Causes of die casting die damage

2022-08-10

In die casting production, the common forms of mold damage are crack and crack. Stress is the main cause of die damage. Thermal, mechanical, chemical and operational impact are all sources of stress, including mechanical stress and thermal stress. The stress is generated from:



(1) In the process of mold processing and manufacturing



1. Blank forging quality problem. Some molds have cracks after only a few hundred pieces are produced, and the cracks develop rapidly. It is possible that only the external dimensions are taken into account during forging, while the loose defects such as dendritic crystals, mixed carbides, shrinkage cavities and bubbles in the steel are extended and elongated along the processing method to form a streamline, which has a great impact on the subsequent quenching deformation, cracking, embrittlement and failure tendency during use.



2. The cutting stress generated during final processing such as turning, milling and planing can be obtained through intermediate annealing.



3. Grinding stress is generated during grinding of quenched steel, and friction heat is generated during grinding, resulting in softening layer and decarburization layer, which reduces thermal fatigue strength and easily leads to hot crack and early crack. After finishing grinding, H13 steel can be heated to 510-570 ℃ and maintained for one hour every 25mm for stress annealing.



4. Electric discharge machining produces stress. A layer of white and bright layer enriched with electric elements and dielectric elements is produced on the surface of the mold, which is hard and brittle. This layer itself will have cracks and stress. During EDM, high frequency shall be adopted to reduce the white bright layer to a minimum, and polishing method shall be used to remove it, and tempering treatment shall be carried out. Tempering shall be carried out at tempering temperature.



(2) During mold processing



Improper heat treatment will lead to mold cracking and premature scrapping. In particular, surface cracking and cracking will occur after thousands of die casting times if only quenching and tempering are adopted, and then surface nitriding process is carried out. The stress generated during steel quenching is the result of the superposition of the thermal stress during cooling and the structural stress during phase transformation. The quenching stress is the cause of deformation and cracking, and the stress is generated by tempering.



(3) In the process of die casting production



The temperature to which the mold should be preheated before production. Otherwise, when the high-temperature metal liquid is filled, it will produce chilling, which will increase the temperature gradient of the inner and outer layers of the mold, form thermal stress, and make the surface of the mold crack or even crack. In the production process, the mold temperature keeps rising. When the mold temperature is overheated, it is easy to produce die sticking, and the moving parts fail, resulting in die surface damage. A cooling temperature control system shall be set to keep the working temperature of the mold within the range of.
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