PURPOSE: To obtain a deformed pipe having cross section surface without deformation of expanding and reducing opening part, etc.
CONSTITUTION: After desirably giving 0.2-1% axial directional compression plastic strain or 0.1-5% axial directional tension plastic strain in the true strain to the metallic deformed pipe 4 having non-round cross section manufactured from the metallic cylindrical pipe 3 in a roll forming method, the deformed pipe 4, is cut off in the plane crossing at the right angle in the axial direction. The axial directional compression plastic strain is given by applying shock in the axial direction to the one end part or both end parts of the metallic deformed pipe. The axial directional tension plastic strain is given by setting the deformed pipe carry-out speed at quicker than the feeding speed of the pipe stock 3 to forming stands 11-13 in the deformed pipe manufacturing device 10. By this method, the difference of stresses acted in the axial direction of the deformed pipe in the inner and the outer surfaces and the shearing stress are reduced only by the axial directional plastic strain and the deformed pipe having excellent shaped accuracy is cut off.
NAKAKO TAKEFUMI
NISHIO KATSUHIDE
AZUMA TSUTOMU
