The rationality of die-casting part design directly affects the entire die-casting process. When designing die-cast parts, it's essential to fully consider their structural features and the specific requirements of the die-casting process, aiming to minimize defects that may occur during die-casting. By adopting the optimal design solution, we can maximize the quality of the die-cast parts.

1. Properly design the die-cast part wall thickness

When designing the structural layout of aluminum alloy die-cast parts, it's crucial to carefully consider wall thickness, as this parameter plays a uniquely important role in the die-casting process. Wall thickness is closely tied to various aspects of the overall process specifications, including calculations for filling time, selection of runner velocity, determination of solidification duration, analysis of mold temperature gradients, assessment of pressure effects (specifically, the final injection pressure), optimization of holding time, control of ejection temperatures, and even operational efficiency. If the wall thickness is designed too thick, external defects such as shrinkage cavities, porosity, and coarse internal grain structures may occur, leading to reduced mechanical performance and increased part weight—ultimately driving up production costs. Conversely, if the wall thickness is too thin, it can result in poor aluminum melt filling, making it difficult to achieve proper shaping. This often leads to inadequate alloy dissolution, causing issues like surface filling defects or material shortages, which further complicate the die-casting process. Moreover, as the number of air pockets within the casting increases, so do internal defects like porosity and shrinkage cavities. Therefore, while ensuring that the castings maintain adequate strength and rigidity, designers should strive to minimize wall thickness as much as possible, while also maintaining consistent and uniform cross-sectional thickness throughout the part.

2. Properly design reinforcing ribs for die-cast parts

For large flat surfaces or thin-walled die-cast parts, which typically exhibit poor strength and rigidity and are prone to deformation, the use of ribs can effectively prevent shrinkage and cracking, eliminate distortion, and significantly enhance both the strength and stiffness of the component. For excessively tall columns or pedestals, ribs can help optimize stress distribution, reducing the risk of root fractures. Additionally, ribs facilitate the smooth flow of molten metal during casting, improving the filling performance of the part. The root thickness of the rib should not exceed the thickness of the surrounding wall; typically, rib thickness is designed to range between 0.8 and 2.0 mm. As for the draft angle of the ribs, it is generally set between 1° and 3°—with taller ribs requiring a smaller draft angle. Importantly, a fillet must be added at the root of each rib to avoid abrupt changes in the part’s cross-section, while also aiding the flow of molten metal, minimizing stress concentrations, and boosting the overall strength of the component. The radius of the fillet usually approximates the local wall thickness. Finally, the height of the rib should ideally not surpass five times its thickness. Uniform rib thickness is crucial: if the rib is too thin, it may easily fracture under stress; conversely, if it’s too thick, defects such as sink marks or porosity are more likely to occur.

3. Properly design the draft angle for die-cast parts

The draft angle of die-cast parts serves to reduce friction between the casting and the mold cavity, making it easier to remove the part; it also ensures that the die-cast surface remains undamaged while helping extend the mold's lifespan. The draft angle is closely related to the height of the die-cast part—specifically, the greater the height, the smaller the draft angle required. Typically, the draft angle on the outer surface of a die-cast part is about half that of the inner cavity. However, in practical design, the draft angles for both the inner and outer surfaces can be set identically to maintain uniform wall thickness and simplify the overall structural design.

4. Reasonably design machining allowances

When designing die-cast parts, machining should be avoided as much as possible, since it can damage the dense surface layer of the part and compromise its mechanical properties. Additionally, machining may expose internal porosity within the die casting, negatively affecting surface quality, while also driving up part costs. If machining is unavoidable for die-cast components, designs that require large cutting volumes should be minimized. Instead, the structural design should prioritize features that facilitate easy machining or reduce the area needing machining, thereby lowering overall machining costs.

For die-cast parts where certain dimensions require high precision, or where specific planar surfaces demand low surface roughness, it can be challenging to meet these exacting standards solely through the die-casting process. In such cases, subsequent machining becomes necessary. Therefore, when designing these components, engineers should carefully account for and reserve adequate machining allowances in advance. It’s worth noting that the surface of a die-cast part typically exhibits higher strength and hardness compared to its interior. Consequently, during machining, it’s crucial to preserve the integrity and density of the surface layer. However, excessive machining allowances must be avoided, as over-machining could inadvertently lead to porosity and surface defects on the exterior.

5. Spray Coating Design for Aluminum Alloy Die Castings

Die-cast parts typically undergo surface coating using a powder-spraying process, which operates on the principle of electrostatic powder coating: The coating material is polarized via electrodes, while the object to be coated is given an opposite charge. Under the influence of the electric field, the powdered coating adheres evenly to the object's surface. Key features of powder-spraying technology include: It produces no air pollution, and the recovered powder can be reused, significantly reducing material costs. Additionally, the resulting coating exhibits excellent resistance to acids, alkalis, and corrosion.