Multi-pass deformation design for incremental sheet forming: Analytical modeling, finite element analysis and experimental validation

Incremental sheet forming (ISF) is a promising rapid prototyping technology with high potential to shape complex three-dimensional parts. However, a common technical problem encountered in ISF is the non-uniform thickness distribution of formed parts; particularly excessive thinning on severely sloped regions. This may lead to fracture and limit the process formability. Design of multi-stage deformation passes (intermediate shapes or preforms) before the final part, is a desirable and practical way to control the material flow in order to obtain a more uniform thickness distribution and avoid forming failure. In the present paper, a systematic methodology for designing multi-stage deformation passes considering the predicted thickness strains given the design shape is proposed based on the shear deformation and the strain compensation mechanism. In this methodology, two analytical models (M1 and M2) are developed by taking into account; the global average thickness strain and only the material in the final part region used in the forming (M1), and the local weighted average thickness strain and the additional material around the final part region used in the forming (M2), respectively. The feasibility of the proposed design methodology is validated by finite element analysis (FEA) and experimental tests using an Amino ISF machine. The results show that a more uniform thickness strain distribution can be derived using M2. The incurrence of the highest strains can be delayed in the intermediate stages and the flow of material is allowed into the deformed region, thereby allowing a compressive stress state to develop and enabling steeper shapes to be formed. Therefore, the process formability can be enhanced via the optimized design of deformation passes.