Hybrid forming process combining electromagnetic and quasi-static forming of ultra-thin titanium sheets: Formability and mechanism

A novel hybrid forming method combining the electromagnetic (EM) and quasi-static (QS) forming methods is developed to improve the forming performance of ultra-thin titanium sheet and 3D parts with micro-features. To demonstrate the development of this approach, the formability of ultra-thin pure titanium sheets was first systematically investigated using QS bulging, EM bulging, and EM pre-bulging with subsequent QS bulging (EMPB-QS). The two-step EMPB-QS method resulted in a higher forming limit and elongation of ultra-thin pure titanium sheets in the uniaxial tension region than the QS or single-EM methods. The improvement in formability was more pronounced for sheets with larger grains and thicknesses. Microstructure analysis revealed that the formability improvement under uniaxial tension could be attributed to the enhanced deformation twinning effect induced by EM pre-bulging. However, EM bulging decreased the formability of ultra-thin pure titanium sheets, which was ascribed to the early saturation of deformation twinning at high strain rate forming, resulting in a lower post-necking elongation. The application of the proposed two-step stamping method to the fabrication of titanium bipolar plates led to an increase in limit depth, thickness uniformity, and dimensional precision. Hence this study provides a new approach for improving the ductility of titanium sheets and further provide an efficient method for the fabrication of 3D components with micro features of high aspect ratio and dimensional precision.