Revealing the Dominant Forming Mechanism of Single Point Incremental Forming (SPIF) by Splitting Plastic Energy Dissipation

Over the years, a number of studies have been presented which investigate the forming mechanisms of single point incremental forming (SPIF). Different research groups revealed that membrane, bending or shear deformation prevail under the conditions they investigated. The current paper moves a step forward and quantifies the respective contribution of the each forming mechanisms, i.e. membrane stretching, bending, through-thickness shear, involved in the SPIF process. For this purpose, the plastic energy dissipation during the SPIF process is split up into membrane, bending and shear energy terms. A validated numerical model of the SPIF process is used to analyze the internal energy at various part locations. Using an analytical approach, this internal energy is decomposed into the membrane, bending and shear contributions. Further, a parametric study based on FE simulations is used to analyze the sensitivity of the deformation mechanisms to the SPIF process variables. At any particular location on the geometry of a part formed with SPIF, the deformation mechanism is always a combination of these three deformation modes. Dominance of one particular deformation mode over the other two is dependent on the process variables, for example, the bending mode of deformation dominates at larger tool diameters and shear dominates at increasing sheet thickness. The prevalence of each deformation modes as a function of SPIF process variable is discussed. Process outcomes and part quality in SPIF can be designed for maximum formability and geometrical accuracy, by controlling the contribution from each deformation mode through adjusting the process variables.