The essence of high pressure die casting (die casting for short) is a method that makes liquid or semi-liquid metal fill the cavity of die casting mold (die casting mold) at a high speed under high pressure, and forms and solidifies under pressure to obtain the casting.

First, high pressure casting process

1.1 High pressure casting plane layout

At present, the general die-casting island will consider the following configuration; Die-casting machine with vacuum, heat preservation furnace is equipped with quantitative casting system, do and product with the type of spraying system, shorten the spraying time, the robot to take parts, slag bag, code cutting and other work, the last cutting to the gate system; The die-casting island can also be upgraded for automated cleaning under high volume conditions.

1.2 APPLICATION of CAE simulation software

CAE analysis is more and more widely used in die casting industry, represented by PROCAST, MAGMA, flow-3D, etc. According to the calculation results of filling flow and velocity distribution, the simulation can accurately predict the defects such as enrolling, inclusion and bad filling, which greatly improves the yield and saves a very objective cost. It is a very useful tool to quickly and scientifically design the whole casting system (gate, sprue and overflow tank, etc.) for die casting. Optimize casting process parameters, reduce the number of mold testing, reduce casting cost, improve product quality. CAE software was used for general analysis of filling, solidification, porosity distribution and velocity distribution reports (as shown in Figure 2).

1.3 Application of vacuum die casting

With the continuous supply of product quality requirements, the use of vacuum to solve the problem of filling and air tightness of castings has been well developed, and vacuum valve is generally used, the most commonly used vacuum valve has the following two structures. Figure 3 is the schematic diagram of the vacuum valve. Like ordinary die casting process, after aluminum water enters the chamber, vacuumization begins to start. Then, when the die casting machine starts at high speed, the kinetic energy of aluminum water is relied on to touch the spring plate of the vacuum valve. When using a mechanical vacuum valve, it is generally closed when preheating the mold. When the preheating is complete, the vacuum valve can be used only when the high speed and pressurization is started. Mechanical vacuum valve has the advantages of simple use, but the processing accuracy of vacuum valve is high, and the cost of vacuum valve is relatively high. Figure 4 is the schematic diagram of the hydraulic vacuum valve. The principle of the mechanical vacuum valve is the same. When the punch starts, the vacuum starts, but the principle of closing the vacuum valve is different. When the hydraulic vacuum valve is generally started at high speed, the type is sent to the hydraulic system of the vacuum valve at the same time, and the vacuum valve is closed. The cost of hydraulic vacuum valve is relatively low, but it requires that the die casting process parameters and mold design should match, otherwise the aluminum water die casting into the vacuum valve will cause blockage.

Two, die casting machine new technology application

1. High vacuum die casting technology

At present, the imported die casting machine is represented by Buhler and Fuller, and the two die casting machine suppliers are good at high vacuum application. Buhler's high vacuum technology, mainly in the pressure chamber and the mold back design of the vacuum interface, easy to pump air from the beginning of the pressure chamber, while the vacuum on the mold back to help vacuum the cavity more thoroughly. And Fulai's high vacuum technology will directly seal the chamber, at the bottom of the chamber design a pipe directly inserted into the insulation furnace, the mold to complete the seal, using the cavity vacuum stroke negative pressure, the aluminum liquid in the insulation furnace into the chamber, and then die casting molding. The biggest advantage of this technology is that it avoids the contact stroke oxidation of aluminum water and air and can be subjected to T6 heat treatment, which has been mass-produced in Europe for structural parts of automobiles.

2. Quick mold change

Improving production efficiency and reducing manufacturing cost is the goal of every manufacturing enterprise. OEE is internationally defined as: OEE stands for Overall Equipment Effectiveness. It is composed of availability, performance and quality index, namely: OEE= availability X performance X quality index. For die casting, die exchange is one of the six major losses. Rapid mold change has become the goal of lean production. Mold exchange can generally be defined as the time from the last qualified product to the next set of mold exchange to produce the first qualified product on the die casting machine. In Japan for 800 tons of cold chamber die casting machine, the general die exchange time is 10-20 minutes; In China, the mold exchange time is relatively long, more than 10 hours is also very common. In addition to schedule management, operation standardization and tool management, die exchange is related to the evaluation of whether the conditions for die change are as follows:

(a) the mold can quickly positioning (b) the mold can fast fixture (die or clamping screw) (c) between the die casting machine and the mold ejection structure whether can quick links (d) core pulling oil cylinder can quick links (e) whether the oil cylinder stroke signal can quick links (f) whether the process parameters to read very fast (g) Whether the preheating modulus is the lowest (if necessary, the mold temperature machine is used to preheat the mold).

Three, die casting products

At present, aluminum alloy die casting products are divided into three categories according to the amount. The first category is automobile, motorcycle, engine transmission shell represented by engine engine, cylinder body and so on. The second type is base station shell and filter shell represented by network communication, and the third type is body structure with higher mechanical performance requirements. As shown in the figure, it is a typical aluminum alloy die casting product:

Fourth, concluding remarks

Aluminum alloy has high specific strength and good corrosion resistance, excellent electrical conductivity. Under the social environment of energy saving and emission reduction and green environmental protection, aluminum alloy die casting has developed rapidly in China. I believe that in the near future, aluminum alloy products will be more diversified. The main deformation is in the following aspects; 1) With the development of products, it will drive the development of new die cast aluminum alloy materials, such as: high thermal conductivity, high strength and high toughness direction; 2) new die casting aluminum alloy materials will also be driving the development of the new die casting technology, such as semi-solid die casting process, the high vacuum suction casting 3) technology development will also give equipment, auxiliary materials put forward higher requirements, such as: large die casting, die temperature machine, spraying equipment, mold release the matching machine, vacuum machine, cold machine, mould temperature control and detection system, etc