Introduction: In recent years, requirements for automobiles have gradually shifted towards high performance, low pollution, and low energy consumption. Since vehicle quality plays a decisive role in fuel economy, lightweight design has become an important indicator in automotive design. Due to development of high-pressure die-casting technology, and because aluminum alloys have high strength, low density, corrosion resistance, and easy recyclability, application of die-cast aluminum alloys in automobiles has increased significantly. Die-cast aluminum alloy products account for 54% to 70% of aluminum used in automobiles. During die-casting production process, molten metal fills mold cavity at extremely high speed under high pressure, making castings prone to defects such as porosity, shrinkage cavities, and shrinkage porosity, affecting quality of castings and even leading to scrap.
Radiator cover is a crucial component of automotive cooling system, requiring excellent sealing and sufficient strength to withstand varying degrees of vehicle vibration during operation. It is typically made of aluminum alloy. This study uses AnyCasting software to numerically simulate filling and solidification processes during die-casting of radiator cover. Orthogonal experiments were conducted to optimize die-casting process parameters and mitigate defects. Finally, a prototype was manufactured to provide a reference for actual production.
Automotive radiator cover casting studied is made of ADC12 aluminum alloy, and its chemical composition is shown in Table 1.
A 3D model of radiator cover was created using UG software, as shown in Figure 1. Casting has a maximum outline dimension of 296 mm * 223 mm * 175 mm, a maximum wall thickness of 19.88 mm, an average wall thickness of 5.71 mm, a volume of 1163.22 cm³, and a mass of 3.14 kg. This casting is a shell-type part with an irregular structure, uneven wall thickness, numerous cavities, and multiple concave areas, resulting in a complex overall shape. After calculating clamping force, a DCC900 cold chamber die-casting machine was used for production.
Gating system plays a crucial role in flow direction of molten metal, venting conditions, heat distribution in mold, pressure transmission, filling time, and flow rate of molten metal at ingate. This casting is a shell with a complex overall shape and uneven wall thickness, making forming quite difficult. Gating system layout is shown in Figure 2.

Table 1 Chemical composition (%) of ADC12 aluminum alloy

 

Figure 1 3D view of automotive radiator cover casting

 

Figure 2 Location of gating system in automotive radiator cover casting
A 3D model of casting and gating system was created using UG software, imported into AnyCasting software. Casting was meshed, resulting in 50,084,892 meshes. Casting material is ADC12 alloy, and mold material is H13 steel.
Heat transfer coefficient between molten metal and mold is 0.15 W/(cm²·K), between mold and cooling channels is 0.40 W/(cm²·K), between mold and environment is 0.001 W/(cm²·K). During high-pressure die casting, room temperature is 25 ℃, pouring temperature is 640 ℃, mold preheating temperature is 200 ℃, low-speed injection velocity is 0.3 m/s, and high-speed injection velocity is 4 m/s.
Casting filling sequence is shown in Figure 3. It can be seen that the entire filling process takes 0.3968 s, with low-speed injection time being 0.3533 s and high-speed injection time being 0.0435 s. During low-speed filling stage, injection velocity is 0.3 m/s to prevent molten metal from splashing out of feed port and to allow sufficient time for air in pressure chamber to escape. Solidification field of casting is shown in Figure 4, and the entire solidification process took 106.0472 s. Air entrapment defect in casting is shown in Figure 5, and air entrapment sequence was analyzed using a reverse cloud map. Defect analysis is shown in Figure 6. Using probabilistic defect parameter module in AnyCasting software, residual melt modulus method was used to analyze shrinkage cavities, porosity, other defects on both exterior and interior of casting. Activating profile and observing interior of casting reveals bright areas, which are locations of shrinkage cavities, porosity, and other defects. These defects are mostly distributed in complex structures and thicker walls, such as corners, reinforcing ribs, and core-pulling areas. Defect analysis shows that defects in areas such as sprue and overflow channels do not affect the overall structure of casting and are considered redundant. They can be removed during machining. Further process optimization is needed to address internal defects in casting.

 

Figure 3. Filling sequence diagram of automotive radiator cover

 

Figure 4. Solidification sequence diagram of automotive radiator cover casting

 

Figure 5. Analysis of air entrapment defects in automotive radiator cover casting

 

Figure 6. Defect analysis diagram at different locations of casting
Based on above numerical simulation results, cooling system was optimized to address defects such as shrinkage cavities appearing inside casting. Cooling water channels were arranged at locations where defects occurred to accelerate cooling rate in that area, improve solidification sequence of casting, avoid or improve defects such as shrinkage cavities and porosity caused by solidification speed and sequence. A 3D model of cooling water circuit was created using UG software and imported into AnyCasting software, setting inlet water temperature to 25 ℃ and outlet water temperature to 70 ℃. Casting cooling system is shown in Figure 7. Figure 8 shows optimized defect analysis diagram. Comparison with Figure 6 reveals that defects at the bottom left side of casting in Figure 8b are significantly reduced, and most defects located in casting shell at the bottom of casting in Figure 8c are eliminated. A small number of defects exist near ingate and can be further optimized by adjusting process parameters.

 

Figure 7 Distribution of casting cooling system

 

Figure 8 Optimized casting defect analysis diagram
Casting temperature, mold preheating temperature, and injection speed were selected as factors in orthogonal experiment. A factor level table for orthogonal experiment was designed, as shown in Table 2. Orthogonal experiment was designed with 3 factors and 3 levels, using an L9(33) orthogonal table. Simulation analysis was performed using AnyCasting software, and shrinkage cavity volume of casting was calculated using quantitative analysis module in software. This volume was used as an evaluation index, and Table 3 shows orthogonal experiment results.

Table 2 Orthogonal factor level table

Table 3 Orthogonal experiment scheme and results table
To determine influence of three factors on shrinkage cavity volume, simulation results were analyzed, and a shrinkage cavity volume difference analysis table was created, as shown in Table 4. Table 4 shows that influence of three factors on shrinkage cavity volume is as follows: mold preheating temperature > injection speed > casting temperature. Mold preheating temperature has the most significant influence on shrinkage cavity volume, while casting temperature and injection speed have relatively small influences. Figure 9 shows main effect diagram of process parameters on mean shrinkage cavity volume. It can be seen that shrinkage cavity volume of casting is minimized when pouring temperature is 660 ℃, mold preheating temperature is 180 ℃, and injection speed is 3 m/s.

Table 4: Shrinkage Cavity Volume Variation Analysis Table

 

Figure 9: Main Effect Diagram of Process Parameters on Mean Shrinkage Cavity Volume
To further verify feasibility of optimized die-casting process and mold structure, trial production was conducted using a Lijing DCC900 die-casting machine with a pouring temperature of 680 ℃, a mold preheating temperature of 180 ℃, and an injection speed of 3 m/s. Prototype casting is shown in Figure 10. Figure 10a shows that casting quality is good, with no surface defects. X-ray flaw detectors were used to inspect internal structure of casting; results are shown in Figure 10b. It is evident that there are no obvious shrinkage cavities or porosity defects inside casting, and casting quality meets production requirements.

 

Figure 10. Actual casting image and X-ray inspection image
Conclusions
(1) Process analysis was conducted on cooler cover casting to analyze its structural characteristics. A 3D model of casting and a die-casting mold design were created using UG software.
(2) An orthogonal experiment was designed, selecting pouring temperature, mold preheating temperature, and injection speed as factors. Nine sets of experiments were conducted through numerical simulation, using shrinkage volume as evaluation criterion. Optimized process parameters were obtained: pouring temperature 680 ℃, mold preheating temperature 180 ℃, and injection speed 3 m/s.
(3) Optimized scheme was used to trial-produce product, and X-ray inspection was performed on trial-produced product. Results showed that product quality was good.