Analytical modeling and experimental validation of the forming force in several typical incremental sheet forming processes

Incremental sheet forming (ISF) is recognized as an advanced forming process which is highly flexible in cost-effectively producing small batched sheet metal parts. The forming force is dramatically reduced due to the local deformation and successive forming characteristics compared with traditional stamping process, and has vital impact on forming quality. It may however, be noted, that the forming force prediction models widely used are empirical ones, which needs further improvement for wider applicability. Besides, the force fluctuation in ISF has impact on the geometric accuracy, which has been less studied so far. In the present work, the analytical models for predicting the forming force for single-pass single point incremental forming (SPIF), multi-pass incremental forming (MPIF) and incremental hole flanging (IHF) processes are developed based on the new analytical models used to calculate the contact area and the through-thickness stress. A series of experiments of typical sheet metal parts in different geometries for different materials with varied process parameters including wall angle, step depth, tool radius and sheet metal thickness are used to validate the proposed analytical models. The new prediction models are proved to calculate the forming force and force components along the axial, tangential and radial directions with high accuracy for SPIF, MPISF and IHF processes. Moreover, the mechanism of force fluctuation is also investigated, and ifs proved that the force fluctuation is caused by varied elastic deflection of the deforming sheet metal.