| 摘要 |
PROBLEM TO BE SOLVED: To make it possible to add a high strain area securely and uniformly to a workpiece using forging dies normally used without manufacturing new forging dies each time when product dimensions are changed, by putting a spare metallic material having a deformation resistance value similar to that of the workpiece at the forging temperature between the workpiece and the forging dies. SOLUTION: This method uses a preform 8 wherein disk-like spare metallic material 2 with the same diameter are arranged on the top and the bottom of a cylindrical workpiece 1 respectively. It is possible to optionally select the spare material 2 in consideration of the workpiece 1 and the deformation resistance value at the forging temperature, and the deformation resistance value of the spare material 2 is to be within the range of 50-200% of that of the workpiece at the forging temperature. This preform is forged, and a low- strain area 4 is caused to exist only on the portion of the spare material 7 after forging, and a product portion 3 is added with high strain of a specified value or higher to sufficiently cause plastic deformation. Then, the spare material 7 with the low-strain area 4 is removed to the cut portion 5 by cut processing.
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