Design of Typical Die Casting Gating System
The design of a typical die-casting gating system requires tailoring to the casting’s structural type, size, and intended use. Different types of die-castings, due to differences in shape, wall thickness, and function, place varying demands on the gating system. Common typical die-castings include thin-walled shells, thick-walled structures, complex cavities, and small precision castings. Each type of casting requires its own unique gating system design principles and methods. For example, thin-walled shell castings require a gating system that provides rapid and uniform filling to avoid cold shuts and underfilling; thick-walled structures, on the other hand, require controlled filling speeds to minimize air entrapment and shrinkage defects. Therefore, understanding the design principles of typical die-casting gating systems is crucial for improving die-casting production efficiency and casting quality.
The gating system design for thin-walled die-castings (such as automotive transmission housings and electronic equipment enclosures) focuses on rapid filling. These components are characterized by thin walls (typically 1-3 mm), large surface areas, and complex structures. The molten metal cools rapidly during the filling process, making cold shuts and under-casting more likely. Therefore, the gating system requires a high-flow, high-speed design. The ingates should be located at the center or symmetrically located within the casting, with multiple ingates feeding simultaneously to ensure the molten metal fills the mold cavity within 0.05-0.1 seconds. The runners feature a trapezoidal cross-section with a large cross-sectional area to minimize pressure loss, while the sprues are tapered with a 3-5° taper to increase the flow rate of the molten metal. Additionally, sufficient overflow and venting channels should be provided at the edges and corners of the casting to allow for the timely discharge of gases and cold material. For example, a certain automobile gearbox housing casting uses four symmetrically distributed inner gates with a thickness of 2mm and a width of 30mm. The filling time is controlled at 0.08 seconds. Combined with an annular cross runner and dense exhaust grooves, the cold shut defect rate of the casting is reduced from 25% to below 5%.
The gating system design for thick-walled die-castings (such as engine blocks and large brackets) focuses on minimizing air entrapment and shrinkage. These components are characterized by thick walls (typically 5-15 mm), large volumes, and long solidification times. Turbulent flow during the filling process can easily lead to air pores and shrinkage during solidification. Therefore, the gating system must employ a low-flow, stable filling strategy. The ingates should be located in thick-walled areas of the casting or near risers to facilitate shrinkage feeding. The ingates should be 0.4-0.6 times the thickness of the casting wall, and the flow rate should be controlled at 15-25 m/s to avoid turbulence caused by excessive velocities. The runners are short and have a large cross-sectional area to ensure stable molten metal pressure. A smooth transition is used between the sprue and the runner to reduce eddy currents. Furthermore, overflow troughs are installed in thick-walled areas of the casting as risers, utilizing pressure from the pressurization phase for shrinkage feeding. For example, in a certain engine cylinder casting, the ingate is set at the thick wall at the bottom of the cylinder. The ingate thickness is 8mm, the flow rate is 20m/s, and with the stepped cross runner and bottom overflow groove, the shrinkage defect rate of the casting is reduced from 30% to 8%.
Uniform filling and venting are key to the gating system design of complex-cavity die-casting parts (such as hydraulic valve bodies and multi-channel joints). These parts are characterized by complex cavities, multiple deep cavities, and narrow slots. The molten metal filling path is long and tortuous, making it prone to uneven filling and gas entrapment. Therefore, the gating system must adopt a zoned filling and gradual advancement design. Multiple ingates are positioned according to the cavity structure, with each ingate responsible for filling a specific area. By controlling the size and position of each ingate, the molten metal flow front advances synchronously. The runner adopts a branching design, with each branch corresponding to an ingate. Arc transitions are provided at the branches to reduce pressure loss. The shape of the ingates is determined by the shape of the cavity inlet, using fan-shaped or rectangular shapes to ensure smooth entry of the molten metal into narrow slots and deep cavities. Furthermore, venting grooves are positioned at the end of each deep cavity and narrow slot, and vacuum-assisted venting technology is used to improve venting efficiency. For example, a hydraulic valve body casting has three deep cavities perpendicular to each other, and uses three corresponding inner gates for feeding respectively. The width of the inner gate is determined according to the cross-sectional area of the cavity. Combined with the vacuum exhaust system, the porosity defect rate of the casting is reduced from 40% to 10%.
The gating system design for small, precision die-casting parts (such as connectors and small gears) aims to ensure dimensional accuracy and surface quality. These parts are characterized by small size (typically weighing less than 50g), high precision (dimensional tolerances of IT8-IT10), and low surface roughness requirements (Ra 0.8μm or less). Therefore, the gating system requires a sophisticated, low-impact design. Ingates are small and numerous, with a thickness of 0.5-1.5mm and a width of 3-10mm. The flow rate is controlled at 20-30m/s to avoid excessive impact from the molten metal and deformation of the casting. The runners and sprues are small, with circular or trapezoidal cross-sections, ensuring smooth molten metal flow. The sprue bushings are precisely fitted to the pressure chamber to minimize splashing and air entrainment. Furthermore, any remaining components of the gating system (such as the gates and runners) should be easily removable without compromising the dimensional accuracy of the casting. For example, a small connector casting uses two symmetrical ingates with a thickness of 0.8mm and a width of 5mm. Combined with a small cross runner, the dimensional accuracy of the casting is improved from 70% to 95%, and the surface roughness can reach below Ra0.8μm.
