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Research on powder metallurgy vacuum sintering of automobile transmission

With the rapid development of the automotive transmission industry, the requirements for gears as core components are also increasing. Requirements such as lightweight, low cost, low energy consumption, and new materials have become new challenges in its development.
Advantages of powder metallurgy vacuum sintered gear technology: ① The overall material utilization rate can reach more than 95%; ② No or only a very small amount of cutting is required; ③ Parts have stable dimensions, good consistency, and high precision; ④ High production efficiency, suitable for large batches Production costs are lower than cutting.
Powder metallurgy manufacturing uses integrated molding technology to cast metal powder into a special rigid closed mold. Therefore, the redesign of the part structure can eliminate some empty grooves on the steel parts and make the structure more compact.

At the same time, the following problems need to be considered when designing the structure.
(1) Avoid local thin-walled materials to facilitate powder loading and compaction and prevent cracks.
(2) Try to avoid designing grooves and counterbores on the side walls, because smooth side walls are conducive to compaction or reducing residual materials.
(3) Try to design a relatively simple and symmetrical shape structure to avoid excessive changes in cross-sectional area, narrow grooves, spherical surfaces, etc., to facilitate mold manufacturing and compaction.
(4) The transition joints on each side wall should be designed with rounded corners to avoid sharp edges and prevent stress concentration in the mold and compact.

Research on powder metallurgy vacuum sintering gear process
Usually, the density of components produced by ordinary powder metallurgy processes that only use one pressing and one sintering is basically below 7.2 g/cm3, such as shift drum gears and synchronizer hubs in transmissions, and their surfaces and There are a large number of pores inside, which greatly reduces its fatigue resistance. The transmission gears need to withstand high loads at high speeds and are prone to failures such as broken teeth and pitting corrosion on the tooth surface. Based on the above reasons, powder metallurgy vacuum sintered transmission gears require the correct selection of materials, and after the pressing and vacuum sintering processes, surface densification treatment, and finally vacuum heat treatment and subsequent machining treatments are performed to obtain excellent mechanical properties. This process is completed by a special gear rolling machine. Two specially designed active rolling gears based on the involute geometry of the gear product squeeze the “pre-machined gear” in the middle. The rolling gear rotates at high speed and at the same time applies pressure to the tooth surface and tooth root surface of the “pre-gear”, resulting in a dense surface rolling effect.

Vacuum heat treatment process
The surface densified gear needs to be vacuum carburized to improve its mechanical properties. After vacuum heat treatment, the surface hardness of the part can reach 560~660 HV10, and the core hardness will reach 250~320 HV10. The comprehensive performance basically meets the usage requirements. (1) As a green and environmentally friendly sustainable technology, powder metallurgy vacuum sintering gears will bring higher raw material utilization and lower energy loss. Its fewer processing steps also mean less equipment investment and smaller factory area planning, and its production efficiency is higher and its cost-effectiveness is obvious.
(2) Through reasonable design, powder metallurgy vacuum sintered gears have sufficient design margin, weight reduction, stress reduction, noise suppression, shock absorption and other capabilities. In the gear design and development stage, engineers have a new choice.
(3) Powder metallurgy vacuum sintering gears require the investment of a large number of molds. In the unfrozen design stage, the cost risk of mold design changes is greater; since the production of medium and low-volume parts using the powder metallurgy process is not economical, it is highly recommended. Used when batch requirements are required.