There are many processing methods of gear, but the main methods are gear hobbing, gear shaping, shaving and gear grinding. Others include milling, planing, combing, extruding, honing and grinding. In recent years, with the development of machining technology, such as hard tooth surface technology and computer numerical control technology, all kinds of machining methods have taken on a new look.
（1） Gear hobbing
Gear hobbing was applied in 1897. It is the most widely used method of gear cutting. It can process involute gear, arc gear, cycloid gear, sprocket, ratchet, worm gear and enveloping worm. Generally, the hobbing accuracy can reach 4-7 levels. Surface roughness ra3.2 ~ 1.6um. The maximum machining diameter of domestic gear hobbing machine (y31800a) is 8m, and the maximum module is 40mm. At present, the cutting speed of high-speed steel hob is up to 100-200 M / min, and the hardness of machining tooth surface is up to 300-400 Hb. The cutting speed of carbide hob is up to 300m / min, and the hardness of hobbing tooth surface is up to HRC62. Hobbing is an efficient method of cutting teeth.
At present, the advanced technologies of gear hobbing are as follows:
1.Gear hobbing of multi head hob
Generally, the efficiency of double head hob can be increased by about 40%. But the deviation of each head of hob affects the accuracy of gear tooth direction.
2.CNC gear hobbing machine or general gear hobbing machine installation digital display device
In the 1980s, foreign countries have made CNC machine tools, that is, using computer numerical control and electronic system to coordinate various movements of machine tools, which can reduce adjustment time and improve processing accuracy.
3.Gear hobbing technology with hard tooth surface
Hard face hobbing extends the field of hobbing. This method is also called scraping tooth machining. Scraping can be used as a pre-processing procedure before grinding of large gear to remove quenching deformation until there is a reasonable grinding allowance, so as to reduce grinding time and cost. As a finishing process, scraping can achieve 6-level accuracy. If it is combined with worm honing, it can obtain good tooth surface quality and avoid grinding burns and cracks. Compared with simple grinding, the efficiency can be increased by 1-5 times and the cost can be reduced by more than half.
The tooth of hob with hard tooth surface is made of cemented carbide or cermet material and coated with titanium nitride. These new materials have been able to control the cutting edge collapse. At the same time, it also provides the possibility of dry cutting (without cutting oil). The advantages of dry cutting are that there is no need to prepare and treat the coolant, no need for oil mist treatment (discharged by air), no pollution of dry chips and no requirement for cleaning parts. If cutting oil is used in cutting, the tool life can be increased.
4.Large gear hobbing
Large gear hobbing, due to the large volume and heavy weight of the workpiece, is inconvenient to install and clamp. So large teeth
The development trend of gear hobbing equipment is comprehensive machining.
（2） Pinion and comb
Gear shaping is a widely used method of cutting teeth, especially suitable for machining internal gear and multi gear. After using special tools and accessories, it can also process silent sprocket, ratchet, internal and external splines, tooth belt pulley, sector gear, incomplete tooth gear, special tooth combination, rack, end gear and taper gear, etc. CNC gear shaper can process elliptical gear, non-circular gear and special shape gear.
Comb is to use a rack knife to cut cylindrical gears. It is characterized by high machining accuracy, up to din5 level. Because of its simple structure, convenient manufacturing, high precision and many times of grinding, it is convenient to use carbide blade and CBN blade to process hardened gear.
Shaving is an efficient method of gear finishing, which was first used in the United States in 1926. Compared with gear grinding, shaving has the advantages of high efficiency, low cost and no burn and crack on the tooth surface. Therefore, it is widely used in the gear processing of automobiles, tractors and machine tools. The diagonal shaving method and radial shaving method can also be used for the finishing of gears with shoulder.
Honing is a technology of gear surface finishing, which can effectively improve the quality of gear surface, and reduce the roughness from ra2.5 to Ra0.63. Some honing methods can also improve the accuracy of gears to a certain extent. Because of high efficiency, low cost and no burn on the tooth surface, they are widely used in the processing of soft and hard gears with accuracy below grade 7.
Honing methods include gear honing, external honing, worm honing and internal honing.
Gear honing with external meshing has been widely used, which can effectively reduce the surface roughness of gear, but the ability to improve the accuracy of gear is very small.
（5） Grinding teeth
Gear grinding is the most effective and reliable way to obtain high-precision gears. In developed countries, hard tooth surface gear is used, and gear grinding becomes the main processing method of high-precision gear. At present, the grinding accuracy of disc wheel and large plane wheel can reach din2, but the efficiency is very low. The grinding accuracy of worm wheel is up to din3 ~ 4, and the efficiency is high. It is suitable for medium and small module gear grinding, but the modification of grinding wheel is complex.
The main problems of gear grinding are low efficiency and high cost, especially large size gear. Therefore, improving the efficiency of gear grinding and reducing the cost become the main research direction at present. In this respect, new technologies emerging in recent years include:
The efficiency of grinding teeth can be improved by improving grinding methods, such as reducing grinding times, compressing developing length and shortening grinding stroke.
CBN grinding wheel with cubic boron nitride (CBN) wheel has the advantages of high hardness, good wear resistance, long service life, good accuracy retention, good cutting performance and large thermal diffusion coefficient. Therefore, the grinding efficiency of CBN wheel is 5-10 times higher than that of single crystal steel jade wheel. The surface is not easy to burn and crack, the surface is in the state of compressive stress, and the fatigue strength is high.
（6） Spiral bevel gear machining
Spiral bevel gear and hypoid gear are widely used in the driving of automobiles, tractors, engineering machinery, petroleum geological drilling machines, tanks, helicopters and machine tools. The design and manufacturing quality of this kind of gear mainly depends on two factors. One is the accuracy of processing equipment and its fixture. The other is the accuracy of tooth profile guaranteed by the adjustment parameters of machine tool and cutter determined by complex conjugate calculation, which is the key to improve the quality of this kind of gear.
In the processing of spiral bevel gear. American Gleason company occupies a very important position. In the past ten years, Gleason company has created efficient hypoid gear grinding machine and CNC multi-functional gear milling machine in terms of processing equipment. In terms of quality inspection, analysis and control technology, a computer-aided detection system with three-dimensional measurement function is developed, which can quickly and accurately measure the tooth profile error, and obtain the best adjustment parameters of tooth cutting correction. In the aspect of design and manufacturing technology, a set of parameters calculation including geometry, strength design, tooth cutting (or grinding) adjustment is developed, which takes into account the tooth edge and tooth contact analysis and finite
The computer software system of element stress contact analysis.
China has been able to manufacture more advanced spiral bevel gear cutting machine tools, such as y2250a, y2080i, etc. In the aspect of software development, the design and manufacturing application technology software system of spiral bevel gear and hypoid gear developed by Chongqing University and Beijing Agricultural Engineering University can complete the design of gear geometric parameters, the calculation of adjustment parameters of machine tool from cutter head during machining, the analysis of gear tooth contact under light load (TCA) and the calculation of adjustment parameters of precision grinding.
（7） Grind teeth
In order to improve the tooth surface roughness, grinding can be used. Sometimes, due to the assembly error and load deformation and other factors, the gear with high original accuracy will be damaged under full load, which can also be improved by gear grinding. When lapping teeth, it is necessary to use gear special abrasive to avoid damage to the tooth surface, or cleaning after lapping, which will cause damage to the tooth surface after gear operation, as well as the abrasive entering into the bearing and damaging the bearing.
（8） Gear inspection
Gear detection technology plays an important role in gear manufacturing. Without advanced detection technology and instruments, it is impossible to produce gears with excellent performance. Modern gear detection technology is developing in the direction of non-contact, precision, multi-function, high-speed, automation, intelligence, integration (computer control) and economy. In the field of detection, solve the problem of detection of large module and small module gear.
At present, there are two kinds of gear detection methods: single error measurement and comprehensive error measurement. In 1968, Chengdu Tool Research Institute of China initiated the theory and method of gear overall error measurement. The internal relationship between the transmission characteristics and various errors of gears is revealed, which provides the basis for controlling the transmission quality and improving the design and manufacture of gears. After 1970, Chengdu Tool Research Institute of China, Harbin and Beijing measuring tool and cutting tool factory respectively developed cross-section overall error measuring instrument by using this method. Thus, the gear measurement technology in our country is developed to a new stage of dynamic comprehensive measurement.