Patent ID: 9375769
Filing Date: 2016-06-28
CPC Classification: B21C,B21D,B21K,C21D,F16C

Claim Text:
1. A method for manufacturing a drive shaft, comprising: providing a metallic pipe having a first pipe portion at one end of the pipe, a second pipe portion at an opposite end of the pipe, an intermediate pipe portion between the first and second pipe portions, the metallic pipe further including an inner circumferential surface, an outer circumferential surface and a central axis defining an axial direction of the pipe; forming a first shaft unit by shrinking the first pipe portion of the metallic pipe such that the first shaft unit has a first strength; decreasing the thickness of the intermediate pip portion of the metallic pipe by drawing down the intermediate pipe portion which is integral with the first shaft unit; forming a strength decrease unit at an inner surface of the second pipe portion of the metallic pipe by heat treating such that the strength decrease unit has a second strength smaller than the first strength, and the second pipe portion is spaced from the first pipe portion; and forming a second shaft unit by shrinking the second pipe portion of the metallic pipe; wherein the second shaft unit is formed by applying a compression force to the second pipe portion in a vertical direction with respect to the axial direction of the metallic pipe; and providing divided flat molds with an outside surface and inside slanted contact surfaces for applying the compression force to the second pipe portion and wherein the second shaft unit is formed by moving the divided flat molds with slanted contact surfaces into contact with the outer circumferential surface of the metallic pipe at the second pipe portion.