1. Influence of wall thickness on performance.
(1) the wall thickness of die casting is related to performance.
(2) the wall thickness of the die casting affects the filling cavity state of the metal liquid, and finally influences the surface quality of the casting.
(3) the wall thickness of die casting affects the consumption and cost of metal.
In the design of die casting, the reliability of the strength and rigidity is often guaranteed, and the better the wall thickness, the better. In fact, as the wall thickness increases, the mechanical properties of die castings decrease obviously. The reason is that during the die-casting process, when the metal liquid enters the human cavity with high pressure and high speed, it quickly cools and solidifies after contact with the cavity surface. A fine grain structure is formed on the surface of the chilled die casting. The thickness of the dense fine grain structure is about 0.05 ~ 0.3mm. Therefore, the thin-walled die casting has higher mechanical properties. Instead, thick wall die casting center layer of grain is bigger, when feeding, poor exhaust easy generation internal shrinkage, porosity, defects such as surface sag, the mechanical properties of die casting and decreased with the increase of wall thickness, as shown in figure 4-16.
The effect of casting thickness on performance.
As the wall increases, the metal is consumed more and the cost increases. However, if the minimum wall thickness is calculated from the structure, and the complexity of the casting is ignored, the state of the liquid metal filling cavity is not ideal, and the defects such as forming defects are formed.
2. Minimum wall thickness
Under the premise that meet the requirements of product function, considering the influence of each process after process, with the lowest consumption of metal, and achieved good formability and manufacturability, select normal uniform wall thickness is preferred. See table 4-2 for specific dimensions. The wall thickness of die casting is generally 1~5 mm.
Table 4-2 the minimum wall thickness and normal wall thickness of die castings.
Some castings are limited by function and appearance, which cannot be designed to be uniform wall thickness, for thick, thin and uneven structure. The inner and outer circles also transition accordingly. Avoid casting defects due to sudden changes in wall thickness.
3. Uniform wall thickness design.
The wall thickness is as uniform as possible by reducing the casting area or some parts of the casting cavity. As shown in fig.4-17, the design of (a) is changed to (b) design, which keeps the casting appearance structure and assembly hole unchanged, and reduces the thickness of the thick wall, avoiding the defects in the thick wall and reducing the cost of materials. Figure 4-18 is a uniform wall thickness design.
4. The design of casting wall thickness considering electroplating.
In order to obtain the uniform coating, the electroplating is considered in the design of the die casting parts which need to be electroplated.
FIG. 4-19 shows the design of wall thickness to suit the requirements of electroplating, thus obtaining a uniform electroplating layer.