Process of making variable wall thickness tubing

Abstract

A method for manufacturing a tube with varying wall thickness includes the step of drawing a tube over a generally cylindrical mandrel having an outer diameter that fluctuates along the length of the mandrel between a first diameter and a second diameter. The tube is drawn over the mandrel to form a tube wall having a thickness that fluctuates along the length of the tube between a first wall thickness and a second wall thickness. After the tube is drawn over the mandrel, the mandrel is removed from the tube. The outer surface of the tube may be finished to form a substantially uniform outer diameter along the length of the tube.

1 . A method for manufacturing a variable-wall thickness tube, said method comprising the steps of: 
 A. forming a generally cylindrical tube;    B. drawing the tube through a first die to reduce the outer diameter of the tube to an intermediate outer diameter;    C. placing the tube over a mandrel having an outer diameter that fluctuates along the length of the mandrel between a first diameter and a second diameter;    D. drawing the tube and mandrel through a second die to form a tube wall having a thickness that fluctuates along the length of the tube between a first wall thickness and a second wall thickness; and    E. removing the mandrel from the tube.    
   
   
       2 . The method of  claim 1 , comprising the step of finishing the outer surface of the tube so that the tube has a substantially uniform outer finished diameter.  
   
   
       3 . The method of  claim 2 , wherein the step of finishing the outer surface comprises the step of tube sinking.  
   
   
       4 . The method of  claim 2 , comprising the steps of straightening and cutting the tube to a predetermined length after the outer surface finishing step.  
   
   
       5 . The method of  claim 1 , wherein the step of forming the generally cylindrical tube comprises the step of bending a metal strip having a pair of side edges to form a cylinder and welding the side edges together.  
   
   
       6 . The method of  claim 1 , wherein the step of forming the generally cylindrical tube comprises the step of drilling a bore through the center of a piece of bar stock.  
   
   
       7 . The method of  claim 1 , comprising the step of annealing the tube after the outer surface finishing step.  
   
   
       8 . The method of  claim 1 , wherein the step of removing the mandrel from the tube comprises the step of running the mandrel and the tube through a roll type tube straightener to provide clearance between the tube and the mandrel and allow extraction of the mandrel from the tubing.  
   
   
       9 . A method for manufacturing a plurality of variable wall thickness tubes, said method comprising the steps of: 
 A. drawing a length of tubing through a first die;    B. placing the tubing over a mandrel rod comprising a variable diameter section and a uniform diameter section abutting said variable diameter section;    C. drawing the tubing and mandrel rod through a second die to form a first tubing section and a second tubing section, said first tubing section having a fluctuating inner diameter, and said second tubing section having a uniform inner diameter;    D. removing the mandrel from the tubing; and    E. cutting the tubing transversely through each of said second tubing sections to form a plurality of tubes.    
   
   
       10 . The method of  claim 9  comprising the step of finishing the outer surface of the tubing so that the tubing has a substantially uniform outer diameter.  
   
   
       11 . The method of  claim 10  comprising the step of removing the tubing from the mandrel after drawing the tubing and mandrel through the second die and prior to the finishing step.  
   
   
       12 . The method of  claim 10 , wherein the step of finishing the outer surface comprises the step of sink drawing the tubing.  
   
   
       13 . The method of  claim 9 , wherein the mandrel rod has a second variable diameter section abutting said uniform diameter section, and a second uniform diameter section abutting the second variable diameter section.  
   
   
       14 . The method of  claim 9 , wherein the step of removing the mandrel from the tubing comprises the step of running the mandrel and the tubing through a roll type tube straightener to provide clearance between the tubing and the mandrel and allow extraction of the mandrel from the tubing.  
   
   
       15 . A method for manufacturing a plurality of variable wall thickness tubes, said method comprising the steps of: 
 A. drawing a piece of tubing through a first die to reduce the outer diameter of the tubing to an intermediate outer diameter;    B. placing the tubing over a mandrel rod comprising: 
 a plurality of first sections having a uniform rod diameter; and  
 a plurality of second sections arranged alternately with said first sections, each of said second sections having a rod diameter that fluctuates between a first rod diameter and a second rod diameter;  
   C. drawing the tubing and mandrel rod through a second die to form: 
 a plurality of first tubing sections, each of said first tubing sections having an inner diameter that fluctuates between a first inner diameter and a second inner diameter that is less than the first inner diameter; and  
 a plurality of second tubing sections, each of said second tubing sections having a uniform inner diameter that is less than the first inner diameter of the first tubing sections;  
   D. removing the mandrel from the tubing; and    E. cutting the tubing through each of said second tubing sections to form a plurality of tubes.    
   
   
       16 . The method of  claim 15  comprising the step of finishing the outer surface of the tubing so that the tubing has a substantially uniform outer diameter.  
   
   
       17 . A method for manufacturing a variable-wall thickness tube, said method comprising the steps of: 
 A. placing a generally cylindrical tube over a mandrel having an outer diameter that fluctuates along the length of the mandrel between a first diameter and a second diameter;    B. drawing the tube and mandrel through a die to form a tube wall having a thickness that fluctuates along the length of the tube between a first wall thickness and a second wall thickness; and    C. removing the mandrel from the tube.    
   
   
       18 . The method of  claim 17  comprising the step of finishing the outer surface of the tube so that the tube has a substantially uniform outer finished diameter.