Common materials and technical requirements for die casting molds
The working environment of the die-casting mold is characterized by high temperature (200-600℃), high pressure (40-150MPa), high-speed flushing and alternating hot and cold. Therefore, there are strict requirements on the mechanical properties, wear resistance, heat resistance and processing performance of the material. Parts in different parts need to select appropriate materials according to the working conditions and meet the corresponding technical requirements. Molded parts (cavities, cores, inserts, etc.) come into direct contact with high-temperature molten metal and must withstand maximum thermal shock and wear. Commonly used materials include H13 (4Cr5MoSiV1), 3Cr2W8V, and 718H. After quenching and double tempering, H13 steel must achieve a hardness of HRC45-50, an impact toughness αk ≥ 25J/cm², and a high-temperature hardness (600°C) ≥ HRC38 to meet the requirements of aluminum alloy die-casting molds. 3Cr2W8V steel offers superior heat resistance and is suitable for die-casting molds made of high-melting-point materials such as copper alloys. Its hardness is controlled at HRC40-45, and its high-temperature strength (600°C) ≥ 800MPa.
Structural components (such as formwork, base plates, and support plates) primarily support and transmit force, requiring sufficient strength and rigidity. Commonly used materials include 45 steel, S50C, and QT500-7 ductile iron. After quenching and tempering, 45 steel must achieve a hardness of HB220-250 and a tensile strength of ≥600 MPa to ensure resistance to deformation under clamping forces. S50C steel offers slightly better performance than 45 steel and is suitable for medium-sized formwork. After quenching and tempering, it achieves a HB240-280 and a yield strength of ≥350 MPa. QT500-7 ductile iron offers excellent shock absorption and castability, making it suitable for large formwork. It has a tensile strength of ≥500 MPa and an elongation of ≥7%, allowing casting to reduce machining requirements. Technical requirements for structural component processing include flatness ≤ 0.02 mm/m, parallelism ≤ 0.01 mm/100 mm, and surface roughness Ra ≤ 1.6 μm to ensure good fit with adjacent components.
Guide components (guide pins, guide bushings, guide keys, etc.) must ensure precision and smooth mold opening and closing. Materials used are primarily SUJ2 (high-carbon chromium bearing steel) and 20CrMnTi. SUJ2 steel must achieve a hardness of HRC58-62 after through-hardening, with a surface roughness Ra ≤ 0.4μm and a roundness ≤ 0.005mm, ensuring a clearance of 0.01-0.03mm with the guide bushing. 20CrMnTi steel, after carburizing and quenching, achieves a surface hardness of HRC58-62 and a core hardness of HRC30-40, offering both high wear resistance and good toughness. Suitable for large guide pins, the carburized layer depth is 0.8-1.2mm to prevent surface flaking. The mating surfaces of guide components are ground and honed to a straightness of ≤ 0.01mm/m to ensure guiding accuracy.
Ejection mechanism components (push rods, push tubes, reset rods, etc.) require reciprocating motion in high-temperature environments. Commonly used materials are T8A, Cr12MoV, and H13. T8A steel, with a hardness of HRC50-55 after quenching and tempering, is suitable for push rods. Straightness must be maintained at ≤0.01mm/m, and surface roughness Ra≤0.8μm to prevent binding. Cr12MoV steel, with superior wear resistance, is suitable for push tubes. It has a hardness of HRC58-62 after quenching, and a clearance between the inner hole and the core of 0.01-0.02mm. H13 steel is suitable for ejection parts operating in high temperatures, with a hardness of HRC45-50 and excellent thermal fatigue resistance. Technical requirements for ejection components include a diameter tolerance of h7, a length tolerance of ±0.02mm, and a clearance of 0.05-0.1mm with the template hole to ensure flexible movement.
The material selection and technical requirements of auxiliary parts (gate bushing, diverter cone, exhaust insert, etc.) must be determined according to their functions. The gate bushing is in direct contact with the molten metal and must be made of H13 or 3Cr2W8V steel. The hardness after quenching should be HRC45-50, the inner hole surface roughness should be Ra≤0.4μm, and the taper tolerance should be ≤0.01mm/100mm to prevent obstruction of the molten metal flow. The diverter cone needs to withstand the direct impact of the molten metal and is made of H13 steel with a nitriding treatment on the surface (nitriding layer depth 0.1-0.2mm, hardness HV ≥800) to improve wear resistance. The exhaust insert must have good air permeability and should be made of powder metallurgy material (such as FCMP-10) with a porosity of 15%-20% to ensure smooth exhaust while preventing molten metal leakage. All die-casting mold materials must undergo strict flaw detection testing. Molded parts must undergo UT (ultrasonic flaw detection) testing, and internal defects larger than φ2mm are not allowed. Structural parts must undergo MT (magnetic particle testing) testing, and the surface must not have defects such as cracks and folds to ensure the safety and reliability of the mold.
