An Approach for Modeling Sheet Metal Forming for Process Controller Design

Varying the blank holder force during forming can lead to higher formability and accuracy, and better part consistency. Process control, using on-line adjustment of the blank holder force to follow a reference process variable (e.g., the punch force, the draw-in, etc.) trajectory has been applied to sheet metal forming. However, process controller design has not been thoroughly addressed. In this paper, the essential part for systematic process controller design, i.e., modeling a sheet metal forming process, will be addressed in terms of control terminology (e.g., the process model, the model uncertainty and the disturbance). A process model for u-channel forming, i.e., a mathematical relationship between the blank holder force and the punch force, is presented and experimentally validated. Characterization of the model uncertainty mainly due to small variations in blank size, sheet thickness, material properties and tooling shape due to die wear and the disturbance which is mainly due to friction is developed.