Analysis of the causes of damage to die-casting molds and preventive measures
Causes of damage to die-casting molds: 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:
I, In the mold manufacturing process
1. The quality 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. The cutting stress generated during the final machining of the car, milling, planing, etc., which can be eliminated by intermediate annealing.
3. The grinding stress is generated during the grinding of the hardened steel. The friction heat is generated during the grinding, and the softening layer and the decarburization layer are generated, which reduces the thermal fatigue strength and easily leads to thermal cracking and early cracking. 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.
II, improper heat treatment during mold processing will cause the mold to crack and prematurely scrapped.
In particular, only quenching and tempering, no quenching, and surface nitriding process will occur, and surface cracking and cracking will occur after several thousand die castings. 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.
III, in the process of die casting production
The mold temperature mold should be preheated to a certain temperature before production. Otherwise, when the high temperature metal liquid is filled, chilling occurs, which causes the temperature gradient of the inner and outer layers of the mold to increase, forming thermal stress, causing the mold surface to crack or even crack. During the production process, the mold temperature is continuously increased. When the mold temperature is overheated, the mold is easily generated, and the moving parts are broken, resulting in damage to the mold surface. The cooling temperature control system should be set to keep the working temperature of the mold within a certain range.
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