Design of cooling system for die casting mold
The design of a die-casting mold cooling system is crucial for ensuring stable die-casting quality and improving production efficiency. Its core objective is to achieve uniform temperature distribution and rapid cooling in the mold cavity through rational water channel layout and flow control, thereby controlling the solidification rate and shrinkage characteristics of the die-casting. The cooling system design requires a customized plan based on the die-casting’s structural shape, wall thickness distribution, and die-casting alloy characteristics to avoid defects such as shrinkage cavities and porosity caused by insufficient local cooling, or cracks caused by excessive cooling. For example, for die-castings with large variations in wall thickness (e.g., a sudden change from 2mm to 8mm), enhanced cooling structures, such as spiral water channels or jet cooling, are required in thick-walled areas to ensure that the solidification rate in these areas is roughly the same as that in thin-walled areas, thereby reducing internal stress.
The layout design of cooling water channels should adhere to the principle of “close proximity to the cavity and even distribution.” The distance between the channel centerline and the cavity surface is typically 20-30mm, with spacing of 50-100mm to ensure rapid heat transfer to the cooling medium. The channel diameter is determined by mold size and heat dissipation requirements. Small molds use channels with diameters of 8-12mm, medium-sized molds use 12-16mm, and large molds require 16-20mm to ensure sufficient flow and heat dissipation area. For complex cavities, custom-shaped channels or 3D-printed conformable channels can be used to precisely conform to the cavity contour. For example, in a curved cavity die-cast mold for an automotive door handle, conformable channels ensure a cooling distance within 25mm ± 2mm, with a temperature differential of no more than 5°C. The channel routing should avoid interference with components such as ejectors and cores. When this is unavoidable, bridge channels or offset designs should be used to ensure component functionality is not compromised.
The cooling system circuit design should be designed using either a series or parallel configuration based on the mold structure. Parallel circuits are suitable for applications requiring independent temperature control of each zone. Each branch can adjust the cooling intensity using a flow valve, such as for independent cooling of each cavity in a multi-cavity mold. Series circuits are suitable for molds with simple shapes and uniform temperature distribution. While this simple structure offers limited flow control flexibility, large molds often utilize a combined circuit combining zoned parallel and overall series cooling. For example, in an engine block die-casting mold, the cylinder barrel, water jacket, and flange are divided into three or four independent cooling units. Each unit is connected in series internally, while the other units are connected in parallel. This ensures temperature control in each zone and simplifies piping connections. The circuit inlet and outlet should be located on the non-working side of the mold, using standard quick-connect connectors (such as DME or HASCO) to facilitate integration with the die-casting machine’s cooling system. Connector specifications are determined by the water channel diameter: a φ12mm water channel corresponds to a G1/4 connector, while a φ16mm water channel corresponds to a G3/8 connector.
The choice of cooling medium and its parameter control significantly impact cooling performance. Commonly used cooling media include industrial water, ethylene glycol solution, and oil. Industrial water offers low cost and high heat dissipation efficiency (approximately 2500 W/(m · K) ), making it suitable for most die-casting applications. Ethylene glycol solution ( 30%-50% concentration ) lowers the freezing point and is suitable for low-temperature environments. Oils offer lower heat dissipation efficiency but maintain a stable viscosity, making them suitable for precise temperature control. The inlet temperature of the cooling medium is typically controlled between 20-30 °C, with the outlet temperature not exceeding 50 °C. Excessive temperature differences can cause mold temperature fluctuations, affecting the dimensional stability of the die-cast part. The flow rate should be calculated based on the required heat dissipation. Generally, a flow rate of 0.5-1 L/min per square centimeter of projected cavity area is required. For example, a 1000 cm² cavity requires a flow rate of 500-1000 L/h. For thick-walled areas, high-pressure spray cooling can be used. High-pressure water (0.5-1 MPa) is atomized through a nozzle and sprayed directly onto the core surface. This improves heat dissipation efficiency by 30%-50% compared to conventional water channels.
The cooling system’s auxiliary structural design includes exhaust devices, seals, and cleaning ports. An exhaust valve should be installed at the end of the water channel to expel air from the system and prevent air blockage that affects cooling efficiency. A heat-resistant seal (such as a fluororubber O-ring) should be installed at the connection between the water channel and the mold plate to prevent water leakage. The cross-sectional diameter of the seal should be 0.1-0.2mm larger than the groove to ensure a reliable seal. For long or curved water channels, cleaning ports (such as plug holes) should be appropriately located to facilitate regular removal of scale and impurities using high-pressure water or specialized cleaning tools to prevent clogging. For example, after six months of use, a φ12mm water channel should be cleaned through the cleaning port to ensure that the diameter is at least 90% of its original diameter. Once the cooling system design is complete, CFD (computational fluid dynamics) software is used for simulation analysis to optimize the water channel layout and flow parameters. The actual cooling effect is then verified through trial molds. The cooling system is fine-tuned based on defects in the die-casting (such as shrinkage location and deformation) until optimal performance is achieved.
