Rapid tooling of EDM electrodes by means of selective laser sintering

Abstract

Besides using the selective laser sintering of metal powder for tooling of, e.g., moulding dies, the sintering of EDM-electrodes is one modern development in the field of the Rapid Tooling. The electrodes are built up layer by layer using the 3-D CAD data. So far, a bronze–nickel powder mixture has been used. The made optimization of the sintering process parameters showed that the speed and the sintering strategy have the biggest impact onto the quality of the sintered electrodes, besides the laser power and the hatch distance. Slower scan speed leads to a higher particle density by a lower roughness. A 90° rotation of the scan direction at every other layer (gitter scanning) leads to an increase in strength and a decrease in porosity compared to the alternate scanning (no rotation). The minimum porosity achieved was 20% by using the bronze–nickel powder. The behavior of sintered electrodes has been investigated in relative electrode wear and workpiece removal rate during EDM-experiments. It could be proved that they are useable as electrode wear compared to massive copper electrodes. The wear behavior leads to an unacceptable change of the shape of the electrodes and furthermore, of the workpiece. The so-far made investigations showed that a decrease in porosity of the electrodes leads to a decrease electrode wear and increased workpiece removal. An improvement is possible during the EDM-process by shortening the pulse duration ( t i<10 μs) and the pulse interval ( t 0<5 μs) as long as the flushing of the frontal gap is guaranteed to prevent a process failure. A specific after-treatment of the electrodes by infiltration with silver-containing solder results in an almost fully dense tool body and a decrease in relative electrode wear by 30–50% in contrast to an infiltration with tin-containing solder that worsen the erosion behavior. The investigation of the impact of the workpiece material onto the relative wear of the selective laser sintered electrodes showed a decrease in tool wear when the pulse duration is set to t i=10–70 μs by spark erosion of X210Cr12 and C45 steel. The reason for that lies in the high content of chrome in the steel that leads to a lower workpiece removal rate due to the higher melting point of the material. Even by a low pulse energy, an arc may occur. Future research projects will concentrate especially on the future optimization of the process parameters of the EDM as well as on variations of the metal powder for the laser sintered electrodes. The aim is to decrease the porosity and the roughness of the sintered tools. By improving the laser beam absorption ability by the metal powder, the strength of the tool can be increased.