Effect of CBN grinding on the bending strength of carburized gears

The surface condition of a carburized gear is improved by CBN grinding, in addition to the generation of a compressive residual stress at the ground s urface. To clarify the effect of these merits on the strength enhancement, a bending fatigue test is performed for the carburized and the CBN-ground g ears. The fillet trs well as involute tooth surface is ground by an electro plated threaded CBN wheel. The lore axial feed rate and the spark-out treat ment are effective in improving the surface finish and increasing the compr essive residual stress, and the strengths of CBN-ground gears are increased from 100 MPa to 160 MPa in comparison with the carburized gears. Moreover, the test results are discussed on the basis of the fracture mechanics-base d strength evaluation which has been proposed by the authors. This analysis demonstrates that the influence of CBN grinding on strength is smaller tha n the effects of surface-treatments such as shot peening and chemical polis hing.