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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Lean vacuum Heat Treatment for Distortion Control

In the production process of automobile transmission gears, vacuum carburizing and quenching process is an important heat treatment process in gear production. After vacuum carburizing and quenching, the strength, wear resistance and service life of the gears have been greatly improved. The vacuum carburizing and quenching process is relatively complicated. Under the influence of high-temperature carburizing and quenching factors, the gears will deform in different ways during the process of organizational transformation. As a subsequent process of gear production, factors such as large heat treatment deformation and poor deformation consistency will lead to frequent rework of gear assembly, high scrap rate, and reduced performance of gear assembly.

Vacuum heat treatment deformation generally refers to the quenching deformation of the workpiece, which is mainly caused by internal stress. Internal stress is divided into thermal stress and organizational stress. Thermal stress is related to the linear expansion coefficient of the material, while organizational stress and organizational changes are related to the specific volume change of the organization. The organization after vacuum quenching is usually martensitic. The specific volume of this quenched martensite is larger than that of other organizations. Therefore, the workpiece after vacuum quenching will have a volume expansion phenomenon. The thermal stress and organizational stress formed due to volume change and uneven heating and cooling of various parts of the workpiece will cause the workpiece to deform or warp. When the size of the vacuum quenched workpiece increases, the distortion and warping will be more serious.
During the vacuum carburizing process of gears, deformation occurs due to the action of structural stress and thermal stress. The size and law of deformation depend on the chemical composition of the carburizing steel (blank material), the geometric shape and size of the workpiece, the processing state before vacuum heat treatment, and the process parameters of vacuum heat treatment. For mass production, compared with controlling the size and consistency of deformation, obtaining the deformation law is more meaningful for adjusting the processing parameters before vacuum heat treatment.

Based on the premise that the same workpiece in actual mass production uses the same batch of blanks and the same machining process, the same furnace workpiece is discrete, highly dispersed, and has poor consistency after vacuum heat treatment at different positions. Heating uniformity and cooling uniformity become the primary factors affecting the consistency of the workpiece. Uneven heating and cooling lead to different temperature gradients in various parts of the furnace, and different thermal stresses and structural stresses are generated, resulting in inconsistent deformation of various parts after vacuum heat treatment.

The factors affecting the uniformity of the heat change and cold treatment process of the workpiece in the same furnace at different positions in the furnace are not only affected by the equipment, such as the arrangement position of the heating pipe in the equipment, the direction of the circulating air, the stirring speed, etc.; they are also affected by the way of loading parts, especially when the parts are transferred from carburizing to quenching and cooling, the heat dissipation of each part is inconsistent due to the time difference, and the cooling speed varies greatly.
1) The use of matrix tooling can effectively suppress the deformation of gear vacuum heat treatment, and the consistency is better in terms of tooth shape, accuracy, and flatness, and the deformation can be better controlled by reverse adjustment; 2) The use of matrix structure tooling makes the layer depth and surface hardness of the whole furnace parts more uniform; 3) The matrix structure tooling is applied to vacuum heat treatment production, which can better improve and control product quality.

This paper explains the research on vacuum heat treatment deformation through the changes in tooling conditions. The control of vacuum carburizing heat treatment deformation is affected by many parameters such as materials, preliminary heat treatment, heat treatment tooling, parameters, etc. The final control method should adopt the most suitable actual state.