How does the grinding process in gear machining affect the hardness of ZLY180-10-VII reducer gears

The grinding process in gear machining mainly affects the hardness of ZLY180-10-VII reducer gears through the following aspects:

The influence of grinding heat

Tempering softening: During the grinding process, a large amount of grinding heat is generated. If the heat is not dissipated in time, it will cause the surface temperature of the gear to rise. When the temperature reaches the tempering temperature range, tempering occurs on the surface of the gear, resulting in a decrease in hardness. In some cases, a tempering layer is formed at a distance of 0.1mm from the surface after gear grinding, resulting in a significant decrease in hardness.

Secondary quenching and hardening: If the grinding heat causes the surface temperature of the gear to rise above the austenitization temperature, then under the rapid cooling effect of the coolant, secondary quenching will occur, forming secondary quenched martensite and significantly increasing the surface hardness. But this hardening layer has a shallow depth and may generate significant tensile stress, which can easily lead to the formation of cracks.

The influence of grinding parameters

Grinding speed: Increasing the grinding speed will result in more material being cut off, thereby generating more frictional heat, causing the surface temperature of the workpiece to rise, which may cause changes in hardness. When the grinding line speed is too high, the surface of the workpiece may undergo tempering softening or quenching hardening, which affects the surface hardness and wear resistance.

Feed rate: Feed rate has a significant impact on the hardness of the grinding surface. When the feed rate exceeds a certain value, the surface of the workpiece will suffer from grinding burns, and the hardness will be significantly higher than the initial surface hardness. For example, when the feed rate is 200mm/min, hardening occurs on the surface of the workpiece during grinding, with a hardness value of up to 553.7HV. This is because the excessively high feed rate leads to an increase in grinding force and heat, resulting in martensitic transformation of the surface layer.

Grinding pressure: Higher grinding pressure will increase the friction between the grinding wheel and the gear surface, generating more heat and affecting the hardness of the gear surface. Meanwhile, excessive grinding pressure may also cause plastic deformation on the surface of the gear, resulting in uneven distribution of surface hardness.

The influence of grinding wheel characteristics

Grinding wheel hardness: Softer grinding wheels have better self sharpening properties. The abrasive particles on the working surface of the grinding wheel are often in a sharp state, which can reduce the energy generated by friction and plastic deformation, thereby reducing the grinding temperature and minimizing the impact on gear hardness. However, harder grinding wheels can easily lead to an increase in grinding temperature, which may cause changes in the surface hardness of the gear.

Grinding wheel grain size: The grinding wheel has a coarse grain size, with fewer abrasive particles per unit area on the working surface, less contact area with the workpiece, and less grinding heat generated per unit time. The grinding temperature is relatively low, and its impact on gear hardness is minimal. On the contrary, fine-grained grinding wheels may increase the grinding temperature and affect the hardness of gears.