How to Improve the Quality of Gear Forgings

How to Improve the Quality of Gear Forgings

How to improve the quality of gear forgings? Yidu Tongxin Precision Forging Co., Ltd. points out: Hardness is a very important quality inspection indicator for gear forgings during heat treatment. This is not only because the hardness test is fast, simple and does not damage the forgings, but also because the hardness value can be used to infer other mechanical properties. Reasonably determining the hardness value after heat treatment will give the forgings excellent performance, which is of great significance for improving quality and extending durability.

To improve the quality of gear forgings, in addition to the hardness value, other mechanical performance indicators must also be specified:

1. A proper balance between strength and toughness. Generally, the strength and toughness of steel materials are mutually complementary. For structural forgings, the one-time impact toughness is often used as a safety criterion, aiming for high toughness without sacrificing strength, resulting in coarse and heavy mechanical products with short service life. On the contrary, for tools and molds, in order to improve wear resistance, high hardness and high strength (torsional strength) are pursued, while the role of toughness in reducing mold chipping and breakage is ignored, and the service life is also not long. Therefore, the working conditions and failure forms of forgings should be investigated and analyzed, and based on the proper balance of strength and toughness, the strength and toughness indicators that forgings should adopt should be determined.

2. Properly handle the relationship among material strength, structural strength and system strength. All material strength indicators are measured using standard specimens, and they depend on the material's microstructure (including surface condition, residual stress and stress state). The structural strength of forgings is affected by size factors and notch effects, while the system strength is related to the interaction with other forgings. There are significant differences among these three aspects. For example, the fatigue strength of a smooth test bar of the material is high, but the fatigue strength of the actual object may be very low. Therefore, for some important parts, it is more appropriate to determine the mechanical performance indicators based on the results of simulation tests.

3. The strength matching of the components should be reasonable. A large number of experiments and practical applications have shown that when the components (such as worm gears, chain sprockets, ball bearings and rings, and transmission gears, etc.) achieve strength matching, the service life can be extended. For example, the hardness of the ball should be 2HRC higher than that of the ring, and the surface hardness of the driving gear of the rear axle of a car should be 2-5HRC higher than that of the driven gear seat. When the same steel is processed using the same method to obtain friction pairs with the same hardness, the wear resistance is relatively poor.

4. For surface-hardened forgings, the strength of the core and the surface should be reasonably matched. When surface-hardening parts (such as carburizing and quenching, carbon-nitrogen co-quenching, nitriding, induction quenching, etc.) are processed, when the depth of the hardened layer is fixed, the core should have an appropriate strength to ensure that the strength of the core and the surface achieve a good matching state, thereby ensuring that the forging has a long service life. If the strength of the core is too low, the transition zone is prone to generating fatigue sources, resulting in a decline in fatigue performance; if the strength of the core is too high, the surface residual compressive stress is small, and the fatigue life is also not long.