Mold heat treatment is an important process to ensure the performance of the mold, which has a direct impact on the manufacturing precision of the mold, the strength of the plastic mold, the working life of the mold, and the manufacturing cost of the mold. Mold heat treatment is to play the potential of mold materials and improve the performance of the mold. The performance of the mold must meet: high strength, including high temperature strength, resistance to cold and heat fatigue, high hardness (wear resistance) and high toughness, and also requires good machinability, including good polishability. ) weldability and corrosion resistance, etc. The deformation of the plastic mold after heat treatment is generally considered to be caused by cooling, which is not true. Molds, especially complex molds, have a great influence on the deformation of the molds. The comparison of some mold heating processes shows that the heating speed is faster and tends to produce larger deformation.
(1) Reasons for deformation
Any metal should be expanded when heated. Because the steel is heated, the temperature of each part in the same mold is uneven (that is, the uneven heating) will inevitably cause the inconsistency of the expansion of the various parts in the mold, resulting in heating. Uneven internal stress. At temperatures below the phase transition point of the steel, uneven heating mainly produces thermal stress, which is unevenly heated beyond the phase transition temperature, and also causes unequality of the structural transformation, which causes both tissue stress. Therefore, the faster the heating rate, the greater the difference in temperature between the surface of the plastic mold and the core, the greater the stress, and the greater the deformation caused by the heat treatment of the mold.
(2) Preventive measures
When the complex mold is heated below the phase change point, it should be heated slowly. Generally, the mold vacuum heat treatment deformation is much smaller than the salt bath furnace heat quenching.
Preheating, one preheating for low alloy steel molds (550-620 & deg; C);
For pre-heating of high alloy steel molds (550-620 & deg; C and 800-850 & deg; C).