Aluminum Alloy Die Casting Design Points
Tue Jul 11 15:13:01 CST 2023
1. Reasonably design the wall thickness of die castings
When designing the structure of aluminum alloy die castings, the wall thickness should be fully considered. The wall thickness is a factor with special significance in the die casting process. The wall thickness has a close relationship with the entire process specification, such as the calculation of filling time and the selection of ingate speed. , the calculation of solidification time, the analysis of mold temperature gradient, the effect of pressure (final specific pressure), the length of mold retention time, the level of casting ejection temperature and operating efficiency; if the design wall thickness is too thick, shrinkage cavity, trachoma and air hole will appear , Coarse internal crystal grains and other external surface defects will reduce the mechanical properties and increase the cost of parts; if the design wall thickness is too thin, it will cause poor filling of aluminum liquid, difficulty in forming, poor dissolution of aluminum alloy, and difficulty in filling the surface of castings , lack of material and other defects, and bring difficulties to the die-casting process; with the increase of pores in die-casting parts, the defects such as internal pores and shrinkage cavities increase. Therefore, under the premise of ensuring sufficient strength and rigidity of the casting, the casting wall Thick and keep the thickness of the section uniform.
2. Reasonable design of die casting ribs
For die-castings with large planes or thin walls, their strength and rigidity are poor, and they are easy to deform. At this time, the use of reinforcing ribs can effectively prevent the shrinkage and fracture of die-castings, eliminate deformation, and enhance the strength and rigidity of die-castings. For structures such as platforms and platforms, reinforcing ribs can be used to improve stress distribution and prevent root fractures. At the same time, reinforcing ribs can assist the flow of molten metal and improve the filling performance of castings. The thickness of the root of the reinforcing rib is not greater than the thickness of the wall here, and the general thickness is designed to be 0.8-2.0mm; the demoulding slope of the reinforcing rib is generally designed to be 1°-3°, and the higher the height, the smaller the design demoulding slope; Fillets need to be added to the root of the ribs to avoid sharp changes in the cross-section of the part, and at the same time assist the flow of molten metal, reduce the stress concentration of the part, and improve the strength of the part. The fillet is generally close to the wall thickness here; the height of the rib generally does not exceed 5 of its thickness Times, the thickness of the reinforcing rib is generally required to be uniform, if the design is too thin, the reinforcing rib itself is easy to break, if it is too thick, it is easy to produce defects such as depressions and pores.
3. Reasonable design of die casting slope
The role of the draft angle of the die casting is to reduce the friction between the casting and the mold cavity, making it easy to take out the casting; ensuring that the die casting surface is not strained, and at the same time prolonging the life of the mold. The draft angle is related to the height of the die casting, the larger the height, the smaller the draft angle. In general, the draft slope of the outer surface of the die casting is about 1/2 of the draft slope of the inner cavity, but in actual design, the draft slope of the inner and outer surfaces of the die casting can be designed to be consistent to maintain the wall thickness Uniform, simplified structure design.
4. Reasonably design the machining allowance
When designing die-casting parts, machining should be avoided as much as possible. Machining will destroy the dense layer on the surface of the part and affect the mechanical properties of the part; it will expose the internal pores of the die-casting part, affecting the surface quality and increasing the cost of the part. When machining cannot be avoided for die-casting parts, designs with large cutting volume should be avoided as far as possible, and the structural design should be as easy as possible for machining or reduce the machining area and reduce machining costs.
Die-casting parts have higher dimensional accuracy requirements, or some plane surface roughness requirements, and the die-casting process is difficult to meet the requirements. At this time, follow-up processing is required. For this part of the structure, the processing allowance should be reserved as much as possible during design. The strength and hardness of the surface of die-casting parts are higher than those of the interior. When machining, attention should be paid to retaining the density of the surface, so the machining allowance should not be excessive. Too much machining may cause pores and outer surface defects.
5. Spraying design of aluminum alloy die castings
The surface spraying design of die castings generally adopts the powder spraying process, and its principle is electrostatic powder spraying: the coating is mainly polarized through the electrodes, and then the object to be sprayed is charged with the opposite charge, and the powder is evenly attached to the surface of the object under the action of the electric field force . Features of powder spraying process: powder electrostatic spraying will not cause air pollution, powder can be recycled to reduce material consumption costs, coating performance is good in acid resistance, alkali resistance and corrosion resistance.