The damage to the object may be natural or man-made. So what causes the damage of die-casting production mold? In die-casting production, the most common form of mold damage is cracks and cracks. Stress is the main cause of mold damage. Thermal, mechanical, chemical, and operational shocks are all sources of stress, including mechanical stress and thermal stress. What is stress and under what circumstances:
The rough forging quality problem in the mold processing process. Some molds have cracks after only a few hundred pieces are produced, and the cracks develop very quickly. It is possible that only the external dimensions are guaranteed during forging, and the loose defects such as dendrites, inclusion carbides, shrinkage cavities, and bubbles in the steel are extended and elongated along the processing method to form streamlines. This streamline affects the future The final quenching deformation, cracking, embrittlement during use, and failure tendency have a great influence.
Hardened steel produces grinding stress during grinding, friction heat is produced during grinding, softened layer and decarburized layer are produced, and thermal fatigue strength is reduced, and it is easy to cause hot cracks and early cracks. After fine grinding, h13 steel can be heated to 510-570℃, and the thickness is kept at 25mm for one hour for stress relief annealing.
EDM produces stress. The surface of the mold produces a bright white layer rich in electrode elements and dielectric elements, which is hard and brittle. This layer itself will have cracks and stress. High frequency should be used in EDM to minimize the white layer, polishing method must be used to remove, and tempering treatment, tempering is carried out at the third tempering temperature.
Die cracking and premature scrapping are caused by improper operation in the heat treatment process, especially when only quenching and tempering is used, without quenching, and then surface nitriding process, surface cracks and cracks will appear after several thousand die castings. The stress produced when steel is quenched is the result of the superposition of the thermal stress during the cooling process and the structural stress during the phase transformation. The quenching stress is the cause of deformation and cracking, and the solid must be tempered to eliminate the stress.
During the die-casting production process, the mold temperature and the mold should be preheated to a certain temperature before production. Otherwise, chilling will occur when the high-temperature molten metal is filled, which will cause the temperature gradient of the inner and outer layers of the mold to increase, forming thermal stress, and cracking the mold surface. , Even cracking. So pay attention to setting up a cooling temperature control system. When the mold temperature is overheated, it will not cause damage to the mold surface and keep the work going normally.