PLASTIC WORKING METHOD FOR A HOLED MEMBER

摘要

The present invention relates to a plastic working method for a holed member to obtain a holed member with a through hole at the center by plastic working and its object is to securely prevent any defect such as an underfill from occurring. The present invention comprises a roughing process and a finishing process. In its finishing process, with an intermediate material placed under compressive force caused by a punch and a counter punch, a large diameter part or a diameter enlarging part of a mandrel is pulled out of the through hole of the intermediate material with inserting a small diameter part of the mandrel to the same through hole so that the gap between the small diameter part of the mandrel and the through hole is filled with the material.