Due to their complex structure and significant variations in wall thickness, the prevention and control of porosity defects in electronic communication die castings require coordinated optimization across multiple dimensions, including materials, molds, processes, and equipment. Porosity formation primarily stems from gas entrapment in the molten metal, gas content in the material, poor mold venting, and improper process parameters, necessitating systematic measures for end-to-end control.
Material selection and pretreatment are fundamental to porosity prevention. Electronic communication die castings often utilize aluminum alloys, requiring strict control of raw material purity and avoiding the use of recycled materials containing oxides, hydrides, or grease. During the smelting process, moisture in the air readily reacts with molten aluminum to generate hydrogen gas, necessitating the removal of dissolved gases through refining processes (such as rotary degassing and inert gas blowing). For instance, using refining agents containing boron nitride can improve degassing efficiency while reducing smelting time to minimize the risk of gas inhalation. Furthermore, clean and dry tools should be used during molten metal transfer, and transfer time should be minimized to avoid exposure to humid environments.
Mold design should prioritize venting as a core optimization objective. The layout of the venting channels directly affects gas discharge efficiency. Venting channels must be installed in the final gas filling area, at the melt confluence, and in dead corners, ensuring their depth, width, and unobstructed exit. For example, adding overflow channels in thick or difficult-to-fill areas can guide the orderly discharge of gas. Mold temperature control is equally crucial. Cooling/heating channels must be used to achieve uniform and stable temperatures in all areas, preventing gas stagnation due to localized overheating. For complex structural parts, vacuum die casting technology can be used, where a vacuum system controls the cavity vacuum within a reasonable range, significantly reducing the risk of air entrapment. Optimizing process parameters is a key aspect of controlling porosity. Injection speed needs to be dynamically adjusted according to the casting structure to avoid high-speed injection (>40m/s) causing turbulent flow of molten metal that entraps air. For example, the optimal slow injection speed curve should be determined experimentally to ensure smooth molten metal filling of the cavity. Sufficient pressurization pressure (>400bar) is required to break air bubbles and compact the casting. The pouring temperature must balance fluidity and gas solubility. While ensuring the molten metal's filling capacity, the lowest possible temperature should be used to minimize gas absorption. Furthermore, the coating must be used correctly; a high-quality coating with low volatile content and good high-temperature stability should be selected. It should be sprayed evenly, thinly, and comprehensively, and fully dried before mold closing to prevent volatile gases from being drawn into the molten alloy.
Equipment maintenance is fundamental to ensuring process stability. The pressure chamber filling degree must be controlled within a reasonable range (>35%) to prevent air entrapment. The injection delay of the cold chamber die-casting machine must be strictly controlled within the standard (<0.3s) to reduce gas carried by oxide scale. Regularly check the degassing equipment, mold sealing, and cooling system to ensure they are in optimal working condition. For example, the gaps between the mold parting surface and the insert mating surface must be controlled to a minimum to prevent gas leakage and porosity.
Production process management requires strengthened detail control. Before each shift, the cavity, venting groove, and overflow groove must be cleaned of residue and coating carbon deposits to ensure unobstructed venting. Raw materials must be strictly managed, and baked before use to remove moisture and oil. Operators must receive professional training to improve their ability to identify and handle porosity defects, and strictly adhere to the established process parameters and operating procedures. For example, by monitoring key process parameters (such as injection speed and pouring temperature) in real time, anomalies can be detected and adjusted promptly, avoiding batch porosity defects.
Quality inspection and feedback mechanisms are crucial components of closed-loop control. X-ray inspection technology can accurately identify porosity morphology (e.g., regular circles indicate air entrapment, irregular dendrites indicate precipitation pores), and the process window can be optimized using PQ² diagrams. For porosity that frequently occurs in fixed locations, improvements need to be made to the mold design, such as adding local extrusion mechanisms or optimizing the venting structure. By establishing a historical data traceability system, the correlation between porosity defects and process parameters and environmental conditions can be analyzed, providing a basis for continuous improvement.
