Optimal Forming of Aluminum 2008-T4 Conical Cups Using Force Trajectory Control 930286

In this paper we investigate the optimal forming of conical cups of AL 2008-T4 through the use of real-time process control. We consider a flat, frictional binder the force of which can be determined precisely through closed-loop control. Initially the force is held constant throughout the forming of the cup, and various levels of force are tested experimentally and with numerical simulation. Excellent agreement between experiment and simulation is observed. The effects of binder force on cup shape, thickness distribution, failure mode and cup failure height are investigated, and an “optimal” constant binder force is determined. For this optimal case, the corresponding punch force is recorded as a function of punch displacement and is used in subsequent closed-loop control experiments.

In addition to the constant force test, a trial variable binder force test was performed to extend the failure height beyond that obtained using the “optimal” constant force level. It was found that this method could indeed improve performance, and the cause of this improvement is examined through the use of the numerical model. Numerical simulation is then used to compute a “best” variable binder force history and the further improvement in cup failure height is obtained.

Although optimal forming trajectories were found under constant and variable binder force conditions, there is no guarantee that lubrication or sheet conditions will remain constant during an actual forming operation. Therefore, the process must be controlled in order to include such disturbances in the loop. Accordingly, a closed-loop tangential force controller is constructed and made to track the pre-determined force trajectory corresponding to the optimal conditions. Results show that optimal conditions can be maintained upon significant variation of initial binder force.