Compression springs and methods of making same

Abstract

Compression springs, such as helical compression springs, include end portions with selectively contoured inner contact surfaces. The selective contours of the inner contact surfaces may take the form of planar, grooved, concave, or other shaped, non-circular surfaces. In addition, enough of the inner contact surface is contoured to reduce the contact stress and/or stress concentration effects on the adjacent coils when the compression spring is placed under load and the adjacent coil engages or contacts the respective end portion. The selective contouring of the end portions may be accomplished by holding the spring in a holder and moving a cutter relative to the end portion of the spring to remove the desired amount of material from the end portion.

1 . A compression spring comprising:
 a coil body arranged in a helical configuration with a mean coil diameter relative to a coil axis, the coil body formed with round-wire having a wire diameter; and   an end portion extending from the coil body, the end portion having a thickness in a direction substantially parallel to the coil axis, the thickness being less than the wire diameter and defined by a first surface facing substantially away from the coil body and a second surface facing substantially toward the coil body, the second surface having a grooved portion formed into the thickness of the end portion.   
   
   
       2 . The compression spring of  claim 1  wherein the mean coil diameter varies along the coil axis. 
   
   
       3 . The compression spring of  claim 1  wherein the first surface of the end portion is non-circular. 
   
   
       4 . The compression spring of  claim 1  wherein the coil body includes a plurality of coils arranged with a desired pitch. 
   
   
       5 . The compression spring of  claim 1  wherein the grooved portion includes an arcuate shape having a desired radius. 
   
   
       6 . The compression spring of  claim 1  wherein the second surface includes an arcuate, concave shape having a first radius that is greater than the radius of the wire diameter. 
   
   
       7 . The compression spring of  claim 1 , wherein the first and second surfaces cooperate to form a concavo-convex end portion, the second surface having the concave shape. 
   
   
       8 . A method of making a compression spring, the method comprising:
 fixing the compression spring to a holder, the compression spring having an end portion extending from a coil body, the end portion having a thickness defined by a first surface facing substantially away from the coil body and a second surface facing substantially toward the coil body;   moving a cutter in proximity to, yet spaced apart from, the second surface of the end portion;   moving the holder to place the second surface of the end portion into contact with the cutter; and   machining the second surface to reduce the thickness of the end portion.   
   
   
       9 . The method of  claim 8  wherein fixing the compression spring to a holder includes clamping at least a portion of the compression spring in a collet. 
   
   
       10 . The method of  claim 8  wherein moving the cutter includes moving a milling cutter. 
   
   
       11 . The method of  claim 8  wherein moving the cutter includes moving a grinding wheel. 
   
   
       12 . The method of  claim 8  wherein moving the holder to place the second surface of the end portion into contact with the cutter includes rotating the holder on a multi-axis rotary tool. 
   
   
       13 . The method of  claim 9  wherein moving the holder includes moving the collet. 
   
   
       14 . The method of  claim 8  wherein machining the second surface to reduce the thickness of the end portion includes removing an amount of material from the end portion with the cutter. 
   
   
       15 . The method of  claim 8  wherein machining the second surface includes making the second surface substantially planar. 
   
   
       16 . The method of  claim 8  wherein machining the second surface includes forming an arcuate, concave surface having a desired radius. 
   
   
       17 . The method of  claim 8 , wherein machining the second surface includes forming non-planar and non-circular surface having a desired cross-sectional profile. 
   
   
       18 . The method of  claim 8 , further comprising:
 breaking off a free edge of the end portion.   
   
   
       19 . The method of  claim 18 , further comprising:
 chamfering the free edge of the end portion.   
   
   
       20 . The method of  claim 8  wherein machining the second surface includes grinding the second surface.