Akira Katsuki

Fundamental Research on Hob Materials.

In order to develop hob material which decreases wear, the influence of composition, heat treatment, hardness, and transverse rupture strength (TRS) of a hob on flank wear and crater wear was investigated in this paper. Experiments were carried out with a simple fly tool. Powder metal high-speed steel (PM-HSS) is better than normal HSS in decreasing wear. Among the materials tested, PM-HSS containing high vanadium and high cobalt performed best. The influence of heat treatment on hob wear is different according to the composition of the materials. At a low quenching temperature and a high tempering temperature for PM-HSS containing high vanadium and high cobalt, hob wear decreases. Corner wear and crater wear decrease with increasing hardness, and with decreasing TRS. Materials having more than 900 Hv hardness and 3 000 N/mm2 TRS are suitable for making hobs.

Effect of Alcohol in Preventing Hob Wear.

Low-grade alcohol in varied quantities was added to machine oil 7, rape-seed oil and chlorinated fatty oil. Hob wear was prevented when any of the tested alcohols was added to machine oil 7. Particularly at a high cutting speed of 159m/min, the width of corner wear decreased considerably. For rape-seed oil and chlorinated fatty oil, the alcohols decreased hob wear, but the effects of alcohols in preventing the wear were different. Among the three kinds of cutting oils tested, machine oil 7 gave the best performance, causing very little wear when alcohol was added. Rape-seed oil was the next best. The addition of 2% n-propyl alcohol to machine oil 7 is optimal for practical applications. The surface roughness of a groove cut obtained with the addition of alcohol to machine oil 7 or rape-seed oil becomes smaller than that obtained with the cutting oil alone.

Influence of Viscosity of Base Oil on Effect of Additive in Cutting Oil for Hobbing.

It has been already reported that EP additives used in cutting oil for hobbing exert a notable influence on hob wear. However, systematic studies on the effect of the viscosity for cutting oil and on the effect of the viscosity of base oil on action of additives are rather rare. Since there exist generally interactions between an additive and a base oil, the difference in the viscosity of base oil should affect action of an additive. Therefore, finding optimum viscosity conditions in which hob wear and finished surface roughness of gear are minimized, will be necessary for obtaining a standard for selecting or designing an appropriate base oil for additive. From this viewpoint, the effect of viscosity of base oil, moreover, the effect of additive in base oil with a variety of viscosity on hob wear and finished surface were investigated in this paper. Experiments were carried out with a single fly tool. Hob wear tends to be smaller with higher viscosity of base oil. The viscosity of base oil hardly affected finished surface roughness. Among the additives used, the chlorinated fatty acid ester added to the high viscosity base oil showed a best performance and the optimal content of chlorine was 3%.