High efficiency surface finishing of metal mold by large-area electron beam irradiation (3rd report) -Relationship between crater generation and workpiece material

A new finishing process for metal molds by large-area electron beam irradiation (EB polishing) was proposed and the fundamental effects of EB irradiation conditions on surface finishing, the surface modification effect and others were investigated in the previous report As a result, the surface roughness on the whole surface within 60mm in diameter could be reduced from 6μmRz to less than 1μmRz in just a few minutes under a proper condition, and the surface roughness could be well improved even if the surface tilting angle is close to 90 degrees. In addition, the corrosion resistance of metal mold surface could be improved. However, small craters sometimes were generated on the EB irradiated surface, which might deteriorate the quality of products. In this study, the relationship between crater generation and workpiece material was examined. Experimental results made it clear that the generation of crater and its disappearance were repeated on the surface with EB irradiation, and the generation of crater greatly depends on the nonmetallic additives in base material, particularly on MnS. Moreover, the impurity of workpiece material also has a significant influence on the crater generation.