Yoke for universal joint, and production process for the same

In a method of forming a yoke for a universal joint with mutually coaxial circular holes by press punching tip end portions of a pair of opposed arms of a yoke work-piece which is produced by press forming a metal sheet blank to form said pair of opposed arms, the improvement wherein said circular holes are formed by a process including:

• punching a pair of coaxial provisional circular holes through the respective tip end portions of said arms in a state in which each arm has a back surface, relative to a provisional punching direction of the arm, supported by a die with an outer periphery of the arm being fitted in and restrained by a restraining member in a vicinity of a portion in which the corresponding provisional circular hole is formed;
• and
• finish punching the provisional circular hole of each arm by inserting a finishing punch into the provisional circular hole in a finish punching direction opposite to said provisional punching direction of the arm in a state in which a back surface of the arm, relative to the finish punching direction, is supported by a die and the outer periphery of the arm is fitted in and restrained by a restraining member in a vicinity of the provisional circular hole, so as to produce a finished circular hole having inner-half and outer-half surfaces of substantially equal accuracy.

A yoke for a universal joint which is produced by press forming a steel sheet to have a pair of opposed arms and then by press punching tip end portions of the arms to have mutually coaxial circular holes opposed to each other, wherein said circular holes are formed by a process including:

• punching a pair of coaxial provisional circular holes through the respective tip end portions of said arms in a state in which each arm has a back surface, relative to a provisional punching direction of the arm, supported by a die with an outer periphery of a tip end portion of the arm being fitted in and restrained by a complementarily shaped portion of a restraining member;
• and
• finish punching the provisional circular hole of each arm by inserting a finishing punch into the provisional circular hole in a finish punching direction opposite to said provisional punching direction of the arm in a state in which a back surface of the arm, relative to the finish punching direction, is supported by a die and the outer periphery of the tip end portion of the arm is fitted in and restrained by a complementarily shaped portion of a restraining member, so as to produce a finished circular hole having inner-half and outer-half surfaces of substantially equal accuracy.

In a method of forming a yoke for a universal joint with mutually coaxial circular holes by press punching tip end portions of a pair of opposed arms of a yoke work-piece which is produced by press forming a metal sheet blank to form said pair of opposed arms, the improvement wherein said circular holes are formed by a process including:

• punching a pair of coaxial provisional circular holes through the respective tip end portions of said arms in a state in which each arm has a back surface, relative to a provisional punching direction of the arm, supported by a die with an outer periphery of a tip end portion of the arm being fitted in and restrained by a complementarily shaped portion of a restraining member;
• and
• finish punching the provisional circular hole of each arm by inserting a finishing punch into the provisional circular hole in a finish punching direction opposite to said provisional punching direction of the arm in a state in which a back surface of the arm, relative to the finish punching direction, is supported by a die and the outer periphery of the tip end portion of the arm is fitted in and restrained by a complementarily shaped portion of a restraining member, so as to produce a finished circular hole having inner-half and outer-half surfaces of substantially equal accuracy.