Evaluation of Electrical Discharge Machining of Radial Inner Flow Channel Holes Using Soft Shaft Electrodes

Abstract To reduce the difficulty in machining inner holes and break the limitation of cavity size on hole depth, a technique using soft shaft electrodes to machine the radial inner flow channel holes was proposed and developed. This technique was used to directly EDM machine inside the cavity after the electrodes were bent. First, the designed soft shaft electrode structure reduced the bending stiffness of the electrode, making the radius of curvature of the soft shaft electrode was less than 10% that of a cylindrical electrode under the same conditions. Second, the effect of the working fluid on EDM machining with soft shaft electrodes was studied, and Na2CO3 solution was selected as the working fluid to eliminate the taper shape and inlet fillet of the holes. Then, the effects of processing parameters, including voltage, pulse width, and duty cycle, on processing time were studied. Finally, a radial inner flow channel hole over 25 mm deep was machined inside the 20 mm diameter circular cavity. The experiment results showed that the soft shaft electrode could directly machine the radial inner flow channel hole with small diameter and large depth-diameter ratio inside the cavity, and solved the contradiction among the part structure, electrode size and the depth of the inner hole. The use of Na2CO3 solution as the working fluid prevented electrolysis on the machined surface, optimized removal conditions of debris, improved processing speed and processing quality, and reduced electrode loss length.