With the global shortage of resources and the aggravation of environmental pollution, people pay more and more attention to the efficient, energy-saving and low pollution gear green manufacturing method. In order to improve the manufacturing efficiency and performance and save resources, researchers have studied the metal flow direction, residual stress and gear strength of forward extrusion and transverse extrusion rolling gears, the forming roll ofwith small number of teeth and large helix angle, and the optimization of grinding amount based on high productivity and low burn. Tachikawa et al. Studied the mechanism of forming deviation of forming roll of with small number of teeth and large helix angle, and found that the extrusion rate of die can affect the tooth profile deviation. Schoo et al. Analyzed the process optimization and control of gear profile grinding by Barkhausen noise method. Heuer et al. Improve the productivity of tooth surface grinding by optimizing the distribution of cutting amount. Hohn et al. Studied the influence of grinding burn on the bearing capacity of heat-treated gear tooth surface.
In order to reduce or avoid environmental pollution, researchers have studied the dry cutting or least cutting fluid hobbing, the dry cutting effect of TiSiN coating hob, the influence of the hardness ofon the dry hobbing, the processing of gear without mineral oil coolant, special cutting oil, etc. Shutou et al. Compared the cutting performance of the least cutting fluid gear with that of the dry gear. Kurokawa et al. Studied the wear resistance of high-speed steel hobs coated with titanium group ceramic (such as tin, TiCN, TiSiN and TiAlN) and the effect of coating oxidation on the wear of crater. Dwuletzki et al. Put forward a new cooling liquid without mineral oil, which can cool and lubricate gears by using a new viscous water-based lubricant. Baly et al. Pointed out that sulfur content, activity and wettability of cutting oil have an important influence on the performance of cutting oil through the experimental study of special cutting oil.
With the development of research on gear materials, gear materials are no longer limited to ordinary forged steel, sintered metal materials, different metal and plastic materials, and polymer materials are widely used in gear transmission according to different purposes of gear transmission. Gear researchers have done a lot of research on the performance of gears made of sintered metal materials, plastic materials and polymer materials. Fiodin and Dizdar compared the performance of sintered and forged gears, and pointed out that sintered gears have the advantages of less consumables, less material removal and low cost compared with forged gears, but the performance of sintered gears is not as good as forged gears. The key to improve the performance of sintered gear is to make the hardened layer of gear surface deeper and obtain high density gear core. Letzelter et al. Established the load distribution model between teeth of plastic gear, which can obtain the transmission error, meshing stiffness, meshing force, load distribution between teeth and root stress under different temperature, humidity and rotation speed. Predki et al. Studied the load-carrying capacity of steel / plastic matched cross helical gears, and proposed a new prediction method of load-carrying capacity. Wood et al. Compared the transmission performance of steel, steel plastic and plastic gear pair, found that the torque and transmission error of steel plastic gear pair fluctuated obviously, while plastic gear pair can improve this situation. For the same plastic, plastic gear pair is better than steel plastic gear pair. Small et al. Studied the performance range of PEEK polymer (a kind of high-performance thermoplastic polymer) gear, pointed out that using this kind of gear instead of metal gear can improve transmission efficiency, reduce noise and greatly reduce inertia mass. Nakamura et al. Used unbalanced magnetron sputtering method to form a diamond-like carbon coating on the surface of polyacetal gear (a plastic gear widely used in Japan) in the mixed gas environment of argon and methane. Through the experimental study, it was found that the durability of the polyacetal gear with diamond-like carbon coating on the surface was greatly improved.