Research On Vacuum Control Technology For High Vacuum Die Casting

High vacuum pressure casting is an advanced materials shaping method since the air is pumped from the mould cavity so the liquid metal can be filled in the mould under high vacuum (the degree of vacuum in mould reaches 90KPa or the absolute pressure is less than 10KPa). In this way, the porosity of products can be restrained and the mechanical property is enhanced. However, the bottleneck including structure designing and vacuum controlling limits the application of this technology. Because the research in this field is nearly hitherto blank, in this paper, Minimum Fill Time(MFT)based on high vacuum pressure casting is adopted to improve the design of vacuum valve. Due to its great rationality and reliability, the meliorated stop valve and its matching control system which is based on PLC technique will have significant impacts on the technology of high vacuum pressure casting and die casting industry in China.The prepared vacuum stop valve follows the existing structure comprised initiative and driven piston where the transmission is conducted according to the lever principle. To ensure the reliability and fast response of closure airway in driven piston, the servo drive is devised. Meanwhile, the common spring in reposition mechanism is replaced by the air one, and this amendment assures to avoid the failure and unreliability during the move. This brand new design can be applied in various technology modes of die casting for its flexibility, celerity and reliability.The vacuum control system contains hardware and software. The former one employs PLC as the host compute control unit, embedded touch screen combined A/D conversion module as the kernel of whole system. The logic control of vacuum pump, electromagnetic valve and sensor output is operated by the system above; the latter one is based on the technology of PLC and the touch screen is composed of PLC microcomputer control program and configuration system. The advantages include convenience for display, visualized, simple interface and so on. The developed vacuum control system can automatically match the corresponding die casting machine since it contains three operation modes: regular, low and high vacuum pressure, all of which can be adapted to different working states. Additionally, this system can automatically detect the vacuum degree of the mould cavity, blocks in vacuum line; moreover, it is also able to clean the line and monitor/alert the operation status itself.