Manufacturing method of differential thickness steel pipe and differential thickness steel pipe

摘要

This method for manufacturing a differential thickness steel pipe is a method for manufacturing a differential thickness steel pipe from a hollow cylindrical base pipe, wherein the base pipe is disposed in a die and the movement of the base pipe in the longitudinal direction is restricted. A locking step of pushing the plug from one end side of the element tube to enlarge the outer shape of the one end side and locking the die with the die; while releasing the restriction of the element tube, the locking of the element tube A squeezing process step of forming a thin portion by adding a squeezing process that expands the inner shape while maintaining the outer shape of the element tube by pushing the plug further toward the other end side of the element tube while maintaining Having