Yoke of universal joint and method of producing same

A yoke of a universal joint, the yoke being substantially U-shaped and including a base portion and first and second arm portions, the yoke being prepared by a method and comprising the following steps in sequence:

• (a) shearing a metal plate which is rectangular in shape and has a first uniform width and a first uniform thickness so as to form a blank which is rectangular in shape and consists of a middle portion and first and second end portions;
• (b) squeezing the middle portion of the blank by cold forging so that the middle portion is expanded to have first and second peripheral bulge portions which are opposed to each other and so that the expanded middle portion becomes substantially oval in shape and thinner than the first and second end portions in thickness;
• and
• (c) pressing the blank with a press machine to produce the yoke so that the expanded middle portion and the first and second end portions of the blank are turned into the base portion and the first and second arm portions of the yoke, respectively.

A method of producing a yoke of a universal joint, which is substantially U-shaped, monolithic in construction and produced from a blank having a middle portion and first and second end portions, the yoke comprising:

• first and second arm portions which are respectively prepared from the first and second end portions of the blank, opposed to each other in a direction perpendicular to a longitudinal direction of the yoke and uniform in thickness, and
• a base portion which is prepared from the middle portion of the blank and substantially parabolic in shape, the base portion being thinner than the first and second arm portions in thickness as a result of cold forging of the middle portion,
• the method comprising the following steps in sequence:
• (a) shearing a metal plate which is rectangular in shape and has certain uniform width and thickness so as to form a blank which is rectangular in shape and consists of a middle portion and first and second end portions;
• (b) squeezing the middle portion of the blank by cold forging so that the middle portion is expanded to have first and second peripheral bulge portions which are opposed to each other and that the expanded middle portion becomes substantially oval in shape and thinner than the first and second end portions in thickness;
• and
• (c) pressing the blank with a press machine to produce the yoke so that the expanded middle portion and the first and second end portions of the blank are turned into the base portion and the first and second arm portions of the yoke, respectively.