US 12,214,395 B2
Extrusion molding method for differential thickness pipe and extrusion molding apparatus for differential thickness pipe
Kentaro Nozu, Nagoya (JP); and Michiharu Nakagaki, Nagoya (JP)
Assigned to SANGO CO., LTD., Nagoya (JP)
Appl. No. 17/640,573
Filed by SANGO CO., LTD., Nagoya (JP)
PCT Filed Jun. 10, 2020, PCT No. PCT/JP2020/022822
§ 371(c)(1), (2) Date Mar. 4, 2022,
PCT Pub. No. WO2021/044689, PCT Pub. Date Mar. 11, 2021.
Claims priority of application No. 2019-162744 (JP), filed on Sep. 6, 2019.
Prior Publication US 2022/0314290 A1, Oct. 6, 2022
Int. Cl. B21C 25/08 (2006.01); B21C 23/08 (2006.01)
CPC B21C 25/08 (2013.01) [B21C 23/085 (2013.01)] 15 Claims
OG exemplary drawing
 
6. An extrusion molding method for a differential thickness pipe, including a first step that is a step in which, in a first extrusion molding apparatus comprising a first core bar having a predetermined shape, a first die having a first die hole that is a through hole having a predetermined shape, and a first drive mechanism configured so as to press said first core bar into said first die hole, a differential thickness pipe having a predetermined shape is molded by pressing a pair of a first raw pipe having a predetermined shape and said first core bar into said first die hole with said first drive mechanism in a state where said first core bar is inserted at a predetermined position in said first raw pipe to perform extrusion processing, wherein:
said first raw pipe is a tubular member having a first wall thickness that is a predetermined wall thickness and a first outer diameter that is a predetermined outer diameter,
said differential thickness pipe includes:
a first thin-walled portion that is a portion having a second wall thickness that is a predetermined wall thickness smaller than said first wall thickness and a second outer diameter that is a predetermined outer diameter smaller than said first outer diameter, and
a first thick-walled portion that is a portion having an outer diameter equal to the second outer diameter and a third wall thickness that is a predetermined wall thickness larger than said second wall thickness,
said first core bar includes:
a first small cross section portion that is a portion formed on a tip end side that is a downstream side in an extrusion direction and having a first cross section that is a cross section corresponding to a cross section of an internal space of said first thick-walled portion,
a first large cross section portion that is a portion formed on a base end side that is an upstream side in said extrusion direction and having a second cross section that is a cross section corresponding to a cross section of an internal space of said first thin-walled portion, and
a first cross section increasing portion that is a portion formed between said first small cross section portion and said first large cross section portion and having a cross section expanding from said first cross section to said second cross section as approaching from said first small cross section portion to said first large cross section portion,
said first die hole includes:
a first large inner diameter portion that is a portion formed on a base end side and having a first inner diameter that is an inner diameter corresponding to said first outer diameter,
a first small inner diameter portion that is a portion formed on a tip end side and having a second inner diameter that is an inner diameter corresponding to said second outer diameter, and
a first inner diameter reducing portion that is a portion formed between said first large inner diameter portion and said first small inner diameter portion and having an inner diameter decreasing from said first inner diameter to said second inner diameter as approaching from said first large inner diameter portion to said first small inner diameter portion, and
when said extrusion processing is started in said first step, an end portion on a base end side of said first small cross section portion is in a position closer to a base end of said first raw pipe than an end portion on a base end side of said first small inner diameter portion, in said extrusion direction, and
said first extrusion molding apparatus further comprises a second core bar that is a core bar having a cylindrical columnar shape with an outer diameter equal to said second outer diameter,
said first step is performed in a state where said second core bar is inserted into said first small inner diameter portion from a tip end side of said first die hole and is energized toward a direction opposite to said extrusion direction, and
at least when said extrusion processing is started in said first step, an end portion on a base end side of said second core bar is in contact with an end portion on said tip end side of said first core bar.