There are many things to pay attention to in gear forgings, but not every item must be strictly paid attention to. How to improve the quality of gear forgings? The following article mainly tells you about it.
Hardness is an important quality inspection index for heat treatment of gear forgings. This is not only because the hardness test is fast, simple and does not damage the forgings, but also other mechanical properties can be inferred from the hardness value. Reasonable determination of the hardness value after heat treatment will give the open die forgings a good quality. It plays an important role in improving quality and prolonging durability.
In addition to the hardness value required to improve the quality of gear forgings, other mechanical performance indicators must also be specified:
- Reasonable coordination of strength and toughness. Generally, the strength and toughness of steel materials are mutually beneficial. For structural forgings, primary impact toughness is often used as a safety criterion, and high toughness indicators are pursued without sacrificing strength, resulting in bulky mechanical products and short lifespan. On the contrary, for tools and dies, high hardness and high strength (torsional strength) are pursued in order to improve wear resistance, while the effect of toughness on reducing die chipping and fracture is ignored, and the service life is not long. Therefore, the working conditions and failure modes of forgings should be investigated and analyzed, and the strength and toughness indicators that should be selected for forgings should be determined according to the reasonable combination of strength and toughness.
- Correctly handle the relationship between material strength, structural strength and system strength. Various material strength indicators are measured with standard samples, which depend on the organizational state of the material (including surface state, 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 of other forgings. There is a big difference between these three, for example, the fatigue strength of the smooth test bar of the material is high, but the fatigue strength of the real object may be very low. Therefore, for some important parts, it is more appropriate to determine the mechanical performance index according to the simulation test results.
- The strength matching of the assembly should be reasonable. A large number of tests and actual use have shown that when the assembly (such as worm gear, chain sprocket, ball and ferrule, and transmission gear, etc.) achieves a strength match, the service life can be extended. For example, the hardness of the ball should be 2HRC higher than that of the ferrule, and the surface hardness of the driving gear of the rear axle of the car is 2-5HRC higher than that of the driven gear seat. The same kind of steel is treated by the same method to form friction pairs with the same hardness, and the wear resistance is relatively poor.
- For Bicycle forgings with surface strengthening, the core and surface strength should be reasonably matched. When surface strengthening parts (such as carburizing and quenching, carbonitriding and quenching, nitriding, induction hardening, etc.), when the depth of hardened layer is constant, the core should have appropriate strength, so that the core and surface strength can reach a good matching state. To ensure that the forging has a high service life. If the strength of the core is too low, fatigue sources are likely to be generated in the transition zone, resulting in a decrease in fatigue performance; if the strength of the core is too high, the residual compressive stress on the surface is small, and the fatigue life is not long.