| 摘要 |
PURPOSE:To improve the finishing accuracy of a valve seat face by forged- forming a rough shaped clutch piston provided with a recessed part for fitting a relief valve and forming with extrusion a bulging part on the back face after executing a sizing on the recessed part. CONSTITUTION:A blank is formed by shearing a bar like blank having the specified outer diameter and after executing a shot peening preforming, forming and punching are executed by hot forging. In this case, the rough shaped clutch piston 1 forming the recessed part 12 of a relief valve fitting part 2 is formed. A sizing is then executed by the punch 20 for sizing having a projection part 22 to form with extrusion a bulging part 11 on the back face of the recessed part 12. The clutch piston 1 is obtd. with grinding in succession. The residual stress of the valve fitting part is thus released to reduce the buckling after removing the coining load. Consequently the finishing accuracy of valve seat faces 24, 25 is improved.
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