# Lattice Structure for Improving Cooling Uniformity in HPDC Mould Corners
## 5 Results and Discussions
### Lattice Structure Sleeves' Effect on Cooling  
In this section, the cast/mould interface temperature was monitored when applying the three lattice structure sleeves and compared to the baseline design. The temperature distributions at the cast/mould interface, cast surface, and on the surfaces of the lattice structures and cooling pipe are shown in Figure 5. The figure demonstrates that the previously low temperatures on the two sides of the corner, initially around 240 \({}^{\circ}\)C for the baseline, as shown in Figure 5a, significantly increased and became closer to the corner temperature. Maintaining the mould interface temperature at 240 \({}^{\circ}\)C during moulding can expose the mould to suboptimal temperatures below the threshold for the subsequent cycle after demoulding and lubricant application. Previous studies [23] have indicated that increasing the die operating temperature from 205 \({}^{\circ}\)C to 315 \({}^{\circ}\)C can potentially double die production. This improvement in die service life is attributed to reduced dynamic thermal stress due to the smaller temperature differential between the injected hot aluminium and the mould in each cycle. Figure 5c shows that the temperature at the ends of the corner sides increases to values closer to the corner temperature when a 3 mm thick FCC lattice sleeve is applied, compared to the 1.5 mm sleeve thickness shown in Figure 5b. In all three cases, the temperature distribution in the cast part is improved relative to the baseline case. However, it is notable that the corner temperature also increases, suggesting that the imposed restrictions on heat transfer have an impact on cooling efficiency at the corner. To further assess the impact of lattice structure sleeves on corner temperature, the temperature variation along the side of the corner was evaluated using the probe points shown earlier in Figure 4. As illustrated in Figure 6, all three cases exhibit reduced temperature variation; however, the corner temperature increases as the thermal resistance imposed by the lattice structure increases. Specifically, the corner temperature rises from 340 \({}^{\circ}\)C to 370 \({}^{\circ}\)C and 400 \({}^{\circ}\)C for the 1.5 mm and 3 mm sleeves, respectively. By removing the closest lattice structure to the corner while retaining the others and using 1.5 mm sleeves, the corner temperature increases to 356 \({}^{\circ}\)C, which is still slightly higher than the corner temperature without the sleeves (16 \({}^{\circ}\)C difference). Nevertheless, this configuration results in more uniform cooling distribution across the cast part, with a small rise in corner temperature. The difference between the maximum and minimum temperatures decreases from 88 \({}^{\circ}\)C in the baseline case to 50 \({}^{\circ}\)C along the selected probe points, representing approximately a 42% improvement in temperature uniformity. The rate of heat transfer is directly proportional with the temperature difference and inversely proportional with thermal resistance. By adding additional thermal resistance using lattice structures on the two corner sides, the average mould/cast interface surface temperature increases, with a greater temperature rise on the sides compared to the corner, thereby improving temperature uniformity. The increase in corner temperature may lead to longer moulding times (cycle time) if the corner is the hottest location in the entire industrial mould. However, as long as the corner temperature remains lower than the hottest location, the method enhances uniformity without sacrificing cycle time. To reduce the corner temperature, additional techniques targeting hot spots, such as the use of bubblers or positioning cooling channels closer to the corners, can be combined with the lattice structure method. Therefore, this approach can complement existing methods to achieve better temperature uniformity. Figure 5: Temperature distribution in the cast, interface, lattice structure, and pipe surfaces.