To obtain a low producing cost and also, the satisfy the strength by bending a pipe to almost L-shape, loading axial force from both ends and bulging an excess thickness developed in the inner surface to the inward recessed parts of a bulging die to form outer ribs.
Oil is filled up in a preform 2 incorporated into a cavity C and pressurize-closed jigs 4, 5 are inserted into both end opening parts 2c, 2d and the forming pressures F are applied. The axial force is applied to the perform 2 and the excess thickness is developed by the shifting of the material onto the inner curved surface 2a of the preform 2. This excess thickness is bulged into gap parts C1 of the inward recessed 3e, 3f of the bulging die 3 to form the outer ribs. The outer curved surface 2b of the preform 2b is bulged to the outer curved wall surface 3b of the bulging die 3 to form the outer curved surface of the bending part of a formed product. Thereafter, the obtd. formed product is pressed into a slightly flat state to form a pressed product. A hollow L-shaped suspension arm is obtd. by applying boring, trimming and burring.
UENO KOICHI
EGAWA TETSUJI
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