In incremental sheet forming higher limiting strain can be achieved compared to the conventional sheet metal forming process, which results in increased formability. The higher level of strain may be ...accompanied by non-uniform thinning. Thus, the different sections in a component may undergo different levels of deformation. In the present work a truncated cone of AA1050 H14 alloy was formed using the incremental sheetmetal forming (ISF) technique. The deformation mechanism during ISF was studied by investigating the microstructural and texture evolution in the truncated cone along the thickness of the cone wall. High resolution electron backscatter diffraction was performed at different sections of the formed truncated cone. The results show the formation of subgrains in different sections of the cone. At higher strains, grains become thin and elongated which results in grain fragmentation and formation of small grains. These small grains undergo complete recovery process and new grain boundaries (low and high angle) are formed within the thin elongated grains. Further, the evolution of shear texture shows the evidence of shear mode of deformation during incremental sheet forming. Thus, the presence of through thickness shear could be used for understanding the higher forming limit in the ISF process.
The formability of sheet metals is frequently characterized by the forming limit curve (FLC), which is determined by applying proportional loading paths until the onset of necking. However, metal ...forming processes usually involve strain-path changes that can affect the limit strains. The purpose of the present work is to study the consequence of strain path changes on the formability of a 0.65 mm thick Zn-Cu-Ti sheet, by means of tests carried out in bi-linear stages. For this propose, tensile limit strains were determined by uniaxial deformation of biaxially pre-strained specimens. The FLC was first determined for six strain paths, obtained from hydraulic bulge and uniaxial tests with diverse specimen geometries. For the bi-linear strain paths, the tensile limit strains of the biaxially pre-deformed zinc sheet are significantly higher than the FLC of non pre-strained samples for the three orientations studied, revealing interdependence between the material’s formability, the loading history and microstructure evolution.
The present study investigates the effects of the process parameters on cold forming process of an automotive component in AISI 1006 low carbon steel. The material formability was characterised up to ...250°C. The material flow behaviour and the related thermal distributions during the geometrical transformations were analyzed. Coining and forming operations were investigated by using a coupled 3D Thermo-mechanical FEM with different die geometries and friction conditions in order to optimize the final die geometry and to reduce the energy consumption. FEM simulation results were validated by comparison with the experimental trials. The detailed study of the component allowed defining the energy required by the severe bending of the initial thick plate. The FEM predictions led to a reduction of deformation energy of about 20%, a mass reduction of 28% on the final product and permitted avoiding secondary machining operations.
In automotive manufacturing, high strength materials, and aluminum alloys are widely used to address the requirement of ensuring a lightweight car body and correspondingly, reducing pollution. In ...this context of complexity of materials and structures, an optimized process design with finite element analyses (FEA) is mandatory, as well as a correct definition of the material forming limits. For this purpose, in sheet metal forming, the forming limit curve (FLC) is used. The FLC is defined by the onset of necking. The standard evaluation method according to DIN EN ISO 12004-2 is based on the cross-section method and assumes that the failure occurs due to a clear localized necking. However, this approach has its limitations, specifically in the case of brittle materials that do not exhibit a distinct necking phase. To overcome this challenge, a pattern recognition-based evaluation is proposed. Although pattern recognition and machine learning techniques have been widely employed in the medical field, few studies have investigated them in the context of analyzing metal sheet forming limits. The application of pattern recognition in metal forming is subject to the exact definition of the forming behaviors. Thereby, it is challenging to relate patterns on the strain distribution during Nakajima tests with the onset of necking for the FLC determination. Thus, the first approach was based on the crack evaluation, since this class is well-defined. However, of substantial interest is the evaluation of the general material instabilities that precede failure. Therefore, in the present study, the analysis of the material behavior during stretching is conducted in order to characterize instability classes. The results of Nakajima tests are investigated using an optical measurement system. A conventional pattern recognition approach based on texture features, considering the outcomes of expert interviews for the definition of classes is used for the FLC determination. Moreover, an analysis of the validity of the supervised learning is conducted. The results show a good prediction of the onset of necking, even for high strength materials with a recall of up to 92%. Some deviations are observed in the determination of the diffuse necking. The discrepancies of the different experts' prognoses highlight the user-dependency of the FLC, suggesting further investigations with an data-driven approach, could be beneficial.
•Role of Bain variants on plastic anisotropy and formability in duplex stainless steels.•Viscoplastic self-consistent model is used for predicting Lankford coefficients.•Multiple orientation ...relationships behave similarly during deformation.•Ferrite having Bain-C variant type texture is most suitable for deep drawing.
Crystallographic texture is known to have significant effect on the plastic anisotropy and formability in materials. In single phase materials, the texture is often a function of prior thermomechanical processing. However in materials with multiple phases such as duplex stainless steels (DSS), the texture is also influenced by the orientation relationship (OR) maintained during the phase transformations. In the present work, we study the role of OR and their Bain variant classifications on the plastic anisotropy and, in turn, on the formability of DSS. Crystal plasticity modelling is used to calculate the in-plane anisotropy of the r-values for DSS with different initial austenite textures. Further, finite element simulations of the deep drawing process are presented to obtain the earing profiles and show the Bain variant dependency on the formability.
Infilling strategies play an important role in kriging based optimization, especially when computationally expensive simulations are involved. In order to improve the efficiency of constructing a ...high-precision kriging model, an improved expected improvement criterion (IEI) and a parallel infilling strategy are proposed based on the maximum expected improvement (EI) criterion. In the proposed parallel infilling strategy, new sample points are generated by employing IEI criterion coupled with EI criterion. During the improved sampling process, redundant and pseudo sample are deleted in order to avoid failure of constructing a kriging model. An improved weighted particle swarm optimization (WPSO) algorithm is proposed to improve optimization efficiency. The proposed parallel infilling strategy is applied to nonlinear function optimization and variable blank holder force (VBHF) optimization in a double-c stamped part. Based on the LHD and software DYNAFORM, kriging models between the VBHF and forming quality are constructed. Compared with the initial kriging models, the meat relative error of kriging models with the proposed parallel infilling strategy for the wrinkling and average thinning rate are reduced by 95% and 55%, respectively. The optimal VBHF is obtained by the WPSO. The results show that, cracking has been completely eliminated and wrinkling has been decreased, greatly improving the forming quality of the double-c stamped part.
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