JPS55147448A - Head forming method of eyebolt for clamping - Google Patents

Abstract

PURPOSE: To make the head part stronger than thread part within the limited size by forming the upper half of the circular head part to the specific shape and subjecting the base metal bulged by pressure-sandwiching to compression plastic deformation by the upper die at the time of forming the circular head part for shaft hole being flat at the front and rear through pressure-sandwiching of the upper and lower dies to the end part of a round bar blank.

CONSTITUTION: A steel round bar blank 1 of the diameter conforming to the thread part of a clamp bolt for assembling scaffolding steel pipes or the like is pressure-sandwiched in the axial direction by upper and lower dies 2, 3 in the preliminary process of cold pressing. At this time the portions which become the front and rear planes of the bye bolt head part are defined of bulging by inside walls 2a, 3a. Next, it is pressure-sandwiched in the axial direction by upper and lower dies 5, 6 in the finishing process so that the entire region of both edge parts 7a of the outside circumferential surface of the upper half of the circular head part or the region other than said peak part is formed to a circular peak part 7 lower than its central strip-form region 7b. The blank is then pressure-sandwiched by the upper, lower dies 5, 6 until the blank base metal bulging at the molding contacts the upper die inside surface forming both edge parts 7a and causes compression plastic deformation. This lets both edge 7a surfaces be compression fortified. The forging flashes 4, 8 in the fore- and post-processes are removed and a shaft hole is opened in the head part.

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