FORMATION OF CRANK BLANK FOR BICYCLE

摘要

PURPOSE:To simply form a crank blank as a preform at the time of forging a crank product for bicycle having comparatively complicate shape at a low cost and to finally realize the high strength product. CONSTITUTION:At the time of forging the crank parts for bicycle integrating a base part and one or more arm parts projectingly formed from the base part and forming the base part and the arm parts along the different surfaces respectively, a die device (k) providing a cavity 6 having the similar shape as the crank product for bicycle is used. The cavity 6 is provided with a main space and an extending space 6b and uses the one arranging a contracting de part 6d at the boundary part between the main space and the extending space. The bar-like blank is inserted into a through-hole and by compressing this bar-like blank with a punch 7, this blank is deformed and fluid-extended in the extending space through the main space and the contracting part from the through-hole.