Post processing of EDM-machined microstructures by ultra short pulsed laser ablation

By laser ablation with ultra short laser pulses smallest microstructures with sizes in the micrometer region can be manufactured in hardened steel. However, machining times are slow if good surface qualities are required. Micro-EDM (electric discharge machining) is also capable of removing material without any process forces but with a higher processing speed if the structure sizes exceed a certain value. However, the surface quality is worse than with laser ablation. With the combination of both processes specific advantages can be utilized while disadvantages can partially be eliminated. The wbk – Institute of Production Science in Karlsruhe, Germany examines the integrated machining by EDM and laser ablation without reclamping in a single machine tool. A Nd:YAG laser with a pulse duration of 13 picoseconds and a die-sinking-EDM-head (Electric discharge machining) are integrated in a five-axes machining center. With the combined machine tool, the manufacturing time can be substantially decreased, e.g. by eroding the larger structures with a die-sinking electrode and subsequently ablating the fine details with the laser beam. Also the worse surface quality of EDM-machined structures can be enhanced by post processing with an ultra-short-pulsed laser beam. The surface roughness can be decreased from R_a = 0.8 µm to R_a = 0.22 µm after ablating three layers by ultra short laser pulses.