Gear vacuum heat treatment process

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The deformation of vacuum heat treatment of vacuum carburizing gear directly affects the accuracy, strength, noise and life of the gear. Even if the gear grinding process is added after the vacuum carburizing heat treatment, the deformation will still reduce the accuracy level of the gear. There are many factors that affect the deformation of vacuum carburizing heat treatment. Only by controlling various factors can the deformation be controlled to a small extent. Controlling gear deformation must also be addressed throughout the gear manufacturing process.

(1) Influence of metallurgical factors of gear material on deformation

Tests show that the higher the hardenability of steel. greater deformation. When the hardness of the core is higher than 40HRC, the deformation will increase significantly. Therefore, there are certain requirements for the hardenability of steel, and the narrower the hardenability band. The more stable the deformation is, the steel mills are required to provide “low and stable deformation” steel. The A1/N content ratio is controlled within the range of 1 to 2.5, which can narrow the hardenability zone and reduce the deformation. In addition, the box segregation and band-like structure of the material affect the uneven deformation of the spline hole of the gear and the uneven carburization.

(2) Influence of preliminary vacuum heat treatment on gear deformation

Excessive normalizing hardness, mixed crystals, a large amount of sorbite or Widmanners structure will increase the deformation of the inner hole, so vacuum temperature-controlled normalizing or vacuum isothermal annealing should be used to treat forgings.

(3) Influence of vacuum carburizing process on deformation

uniformity of temperature. The uniformity of the carbon layer and the uniformity of the temperature of the cooling medium will affect the gear deformation. At the same time, the higher the vacuum carburizing temperature, the thicker the vacuum carburizing layer. The oil temperature is low and the gear deformation is large. Therefore, it is necessary to improve the equipment, optimize the process, and improve the quality of gear vacuum heat treatment.

(4) Influence of vacuum quenching on deformation

The cooling behavior of vacuum quenching is the most important factor affecting gear deformation. The deformation of vacuum hot oil quenching is smaller than that of vacuum cold oil quenching, and it is generally controlled at 100℃±120℃. The cooling capacity of the oil is also critical to deformation. Both the stirring method and the intensity affect the deformation. The disc gears quenched on the quenching press are subject to the deformation of various gears. Adjust the parameters of the punching press to reduce the deformation, adjust the pressure of the inner and outer die and the expansion block, the size of the fuel injection volume of each section and the upper work surface to control the deformation.

Clamping method and fixture

The purpose is to make the workpiece heating and cooling uniform, and the carburized layer of each part of the workpiece to be uniform, so as to reduce the uneven thermal stress and the uneven tissue stress, to reduce the deformation, and to change the clamping method. The disc parts are perpendicular to the oil surface, and the shaft parts are vertical Installation, use compensation washers, support washers, superimposed washers, etc., spline hole parts can be used with carburized mandrels, etc.

 

machining fit

First, master the deformation law of vacuum heat treatment, move the position of the tolerance zone, and improve the product qualification rate;

Second, according to the deformation law, applying reverse deformation and pre-expanding holes at the shrinking end, the qualified rate of deformation after vacuum quenching is improved;

Third, the method of reserving the machining amount is used for asymmetrical or uneven thickness parts. Reprocessing after vacuum heat treatment;

Fourth, after vacuum heat treatment, use a push knife to finish the spline hole, or electrolytic machining fine-grinding the spline hole, or vacuum carburizing and then heating the mandrel for quenching, and then extruding the mandrel to ensure that the size of the spline hole is reduced. small deformation.

Equipment selection: The RVN series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.