Method of and apparatus for making a pipe of different wall thickness

Abstract

In a method of making a pipe of different wall thickness, a mandrel with at least one outer recessed axial section is inserted into a tubular blank. Subsequently a drawing die, having an inner diameter smaller than an outer diameter of the tubular blank, is pushed over the tubular blank while the pipe is held in place with respect to the mandrel in drawing direction, thereby pressing a wall portion of the blank into the recessed axial section of the die to form a pipe with a wall portion of greater wall thickness. As the mandrel is then withdrawn from the pipe, the wall portion of greater wall thickness of the pipe is pressed radially outwards.

What is claimed is:  
     
         1 . A method of making a pipe of different wall thickness, comprising the steps of: 
 inserting a mandrel with at least one outer recessed axial section into a tubular blank;    pushing a drawing die, having an inner diameter smaller than an outer diameter of the tubular blank, over the tubular blank while the tubular blank is held in place with respect to the mandrel in drawing direction, thereby pressing a wall portion of the tubular blank into the recessed axial section of the die to form a pipe with different wall thickness; and    withdrawing the mandrel from the pipe whereby the wall portion of the pipe is pressed radially outwards.    
     
     
         2 . The method of  claim 1 , and further comprising the step of pushing the drawing die again over the pipe after the mandrel is withdrawn from the pipe to thereby press inwards the wall portion of the pipe.  
     
     
         3 . The method of  claim 1 , and further comprising the step of forming a radially inwardly projecting shoulder at an end face of the tubular blank, before the mandrel is inserted in the blank.  
     
     
         4 . The method of  claim 3 , wherein the shoulder is formed at the end face which is first contacted by the drawing die.  
     
     
         5 . A method of making a pipe of different wall thickness, comprising the steps of: 
 providing a pipe of substantially constant wall thickness;    inserting a mandrel with at least one outer recessed section into the pipe until the mandrel is secured against axial displacement relative to the pipe;    pushing a drawing die over the pipe, thereby lengthening the pipe and pressing a wall portion of the pipe into the recessed section of the mandrel so as to provide the pipe with a wall portion of greater wall thickness; and    withdrawing the mandrel from the pipe, thereby pressing the wall portion of greater wall thickness outwardly.    
     
     
         6 . The method of  claim 5 , wherein the drawing die has an inner diameter which is smaller than an outer diameter of the pipe.  
     
     
         7 . The method of  claim 5 , and further comprising the step of pushing the drawing die again over the pipe, after the mandrel has been withdrawn, to thereby force the wall portion of greater wall thickness inwardly.  
     
     
         8 . The method of  claim 5 , and further comprising the step of forming a radially inwardly projecting shoulder at an end face of the pipe for abutment by the mandrel.  
     
     
         9 . The method of  claim 8 , wherein the shoulder is formed at the end face which is first contacted by the drawing die.  
     
     
         10 . Apparatus for making a pipe of different wall thickness, comprising: 
 a mandrel having an axial length and intended for insertion into a tubular blank, wherein the mandrel has at least one outer recessed section extending in axial direction; and    a drawing die intended for interaction with the mandrel and having an inner diameter which is smaller than an outer diameter of the tubular blank,    wherein an inside radius of the drawing die and a radius of the mandrel define a distance which is smaller than a wall thickness of the tubular blank.    
     
     
         11 . The apparatus of  claim 10 , wherein the mandrel has an axial length, wherein the outer recessed section extends over a portion of the axial length of the mandrel such as to be bounded on opposite sides thereof.  
     
     
         12 . The apparatus of  claim 10 , wherein the recessed section of the mandrel has a depth which equals at a maximum the wall thickness of the tubular blank.  
     
     
         13 . The apparatus of  claim 10 , wherein the mandrel is formed with a plurality of circumferentially spaced recessed sections extending in the axial direction in parallel relationship.  
     
     
         14 . The apparatus of  claim 13 , wherein the recessed sections have varying configuration.  
     
     
         15 . Apparatus for making a pipe of different wall thickness, comprising: 
 a mandrel having an axial length and intended for insertion into a pipe of substantially constant wall thickness, wherein the mandrel has at least one outer recessed section extending in axial direction; and    a drawing die intended for interaction with the mandrel and having an inner diameter which is smaller than an outer diameter of the pipe, wherein the inner diameter of the drawing die and a maximum outer diameter of the mandrel define a distance which is smaller than the wall thickness of the pipe.    
     
     
         16 . The apparatus of  claim 15 , wherein the recessed section of the mandrel has a depth which equals at a maximum the wall thickness of the pipe.