1. Introduction
Spiral bevel gear play a crucial role in many mechanical transmission systems, especially in the aviation industry. They are widely used in helicopter main reduction systems to transmit power. In order to meet the requirements of aviation products, such as high reliability, high precision, high strength, good wear resistance and light weight, spiral bevel gear need to have excellent performance. However, due to their complex structures and diverse forms, the processing of spiral bevel gear is very difficult. In addition, after heat treatment processes such as carburizing, quenching and tempering, the deformation of spiral bevel gear is often large, which seriously affects the quality and performance of the gears. Therefore, it is of great significance to study the heat treatment deformation compensation technology of spiral bevel gear.
1.1 Structure and Characteristics of Spiral Bevel Gear
Spiral bevel gear has complex three-dimensional structure. They consist of a gear body, teeth, and various geometric features. The teeth of spiral bevel gear is helical, which allows for smoother and more efficient power transmission compared to straight bevel gear. The geometry of the gears is designed to ensure proper meshing and load distribution during operation.
1.2 Importance of Heat Treatment in Gear Manufacturing
Heat treatment is an essential process in gear manufacturing. It can improve the mechanical properties of gears, such as hardness, strength, and wear resistance. Through heat treatment processes like carburizing, a carbon-rich layer is formed on the surface of spiral bevel gear, increasing its surface hardness while maintaining a certain degree of toughness in the core. Quenching and tempering are then used to further adjust the microstructure and mechanical properties of spiral bevel gear.
1.3 Problems Caused by Heat Treatment Deformation
Heat treatment deformation can lead to a series of problems. It may cause dimensional inaccuracies, resulting in improper meshing between gears. This can lead to increased vibration, noise, and reduced transmission efficiency. In severe cases, the deformed gears may not meet the design requirements and have to be scrapped, increasing production costs and reducing productivity.
2. Heat Treatment Processes and Their Effects on Spiral Bevel Gear
2.1 Carburizing Process
Carburizing is a commonly used heat treatment process for spiral bevel gear. It involves introducing carbon into the surface layer of spiral bevel gear at an elevated temperature in a carbon-rich environment. The carburizing process can significantly increase the surface hardness of spiral bevel gear, improving its wear resistance. However, during the carburizing process, thermal stresses are generated due to the temperature gradient between the surface and the core of spiral bevel gear. These thermal stresses can cause deformation of spiral bevel gear.
| Carburizing Parameters | Effects on Gear |
|---|---|
| Temperature | Higher temperature can accelerate carbon diffusion but may also increase deformation risk. |
| Time | Longer carburizing time generally leads to a thicker carburized layer but may also cause more significant deformation. |
| Carbon Potential | Appropriate carbon potential is crucial for achieving the desired surface hardness and microstructure. |
2.2 Quenching Process
Quenching is a rapid cooling process after carburizing. It is used to fix the microstructure obtained during carburizing and further increase the hardness of spiral bevel gear. The quenching process can cause significant thermal and transformation stresses in spiral bevel gear, which are the main causes of deformation. Different quenching media and methods have different effects on the deformation of spiral bevel gear.
| Quenching Parameters | Effects on Gear |
|---|---|
| Quenching Medium | Water quenching usually results in higher cooling rates and greater deformation compared to oil quenching. |
| Quenching Method | Pressurized quenching can control the deformation to some extent by applying external pressure during quenching. |
| Cooling Rate | Faster cooling rates generally lead to larger deformation. |
2.3 Tempering Process
Tempering is a heat treatment process carried out after quenching. It is used to relieve the internal stresses generated during quenching and improve the toughness of spiral bevel gear. Although tempering can reduce some of the stresses, it may not completely eliminate the deformation caused by the previous heat treatment processes.
3. Measurement and Analysis of Heat Treatment Deformation
3.1 Measurement Methods
Accurate measurement of heat treatment deformation is essential for understanding the deformation behavior of spiral bevel gear and formulating effective compensation strategies. The following are some commonly used measurement methods:
3.1.1 Gear Measuring Machine
The spiral bevel gear measuring machine can measure various parameters related tospiral bevel gear teeth, such as tooth profile, tooth thickness, and adjacent and cumulative errors. By comparing the measured data before and after heat treatment, the deformation of spiral bevel gear teeth can be analyzed.
3.1.2 Coordinate Measuring Machine
The coordinate measuring machine is used to measure the geometric dimensions and shapes of spiral bevel gear body. It can measure parameters such as the diameter, height, and position of spiral bevel gear, providing a comprehensive understanding of the deformation of the entire gear.
3.2 Analysis of Deformation Data
After obtaining the measurement data, it is necessary to analyze the deformation data to understand the deformation patterns and trends. The following are some common analysis methods:
3.2.1 Statistical Analysis
Statistical analysis methods can be used to calculate the mean, standard deviation, and other statistical parameters of the deformation data. These statistical parameters can help to evaluate the degree of deformation and the consistency of the deformation among different gears.
3.2.2 Trend Analysis
Trend analysis is used to observe the changes in deformation data over time or with different heat treatment parameters. By analyzing the trend of deformation, it is possible to predict the deformation behavior of gears under different conditions and optimize the heat treatment process accordingly.
4. Compensation Technologies for Heat Treatment Deformation
4.1 Machining Compensation
Machining compensation is a commonly used method to correct the deformation of spiral bevel gear. It involves adjusting the machining parameters or processes based on the measured deformation data to achieve the desired gear dimensions and accuracy.
4.1.1 Grinding Compensation
Grinding is an important machining process for spiral bevel gear. By adjusting the grinding parameters such as grinding wheel speed, feed rate, and depth of cut, the deformation of spiral bevel gear can be compensated. For example, if spiral bevel gear has a larger diameter after heat treatment, a smaller depth of cut can be used during grinding to reduce the diameter to the desired value.
| Grinding Parameters | Compensation Effects |
|---|---|
| Grinding Wheel Speed | Higher speed may result in better surface finish but may also affect the compensation accuracy. |
| Feed Rate | Appropriate feed rate is crucial for achieving the desired compensation effect. |
| Depth of Cut | Adjusting the depth of cut can directly control the amount of material removed and thus the compensation of spiral bevel gear diameter. |
4.1.2 Milling Compensation
Milling is another machining process that can be used for compensation. By adjusting the milling cutter path and parameters, the deformation of the gear can be corrected. For example, if the gear has a deformed tooth profile, the milling cutter path can be adjusted to reshape the tooth profile.
4.2 Heat Treatment Parameter Adjustment
Adjusting the heat treatment parameters is another effective way to control the deformation of spiral bevel gear. By optimizing the carburizing temperature, time, carbon potential, quenching medium, quenching method, and tempering parameters, the deformation of spiral bevel gear can be reduced.
| Heat Treatment Parameters | Adjustment Effects |
|---|---|
| Carburizing Temperature | Lowering the temperature may reduce deformation but may also affect the surface hardness. |
| Carburizing Time | Reducing the time may decrease deformation but may also result in a thinner carburized layer. |
| Carbon Potential | Adjusting the carbon potential can affect the microstructure and mechanical properties of spiral bevel gear. |
| Quenching Medium | Changing the quenching medium can affect the cooling rate and deformation. |
| Quenching Method | Selecting a different quenching method can control the deformation more effectively. |
| Tempering Parameters | Optimizing the tempering parameters can relieve stresses and reduce deformation. |
4.3 Fixture Design and Optimization
The design and optimization of fixtures play an important role in reducing the deformation of spiral bevel gear during heat treatment. A well-designed fixture can provide uniform support and restraint to the gear, minimizing the effects of thermal stresses and preventing deformation.
| Fixture Design Elements | Effects on Gear Deformation |
|---|---|
| Support Structure | A stable support structure can ensure spiral bevel gear is held in a proper position during heat treatment. |
| Restraint Mechanism | Appropriate restraint mechanisms can prevent spiral bevel gear from moving or deforming during heat treatment. |
| Material Selection | The choice of fixture material can affect its thermal conductivity and mechanical properties, which in turn affect the deformation of spiral bevel gear. |
5. Case Studies
5.1 Case Study 1: Input Spiral Bevel Gear
The input spiral bevel gear is a key component in the main reducer. It has a complex structure and requires carburizing at multiple locations with different depths.
5.1.1 Cold Process Difficulties
The input gear is designed as a hollow thin-walled part with a minimum thickness of 4mm at the auxiliary plate. The different carburizing requirements at various locations increase the difficulty of controlling the carburizing deformation.
5.1.2 Hot Process Difficulties
The carburizing temperature, the influence of gravity, and the quenching process all pose challenges to the heat treatment of the input gear. High carburizing temperatures can cause large deformations, and the influence of gravity can also affect the deformation state. The quenching process involves complex factors such as quenching mode, temperature, medium, and stirring.
5.1.3 Deformation Compensation Measures
To compensate for the deformation, the following measures were taken:
- After heat treatment, the center hole was reamed to eliminate its deformation, and then the bearing installation shaft diameters were rough-ground as a reference.
- The installation distance end face was processed to a certain extent using a common lathe to avoid grinding burns.
- The spiral bevel gear measuring machine was used to evaluate the shaft diameter and end face reference, and the compensation machining allowance for the installation distance end face was calculated based on the measured data.
5.2 Case Study 2: Double Spiral Bevel Gear
The double spiral bevel gear is a thin-walled part with a complex structure and different carburizing layer depths for the large and small teeth.
5.2.1 Cold Process Difficulties
The double gear has a complex structure with two rows of spiral bevel gear, and the carburizing layer depths at different locations require secondary carburizing, increasing the difficulty of deformation control. The outer dimension is large, and the flatness requirement of the intermediate auxiliary plate is strict.
5.2.1 Hot Process Difficulties
The carburizing heat treatment process causes complex deformations due to the complex structure of the double gear. The deformation can lead to uneven grinding allowances during tooth grinding, which can affect the surface strength and increase the risk of tooth surface failure.
5.2.3 Deformation Compensation Measures
The following deformation compensation measures were implemented:
- Before heat treatment, the root cone and tooth thickness of the large tooth were adjusted to compensate for the post-heat treatment expansion. The tooth surface was also adjusted to correct the deformation pattern.
- After heat treatment, the root cone and tooth thickness of the two rows of teeth were measured, and the installation distance end face was compensated based on the calculated results.
6. Conclusion
The heat treatment deformation of spiral bevel gear is a complex problem that affects the quality and performance of gears. Through accurate measurement, analysis, and the application of appropriate compensation technologies, the deformation of spiral bevel gear can be effectively controlled. Machining compensation, heat treatment parameter adjustment, and fixture design optimization are all important methods for reducing deformation. Case studies have demonstrated the effectiveness of these methods in practical applications. However, further research is still needed to continuously improve the heat treatment deformation compensation technology of spiral bevel gear to meet the increasingly high requirements of the aviation industry and other fields.