Method and apparatus of hardening gears by induction heating

Abstract

A method of hardening the radially, outwardly facing surfaces of a generally circular, toothed workpiece adapted to rotate about a central axis generally concentric with the outwardly facing surfaces whereby the extremities of the surfaces define an outer circle by the tips of the teeth of the workpiece. This type of workpiece is generally a gear. The method comprises the steps of providing first and second induction heating coils, locating the workpiece concentric in the first induction heating coil, energizing the first induction heating coil with a first alternating frequency current for a first time period, deenergizing the first coil with the workpiece therein for a first time delay period, again energizing this first induction heating coil with a second alternating frequency current for a second time period substantially less than the first time period, immediately transferring the workpiece concentrically into the second induction heating coil in a second delay time, then energizing the second induction heating coil with a radio frequency current for a third time period and immediately quenching the outer surfaces by quenching liquid sprayed against the surfaces while the workpiece is in the second induction heating coil. This process can be employed for hardening various convoluted surfaces where the area to be hardened, compared to the mass adjacent thereto, is substantially less than the area compared to adjacent mass at the protruding convolution, i.e. generally gear teeth.