Implementation of a tribology-based process control system for deep drawing processes

Modern deep drawn parts have complex designs and are driven to the limits of the material formability in order to reduce costs. This leads to small process windows and unstable forming processes with high scrap rates. Especially at the beginning of a batch, when the tools are warming up, high scrap rates can occur due to the changing friction behaviour of the system tool – lubricant – metal sheet. To make processes independent from user experience and know-how, process control systems that can compensate for the transient behaviour of the process are desired. In this work, a process control system that is based on the numerical simulation of the friction behaviour of the deep drawing process is presented. The system makes use of numerical simulations of the transient behaviour during warming up of the tools. These simulations are used to generate metamodels of the process, which are used to design and optimize the control algorithm. The control system is tested with an automotive part from Opel. The control system itself consists of two parts: a feed forward controller and a feedback loop. In the feedforward loop the in-line acquired temperature will be used as an indicator for the friction conditions. It will make use of metamodels generated based on numerical simulations in order to depict the process behaviour. The feedback loop will use the in-line measured draw-in as a state variable in order to account for all other process influences. Simulation results, the generation of metamodels, as well as the first off-line tests of the process control are shown in this contribution.