| 摘要 |
PROBLEM TO BE SOLVED: To suppress occurrence of a shrink, a flaw due to shrink, etc., on the rear side of a head part of the piston of an internal combustion engine when the piston is forged. SOLUTION: In a main body 1 consisting of a head part 5, a skirt part 11 extending from the outer peripheral part of rear side the head part 5 in the piston axial direction and a pin boss part 1 arranged in the rear side of the head part 5, the main body 1 is formed by forging so that a die is moved in the piston axial direction, the end part 11a of the piston in the piston axial direction is formed to a free end free from restriction of the die.
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