Closed-Loop Control of Sheet Metal Forming Processes

The process of forming metal sheets involves large plastic deformation of the workpiece material. The outcome of these processes, therefore, are highly dependent upon the yield point and flow stress characteristics of the material. To overcome the problems associated with uncertain and highly variable forming properties, a control strategy is presented that is based on closing the loop around the forming process and workpiece rather than just the processing machine. In this way the variations in material properties and the uncertainty of die-sheet interface forces can be overcome on a part by part basis. The details of such a process are discussed briefly in the context of conventional NC control and in detail for sheet metal forming. Examples of closed-loop control are presented for brake forming, roll bending and general die forming. Specific experimental results for these cases illustrate that part control of sheet metal forming is quite feasible, and promises to improve the ultimate utility of such processes by reducing setup time, and by improving the part consistency.