Method for hardening groove walls of the ring groove of a steel piston

Abstract

A method for hardening groove walls of the ring groove of a steel piston by a laser beam consists of conducting process gas that contains oxygen onto a groove wall of the steel piston, and putting the steel piston into rotation. The groove wall is irradiated with the laser beam until an oxide layer has formed on the groove wall. Subsequently, the feed of the process gas is turned off, and the groove wall is heated and hardened, in tracks. The degree of heat conductivity of the groove wall is improved by the oxide layer on the groove wall, thereby bringing about faster heating and hardening of the groove wall. The reflectivity of the groove wall is also reduced in this way, so that only little light is reflected by the groove wall onto other regions of the groove, so that these regions are not unintentionally heated and hardened.

1 . A method for hardening groove walls of the ring groove of a steel piston that is mounted so as to rotate about its piston axis, by means of a laser beam directed at a groove wall, the method comprising the following steps:
 conducting process gas that contains oxygen onto the groove wall of the steel piston;   putting the steel piston into rotation;   irradiating the groove wall surrounded by the process gas with the laser beam, until an oxide layer has formed on the groove wall;   turning off a feed of the process gas; and   heating and hardening the groove wall by means of the laser beam, in tracks.   
   
   
       2 . The method according to  claim 1 , wherein the process gas consists of a mixture of argon and oxygen. 
   
   
       3 . The method according to  claim 1 , wherein the process gas consists of a mixture of nitrogen and oxygen. 
   
   
       4 . The method according to  claim 1 , wherein the process gas consists of a mixture of nitrogen, argon, and oxygen. 
   
   
       5 . The method according to  claim 1 , wherein at least approximately 1% oxygen is mixed into the process gas.