A high accuracy hydraulic pressing actuation system for superplasticity forming equipment

The hydraulic pressing system is a major part of the superplastic forming equipment, which is used to moving and pressing modules. It requires to move the module quickly during opening or closing module chamber for saving heat energy, and also requires high accuracy pressing force control during superplastic blow forming process. Therefore, it usually requires a high flow rate and high frequency band width servo valve. But for servo valve, the band width is usually decreased when the flow rate becomes large. Meanwhile, high flow rate servo valve is very high cost. Indeed, it also very difficult to achieve high accuracy loading control for high flow rate servo since it is a static condition and the required flow rate is very small, which is smaller than to the resolution ratio of the servo valve. The proportional valve is low cost but it usually can not meet high accuracy pressure loading control since it has dead zone and hysteresis. This paper presents a new hybrid control scheme which using a high flow rate proportional valve combine with a small flow rate servo to control the pressing cylinder. The high flow rate proportional valve is used for motion control which requires of high flow rate and low accuracy, and the small flow servo valve to achieve high accuracy pressing load control while control accuracy is the most important. In the present study, the feasibility and the control algorithm is studied by AMEsim. The simulation results illustrate that the proposed scheme can meet the requirements of the requirement of the forming system.