Heat Treatment of Buick Automatic Transmission Parts on Low Pressure Vacuum Carburizing Furnace

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1. Part Description and Existing Problems

Due to the material selection and shape design of some parts of Buick 4T65E transmission, it is quite unfavorable for heat treatment deformation control. The most typical is the thin-walled parts such as the main reduction sun gear shaft. The parts are made of SAE4130 annealed welded seamless steel pipes. The wall thickness of the bearing block is only 2mm, and the bearing block adopts grinding + polishing process after heating, and the machining allowance is only on one side. 0. 02mm. After treatment according to the conventional controllable atmosphere carburizing and quenching process, the deformation of the parts is difficult to control. The outer diameter of the bearing gear is out of round and the deformation reaches more than 0.10mm, causing the bearing gear to be worn out, and the two-end external spline The M value after heating fluctuates greatly, which affects the assembly, and the qualified rate of finished products is only about 70%.

Figure 1: Appearance of the workpiece before and after heating

2. Main Research Content and Technical Key

1). Develop a new suitable low-pressure vacuum carburizing and high-pressure gas quenching heat treatment process.
The vacuum carburizing process is a high-speed carburizing process in which a carburizing atmosphere (pure propane gas) and a protective atmosphere (pure nitrogen) are pulsed at a high temperature. Due to the extremely low oxygen content in the furnace, the conventional process The main control parameter-carbon potential, cannot be measured. For the vacuum carburizing process, the most important process parameters are the carburizing temperature, vacuum degree, time beat of each pulse and gas flow rate. .

Because the cooling medium of gas quenching and oil quenching is different, there are big differences in the cooling method, the contact method of the medium and the workpiece, the circulation of the medium and the cooling method, so when the gas quenching process is used, the part loading Fixture design is a very important part. High-purity nitrogen is used for quenching, and the gas quenching pressure is 16bar.

3. Usage Effect

1). Quality

After adopting the new low-pressure vacuum carburizing process, the thermal pass rate of the main deceleration sun gear shaft has increased from 70% to more than 99.5%, which exceeds the general quality level of the United States and completely solves the quality of the part before assembly. problem.

2). Economic Benefits

Due to the increase in the qualification rate of the parts, and the omission of the post-cleaning and cleaning shot peening procedures in the heat treatment process, the manufacturing cost of the parts is greatly reduced.

3). Other Advantages

Low-pressure vacuum carburizing and high-pressure gas quenching technologies are currently the most advanced new heat treatment technologies in the world. Compared with the traditional atmosphere carburizing oil quenching technology, it has many advantages.

A. The vacuum carburizing speed is fast, and the high temperature carburizing process can be used, which can significantly shorten the process time (saving 20-40%), and reduce the heat preservation time of the parts at high temperatures, which is beneficial to reduce high temperature distortion.

B. The quenching intensity of high-pressure gas quenching is lower than that of oil quenching. Under the premise of ensuring the hardness of the parts, the cooling deformation of the parts is also much smaller.

C. High pressure gas quenching does not have three stages in the oil quenching process, only the convection conduction process, the workpiece is easy to obtain higher hardness.

D. There are no oxygen atoms in the low-pressure vacuum carburizing process, which can avoid the appearance of bad structures on the surface of the workpiece and improve the service performance of the workpiece.

E. The surface cleanliness of the processed workpiece is high, without the need for post-cleaning and cleaning shot blasting procedures, reducing production costs.

F. Good environmental protection: no fire cloth, no SO2, Co emission problems.

For parts with stricter deformation requirements, users can test and study the new process on the low-pressure vacuum carburizing furnace. When choosing the right tooling and the new low-pressure vacuum carburizing process, the technical problems of these parts can be solved on the low-pressure vacuum carburizing furnace. Since the deformation of the parts is relatively small, the processing procedures of the parts can be shortened as a whole, and the amount of grinding after heating can be reduced, so the production cost of the parts can be greatly reduced.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. It mainly produces true air quenching furnaces, double chamber vacuum oil quenching furnaces, vacuum annealing furnaces, vacuum tempering furnaces, and other vacuum furnaces.

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