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

Electrical discharge machining (EDM) has become common place in the tool and die industry as an alternative to conventional machining and now accounts for 2% ofworldwide machiningl , with a substantially greater concentration ofuse in the tool making industry.EDM has the advantage of allowing tool steel billets to be heat treated to full hardness before the cavity is produced, obviating the need for heat treatment after machining--a step that often results in the loss of dimensional accuracy due to distortion in the quenching from high temperature austenite to martensite at room temperature. Any material with less than 1 ohm-m ofelectrical resistivity, regardless ofhardness, can be machined using EDM. 1 EDM also allows the convenient production of complex shapes in the tool cavity, as complex topographies can often be more easily machined on the electrode than inside a cavity. Even certain simple shapes such as rectangular or square cavities are far easier to produce using EDM than conventional machining. EDM machining, however, is precluded from many market niches by the relatively high cost ofelectrode production In visiting with approximately sixty representatives from the EDM industry, we have learned that the cost of electrode fabrication is often greater than 50%, and sometimes as great as 80%, ofthe total cost offabricating a die using EDM. 2 ,3 The wear ratio ofthe two most commonly used electrode materials, graphite and copper, requires the use ofmultiple electrodes in the production of each cavity, because the electrode wears away and loses its initial shape too quickly. Thus, the replacement ofgraphite and copper electrodes with electrodes made ofmaterials which are more resistant to electric spark erosion would significantly improve the cost effectiveness ofEDM tool production. Many tools have multiple cavities that use a different electrode for each separate cavity because it is easier to machine several small, simply-shaped electrodes than it is to machine one large, complex electrode. This requires a greater total sink time in the EDM machine, since multiple cavities are machined sequentially rather than simultaneously. The ability to create a large, complex electrode quickly would greatly reduce the time and money spent in tool production using EDM. If the rapid prototyping technology4-7 that has emerged during the past ten years could be utilized to fabricate EDM electrodes, the cost of producing electrodes with complex shapes could be substantially reduced, and new material systems which are difficult to machine could be utilized for the electrodes. Complex electrodes capable of making multiple imprints/cavities in dies simultaneously could be fabricated just as easily as simple electrodes using rapid prototyping equipment, which would increase the precision ofthe cavities' placement relative to one another, 278 dramatically reducing the EDM machine time required. A die which might, for instance, require as many as 15 imprints, which are now done sequentially, could be done in one EDM operation, reducing the time in the EDM machine and increasing the precision of placement ofthe imprints relative to one another. 3 This would be a significant contribution to the tool and die industry. Texas A&M University has undertaken research to produce EDM electrodes using rapid prototyping. Specifically, the development of a process for rapid prototyping ofEDM electrodes, using selective laser sintering (SLS) ofpolYmer coated intermetallic powders which are subsequently infiltrated with a highly conductive metal, is being investigated.