Effect of Fillet Rolling at the Root of the Tooth on Bending Fatigue Strength of Spur Gears. ADI, S45C Gears.

Abstract

In order to obtain higher bending fatigue strength of gear teeth required to cope with severe driving conditions of gears, shot peening is widely used. It is a very effective method to improve the bending fatigue strength as is well known, but it also roughers the tooth surface, resulting in lowered tooth surface strength. To overcome this weak point, fillet rolling at the root of the tooth is proposed. The surfaces at the roots of S45C gears and austempered ductile iron (ADI) gears are markedly work hardened by this method. Bending fatigue strength of fillet-rolled gears is investigated compared with that of unrolled gears. Bending fatigue strength of S45C gears is improved by up to 33%, but that of ADI gears is lowered by about 9% due to microcracks connecting neighboring graphite grains just below the surface of the tooth face, produced in fillet rolling. Bending fatigue strength of ADI gears, where a 3-mm-thick layer is removed from both side edges by turning, is improved by about 16%.