Research On CNC Relief Grinding Technology Of Double-enveloping Worm Gear Hob

Because of double-enveloping worm gearing’s unique driving characteristics, it can have heavier load capacity, higher transmission efficiency and longer lifetime comparing to traditional cylindrical worm gearing, while maintaining the original characteristics of worm gearing. Especially, the planar double-enveloping worm gearing is first developed from China, China’s scholars have done a lot of theoretical research and analysis and this form of gearing has an in-depth development in China. But the fabrica-tion techniques of double-enveloping worm gearing did not have a sufficient accumulation of technology, limiting the widespread use of this type of worm gearing. The processing of double-enveloping worm gear hob of this drive system is one of the most complex parts, it is still unable to achieve automatic relief grinding, the manufacturers still relief their hobs by manual by workers. This severely reduces the level of automation of its manufacture, it’s such a low efficiency manner. Every cutting edge of planar double-enveloping worm hob has a different curve shape and they still have no regularity, leading to difficulties in its automated relief grinding. All the teeth of cylindrical worm gear hob have the same shape cutting edges, so the hob can be effectively relieved after calculated the profile of the relief grinding wheel. In this paper, a relief grinding method is proposed based 4-axis CNC double-enveloping worm gearing grinding machine to accomplish the automatic relief grinding of double-enveloping worm gear hob, also the relief work can be adapted to all kinds of land width and relief angle designs.To fulfill the designed land width and relief angle, the unit normal vector of the planar grinding wheel need to coincide with the unit normal vector of the relief surface at points on the land edge to ensure the relief angle. And the grinding plane will get in touch with the point on the land edge to confine the designed land width. The rim of the grinding wheel should always be contacted with the root arc of the hob, after that, the location of the grinding wheel can be fully defined to avoid the incomplete relief or get the wheel interference with the hob. The mathematical expression of these constraints is built. The mathematical model of the relief surface processed by this method is also built.Having established the virtual manufacturing system of a 4-axis CNC grinding machine including the B, C, X, Z motion axis. Manufacturing of the thread grinding, milling of hob flutes and relief grinding is simulated by this system. The simulation gives this relief method a visual and measurable verification. Using this virtual method, an error analysis test is designed. Some factors that influence the manufactured land width and relief angle are analyzed. Meanwhile, the effect law is given according to the test data.The experiment of the relief grinding of a used hob has been carried out. The thread re-grinding and relief grinding of this used hob are done on a 4-axis CNC grinding machine having the B, C, X, Z motion axis in a factory. The actual relief work also gives this relief method a verification. And the setting error and machining error of the hob are compensated by a provided method during the relief grinding process.