Stress includes thermal stress and mechanical stress, which are mainly caused by mechanical, chemical, operational shock, and heat. Specifically, it is produced in the following aspects:
1. In the process of die-casting production
1. A cooling temperature control system should be installed to keep the mold working temperature within a certain range.
2. During the production process, the mold temperature continues to rise. When the mold temperature is overheated, mold sticking is easy to occur, and the moving parts fail to cause damage to the mold surface.
3. 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 increase the temperature gradient of the inner and outer layers of the mold, form thermal stress, and cause cracks or even cracks on the mold surface.
2. During mold processing
1. The stress produced during steel quenching 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.
2. Improper heat treatment will lead to cracking of the mold and premature scrapping, especially when only quenching and tempering is used, and the surface nitriding process is performed without quenching. Surface cracks and cracks will appear after die casting several thousand times.
Three, in the mold processing and manufacturing process
1. EDM produces stress. A bright white layer enriched with electrode elements and dielectric elements is formed on the surface of the mold, 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, it must be polished and removed, and tempered. The tempering is carried out at the tempering temperature.
2. The quality of blank 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 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 to form a streamline. This streamline will affect the final The quenching deformation, cracking, embrittlement during use, and failure tendency have a great influence.
3. Grinding stress is generated during grinding of hardened steel, friction heat is generated during grinding, softening layer and decarburization layer are generated, thermal fatigue strength is reduced, and hot cracking and early cracking are easily caused. After precision grinding, h13 steel can be heated to 510-570°C, with a thickness of 25mm for one hour for stress relief annealing.
4. Cutting stress generated during final processing such as turning, milling, planing, etc., this stress can be eliminated by intermediate annealing.
I believe that step by step and careful inspection in the above three processes will inevitably reduce the loss caused by stress, and the output of die-casting molds will also be improved to a certain extent.
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