| 摘要 |
PROBLEM TO BE SOLVED: To form a hole small in deformation in a die-less manner in a thick- walled pipe by applying the shear force in the cutting line direction of the pipe with the pipe in a restricted condition to form a notch-like hole. SOLUTION: A punch having a flat section in which the thickness is smaller than the width and a blade portion at its forward end having a tip angle of >=35 deg. is attached and fixed to a punch holder 9 fixed to an inner slide 7. A major portion of a pipe P is restricted by fitting grooves 100, 200 to lower the inner slide 7. The punch 3 is lowered orthogonal to the axial direction of the pipe P, and moves in the cutting line direction of the pipe P through a notch 21 of an upper pipe holder 2. A blade tip projecting from the blade portion is bitten into a side of the pipe P to shear-cut the pipe step by step with the width equivalent to the thickness of the blade portion into a clear-cut section. Since the punch 3 has the tip angle of >=35 deg., generated chips flow along an inclined bottom surface of the blade portion, and are not deposited on a bottom surface of the punch 3.
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