Gear Classification
They can be divided into 4 categories.
① Cylindrical gears. Based on the structure of the parts, they can be divided into disc gears and shaft gears; based on the tooth profile, they can be divided into spur gears and helical gears. They are used for the transmission of power and motion along parallel shafts, such as speed changes in gearboxes and engine ignition timing.
② Bevel gears. Based on tooth profile, they can be divided into straight bevel gears and spiral bevel gears, used for transmitting power and motion across or intersecting shafts, such as differentials and reducers in the rear axle. Spiral bevel gears, based on differences in tooth profile machining principles and methods, have formed different international systems, commonly referred to as standards. The Chinese automotive industry primarily uses circular arc tapered gears (also known as the Glisson system) or cycloidal equal-height gears (also known as the Olecon system).
③ Gear rings. For example, sliding gear sleeves used for speed change connections and gear rings used for planetary gear transmissions are internal gear rings, while synchronizer gear rings used for speed change synchronization control are external gear rings.
④ Special purpose gears. Such as oil pump gears, speedometer worm gears, steering racks, etc.
Gear machining process
Automotive gears are generally produced in large-scale, specialized production. Cylindrical gears and bevel gears are widely represented, and different combinations of processes are required depending on their structure and precision. Due to the large investment in equipment, the selection of process methods usually takes full account of existing resources.
Controlling minute deformations and process stability during gear machining is relatively complex. After forging, most blanks undergo isothermal normalizing to achieve good machinability and a uniform microstructure that minimizes deformation. For low-speed cylindrical gears with less stringent precision requirements, pre-heat shaving is possible, followed by no further machining. The application of radial shaving expands the scope of shaving applications. Post-heat machining of cylindrical gears includes honing and grinding. Honing is low-cost but has weak tooth profile correction capabilities, while grinding offers high precision but is expensive. Employing tooth tip edge trimming along the tooth height direction and drum-shaped tooth profile trimming along the tooth length direction can significantly reduce gear meshing noise and improve transmission performance, making it a widely studied research area.
Straight bevel gears are mainly used in differential gears. Due to their low speed and relatively low precision requirements, precision forging of tooth profiles is an important development direction. In the machining calculations and machine tool adjustments of spiral bevel gears, the previously very complex and time-consuming manual operations have been replaced by modern specialized software and computer programs. The introduction of finite element analysis has made process parameter design more reliable and convenient. Post-heat finishing of spiral bevel gears includes gear grinding and lapping. Due to the high cost, low efficiency, and limitations of lapping, lapping is currently the most common method. Lapping has very weak geometric correction capabilities; therefore, the driven gears of spiral bevel gears often employ carburizing and pressure quenching processes. The development of gear materials and their heat treatment technologies is a challenging issue in gear machining related to deformation control.
Gear machining tools
Automotive gear processing machine tools can be divided into two main categories: cylindrical gear processing machine tools and bevel gear processing machine tools, which have different levels of precision and applicable ranges.
Gear machining tools can be categorized by process method into hobbing, shaping, shaving, honing, grinding, extrusion, and chamfering machines; bevel gear machining tools can be categorized by process method into milling, planing, broaching, grinding, lapping, chamfering, rolling inspection, and quenching machines. China's gear machining tools have basically formed a relatively complete series, and six-axis CNC grinding machines for spiral bevel gears with internationally advanced technology have been developed. However, the overall manufacturing level of gear machine tools still lags significantly behind Europe and the United States in terms of precision, lifespan, stability, and the application of CNC technology.
Gear machining tools
Gear machining involves specialized and complex tooling systems, requiring the selection and design of different tools based on the specific gear product and machining method. Examples include hobs, shaving cutters, and gear shapers for cylindrical gears; broaches for spur bevel gears; and various milling cutters for spiral bevel gears. Therefore, the sharpening of gear tools generally requires specialized machine tools, such as hob grinders, multi-functional shaving cutter grinders, and spiral bevel gear tool grinders.
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