The Production of Electrical Discharge Machining Electrodes Using SLS: Preliminary Results (2018)

Electrical discharge machining (EDM) has become common place in the tool and die industry\nas an alternative to conventional machining and now accounts for 2% ofworldwide machiningl\n, with\na substantially greater concentration ofuse in the tool making industry.EDM has the advantage of\nallowing tool steel billets to be heat treated to full hardness before the cavity is produced, obviating\nthe need for heat treatment after machining--a step that often results in the loss of dimensional\naccuracy due to distortion in the quenching from high temperature austenite to martensite at room\ntemperature. Any material with less than 1 ohm-m ofelectrical resistivity, regardless ofhardness, can\nbe machined using EDM. 1 EDM also allows the convenient production of complex shapes in the tool\ncavity, as complex topographies can often be more easily machined on the electrode than inside a\ncavity. Even certain simple shapes such as rectangular or square cavities are far easier to produce\nusing EDM than conventional machining.\nEDM machining, however, is precluded from many market niches by the relatively high cost\nofelectrode production In visiting with approximately sixty representatives from the EDM industry,\nwe have learned that the cost of electrode fabrication is often greater than 50%, and sometimes as\ngreat as 80%, ofthe total cost offabricating a die using EDM. 2\n,3 The wear ratio ofthe two most\ncommonly used electrode materials, graphite and copper, requires the use ofmultiple electrodes in\nthe production of each cavity, because the electrode wears away and loses its initial shape too\nquickly. Thus, the replacement ofgraphite and copper electrodes with electrodes made ofmaterials\nwhich are more resistant to electric spark erosion would significantly improve the cost effectiveness\nofEDM tool production.\nMany tools have multiple cavities that use a different electrode for each separate cavity\nbecause it is easier to machine several small, simply-shaped electrodes than it is to machine one large,\ncomplex electrode. This requires a greater total sink time in the EDM machine, since multiple cavities\nare machined sequentially rather than simultaneously. The ability to create a large, complex electrode\nquickly would greatly reduce the time and money spent in tool production using EDM.\nIf the rapid prototyping technology4-7 that has emerged during the past ten years could be\nutilized to fabricate EDM electrodes, the cost of producing electrodes with complex shapes could be\nsubstantially reduced, and new material systems which are difficult to machine could be utilized for\nthe electrodes. Complex electrodes capable of making multiple imprints/cavities in dies\nsimultaneously could be fabricated just as easily as simple electrodes using rapid prototyping\nequipment, which would increase the precision ofthe cavities' placement relative to one another,\n278\ndramatically reducing the EDM machine time required. A die which might, for instance, require as\nmany as 15 imprints, which are now done sequentially, could be done in one EDM operation,\nreducing the time in the EDM machine and increasing the precision of placement ofthe imprints\nrelative to one another. 3 This would be a significant contribution to the tool and die industry.\nTexas A&M University has undertaken research to produce EDM electrodes using rapid\nprototyping. Specifically, the development of a process for rapid prototyping ofEDM electrodes,\nusing selective laser sintering (SLS) ofpolYmer coated intermetallic powders which are subsequently\ninfiltrated with a highly conductive metal, is being investigated.