Device and method of producing ball joint

A pair of dies for manufacturing a ball joint having a ball accommodated inside a socket that includes a wall having an outer surface, each of the pair of dies comprising:

• a first subsidiary pressing surface disposed so as to abut against the outer surface of a first portion of the wall of the socket which is near to the front end of the wall;
• and
• a second subsidiary pressing surface disposed so as to abut against the outer surface of a second portion of the wall which is distant from the front end of the wall;
• wherein:
• the pair of dies is configured to sandwich the socket and reduce a diameter of the wall of the socket by repeated and intermittent pressing in an inward radial direction against the outer surface of the wall of the socket;
• the first subsidiary pressing surface of each of the pair of dies is configured to press against the first portion to thereby reduce the diameter thereof during an early phase of repetition of the intermittent pressing;
• the second subsidiary pressing surface of each of the pair of dies is configured to press against the second portion to thereby reduce the diameter thereof during a later phase of repetition of the intermittent pressing;
• each of the first and second subsidiary pressing surfaces has a substantially concave spherical surface shape characterized by a radius and a center of curvature;
• and
• at least one of the radius and the center of curvature of the first subsidiary pressing surface differs from the respective radius and the center of curvature of the second subsidiary pressing surface.

A method of manufacturing a ball joint provided with a first member having a ball section and a second member having a substantially cylindrical socket which accommodates the ball section, the method comprising:

• disposing a pair dies for reducing the diameter of a wall surrounding an opening of the socket of the second member so as to sandwich the wall of the socket from an outer side thereof in a radial direction, wherein:
• each die includes a first subsidiary pressing surface to abut against the outer surface of a first portion of the wall of the socket which is near to the front end of the wall, and a second subsidiary pressing surface to abut against the outer surface of a second portion of the wall which is distant from the front end of the wall;
• each subsidiary pressing surface has a substantially spherical shape characterized by a radius and a center of curvature;
• and
• at least one of the radius and the center of curvature of the first subsidiary pressing surface differs from the respective radius and the center of curvature of the second subsidiary pressing surface;
• pressing the outer surface of the wall of the socket repeatedly and intermittently in an inward radial direction by the disposed pair of dies, in a state where the ball section is accommodated inside the socket during an early phase of the repeated and intermittent pressing by the first subsidiary pressing surface pressing against the first portion to thereby reduce the diameter of the first portion;
• and
• pressing the outer surface of the wall of the socket repeatedly and intermittently in the inward radial direction by the disposed pair of dies during a later phase of the repeated and intermittent pressing by the second subsidiary pressing surface pressing against the second portion to thereby reduce the diameter of the second portion.