Relief grinding of planar double-enveloping worm gear hob using a four-axis CNC grinding machine

Compared with single-enveloping worm gearing, double-enveloping worm gearing can provide the same load capacity with a more compact volume and a higher efficiency. However, that the relief grinding of its hob can not be finished automatically till now limits its applications because all of the cutting edges on the hob have different shapes and spiral angles. In this paper, a pioneering method is proposed to relief grind the planar double-enveloping worm gear hob by adding two additional translational motions of the generating plane in addition to the rotation motions of the hob and the generating plane. A mathematic model is built for the relief grinding of the hob. A series of related data of the four motion parameters when grinding different points of the land edges of the different hob teeth are solved out, and the relief surfaces of different hob teeth can be ground continuously by using the data. The method is verified by using software VERICUT. Furthermore, a worm gear hob is relief ground on a four-axis CNC enveloping worm grinding machine by using this method.