With the improvement of gear hobbing technology, gear hobs are gradually developing towards integration, small diameter and multi head. The selection principles of gear hobs are as follows:
(1) Selection of gear hob head number. When rough machining gears, the requirements for gear machining efficiency are relatively high. Under the same cutting conditions, the double head gear hob can improve the gear processing efficiency by about 42%, and the three head gear hob can improve by about 55%, so multi head gear hob is often used. When finishing the gear, the machining accuracy of the gear tooth surface is relatively high, so the single head gear hob should be selected.
(2) Selection of helical direction of gear hob. When machining spur cylindrical gears with gear hobs, either left-hand gear hobs or right-hand gear hobs can be selected. When processing helical cylindrical gears, gear hobs with the same helical direction as the processed gears should be selected as far as possible, that is, right-hand hobs should be selected for right-hand gears and left-hand hobs should be selected for left-hand gears. Because the advantages of this selection are: the hob installation angle is small, the component action direction of the cutting force acting on the gear blank is opposite to the rotation direction of the gear blank, eliminating the gap, which is more conducive to cutting and improving the motion stability and machining accuracy of the gear hobbing machine. The gear hob selected is a right-hand hob.
(3) Gear hobs are selected according to the requirements of processing technology. Gear hobs that are more suitable for this process will be selected if different processing processes are used. If shaving is required after gear hobbing, the reserved shaving (pre shaving) hob shall be selected. For gear grinding after gear hobbing, the hob with grinding (before grinding) shall be selected.