Die-casting production process is simple and concentrated, process flow is short, and workpieces produced have smooth surfaces, high dimensional accuracy, and good mechanical properties, so it has been widely used in industrial production. ES8B2 upper cover produced by die-casting process has complex structures at both ends of casting, which results in an irregular filling process and is prone to defects such as air entrainment. Process design requires repeated adjustments. During die-casting production process, Flow-3D software is used to numerically simulate process, and die-casting process is optimized based on simulation results to improve quality of castings, reduce scrap rate, and reduce production costs.
Based on structural characteristics of ES8B2 upper cover, gating system and overflow system were designed, and Flow-3D software was used to simulate casting process plan. Simulation results of initial plan show that temperature of gating system and its surrounding areas is higher, temperatures of both ends of cavity and overflow groove are lower, and more air entrainment is generated at both ends of cavity. Optimize initial plan, change shape of runner, adjust position and size of overflow tank. Simulation results of optimized plan showed that temperature distribution was high in the middle and low at both ends, and more air entrainment appeared at both ends of cavity; plan was optimized again to increase area of inner gate, area of overflow port, volume of overflow tank and cross-sectional area of connecting ribs. Simulation results show that air entrainment in mold cavity is significantly reduced, pores in casting are reduced, and defects are reduced. Actual production casting has a smooth surface and fewer defects, which meets production requirements.
Graphical results
Volume of ES8B2 upper cover casting is 205.57cm3, curved surface area is 828.8cm2, weight is 555g, and the overall size is φ130mm*140.8mm. Main body of casting is a cylinder (see Figure 1). Inner diameter of cylinder is 45.8mm, and outer diameter is 55mm, one end of cylinder is a combined structure of a cuboid and a cylinder, and the other end is a stepped complex cylindrical structure, with an average wall thickness of 4.03mm. J1116G die-casting machine is selected and produced in the form of 1 mold with 1 piece. Casting material is ADC12 aluminum alloy, and chemical composition is shown in Table 1.

 

Figure 1 Casting solid three-dimensional model

Table 1 Chemical composition of ADC12 aluminum alloy (%)

 

Figure 2 Schematic diagram of parting surface of casting

 

Figure 3 Diagram of casting with pouring and overflow system
If die-casting process is unreasonable, die-casting parts will produce defects such as shrinkage cavities, shrinkage porosity, and cracks. In order to reduce costs, Flow-3D software is used to simulate and optimize design plan. Convert three-dimensional drawing to STL format, set pouring temperature to 680℃, mold temperature to 200℃, filling speed to 30m/s, and grid unit size to 0.12mm. Import solid model in STL format into Flow-3D software for mesh division, and finally conduct simulation.

 

Figure 4 Temperature field distribution of initial plan casting filling process

 

Figure 5 Air entrainment distribution in initial solution casting
Simulation of optimization plan 1: Adjust pouring system and overflow system. Design of inner gate remains unchanged, and shape of horizontal runner is improved to give more space to side core-pulling mechanism. Cross-sectional area of runner and inner gate are same, area of connection end of runner and sprue is Ar=1.78Ag, thickness is 10mm, and length is 25mm; size of sprue remains unchanged. Size design of overflow tank, size of overflow tank at the end of thin tube is 36mm*24mm*20mm; size of two overflow tanks near end of the thin tube is 30mm*22 mm*12mm; size of two overflow tanks in the middle is 25mm*22mm*12mm; dimensions of 4 overflow troughs on the right end are: overflow trough size at platform is 36mm*24mm*15mm; size of overflow trough at two holes is 30mm*20mm*12mm; last dimension is 30mm* 20mm*12mm; overflow grooves are connected by connecting ribs, and their cross-section is a semicircle of φ8mm. Shape is shown in Figure 6.

 

Figure 6 Three-dimensional diagram of casting pouring system of optimization plan 1

 

Figure 7 Temperature field distribution of casting filling process in optimization plan 1

 

Figure 8 Gas entrainment distribution of castings under optimization plan 1
It can be seen that design changes have caused more air entrainment. Compared with initial plan, more serious air entrainment appeared at both ends of casting, and there was more air entrainment in rough barrel part. Reasons for this situation are that overflow port and overflow groove are small and unreasonable in location, which cannot effectively collect gas; cross-sectional area of inner gate is small; and design of lateral runner is unreasonable. Compared with initial plan, this design has many modified parts, and air entrainment volume is not well controlled, so it needs to be optimized again.
Simulation of optimization plan 2: Filling time is set to 0.054s, and Ag=185.57mm2 is calculated. In order to facilitate mold filling, area of inner gate should be appropriately increased, Ag=195mm2, and length of inner gate should be 3mm. Based on area of inner gate, calculated width is 65mm and height is 3mm. Cross-sectional area of smooth connection between lateral runner and inner gate is Ar=2.75Ag, thickness is 10mm, and length is 55mm; cross-sectional area connected to sprue is 300mm2. Adjust position and size of overflow groove to enhance its ability to collect gas in cavity. Dimensions of overflow trough include size of overflow trough at the end of thin barrel, which is 36mm*24mm*20mm; size of two overflow troughs near end of thin barrel is 32mm*24mm*14mm; size of two overflow troughs in the middle is 20mm* 28mm*12mm; dimensions of 4 overflow troughs at the far right end are: overflow trough size at platform is 36mm*24mm*15mm; overflow trough size at the two holes is 30mm*20mm*12mm; last size is 30mm *20mm*12mm, connecting rib cross-section is a semicircle of φ12mm, its shape is shown in Figure 9.

 

Figure 9 Three-dimensional diagram of casting pouring system of optimization plan 2

 

Figure 10 Optimization scheme 2 temperature field distribution during casting filling process

 

Figure 11 Gas entrainment distribution of castings under optimization scheme 2

 

Figure 12 Actual production castings
It can be seen that compared with initial plan, optimized plan appropriately adds overflow grooves at confluence and both ends of casting, which can better discharge gas in cavity and reduce pore defects in casting. Places with high air entrainment volumes are located at overflow trough. Theoretically, gas content in casting is low and does not affect quality of casting. It can be seen from Figure 12 that surface of casting is smooth, has no defects, has fewer pores and pinholes, which meets requirements.