Metal pipe, and method and device for processing the same

Abstract

A method for processing a metal pipe 1 to make part of the metal pipe 1 in an axial direction thereof into a thick portion 10 , the method includes: forming a shoulder as a stress concentration portion in an axial center of the metal pipe 1 to concentrate a stress thereon; setting the metal pipe 1 in an outer die 20 ; and forming the thick portion 10 by inserting an inner die 25 in the metal pipe 1 to provide space S for forming the thick portion 10 between the inner and outer dies 25 and 20 , and applying the axial pressure to the metal pipe 1 to concentrate the stress on the shoulder to deform the shoulder after the forming and the setting, thereby forming the thick portion 10 from the deformed stress concentration portion as a starting point.

1 . A method for processing a metal pipe to make part of the metal pipe in an axial direction thereof into a thick portion thicker than a different portion, the method comprising:
 forming a stress concentration portion in an axial center of the metal pipe to concentrate a stress on the stress concentration portion when an axial pressure is applied to the metal pipe;   setting the metal pipe in an outer die for holding an outer peripheral surface of the metal pipe; and   forming the thick portion by inserting an inner die in the metal pipe to provide space for forming the thick portion between the inner die and the outer die, and applying the axial pressure to the metal pipe to concentrate the stress on the stress concentration portion to deform the stress concentration portion after the forming of the stress concentration portion and the setting of the metal pipe, thereby forming the thick portion from the deformed stress concentration portion as a starting point.   
     
     
         2 . The method of  claim 1 , wherein
 a shoulder is formed in the metal pipe in the forming of the stress concentration portion to use the shoulder as the stress concentration portion.   
     
     
         3 . The method of  claim 2 , wherein
 the shoulder is formed by expanding the metal pipe in the forming of the stress concentration portion.   
     
     
         4 . A device for processing a metal pipe to make part of the metal pipe in an axial direction thereof into a thick portion thicker than a different portion, the device comprising:
 a stress concentration portion formation device for forming a stress concentration portion in an axial center of the metal pipe to concentrate a stress on the stress concentration portion when an axial pressure is applied to the metal pipe;   an outer die for holding an outer peripheral surface of the metal pipe;   an inner die which is inserted in the metal pipe to provide space for forming the thick portion between the outer die and the inner die, and comes into contact with an end of the metal pipe; and   a drive which presses the inner die in the axial direction of the metal pipe to apply an axial pressure to the end of the metal pipe.   
     
     
         5 . The device of  claim 4 , wherein
 the inner die includes a first die which is inserted in part of the metal pipe except for part of the metal pipe for forming the thick portion, and a second die which is separated from the first die, and is inserted in the part of the metal pipe for forming the thick portion, and   the second die is driven by the drive.   
     
     
         6 . A metal pipe processed by the method of  claim 1 . 
     
     
         7 . A metal pipe processed by the method of  claim 2 . 
     
     
         8 . A metal pipe processed by the method of  claim 3 .