In die casting production, the most common forms of drawing die damage are cracks and cracks. Stress is the main cause of drawing die damage. Thermal, mechanical, chemical, and operational shocks are all sources of stress, including mechanical stress and thermal stress. Stress occurs. The main reasons for its occurrence can be summarized as follows:
One, in the drawing die processing and manufacturing process
1. The rough forging quality problem, some drawing die 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 a streamline. This streamline affects the future The final quenching deformation, cracking, embrittlement during use, and failure tendency have a great influence.
2. 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°C, with a thickness of 25mm for one hour for stress relief annealing.
3. Cutting stress generated during final processing such as turning, milling, planing, etc., this stress can be eliminated by intermediate annealing.
4, EDM produces stress. A bright white layer enriched with electrode elements and dielectric elements is formed on the surface of the drawing die, 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.
2. Improper heat treatment during drawing die processing will result in drawing die cracking and premature scrapping. Especially if only quenching and tempering is used, and surface nitriding process is performed without quenching, surface cracks and cracks will appear after die-casting several thousand times. . The stress produced during quenching of steel 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.
3. During the die-casting production process, the drawing die temperature drawing die 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 drawing die to increase, forming thermal stress, and causing the drawing die surface Cracked, even cracked. In the production process, the drawing die temperature continues to rise. When the drawing die temperature is overheated, it is easy to produce drawing die sticking, and the failure of moving parts causes damage to the drawing die surface. A cooling temperature control system should be installed to keep the drawing die working temperature within a certain range.
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