Effect of Mold Geometry on Deformation

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The influence of mold geometry on heat treatment deformation is actually still through thermal stress and tissue stress. Since the shapes of molds are diverse, it is still difficult to summarize the exact deformation law from them.

For symmetrical molds, the deformation tendency of the cavity can be considered according to the cavity size, external dimensions and height. When the wall of the mold and mold parts is thin and the height is small, it is easier to harden through. At this time, it may be that the tissue stress plays a leading role, so the cavity often tends to expand. On the contrary, if the wall thickness and height are large, it is not easy to harden through. At this time, thermal stress may play a leading role, so the cavity often tends to shrink. What is said here is the general trend. In production practice, it is also necessary to consider the specific shape of the parts, the type of steel used and the heat treatment process, and constantly summarize experience through practice. Since in actual production, the external dimensions of the mold are often not the main working dimensions, and the deformation can be corrected by grinding, etc., the above analysis is mainly about the deformation trend of the cavity.

For the deformation of asymmetric molds, it is also the result of the combined effect of thermal stress and tissue stress. For example, for thin-walled and thin-edge Spiral Bevel Gear Mold, due to the thin mold wall, the temperature difference between the inside and outside during quenching is small, so the thermal stress is small; but it is easy to quench through, the organizational 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 study and improve the mold design, such as avoiding mold structures with large differences in cross-sectional sizes as much as possible, striving for symmetry in mold shape, and using spliced ​​structures for complex molds.

When the mold shape cannot be changed, in order to reduce deformation, some other measures can also be taken. The overall consideration of these measures is to improve the cooling conditions so that each part can be cooled evenly; in addition, various compulsory measures can also be used to limit the quenching deformation of the parts. For example, adding process holes is a measure to make each part cool evenly, that is, opening holes in certain parts of the mold so that each part of the mold can be cooled evenly to reduce deformation. It is also possible to wrap the periphery of the mold and Die Punching Needles that is easy to expand after quenching with asbestos to increase the cooling difference between the inner hole and the outer layer and shrink the cavity. Leaving or adding ribs on the mold is another compulsory measure to reduce deformation. It is particularly suitable for molds with expanded cavities and molds with slots that are prone to expansion or contraction.