Ball Screw And A Method For Manufacturing The Same

Abstract

A ball screw has a nut formed with a helical ball rolling groove on its inner circumference. A screw shaft is formed with a helical ball rolling groove on its inner circumference. The screw shaft is inserted into the nut. A number of balls are rollably contained within a ball rolling passage formed by oppositely arranged helical ball rolling grooves of the nut and the screw shaft, respectively. The nut is made of case hardened steel. The ball rolling groove is formed by cutting and surface hardening, by vacuum carburizing hardening, without any after-processing.

What is claimed is: 
     
         1 . A method for manufacturing a ball screw comprising:
 a nut formed with a helical ball rolling groove on its inner circumference, the nut is made of case hardened steel;   a screw shaft with a helical ball rolling groove formed on its outer circumference, the screw shaft inserted into the nut;   a number of balls rollably contained within a ball rolling passage formed by oppositely arranged helical ball rolling grooves of the nut and the screw shaft, respectively, comprising the steps of:   cutting the nut ball rolling groove with a universal turning tool;   hardening the nut ball rolling groove by vacuum carburizing hardening.   
     
     
         2 . The method for manufacturing the ball screw of  claim 1 , further comprising forming a whole configuration of the ball rolling groove using a universal turning tool with a cutting edge having its nose radius being smaller than a radius of curvature of the ball rolling groove by moving the universal turning tool several times by an effective length of the ball rolling groove, and by successively shifting, each time, the moving path of the universal turning tool along a circular arc direction of a cross-sectional configuration of the ball rolling groove. 
     
     
         3 . The method for manufacturing a ball screw of  claim 1 , further comprising shot blasting the nut ball rolling groove after the vacuum carburizing hardening. 
     
     
         4 . The method for manufacturing a ball screw of  claim 2 , further comprising shot blasting the nut ball rolling groove after the vacuum carburizing hardening. 
     
     
         5 . The method for manufacturing a ball screw of  claim 1 , further comprising exposing the nut ball rolling groove to a tumbler treatment after the vacuum carburizing hardening. 
     
     
         6 . The method for manufacturing the ball screw of  claim 2 , further comprising forming a whole configuration of the ball rolling groove using a universal turning tool with a cutting edge having its nose radius being smaller than a radius of curvature of the ball rolling groove by moving the universal turning tool several times by an effective length of the ball rolling groove, and by successively shifting, each time, the moving path of the universal turning tool along a circular arc direction of a cross-sectional configuration of the ball rolling groove.