Views:4 Author:Site Editor Publish Time: 2019-06-12 Origin:Site
Recently, vacuum aluminum alloy die casting mainly relies on the gas in the cavity, and there are mainly two forms:
(1) pumping directly from the mold;
(2) Place the mold in the vacuum box to pump air. When vacuum aluminum alloy die casting is used, the design of the exhaust position and exhaust area of the mold is critical. There is a "critical area" in the exhaust passage, which is related to the amount of gas extracted in the cavity, the pumping time, and the filling time. When the area of the exhaust passage is larger than the critical area, the vacuum aluminum alloy die-casting effect is obvious; otherwise, it is not obvious.
The choice of vacuum system is also very important, requiring that the vacuum in the cavity be maintained until the vacuum pump is turned off. Oxygen-casting and casting technology The gas in the pores of die-casting parts is mostly N2 and H2, and there is almost no O2. The main reason is that O2 reacts with active metals to form solid oxides, which provides a theoretical basis for oxygenation die-casting technology. Oxygen-filled die casting is to fill the cavity with oxygen before the die-casting.
Since the pressure casting completes the filling process in a very short time, it is easy to cause the gas to be caught and affect the quality of the die casting. For this purpose, oxygen-added die casting machines and vacuum die-casting machines have been developed, and medium-pressure die-casting machines have also achieved rapid development. Some die-casting machines have a tilting form. The die casting process automation and die casting computer control and die casting flexible processing unit (FMC) have also been gradually developed.
(1) Oxygen pressure casting is to fill the pressure chamber and the cavity with oxygen before the aluminum metal liquid fills the cavity to replace the air and other gases. The utility model has the advantages that the pores are eliminated or reduced, the quality of the casting is improved, the structure is simple, the operation is convenient, and the investment is small.
(2) Vacuum pressure casting is to first remove the air in the die-casting cavity and then press the liquid metal. Its characteristics are: it can eliminate or reduce the pores inside the die casting, improve the mechanical properties and surface quality of the casting; the back pressure of the cavity is greatly reduced during die casting, and the alloy with lower specific pressure and poor casting performance can be used.
Advantages of vacuum die casting
1 Vacuum die casting can eliminate or reduce the pores inside the die casting, improve the mechanical properties and surface quality of the die casting, and improve the plating performance;
2 Vacuum die-casting method greatly reduces the back pressure of the cavity, and can use lower specific pressure and alloy with poor casting performance. It is possible to die-cast large castings with small machines;
3 The vacuum die casting method improves the filling conditions and can die-cast thinner castings;
4 The vacuum die casting method has almost the same production efficiency as the ordinary die casting method.
Disadvantages of vacuum die casting
1 The mold sealing structure is complicated, and the manufacturing and installation are difficult, so the cost is high;
2 If the vacuum die casting method is not properly controlled, the effect is not very significant.
Compared with ordinary die casting method, vacuum die casting has the following characteristics:
(1) The porosity is greatly reduced;
(2) The vacuum die-casting casting has high hardness and fine microstructure;
(3) The mechanical properties of vacuum aluminum alloy die castings are relatively high.
The aluminum-magnesium alloy die-casting parts produced by the vacuum die-casting method have been proved to be able to adopt welding, heat treatment and other processing methods, and the room temperature performance has also been improved: for example, the AM60B magnesium alloy automobile has been successfully produced by the vacuum die casting method on the cold chamber die casting machine. The hub, on the hot chamber die casting machine with a clamping force of 2940kN, uses the vacuum die casting method to produce the AM60B magnesium alloy automobile steering wheel. The elongation of the die casting is increased from 8% to over 16%.
As long as it is properly controlled, vacuum die casting can provide a satisfactory improvement in die casting performance. The cost increase caused by the mold sealing will be well solved with the popularization of technology and the cost sharing brought by mass production. Compared with the traditional die-casting method, the laminar flow filling method/ultra-low speed die casting method has low production efficiency, and the gate cleaning is difficult, which is difficult to apply to mass production; the oxygenation die casting method has complicated operation steps, and the process parameters are difficult to control and difficult to control. Large-scale application in actual production; only vacuum die-casting method, simple process, convenient operation, almost the same production efficiency as ordinary die-casting method, easy to promote in actual production. Therefore, since its appearance, the vacuum die casting method has shown strong vitality, and with the improvement of related technologies, its application has become more and more extensive.