavax as the edge suffers from BUE formation edge chipping, respectively. A sapphire tool with a nose radius can be made in the future for fabricating practically useful optical components made of OFHC copper and free-cutting brass. Declarations Author Contributions All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Amit Dodmani, Sathyan Subbiah and A.Senthil Kumar. The first draft of the manuscript was written by Amit Dodmani and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Funding This research received financial support from Global Engagement office, Indian Institute of Technology Madras (IITM). Competing interests The authors declare no competing interests. References Balasubramaniam R, Sarepaka RV, Subbiah S (2017) Diamond Turn Machining Dodmani A, Subbaih S, Senthil Kumar A (2023) Sapphire as a Single-Crystal Cutting Tool for Machining Ferrous-Based Optics. 613–616. https://doi.org/10.3850/978-981-18-6021-8_or-12-0101.html Pishchik V, Lytvynov LA, Dobrovinskaya ER (2009) Sapphire Madhavan V, Chandrasekar S, Farris TN (2002) Direct observations of the chip-tool interface in the low speed cutting of pure metals. J Tribol 124:617–626. https://doi.org/10.1115/1.1398546 Huang C, Lee S, Sullivan JP, Chandrasekar S (2007) In situ measurement of fluid film thickness in machining. Tribol Lett 28:39–44. https://doi.org/10.1007/s11249-007-9245-6 Society R (2018) Stress Analysis in Machining with the Use of Sapphire Tools Author (s): A. Bagchi and P. K. Wright Source : Proceedings of the Royal Society of London. Series A, Mathematical and Physical Published by : Royal Society Stable URL : https://www.jstor . 409:99–113 Park SS, Wei Y, Jin XL (2018) Direct laser assisted machining with a sapphire tool for bulk metallic glass. CIRP Ann 67:193–196. https://doi.org/10.1016/j.cirp.2018.04.070 Oishi K (1996) Mirror cutting of aluminum with sapphire tool. J Mater Process Technol 62:331–334. https://doi.org/10.1016/S0924-0136(96)02430-2 Is O, Work L (1986) pare damage-free sapphire surfaces. The starting material. Appl Opt 25:2639–2640 Lee T, Jeong H, Lee S et al (2021) Material removal model for lapping process based on spiral groove density. Appl Sci 11. https://doi.org/10.3390/app11093950 Aida H, Doi T, Takeda H et al (2012) Ultraprecision CMP for sapphire, GaN, and SiC for advanced optoelectronics materials. Curr Appl Phys 12:S41–S46. https://doi.org/10.1016/j.cap.2012.02.016 Dodmani A, Subbiah S (2022) Accurate measurement of cutting-edge radius on a single-crystal diamond tool. Manuf Lett 33:469–478. https://doi.org/10.1016/j.mfglet.2022.08.004 Zong WJ, Li D, Sun T, Cheng K (2006) Contact accuracy and orientations affecting the lapped tool sharpness of diamond cutting tools by mechanical lapping. Diam Relat Mater 15:1424–1433. https://doi.org/10.1016/j.diamond.2005.10.066 Jordan JL, Siviour CR, Sunny G et al (2013) Strain rate-dependant mechanical properties of OFHC copper. J Mater Sci 48:7134–7141. https://doi.org/10.1007/s10853-013-7529-9 Venkatesh V, Swain N, Srinivas G et al (2017) Review on the machining characteristics and research prospects of conventional microscale machining operations. Mater Manuf Process 32:235–262. https://doi.org/10.1080/10426914.2016.1151045 Ng CK, Melkote SN, Rahman M, Senthil Kumar A (2006) Experimental study of micro- and nano-scale cutting of aluminum 7075-T6. Int J Mach Tools Manuf 46:929–936. https://doi.org/10.1016/j.ijmachtools.2005.08.004 Islam S, Khandoker N, Izham M et al (2017) Development of a Low Cost MQL Setup for Turning Operations. MATEC Web Conf 95. https://doi.org/10.1051/matecconf/20179510004 Wang H, You Z, Lu L (2018) Kinematic and isotropic strain hardening in copper with highly aligned nanoscale twins. Mater Res Lett 6:333–338. https://doi.org/10.1080/21663831.2018.1455752 Klocke F, Nobel C, Veselovac D (2016) Influence of Tool Coating, Tool Material, and Cutting Speed on the Machinability of Low-Leaded Brass Alloys in Turning. Mater Manuf Process 31:1895–1903. https://doi.org/10.1080/10426914.2015.1127944 Xu D, Feng P, Li W et al (2014) Research on chip formation parameters of aluminum alloy 6061-T6 based on high-speed orthogonal cutting model. Int J Adv Manuf Technol 72:955–962. https://doi.org/10.1007/s00170-014-5700-3 Ahmad Fauzi MN, Uday MB, Zuhailawati H, Ismail AB (2010) Microstructure and mechanical properties of alumina-6061 aluminum alloy joined by friction welding. Mater Des 31:670–676. https://doi.org/10.1016/j.matdes.2009.08.019 Wang SJ, To S, Cheung CF (2012) Effect of workpiece material on surface roughness in ultraprecision raster milling. Mater Manuf Process 27:1022–1028. https://doi.org/10.1080/10426914.2011.654165 Cite Share Download PDF Status: Published Journal Publication published 14 Jul, 2025 Read the published version in The International Journal of Advanced Manufacturing Technology → Version 1 posted Editorial decision: Major Revisions Needed 30 Jun, 2024 Reviewers agreed at journal 20 Feb, 2024 Reviewers invited by journal 19 Feb, 2024 Editor assigned by journal 19 Jan, 2024 First submitted to journal 19 Jan, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-3878526","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":273849152,"identity":"887f2e18-cc3e-4d5e-a5b8-48d9d85abbf0","order_by":0,"name":"Amit Dodmani","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Amit","middleName":"","lastName":"Dodmani","suffix":""},{"id":273849153,"identity":"3be57601-c563-488d-922c-7d2cd7cac685","order_by":1,"name":"Sathyan Subbiah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1ElEQVRIiWNgGAWjYHACNjDJz8zYAOEzE9TBDNEi2czY2ECaFoMDDDBrCAD59vPHHvPU3LE3Ps7c/ugGg508AzvvAbxaDM4ksxvzHHuWuO0wY2NzDkOyYQMzXwJ+LQzJbNI8bIcTzCBamBMYmHkM8Dus/zFQy7/D9sbNYC31hLUw3ADawtt2mHEDM1jLYcJaDG48NpOc23c4cQbQYbNzDI4bthF2WOIziTffDtvz9x9/8Dmnolqen/8MAYcBARMPwlJYYiAAGH8Qo2oUjIJRMApGLgAAZrw8m9ArokkAAAAASUVORK5CYII=","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":true,"prefix":"","firstName":"Sathyan","middleName":"","lastName":"Subbiah","suffix":""},{"id":273849154,"identity":"f93906d8-835e-4099-9150-1298a81c6339","order_by":2,"name":"A. Senthil Kumar","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"A.","middleName":"Senthil","lastName":"Kumar","suffix":""}],"badges":[],"createdAt":"2024-01-19 11:06:24","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3878526/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3878526/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00170-025-16071-z","type":"published","date":"2025-07-14T15:57:13+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":51480475,"identity":"559e4364-3480-4272-ab29-2b61cd10f7af","added_by":"auto","created_at":"2024-02-22 11:07:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":188552,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the sapphire tool fabrication a) the cylindrical sapphire crystal with 12 mm diameter and 6 mm thickness b) Sapphire crystal held at 7° to vertical by aluminum fixture to generate clearance angle c) Sapphire crystal secured in a copper block d) material removal e) Sapphire tool with 0° rake angle, 7° clearance angle and straight cutting edge of width 5 mm\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/2afaed53dd3e0aafb346855d.png"},{"id":51480127,"identity":"9c4db82c-1e88-4d02-9b9a-86a62a8cff19","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":118075,"visible":true,"origin":"","legend":"\u003cp\u003eSteps in sapphire tool fabrication a) Step1 - lapping of sapphire performed using boron carbide abrasives on a cast iron lap. b) Step2 – polishing process where diamond slurry is applied using a spiral groove copper lap. c) Step3 - chemical mechanical polishing using colloidal silica on polyurethane pad\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/5372ef68b0da5c07bdb5e641.png"},{"id":51480130,"identity":"fa05c9d7-a391-4d6d-8361-aacae946860a","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1067568,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool fabrication setup in a) tribo-bruker CMP. b) sapphire tool is held in the fixture and d) the constant load is applied by the Z stage and force controller ensures the constant loading is maintained during the lapping, polishing and CMP. Peristaltic pump is used to pump and control slurry flowrate\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/a554b6273d4043d8a7269883.png"},{"id":51480129,"identity":"6cccab80-46c0-44ec-b560-1245d76d92e0","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":382248,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool edge radius measurement experimental setup in KERN Evo ultra-precision machining center\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/88b52d2633a246d843218fb8.png"},{"id":51480128,"identity":"df9f8f4e-23a2-4671-8905-8e5113ab3e98","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":877860,"visible":true,"origin":"","legend":"\u003cp\u003eOrthogonal cutting experimental setup in the Toshiba ULG-100C (H³). The cylindrical workpiece with three concentric thin channels of width 0.5 mm is mounted on the workpiece holder which is held by vacuum chuck. The sapphire tool is secured on the copper block to tool holder which is mounted on the dynamometer\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/125971d8b9a4cb88b49bef63.png"},{"id":51480138,"identity":"61d119b4-1670-42b1-8e6d-4bd00c9c9b98","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":624135,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eS\u003c/strong\u003echematic and micrograph of the flank face, cutting edge, and the indentation profile of the sapphire tool after lapping, polishing, and CMP process correspondingly\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/53668b010866d1076f8f6ddc.png"},{"id":51480584,"identity":"47010300-5f03-439d-8889-01dd8ab26f8e","added_by":"auto","created_at":"2024-02-22 11:15:17","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":146052,"visible":true,"origin":"","legend":"\u003cp\u003ea) Thrust and cutting force (N) plotted against cutting speed (m/s) for a constant uncut chip thickness of 1 µm. b) Thrust and cutting force (N) plotted against uncut chip thickness (µm) for a constant cutting speed of 1 m/s\u003c/p\u003e","description":"","filename":"image18.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/8087f9893b82c3b3125c98c2.png"},{"id":51480477,"identity":"4e9643dd-5a04-4a50-8566-77a660fcfa2e","added_by":"auto","created_at":"2024-02-22 11:07:17","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":24567,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic for calculation of effective rake angle(α)\u003c/p\u003e","description":"","filename":"image19.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/890b791c8c9b9885acf11bbe.png"},{"id":51480141,"identity":"98b9d0e3-cb72-42ab-82a9-aaee208b0f3c","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":106740,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against cutting speed (m/s) for a constant uncut chip thickness of 1 µm. b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting speed (m/s) at a constant uncut chip thickness (UCT) of 1 µm\u003c/p\u003e","description":"","filename":"image20.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/ce937f636f628e0451dd038f.png"},{"id":51480139,"identity":"9ab24e26-4c01-46b1-82c3-4fb8a40da9b9","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":116458,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against uncut chip thickness (µm) for a constant cutting speed of 1 m/s b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) vs uncut chip thickness at a constant cutting speed of 1 m/s\u003c/p\u003e","description":"","filename":"image21.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/4a9179c6560f3c70ca4f6741.png"},{"id":51480136,"identity":"9893ecac-4bd6-473f-b31d-4002c2e276b1","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":505978,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the OFHC Copper machined chips collected at a) cutting speed of 1 m/s and b) cutting speed of 3 m/s for constant UCT of 1 µm\u003c/p\u003e","description":"","filename":"image22.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/785b0625afac24bc7efd70dc.png"},{"id":51480132,"identity":"24a15e07-0d06-454b-82e4-d39173d4a9d7","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":489251,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the free cutting brass machined chips collected at a) UCT of 0.1 µm and b) UCT of 3 µm for a constant cutting speed of 1 m/\u003c/p\u003e","description":"","filename":"image23.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/6475a11b22eab22982042bbb.png"},{"id":51480134,"identity":"0f2aa347-5713-472e-9fec-a0e8f8cfb26e","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":612003,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool cutting a) rake face and b) flank face after machining OFHC copper with a cutting distance of 10 m, uncut chip thickness (UCT) of 3 µm, and cutting speed of 1 m/s. Negligible tool wear is observed\u003c/p\u003e","description":"","filename":"image24.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/041795e6a4e325e81a330cd0.png"},{"id":51480478,"identity":"68a86f2f-10c5-4498-8ac0-a545beb46a7a","added_by":"auto","created_at":"2024-02-22 11:07:17","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":129805,"visible":true,"origin":"","legend":"\u003cp\u003ea) Thrust and cutting force (N) plotted against cutting speed (m/s) for a constant uncut chip thickness of 1 µm. b) Thrust and cutting force (N) plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s\u003c/p\u003e","description":"","filename":"image25.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/1fa99147dbdf674405ab17dc.png"},{"id":51480144,"identity":"cc7c2109-465c-4dbb-a404-3d35097bedc8","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":100818,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against cutting speed (m/s) for a constant uncut chip thickness of 1 µm. b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting speed (m/s), plotted for a UCT (Uncut Chip Thickness) of 1 µm\u003c/p\u003e","description":"","filename":"image26.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/355253ff488a797ea9b6783e.png"},{"id":51480480,"identity":"676af017-18ec-4692-9081-c24fbd89b998","added_by":"auto","created_at":"2024-02-22 11:07:18","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":107830,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) vs Uncut chip thickness at a constant cutting speed of 2 m/s\u003c/p\u003e","description":"","filename":"image27.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/9b70186063f60d10447eb2e1.png"},{"id":51480481,"identity":"b9883236-2cac-4ea7-a9c7-4c29ddc33364","added_by":"auto","created_at":"2024-02-22 11:07:18","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":430078,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the Free cutting brass machined chips collected at a) cutting speed of 1 m/s and b) cutting speed of 3 m/s for constant UCT of 1 µm\u003c/p\u003e","description":"","filename":"image28.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/d56fb5d3403e90729aff4d28.png"},{"id":51480150,"identity":"9816528e-9cd5-472d-b2a6-336259b0c106","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":441040,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the Free cutting brass machined chips collected at a) UCT of 0.1 µm and b) UCT of 3 µm for a constant cutting speed of 2 m/s\u003c/p\u003e","description":"","filename":"image29.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/4aa42e3f360eef2309f5f902.png"},{"id":51480140,"identity":"8016f0c7-93c2-4c1a-a8ab-a052df244688","added_by":"auto","created_at":"2024-02-22 10:59:17","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":583724,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool cutting edge a) rake face and b) flank face after machining free cutting brass with a cutting distance of 10 m, uncut chip thickness (UCT) of 3 µm, and cutting speed of 1 m/s. Negligible tool wear is observed\u003c/p\u003e","description":"","filename":"image30.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/fef9acedaaddb63b4ee320c5.png"},{"id":51480147,"identity":"f9905338-b211-461b-89a9-4490f31af549","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":20,"title":"Figure 20","display":"","copyAsset":false,"role":"figure","size":122734,"visible":true,"origin":"","legend":"\u003cp\u003ea) Thrust and cutting force (N) plotted against cutting speed (m/s) for a constant uncut chip thickness of 2 µm. b) Thrust and cutting force (N) plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s\u003c/p\u003e","description":"","filename":"image31.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/1a577f32905bc842994e1e23.png"},{"id":51480479,"identity":"c44cd29f-1b0c-43ef-a7f5-fe839ea130e0","added_by":"auto","created_at":"2024-02-22 11:07:18","extension":"png","order_by":21,"title":"Figure 21","display":"","copyAsset":false,"role":"figure","size":95186,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against cutting speed (m/s) for a constant uncut chip thickness of 2 µm. b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting Speed (m/s) at a constant uncut chip thickness (UCT) of 2 µm\u003c/p\u003e","description":"","filename":"image32.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/b80ed6e2aec94c05b8a26b00.png"},{"id":51480143,"identity":"5a2d7962-b447-4e01-8e41-a45e84055296","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":22,"title":"Figure 22","display":"","copyAsset":false,"role":"figure","size":105841,"visible":true,"origin":"","legend":"\u003cp\u003ea) Apparent coefficient of friction plotted against uncut chip thickness (µm) for a constant cutting speed of 2 m/s b) Relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) vs uncut chip thickness at a constant cutting speed of 2 m/s\u003c/p\u003e","description":"","filename":"image33.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/927bbfcf765395a1c180ad9f.png"},{"id":51480153,"identity":"f14b8d7f-4347-4072-86fe-b555f426b6c7","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":23,"title":"Figure 23","display":"","copyAsset":false,"role":"figure","size":382160,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the Al 6061 machined chips collected at a) cutting speed of 1 m/s and b) cutting speed of 3 m/s for constant UCT of 1 µm\u003c/p\u003e","description":"","filename":"image34.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/fdf396ac8dde2c8839851e9d.png"},{"id":51480151,"identity":"c1937abd-4f0e-4454-8f1f-e8cc9f4ab349","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":24,"title":"Figure 24","display":"","copyAsset":false,"role":"figure","size":564280,"visible":true,"origin":"","legend":"\u003cp\u003eMicrographs of the Al 6061 machined chips collected at a) UCT of 0.5 µm and b) UCT of 3 µm for a constant cutting speed of 1 m/s\u003c/p\u003e","description":"","filename":"image35.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/a9d5e4b679fda915f2167335.png"},{"id":51480142,"identity":"8b42ad10-fa6d-4feb-b1fb-191f3a8d5fe4","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":25,"title":"Figure 25","display":"","copyAsset":false,"role":"figure","size":268477,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool cutting edge a) rake face and b) flank face after machining Al 6061 with a cutting distance of 10 m, uncut chip thickness (UCT) of 3 µm, and cutting speed of 1 m/s. Built-up edge (BUE) formation caused excess wear on rake face\u003c/p\u003e","description":"","filename":"image36.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/cb50e890a38d8d5e77273c96.png"},{"id":51480149,"identity":"e3f5c24f-03e0-49fe-90cd-5a950c1a228c","added_by":"auto","created_at":"2024-02-22 10:59:18","extension":"png","order_by":26,"title":"Figure 26","display":"","copyAsset":false,"role":"figure","size":293561,"visible":true,"origin":"","legend":"\u003cp\u003eSapphire tool cutting edge\u003cstrong\u003e \u003c/strong\u003ea) rake face and b) flank face after machining stavax ESR with a cutting distance of 1 m, uncut chip thickness (UCT) of 1 µm, and cutting speed of 1 m/s. Edge chipping at the cutting edge on both rake and flank face of sapphire tool\u003c/p\u003e","description":"","filename":"image37.png","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/332fadd5343b7a0f0b6c9af1.png"},{"id":87219449,"identity":"c661e188-f964-462d-9555-bddf5a5c0401","added_by":"auto","created_at":"2025-07-21 16:05:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":12496519,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3878526/v1/ba88deec-37ce-4273-a8af-5a377238fab9.pdf"}],"financialInterests":"","formattedTitle":"Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eUltra-precision machining generates optical components with smooth surfaces and precise tolerances using single-crystal diamond (SCD) tools[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. To attain an optical quality surface finish, a smooth shearing/cutting action minimizing surface defects such as feed marks, undulations, and chatter marks is needed. This requires small uncut chip thickness with even smaller cutting-edge radius ranging from tens of nanometers to a few hundred nanometers. To achieve such a sharp edge radius, materials that are available in single crystal form and in large sizes are the ideal choice for the cutting tool. Diamond is one such material which due to its mechanical properties can also retain its sharp cutting-edge radius over longer periods of machining. However, SCD material and its processing into cutting tools with the desired geometry and edge sharpness are expensive. Hence, an alternative single crystal cutting tool material would be desirable from an economic point of view.\u003c/p\u003e \u003cp\u003eThere are several materials that are available in bulk form as single crystals and although not as hard as diamond but are several times harder than the workpiece materials subjected to ultra-precision machining[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Sapphire, or single crystal alumina, is one such crystal with a hardness of 22 GPa available in bulk sizes, and costs 40 times less than diamond[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Sapphire has exceptional properties, such as optical transparency, high wear resistance, hardness, refractoriness, and chemical inertness, and hence is widely used in various industries, including optics, semiconductors, watchmaking, and medical industries, and so is readily available. Hence, sapphire can be explored as an alternate cutting tool material in ultra-precision machining.\u003c/p\u003e \u003cp\u003eSapphire, being transparent, has been used as a cutting tool to better observe and visualize the mechanics of machining. Madhavan et al.[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] used sapphire\u0026rsquo;s optical transparent property to observe the tool-chip interface in-situ while machining copper, aluminium and lead with sapphire tool. Hunag et al.[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e] reported on an in-situ cutting fluid film measurement method during machining using sapphire tool. Using sapphire\u0026rsquo;s stress birefringent property Bagchi et al.[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e] studied the stress distribution at the tool-chip interface while machining brass and steel with a sapphire cutting tool. Sapphire's transparency has also been exploited to allow laser energy to reach the tool-chip contact zone. Park et al.[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e] performed direct laser assisted machining of bulk metallic glass using sapphire cutting tool. There is one study reported on the use of sapphire for optical component machining. Oishi[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] used sapphire cutting tool for mirror cutting of the A2014 aluminium but reported occurrence of built-up edge formation due to affinity of aluminium present in both materials. In all the above studies involving sapphire as a cutting tool, there is no mention of how the sapphire cutting edge was fabricated and what cutting edge sharpness can be achieved in sapphire tools.\u003c/p\u003e \u003cp\u003eFabricating cutting tool from sapphire involves creating smooth planar and non-planar surface regions (rake, flank) and cutting edges where the surfaces meet. While there are many reports of polishing bulk surface regions of sapphire wafers, none that report formation of controlled geometry sharp edges formed by two smooth meeting surfaces. Presently sapphire wafers are subjected to lapping, polishing, and chemical mechanically planarization (CMP) to achieve a surface finish up to a few angstroms for growing high-quality gallium nitride (GaN) thin film. Parks et al.[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e] reported lapping of sapphire wafers with #400 boron carbide (BC) abrasives on a cast-iron plate, observed a high material removal rate of 5\u0026ndash;10 \u0026micro;m/min and achieved a surface roughness of 400\u0026ndash;600 nm. Taekyung et al.[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e] used Kemet copper lap having grooves to hold the diamond slurry for longer durations, reported a low material removal rate of 0.5\u0026ndash;1 \u0026micro;m/min, this improved the surface roughness of the wafer and obtained 10\u0026ndash;20 nm Ra. Aida et al.[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e] reported chemical mechanical polishing of sapphire using poly urethane pad and colloidal silica as the slurry, achieved an excellent surface finish of 10\u0026ndash;20 \u0026Aring; Ra and the material removal rate was very low 50 nm/hr. These series of steps can be used to form the rake and flank faces of a sapphire tool. It is however not clear how sharp and smooth will be the edge that forms from the meeting of these two surfaces.\u003c/p\u003e \u003cp\u003eThis study aims to form a sharp cutting edge on a sapphire single crystal tool and evaluate its potential as a cutting tool for ultra-precision machining. We developed a setup to fabricate a sharp single crystal sapphire tool with zero rake angle, a seven-degree clearance angle, and a straight cutting edge of 6 mm. The flank face, with a seven-degree clearance angle, is carved out using lapping by BC slurry on a cast iron plate. Subsequently, diamond slurry on a copper lap is employed to remove lay marks from the previous step. Finally, the CMP process is employed to enhance the sharpness of the cutting edge further. The edge sharpness was characterized using an edge reversal method using split block method[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Orthogonal cutting experiments were performed using these sharp sapphire tools in an ultra-precision machining lathe. The workpiece materials selected were oxygen-free high conductivity (OFHC) copper, free-cutting brass, Al 6061 and Stavax ESR because these are commonly used materials for metal optics. We investigated the effect of cutting parameters, such as cutting speed and uncut chip thickness, on surface finish, cutting force, thrust force, friction coefficient, and chip morphology while using sapphire tools.\u003c/p\u003e"},{"header":"2 Methodology and experimental setup","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Fabrication of the sapphire cutting tool\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eA sapphire cutting tool with 0\u0026deg; rake angle, 7\u0026deg; clearance angle and straight cutting edge of width 5 mm is carved out from the cylindrical sapphire crystal having 12 mm diameter and 6 mm thickness as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea. The top flat surface of the cylindrical crystal has a surface finish of 5\u0026Aring;, this surface is chosen as rake face and the curved surface is lapped to create the flank face. This conversion from a sapphire crystal to a sapphire tool involves lapping the cylindrical face until a straight cutting edge of 5 mm width is achieved. During the lapping process, material removal occurs as abrasive particles in a slurry traverse and scratch the crystal's surface in the presence of relative rotational motion between the sapphire crystal and the platen, all while pressure is applied to the crystal.\u003c/p\u003e \u003cp\u003eThe sapphire tool is secured in a copper block as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec. This fixture serves the dual purpose of maintaining the crystal's stability without causing any positional disturbance during the lapping and since copper being a soft material, applying minimal pressure to prevent the initiation or propagation of cracks that could lead to the breakage of the sapphire crystal. The copper block is oriented at a 7\u0026deg; to the vertical plane, to generate a flat face with a clearance angle of 7\u0026deg;. This assembly is further held in a custom-made aluminum adapter, which is subsequently affixed to the CMP head as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. When the load is applied through the CMP head onto the crystal against the lapping material, material removal occurs, resulting in the generation of a sharp cutting edge with a clearance angle of 7\u0026deg; as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ee.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe fabrication of the sapphire tool involves a three-step process comprising lapping, polishing, and chemical mechanical polishing (CMP) as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Initially, lapping is performed using boron carbide abrasives on a cast iron lap as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea. This step prioritizes high material removal, utilizing larger abrasive particles to achieve an elevated material removal rate. Given the goal of transforming the cylindrical sapphire crystal into a sapphire tool with a straight cutting edge of 5 mm width, high material removal rate is essential. However, this lapping process results in increased surface roughness due to its aggressive material removal, causing fracturing and chipping which leads to poor edge sharpness.\u003c/p\u003e \u003cp\u003eTo address this, in the second step of the process, diamond slurry is applied using a spiral groove copper lap for polishing as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. A lapping platen made of resin-copper, created by sintering copper powder and resin, is utilized. This Cu-resin plate demonstrates a higher material removal rate (MRR) compared to other metal-resin plates. The grooves in the plate play a crucial role by spontaneously refreshing the slurry, clearing debris generated during the process, and increasing the surface area of the platen. While this step has a lower material removal rate, i.e., a few microns per minute, it effectively reduces surface roughness on the flank face and eliminates lay marks from the previous process. This contributes to an enhancement in edge quality and overall sharpness of the sapphire tool.\u003c/p\u003e \u003cp\u003eTo further enhance the surface finish on the flank face and cutting-edge sharpness chemical mechanical polishing (CMP) process is employed in the final step as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec. CMP serves as the final treatment, ensuring atomic-level surface flatness by eliminating damage on or near the surface caused during mechanical polishing. The polishing of sapphire using colloidal silica is thought to involve a chemical reaction that results in aluminum silicate dihydrate formation. Simultaneously, the continually forming hydrated surface layer is removed by the spherical colloidal silica particles, contributing to the desired surface quality and overall sharpness of the sapphire tool.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Bruker TriboLab CMP machine was employed in the fabrication of sharp sapphire tool as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The machine is specifically designed for chemical mechanical polishing of silicon wafers, which are commonly utilized in semiconductor devices. The machine has a servo-controlled precision loading stage, integrated high-speed/high-torque upper and lower rotational drive motors with adjustable platen and wafer head rotation speed ranging from 1 to 500 RPM, and a wafer head load range of 4 to 400 N. Incorporates a programmable peristaltic pump to regulate the slurry flow rate. Renowned for its robustness, high repeatability, and minimal vibration, the TriboLab CMP machine offers the flexibility to formulate custom recipes by adjusting polishing load, lap wheel rotational speed and slurry rate. These capabilities make the TriboLab CMP machine highly effective for the fabrication of sharp sapphire tools.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSapphire tool fabrication process parameters\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSteps\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLap wheel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSlurry\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSlurry rate\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eLoad\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eVelocity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eHead Oscillation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eTotal time\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCast iron\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e300 gm BC\u0026thinsp;+\u0026thinsp;150 ml Suspension\u0026thinsp;+\u0026thinsp;3L DI water\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e30 ml/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12 N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e50 cm/s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e25 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpiral groove copper\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e3 \u0026micro;m diamond slurry\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e8 ml/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10 N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e50 cm/s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e15 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePolyurethane Pad\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eColloidal silica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e20 ml/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8 N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e50 cm/s\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eX-axis\u003c/p\u003e \u003cp\u003e1 mm\u003c/p\u003e \u003cp\u003e20 cycles/min\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e60 min\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e contains the process parameters used for fabrication sapphire tool fabrication. The initial stage involves lapping the sapphire using boron carbide slurry on a cast iron lap with a lapping load of 12 N. The boron carbide slurry is created by mixing 250 grams of #400 boron carbide with 3 liters of de-ionized water and 150 ml of suspension. The slurry rate is consistently maintained at 30 ml/min, resulting in the formation of a sapphire tool with a 6mm width cutting edge and a 7\u0026deg; clearance angle. In the second step, polishing is carried out using 3\u0026micro;m diamond slurry on a spiral-grooved copper lap with a 10N load for 15 minutes. Due to the grooves facilitating the replenishment of abrasive particles in the slurry, the slurry rate is intentionally kept low at 8 ml/min.\u003c/p\u003e \u003cp\u003eThe final step, chemical mechanical polishing (CMP), is executed using colloidal silica on a polyurethane pad with a 10 N load. Given the very low MRR in this process, the duration is extended to 60 minutes. The slurry rate is maintained at a constant 20 ml/min, and the pH of the slurry is set at 10.5. To eliminate any polishing marks, the CMP head undergoes oscillation of traverse at 1 mm in the X direction with 20 cycles per minute.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Edge radius measurement of Sapphire tool\u003c/h2\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe indentation experiments were conducted in an ultraprecision CNC machining center (KERN Microtechnik- Evo), having a positioning resolution of 100 nm. Two 99.9.% pure copper blocks of size 10 mm x 5 mm x 6 mm were prepared from grinding and polishing the surfaces. The mating surfaces have a surface roughness of 40 nm Ra. The flatness of the copper side surface is 3.7 \u0026micro;m on a 10 mm x 7 mm surface. The surfaces of the copper samples were cleaned with acetone and held together in the precision vise. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e displays the experimental setup. The precision vise was mounted on the Kistler Minidyn dynamometer. The edge radius of the sapphire tool was measured using the edge reversal technique, as reported by Dodmani et al.[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e] Cutting edge of the tool was indented onto the surface of a split copper block. The two blocks were then separated, and the cross section of the cutting-edge profile was observed in a scanning electron microscope (SEM) to measure the edge radius of the sapphire tool.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Orthogonal cutting setup\u003c/h2\u003e \u003cp\u003eOrthogonal cutting (tube end turning) is performed in Toshiba ULG-100C (H\u0026sup3;) an ultra-precision aspheric grinder. The machine has positioning resolution of 1 nm in the X, Y and Z-axes and is equipped with aerostatic bearing for work spindle with vacuum chuck. A cylindrical workpiece is fabricated, having three concentric channels with a width of 0.5 mm, located at diameters of 42 mm, 28 mm, and 14 mm as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e displays the materials selected for the workpiece and their respective chemical compositions. The workpiece is secured on to a 100 mm diameter flat disc held by vacuum chuck.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e displays the experimental setup of orthogonal cutting in the machine. Rough cutting passes are performed using CBN tool to make the surface flat and set zero reference. The sapphire cutting tool is rigidly held in a copper block which is mounted on EN8 Tool holder that is attached directly to the Kistler Type 9256 three-component piezoelectric force dynamometer as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e. The tool\u0026rsquo;s cutting edge is positioned 500 \u0026micro;m away from the zero reference prior to machining to ensure the gradual engagement of tool\u0026rsquo;s cutting edge with workpiece. The orthogonal cutting parameters like cutting speeds and uncut chip thickness are shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The experiments are performed by maintaining a constant uncut chip thickness while varying the cutting speed, and alternatively keeping the cutting speed constant while varying the uncut chip thickness. The effect of cutting parameters on surface finish, cutting force, thrust force, friction coefficient and chips are studied.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eOrthogonal cutting conditions\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWorkpiece Material\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eOFHC Copper, Free cutting brass, Al 6061, and Stavax ESR\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCutting tool\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSingle crystal alumina (Sapphire)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRake angle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eClearance angle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7\u0026deg;\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEdge radius\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e432 nm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUncut chip thickness\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.1 \u0026micro;m, 0.5 \u0026micro;m, 1 \u0026micro;m, 2 \u0026micro;m, 3 \u0026micro;m\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCutting velocity\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1 m/s, 1.5 m/s, 2 m/s, 3 m/s\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical composition of workpiece materials\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWorkpiece Material\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eChemical Composition\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eOFHC Copper \u0026ndash; C10200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e99.9% Cu\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFree Cutting Brass -C38500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e59% Cu, 37% Zn, 3.5% Pb\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAl 6061\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e97.9% Al, 0.6% Si, 1.0% Mg, 0.2% Cr, 0.28% Cu\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eStavax ESR steel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e84.47% Fe, 13.6% Cr, 0.75% Si, 0.5% Mn, 0.38% C, 0.3% V\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Result and discussions","content":"\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Sapphire tool fabrication and edge radius measurement\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;6 presents the schematic and SEM images of the flank face, cutting edge, and the indentation profile of the sapphire tool after each stage of lapping, polishing, and CMP. Initially, the sapphire tool underwent lapping using #400 boron carbide abrasives on a cast iron lap, resulting in a material removal rate of 10 \u0026micro;m/min. After this step, a sapphire tool featuring a 6mm width cutting edge and a 7\u0026deg; clearance angle was successfully fabricated. Figure\u0026nbsp;6(step1-b) illustrates the SEM image of the cutting edge that appears blunt. This is evident from the Fig.\u0026nbsp;6(step1-c) that depicts the SEM image of the indentation profile of sapphire tool, the edge radius measured was 13.5 \u0026micro;m. Hence, the need for further refinement in the polishing process to fabricate the sharp sapphire tool with lesser cutting-edge radius.\u003c/p\u003e \u003cp\u003eSubsequently, following the initial lapping process, the tool underwent polishing using a 3 \u0026micro;m diamond slurry applied on a spiral groove copper. The material removal rate in this process was 0.5 \u0026micro;m/min. The flank surface finish experienced a significant improvement, observed a decrease in surface roughness from 170 nm R\u003csub\u003ea\u003c/sub\u003e to 13.2 nm R\u003csub\u003ea\u003c/sub\u003e and the same is evident from Fig.\u0026nbsp;6(step2-a). The sharpness of the cutting tool is dependent on the edge chipping[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Higher MRR tends to cause increased chipping, consequently reducing sharpness and vice versa. The lapping process has high MRR compared to polishing process therefore, the sharpness of cutting edge improved in the polishing process as observed in Fig.\u0026nbsp;6(step2-b). From the sapphire tool\u0026rsquo;s indentation profile as shown in Fig.\u0026nbsp;6(step2-c), the edge radius measured was 2.8 \u0026micro;m.\u003c/p\u003e \u003cp\u003eTo further eliminate polishing marks on the flank face of the sapphire tool and improve the sharpness the CMP process was employed. The flank face\u0026rsquo;s surface finish enhanced from 13.2 nm R\u003csub\u003ea\u003c/sub\u003e to 2 nm R\u003csub\u003ea\u003c/sub\u003e as shown in Fig.\u0026nbsp;6(step3-a). The MRR of the CMP process is in few nanometers per minute which is least among polishing and lapping. Hence, least edge chipping was observed in this process which resulted in a sharp cutting edge as depicted in Fig.\u0026nbsp;6(step3-b). From the sapphire tool\u0026rsquo;s indentation profile as shown in Fig.\u0026nbsp;6(step3-c), the cutting-edge radius measured was 430nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Performance of sapphire tool while machining OFHC copper\u003c/h2\u003e \u003cp\u003eThrust forces and cutting forces during the orthogonal cutting are measured from Kistler Type 9256 three-component piezoelectric force dynamometer. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003ea displays the plot of cutting and thrust force against cutting speed, at a constant UCT of 1 \u0026micro;m. Cutting force is greater than the thrust force indicating material removal is taking place in shear mode as UCT 1 \u0026micro;m. However, it is observed that the cutting force increases with an increase in cutting speed. Due to its high ductility and low yield strength, OFHC copper displays a greater effect of strain rate hardening with an increase in cutting speed[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e], rather than thermal softening.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003eb displays the plot of cutting and thrust force against UCT, at a constant cutting speed of 1 m/s. As the UCT is increased from 0.1 \u0026micro;m to 3 \u0026micro;m, both the cutting force and thrust force increase due to higher material removal rate. Ploughing material removal mode is predominant when UCT is less than 0.5 \u0026micro;m, as the thrust force is greater than the cutting force. However, at UCT greater than 0.5 \u0026micro;m, shear material mode dominates, as the cutting force becomes greater than the thrust force[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Consequently, increasing UCT results in improved surface finish.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe apparent coefficient friction (\u0026micro;) between the rake face of the tool and chip is obtained from the Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Where, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({F}_{c }\\)\u003c/span\u003e\u003c/span\u003eis cutting force, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({F}_{t }\\)\u003c/span\u003e\u003c/span\u003eis thrust force and α is the effective rake angle.\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\mu = \\frac{{F}_{t}+ {F}_{c }\\text{tan}\\alpha }{{F}_{c}- {F}_{t }\\text{tan}\\alpha }$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe effective rake angle (α) is the angle between the vertical axis and the tangent to the contact point between the cutting tool and the UCT as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e8\u003c/span\u003e. When the uncut chip thickness is less than the edge radius, the effective rake angle is obtained from Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. Where, \u003cem\u003eα\u003c/em\u003e is the effective rake angle, \u003cem\u003et\u003c/em\u003e is the uncut chip thickness and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({r}_{e}\\)\u003c/span\u003e\u003c/span\u003e is the cutting-edge radius of the Sapphire tool.\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\alpha ={\\text{sin}}^{-1}\\frac{({r}_{e}-t)}{{r}_{e}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhen the UCT is 100 nm, which is below the cutting-edge radius of 432 nm, the application of Eq.\u0026nbsp;\u003cspan refid=\"Equ2\" class=\"InternalRef\"\u003e2\u003c/span\u003e results in an effective rake angle of 50\u0026deg;. In all other cases where UCT exceeds the edge radius i.e., 432 nm the effective rake angle (α) becomes zero degree because the rake angle of the Sapphire tool is also zero. The values of α are substituted in the Eq.\u0026nbsp;\u003cspan refid=\"Equ1\" class=\"InternalRef\"\u003e1\u003c/span\u003e accordingly to determine the apparent coefficient of friction (\u0026micro;). Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ea displays the relationship between coefficient of friction and cutting speed (m/s), plotted for a UCT of 1 \u0026micro;m. It is observed that the friction coefficient decreases from 0.88 at 1 m/s cutting speed to 0.815 at 2 m/s cutting speed and further increases to 0.822 at 3 m/s.\u003c/p\u003e \u003cp\u003eThe average surface roughness R\u003csub\u003ea\u003c/sub\u003e on the machined surface across the cutting direction is measured using Olympus confocal microscope. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting speed (m/s), plotted for a UCT of 1 \u0026micro;m. It is observed that the surface roughness tends to decrease from 43 nm to 12 nm as the cutting speed is increased from 1 m/s to 2 m/s. This is due to the decrease in the friction coefficient from 0.88 at 1 m/s cutting speed to 0.815 at 2 m/s as displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ea. The reduction in the coefficient of friction causes less adhesion between the tool rake face and the chip thus improving the chip separation and achieving better surface finish on the surface. Subsequently, there is a slight increase in average surface roughness to 14 nm at a cutting speed of 3 m/s. This can be attributed to an increase in the friction coefficient from 0.8148 at 2 m/s to 0.822 at 3 m/s as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e9\u003c/span\u003ea. As the adhesion between tool and chip increases it deteriorates the chip separation hence increase in the surface roughness.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003ea illustrates the plot of the apparent coefficient of friction plotted against UCT (\u0026micro;m) for a constant cutting speed of 1 m/s. It is observed that the friction coefficient decreases from 3.14 at 0.1 \u0026micro;m UCT to 0.78 at 2 \u0026micro;m UCT and further increases to 0.805 at 3 \u0026micro;m UCT. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e10\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and UCT (\u0026micro;m), plotted for a constant cutting speed of 1 m/s. The surface roughness R\u003csub\u003ea\u003c/sub\u003e decreased from 69 nm to 9 nm with increase in UCT from 0.1 \u0026micro;m to 2 \u0026micro;m. This is due to the decrease in the apparent friction coefficient from 3.14 at 0.1 \u0026micro;m UCT to 0.78 at 2 \u0026micro;m because the material removal mode changes from ploughing at 0.1 \u0026micro;m to shearing at 2 \u0026micro;m. Consequently, the average surface roughness increased to 36 nm at 3 \u0026micro;m UCT as friction coefficient increased to 0.805. As, the increase in depth of cut caused increased the tool-chip contact length increasing the adhesion as result of which poor surface finish on workpiece surface[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAfter machining OFHC copper the chips are collected and observed under a scanning electron microscope. The use of sapphire tool used for machining OFHC copper produced small, discontinuous, and straight chips which indicates the material removal is occurred through fracture. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e11\u003c/span\u003e displays the chip morphology at cutting speeds of 1m/s and 3m/s. It is observed that at the higher speed of 3m/s, the edges of the chips are torn, suggesting that brittle fracture is the dominant mechanism due to strain rate hardening.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e12\u003c/span\u003e displays the chip morphology at UCT of 0.1 \u0026micro;m and 3 \u0026micro;m. It is seen that at UCT 0.1 \u0026micro;m chips produced are long and continuous implies that material removal is through plastic deformation than fracture, because the UCT is less than the cutting-edge radius. On contrary at UCT 3 \u0026micro;m chips are short, thick, and discontinuous because fracture material removal mode is dominant as UCT is much greater than cutting-edge radius.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e13\u003c/span\u003e displays the sapphire tool\u0026rsquo;s cutting edge after machining OFHC copper with cutting distance of 10 m. From the image it is clear that tool wear is negligible because the sapphire being many times harder than the copper. Hence, sapphire can be considered as tool material for ultraprecision turning of the OFHC copper.\u003c/p\u003e \u003cp\u003eTo summarize the performance of sapphire tool while machining OFHC copper. It was observed that increasing the cutting speed from 1 m/s to 3 m/s resulted in an overall increase in both the cutting and thrust forces. This can be attributed to the strain rate hardening behaviour of OFHC copper due to its high ductility and low yield strength. Evidently the chips generated at 3 m/s had more torn edges compared to those produced at 1 m/s indicating presence of brittle fracture due to the strain hardening. The cutting force value increased significantly than the thrust force as the cutting speed increased from 1 m/s to 3 m/s indicating shear mode of fracture being dominant. Therefore, a corresponding reduction in surface roughness was observed, decreasing from 43 nm to 14 nm.\u003c/p\u003e \u003cp\u003eAs the UCT increased from 0.1 \u0026micro;m to 3 \u0026micro;m, there was a raise in both the cutting force and thrust force due to the greater amount of material being removed during the machining process. Initially, up to a UCT of 0.5 \u0026micro;m, the thrust force exceeded the cutting force as the UCT value approached the edge radius. However, once the UCT exceeded 0.5 \u0026micro;m, the cutting force surpassed the thrust force. Consequently, at a UCT of 0.1 \u0026micro;m, the chips produced exhibited a straight and continuous morphology, indicating that plastic deformation was the dominant mechanism of material removal. On the other hand, at a UCT of 3 \u0026micro;m, the chips were shorter, thicker, and discontinuous, indicating that fracture was the predominant mode of material removal. This was reflected the surface roughness, where an increase in UCT from 0.1 \u0026micro;m to 3 \u0026micro;m resulted in a decrease in average surface roughness (R\u003csub\u003ea\u003c/sub\u003e) from 69 nm to 36 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Performance of sapphire tool while machining of free cutting brass\u003c/h2\u003e \u003cp\u003eThe cutting and thrust forces (N) against cutting speed (m/s) for a constant UCT (uncut chip thickness) of 1 \u0026micro;m are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e14\u003c/span\u003ea. It is notable that the thrust force exceeds the cutting force, which is attributed to the high ductility and severe plastic deformation exhibited by brass during machining. Subsequently, a decrease in both thrust and cutting forces is observed as the cutting speed is increased from 1 m/s to 3 m/s. This decrease can be attributed to the effect of thermal softening, which is more prominent in free cutting brass due to its high ductility and plasticity[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e14\u003c/span\u003eb displays the plot of cutting and thrust force (N) against UCT (\u0026micro;m), at a constant cutting speed of 2 m/s. It can be observed that the cutting force continuously increases as the UCT is increased from 0.1 \u0026micro;m to 3 \u0026micro;m, due to the corresponding increase in material removal rate. Additionally, it is noted that until a UCT of 2 \u0026micro;m, the thrust force exceeds the cutting force, suggesting that ploughing material removal mode is dominant during this range. However, after the 2 \u0026micro;m UCT mark, the cutting force becomes greater than the thrust force, indicating the dominance of the shear material removal mode. Consequently, an increase in UCT leads to an improvement in surface finish.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e15\u003c/span\u003ea illustrates the plot of apparent coefficient of friction against cutting speed for constant uncut chip thickness of 1 \u0026micro;m. The friction coefficient declines from 2.18 at 1 m/s cutting speed to 1.28 at 3 m/s cutting speed. The average surface roughness R\u003csub\u003ea\u003c/sub\u003e on the machined surface across the cutting direction is measured. Figure\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e15\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting speed (m/s), plotted for a UCT of 1 \u0026micro;m. It is observed that the surface roughness tends to decrease from 91 nm to 38 nm as the cutting speed is increased from 1 m/s to 3 m/s. The decline in the roughness is due to the decrease in the friction coefficient from 2.18 at 1 m/s cutting speed to 1.28 at 3 m/s as displayed in Fig.\u0026nbsp;\u003cspan refid=\"Fig14\" class=\"InternalRef\"\u003e15\u003c/span\u003ea. Thermal softening is more prominent in the machining of free cutting brass with an increase in the cutting speed that leads to decrease in apparent coefficient of friction. The chip separation becomes easy at higher cutting speeds as a result we achieved better surface finish.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e16\u003c/span\u003ea displays the plot of apparent coefficient of friction plotted against uncut chip thickness (\u0026micro;m) for a constant cutting speed of 2 m/s. The friction coefficient declines from 4.35 at 0.1 \u0026micro;m UCT to 0.59 at 3 \u0026micro;m UCT. Figure\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e16\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e and UCT, plotted for a constant cutting speed of 2 m/s. The surface roughness R\u003csub\u003ea\u003c/sub\u003e decreased from 71 nm to 34 nm as UCT increases from 0.1 \u0026micro;m to 3 \u0026micro;m. This reduction in roughness is due to the decrease in the apparent friction coefficient from 4.35 at 0.1 \u0026micro;m UCT to 0.59 at 3 \u0026micro;m as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig15\" class=\"InternalRef\"\u003e16\u003c/span\u003ea. The change in friction coefficient is a result of shift in material removal mode ploughing at 0.1 \u0026micro;m to shearing at 3 \u0026micro;m. The interaction between the tool and chip changes from sticking to sliding.\u003c/p\u003e \u003cp\u003eAfter machining free cutting brass, the chips are collected and observed under a scanning electron microscope (SEM). The use of sapphire as a tool material in machining free cutting brass results in the production of continuous, and ribbon-like chips, which suggests that material removal occurs primarily through plastic deformation. Figure\u0026nbsp;\u003cspan refid=\"Fig16\" class=\"InternalRef\"\u003e17\u003c/span\u003e shows the chip morphology at cutting speeds of 1m/s and 3m/s. It is noted that the curl of the chip increases at the higher speed of 3m/s. Additionally, the chip surface in contact with the cutting tool has fewer scratches and pits (is smoother) and appears shiny in the case of a 3 m/s cutting speed compared to that produced with a 1 m/s cutting speed. This suggests that thermal softening occurs at high cutting speeds.\u003c/p\u003e\u003cp\u003eThe morphology of chips produced at UCT of 0.1 \u0026micro;m and 3 \u0026micro;m is presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig17\" class=\"InternalRef\"\u003e18\u003c/span\u003e. It can be observed that when the UCT is 0.1 \u0026micro;m, the chips produced are long, straight, and exhibit torn edges, indicating that brass behaves as a brittle material. This phenomenon occurs when the UCT is less than the cutting-edge radius. Conversely, at UCT of 3 \u0026micro;m, the chips are continuous and ribbon-like. This condition favors a ductile mode of machining in brass, as the UCT is greater than the edge radius.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig18\" class=\"InternalRef\"\u003e19\u003c/span\u003e displays the sapphire tool\u0026rsquo;s cutting edge after machining free cutting brass with cutting distance of 10 m. From the image it is clear that tool wear is negligible because the sapphire being many times harder than the copper. Hence, Sapphire is a suitable material for cutting tool in ultraprecision turning of the Free cutting brass.\u003c/p\u003e \u003cp\u003eTo sum up the performance of the sapphire tool in machining of free cutting brass. It was observed that the cutting and thrust forces decreased as the cutting speed was increased from 1 m/s to 3 m/s. The higher ductility and significant plastic deformation exhibited by brass resulted in a thrust force higher than the cutting force. This was evident from the chip morphology, which showed continuous and ribbon-like chips, indicating that material removal predominantly occurred through plastic deformation. Additionally, both cutting forces exhibited a decrease as the cutting speed increased due to the occurrence of thermal softening. Furthermore, an increase in chip curling and a smoother contact surface of the chip were observed as the cutting speed increased, indicating the influence of thermal softening. Therefore, the surface finish improved from 91 nm to 38 nm as the cutting speed was increased from 1 m/s to 3 m/s.\u003c/p\u003e \u003cp\u003eThe increase in UCT from 0.1 \u0026micro;m to 3 \u0026micro;m led to an increase in cutting force due to higher material removal, while thrust force decreased. The dominance of ploughing mode of material removal was indicated by the higher thrust force until a UCT of 2 \u0026micro;m, after which shear mode material removal prevailed. Chip morphology also reflected this behavior, with long and straight chips with torn edges at 0.1 \u0026micro;m UCT, indicating the brittle behavior of the brass during ploughing. In contrast, at 3 \u0026micro;m UCT, continuous and ribbon-like chips were observed, signifying shear mode material removal. As a result, the average surface roughness decreased from 71 nm at 0.1 \u0026micro;m UCT to 34 nm at 3 \u0026micro;m UCT.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Performance of Sapphire tool while machining of Al 6061\u003c/h2\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e20\u003c/span\u003ea illustrates the relationship between cutting speed (m/s) and the cutting and thrust forces (N) at a constant UCT of 2 \u0026micro;m. The cutting force surpasses the thrust force, indicating the predominant material removal mechanism in shear mode. Moreover, as the cutting speed rises from 1 m/s to 3 m/s, both the thrust and cutting forces demonstrate a decrease. This reduction can be attributed to the decline in tool-chip contact area and the decrease in shear strength within the flow zone, which occurs as the cutting speed increases, resulting in elevated temperatures[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig19\" class=\"InternalRef\"\u003e20\u003c/span\u003eb exhibits the plot of cutting and thrust forces (N) against UCT (\u0026micro;m) at a constant cutting speed of 2 m/s. It can be observed that the thrust and cutting forces continuously increase as the UCT is increased from 0.5 \u0026micro;m to 3 \u0026micro;m, due to the corresponding increase in material removal rate.\u003c/p\u003e\u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e21\u003c/span\u003ea displays the plot of apparent coefficient of friction against cutting speed for constant uncut chip thickness of 2 \u0026micro;m. The friction coefficient decreases from 0.842 at 1 m/s cutting speed to 0.802 at 3 m/s cutting speed. The average surface roughness R\u003csub\u003ea\u003c/sub\u003e on the machined surface across the cutting direction is measured. Figure\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e21\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e (nm) and cutting speed (m/s), plotted for a UCT of 2 \u0026micro;m. It is observed that the surface roughness tends to decrease from 50 nm to 14 nm as the cutting speed is increased from 1 m/s to 3 m/s. The reduction in the surface roughness is caused due to a decline in the friction coefficient from 0.842 at 1 m/s to 0.802 at 3 m/s as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig20\" class=\"InternalRef\"\u003e21\u003c/span\u003ea. The thermal softening at higher cutting speed causes the reduction apparent friction coefficient.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e22\u003c/span\u003ea illustrates the plot of apparent coefficient of friction plotted against uncut chip thickness (\u0026micro;m) for a constant cutting speed of 2 m/s. The friction coefficient declines from 0.936 at 0.5 \u0026micro;m UCT to 0.827 at 3 \u0026micro;m UCT. Figure\u0026nbsp;\u003cspan refid=\"Fig21\" class=\"InternalRef\"\u003e22\u003c/span\u003eb displays the relationship between average surface roughness R\u003csub\u003ea\u003c/sub\u003e and UCT, plotted for a constant cutting speed of 2 m/s. The surface roughness R\u003csub\u003ea\u003c/sub\u003e decreased from 90 nm to 34 nm as UCT increases from 0.5 \u0026micro;m to 3 \u0026micro;m. This reduction in roughness is due to the decrease in the apparent friction coefficient from 0.936 at 0.5 \u0026micro;m UCT to 0.827 at 3 \u0026micro;m. The change in friction coefficient is attributed to change in material removal mechanism from ploughing at 0.5 \u0026micro;m to shearing at 3 \u0026micro;m. Additionally, built-up edge (BUE) formation is more prominent at lower UCT like causing the increase in the apparent coefficient of friction. The adhesion between the chip and tool rake face increases the BUE formation resulting in poor surface finish. Therefore, surface finish improved from 90 nm at 0.5 \u0026micro;m UCT to 34 nm at 3 \u0026micro;m UCT.\u003c/p\u003e \u003cp\u003eAfter machining Al 6061, the chips are collected and observed under a SEM. Figure\u0026nbsp;\u003cspan refid=\"Fig22\" class=\"InternalRef\"\u003e23\u003c/span\u003e illustrates the chip morphology at cutting speeds of 1m/s and 3m/s. It is observed that as the cutting speed increases, the chip thickness decreases. Machining of Al 6061 with sapphire tool results in the production of continuous chips, no curling of chips is observed. The chip formed where of continuous shape, with a relatively uniform thickness and smooth surface. The formation of such continuous chips can be attributed to the more ductile behavior exhibited by Al 6061.\u003c/p\u003e \u003cp\u003eAt lower cutting speeds, the rate of deformation and strain on the material being machined is reduced. This slower cutting speed provides more time for the material to undergo plastic deformation and flow smoothly along the shear plane. Consequently, the chip formed during machining exhibits a continuous shape with a relatively uniform thickness and smooth surface. The lower cutting speeds result in lower forces acting on the material, creating a more stable and predictable chip formation process. The material can undergo substantial plastic deformation before reaching its failure point, leading to the formation of a continuous chip rather than fragmentation or serration.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe chip morphology at different UCT of 0.5 \u0026micro;m and 3 \u0026micro;m is depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig23\" class=\"InternalRef\"\u003e24\u003c/span\u003e. When the UCT is 0.5 \u0026micro;m, the chips formed are discontinuous due to inadequate tool-workpiece contact length. However, as the UCT is increased from 0.5 \u0026micro;m to 3 \u0026micro;m, the chips transition to a continuous form with regular lamella formation. This transformation is attributed to the higher UCT, which causes the material ahead of the tool to be moved in the cutting direction, leading to the creation of a shear band. As a result, the work material is removed through a conventional shearing mechanism, resulting in the generation of long continuous chips. Moreover, the increased UCT reduces the surface fragmentation of microchips by expanding the layer of material removal.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig24\" class=\"InternalRef\"\u003e25\u003c/span\u003e showcases the cutting edge of the sapphire tool after machining Al 6061 with a cutting distance of 10 m. The presence of significant wear on the rake surface and the absence of wear on the flank surface indicate the formation of a built-up edge. Oishi[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] observed similar phenomena during machining of Aluminium 2014 T6 alloy with alumina tool. The built-up edge occurs due to the affinity of the alumina towards the aluminum in Al 6061. During the machining process, increase in temperature at tool-chip interface causes welding between alumina at cutting and Al6061 this results in built-up edge formation[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Furthermore, Al 6061 contains precipitation hardening Mg-Si alloys which are hard and brittle cause irregular machining conditions[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. This leads to high tool wear and poor surface roughness.\u003c/p\u003e \u003cp\u003eTo summarize the machining of Al 6061 using Sapphire tool. It was observed that the cutting and thrust forces decreased as the cutting speed increased from 1 m/s to 3 m/s. This reduction was attributed to a smaller tool-chip contact area and a decrease in shear strength within the flow zone at elevated temperatures. Evidently, the chip morphology exhibited a decrease in thickness as the cutting speed increased from 1 m/s to 3 m/s. The chips generated during the machining process displayed a continuous and uniform thickness, which can be attributed to the ductile behavior of Al 6061. Consequently, an improvement in surface finish was observed, with the surface roughness (Ra) decreasing from 50 nm to 14 nm as the cutting speed increased from 1 m/s to 3 m/s.\u003c/p\u003e \u003cp\u003eAs the UCT increased from 0.5 \u0026micro;m to 3 \u0026micro;m, there was a raise in both the cutting force and thrust force due to the greater amount of material being removed during the machining process. The cutting force was higher than the thrust force indicating shear mode material removal. Consequently, at a UCT of 0.5 \u0026micro;m, the chips formed are discontinuous due to inadequate tool-workpiece contact length. However, at 3 \u0026micro;m the chips were continuous with regular lamella formation, and thicker. Furthermore, the surface finish improved from 90 nm at 0.5 \u0026micro;m UCT to 34 nm at 3 \u0026micro;m UCT. However, during the machining of Al 6061 using the Sapphire tool, the presence of built-up edge formation was observed. This was evident from the examination of the cutting edge, where significant wear was observed on the rake face, while the flank surface showed no signs of wear.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Performance of sapphire tool while machining Stavax ESR steel.\u003c/h2\u003e \u003cp\u003eStavax ESR, known for its high hardness, toughness, and yield strength, posed challenges when machined with a sapphire tool. During the machining observed chatter and severe tool wear. As depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig25\" class=\"InternalRef\"\u003e26\u003c/span\u003e edge chipping was observed on both the rake and flank faces of the tool. Consequently, the surface finish of the workpiece was poor, and didn\u0026rsquo;t have the desired optical quality finish. Consequently, we were unable to conduct an in-depth analysis of the impact of process parameters such as uncut chip thickness and cutting speed on critical factors like cutting thrust forces, surface roughness, and chip morphology. As a result, it can be concluded that sapphire cutting tool is unsuitable for ultra-precision machining of Stavax ESR steel.\u003c/p\u003e \u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eSapphire, a single crystal alumina, possesses exceptional properties such as a hardness of 22 GPa, chemical inertness, and the ability to be grown in bulk sizes. These qualities position it as a promising candidate for cutting tool materials in ultra-precision machining. This study focuses on the fabrication technique of a sharp sapphire tool, the measurement of its cutting-edge radius, and its performance in ultra-precision machining of non-ferrous alloys.\u003c/p\u003e \u003cp\u003eSapphire as an alternative to single crystal diamond tool for ultra-precision machining has been tested in this study. The sapphire tool with uniform sharp cutting edge is fabricated with a specialized setup employing a series of operations such as lapping, polishing, and chemical mechanical polishing. The performance of the fabricated sapphire tool is evaluated via orthogonal cutting of OFHC copper, free-cutting brass, Al 6061 and Stavax ESR steel using an ultra-precision lathe. The study revealed the following observations:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eWhile machining OFHC copper, with increase in cutting speed, the cutting and thrust force increase due to the strain rate hardening effect. However, the friction coefficient decreases resulting in improvement of surface finish from 43nm Ra at 1m/s to 12nm Ra at 3m/s for constant UCT 1\u0026micro;m. Also, roughness decreased from 69nm Ra at 1\u0026micro;m to 36nm Ra at 3\u0026micro;m for constant speed 1m/s because of shear mode of material removal as evident from chip morphology. Furthermore, the sapphire tool cutting-edge retained its geometry with very little wear after machining OFHC copper.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eMachining of free-cutting brass showed that with the increase in cutting speed, the cutting and thrust force decrease due to thermal softening. The friction coefficient decreases, resulting in improved surface finish from 91nm Ra at 1m/s to 38nm Ra at 3m/s for constant UCT 1\u0026micro;m. An increase in uncut chip thickness (UCT) resulted in a rise in cutting force, while thrust force decreased as the material removal mode shifted from ploughing to shearing. The surface finish is enhanced from 71nm Ra at 1\u0026micro;m to 34nm Ra at 3\u0026micro;m for constant speed 1m/s because of the shearing mode of material removal at elevated uncut chip thickness (UCT). Furthermore, the sapphire tool cutting-edge suffered very less wear after machining free-cutting brass.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDuring the machining of Al 6061, as the cutting speed increases, both cutting and thrust forces decrease because of the effect of thermal softening. Furthermore, surface finish improved from 50nm Ra at 1m/s to 14nm Ra at 3m/s for constant UCT 1\u0026micro;m. Increase in uncut chip thickness (UCT), both cutting and thrust raises due to high material removal. The surface roughness decreased from 90nm Ra at 1\u0026micro;m to 34nm Ra at 3\u0026micro;m for constant speed 1m/s because of shear mode of material removal at high UCT. However, a built-up edge (BUE) was observed on the rake face at the sapphire tool's cutting edge during the machining of Al 6061 due to the affinity of alumina towards the aluminum in the workpiece.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDuring machining of Stavax-ESR, known for its high hardness and toughness, edge chipping occurred at the cutting edge of the sapphire tool, resulting in a poor surface finish on the machined surface.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eIn summary, sapphire tools have good potential to machine OFHC copper and free-cutting brass with very less tool wear and achieve optical quality surface finish with surface roughness in the range of 10\u0026ndash;40 nm. However, the sapphire cutting tool may not be suitable for machining Al6061 and Stavax as the edge suffers from BUE formation edge chipping, respectively. A sapphire tool with a nose radius can be made in the future for fabricating practically useful optical components made of OFHC copper and free-cutting brass.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Amit Dodmani, Sathyan Subbiah and A.Senthil Kumar. The first draft of the manuscript was written by Amit Dodmani and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received financial support from Global Engagement office, Indian Institute of Technology Madras (IITM).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003eThe authors declare no competing interests.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eBalasubramaniam R, Sarepaka RV, Subbiah S (2017) Diamond Turn Machining\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDodmani A, Subbaih S, Senthil Kumar A (2023) Sapphire as a Single-Crystal Cutting Tool for Machining Ferrous-Based Optics. 613\u0026ndash;616. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3850/978-981-18-6021-8_or-12-0101.html\u003c/span\u003e\u003cspan address=\"10.3850/978-981-18-6021-8_or-12-0101.html\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePishchik V, Lytvynov LA, Dobrovinskaya ER (2009) Sapphire\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMadhavan V, Chandrasekar S, Farris TN (2002) Direct observations of the chip-tool interface in the low speed cutting of pure metals. J Tribol 124:617\u0026ndash;626. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1115/1.1398546\u003c/span\u003e\u003cspan address=\"10.1115/1.1398546\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHuang C, Lee S, Sullivan JP, Chandrasekar S (2007) In situ measurement of fluid film thickness in machining. Tribol Lett 28:39\u0026ndash;44. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11249-007-9245-6\u003c/span\u003e\u003cspan address=\"10.1007/s11249-007-9245-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSociety R (2018) Stress Analysis in Machining with the Use of Sapphire Tools Author (s): A. Bagchi and P. K. Wright Source : Proceedings of the Royal Society of London. Series A, Mathematical and Physical Published by : Royal Society Stable URL : \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.jstor\u003c/span\u003e\u003cspan address=\"https://www.jstor\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e. 409:99\u0026ndash;113\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePark SS, Wei Y, Jin XL (2018) Direct laser assisted machining with a sapphire tool for bulk metallic glass. CIRP Ann 67:193\u0026ndash;196. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cirp.2018.04.070\u003c/span\u003e\u003cspan address=\"10.1016/j.cirp.2018.04.070\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOishi K (1996) Mirror cutting of aluminum with sapphire tool. J Mater Process Technol 62:331\u0026ndash;334. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/S0924-0136(96)02430-2\u003c/span\u003e\u003cspan address=\"10.1016/S0924-0136(96)02430-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIs O, Work L (1986) pare damage-free sapphire surfaces. The starting material. Appl Opt 25:2639\u0026ndash;2640\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLee T, Jeong H, Lee S et al (2021) Material removal model for lapping process based on spiral groove density. Appl Sci 11. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/app11093950\u003c/span\u003e\u003cspan address=\"10.3390/app11093950\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAida H, Doi T, Takeda H et al (2012) Ultraprecision CMP for sapphire, GaN, and SiC for advanced optoelectronics materials. Curr Appl Phys 12:S41\u0026ndash;S46. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cap.2012.02.016\u003c/span\u003e\u003cspan address=\"10.1016/j.cap.2012.02.016\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDodmani A, Subbiah S (2022) Accurate measurement of cutting-edge radius on a single-crystal diamond tool. Manuf Lett 33:469\u0026ndash;478. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.mfglet.2022.08.004\u003c/span\u003e\u003cspan address=\"10.1016/j.mfglet.2022.08.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZong WJ, Li D, Sun T, Cheng K (2006) Contact accuracy and orientations affecting the lapped tool sharpness of diamond cutting tools by mechanical lapping. Diam Relat Mater 15:1424\u0026ndash;1433. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.diamond.2005.10.066\u003c/span\u003e\u003cspan address=\"10.1016/j.diamond.2005.10.066\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJordan JL, Siviour CR, Sunny G et al (2013) Strain rate-dependant mechanical properties of OFHC copper. J Mater Sci 48:7134\u0026ndash;7141. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s10853-013-7529-9\u003c/span\u003e\u003cspan address=\"10.1007/s10853-013-7529-9\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eVenkatesh V, Swain N, Srinivas G et al (2017) Review on the machining characteristics and research prospects of conventional microscale machining operations. Mater Manuf Process 32:235\u0026ndash;262. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/10426914.2016.1151045\u003c/span\u003e\u003cspan address=\"10.1080/10426914.2016.1151045\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNg CK, Melkote SN, Rahman M, Senthil Kumar A (2006) Experimental study of micro- and nano-scale cutting of aluminum 7075-T6. Int J Mach Tools Manuf 46:929\u0026ndash;936. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijmachtools.2005.08.004\u003c/span\u003e\u003cspan address=\"10.1016/j.ijmachtools.2005.08.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eIslam S, Khandoker N, Izham M et al (2017) Development of a Low Cost MQL Setup for Turning Operations. MATEC Web Conf 95. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1051/matecconf/20179510004\u003c/span\u003e\u003cspan address=\"10.1051/matecconf/20179510004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang H, You Z, Lu L (2018) Kinematic and isotropic strain hardening in copper with highly aligned nanoscale twins. Mater Res Lett 6:333\u0026ndash;338. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/21663831.2018.1455752\u003c/span\u003e\u003cspan address=\"10.1080/21663831.2018.1455752\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKlocke F, Nobel C, Veselovac D (2016) Influence of Tool Coating, Tool Material, and Cutting Speed on the Machinability of Low-Leaded Brass Alloys in Turning. Mater Manuf Process 31:1895\u0026ndash;1903. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/10426914.2015.1127944\u003c/span\u003e\u003cspan address=\"10.1080/10426914.2015.1127944\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXu D, Feng P, Li W et al (2014) Research on chip formation parameters of aluminum alloy 6061-T6 based on high-speed orthogonal cutting model. Int J Adv Manuf Technol 72:955\u0026ndash;962. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00170-014-5700-3\u003c/span\u003e\u003cspan address=\"10.1007/s00170-014-5700-3\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAhmad Fauzi MN, Uday MB, Zuhailawati H, Ismail AB (2010) Microstructure and mechanical properties of alumina-6061 aluminum alloy joined by friction welding. Mater Des 31:670\u0026ndash;676. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matdes.2009.08.019\u003c/span\u003e\u003cspan address=\"10.1016/j.matdes.2009.08.019\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang SJ, To S, Cheung CF (2012) Effect of workpiece material on surface roughness in ultraprecision raster milling. Mater Manuf Process 27:1022\u0026ndash;1028. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/10426914.2011.654165\u003c/span\u003e\u003cspan address=\"10.1080/10426914.2011.654165\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Sapphire, orthogonal cutting, ultra-precision machining, OFHC Copper, Free cutting brass","lastPublishedDoi":"10.21203/rs.3.rs-3878526/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3878526/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAchieving a smooth surface finish in optical components by machining requires wear resistant sharp cutting tools. Single crystal diamond as a cutting tool material has met this requirement so far, but at a cost disadvantage. An economical alternative, such as alumina single crystal(sapphire), with sufficient hardness, wear resistance, and chemical inertness, is explored in this work. A sapphire cutting tool with a zero rake, seven-degree clearance, and edge radius of about 430 nm is fabricated using lapping, polishing, and chemical mechanical polishing processes. The performance of the tool was evaluated via orthogonal cutting of OFHC copper, free-cutting brass, Al6061, and Stavax ESR steel. The influence of parameters, such as cutting speed and uncut chip thickness, on surface finish, cutting force, thrust force, friction coefficient, and chip morphology are analyzed. It was observed that the sapphire tool generates surfaces with average roughness ranging from 10\u0026ndash;40 nm on copper and aluminum alloys. However, minimal tool wear observed in the machining of copper alloys and excessive in the aluminum alloy and Stavax. Furthermore, built-up edge was significant in Al6061, and edge chipping was dominant in Stavax during machining. Sapphire is a suitable alternative cutting tool material for machining copper alloys.\u003c/p\u003e","manuscriptTitle":"Fabrication, characterization, and testing of a sharp cutting-edge radius sapphire tool for ultra-precision machining","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-02-22 10:59:12","doi":"10.21203/rs.3.rs-3878526/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revisions Needed","date":"2024-06-30T09:51:45+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-02-20T11:21:51+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-02-19T13:05:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-01-19T13:46:00+00:00","index":"","fulltext":""},{"type":"submitted","content":"The International Journal of Advanced Manufacturing Technology","date":"2024-01-19T08:06:12+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"the-international-journal-of-advanced-manufacturing-technology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"jamt","sideBox":"Learn more about [The International Journal of Advanced Manufacturing Technology](https://www.springer.com/journal/170)","snPcode":"170","submissionUrl":"https://submission.nature.com/new-submission/170/3","title":"The International Journal of Advanced Manufacturing Technology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"8d6ae750-b376-49be-ba1b-aebe524fe889","owner":[],"postedDate":"February 22nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-21T16:03:37+00:00","versionOfRecord":{"articleIdentity":"rs-3878526","link":"https://doi.org/10.1007/s00170-025-16071-z","journal":{"identity":"the-international-journal-of-advanced-manufacturing-technology","isVorOnly":false,"title":"The International Journal of Advanced Manufacturing Technology"},"publishedOn":"2025-07-14 15:57:13","publishedOnDateReadable":"July 14th, 2025"},"versionCreatedAt":"2024-02-22 10:59:12","video":"","vorDoi":"10.1007/s00170-025-16071-z","vorDoiUrl":"https://doi.org/10.1007/s00170-025-16071-z","workflowStages":[]},"version":"v1","identity":"rs-3878526","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3878526","identity":"rs-3878526","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}