Method and apparatus for heat treating an internal bore in a workpiece

A method of heat treating the bore in a ferrous cylinder liner to increase the metallurgical hardness of its surface to a predetermined depth, comprising;

• shaping an annular laser beam from a suitable source into an elongated focal pattern;
• oscillating said elongated focal pattern to provide a rectangular pattern in cross section with a more evenly distributed energy level;
• directing said rectangular pattern generally axially inwardly of such bore;
• reflecting said rectangular pattern from a mirror substantially transversely directly upon the surface of said bore to provide a relatively uniform heating zone thereat;
• and
• effecting relative motion between the ferrous cylinder liner and said mirror so that said bore is progressively spannably heat treated while minimizing heat transfer to the entire cylinder liner.

A method of heat treating a cylindrical bore in a metallic workpiece to provide a hard uniform surface layer on a tough body portion without melting the internal surface of the bore comprising;

• directing a laser beam generally axially inwardly toward such bore with said laser beam having a relatively instantaneously generated elongated focal pattern in cross section;
• reflecting said laser beam from a mirror onto a surface of said bore;
• rapidly oscillating said laser beam transversely of said elongated focal pattern to effect a rectangular heating pattern on the surface of said bore having a more uniform and improved energy distribution thereat;
• and
• effecting relative motion between such workpiece and said mirror so that said bore is progressively scannably heat treated to minimize heating of the entire workpiece.

A method of heat treating a cylinder bore in an engine block to increase its surface hardness comprising;

• shaping an annular laser beam into an elongated focal pattern;
• oscillating said elongated focal pattern to provide a rectangular pattern in cross section with a more evenly distributed energy level;
• directing said rectangular pattern generally axially inwardly toward such cylinder bore;
• reflecting said laser beam pattern from mirror means upon a surface of said cylinder bore to provide a uniformly hot heating zone thereat;
• and
• simultaneously rotating and positioning said mirror means for scannably aiming said laser beam pattern and effecting continuous traveling of said heating zone along an annular path on the surface of said cylinder bore for progressive heat treatment thereof.