Die casting wall thickness, connection type and fillet of the connection
The thickness, connection type, and fillet radius of die-cast parts are key elements in casting structure design, directly affecting the molding quality, mechanical properties, and service life of the die-cast part. Proper design of these parameters can reduce defects in the die-casting process, improve production efficiency, and reduce production costs. When designing die-cast parts, it is necessary to comprehensively consider factors such as the die-casting properties of the alloy, the mold structure, and the operating environment. The wall thickness, connection type, and fillet radius must be optimized to ensure that the die-cast part meets the requirements of the application.
The wall thickness of die-cast parts must be designed to be reasonable and uniform. Excessively thick walls slow the cooling of the molten metal during solidification, leading to defects such as shrinkage cavities and porosity, while also increasing the weight and cost of the casting. Excessively thin walls can compromise the fluidity of the molten metal, making it prone to problems such as underfilling and cold shuts, compromising the integrity of the casting. Different die-casting alloys have different minimum wall thickness requirements. For example, zinc alloys have excellent fluidity, allowing for a minimum wall thickness of 0.5-1mm; aluminum alloys typically have a minimum wall thickness of 1-2mm; and copper alloys have poor fluidity, with a minimum wall thickness of 2-3mm. Furthermore, wall thickness should be as uniform as possible to avoid sudden changes in thickness. These can cause uneven shrinkage during cooling, leading to deformation and cracking. Where necessary, gradual transitions should be used, with the transition length at least 3-5 times the wall thickness difference, to reduce stress concentration.
The connection type of a die-cast part’s walls significantly impacts its strength and molding quality. Common connection types include right-angle, bevel, and fillet. While the right-angle connection is the simplest, it can easily generate stress concentration during the die-casting process. Furthermore, the molten metal flow is impeded at right angles, leading to eddies and air entanglement, which can cause defects such as porosity and shrinkage, while also reducing the strength of the joint. Bevel connections, by replacing right angles with bevels at a certain angle, can improve molten metal flow and reduce stress concentration, but the effect is not as pronounced as fillet connections. Fillet connections are the most ideal connection type, ensuring smooth molten metal flow, avoiding eddies and air entanglement, and reducing defects. Furthermore, filleting disperses stress, improving joint strength and fatigue resistance. Fillet connections should be preferred during design, and the fillet radius should be appropriately increased for areas subject to higher stresses.
The fillet design of joints not only affects the mechanical properties of the casting but also has a significant impact on the performance of the die-casting process. A fillet radius that is too small will fail to disperse stress and improve molten metal flow. A fillet radius that is too large will increase the local thickness of the casting, leading to defects such as shrinkage cavities and porosity. Generally speaking, the fillet radius should be determined based on the thickness of the connecting walls. When the two walls are of equal thickness, the fillet radius should be 0.2-0.5 times the wall thickness. When the two walls are of unequal thickness, the fillet radius should be 0.5-1 times the thickness of the thinner wall. For external corners, the fillet radius can be appropriately reduced; for internal corners, the fillet radius should be appropriately increased to facilitate molten metal filling and reduce stress concentration. Furthermore, uniform fillet radius is crucial, avoiding sudden changes in fillet radius within the same joint. This can lead to poor molten metal flow and stress concentration, compromising casting quality.
The complexity of the casting structure and the functional requirements will also affect the wall thickness, connection form and fillet design. For die castings with complex shapes, the wall thickness must be reasonably adjusted while ensuring strength to avoid areas that are too thick or too thin. For example, in castings with ribs, the thickness of the ribs is usually 0.5-0.7 times the thickness of the adjacent walls, which can enhance the rigidity of the casting without causing defects due to excessive thickness. The choice of connection form needs to be determined according to the stress conditions and assembly requirements of the casting. For connection parts that bear greater loads, a reinforced connection form should be adopted, such as adding reinforcing ribs or using thick wall transitions, while combining larger fillet radii to increase strength. Under the premise of meeting functional requirements, the connection form should be simplified as much as possible, and complex corners and connection structures should be reduced to reduce the difficulty of mold manufacturing and the complexity of die casting process control.
The mold design and die-casting process must be compatible with the wall thickness, connection type, and corner radius of the die-casting. For castings with uniform wall thickness, reasonable connections, and appropriately radiused corners, the mold cavity design is relatively simple, making the filling and solidification of the molten metal easier to control and reducing defects. The mold’s runner and venting system design should be optimized based on the wall thickness distribution and connection type of the casting to ensure that the molten metal can be smoothly filled into all areas, especially those with thinner walls and complex connections. In terms of die-casting process parameters, for thicker-walled castings, the injection pressure and holding time should be appropriately increased to reduce shrinkage cavities and porosity; for thinner-walled castings, the injection speed and mold temperature should be increased to ensure complete filling. Through the coordinated optimization of mold design, process parameters, and casting structure design, the performance advantages of die-castings can be fully utilized, ensuring the stability and reliability of product quality.
In summary, the design of die-casting wall thickness, connection form, and joint radius is a systematic process that requires comprehensive consideration of multiple factors. A sound design can improve the molding quality, mechanical properties, and service life of die-casting parts, while reducing production costs and difficulty. In practice, these parameters should be optimized based on specific application requirements and production conditions, and closely integrated with mold design and die-casting process to achieve high-quality die-casting products.
