Aluminum die casting is a kind of pressure casting parts, which uses the die casting machine with the casting mold installed. The aluminum or aluminum alloy heated to liquid state is poured into the feed port of the die casting machine, and the aluminum parts or aluminum alloy parts with the shape and size limited by the mold are cast by the die casting machine. Such parts are usually called aluminum die casting.

Advantages of aluminum die casting:

(1) It can manufacture metal parts with complex shape, clear outline and thin-walled deep cavity. Because of the high fluidity of molten metal at high pressure and high speed, it is possible to obtain metal parts difficult to be processed by other processes.

(2) The dimensional accuracy of die castings is high, up to grade it11-13, sometimes to grade it9, and the surface roughness reaches ra0.8-3.2um.

(3) The material utilization rate is high. Due to the high precision of die casting, only a small amount of machining can be used, and some die castings can be directly assembled. The utilization rate of the blank is about 90%.

(4) Production. Due to high-speed mold filling, short filling time, metal industry solidification, die casting operation cycle speed is fast. In various casting processes, die casting method has high productivity and is suitable for mass production.

(5) Easy to use inserts. It is easy to set the positioning mechanism on the die casting die, which is convenient for inlay casting, and can meet the local special performance requirements of the die casting.

Due to the poor adhesion of the coating on the surface of aluminum and aluminum alloy substrate, a conversion film is formed on the surface of aluminum and aluminum alloy after surface pretreatment. This can not only enhance the adhesion of the film, but also improve the performance. The surface treatment of aluminum and aluminum alloy is generally as follows: alkali washing → hot water cleaning → cold water cleaning → removing oxide film → cold water cleaning → chemical conversion → cold water cleaning → cold water cleaning → deionized water cleaning → draining → drying.

The reason of insufficient casting of aluminum die casting is that the heat conduction of metal mold is too fast and the melting point of aluminum is low, which leads to the liquid aluminum cooling ahead of time without filling the mold cavity. In order to avoid insufficient casting of aluminum castings, the following problems should be paid attention to:

1. Increase the casting temperature;

2. Heat and heat the mold, or spray heat preservation coating inside the mold;

3. Improve the gating system to make the casting smooth and shorten the filling time;

4. If the wall thickness is too thin, other processes should be considered, such as die casting.

In the production of die castings, in addition to the quality and dimensional accuracy of the surface and interior of castings, there is also a very important push mark, that is, the degree of casting deformation also needs to be controlled. In order to improve the combined press rate, lay a good quality foundation for the next process.

For some die castings, it is not because the dimensional accuracy of the storage parts can not meet the requirements and the machining process needs to be increased, but because the castings have various deformations. Through some special treatment, and according to the process parameters of die casting, the casting will generally achieve high dimensional accuracy, which can meet the needs of products.

In order to control the deformation of casting, the reason should be found out first. There are many reasons for casting deformation, some of which are regular, but others are not. The general reasons and control methods are introduced as follows:

(l) Control the casting time, do not shorten the mold retention time to improve productivity. The temperature of the casting is too high when it is out of the mold, so the casting is easy to deform after ejection because it is still in a soft state. However, the remaining time should not be too long, which will increase the ejection force and lead to deformation. Therefore, it is necessary to grasp the right time to reduce the deformation. The general regularity of casting deformation caused by the length of mold retention time is poor.

(2) During the design and manufacture of the die, it is necessary to make the casting wrapping force on the moving die greater than that on the fixed die. The method of increasing or decreasing the demoulding slope can be adopted until the proper size of forced die retention and the extruding belt (the push rod should be added at the corresponding position), otherwise, the casting will be deformed due to the part sticking to the fixed mold when opening the mold. Although not every casting has the same degree of deformation, the parts and forms of deformation are basically the same. Especially for the castings with symmetrical shapes of moving and fixed dies, it is necessary to increase the dynamic die and reduce the wrapping force of the fixed die, so that the wrapping force of the moving die is larger than that of the corresponding fixed die.

(3) In mold design, the push rod should be set to balance the jacking force. The so-called jacking force balance refers to the packing force, not just the distribution of the push rod in the shape of the casting. The push rod should be reinforced with steps as far as possible, and the length of the smooth section of the push rod should be shortened as far as possible, so as to increase the strength and rigidity of the push rod, and avoid the uneven jacking force caused by the elastic bending of the push rod during ejection The casting is deformed. At the same time, the die should have enough rigidity to avoid excessive deformation after being put into production.