Gate design in die casting mold
The design of the die-casting mold’s ingate is a core component of the pouring system that directly impacts casting quality. It serves as the final passage for the molten metal to enter the mold cavity, and its position, shape, size, and number directly determine the filling speed, flow pattern, and solidification process of the molten metal. A rational ingate design can directly lead to defects such as porosity, cold shuts, shrinkage, and deformation in the casting. Therefore, a refined design is required based on the casting’s structural characteristics, alloy properties, and quality requirements. For example, for thin-walled, complex castings, the ingate must provide a sufficiently high filling speed to ensure the molten metal fills the mold cavity before solidification. For thick-walled castings, the ingate speed must be controlled to avoid excessive porosity caused by turbulent flow.
The location of the ingate is a primary design consideration. The fundamental principle is to ensure that the molten metal fills the mold cavity evenly and orderly, avoiding eddies and air entrainment. For symmetrical castings, the ingate should be located at the center of the mold cavity to ensure symmetrical filling of the molten metal, minimizing filling time variations. For asymmetrical castings, the ingate should be located farthest from the mold cavity, allowing the molten metal to gradually fill from far to near, thus avoiding localized overheating caused by a short filling path. The ingate should be positioned away from critical functional areas of the casting, such as bearing holes and sealing surfaces, to prevent gate marks from affecting assembly and performance. Furthermore, the ingate’s location should facilitate venting, ensuring that gases in the mold cavity can be discharged smoothly during the filling process. Generally, the direction of molten metal flow should align with the location of the venting grooves to create a “push-air” effect.
The shape design of the ingate needs to be determined according to the structure and filling requirements of the casting. Common shapes include rectangular, trapezoidal, circular, and fan-shaped. Rectangular ingates have the characteristics of large flow rate and fast filling speed. They are suitable for thin-walled castings and occasions requiring fast filling. The ratio of its width to thickness is generally 3-5:1 to ensure stable flow of molten metal. The cross-section of the trapezoidal ingate gradually decreases from the inlet to the outlet, which can gradually increase the flow rate of the molten metal. It is suitable for castings of medium thickness and can reduce flow resistance and pressure loss. The circular ingate has the smallest flow resistance, but is more difficult to process. It is suitable for occasions with high requirements for flow rate uniformity. The fan-shaped ingate is suitable for large-area flat-plate castings. It can make the molten metal diffuse and fill in a fan-shaped manner, reduce impact and air entrainment during the filling process, and improve the surface quality of the casting.
The ingate’s dimensions must be precisely calculated, with its width, thickness, and length matching the casting’s wall thickness, volume, and filling rate. The thickness of the ingate is a key parameter, generally 0.6-0.8 times the casting’s wall thickness. For thin-walled castings, this can be increased to 0.8-1.0 times to ensure adequate flow; for thick-walled castings, it can be reduced to 0.4-0.6 times to control filling rate. The ingate’s width is determined by the molten metal flow rate, calculated as follows: ingate width = (casting volume ÷ filling time) ÷ (ingate thickness × molten metal flow rate). For example, for an aluminum alloy casting with a volume of 200 cm³, a filling time of 0.08 seconds, an ingate thickness of 2 mm, and a molten metal velocity of 40 m/s (4000 cm/s), the ingate width is (200 ÷ 0.08) ÷ (0.2 × 4000) = 2500 ÷ 800 = 3.125 cm, or 31.25 mm. The ingate length should be minimized, generally 1-3 mm, to reduce pressure and heat loss. An excessively long ingate can cause the molten metal to solidify before entering the mold cavity, affecting filling efficiency.
The number of ingates designed should be determined based on the complexity of the casting. A single ingate is suitable for simple, symmetrical castings, simplifying the mold structure and reducing gate marks. Multiple ingates are suitable for complex, large, or asymmetrical castings. Simultaneous feeding through multiple ingates ensures simultaneous filling of all areas of the cavity, minimizing filling time variations. Multiple ingates should be arranged evenly and symmetrically, and the size of each ingate should be allocated based on the volume of the area it is responsible for filling, to avoid situations where a single ingate has excessive or insufficient flow. For example, for complex castings with multiple ribs, small ingates can be placed near each rib to ensure adequate filling. After the ingate design is completed, its performance should be verified through simulation analysis, observing the filling sequence, pressure distribution, and temperature changes of the molten metal, and adjusting any inappropriate features. A company initially designed an ingate for a die-cast automotive engine bracket. The initial use of a single ingate resulted in insufficient filling of the distal rib. Switching to three symmetrically distributed ingates significantly improved filling performance, increasing the casting pass rate from 68% to 95%.
