Analysis Of Heat Treatment Deformation Control Method For Transmission Gear

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The gearbox is the main component of the car and an important force unit of the car. Heavy-duty vehicles are subject to frequent impacts due to heavy loads and poor road conditions. In view of this, heavy-duty vehicle transmission gears should have mechanical properties such as high strength, high wear resistance, high fatigue strength, and high impact toughness. It is necessary to strictly control the heat treatment process.

1. Reasons for gear deformation after heat treatment

The main component of the gear is steel. After it is heat treated, as the temperature increases, the toughness of the steel will continue to decrease. If the local stress on the gear can no longer be affected by the heat, it will cause the gear to deform, because the residual stress will only Partially manifested in the gear, so the gear will produce irregular deformation. When the gear is undergoing heat treatment, because the heating speed is too fast, the surface of the gear will heat up too quickly, and the internal temperature of the gear will increase relatively slowly. If there is a difference between the surface and the internal temperature, it will cause the gear Irregular deformation occurs, which in turn leads to a certain particularity in the shape of the gear.

2. Factors affecting heat treatment deformation

The deformation of the gear after heat treatment involves factors on various levels, such as the design of the gear, the material used, the method and process of preheating, machining technology and cutting tools, heat treatment technology and equipment, and the entire manufacturing process. Qualified materials, precise forging, standardized pre-heat treatment, and efficient cold and hot processing can reduce and stabilize heat treatment deformation. In view of this, it is necessary to strictly control the deformation of the gear after heat treatment.

2.1 The influence of gear design shape on heat treatment deformation

The design structure of the gear will greatly affect the deformation of the heat treatment. For example, the design structure of the gear is asymmetrical and the structure uniformity is poor. Actually, the problem of uneven stress often occurs during the quenching process, which causes irregular deformations. problem. The degree of influence of heat treatment deformation is determined by design, material, heat treatment and so on. In view of this, in the process of design, we must ensure that the wall thickness is not too thin, and should be uniform and symmetrical, and the ratio of the cross-sectional dimensions should not be too wide.

2.2 The influence of forging on heat treatment deformation

Forging can improve the uniformity of the tooth blank structure, and the band structure can effectively prevent heat treatment deformation. However, the forging problem will make the heat treatment deformation more severe, and the forging will cause the metal streamline to appear asymmetry. The forging temperature is too high, and the unevenness problem will occur after cooling after forging, and ultimately lead to a big difference in heat treatment deformation. After the tooth blank is forged, the streamline shape of the metal fiber usually has a symmetrical distribution along the outer profile of the tooth blank and a longitudinal section. The upper streamline should present a closed shape. The deformation of the streamlined blank after heat treatment is relatively regular, and the control is less difficult.

2.3 The influence of machining tool and cutting amount on heat treatment deformation

The residual stress of the workpiece caused by machining, and after preheating the workpiece, the plasticity of the workpiece is very good. If the cutting feed is too large or the tool wear is severe, dislocation deformation will occur in the actual machining process. And the formation of internal residual stress, and is released in the process of heat treatment, resulting in severe deformation of the workpiece.

2.4 The influence of heat treatment process on heat treatment deformation

Nowadays, the most commonly used heat treatment method for gearbox gears in my country is the carburizing and quenching method, and the carburizing and quenching technology has the following advantages: relatively mature technology, widely used, and low cost, which is the key research direction of today’s heat treatment experts.

3. Measures to control heat treatment deformation of gearbox gears

First, when designing a gear design, parts with uniform and symmetrical wall thickness should be used. If the part has areas with relatively thin wall thickness, during heat treatment, the cooling rate of the thin-walled area is relatively high, and there is a greater chance of curling. In this way, it is necessary to design two separate parts, and then the thin-walled parts can effectively control the heat treatment deformation, and can effectively simplify the processing process.

Second, because most companies today are based on the reality of their own products. Need to clarify the actual scope of hardenability, so that the heat treatment deformation can be effectively controlled. Of course, the grain size in the raw material is also very critical. All metal materials are polycrystals composed of crystal grains. Since the characteristics of all crystal grains are different, the combination of these different crystal grains can offset their forces. In this way, the characteristics of anisotropy can be generated between the metal materials. In view of this, in order to be able to propose the anisotropy of the raw materials, it is necessary to choose a constituent material with smaller crystal grains, and the number of crystal grains should be relatively large, so that the heat treatment deformation will show significant uniformity.

Third, nowadays, some companies have gradually chosen isothermal annealing technology to complete the pre-heat treatment process, which has significantly improved the effectiveness of the pre-heat treatment. For some alloy steels with relatively stable austenite, the use of isothermal annealing technology can greatly shorten the annealing cycle and effectively stabilize the heat treatment deformation.

Fourth, in the actual processing process, if residual stress is generated, although it cannot be completely avoided, effective processing tools and auxiliary equipment can be used to effectively avoid the generation of residual stress.

Fifth, the temperature of carburizing treatment is an important influencing factor for the smooth implementation of carburizing and quenching technology. The decisive factor of the carburizing rate of parts is the temperature of carburizing treatment, and there is a positive correlation between the carburizing temperature and crystal expansion. Therefore, heat treatment workers must strictly control and coordinate production, so as to meet the corresponding production needs.

4. Summary

In short, in the process of heat treatment, the relevant operators must effectively master the relevant processing technology of the gear, and understand the various factors that affect the heat treatment deformation, and then effectively control the heat treatment work, strictly control the deformation of the gear, and make the gear The quality is guaranteed, the comprehensive competitiveness of the enterprise in the market is improved, and the sustainable development of the enterprise is promoted.

Editor: Frank Lee

Copyright: SIMUWU Vacuum Furnace