The gating system of die-casting molds plays a crucial role in controlling the flow direction and state of molten metal within the mold, as well as the pressure transmission, venting, and overflow conditions. Additionally, it can regulate process parameters such as filling speed, filling time, and temperature distribution in the mold. Therefore, the design of the gating system is a key factor in determining the final quality of die-cast parts, while also significantly impacting production efficiency and mold lifespan. Consequently, the design of the gating system must be systematically considered, requiring the application of classical fluid filling theory and the integration of product structure to arrange vents and gates.

1. Position design of the sprue
In the design of the pouring system, the design of the sprue can be said to be extremely important. Before determining the position of the sprue, it is necessary to fully anticipate whether the selected sprue position will affect the flow state of the metal liquid filling the mold cavity based on the basic situation of the die-casting mold cavity or the different types of parting surfaces. It is necessary to analyze the possible dead corners and trapped areas during the filling process in order to design and arrange appropriate exhaust and overflow systems. Therefore, the following principles should be followed:

(1) It is necessary to minimize the meandering and twisting of the metal liquid flowing into the mold cavity, avoid generating excessive vortices, or reduce the amount of trapped gas;

(2) The imported metal liquid should first fill the parts deep in the mold cavity that are difficult to exhaust, rather than immediately sealing the parting surface to cause poor exhaust;

(3) It is necessary to consider reducing the diversion of metal liquid in the mold cavity to prevent the formation of cold joints or cold barriers at the confluence of diverted metal liquid;

(4) It is generally set at the thick wall of the die casting, which is conducive to the pressure transmission of the compensating liquid flow after the metal liquid fills the mold cavity;

(5) For parts with high precision requirements, low surface roughness values, and no machining, it is not advisable to design and arrange internal gates to prevent leaving marks after removing the gates;

(6) It is necessary to avoid direct impact of metal liquid on the core as much as possible to reduce the loss of kinetic energy, prevent erosion and mold sticking, especially to avoid impacting those small or threaded cores to prevent deformation and bending;

(7) The setting of the sprue should consider the temperature field distribution of the mold cavity, so that the distal end of the mold cavity can also be filled well;

(8) The cutting method of the pouring system after die-casting molding also needs to be considered.

2. Design of transverse gate
A sprue is a passage for liquid metal to flow from the end of a sprue to between the sprues. Its function is to introduce the liquid metal into the sprues, and when the die casting cools, it can be used to replenish and transfer static pressure. Therefore, the design points of the transverse gate are as follows:

(1) The cross-sectional area needs to gradually decrease from the end of the sprue to the sprue. Otherwise, if there is an increase in cross-sectional area in the sprue, it will cause negative pressure in the metal liquid flowing through it, which will inevitably absorb the air on the parting surface and increase the eddy current during the flow of the metal liquid;

(2) The cross-sectional area of the runner must be greater than that of the sprue in any case;

(3) The cross-sectional area of the primary runner in a multi cavity die-casting mold must be greater than the sum of the cross-sectional areas of the secondary runners;

(4) In order to reduce the flow resistance of the metal melt and achieve a balanced flow rate, the runner should not suddenly expand or contract;

(5) In order to improve the thermal balance conditions of die-casting molds, blind runners can be designed and installed according to process requirements. At the same time, blind runners also have the function of accommodating cold and dirty metals and gases.

3. Design of overflow channel
The function of the overflow channel is as follows:

(1) To accommodate the cold and dirty metal liquid that enters the mold cavity earliest, as well as the gas and oxide inclusions mixed in it, in order to prevent cold insulation, slag inclusion, and porosity in the die-casting parts;

(2) In the case of selecting a gating system, the setting of overflow channels can be designed together with the gating system to jointly control the flow state of the metal liquid, prevent local eddy currents, create favorable filling conditions, and avoid defects in the die-casting parts; Sometimes, it is also used to transfer areas with shrinkage, porosity, vortex entrapment, and cold joint marks;

(3) In some cases, the overflow groove can be used as the position where the top rod is pushed out during the demolding of the die casting to prevent deformation of the die casting and avoid leaving traces of the top rod on the surface of the die casting;

(4) Adjusting the temperature distribution of the mold cavity can improve the thermal equilibrium state of the mold cavity, especially for thin-walled or long filled distance die-casting parts, which can reduce phenomena such as cold shut, surface flow marks, and insufficient filling of the die-casting parts;

(5) When the clamping force of the die casting on the moving and fixed parts is relatively close, in order to prevent the die casting from remaining in the fixed mold during mold opening, some overflow grooves can be set on the moving mold to increase the clamping force of the die casting on the moving mold, ensuring that the die casting remains in the moving mold during mold opening and separation, and facilitating the subsequent ejection and demolding of the ejection mechanism;

(6) For directional vacuum die casting and vacuum die casting, the overflow groove is often used as the starting point for gas extraction.

4. Location selection of overflow channel
The selection of the location of the overflow channel should follow the following principles:

(1) The overflow tank should be set up at the confluence of two metal liquid streams to remove gases, coating residues, and cold metal liquids concentrated at that location;

(2) The overflow tank should be set up at the location where the metal liquid will first impact, in order to eliminate the gas and cold contaminated metal liquid in front of the metal liquid flow, thereby stabilizing the flow state and reducing eddy currents;

(3) The overflow groove should be located at the local wall thickness of the die casting, and its capacity and overflow port thickness should be increased to transfer gas, shrinkage porosity, and slag to this area, in order to improve the quality of the die casting wall thickness;

(4) Overflow slots should be opened on both sides of the sprue or in blind spots where metal liquid cannot be filled smoothly, in order to facilitate drainage and filling;

(5) The overflow groove should be located at the latest filling point of the metal liquid to improve the thermal balance state and filling and exhaust conditions of the die-casting mold;

(6) When designing the overflow groove, it is also important to note that after removing the overflow groove, it should not damage or affect the appearance of the die casting;

(7) It is not advisable to have multiple overflow ports on the same overflow tank to avoid the phenomenon of molten metal flowing back from the overflow tank to the mold cavity and causing reverse flow of molten metal.