In die casting production, the most common form of mold damage is cracking and cracking. Stress is the main cause of mold damage. Thermal, mechanical, chemical, and operational shocks are sources of stress, including mechanical and thermal stresses, which are generated by:
In the mold manufacturing process
1) Quality problems of rough forging
Some molds produce cracks only when they are produced in a few hundred pieces, and cracks develop rapidly. It is possible that only the outer dimensions are ensured during forging, and the loose defects such as dendrites, inclusions, shrinkage cavities, and bubbles in the steel are stretched and elongated along the processing method to form a streamline, and this streamline is for the future. The final quenching deformation, cracking, brittle fracture during use, and failure tendency have a great impact.
2) Cutting stress generated during final machining such as turning, milling, planing, etc., which can be eliminated by intermediate annealing.
3) Grinding stress occurs during hardening of steel, friction heat is generated during grinding, softening layer and decarburization layer are generated, thermal fatigue strength is reduced, and thermal cracking and early cracking are easily caused. After the fine grinding of h13 steel, it can be heated to 510-570 ° C, and the thickness is maintained every 25 mm for one hour for stress relief annealing.
4) EDM produces stress. The surface of the mold produces a white bright layer rich in electrode elements and dielectric elements, which is hard and brittle. This layer itself has cracks and stress. EDM should use a high frequency to minimize the white layer. It must be removed by polishing and tempered. The tempering is carried out at the tertiary tempering temperature.
2. During mold processing
Improper heat treatment will cause the mold to crack and be prematurely scrapped. In particular, only quenching and tempering, no quenching, and surface nitriding will occur, and surface cracking and cracking will occur after several thousand die casting.
The stress generated when the steel is quenched is the result of the superposition of the thermal stress during the cooling process and the structural stress during the phase change. The quenching stress is the cause of the deformation and cracking, and the solid must be tempered to eliminate the stress.
