A Comparative Study of Polarity-related Effects in Single Discharge EDM of Titanium and Iron Alloys

Abstract

In comparison to steel, titanium alloys react differently to the choice of process parameters in sinking electrical discharge machining (EDM), especially concerning the applied electrical polarity of the tool. With an anodic tool polarity, sinking EDM removal on titanium Ti6Al4V is scarce due to titanium carbide formation, while on steel removal occurs as expected. To understand the behavior of titanium alloys, a comparative study between titanium and iron alloys in single and successive discharge experiments is performed. Ironically, single discharge removal is scarce with an anodic tool on both iron and titanium alloys. However, in ten successive discharges experiments, removal with an anodic tool increases disproportionately. Finally, the continuous EDM process with an anodic tool stops to be effective for the Ti6Al4V machining while for steel is effective as well as efficient in terms of low tool wear. The explanation proposed is the recast layer that has a lower thermal conductivity on which successive discharges would remove material more easily. As a result, the formation of titanium carbide in Ti6Al4V machining is likely not occurring in single discharges due to lack of continuous heat needed for carbon transfer.