| 摘要 |
PROBLEM TO BE SOLVED: To solve a problem wherein a dispersion conventionally exists between molded pistons. SOLUTION: This piston forming method comprises cutting a billet at a predetermined length to obtain a billet piece, preliminarily pressing the billet piece to form a centering positioning portion thereon, and then pressing and extrusion molding the billet piece with punching work using the centering positioning portion as a criterion to mold a cylindrically peripheral wall and a fitting portion in a concentric shape at the same time. In this case, pressing and extrusion molding can be performed so that the outer diameter of the cylindrically peripheral wall is a predetermined (designed) size without the need for cutting the outer peripheral face of the cylindrically peripheral wall. In this case, the billet is constrained and cut and the billet piece is cut at a predetermined length, whereby the pressing and extrusion molding is performed so that the outer diameter of cylindrically peripheral wall is the predetermined size without the need for cutting the outer peripheral face of the cylindrically peripheral wall. This piston is obtained by pressing and extrusion molding the billet piece in this method to mold the cylindrical peripheral wall and the fitting portion. COPYRIGHT: (C)2009,JPO&INPIT
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