Entrance mark control on precision WEDM

A tiny hollow space on the interface between the approach and the machining path may cause critical damage during superfine machining by wire-cut electrical discharge machine (WEDM). This paper points out that this space is caused by the reduction of the machined volume near the approach point. To resolve this problem, a compensation method for the mark using offtime control based on the machining volume model is proposed. It is found that the accuracy of this method can be increased if the influence of offtime control on wire vibration is taken into account. It appears that the mark can be lost in the surface roughness by using this method. The method is practical because it can be applied according to the variation in workpiece thickness without any tuning of parameters. In addition, it is shown that the proposed method does not only reduce the mark, but also easily changes it from concave to convex. This feature is advantageous because the volume of polishing after the WEDM process is greatly reduced. Therefore, the proposed method is proven to be quite useful in precision processing by WEDM.