Stretching the limits of forming processes by robust optimization: A numerical and experimental demonstrator

Robust design of forming processes is gaining attention throughout the industry. Many numerical robust optimization approaches have been proposed in literature and applied to a range of metal forming applications, often making use of a metamodel-based approach. However, published research is confined to numerical studies only. Experimental validation of the numerically predicted and improved process robustness is lacking. In this work, a deterministic and a robust optimization study is performed considering a stretch-drawing process of a hemispherical cup, covering both numerical work and experimental validation. For the robust optimization study, both the effect of material property scatter and process scatter are taken into account. For quantifying the material scatter that can be encountered in a production environment, samples from 37 coils of a drawing quality forming steel DX54D+Z (EN 10327:2004) from multiple casts have been collected. The numerically determined deterministic and robust optimum is subsequently validated by 2 sets of experiments using the collective of materials. The predicted difference in robustness between both optima, and the improved robustness of the robust optimum is also observed in the experiments. This demonstrates how robust optimization can assist in further stretching the limits of forming processes, while remaining robust with respect to sources of variation.