| 摘要 |
PROBLEM TO BE SOLVED: To provide a method of manufacturing a closed-shape frame which is excellent in working efficiency and profitability as compared with a previous method of manufacturing a pipe by making a punching method operate continuously. SOLUTION: A plurality of stages of presses 1 having one or a plurality of a punching punches 10 at the tip in the pressing direction are provided along the moving direction of a sheet and the punching punch 10 is provided with a double cutting edge which formes a closed shape on the inside and the outside. In this method of manufacturing the closed-shape frame, the above problem is achieved on the basis of performing cutting by punching from the plate with the cutting edge of the final stage, while successively deeply entering the cutting edge of the punching punch 10 into the same portion by pressing the plurality of stages of the presses 1 in the same portion of the sheet which is successively moved in accordance with the movement of the sheet. COPYRIGHT: (C)2009,JPO&INPIT
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