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This study was aimed at developing a new prehole shearing process to promote excellent formability of the subsequent hole-expansion process for manufacturing automobile wheel disks made of high-tensile-stress steel. A "simplified opposed-dies shearing process" was newly proposed for forming a prehole for the hole-expansion process, since the original opposed-dies shearing process requires relatively complicated tool sets regardless of its excellent properties for hole expansion. As a result of the series of experiments with the simplified opposed-dies shearing process as the prehole forming process for the hole expansion process, the simplified opposed-dies shearing process was found to show an improvement of 0.3 in the expansion ratio over that in the case of the conventional shearing process.

The newly proposed punching process to form a burr-free hole for the air valve mounted on the wheel rim of an automobile was experimentally studied to evaluate the process parameters required to realize the burr-free punching process. The proposed burr-free punching process employs the mechanism of concise reciprocating shearing that had been originally developed as burr-free blanking. The two-step of experiments on the laboratory scale with actual steel material were conducted to evaluate the parameters of the punching process. In the first step simple rectangular test pieces were adopted and then an actual automobile product shape was employed in the second step. As a result of a series of these simulated experiments, some admissible sets of process parameters to realize burr-free punching were quantitatively found and the mechanism of forming a desirable separated surface shape was qualitatively discussed from the viewpoint of the clearance condition in the partial shearing.