Improving accuracy of curved corners in wire EDM successive cutting

Abstract

Wire electrical discharge machining (WEDM) has a significant position among production technologies mainly due to its capacity of machining hard materials and intricate shapes. One of the major problems with this process is the error in cutting small-radius corners. Processing forces acting on the wire and low rigidity of the wire are responsible for wire deflection, which has a direct influence on the accuracy of the corner cutting. In this research, investigation is focused on small-radius convex and concave corner radii errors, and alternative solutions are proposed for the case of successive cuts (one roughing and two finishings). Initial experiments are carried out for roughing operation by considering frequency of discharges and feed speed as input variables. Residual materials on straight and small-radius convex curved paths are the output parameters. One important conclusion is that roughing is the most influential stage of cutting by WEDM. Results also indicate that optimization of these input parameters has a better influence on controlling the residual material thickness on straight paths than on small-radius convex curved corners. Further experiments are carried out by considering the influence of corner angle and corner radii on small-radius concave corners in successive corner cuts. Errors at radii of different corner angles are identified and relations established to arc length and residual material thickness in the curved corner. Finally, an effective approach is presented to improve accuracy of small-radius concave corners at finishing stage. The main conclusion is that to achieve accurate corner radii, one must increase the traversed corner arc length by wire in the small-radius concave corner.