In the early automobile gear production, heat treatment induction quenching was widely used because of its high production efficiency, small workpiece deformation, energy conservation and environmental protection, easy automation and so on. According to the strength standard of American AGM a gear, the contact fatigue strength of heat-treated induction hardened gear can reach 1200 ~ 1300m PA, and the bending fatigue strength of tooth root can also reach 310 ~ 380m PA. Domestic manufacturers mainly adopt the medium frequency oil buried profile quenching process, while some thin-walled small gear sleeves and internal splines in automobile transmissions adopt high-frequency induction quenching. Because of their high efficiency, small distortion and low pollution, they have been successfully incorporated into the production line; Japanese railway locomotive gears, including high-speed locomotive gears, are still dominated by heat treatment and induction quenching; In addition, some low-speed and heavy-duty gears with large modulus or diameter can have good technical economy only by heat treatment and induction quenching.
With the higher requirements for the strength and reliability of automobile gears, the problems of gear strength, bearing capacity and service life caused by the fast heating speed of heat treatment induction quenching have not been well solved. The existing high and medium frequency power induction quenching is limited by the matching of gear module and frequency, and the suitable range of gear module is only 2 ~ 5mm, Moreover, the development of domestic heat treatment induction quenching technology is slow and difficult to meet the new requirements. However, with the increasingly demanding application of induction quenching technology and finished products, it is believed that induction quenching will be more and more demanding for environmental protection.
Dual frequency induction heating quenching can obtain the hardening layer evenly distributed along the tooth profile. In recent years, electroheat Technologies LLC, eldecs chwerk induction GmbH and EFD have optimized the process to truly realize the profile quenching of gears, which has been widely used and has become the development trend of induction heat treatment of automobile gears. At present, the induction hardening machine tool for heat treatment has generally adopted the full mechanical type, and is developing in the direction of flexibility, automation and intelligent control.