Die castings simplify molds and extend mold life
Die casting mold costs account for 20-30% of total production costs. Simplifying mold structure and extending mold life are key to reducing costs and improving efficiency. Simplifying molds reduces processing difficulty and shortens manufacturing cycles, while extending mold life reduces replacement frequency and stabilizes product quality. These two considerations must be considered in tandem, ensuring mold strength and wear resistance while simplifying the structure. By optimizing casting design, mold material selection, and manufacturing processes, the cost-effectiveness of the mold can be maximized.
The key to simplifying mold structure is optimizing die-casting design and eliminating unnecessary complex features, thereby reducing the complexity of the mold’s core pulling mechanism, parting surfaces, and cavity. Casting designs should prioritize symmetrical structures and avoid asymmetric core pulling. For example, an asymmetric housing originally required three core pulling mechanisms, but with a symmetrical design, only one was needed, reducing the number of mold parts by 40%. Reducing the number of parting surfaces: molds with a single parting surface are simpler to manufacture and 30-50% less expensive than molds with multiple parting surfaces. For a cover-type part, adjusting the gate position reduced the number of parting surfaces from two to one, reducing mold assembly time by 50%. Avoid difficult-to-machine features such as narrow slits and deep cavities. Narrow slits (width <1mm) require electrospark forming, which is inefficient. For a filter casting, the 0.8mm slit was reduced to 1.2mm, reducing mold processing time from 10 days to 3 days. In addition, if small holes (diameter <3mm) on the casting are not functionally necessary, they can be eliminated or their diameters can be increased to reduce the number of small cores. For example, a connector eliminated two unnecessary φ2mm holes, and the mold core breakage rate was reduced by 80%.
Proper mold material selection is essential for extending mold life. Wear-resistant and heat-resistant materials should be selected based on the die-casting alloy type and production batch. Zinc alloy die-casting molds withstand low temperatures (150-200°C) and can be made of medium-carbon alloy tool steels such as 5CrNiMo, with a hardness of HRC 40-45 and a lifespan of 1-2 million cycles. Aluminum alloy die-casting molds operate at high temperatures (200-300°C) and require H13 hot-work tool steel, which, after quenching and tempering, has a hardness of HRC 44-48 and a lifespan of 500,000-1,000,000 cycles. Copper alloy die-casting operates at the highest temperatures (300-400°C) and requires high-performance H13 or powder metallurgy high-speed steel (such as ASP-60), with a hardness of HRC 48-52 and a lifespan of 100,000-300,000 cycles. An aluminum alloy mold originally made of 4Cr5MoSiV1 steel had a lifespan of only 300,000 cycles. Replacing it with high-quality H13 steel increased its lifespan to 700,000 cycles. In addition, the mold cavity surface can be nitrided (hardness HV800-1000) or PVD coated (such as TiAlN, hardness HV2500) to improve wear resistance. After a mold was coated with TiAlN, its life was extended by 50%.
Optimizing mold manufacturing processes can simultaneously simplify structures and extend mold life. Advanced machining techniques are employed to improve precision and surface quality. High-speed milling (10,000-20,000 rpm) is preferred for cavity machining. This is 3-5 times more efficient than conventional milling, resulting in lower surface roughness (Ra ≤ 0.8 μm), reducing polishing time. One cavity, after high-speed milling, was used directly without polishing, reducing the machining cycle by 40%. Complex cavities are machined using electro-spark machining (EDM) or wire cutting (WEDM) to ensure dimensional accuracy. Wire cutting can achieve an accuracy of ±0.001 mm, making it suitable for precision molds. For a gear mold, using WEDM improved tooth profile accuracy by one level and extended its life by 30%. During mold assembly, ensure close contact between parting surfaces (clearance ≤ 0.01 mm) and a clearance of 0.01-0.02 mm between guide pins and sleeves to reduce mold closing shock. Excessive assembly clearance on one mold resulted in rapid wear on the parting surface. After reassembly and adjustment, the wear rate was reduced by 60%. In addition, the rounded corners and transition areas of the mold need to be smooth to avoid stress concentration. After the right-angle cavity of a certain mold was treated with arc transition, the fatigue life increased by 40%.
Optimizing mold cooling and lubrication systems is crucial to extending mold life. Proper cooling can maintain stable mold temperature and reduce thermal fatigue. Uniform cooling channels, 15-25 mm from the cavity surface and 8-12 mm in diameter, are placed according to the casting shape to ensure mold temperature fluctuations of ≤±5°C. After adding three cooling channels to an aluminum alloy mold, the temperature stabilized at 220-230°C, and the time it took for thermal cracks to occur was extended from 50,000 to 150,000 cycles. Using a combined water-and-oil cooling system, with oil cooling (high thermal conductivity) for hot areas like the core and oil cooling for the cavity, a copper alloy mold’s core oil temperature was controlled at 50-60°C, doubling its lifespan. The lubrication system requires even application of release agent, covering both the cavity and core surfaces to reduce metal adhesion. One mold employed an automated spray system, achieving a release agent application tolerance of ≤5%, reducing cavity wear by 30%. In addition, the scale and oil in the cooling water channel are cleaned regularly to ensure the flow. A mold overheated locally due to water channel blockage. After cleaning, the temperature returned to normal, avoiding early failure of the mold.
Mold maintenance and repair are effective means of extending mold life. Establishing a comprehensive maintenance system allows for timely detection and resolution of problems. Routine maintenance includes pre-shift inspections of guide pin and sleeve lubrication and cooling system flow, and post-shift cleaning of residual metal and scale in the mold cavity. One factory reduced mold downtime by 70% through routine maintenance. Regular inspections (every 10,000-20,000 mold runs) include measuring cavity dimensions, inspecting wear, and repairing worn areas with repair welding. A mold with 0.1mm wear was repaired using laser cladding of H13 material, restoring dimensional accuracy and enabling continued use for 50,000 mold runs. A mold history sheet, documenting usage, repairs, and defect types, can be used to predict service life. One company, through history analysis, discovered that a mold was prone to flash after 80,000 mold runs. Guide pin replacement was performed in advance, preventing mass scrapping. For molds that cannot be repaired, reusable parts (such as guide pins and cylinders) are recycled to reduce costs. The recovery rate of guide pins and mold plates from one scrapped mold reached 60%, saving 20%. By combining simplified design, material optimization, process improvement and maintenance measures, the mold life can be extended by 50-100%, and the overall cost can be reduced.
