The Pressurizing Modeling And The Design Of Control Algorithm For Vacuum Counter-pressure Casting System

Vacuum Counter-Pressure Casting has a wide application prospect in the field of aviation, aerospace, national defense and automotive industry emboding having produced so many, large,thin-walled, complex non-ferrous alloy castings. The casting quality depends on response speed and control precision of the casting system. As the vacuum counter-pressure casting process having the characteristics of non-linear, time-varying, delay serious and so on is a dynamic and parameters unstable process, the object controlled can't be described by simple and fixed mathematical model, in order to let the vacuum counter-pressure casting control system be controlled according to the casting technology, we have to make a deep analysis to the Vacuum Counter-Pressure Casting system pressurized model, at the same time make a research on the control algorithm and how to design a controller.In the paper, firstly we based on the analysis of the vacuum counter-pressure casting process and working principle, analytical modeling establish a relationgship formula applying engineering fluid mechanics theory, the relationgship formula give a relationship between the casting tank pressure and the air tank pressure with the casting tank bulk, air tank bulk, casting tank initial pressure, air tank initial pressure and connecting pipe cross-sectional area,then analyses these equipment parameters how to affect the casting tank pressure particularly, the results show that: the influence of the connecting pipe cross-sectional area to the process pressure step-up rate is obvious, the influence of the air tank initial pressure and the casting tank bulk to the balanced pressure is obvious; Secondly, in order to verify the correctness of the theoretical model, studing the pressurized model again by doing experiments ,we design a vacuum pressure casting test system, which is foundation of the experiment modeling, including testing system hardware circuit design and testing system software design, hardware designed include the pressure detection circuit design, I/V converter and isolation circuit design and A/D conversion circuit design, meanwhile using the technics of multiple threads and the technics of timer to collect, display and store the pressure datas of casting tank and air tank accomplish the software designed, through the MATLAB tools for interpolation fitting method identify the controlled object mathematical model, the results show that: the theoretical model is correct, according to the signal and system theory comes to the vacuum counter-pressure casting system controlled object frequency domain model, which is a second-order model; Finally, based on the controlled object mathematical model, we design a PID controller, a variable parameter PID controller and a fuzzy variable parameter PID controller of the vacuum counter-pressure casting control system, then simulate and analysis the PID controller and fuzzy PID controller, simulation results show that: Fuzzy PID controller has smaller overshoot, faster response time, better control effect than the conventional PID controller. At the same time we analyzes the design principles of the combination digital valve, and we also deduced the combined digital valve design gist on the basis of analysis gas flow law of the pressurized system.The study of this topic in the one hand, provides theory gist to develop the vacuum counter-pressure casting system equipment, in the other hand, according to the established mathematical model, is foundation of researching and realizing the control algorithm, so it solves the problem of system control precision and response speed and has greatly enhanced the quality of castings.