| 摘要 |
<p>PROBLEM TO BE SOLVED: To provide a technology which can make die life longer and enhance inner face precision of a through-hole, in a hole formation method for forming the through-hole in a formed product.SOLUTION: In a preliminary forming process, a cave-in part 26 is formed on one face so as to surround a boss part 11, a projection part 27 is formed on the other face, and a thin wall part 31 is formed between the inner peripheral surface of the cave-in part 26 and the outer peripheral surface of the projection part 27. Next, the thin wall part 31 is ruptured with a punch. Accordingly, shear resistance becomes smaller since the thin wall part has a small thickness related to shearing, so that punching force becomes smaller. A load on punching becomes smaller and service life of the punch becomes longer. As a result, die life can be made longer. Additionally, a rupture surface becomes smaller, so that precision of the inner face of the through-hole can be enhanced.</p> |
