Heat treatment is a critical and complex factor in gear machining that greatly affects how well each gear performs in transmitting power or motion to other components in the assembly. Heat treatment optimizes performance and extends the life of gears in service by altering their chemical, metallurgical and physical properties. These properties are determined by considering gear geometry, power transfer requirements, stresses at various points within the gear under load, duty cycle rates, material types, mating component design and other operating conditions.
Heat treatment improves the physical properties of gear machining. Such as surface hardness, which imparts wear resistance to prevent simple wear of the tooth and bearing surfaces. Heat treatment also improves gear fatigue life by creating underground compressive stress to prevent pitting and deformation caused by high contact stress on gear teeth. These same compressive stresses prevent fatigue failure at the gear root due to cyclic bending.
Physical properties such as surface hardness, core hardness, surface depth, ductility, strength, wear-resistance and compressive stress distribution can vary widely depending on the type of heat treatment applied. For any given type of heat treatment, the results can be adjusted to meet specific application requirements by varying process parameters such as heat source, temperature, cycle time, atmosphere, quenching medium, and tempering cycles.
In the field of transmission gear machining. Selecting an efficient and accurate machining method and gear machining is crucial. Components and production processes, as well as batch sizes, determine the choice of tooling and gear manufacturing methods.
When machining gears during the soft stage, the challenge is often to obtain tight dimensional tolerances. Careful preparation for the hardening stage provides a relatively straightforward hard part turning operation followed by hard machining of the gears. In hard part turning, predictable machining and a good surface finish are critical. All of these should be combined with cost-effectiveness.
In the electric vehicle industry, new transmission designs and flexibility and high efficiency are required, so gear machining processes will undergo significant changes. The focus will move away from common conventional gear machines. And multi-task machining of gear/spline components will become the norm. Power skiving will be in focus as it will replace forming, broaching and spline rolling, and to some hobbings.