The design of die-casting mold vent ducts is crucial for ensuring die-casting quality. Their core function is to promptly expel air, volatile paint gases, and gases trapped within the mold cavity during the molten metal filling process, preventing defects such as porosity, shrinkage, and cold shuts in the casting. The vent duct design must integrate the casting structure, molten metal properties, and die-casting process parameters. Efficient venting is achieved through the rational planning of the vent path, size, and location. If venting is not smooth, the compressed gas within the mold cavity will generate high pressure, hindering the filling of the molten metal and potentially forming bubbles within the casting, severely impacting its mechanical properties and sealing.
The location of the exhaust duct must be precisely located in the gas gathering area. It is usually set at the end of the cavity where the molten metal last reaches, at the corner, at the bottom of the deep cavity, and at the location where two streams of molten metal converge. For example, for castings with complex ribs, the narrow space between the ribs is prone to form air pockets, and exhaust ducts need to be set at the corresponding positions; for large flat castings, the edge corners are often the last areas for gas to be discharged, and continuous exhaust ducts should be arranged along the edges. In addition, the exhaust duct should avoid important functional surfaces and processing surfaces of the casting to prevent the traces of the exhaust duct from affecting the accuracy of the part. In multi-cavity molds, the exhaust duct of each cavity needs to be designed independently to ensure balanced exhaust in each cavity and avoid inconsistent casting quality due to exhaust differences.
The dimensional parameters of the exhaust duct directly affect exhaust efficiency and must be determined based on the fluidity of the molten metal and the die-casting pressure. Common exhaust duct cross-sections are rectangular, with widths typically ranging from 5mm to 20mm. The depth must be strictly controlled: for aluminum alloy castings, the duct depth is 0.02mm to 0.05mm; for zinc alloys, 0.01mm to 0.03mm; and for copper alloys, 0.03mm to 0.06mm. Excessive depth can cause molten metal to overflow and form flash, while too thin a depth prevents effective exhaust. The exhaust duct length is typically no longer than 50mm. Excessive length increases gas flow resistance. Multiple parallel exhaust ducts can be used to shorten the length of each section. For high-pressure die-casting processes, a stepped “shallow groove + deep groove” structure can be employed, with shallow grooves at the front to prevent overflow and deep grooves at the rear to accelerate exhaust, achieving a balanced exhaust efficiency and overflow prevention.
The coordinated design of the exhaust duct and the overflow trough can significantly improve the exhaust effect. As an extension of the exhaust duct, the overflow trough can accommodate the last cold metal liquid and gas to enter. Its volume should be 3-5 times the volume of the exhaust duct. The connection between the exhaust duct and the overflow trough needs to adopt a smooth transition to avoid gas retention caused by right-angle turns. The connection width should be consistent with the exhaust duct to ensure that the gas enters the overflow trough smoothly. For example, an overflow trough is set at the end of the cavity, and the exhaust duct extends from the edge of the cavity to the bottom of the overflow trough, so that the gas first enters the overflow trough through the exhaust duct, and then is discharged with the cold material. This combination design is particularly suitable for complex cavities and can effectively solve the problem of gas being difficult to discharge directly.
The structural form of the exhaust duct must be adapted to different mold structures. Common types include parting surface exhaust ducts, insert gap exhaust ducts, and ejector pin gap exhaust ducts. Parting surface exhaust ducts are simple to process and are opened along the parting surface of the movable and fixed molds, making them suitable for most castings. Insert gap exhaust ducts utilize the clearance between the core and insert to exhaust air, and are suitable for deep cavities or special-shaped parts. The clearance is controlled at 0.02mm-0.04mm. Ejector pin gap exhaust ducts exhaust air through the gap between the ejector pin and the template, and are suitable for exhausting air from the bottom of the cavity. The fit accuracy between the ejector pin and the hole must be guaranteed. For high-demand castings, exhaust plugs can be used to assist in exhaust. Exhaust plugs are made of porous metal materials and installed in the gas accumulation area. They can both efficiently exhaust air and prevent molten metal from overflowing.
The exhaust duct’s maintenance convenience must also be factored into the design. It should feature a structure that facilitates cleaning to prevent clogging with molten metal residue. The duct’s end should extend outside the mold, and a removable cleaning plate can be installed at the outlet to regularly remove accumulated oxide residue. In automated production, a sensor can be installed at the duct outlet to monitor exhaust pressure in real time, providing a prompt alarm when pressure is abnormal, thus avoiding batch defects caused by blockage. By comprehensively optimizing the duct’s location, size, structure, and maintenance design, smooth molten metal filling can be ensured, providing a reliable guarantee for high-quality die-casting parts.
