Laser heat treatment

Abstract

A method of heat treating a surface with a laser, successive passes of the laser over the surface having a large overlap with each individual pass applying insufficient energy to obtain the desired effect on the surface but the overlapping passes applying sufficient energy. Various patterns of laser movement may be used.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
         1 . A method of heat treating a surface with one or more lasers to obtain a change in the structure of the surface without melting the surface, the method comprising:
 directing a beam of a laser of the one or more lasers onto the surface, the beam illuminating at a point in time a portion of the surface, and illuminating at successive points in time further portions of the surface, the portion of the surface and the further portions of the surface defining a path, the path overlapping itself or the path of another laser of the one or more lasers to pass over each point in an area of the surface to be treated more than once, each laser of the one or more lasers supplying insufficient energy to obtain the change in structure of the surface in a single pass.   
     
     
         2 . The method of  claim 1  in which the width of the overlap between successive passes is greater than 50% of the width of each of the successive passes. 
     
     
         3 . The method of  claim 1  in which the width of the overlap between successive passes is at least 75% of the width of each of the successive passes. 
     
     
         4 . The method of  claim 1  in which the width of the overlap between successive passes is greater than 75% of the width of each of the successive passes. 
     
     
         5 . A method of heat treating a surface with one or more lasers to obtain a change in the structure of the surface without melting the surface, the method comprising:
 directing a beam of a laser of the one or more lasers onto the surface, the beam illuminating at a point in time a portion of the surface, and illuminating at successive points in time further portions of the surface, the portion of the surface and the further portions of the surface defining a path, the path overlapping itself or the path of another laser of the one or more lasers to pass over each point in an area of the surface to be treated more than once, the width of the overlap of the path between successive passes being greater than  50 % of the width of the path.   
     
     
         6 . The method of  claim 5  in which the width of the overlap between successive passes is at least 75% of the width of each of the successive passes. 
     
     
         7 . The method of  claim 5  in which the width of the overlap between successive passes is greater than 75% of the width of each of the successive passes. 
     
     
         8 . The method of  claim 1  in which the surface to be treated is steel. 
     
     
         9 . The method of  claim 8  in which the change in the structure of the surface is the formation of a martensitic grain structure. 
     
     
         10 . The method of  claim 1  in which the surface is divided into strips, each pass of the laser traversing the width of a respective strip, and successive passes traversing a strip overlapping within the strip. 
     
     
         11 . The method of  claim 10  in which neighbouring strips overlap each other. 
     
     
         12 . The method of  claim 1  in which the path follows a zig-zag route. 
     
     
         13 . The method of  claim 1  in which the path follows a route with stacked line passes. 
     
     
         14 . The method of  claim 1  in which the path follows a looping route. 
     
     
         15 . The method of  claim 1  in which the path follows a route with S-pattern motion. 
     
     
         16 . The method of  claim 1  in which the surface is divided into segments, each segment having at least two passes with substantially 100% overlap. 
     
     
         17 . The method of  claim 16  in which neighbouring segments overlap each other.