Experimental determination of convective heat transfer coefficient in wire electro discharge machining

Wire electro discharge machining (WEDM) is a fully extended and competitive machining process widely used to produce dies and moulds. However, the risk of wire breakage affects adversely the full potential of WEDM since the overall process efficiency is considerably reduced. These symptoms are especially related to the occurrence of an increase in discharge energy, peak current, as well as increases or decreases in ignition delay time. Because of that, an experimental determination method of the convective heat transfer coefficient in wire electro discharge machining is introduced to prevent the wire breaks during running the machine. Parameters such as peak current and flushing pressure are studied. A special device is developed to measure the average temperature increment of the wire after a period of short circuit discharges, and the thermal load imposed on the wire is also tracked and recorded in advance. Then, based on the thermal model of the wire, the convective coefficient can be calculated accurately. Some tuning experiments are carried out inside and outside a previously cut profile to examine the influence of the kerf on the convective coefficient. With this method, the effect of the coolant flushing pressure on the convective coefficient can be estimated. Based on the results of the analyses, this paper contributes to improve the process performance through a wire breakage