Method and apparatus for localized gear tooth root fillet shot peening

Abstract

A method of manufacturing a gear having root fillets between adjacent teeth that are shot peered to improve compressive strength. A robot moves a shot peening nozzle between adjacent teeth. A servomotor drive indexes the gear in increments corresponding to one or more teeth. The nozzle has a tapered tip that is moved between adjacent tooth faces with clearance relative to the tooth faces.

What is claimed is: 
     
         1 . A method of manufacturing a gear comprising:
 forming a gear including a body and a plurality of teeth;   assembling the gear to a servomotor drive; and   providing a robot with a shot peening system having a nozzle directing shot at root fillets through a nozzle opening disposed between faces of two adjacent teeth, wherein the servomotor drive incrementally rotates the gear and the robot shot peens along a length of the root fillets.   
     
     
         2 . The method of  claim 1  wherein the nozzle is spaced from the root fillets less than a depth of the teeth. 
     
     
         3 . The method of  claim 1  wherein the nozzle is oriented to direct shot aligned with a length of the root fillet at an approach angle offset between 20 and 70 degrees from a tangent line of the root fillets. 
     
     
         4 . The method of  claim 1  wherein the servomotor drive rotates the gear in single tooth increments and the robot follows the length of the root fillets on opposite sides of each tooth between rotation increments. 
     
     
         5 . The method of  claim 1  wherein the gear is a pinion gear. 
     
     
         6 . The method of  claim 1  wherein the gear is a ring gear. 
     
     
         7 . A nozzle for shot peening a gear having a plurality of teeth comprising:
 an air inlet;   a shot feeder; and   a nozzle tip receiving air under pressure from the air inlet and shot media from the shot feeder, wherein the nozzle tip directs the shot media at root fillets through a nozzle opening disposed between faces of two adjacent teeth as the nozzle tip is moved along a length of the root fillets.   
     
     
         8 . The nozzle of  claim 7  wherein the nozzle tip defines a nozzle opening having an inner diameter and is spaced from the root fillet to provide a blast diameter greater than the inner diameter, wherein the shot media is directed towards a space between two adjacent teeth. 
     
     
         9 . The nozzle of  claim 7  wherein the nozzle defines a nozzle opening and is tapered to a radius that fits between two adjacent teeth with at least two millimeters of clearance away from the faces of the teeth when the nozzle opening is held at a specified standoff distance from the root fillet. 
     
     
         10 . The nozzle of  claim 7  wherein the shot media is cut wire shot having a diameter of between 0.02 and 0.032 mm. 
     
     
         11 . The nozzle of  claim 7  wherein the nozzle tip defines a nozzle opening that is at least four times a diameter of the shot media. 
     
     
         12 . The nozzle of  claim 7  wherein the nozzle tip defines a nozzle opening that is between 35% and 75% of a width of the root fillets.