Analysis of die casting die damage

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Lecture on die casting die knowledge: analysis of die casting die damage

I Mold damage analysis

in die casting production, the most common form of mold damage is crack and crack. Stress is the main cause of die damage. Thermal, mechanical, chemical and operational shock are all sources of stress, including mechanical stress and thermal stress. The stress comes from: 1 In the process of mold processing and manufacturing 1. Blank forging quality problems

some molds produce only a few hundred pieces, and cracks develop rapidly. It is possible that only the external dimensions are guaranteed during forging, and the loose defects such as dendritic crystals, mixed carbides, shrinkage cavities, bubbles and so on in the steel are extended and stretched along the processing method to form a streamline, which has a great impact on the final quenching deformation, cracking, embrittlement and failure tendency in the process of use. 2. The cutting stress generated during final machining such as turning, milling and planing can be eliminated by intermediate annealing. 3. Grinding stress is generated during grinding of quenched steel, friction heat is generated during grinding, softening layer and decarburization layer are generated, which reduces the thermal fatigue strength and is easy to lead to hot cracks and early cracks. After fine grinding, H13 steel can be heated to ℃, and the stress relief annealing can be carried out by holding for one hour with a thickness of 25 mm. 4. EDM produces stress. A white bright layer rich in electrode elements and dielectric elements is produced on the surface of the mold, which is hard and brittle, and this layer itself will have cracks and stress. During EDM, high frequency should be used to minimize the white bright layer. Polishing method must be used to remove it, and tempering treatment must be carried out. Tempering is carried out at the three-level tempering temperature

II Improper heat treatment in the process of mold treatment will lead to mold cracking and premature scrapping, especially if only quenching and tempering are used, quenching is not carried out, and then the surface nitriding process is carried out. Surface cracking and cracking will occur after thousands of mold times of die casting

the stress produced during quenching of steel is the result of the superposition of the thermal stress in the cooling process - the stress in May 2013 and the structural stress during phase transformation. The quenching stress is the cause of deformation and cracking, and the solid must be tempered to eliminate the stress

III In the process of die casting production, the mold temperature should be preheated to a certain temperature before production. Otherwise, when the high-temperature metal liquid is filled, it will produce chilling, which will increase the temperature gradient inside and outside the mold, form thermal stress, and make the mold surface crack, even crack

in the production process, the mold temperature keeps rising. When the mold temperature is overheated, it is easy to stick the mold, and the moving parts fail, resulting in mold surface damage

a cooling temperature control system should be set to keep the working temperature of the mold within a certain range

6. Open data structure 2. Filling

liquid metal filling with high pressure and high speed will inevitably produce intense impact and scouring on the mold, resulting in mechanical stress and thermal stress. During the impact process, liquid metal, impurities and gases will also have complex chemical interactions with the mold surface, and accelerate the generation of corrosion and cracks. When the liquid metal is wrapped with gas, it will expand first in the low-pressure area in the cavity. When the gas pressure rises, it will produce inward explosion, pull out the metal particles on the surface of the cavity and cause damage, and cracks will occur due to cavitation erosion

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3, mold opening

in the process of core pulling and mold opening, mechanical stress will also be generated when some components are deformed

4. Production process

in the production process of each die casting, due to the heat exchange between the mold and liquid metal, periodic temperature changes occur on the surface of the mold, causing periodic thermal expansion and contraction, resulting in periodic thermal stress. For example, during pouring, the mold surface is subject to compressive stress due to temperature rise, while after opening the mold and ejecting the casting, the mold surface is subject to tensile stress due to temperature drop. When this alternating stress circulates repeatedly, the stress accumulated in the die becomes larger and larger. When the stress exceeds the fatigue limit of the material, cracks appear on the die surface

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