DIE, METHOD OF MANUFACTURING STEPPED METAL TUBE, AND STEPPED METAL TUBE

摘要

The through hole of a die has an inside surface including a bell portion, an approach portion, and a bearing portion from the entrance side formed in a continuous manner. The diameter of the approach portion is D1 on the entrance side of the approach portion and D2 on the exit side of the approach portion and gradually decreases from the entrance side to the exit side. The diameter satisfies Equation (1): 0.7<=D2/D1<0.97. The die half angle of an inside surface where the diameter D3 is D2/0.97 is not less than the die half angle R2 of an inside surface nearer to the exit side of the approach portion than the inside surface where the diameter is D3, and the axial distance LR from the inside surface where the diameter is D3 to the inside surface where the diameter is D2 satisfies Equation (2): 20<=LR/((D3-D2)/2)<=115. The diameter of the through hole at the bearing portion is fixed at D2, and the length is LB and satisfies Equation (3): 0.3<=LB/D2<=10.