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The influence of mold geometry on deformation

  The influence of mold geometry on heat treatment deformation actually works through thermal stress and structural stress. Since the shape of the mold is diverse, it is still difficult to sum up the exact deformation law from it.
   For symmetrical molds, the deformation tendency of the cavity can be considered according to the cavity size, external dimension and height. When the wall of the mold is thin and the height is small, it is easier to quench through. At this time, it is possible that the tissue stress plays a leading role. Therefore, the cavity often tends to expand. On the contrary, if the wall thickness and height are large, it is not easy to harden. At this time, thermal stress may play a leading role. Therefore, the cavity often tends to shrink. What is mentioned here is a general trend. In production practice, it is necessary to consider the specific shape of the part, the steel grade and the heat treatment process, etc., and continuously summarize experience through practice. In actual production, the external dimensions of the mold are often not the main working dimensions, and can be corrected by grinding after deformation, so the main analysis above is the deformation trend of the cavity.

  As for the deformation of the asymmetric mold, it is also the result of the combined effect of thermal stress and tissue stress. For example, for a thin-walled and thin-sided mold, because the mold wall is thin, the temperature difference between inside and outside is small during quenching, so the thermal stress is small; but it is easy to be quenched and the structure stress is large, so the deformation tends to expand the cavity.
  In order to reduce the deformation of the mold, the heat treatment department should work with the mold design department to improve the mold design, such as avoiding mold structures with large differences in cross-sectional size, symmetrical mold shapes, and split structures for complex molds.

   When the mold shape cannot be changed, in order to reduce the deformation, some other measures can be taken. The general consideration of these measures is to improve the cooling conditions so that each part can be cooled uniformly; in addition, various mandatory measures can also be assisted to limit the quenching deformation of the parts. For example, adding process holes is a measure for uniform cooling of each part, that is, opening holes in some parts of the mold, so that each part of the mold can be uniformly cooled to reduce deformation. It can also be wrapped with asbestos on the periphery of the mold that is easy to expand after quenching to increase the cooling difference between the inner hole and the outer layer and shrink the cavity. Retaining ribs or reinforcing ribs on the mold is another compulsory measure to reduce deformation. It is especially suitable for die with swelling cavity and die with notch that is easy to expand or shrink.

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