2019 Volume 60 Issue 698 Pages 64-69
Precision blanking processes suppress shear droop, fracture, and burr generation on a cut blank surface. However, as the blank size becomes extremely small, as in a microgear, the technology involved becomes extremely difficult. In the previous report1), the authors fabricated microgears by finish blanking and extrusion blanking, evaluated their cut surfaces, and confirmed the effectiveness/advantage of extrusion blanking. However, in the previous study, because of concerns about tool breakage due to punch and die interference, which is a problem of negative clearance processing, the extrusion process comprising two steps was stopped at 90 % of the plate thickness in the first step, and the remaining 10 % that was blanked in the second step became a fractured surface. Therefore, in this experiment, with the aim of preventing such fracture, extrusion processing was additionally carried out to the very limit of 99 % of the plate thickness where the punch and the die were almost in contact, and the plate was severed in the second step. Measurements of the constituent ratio of the whole cut surface, the geometry, and the surface roughness of the cut surface were performed. As a result, the fractured surface could be suppressed, and few burrs were observed.