Gear hobbing technology and equipment

Gear is one of the important basic parts in the fields of automobile, ship, aviation, engineering machinery, daily tools, national defense industry and so on. Gear manufacturing plays an important role in the equipment manufacturing industry. Its performance is not only closely related to the development of national industry, but also closely related to daily life. Gear machining machine is an important basic equipment in equipment manufacturing industry because of its complex structure and difficult manufacturing. According to the principle of machining, the main methods of gear machining are forming method and generating method. There is no gear meshing movement in the forming process, so the machining accuracy is very low; there is meshing movement between the gear cutter and the gear to be machined in the generating process, which envelops the tooth profile (tooth surface) of the gear to be machined, and the production efficiency and machining accuracy are relatively high. The common gear hobbing, gear shaping and shaving (fine machining) are widely used. In gear hobbing machine, straight and helical cylindrical gears can be cut, and splines, worm gears, sprockets, etc. can also be machined. The ownership of gear hobbing machine accounts for about 45 ~ 50% of the total number of gear machine tools.

Although by the end of 1970s, China has basically formed a complete gear manufacturing system, but the level of design and manufacturing is not high, and there is a large gap with the advanced manufacturing level of foreign countries. In recent years, China’s gear industry has surpassed Italy and leaped to the fourth place in the world, but problems such as prominent industrial structural contradictions, overcapacity, lack of independent innovation capacity and so on are prominent. With the transformation and upgrading of manufacturing industry and the gradual deepening of the integration of industrialization and informatization, the gear industry will inevitably present the development trend of design informatization, equipment intelligence, process automation and management modernization, and the gear manufacturing enterprises will gradually change from scale speed type to innovation benefit type. Based on the analysis of the current situation of hobbing technology, combined with the research on the difficulties and key technologies of hobbing, this paper looks forward to the future development trend of hobbing technology and equipment.

Basic principle of gear hobbing

Gear hobbing is based on the meshing principle of spiral gear. The essence of hob is a worm, and the workpiece is the gear meshing with it [2]. In gear hobbing, the hob and the workpiece are in a certain speed ratio, and the axial feed motion is made relative to the full tooth width of the workpiece. By adjusting the meshing speed ratio, a gear with the same module and different number of teeth can be machined with only one tool. The hobs with different tooth profiles can also be used to process various tooth profile gears such as turbine, sprocket, spline, cycloid gear, etc. In general, three kinds of motion are carried out in the hobbing machine at the same time: cutting motion, i.e. rotary motion of the hob; generating motion, i.e. tooth splitting motion; vertical feeding motion, i.e. cutting motion of the hob along the axis of the gear blank. Among them, the gear splitting transmission error directly affects the gear cutting accuracy.

In terms of gear processing principle and process characteristics, gear hobbing is more excellent than gear shaping, tooth extruding and tooth rolling, which enables gear hobbing to process cylindrical straight, helical gear, bevel gear, turbine, spline and other gear parts, and because of the structure type and production efficiency of the gear parts it processes, it has the advantages that other processing technologies are difficult to complete or incomparable, The market share of gear hobbing machine in gear processing equipment is much more than that of other gear processing machines.

Technology development status of gear hobbing machine at home and abroad

Gear hobbing machine can be divided into vertical and horizontal type according to its structure. Small gear hobbing machine and special gear hobbing machine for machining long shaft gear are mostly horizontal type. Small gear hobbing machine is used to process instrument gear; large high-precision gear hobbing machine generally adopts vertical and horizontal combined structure, and motion error detection feedback device is set on the hob spindle and workbench to automatically compensate the error to improve the accuracy. According to the degree of numerical control, it can be divided into ordinary gear hobbing machine, middle and low gear numerical control gear hobbing machine and high-grade numerical control gear hobbing machine. The machining accuracy of general gear hobbing machine is 7 ~ 6, and that of CNC gear hobbing machine is 4 ~ 3.

After more than 100 years of development, gear hobbing technology and equipment in developed countries are becoming more and more mature and complete. In Europe, represented by Liebherr, Germany, its typical LC series products meet the needs of gear processing in different industries and specifications, such as lc82, lc122, lc182, lc282, lc382 and other series of machine tools, which are suitable for the needs of gear processing equipment in light vehicle, minicar and car industries; LC502, LC802, LC1000 and other series of machine tools are suitable for the needs of gear processing equipment in heavy-duty vehicles, lifting transportation and elevator industry. In America, the GP / PE series products of Gleason pfauter hurth joint venture company in the United States, such as gp130, gp200, gp300, gp200s, gp300g, pe300 and pe500, are represented. Their main characteristics are dry cutting technology without coolant and application of all direct drive technology. In Asia, represented by GD series machine tools of Mitsubishi company in Japan, GD10CNC, GD20CNC and GD30CNC are applicable to the needs of gear processing equipment in light vehicle, mini vehicle and car industries, and GD50CNC, GD63CNC and GD100CNC are applicable to the needs of gear processing equipment in heavy vehicle, lifting transportation and elevator industries.

China’s hobbing mechanism manufacturing industry started late, and the overall technical level lags behind foreign countries for 10 – 20 years. Although the domestic CNC gear hobbing machine has been greatly developed and improved since the 1990s, most of them are based on the traditional gear hobbing machine for numerical control transformation. There is a big gap between the domestic CNC gear hobbing machine and foreign advanced products in terms of dynamic / static rigidity, overall transmission accuracy, reliability of numerical control system, etc., and the overall level is in the middle and low level. Domestic gear hobbing machine manufacturers mainly include Chongqing machine tool factory and Nanjing second machine tool factory. The former accounts for more than 60% of the market share of gear hobbing machine. Ys3120cnc6 and other CNC high-speed hobbing machines with six axes and four linkage represent the advanced level of domestic hobbing machines, with parameters such as spindle speed of hob (1200 R / min), radial fast moving speed (3000 mm / min), tangential fast moving speed (2000 mm / min), axial fast moving speed (3000 mm / min), As well as processing performance, configuration conditions, reliability and other aspects with foreign advanced level is still a big gap, equivalent to the level of the late 1990s. Although our country still lags behind in the field of CNC high-speed hobbing, the domestic extra large hobbing machine of more than ten meters has reached the world level.

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