Method for improving the service life of die casting mold
Die-casting molds are expensive due to their long production cycle, high investment, and precise manufacturing. Therefore, it's essential that they have a long service life. However, factors such as material defects, machining issues, and improper use can lead to premature failure, causing significant waste.
The main failure modes of die-casting molds include corner cracks, splitting, hot cracking, wear, and erosion. These failures are often caused by problems in the material itself, processing, usage, maintenance, and heat treatment.
First, material defects
Die-casting molds operate under extreme conditions. For example, aluminum has a melting point between 580°C and 740°C, and during use, the liquid temperature is maintained at around 650°C–720°C. Without proper preheating, the mold surface experiences rapid temperature changes, leading to tensile and compressive stresses. Over time, this causes cracks and other surface damage.
Therefore, the mold material should have excellent thermal fatigue resistance, fracture toughness, and thermal stability. H13 (4Cr5MoV1Si) is widely used in foreign markets, with about 80% of cavities made from this steel. In China, 3Cr2W8V is still common, but it has poor thermal conductivity, a high linear expansion coefficient, and is prone to decarburization, making it less ideal. Maraging steel is suitable for heat-resistant molds, while heat-resistant alloys like tungsten and molybdenum are used in small areas requiring high thermal conductivity. Under proper heat treatment, H13 remains a reliable choice.
To ensure quality, materials must be thoroughly inspected before production. Common methods include macroscopic corrosion testing, metallographic examination, and ultrasonic testing. These help identify porosity, segregation, cracks, and internal defects, preventing early mold failure and saving costs.
Second, processing, use, and maintenance
Mold design should follow strict guidelines. Injection speed, for instance, should not exceed 100m/s. Too high a speed increases mold wear, while too low a speed leads to casting defects. For magnesium, aluminum, and zinc, minimum injection speeds are 27, 18, and 12m/s respectively, with aluminum’s maximum speed limited to 53m/s.
When machining cooling channels, concentricity is crucial. Misalignment can cause cracking during use. The cavity surface should also be smooth to avoid stress concentrations. EDM is commonly used, but it creates a hardened layer on the surface. This layer must be removed using grinding or stress relief techniques to prevent cracks and pitting.
During operation, the casting process should be carefully controlled. Lowering the aluminum temperature, increasing mold preheating, and optimizing injection speed can significantly extend mold life. For example, raising the preheating temperature of an aluminum die-casting mold from 100–130°C to 180–200°C can greatly improve its durability.
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