Investigations of surface defects during laser polishing of tool steel

During laser polishing of tool steel surfaces produced by electric discharge machining with NIR continuous wave laser, small craters were observed on the polished surface. Their formation was observed in situ with high-speed camera. Post mortem investigation of the composition of the craters with energy dispersive X-ray spectroscopy (SEM) has shown that they were caused by copper inclusions on the steel surface. The inclusions are probably coming from the electrode employed during the electric discharge machining process. The low absorption of copper in NIR signifies that the bigger copper particles do not melt at high speed which leads to the formation of the craters.