Effects of Material Properties on the Teeth Accuracy of Spline Shafts in Cold Form Rolling

Abstract

Effects of material properties on the teeth accuracy of spline shafts processed by cold form rolling with rack dies have been experimentally investigated. The materials used were medium-carbon steel bars processed by four kinds of heat treatments. Three of them were quenched from 850°C followed by tempering at 570°C, 630°C,700°C respectively, and the fourth was annealed at 600°C. The remarks obtained by this study are as follows. (1) Teeth accuracy is improved with increasing tempering temperature, while the steel annealed at 600°C has almost the same teeth accuracy as the steel tempered at 700°C. (2) Teeth accuracy shows high correlation with cumulative pitch deviation from the theoretical value. (3) The low teeth accuracy is due to that of the follower side teeth which shows lower formability than the driven side. (4) In order to find a material property which affects teeth accuracy, material flow inside the necking portion in the tensile test was focused from the fact that material flows of the follower side teeth are similar with that of the necking portion. (5) Cup and cone type fracture was observed in the tensile test. The value NPC defined as the width of tapered portion divided by outer diameter of tapered portion is proposed as an index of the formability in cold form rolling, and the reason why the teeth accuracy is improved with increasing this index is investigated on the basis of experimental results.