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Improvement of Machinability of Parts by Vacuum Heat Treatment

In the production process of many enterprises, it is often found that there is a problem of deformation in the cutting process of parts. In order to reduce the quenching deformation of these parts, the salt bath furnace heating isothermal quenching process is generally used for heat treatment. This process has small heat treatment deformation, and the hardness, tensile strength and elongation meet the requirements. However, there is a problem of machining deformation in the cutting process of parts, that is, after finishing turning, the parts are deformed. Even if the cutting process and tooling are improved, it cannot be solved. This directly led to the scrapping of a considerable number of parts due to their deformation exceeding the specified allowable range when the products were submitted for inspection. This kind of problem not only affects the quality of finished products, but also increases the production cost of enterprises, resulting in a waste of human and material resources.

These problems perplexed many enterprises until they adopted vacuum heat treatment technology. Vacuum heat treatment is a heat treatment technology that heats the workpiece under vacuum conditions. Because vacuum can protect, degas, degrease and purify the surface of workpieces, and the vacuum heat treatment furnace has a high degree of automation, vacuum heat treatment can achieve small quenching deformation, no corrosion, and can improve the working conditions of heat treatment. In addition to the above advantages, vacuum heat treatment can also solve the problem of machining deformation after salt bath isothermal quenching.

Principle of improving machinability by vacuum heat treatment

1.The cutting deformation of parts after isothermal quenching is large, and the cutting deformation after vacuum heat treatment is small, both of which are related to the material structure obtained after heat treatment. After isothermal quenching, granular bainite+island structure is obtained, which has poor stability and is easy to change during cutting, thus affecting the cutting accuracy of parts. The tempered sorbite structure obtained after vacuum heat treatment has good stability. Therefore, using vacuum heat treatment instead of isothermal quenching can improve machining accuracy.

2.In addition, the residual stress of parts after vacuum heat treatment is smaller than that after isothermal quenching. One of the main reasons why many companies adopt isothermal quenching is that the deformation of parts after vacuum heat treatment is greater than that of isothermal quenching. However, the deformation of isothermal quenching in subsequent cutting is large and the product qualification rate is low, while the deformation of vacuum heat treater in subsequent cutting is small and the product qualification rate is high. This shows that smaller quenching deformation does not necessarily guarantee smaller subsequent cutting deformation. During isothermal quenching, the internal stress of the part is not fully released, so it seems that the deformation is much smaller. However, during machining, these stresses are gradually released with the cutting operation, resulting in machining deformation, and ultimately leading to the quality problem of the finished product.

For this kind of thin-walled parts with high machining accuracy, not only the quenching deformation is required to be small, but also the final machining deformation is required to be small. In case of contradiction between the two, it shall be ensured that the final cutting deformation of the product is small, so as to improve the overall qualification rate in product manufacturing. Therefore, reducing cutting deformation is more important than reducing quenching deformation, and vacuum heat treatment should be adopted to ensure that the final cutting deformation of products is small.

After vacuum heat treatment is used instead of isothermal quenching, the deformation of heat treatment will increase, but the problem of cutting deformation has been solved satisfactorily. This shows that vacuum heat treatment not only has the advantages of no oxidation decarburization, no chemical corrosion, but also is an effective way to solve the deformation problem of some parts in finishing.

Selection of vacuum heat treatment equipment: The VOGQ series vacuum heat treatment furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment process of tools and dies. Good temperature control accuracy and uniformity ensure the effective implementation of the vacuum heat treatment process. SIMUWU focuses on the manufacturing 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 gas quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.