Impact of Infill Strategy and Process Parameters on Selectivity and Performance of PLA Structures Obtained by 3D Printing

Abstract In recent years, fused deposition manufacturing (FDM) techniques have been seen as the processes of the future. One of the main challenges is to identify the optimal parameterization of the 3D printing process in terms of quality, productivity, and service durability of the resulting structures. Hardness is little studied in the literature dedicated to PLA structures, despite its importance in terms of mechanical strength and wear resistance. The correlations between the hardness of PLA structures and the parameters for adjusting 3D printing processes are almost unstudied in the scientific literature. In contrast, this work evaluates the impact of FDM process parameters on the resulting microhardness characteristics (Top/Bottom) using Design of Experiment (DOE) tools. The impact of input factors such as filling strategy, extrusion temperature and layer number in 3D printing on the behavior of polylactic acid (PLA) was discussed and justified. Response surface optimization (RSM) methodology and ANOVA analyses were used to establish a decision support strategy for the selection and parameterization of FDM processes. As a result, the microhardness of the surfaces (Top/Bottom) on samples (1 cm3) was measured for different combinations of the 3D printing factors. In fact, the coupling between the physical (structural homogeneity) and mechanical (microhardness) characteristics allowed us to establish a performance index to maximize microhardness while minimizing structural heterogeneity. Optimal factors were identified and discussed using ANOVA analysis and multi-objective optimization for the selection of materials and structures. The originality of this work lies in the coupling of the RSM methodology with the ANOVA analysis in the selection of process parameters for the expected microhardness and structural homogeneity performances. The multi-objective optimization approach revealed the optimal 3D printing conditions: A ZIGZAG filling strategy, a temperature of 230°C for a 4-layer construction with a thickness of 0.2 mm. These combinations of process control factors result in optimal performance in terms of surface microhardness and the homogeneity of the resulting PLA structures.