In the machining of gears and racks, the general process method for gears with soft tooth surfaces and medium hard tooth surfaces (300-400HBS) is gear hobbing or slotting after quenching and tempering. For large modulus gears, coarse hobbing, quenching and tempering, and fine hobbing are used. For gears in automobiles, tractors, machine tools, etc., large quantities are required with high precision. After hobbing or slotting, they are shaved or honed. The process for induction hardened gears (42-52HRC) is hobbing or slotting, shaving, induction hardening, and then shaving or honing. For hard tooth surface gears, gear hobbing or slotting is generally carried out first, and sometimes gear shaving is also performed. After heat treatment, the reference surface is refined. When the tooth deformation is large, grinding is carried out. Gears with small tooth deformation and precision requirements of level 7 and below can be honed or ground after heat treatment. High precision and low load are required for gears with hard tooth surfaces, and the ion nitriding process after precision gear hobbing can be used. The performance of well-designed gears mainly depends on the level of gear manufacturing, in addition to material factors. At present, the gear has achieved normal meshing under working conditions. For high-speed gears with a circumferential speed exceeding 100m/s, due to thermal effects during operation, tooth surface thermal deformation should be modified. For low-speed heavy-duty gears, the use of hard tooth surface gears results in poor running in performance and an increase in tooth surface load coefficient, leading to certain elastic deformation of the entire gear device system and uneven distribution of load along the tooth direction. Therefore, tooth profile modification is necessary. In summary, tooth surface modification technology has become an important task in gear manufacturing both domestically and internationally, especially in reducing volume and improving load-bearing capacity.

The main processes for gear and rack machining include gear hobbing, gear shaping, gear shaving, and gear grinding. Other types include milling, planing, combing, extrusion, honing, and grinding. In recent years, the development of machining technology, such as hard tooth surface technology and computer numerical control technology, has brought about a new look in various machining methods.

1. Hobbing

Gear hobbing was applied in 1897 and is currently the most widely used gear cutting method. It can process involute gears, circular arc gears, cycloidal gears, sprockets, ratchets, worm gears, and enveloping worm gears. The gear hobbing accuracy can generally reach levels 4-7. Surface roughness Ra3.2-1.6um. The domestically produced gear hobbing machine (Y31800A) can process a maximum diameter of 8m and a maximum module of 40mm. At present, the cutting speed of high-speed steel hobs can reach 100-200 m/min, and the maximum hardness of the machined tooth surface can reach 300-400HB. The cutting speed of hard alloy hobs can reach

2. Insert and comb teeth

Gear shaping is a widely used cutting method, particularly suitable for machining internal gears and multiple gears. After using special cutting tools and accessories, silent sprockets, ratchets, internal and external splines, toothed pulleys, sector gears, incomplete tooth gears, special tooth combinations, racks, end face gears, and taper gears can also be machined. CNC gear shaping machine can process elliptical gears, non circular gears, and special shaped gears. Comb teeth are used to insert cylindrical gears with a rack and pinion cutter. The characteristic is high machining accuracy, up to DINS level. Due to the simple structure of the cutting tool, convenient manufacturing and grinding, high accuracy, and multiple grinding times, it is easy to use hard alloy blades and cubic boron nitride (CBN) blades to process hardened gears.

3. Shaving teeth

Shaving is an efficient gear precision machining method that was first applied in the United States in 1926. Compared with gear grinding, gear shaving has advantages such as high efficiency, low cost, and no burns or cracks on the tooth surface. So in mass-produced cars, tractors, and machine tools, gears are added

4. Honing teeth

Honing is a surface finishing technology for gear teeth, which can effectively improve the quality of the tooth surface and reduce the roughness from Ra2.5 to below Ra0.63. Some gear honing methods can also improve gear accuracy to a certain extent. Due to high efficiency, low cost, and no burn on the tooth surface, they are widely used in the machining of soft and hard gear surfaces with precision below level 7. The honing methods include gear honing with external meshing, worm type honing, and internal meshing honing. Gear shaped honing wheel external meshing honing has been widely used, which can effectively reduce tooth surface roughness, but has little ability to improve gear accuracy.

5. Grinding teeth

Grinding teeth is the most effective and reliable method to obtain high-precision gears. Developed countries use hard tooth surface gears, and grinding has become the main processing method for high-precision gears. At present, the grinding accuracy of disc shaped grinding wheels and large flat grinding wheels can reach DIN2 level, but the efficiency is very low. The precision of grinding teeth with worm wheel reaches DIN3-4 level, with high efficiency, suitable for grinding teeth of medium and small modulus gears, but the grinding wheel correction is relatively complex. The main problems with gear grinding are low efficiency and high cost, especially for large-sized gears. So improving the efficiency of gear grinding and reducing costs has become the main research direction at present. In this regard, new technologies that have emerged in recent years include improving grinding methods such as reducing grinding times and compressing the expansion