Coil forming system having an expandable mandrel

Abstract

A coil spring forming system includes a mandrel having at least a portion that is selectively expandable so that a central portion of a resulting coil spring has a larger dimension than reduced diameter end sections of the spring. In one example, a plurality of coil shaping surfaces are supported relative to a central portion of the mandrel using a plurality of linkages. The coil shaping surfaces are moved using an actuator (i.e., hydraulic or pneumatic) between expanded and contracted positions to selectively vary the largest outside dimension of the mandrel. In one example, the coil shaping surfaces are spaced apart from each other in the expanded position. In another example, the coil shaping surfaces are arranged such that the mandrel has a generally continuous outer periphery when the surfaces are in the expanded position.

We claim:  
     
         1 . A device for making a coil spring, comprising: 
 a selectively collapsible mandrel having a plurality of coil shaping members supported to be selectively movable between a first position where at least a portion of the mandrel has a first outside dimension and a second position where the mandrel has a second, smaller outside dimension.    
     
     
         2 . The device of  claim 1 , wherein the mandrel has a central portion and the coil shaping members are supported by linkages between the central portion and the shaping members and wherein the linkages are selectively movable to change the outside dimension of the mandrel.  
     
     
         3 . The device of  claim 1 , wherein the mandrel has a central portion and the coil shaping members are supported to be movable relative to the central portion and including link members associated with the shaping members, the link members being one of hydraulically or pneumatically actuated to cause movement of the shaping members relative to the central portion.  
     
     
         4 . The device of  claim 1 , wherein there is arcuate spacing between the shaping members when the shaping members are in the first position.  
     
     
         5 . The device of  claim 4 , wherein the shaping members contact each other in the second position.  
     
     
         6 . The device of  claim 1 , wherein the shaping members form a generally continuous periphery about an outer surface of the mandrel in the first position.  
     
     
         7 . The device of  claim 6 , wherein at least one of the shaping members moves into a folded position as the shaping members move into the second position.  
     
     
         8 . The device of  claim 1 , wherein the mandrel has longitudinal ends and the outside dimension of the mandrel near the ends is smaller when the shaping members are in the first position than the outside dimension at a longitudinally central portion of the mandrel.  
     
     
         9 . The device of  claim 1 , wherein the first outside dimension varies along the length of the mandrel.  
     
     
         10 . The device of  claim 1 , including a lead screw associated with the mandrel such that the lead screw and the mandrel cooperate to form a coil from a metal rod by causing the metal rod to conform to the shape of the mandrel provided by the shaping members such that at least a portion of the coil has an inside dimension corresponding to the first outside dimension of the mandrel.  
     
     
         11 . The device of  claim 1 , wherein the shaping members each have a longitudinal length that is shorter than a longitudinal length of a coil shaping surface of the mandrel.  
     
     
         12 . The device of  claim 1 , wherein the shaping members each comprise steel.  
     
     
         13 . A method of making a coil spring using a mandrel, comprising the steps of: 
 (A) placing the mandrel into a first operative position such that an outside dimension of the mandrel corresponds to a desired inside dimension of the coil;    (B) wrapping a metal rod around the mandrel to thereby form the coil;    (C) reducing the outside dimension of at least a portion of the mandrel; and    (D) subsequently separating the coil from the mandrel.    
     
     
         14 . The method of  claim 13 , wherein the outside dimension of the mandrel is greater near a longitudinal center of the mandrel than near longitudinal ends of the mandrel when performing steps (A) and (B).  
     
     
         15 . The method of  claim 13 , wherein step (A) includes providing a coil shaping surface around an entire periphery of the outside of the mandrel.  
     
     
         16 . The method of  claim 15 , wherein step (C) includes folding at least one of the coil shaping surfaces into a collapsed position.  
     
     
         17 . The method of  claim 13 , wherein step (A) includes providing a coil shaping surface at selected intervals around a periphery of the outside of the mandrel.