Effect of friction in stretch forming and its influence on the forming limit curve

Abstract

Formability is an important property requirement in sheet metal forming and mostly useful to automobile and aerospace industries. Every product design starts with finite element simulation before the die design and material selection stage. The forming limit curve along with finite element results acts as tool to investigate whether the design is feasible. Hence, it is of utmost importance that the forming limit curve is accurate over a wide range of strain path. Generally, a forming limit curve is derived from discrete failure strain points corresponding to different strain ratios by fitting a smooth curve. It has been observed from many studies that the generated forming limit curves are devoid of any failure points corresponding to equibiaxial strain path. This is found to be true even when the test conditions are supposed to produce biaxial state of strain. To understand the reason behind this observation, a set of forming limit diagram experiments and finite element analyses were carried out for high-strength interstitial free steel and interstitial free galvannealed steel with three different friction conditions. It was observed that friction plays an important role in right-hand side of the forming limit curve. Finite element results and experimental validation suggest that failure strain points for biaxial strain paths can be obtained only if the tests are conducted with proper lubrication system.

Investigation of forming limit diagram and mechanical properties of the bimetallic Al/Cu composite sheet at different temperatures which fabricated by explosive welding

“…13,14 The forming limit diagram (FLD) is applied to investigate the limit of major and minor strains that the sheet can tolerate without any necking. 15–17 Many types of research have been done to study the explosive welded sheets. 11 Acarer et al 18 studied the effects of the anvils, explosive loading and stand-off distance parameters on the explosive welding process of similar metals (steel-steel plates) under untreated and heat-treated situations.…”

Effect of specimen orientation to the rolling direction on uniaxial tensile forming and failure limits

“…Two primary test methods, in-plane [4][5][6] and out-ofplane [7][8][9][10][11] formability experiments, are widely adopted to find out the FLDs for sheet metals under different forming situations, including deformation rate and temperature. 12 Various researchers 13,14 have also adopted planar biaxial tensile experiments to determine FLDs for sheet metals, since effect of friction is absent and precise control of strain path is possible.…”

Effect of punch geometry on hole expansion ratio

“…Researchers determine the left side of the FLC from uniaxial tensile and notch tensile tests by local strain measurement on different sheet metals. [1][2][3][4][5][6] However, determination of HER from normal uniaxial tensile test is not possible due to the fundamental difference of deformation process. 7,8 HER is widely used as a limiting criterion during edge stretching operation of sheet metals.…”