Patent ID: 7347486
Filing Date: 2008-03-25
Classification: B21C,B60J,C21D,Y02P,Y10T

Abstract:
1. A metal tube for reinforcing a car body, which is mounted onto the car body of an automobile in a two-end support structure to ensure crash capacity, comprising: a curved portion extending over the entire longitudinal length; and a degree of curve η of not less than 0.002%, the degree of curve η being defined by (S−L)/L×100(%), where S (mm) is the arc length of the curved portion, and L (mm) is the projection length which is determined by projecting the curved portion from an outer periphery to an inner periphery, wherein, when a curved portion is formed for said metal tube, a work tube is successively moved in the axial direction thereof, and the work tube is locally heated at a plastically deformable temperature as well as at a temperature which enables quench hardening, using a high frequency heating coil disposed above the outer periphery of the work tube, and then the work tube is rapidly cooled after a bending moment is applied to the heated portion to form the curved portion incrementally.