PURPOSE: To enlarge the minimum thickness at the outside of a bent part by bending a pipe after positioning the thick-walled part to the outer diameter side of the bent part.
CONSTITUTION: An ordinary pipe 1 that has inevitable thickness deviation such as a thin-walled part 15 and a thick-walled part 16 is inserted into a mandrel 2 from a groove provided in a foaming block 4 and a clamp 5. Then, the pipe 1 is rotated, and the thick-walled part 16 is detected by a thickness detector 9. When the thick-walled part 16 comes to such a position that it becomes the outer diameter side of the bent part after bending, rotation of the pipe 1 is stopped. With an end of the pipe 1 fixed, another end of the pipe 1 is bent by drawing in. Thus, the minimum thickness of the outside of the bent part becomes larger and bent pipes of stable quality can be obtained.
OCHIAI IZUMI
NOZAWA YOSHIO
MATSUI YOSHIO
MIYAGI MASAHIRO
