Causes of damage to die casting production molds:
In die casting production, the common forms of mold damage are 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. Stress occurs in:
(1) In the process of mold processing and manufacturing
1. Quality problems of rough forging. 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 used 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 a streamline. This streamline affects the future The quenching deformation, cracking, embrittlement during use, and failure tendency have a great influence.
2. Cutting stress generated during final processing such as turning, milling, planing, etc., which can be brought by intermediate annealing.
3. Grinding stress is generated during grinding of quenched steel, friction heat is generated during grinding, softened layer and decarburized layer are generated, thermal fatigue strength is reduced, and hot cracks and early cracks are easily caused. After precision grinding, h13 steel can be heated to 510-570℃, and stress annealing is carried out with a thickness of 25mm for one hour.
4. EDM produces stress. The surface of the mold produces a bright white layer rich in electrical and dielectric elements, which is hard and brittle. This layer itself will have cracks and stress. High frequency should be used during EDM to reduce the white layer, polishing method should be used to remove, and tempering treatment should be carried out, and the tempering should be carried out at the tempering temperature.
(2) During mold processing
Improper heat treatment can lead to cracking of the mold and premature scrapping, especially if only quenching and tempering is used, and the surface nitriding process is performed without quenching, surface cracks and cracks will occur 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 it is stressed by tempering.
(3) In the process of die-casting production
The temperature that the mold should be preheated to 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 or even cracking on the mold surface. In the production process, the mold temperature continues to rise. When the mold temperature is overheated, it is easy to produce sticking, and the moving parts will fail to cause damage to the mold surface. A cooling temperature control system should be installed to keep the mold working temperature within the range.