| 摘要 |
PURPOSE:To prevent generation of cracks during processing, enable enlargement of the diameter of a head or increasing of the thickness for improvement of the strength by first heating a material such as piano wire rod to decrease the hardness and applying a pressure force in an axial direction to form the head. CONSTITUTION:A material such as piano wire rod is held using a wire rod fixture 6 after allowing it to protrude a prearranged length from the end, and an inert gas such as argon is filled into a casing 3. Then the protruded part is heated up to an adequate temperature level using a heating device 9 to decrease the hardness of the heated part B. After this, the heated part B is cooled down to a desired temperature, ram 7 is pressed on the heated part B, and spread in a diametral direction while it is compressed in an axial direction to form a disk-like head 1. As a result, the diameter of the head 1 can be enlarged to the value of min 2d as against the diameter (d) of the axial part. The end of the axial part 2 on the head 1 is formed to make almost a right angle with the axial direction, and the end is used as a spring seat surface. |
