| 摘要 |
PROBLEM TO BE SOLVED: To raise productivity and also to reduce thermal energy consumption at the time of forming a round metallic tube having a circular cross section into a square cross section. SOLUTION: At the time of manufacturing a square metallic tube 1A by heating the round metallic tube l and hot forming it, four places 1a in the circumferential direction of the round metallic tube 1, which are planed to become corner parts 1Aa after forming work & are preponderantly heated, deformation resistance in the parts 1a planed for the corners is made smaller than that in the other part. At the time of pressing the intermediate position between adjancent parts 1a planed for the corners in central direction, the parts planed for the corners are quickly bent so as to become corner parts, the productivity is raised and also, by lowering the heating temp. of the part other than the corner parts, the energy consumption is reduced.
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