Some mold materials and steel materials are very good, often because the mold structure design is unreasonable, such as thin edges, sharp corners, grooves, sudden steps, thickness disparity, etc., resulting in greater deformation of the mold after heat treatment.
1. Reasons for deformation
Due to the uneven thickness of the mold or the presence of sharp rounded corners, the thermal stress and structural stress between the various parts of the mold are caused to be different during quenching, resulting in different volume expansions of each part, and deformation of the mold after quenching.
2. Preventive measures
When designing the mold, in the case of meeting the actual production needs, the gap between the thickness of the mold and the structure asymmetry should be minimized. At the junction of the thickness of the mold, the structure design such as smooth transition should be adopted as much as possible. According to the deformation law of the mold, a machining allowance is reserved so that the mold will not be scrapped due to the deformation of the mold after quenching. For molds with particularly complex shapes, in order to make the cooling uniform during quenching, a combined structure can be used.
3. The influence of mold manufacturing process and residual stress
It is often found in factories that some molds with complex shapes and high precision requirements deform greatly after heat treatment. After careful investigation, it is found that the molds have not undergone any pre-heat treatment during machining and final heat treatment.
1. Causes of deformation
The superposition of the residual stress during the machining process and the stress after quenching increases the deformation of the die after heat treatment.
2. Preventive measures
(1) After rough machining and before semi-finish machining, a stress relief annealing should be carried out, that is, (630-680)℃×(3-4)h furnace cooling to below 500℃ and out of furnace air cooling, or 400℃×(2- 3) h stress relief treatment.
(2) Lower the quenching temperature and reduce the residual stress after quenching.
(3) Air cooling with quenching oil at 170ºC (stage quenching).
(4) The use of austempering process can reduce the quenching residual stress.
Using the above measures can reduce the residual stress of the mold after quenching, and the deformation of the mold is smaller.