Magnetic fixtures for enhancement of smoothing effect by electron beam melting

In large-area electron beam (EB) irradiation method developed recently, high energy density EB can be obtained without focusing the beam. Therefore, large-area EB of 60 mm in diameter can be used for instant melting and evaporation of the wide area material surface, and high efficient surface finishing is possible. However, if the workpiece has a hole shape, the EB concentrates in the entrance edge or inside wall of the hole. Thus, it is difficult to smooth the hole bottom surface. Previous study showed that the surface smoothing and micro-deburring effects for non-magnetic workpiece could be improved by setting a magnetic block under the workpiece, since the electrons tend to concentrate the magnetic block along magnetic lines. In this study, smoothing of hole bottom surface was experimentally investigated by setting a magnetic block under a workpiece in large-area EB irradiation. Expansion of smoothing area of the bottom surface was also tried by setting a through hole at the center of the magnetic block. It was clarified that wide area of hole bottom surface could be smoothed by large- area EB irradiation by setting the magnetic block under workpiece. The surface roughness decreased to less than 3.0 μmRz at the area of hole bottom surface. When the hole diameter was 20 mm and hole depth was less than 40 mm, smoothing area of 10 mm in diameter was obtained by using the magnetic block. Moreover, the smoothing area was sufficiently expanded by setting a through hole with an appropriate diameter in magnetic block.