| 摘要 |
PROBLEM TO BE SOLVED: To simplify the equipment for a hydraulic piercing method and to supply a product at a low cost. SOLUTION: A punch 4 is driven by a punching unit 15 so that strike drive power is applied to the punch 4. By applying the shear force from the tip part of the punch 4 to the wall face of a tube 1 not transiently but successively, one strike force by the punch 4 is reduced. By reducing one time punching force by the punch 4, even if a high pressure to expand/deform the tube 1 is not given to the water in the tube, deformation of the tube in punching a tube wall face with the punch is prevented, further, the generation of a burr at a piercing end part is effectively suppressed. Also, a water pressure in the tube 1 is increased with a peak pressure obtained at striking the tube 1 with the punch 4, a tube wall face is supported from the inside so as to improve piercing quality.
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