Compared with the common die casting technology, the high Vacuum Casting technology is relatively simple to operate and has a higher production efficiency. Therefore, since the high Vacuum Casting technology has been put into production, it has received the key attention of major manufacturers and has good economic development and application prospects. With the continuous progress of science and technology and R&D capability in China in recent years, high Vacuum Casting technology has been further optimized and applied. At this stage, the technical research department and our manufacturers focus on how to further play the cost advantage of the technology, improve product quality while further increasing economic benefits.
1.The working principle of die-casting technology
Die casting technology refers to the casting method in which the alloy molten at high temperature is filled into the mold under certain environmental conditions of pressure and speed, and gradually cooled into industrial parts. Die casting technology is one of the most common and fastest growing heat treatment processing and molding processes for materials in actual production. High-Vacuum Casting technology is an advanced production technology that extracts gas from the mold cavity during the filling process in order to effectively reduce dissolved gas and air bubbles generated during the cooling process of the part, thus improving the own mechanical properties and surface quality of the produced part.
There are two main modes of operation for the high pressure Vacuum Casting technology, one is the extraction of the special mold cavities by means of an extractor, and the other is to put the whole die into a vacuum chamber to complete the die casting process. Usually, the first mode requires relatively high sealing and quality of the mold itself, while the second mode has high economic cost of production, which should be selected according to the actual situation and demand of the manufacturer in the production process. The parts produced by high Vacuum Casting technology have the advantages of high denseness, strength and toughness, which meet the production needs of China’s manufacturing industry and have a very broad development prospect.
2.The development and status of high Vacuum Casting technology
Since China’s vigorous development of heavy industry, die-casting technology in China’s modern industrial production process is more and more widely used. Industry as an important part of the country’s comprehensive strength assessment, its development can drive the rapid improvement of the national economic level, but also the foundation of China’s social construction power. However, with the gradual development of industry, the problems brought about by the traditional die-casting production technology are becoming more and more prominent and have seriously affected the development speed of China’s industry. In order to mention the performance of the workpiece produced by die-casting technology, adapt to the actual production requirements, our country related researchers also researched several new die-casting process, such as oxygen pressure, ultra-low-speed die-casting and laminar flow filling die-casting process, etc. These new die-casting process are through reducing the liquid metal in the filling and cooling process and air contact area, and then improve the product performance.
However, the above several die-casting process operation is complicated, the actual production of specific process parameters are difficult to detect and control, so compared to the Vacuum Casting process its application is less. And Vacuum Casting technology can fundamentally isolate the metal liquid and air, so the process performance of die-casting parts has a large improvement, and the operation of high Vacuum Casting technology is as simple and convenient as the traditional die-casting technology, so high Vacuum Casting technology provides full protection for the development of our industry.
High Vacuum Casting technology has a large number of applications in precision manufacturing industries such as aerospace, automotive, and electrical. And with the gradual development of China’s economy, people’s pursuit of daily necessities such as automobiles and home appliances has changed from practicality to design of appearance as well as product quality. High Vacuum Casting technology can carry out thin-walled, complex shape and high dimensional accuracy requirements of parts manufacturing, more in line with the actual development needs of the automotive and other industries, so its application is more and more widespread, from transportation to home appliances, and then to a variety of household goods, everywhere you can see the products of die-casting technology.
But according to the relevant research survey found that China’s existing high Vacuum Casting production process and foreign developed countries have mastered the die-casting technology there is still a certain gap, because China’s industry started late, for its process technology research is less, the relevant enterprises are still in the initial stage, did not form our own excellent brand. And foreign related enterprise’s die-casting technology and operation situation has been mature, its production system and related specification system and quality testing has been perfect, so our country’s die-casting related industry still need further development.
3.Vacuum Casting technology development
Common Vacuum Casting technology mainly has two methods.
(1) Vacuum shut-off valve method.
(2) the method of cooling exhaust tank. In the process of filling the molten metal, the molten metal will cool down and solidify rapidly when it flows through the exhaust tank, which makes it difficult for the molten metal to continue to enter the vacuum pipe, so the smoothness of the exhaust pipe will be restricted, making the vacuum inside the mold cavity fluctuate greatly and the quality of the products produced is unstable, however, because of its lower production cost and simpler mold structure. However, because of its lower production cost and simpler mold structure, it is more used in common Vacuum Casting.
However, the working principle is similar in that the valve is closed quickly by using the kinetic energy of the molten metal during the filling process. In actual production, when the valve is opened, the gas in the mold can be quickly discharged through the exhaust port on the side of the mold; in the process of filling the molten metal, when the molten metal fills the vacuum valve, it will first push the valve spool upward and the molten metal will be filled from both sides of the exhaust hole at the same time, but because the length of the exhaust hole is long, when the molten metal flows to the vacuum pipe, the vacuum valve has been closed, so it will not make the molten metal flow into the vacuum system.
The vacuum level of this method is high and stable, which is very good for the process quality of the workpiece. The high Vacuum Casting process used abroad was developed in Germany and is generally divided into two types: the Vacural method and the MFT method, which uses a pipe to connect the melting furnace to the injection chamber of the mold.
The MFT method uses a vacuum valve that automatically opens or closes to seal the mold cavity, ensuring that the pumping can be done quickly during production and that a high vacuum level is obtained. The melt can be filled quickly by increasing the gate cross-sectional area. The hermeticity of the mold cavity is the key to high Vacuum Casting technology. Only when the pumping technology meets the relevant requirements can the cavity be provided with a high vacuum level, but the sealing of the cavity itself should not be ignored, otherwise it will cause too much air inlet, which will have a serious impact on the die casting parts.
Therefore, in the development process, we have to improve the sealing technology, firstly, we have to set effective sealing plate behind the moving die pad, and set buffer gas groove in front of each sealing plate, secondly, we have to design the sealing groove on the punch, the inner wall of the injection chamber and the bottom plate, if there is gas entering, we have to use the buffer gas groove to reduce the influence of gas on the die as much as possible.
4.Application prospects of high Vacuum Casting technology
High-Vacuum Casting technology has an important meaning and position in modern industrial production process. High-Vacuum Casting technology has the advantages of high productivity, stable product quality, high accuracy of workpiece and low cost of mass production, which can well meet the needs of manufacturers in home appliance, aviation and automobile industries and their related markets. However, because of the high Vacuum Casting technology involves more technical fields, the complete die-casting equipment is expensive and has many limitations, for example, the hot chamber die-casting machine usually can only die-cast small parts, can not process large castings. The cold chamber die casting machine has a narrow range of applications, mainly for hot chamber die casting machine can not process the alloy metal die casting work.
The equipment performance of die-casting machine also seriously affects the quality and productivity of the final workpiece. With China’s relevant die-casting machine control technology and the overall performance of the upgrade, China’s current production of die-casting machines are using electro-hydraulic servo control technology, can be linked with computer technology, and the application of the latest sensors and hydraulic workpiece, in the actual production process can be real-time measurement of various data precision control, for the actual production efficiency and product quality of enterprises to provide effective protection. The die-casting process itself has also been effectively developed, and the latest production process can complete both die-casting and forging production processes in one molding process. Especially for the product size precision requirements of high shape relatively complex automotive production industry development has an important role.