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Range Gear Synchronous Gear Seat WG2210100007

The gear seat of the range gear synchronizer is an important component for switching between high and low gears in the gearbox. It is made of 20CrMnTiH material. Due to the outer diameter of this part being Φ200mm and the total height being only 30.5mm, the heat treatment process of this part is not suitable for the deformation-intensive carburizing direct quenching method. Our company adopts the following heat treatment process: carburizing and air cooling → secondary heating → pressure quenching → cleaning and tempering. The main size parameters that need to be controlled for this part are the pitch diameter value of the outer gear and the M value of the internal spline. After pressure quenching, these two size parameters can generally be effectively controlled most of the time. However, sometimes there will be batch occurrences of unexplained large deformation and out-of-tolerance situations, resulting in product scrapping. We have conducted an analysis and research on this issue, attempting to identify the main cause of the excessive deformation and take measures to improve it, ensuring that the deformation is controlled within the tolerance range.

The cross-section of the synchronizer gear seat is uneven in thickness. During the initial stage of quenching and cooling, the thin-walled parts cool down faster and undergo greater thermal contraction, while the thick-walled parts cool down slowly and undergo less thermal contraction. Therefore, the magnitude of the thermal stress generated is different, which in turn leads to different plastic deformations in various parts of the workpiece. Through the inspection of the outer diameter of the gear seat, it was also found that the Φ200 size forms a trumpet shape after quenching. Therefore, under normal circumstances, our company's heat treatment method of carburizing and air cooling followed by secondary heating and pressure quenching compensates for the different plastic deformations caused by different stresses through the quenching die, enabling the deformation of the workpiece to be controlled within the specified range. However, this batch of workpieces showed significant deformation after carburizing air cooling, and the deformation could not be effectively controlled after pressure quenching, indicating that the deformation degree has exceeded the size range that the quenching die can control. After analysis and discussion, it is preliminarily suspected that the isothermal normalizing treatment of the blank was not good, resulting in excessive organizational stress. After heat treatment, this stress together with the processing stress was released, causing the part to deform uncontrollably. The blank of the gear seat provided by the external cooperative manufacturer for our company undergoes normalizing treatment. After metallographic inspection of one blank of this batch of parts, the normalizing microstructure of the blank was observed under a 100x metallographic microscope.

(1) Through this improvement process, it has been proven that the quenching die can only ensure the key dimensions of the parts within a certain range. If the parts deform too much, it will not be possible to ensure the dimensions; at the same time, it further proves the importance of the pre-treatment of the carburized steel blanks, namely the isothermal annealing process.

(2) This improvement has significantly reduced the amount of waste and scrap for the company. It has also enabled the company's management to gain a deeper understanding of the isothermal normalizing process of the blanks at the technical level, thereby contributing to enhancing the status of heat treatment in the machining industry.

(3) This improvement also indicates that the post-carburizing air cooling process before quenching is also very important. In fact, to ensure that the deformation of the heat-treated workpiece is effectively controlled and follows a regular pattern, it is necessary to strictly control each stage from the raw material to the finished product.