Single point incremental sheet forming investigated by in-process 3D digital image correlation

Abstract

Abstract. Single Point Incremental Forming (SPIF) is a promising sheet metal forming process for prototyping and small batches, in which the blank is formed in a stepwise fashion by a displacement-controlled small-sized tool. Due to specific strain paths induced by the process and limited plastic zones in the contact region between the tool and the workpiece, forming diagrams and forming strategies are different from the classical stamping processes. One major limitation of SPIF is the lack of accuracy of the obtained final parts because of the poor knowledge of the state of stress during the process that requires a good description of the material models and a right choice of the process parameters. In this paper, the SPIF process is experimentally investigated by the mean of surface 3D digital image correlation during the forming of a AW-5086-H111 grade aluminium alloy. Development of strain fields encountered in incremental forming is reported and material formability is evaluated on several formed shapes, taking into account a wide range of straining conditions of this process.

Review on the influence of process parameters in incremental sheet forming

“…Formability in SPIF can be defined by the maximum wall angle (see Fig. 4), and it is measured in terms of a tangent line from the unformed blank to the deformed part of the surface, determined by sine law, t f = t i sin(π/2 − ) = t i sinα, where t i and t f are the initial and final thicknesses of the part, respectively, and α is the semicone angle [19]. Thus, max is usually used as a parameter to measure whether the SPIF Fig.…”

“…The effect of some parameters, such as step size, on the formability of a commercially pure titanium blank was investigated by Hussain et al [44], and the results proved that the formability decreases linearly as the step size increases. Experimental investigation by means of surface 3D digital image correlation was published by Decultot et al [19] in forming of an AW-5086-H111-grade aluminium alloy. It was found that the workpiece formability was reduced with the increase of increment step size.…”

Modelling of ductile fracture in single point incremental forming using a modified GTN model

“…Experimental observations show that fracture is not preceded by localised necking and cracks develop by tensile meridional stresses under stretching conditions but not by plane shear stresses. An experimental work using a surface 3D digital image correlation showed that the fracture occurred in the uniaxial stretching domain [3].…”

Numerical simulation and experimental investigation of ductile fracture in SPIF using modified GTN model

“…When the load increases and reaches the maximum value (3.04 KN), and displacement reaches (11 mm), significant changes in the dimensions of the tensile specimen can be noticed. Furthermore, the material 04013-p. 4 ICNFT 2015 bearing capacity is quickly lost and the void volume fraction reaches the critical value f c (0.2593) (Fig. 3C).…”

“…Experimental observations show that the fracture is not preceded by localized necking and the crack develops under tensile meridional stresses acting under stretching conditions and not by plane shearing stresses. An experimental work using a surface 3D digital image correlation showed that the fracture occurred in the uniaxial stretching domain [4]. To predict the occurrence of failure in the AA5052 sheet, Malhotra et al [5,6] used explicit FEA with a damage-based fracture model, in which the failure envelope depends on the hydrostatic pressure and the lode angle.…”