Effect of Fine Particle Bombarding Process on Tooth Surface Properties and Tooth Surface Strength of Carburized Gears (2nd Report, Effect on Tooth Surface Strength and Influencing Factors)

Recently the application of fine particle bombarding process (denoted as FPB) has been getting wider because of its superior effects compared to conventional shot-peening ; however, the influence on the tooth surface strength of gears has not been clarified. The purpose of this study is to determine quantitatively the effect of FPB on the tooth surface strength of carburized gears and to clarify the factors influencing on the tooth surface strength. First, the author examined the tooth surface properties such as residual stress, roughness, hardness, surface texture, etc. using test gears processed by the FPB under three different conditions of arc height. A test gear performed by conventional impeller-type shot-peening was also used for comparison with the FPB. These results have been described in the 1st report. Next, durability tests were carried out using the gears to measure the tooth surface strength. The results showed that the FPB is effective to increase the tooth surface strength by 1.21 to 1.28 times in Hertzian stress compared to conventional impeller-type shot-peening. Then, the following factors caused by the FPB that influence on the tooth surface strength increase were discussed. ( 1 ) Produced high residual compressive stress, ( 2) Increased hardness, ( 3 ) Good conformability on the tooth surface, ( 4 ) Micro hollows on the tooth surface generated during running. It was found that the latter two are unique factors caused by the FPB process. In the 2nd report, the effect of the FPB on the tooth surface strength is described.