First, the heat treatment in the mold processing process is not appropriate, will cause the mold to crack and prematurely scrapped, especially only the quenching and tempering, no quenching, and then the appearance of nitriding technology, after the thousands of die-casting will show the appearance of cracks and Cracking.
1. The stress occurs when the steel is quenched, which is the result of the superposition of the thermal stress during the cooling process and the arrangement stress during the phase change. The quenching stress is the cause of the deformation and cracking, and it is necessary to temper to eliminate the stress.
Second, in the process of mold processing
1. The quality of the blank casting. Some molds produce cracks only when they produce a few hundred pieces, and the cracks develop very quickly. It is possible that only the external dimension is ensured during casting, and the loose defects such as dendrites, doped carbides, shrinkage cavities, and bubbles in the steel are extended and extended along the processing method to form a streamline, which is for the future. * Final quenching deformation, cracking, brittle cracking during use, and failure tendency have a great impact.
2. Cutting stress occurring during final machining such as turning, milling, and planing. This stress can be eliminated by center annealing.
3. Grinding stress occurs during hardening of steel, friction heat occurs during grinding, softening layer and decarburization layer occur, thermal fatigue strength is reduced, and thermal cracking and early cracking are caused simply. After the fine grinding of h13 steel, it can be heated to 510-570 ° C, and the thickness is maintained for one hour every 25 mm for stress relief annealing.
4, EDM machining stress. A white bright layer enriched in electrode elements and dielectric elements is formed on the outer surface of the mold, which is hard and brittle. This layer itself has cracks and stress. EDM should use high frequency to reduce the white bright layer to * small. It is necessary to remove it by polishing and tempering. The tempering is carried out at the third-stage tempering temperature.
Third, in the process of die casting
1. The stamping die should be preheated to a certain temperature before being produced. Otherwise, the chilling occurs when the high-temperature metal liquid is filled, causing the temperature gradient of the inner and outer layers of the mold to increase, which constitutes thermal stress, causing the mold to crack and even crack. During the production process, the mold temperature is continuously increased. When the mold temperature is overheated, the mold sticking occurs simply, and the moving parts are out of order, causing damage to the mold surface. The cooling temperature control system should be set up, and the working temperature of the mold should be within a certain range.