Influence of workpiece circumferential speed in wire electrical discharge machining

In Wire Electrical Discharge Machining (WEDM) a specific wire run-off speed is applied to compensate wear and avoid wire breakage. Since the workpiece generally stays stationary and short discharge durations are applied, the relative displacement between wire and workpiece during one single discharge is very small. In Wire Electrical Discharge Dressing (WEDD), however, the workpiece rotates at very high circumferential speeds, since dressing is usually performed at grinding speeds. In this work the influence of relative speed in WEDM is assessed. Single discharge experiments were first carried out using circumferential speeds up to 80 m/s. The plasma channel was found to easily slide over the anode, creating elongated craters, and higher removal per single discharge was measured for higher relative speeds. A thermo-electrical model was used to help understand the process, showing that higher melting efficiencies can be reach as relative speeds are increased. The model was also used to predict damages to diamonds grains used in metal bonded grinding wheels. It was found that even if the plasma channel slides over a diamond due to the relative speed, graphitization is not likely to occur. (C) 2013 The Authors. Published by Elsevier B.V.