| 摘要 |
PROBLEM TO BE SOLVED: To provide a tube expanding method for tube material by which tube materials different in thickness can be manufactured respectively from base tubes equal in size, and the tube member excellent in true roundness can be manufactured. SOLUTION: Axial tension force is imparted at an outlet side of a plug, a target value of the axial tension force is calculated by the following formula from a thickness t0 of tube material before tube expanding, an inner diameter di0 of the tube material, a target thickness t1 after tube expanding, a target inner diameter di1 of the tube material after tube expanding and a yield stressσyp of the tube material, the axial tension force is adjusted to the target value. The target value of the axial tension force is preferably 0.02-0.1 times the yield stress of the tube material.σza= Fc×(1-t1/t0)+Fa}×σyp, Fc=a1×(di1/di0)-b1, Fa=a2×(di1/di0)-b2, a1, b1, a2, b2; constant.
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