Close loop control of a hydraulic press for springback analysis

The dimensional accuracy of formed components is an important issue for most stamping applications. The surface distortions and unexpected out of tolerances may cause deviation from the designed target shapes and may lead to assembly difficulties. Some of these problems occur due the elastic recovery characteristics of the sheet metal and is normally called the springback effect. In order to compensate the undesirable springback effects, much work has been performed in measuring and understanding this phenomenon. This paper describes the operation analysis of aluminum stamping on a 100 kN hydraulic press. A real time DSP based control is used to implement the controller and monitoring the press operations. The cylinder piston positions and chamber pressures are acquired with two optical scales and with analogue pressure sensors, respectively. A hybrid controller (force + position) for the punch is implemented in such a way that can be easily switched to control only the force or the position. A computer vision based method to automatically measure springback is also proposed.