In the process of gear heat treatment, due to various environmental factors and other external factors, gear deformation occurs. According to the statistical analysis of these factors, it can be determined that the factors affecting the heat treatment of workpiece are as follows:
1. Gear raw materials
The experimental results show that the uniformity of metal material and composition is one of the main factors affecting the heat treatment quality of gears. In the melting process, especially in the symmetrical solidification process, the uniformity of metal material and composition has a great influence on the heat treatment quality. From the influence factors, there are mainly two aspects: on the one hand, using raw materials with high hardness, on the other hand, using materials with high shrinkage and good toughness can effectively avoid gear deformation due to the increase of inner diameter during heat treatment; The gear can be softened by using high hardness and heat treated raw materials. Combined with the production situation of material hardness of different steel plants at home and abroad,
2. Gear design
In the process of heat treatment, the geometric shape of the gear determines the design of the gear, and the internal stress distribution of the gear with different shapes is different. Therefore, the design and manufacture of the gear is also an important factor affecting its deformation. Therefore, when designing gears, designers should first evaluate the deformation that may occur in the process of heat treatment, and then design according to the results of comprehensive evaluation. Practice has proved that in the process ofand processing, in order to effectively reduce stress and deformation, stress relief measures must be taken in the design stage. However, the cost of this method is high, so it is necessary to further study the measures to control the deformation in the production process.
3. Quenching treatment
During quenching and cooling, the gear may deform. In this case, the uneven heating in the gear is the main reason for the gear deformation, and the heating speed is not well adjusted, which is easy to increase the stress. In addition, the inhomogeneity of heating temperature and heating medium is also one of the causes of heat treatment deformation. With accurate temperature control, the internal and external temperature of gear is higher than that of heat treatment. When hardening, the heating and cooling are uneven, the cooling speed is too fast, and the temperature difference between the inside and outside of the gear increases, which is easy to cause tooth deformation.
Loading mode: in this case, because the gear is in a high temperature state for a long time in the process of heat treatment, slow deformation is very easy to occur. To solve this problem, we must adopt the cutting method or machining method which can ensure the quality of gear processing.
Quenching temperature: technical personnel should also control the heat treatment temperature. When the temperature is too high, the toughness of the gear will be greatly reduced, thus increasing the possibility of brittle fracture. The experimental results show that: for gear transmission components, the alternating temperature can make the gear deformation, but the alternating temperature must meet the basic requirements of gear transmission and heat treatment, and should not be too large.
Quenching medium: in order to avoid tooth profile deformation, mild quenching medium should be selected during gear heat treatment, especially for pinion and thin gear, so as to effectively control gear fluctuation.
4. Gear machining
The processing of gear is also the main factor affecting gear deformation. In the process of cutting, due to the serious damage of the cutting tool, it is easy to have problems such as improper gear alignment and gear workpiece deformation. In addition, when there is stress in the forging metal, the machined tooth surface will also deform, and the machining stress is generated in the process of machining, which directly leads to the gear deformation.
Through high temperature forging, the internal material uniformity of gear is improved, which is also an important part of improving the structural uniformity of gear. However, the non-uniform melting of metal in forging process will lead to the non-uniformity of alloy material, which will affect the heat treatment performance of the alloy. If the melting point is too high and can not be controlled properly, the phenomenon of non-uniformity will still appear in the cooling process. The streamline of the metal fiber on the forging should be evenly distributed according to the external contour of the workpiece, and the strip of the longitudinal part should be closed. Using this line to form a fixed deformation law, the conventional machining is simplified. In addition, if the melting point is too high, the raw material particles will grow up and the billet will be damaged in serious cases.
6. Preheating treatment
The essence of heat treatment is to get a better structure, that is, to refine the grain and eliminate the residual stress. But in the actual production, after the end of the process, through the cooling treatment, the heat treatment process is controlled by the microstructure processing technology, and the actual transformation is carried out from the raw material austenite grain, the microstructure is transformed into ferrite and pearlite, and the ideal shape and hardness are obtained.
7. Machining tools and cutting amount
In the process of machining, the workpiece produces processing stress. After preheating, the shape of the workpiece is significantly improved. In the actual processing, when the cutting amount exceeds the relevant requirements or standards, or the tool is seriously damaged, there will be deviation. At the same time, in the process of heat treatment, the internal residual stress will be released due to heating, resulting in large deformation of the workpiece. Although the residual stress can not be effectively eliminated, the purpose of reducing the residual stress and controlling the influencing factors of deformation can be achieved by selecting the appropriate processing technology or replacing the damaged tools in time.
8. Heat treatment process
Carburizing and quenching technology is widely used in the heat treatment of gears. Carburizing and quenching technology has become the key research direction in the current heat treatment research with its advantages of mature technology, low cost and universal application. The higher the carburizing temperature is, the lower the yield strength will be. Therefore, it is necessary to control the carburizing temperature from the technical point of view and reasonably increase the carburizing temperature from the perspective of production cost. This requires reasonable coordination of relevant technical personnel to ensure practicality and productivity.