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In this research, formability of two layer sheet metals of Al1050 and St12 in single point incremental forming (SPIF) has investigated using numerical and experimental approaches. In order to study the sheet metal formability in this process, the tool paths defined in ABAQUS and CNC machine so that an increasing wall angle is created until the sheet metal reaches its maximum allowable angle and fracture is occurred. Since in this process, the tool exerts local stresses on the sheet metal, 3D simulation of the process is needed. In order to study the effect of process parameters, the analysis is done in three levels of tool radius and vertical step size. In order to derive fracture depth of sheet metal, the force diagram is considered in simulations. It is shown that the outer sheet subjected to higher plastic strains and therefore failure occurred initially at the outer layer. Results also showed that increasing the tool radius and vertical step size speed up process but they have inverse effect on the forming limit angle. For experimentally study and also to validation of simulation results, full factorial experiments with respect to forming speed up to three levels designed and carried out. The difference between FEM and experimental results is about %2.1 in forming limit angle.

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Forming limit diagram (FLD) is one of the useful tools in the assessment of the sheet formability for designing industrial products. Experimental methods have been developed to determine FLDs. Costly and time-consuming experiments have led to several studies on the use of analytical methods and finite element softwares for predicting FLDs. In the present study, the necking and fracture forming limit curves of AA2024 aluminum alloy sheet were experimentally and numerically obtained through the hemispherical stretching test. Different geometries of the initial blank were considered to create different strain paths. The commercial finite element code Abaqus/Explicit was utilized to simulate experimental tests. Using theoretical equations and experimental results, fracture properties of the aluminum sheet in terms of the equivalent plastic strain at fracture, the stress triaxiality and the Lode angle parameter were captured and implemented in the Abaqus software. In order to capture necking forming limit strains, a numerical criterion based on the major strain variation in the necking zone has been considered. The comparison of the results shows that the numerical model can predict the forming and fracture limit strains with the maximum error of about 6%.

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