What materials are generally used for zinc alloy die-casting molds
Mold material selection: The material selection determines many important properties of the mold, such as plasticity, toughness, thermal conductivity, hardenability, creep strength, high temperature yield strength, tempering resistance, thermal expansion coefficient, etc.
1) The plasticity, strength and creep strength of the material at high temperature are the main factors that determine the degree of cracking. The toughness of the material determines the degree of crack propagation.
2) High thermal conductivity can reduce the temperature difference of the mold and reduce the thermal stress.
3) Low coefficient of thermal expansion means that the expansion volume is small and the accumulation of thermal stress is small.
4) High temperature yield strength is conducive to resisting mold cracking. Negotiable
5) Anti-tempering is to make the mold have long-term high temperature softening resistance.
6) Choose high-quality die steel, high purity and uniformity of steel, and less impurities are the key to durability. Good mold design, mold structure should be able to meet the requirements of die-casting process, processability, heat treatment and use.
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The rationality of the structure: the rationality of the structure is first of all the reasonable design of the gating system, and the structural form and layout of the gating system are determined, which provides the basic basis for the overall design of the mold.
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What are the requirements for materials for hot work molding
The temperature difference between the surface and the core of the hot work mold is large under working conditions. According to the different types of molds and cavity structures, the surface temperature fluctuates in the range of about 550~750 °C, and the temperature difference in the core is large. At the beginning of work, if the mold is not preheated or improperly preheated, the heart is lower, often comparable to room temperature. The early plastic deformation failure or cracking failure of the mold cavity at the hot place has a great relationship with the high temperature yield strength or plasticity of the material, so the following performance requirements are put forward for the hot work mold material.
1. Hardness and strength The hot work mold material is required to maintain a certain strength at its service temperature and have good thermal stability to prevent the mold from deforming.
2. Toughness Many hot work dies, especially those for forging hammers, often have to bear large impact loads during the working process, and in order to prevent mold cracking, hot work die materials must have high impact toughness and fracture toughness.
3. Thermal fatigue resistance Most of the hot work molds work under the condition of periodic rapid temperature changes, which will produce stress and do not prevent thermal fatigue cracks on the surface of the mold, requiring the hot work mold material to have good thermal fatigue resistance.
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4. Chemical stability Hot work molds often work at higher temperatures, and the working surface of the mold is in contact with air, liquid metal or other media, so the hot work mold material is required to have oxidation resistance at working temperature or liquid metal erosion.
5. Abrasion resistance Because the hot work die work is not only subject to the friction and wear caused by the deformation of the blank, but also by the high temperature oxidation corrosion and the grinding of the iron oxide pin, which requires the hot work die material to have high hardness and wear resistance.
6. Thermal conductivity In order to prevent the mechanical properties of the hot work mold from declining due to excessive heat accumulation, the temperature of the die surface should be reduced as much as possible and the temperature difference inside the mold should be reduced, which requires the hot work mold material to have high hardness and wear resistance.