Techniques for reducing wall thinning during a hydroforming operation

Abstract

It has been found that a compressive force assists in obtaining desired cold flow characteristics of a tubular steel work piece during a hydroforming operation. It has also been found that the most desirable results are achieved when the compressive force applied to the ends of the tubular steel work piece is just slightly less than the force that drive the tubular steel work piece into its yield point. A work piece previously formed by the above mentioned hydroforming operation may now be bent and subjected to a secondary hydroforming operation to produce a bent hydroformed tubular steel finished work piece having complex geometry.

1 . A hydroforming operation comprising: 
 selecting a suitable tubular steel work piece having two ends, subjecting said work piece to a preliminary hydroforming operation in which said work piece is placed into a presselected die set comprising at least two movable die components where an axial gap exists prior to said preliminary hydroforming operation; expanding said tubular work piece in said die set whilst simultaneously applying a compressive force which is slightly less than a yield point force for said tubular steel work piece is applied to the ends of said tubular steel work piece; whilst closing said gap by moving said movable die components together;    removing said work piece from said presselected die set at the conclusion of said preliminary hydroforming operation,    bending said work piece to form a predetermined shape;    placing said bent work piece in a second die set performing a second hydroforming operation on said work piece whilst said work piece is in said second die set.    
   
   
       2 . A method of hydroforming a tube to a predetermined shape comprising; 
 providing a first die set comprising members of a peculiar configuration having a particular shaped internal cavity shaped therein; and    said first die members being spaced apart to have a space between said dies,    inserting said tube into said first die set and,    applying hydraulic pressure to the tube to cause said tube to conform to the shape of said cavity whilst simultaneously:    applying a predetermined compressive force to the ends of said tube and moving the first die set members together to eliminate said spacing between said first die members.    
   
   
       3 . The method of  claim 2  wherein said predetermined force is slightly less than the force necessary to cause said tube to yield.  
   
   
       4 . The method of  claim 3  wherein said tube is removed from said first die set cavity, and is bent into a second configuration and inserted into a second die set having a second cavity therein; and applying a second hydraulic pressure to said tube to cause said tube to conform to said second cavity, and removing said tube from said second die set.