| 摘要 |
PROBLEM TO BE SOLVED: To improve durability of a core bar bushing. SOLUTION: A relief part 30 of a notched shape is formed to one side face of a core bar bushing 3 to be inserted in a tubular member 1, punching is conducted so that a punch 5 passes the relief part 30 at the position deviated from a center C of the tubular member 1 and in parallel with its axis orthogonal direction. By this method, a hole 2 notched in a chord shape is formed at the outer peripheral part of the tubular member 1 and at the position deviated from the center C. The relief part 30 is extended/formed so as to reach an insert part tip of the core bar bushing 3.
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