Research And Design On The Electro- Hydraulic Control System Of Hydraulic Die-cushion

In recent years, automobile industry has achieved rapid development, which is increasingly showing many novel features, such as personalization, large scale and integration of covering parts. Automobile manufacturers’ demands for forging equipment are higher and higher. In order to cope with the developing trend, heavy press machine must be inevitably pointed to the direction of higher precision, higher efficiency, higher flexibility. With the rapid development of numerical control and servo technology, the numerical control hydraulic die cushion (NCHDC) came out. As the key equipment of automotive production line of stamping, the performance of numerical control hydraulic die cushion determines the quality of automobile covering parts, and to a certain extent, it also restricts the development of automobile industry.At present, the technology of the NCHDC is monopolized by manufacturers of a few foreign countries, such as America, Japan and Germany. Due to the low lever of domestic technology, automobile manufacturers of our country have to rely on import in these companies to meet the demand of complicated process, which leads to a significant increase in manufacturing cost. In order to get rid of the technology monopoly and raise the competitive power of China’s automobile industry, it is quite important to design and develop the NCHDC with our own intellectual property rights. The key technology of the NCHDC contains the position and synchronization control during the pre-accelerated process and the variable pressure control technology of forming process. Only with higher position/speed control precision in the pre-accelerated process, pressure impact of the contact between upper and lower molds can be small, which will avoid artifacts’ invalidity. During the process, variable blank-holder force control technology can effectively guarantee the pressure in the range of optimum blank-holder force, which can improve the quality of the work-piece, if the blank-holder force is too large, the work-piece will be torn, and if too small, the work-piece will be easily wrinkled.According to the above problems, this article takes a 450t numerical control hydraulic die cushion as the research object. By comparing with the advantages and disadvantages of different kinds of blank holder force control methods, we finally choose the hydraulic cushion controlled by servo valves, which has the advantages of accelerated progress, large scope of work beats, higher control precision of position and pressure. PID and fuzzy PID control algorithms are used to analyze control characteristics of the position and pressure system. The effects of fuzzy PID algorithm, which display high adaptability, are relatively good.The detailed content are displayed as followed:In chapter 1, the research background of this object was proposed. Elaborate introduce the recent situation of variable blank-holder force and analyze the advantages and disadvantages of the different control forms of variable blank-holder force. What’s more, this chapter introduced the classification, characteristics and development status of synchronous control technology. Finally, content and meaning of the research subject was proposed.In chapter 2, the working principle and hydraulic system scheme of numerical hydraulic die cushion were introduced. The key parameters and components were determined by calculating with actual working conditions and functions.In chapter 3, mathematic models were established to analyze the functions of position/velocity control system and pressure control system, which could provide some theory parameters for the following simulation and experiment.In chapter 4, I established the AMESim models of the hydraulic system and high frequency servo valve. I used AMESim and MATLAB/Simulink to analyze the position control system and pressure control system. A PID controller, a feed-forward controller and a fuzzy PID controller were designed. The results of the simulation demonstrated that the ability of fuzzy PID controller gave a superior control performance than PID controller:higher control precision, less overshoot, stronger adaptability.In chapter 5, the experimental equipment and control system were designed, and the experimental principle was introduced. PID control algorithm and fuzzy PID control algorithm were used in the experiment to control the position and forging pressure of the system respectively. The experiment results validated the correctness of the simulation results and effectiveness of fuzzy PID.In chapter6, the major work of the study was summarized, the deficiencies and problems in the study were pointed out and the future study of servo hydraulic die cushion was proposed.