Form Rolling of Helical Gear with Small Number of Teeth and Large Helix Angle (Geometrical Discussion on Form Deviation Caused by Die Penetration)

Abstract

Form rolling of helical gears having two teeth and large helix angles was performed in order to apply them to electric actuators for eco-friendly automobiles. However, large form deviations were observed on form rolled gears. In the present paper, geometrical mechanism of the form deviation caused by round dies penetration was discussed. At first, pitch surface of the form rolled gear was assumed to be circular cone because of die penetrations. Height of the circular cone is thought to be equal to axial pitch of form rolled gear. On the other hand, geometrical calculations were performed. Tooth flank generated by penetrating die was calculated. And profile and helix deviations of generated gear flank were also calculated. As a result, helix deviation of periodical wave and a profile slope deviation were recognized on the tooth surface. In order to confirm tooth profile and helix deviations, form roll was performed. Tooth profile deviations on form rolled gears almost agreed with the ones obtained by calculations. Measured deviations on form rolled gears increased as increasing dies penetration depth. However, calculated deviations were smaller than measured ones.