Die Casting Die Design Method
Die-casting mold design is the foundation of die-casting production, directly affecting casting quality, production efficiency, and mold life. Its design method must follow a scientific and systematic process, taking into account the casting structure, alloy properties, and production conditions. First, a detailed demand analysis must be conducted before design, including the casting’s geometry, dimensional accuracy, surface quality requirements, and the fluidity, shrinkage, and other characteristics of the alloy used. For example, for thin-walled and complex aluminum alloy castings, the filling capacity of the molten metal must be considered. The design should ensure that the position and size of the gate are reasonable to ensure that the molten metal can quickly and smoothly fill the cavity. At the same time, it is also necessary to understand the production batch and die-casting machine parameters, such as clamping force, shot capacity, etc., to match the mold to the equipment and avoid equipment overload or low production efficiency.
The core of die-casting mold design is cavity design. The cavity needs to be 3D modeled based on the 3D model of the casting to ensure that the cavity dimensions are consistent with the casting dimensions and to allow for a reasonable amount of shrinkage. Different alloys have different shrinkage rates. Aluminum alloys generally have shrinkage rates of 0.8%-1.2%, while zinc alloys have shrinkage rates of 0.5%-0.8%. During design, the shrinkage must be calculated based on the specific alloy type to ensure that the dimensions of the casting meet the requirements after cooling. The surface roughness of the cavity needs to be controlled below Ra0.8μm to ensure the surface finish of the casting and reduce the flow resistance of the molten metal. For castings with decorative features such as patterns and text, the cavity surface needs to be textured to ensure that the casting accurately replicates the details of the cavity surface.
The gating system design is crucial to die-casting mold design, directly impacting the filling efficiency of the molten metal. This includes the design of the gate, runners, overflow troughs, and vents. The gate’s position and shape should ensure uniform and orderly entry of the molten metal into the mold cavity, avoiding eddies and air entrapment. Symmetrical gates are typically used for symmetrical castings; for complex castings, multiple gates can be used to ensure simultaneous filling of all areas. The runner design must ensure smooth molten metal flow. Cross-sectional dimensions are calculated based on the casting volume and filling speed, typically using circular or trapezoidal cross-sections to minimize flow resistance. Overflow and vent troughs are designed to remove air and cold material from the mold cavity. Overflow troughs are typically located at the last point of molten metal filling and in corners prone to eddies. Vents ensure smooth gas discharge. The width is typically 0.1-0.2mm and the depth 0.05-0.1mm to prevent overflow.
The design of the mold’s cooling system is crucial to casting quality and production efficiency. Cooling channels must be rationally arranged based on the structural characteristics of the casting to ensure uniform temperature across the mold and shorten solidification time. The cooling channels should be as close to the cavity surface as possible, generally 15-25mm apart. The channel diameter is determined by the mold size and cooling requirements, typically 8-12mm. For thick-walled areas of the casting, enhanced cooling is required. Ring or spiral channels can be used to improve heat dissipation efficiency. For thin-walled areas, the amount of cooling water can be appropriately reduced to prevent excessively low mold temperatures from affecting the fluidity of the molten metal. The cooling system also needs to consider water quality and flow rate. Treated soft water should be used to prevent scaling, and the flow rate should be controlled at 1.5-3m/s to ensure stable cooling.
Die-casting mold design also requires attention to the mold’s strength and rigidity, as well as the replaceability of consumable parts. The mold cavity and core must be constructed from high-strength hot-working die steel, such as H13 steel, with a hardness of 44-48 HRC after heat treatment to withstand the impact and wear of high-temperature molten metal. The mold’s guide mechanism requires precise positioning, employing a guide pin and guide sleeve structure to ensure mold clamping accuracy. The clearance between the guide pin and guide sleeve should be controlled at 0.01-0.02mm. Highly wearable areas, such as sprue bushings and ejector pins, should be designed with removable structures to facilitate replacement and repair, reducing mold maintenance costs. Furthermore, after mold design is completed, 3D simulation analysis is performed. Computer software simulates the molten metal filling and solidification processes to predict potential defects, such as air holes and under-gathering. This allows for optimization of the mold structure and improved design reliability. For example, when a company was designing a complex magnesium alloy die-casting mold, it discovered through simulation that the original gate design would lead to uneven filling of the molten metal. After adjusting the gate position and size, the casting qualification rate increased from 60% to 90%.
