| 摘要 |
PURPOSE:To obtain a lightweight metallic pipe having the prescribed length and thin wall thickness, by forming one end of a short-sized metallic pipe into a radially expanded part having thick wall thickness, and stretch forming the total length of the pipe by drawing the remaining part of it. CONSTITUTION:The 1st drawing is performed by pressing a metallic pipe 7 of short-sized blank material into the 1st die hole 5 having the 1st radially expanding part at its upper opening, by a punch 8 in a cold state. Successively, a perfect radially-expanded part is formed at the upper end of the metallic pipe 7 in the 2nd drawing state. Next, the pipe is pressed into the 3rd die hole 14 of the 3rd die 15 in a cold state. The 3rd punch 16 is inserted through the inner hole of the pipe to press its inner peripheral surface, thereby the inner peripheral surface of the pipe 7C is radially expanded to form the pipe into the thin wall thickness, and the pipe is simultaneously stretched in the axial direction to form it into the prescribed length. Then a punch having its diameter slightly larger than that of the punch 16 is pressed into the pipe 7C in a cold state to uniformly press only the surface of the inner peripheral surface of the pipe 7C, thereby forming a specular surface. |
