Patent ID: 9327327
Filing Date: 2016-05-03
CPC Classification: B21C,B21D

Claim Text:
1. A method of manufacturing a pipe with different diameters along a longitudinal direction that has a small diameter portion, a large diameter portion, and a diameter-changing portion provided between the small diameter portion and the large diameter portion and is formed by press forming a blank made of a metal sheet, comprising: providing a U-shaped forming die set including a lower die, wherein the lower die includes a forming surface that forms a U-shaped inner cross section having a pair of vertical walls, wherein a length of the vertical walls of the lower die is longer than a length of the vertical walls of a corresponding portion a U-shaped formed part; press forming the blank with the U-shaped forming die set into the U-shaped formed part having a U-shaped cross section including a pair of vertical walls; providing an O-shaped forming die set including a lower die in which the U-shaped formed part is set and a upper die to which the vertical walls of the U-shaped formed part contact, wherein each of the lower die and the upper die includes a forming surface having an arc portion that forms a circular inner cross section when the upper die and the lower die are mated at die mating lines and the die mating lines in a cross-sectional view are inclined downwardly from the inner cross section when the lower die is mated under the upper die; and press forming the U-shaped formed part with the O-shape forming die set into a circular cross-section formed part, wherein