# Lattice Structure for Improving Cooling Uniformity in HPDC Mould Corners
## 1 Introduction and Literature Review  
Various techniques have been developed and implemented to design conformal cooling channels in complex geometries to achieve the desired cooling throughout the cast [1]. However, there are still challenges in cooling small or thin intrusions within the mould, particularly at sharp corners. Internal corners of the cast are especially difficult to cool uniformly due to their relatively large volume and limited surface area available for cooling, as compared to the two sides of the corner. Consequently, internal corners suffer from higher temperatures due to the restricted surface area exposed to cooling channels [2], while external corners often experience overcooling [3]. The insufficient cooling in internal corners results in delayed solidification, increasing the risk of crack formation due to tension stresses induced by the contraction of adjacent solidified sections [4, 5]. Additionally, soldering defects commonly occur in these areas due to the presence of hot spots [6]. The issue can be addressed by employing smaller cooling channels or positioning the channels closer to the mould/cast surface. However, producing smaller channels is associated with an increase in pressure drop, as well as limitations imposed by the 3D printing process. Additionally, minor contamination on the surfaces of small channels can significantly alter their dimensions, affecting coolant flow rate, heat transfer efficiency,and distribution unless multiple, precisely controlled separate cooling channels are used. Another approach to enhance cooling at specific locations is to position the channels closer to the cast cavity. This method, however, is limited by the substantial increase in dynamic thermal stresses, which can adversely affect the service life of the mould. Several methods have been developed to address localised cooling within the tool. One approach involves using bubblers [7], a commonly employed technique for targeting specific regions in the mould. However, accessing the target regions can be challenging in some cases, and bubblers usually also cool all the areas surrounding its location and may lead to overcooling areas that are already sufficiently cooled. Another technique involves inserting a more conductive material between the regions requiring enhanced cooling and the cooling channels [8; 9]. This method, while promising, faces technical limitations such as mismatched thermal expansion and the complexity of fabricating two materials without defects. A further proposed solution is the incorporation of internal fins or lattice structures within the cooling channels to improve cooling in specific regions [10; 11]. This approach increases the surface area in contact with the coolant. Although integrating fins or lattice structures during the 3D printing process can be achieved without significant additional cost, it necessitates larger channel sizes and may not be practical for small cooling channels due to reduced fluid flow cross-section and potential for partial blockage over extended operation periods. Local overheating is a well-recognized issue in die casting. However, overcooling in certain regions within the die or cavity can also lead to casting defects [12]. Overcooling typically occurs when casting thin sections with complex geometries, such as fins, or when attempting to use bubblers or cooling channels to target specific areas in an intrusion section. In many cases, the sides of these intrusions can become overcooled. Similarly, internal corners may experience excessive cooling on their sides. The overheated section in the mould cavity can be controlled to some extent through external cooling sprays, which can be directed to these specific locations to achieve optimal die temperatures, generally ranging from approximately 150 \({}^{\circ}\)C to 320 \({}^{\circ}\)C, to ensure high-quality casting [13]. However, excessive cooling of the die surface can lead to severe thermal shocks upon contact with molten metal.