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The hot single point incremental forming is usually adopted to fabricate the complex part of AA2024 aluminum alloy. However, the activation mechanism of the slip system still has not been discovered at elevated temperatures. In response, the article has proposed a novel macro–micro analysis method to reveal the activation mechanism of the slip system. The shear stress model, which is demonstrated through the Schmid factor distribution of each crystal plane group, of crystal planes is established to calculate the shear stress of each slip direction. The effect of the forming process parameters on the forming limit angle is analyzed in detail, and the forming temperature is a primary factor for the increase of the forming limit angle. On this basis, the dislocation density of the material is investigated at different temperatures, and the dislocation density of the material is significantly decreased at 180 °C, which can weaken the dislocation pile-up due to the increase of the stacking fault energy. Finally, the slip system number of each crystal plane group is further analyzed at different temperatures, and the novel slip systems of the three crystal plane groups, such as {111}, {100}, and {110}, are both significantly activated at 180 °C.

This investigation aims to propose a novel framework for designing and manufacturing cranial prostheses through incremental sheet metal forming (ISF). First, the three-dimensional models of the defective crania and the prosthesis were constructed from the CT data. Then, to verify the formability of the prosthesis model, a method for testing the mesh sheet’s incremental forming limit (IFL) was proposed with a variable angle cone model. The angle between the normal vector of the fracture point and the Z-axis calculated the IFL. The tests showed that the method could realize the testing of the IFL of the mesh sheet with the reduction of processing time and cost. In addition, finite element modeling and experimental trials were used to evaluate the ISF process of the prosthesis, including thickness distribution and geometric accuracy. The results showed that the incremental forming can form prosthesis samples with high precision, while the thickness distribution is relatively uniform without excessive thinning. Finally, the obtained prosthesis sample was practically assembled with the cranial defect model to verify the fitting effect and feasibility of the prosthesis formed by the ISF process.

Sheet metals subjected to biaxial plane stress loading typically fail due to localized necking in the thickness direction. Classical plasticity models using a smooth yield surface and the normality flow rule cannot predict localized necking at realistic strain levels when both the in-plane principal strains are tensile. In this paper, a recently developed multi-surface model for porous metal plasticity is used to show that the development of vertices on the yield surface at finite strains due to microscopic void growth, and the resulting deviations from plastic flow normality, can result in realistic predictions for the limit strains under biaxial tensile loadings. The shapes of the forming limit curves predicted using an instability analysis are in qualitative agreement with experiments. The effect of constitutive features such as strain hardening and void nucleation on the predicted ductility are discussed.

The Forming Limit Stress Diagram (FLSD) can accurately describe the forming process of high-strength steel. However, obtaining FLSD is relatively difficult. In order to predict fracture in advanced high-strength dual-phase (DP) steels, limit maximum and limit minimum principal strains of sheet were obtained through multiple sets of test and simulation. Two material parameters, strength coefficient K and hardening exponent n are introduced into the FLSD function which is established by the strain-stress transformation function. The function shows that the k-value determines the value of the maximum principal stress, while the n-value affects the curvature of the curve. Verification of correctness by testing and simulation to within 10% accuracy. This paper explores a new approach to FLSD research based on material properties, which can expand the application scope of FLSD.

Single-point incremental forming (SPIF) has emerged as a cost-effective and rapid manufacturing method, especially suitable for small-batch production due to its minimal reliance on molds, swift production, and affordability. Nonetheless, SPIF’s effectiveness is closely tied to the specific characteristics of the employed sheet materials and the intricacies of the desired shapes. Immediate experimentation with SPIF often leads to numerous product defects. Therefore, the pre-emptive use of numerical simulations to predict these defects is of paramount importance. In this study, we focus on the critical role of the forming limit curve (FLC) in SPIF simulations, specifically in anticipating product fractures. To facilitate this, we first construct the forming limit curve for Al1050 sheet material, leveraging the modified maximum force criterion (MMFC). This criterion, well-established in the field, derives FLCs based on the theory of hardening laws in sheet metal yield curves. In conjunction with the MMFC, we introduce a graphical approach that simplifies the prediction of forming limit curves at fracture (FLCF). Within the context of the SPIF method, FLCF is established through both uniaxial tensile deformation (U.T) and simultaneous uniform tensile deformation in bi-axial tensile (B.T). Subsequently, the FLCF predictions are applied in simulations and experiments focused on forming truncated cone parts. Notably, a substantial deviation in fracture height, amounting to 15.97%, is observed between simulated and experimental samples. To enhance FLCF prediction accuracy in SPIF, we propose a novel method based on simulations of truncated cone parts with variable tool radii. A FLCF is then constructed by determining major/minor strains in simulated samples. To ascertain the validity of this enhanced FLCF model, our study includes simulations and tests of truncated cone samples with varying wall angles, revealing a substantial alignment in fracture height between corresponding samples. This research contributes to the advancement of SPIF by enhancing our ability to predict and mitigate product defects, ultimately expanding the applicability of SPIF in diverse industrial contexts.

Magnesium alloys, because of their good specific material strength, can be considered attractive by different industry fields, as the aerospace and the automotive one. However, their use is limited by the poor formability at room temperature. In this research, a numerical approach is proposed in order to determine an analytical expression of material formability in hot incremental forming processes. The numerical model was developed using the commercial software ABAQUS/Explicit. The Johnson-Cook material model was used, and the model was validated through experimental measurements carried out using the ARAMIS system. Different geometries were considered with temperature varying in a range of 25–400 °C and wall angle in a range of 35–60°. An analytical expression of the fracture forming limit, as a function of temperature, was established and finally tested with a different geometry in order to assess the validity.

Heat-assisted forming processes are becoming increasingly important in the manufacturing of sheet metal parts for body-in-white applications. However, the non-isothermal nature of these processes leads to challenges in evaluating the forming limits, since established methods such as Forming Limit Curves (FLCs) only allow the assessment of critical forming strains for steady temperatures. For this reason, a temperature-dependent extension of the well-established GISSMO (Generalized Incremental Stress State Dependent Damage Model) fracture indicator framework is developed by the authors to predict forming failures under non-isothermal conditions. In this paper, a general approach to combine several isothermal FLCs within the temperature-extended GISSMO model into a temperature-dependent forming limit surface is investigated. The general capabilities of the model are tested in a coupled thermo-mechanical FEA using the example of warm forming of an AA5182-O sheet metal cross-die cup. The obtained results are then compared with state of the art of evaluation methods. By taking the strain and temperature path into account, GISSMO predicts greater drawing depths by up to 20% than established methods. In this way the forming and so the lightweight potential of sheet metal parts can by fully exploited. Moreover, the risk and locus of failure can be evaluated directly on the part geometry by a contour plot. An additional advantage of the GISSMO model is the applicability for low triaxialities as well as the possibility to predict the materials behavior beyond necking up to ductile fracture.

The strain paths of electromagnetic forming limit curve are usually limited due to the restricted design of coil, die, or workpiece. The electromagnetic-driven stamping was suggested to obtain the high-speed forming limit curve of AA5182-O aluminum alloy sheet. The hemispherical punch was pushed by the drive plate with the Lorentz forces to impact on the workpiece. The cross-sectional method was used to determine the experimental limit strains of workpieces. The electromagnetic and mechanical fields were sequentially coupled for numerical simulation of the electromagnetic-driven stamping experiment, and the equivalent plastic strain increment ratios of the necking and safe zones were calculated to determine the simulated limit strains. A series of linear strain paths were attained to contain the uniaxial tension to biaxial tension states. The experimental and simulated forming limit curves showed good agreement to validate the electromagnetic-driven stamping experiment. The electromagnetic-driven forming limit curve was compared with the quasi-static and electromagnetic forming limit curves. Although the electromagnetic-driven forming limit curve is lower than the electromagnetic one, it is higher than the quasi-static one.

In this paper, the subject of research is the AZ31B magnesium alloy. Aiming at the poor formability of magnesium alloys at room temperature, we have introduced isothermal local loading technology to improve the formability of magnesium alloys. We combined finite element simulations and experiments to study the effects of forming parameters on the forming limit angle and thinning rate of single-point incremental forming under isothermal local loading. The conclusions were further validated by changes in grain size in micrographs. The results showed that the forming limit angle of the AZ31B magnesium alloy sheet increased as the forming temperature increased. Maximum thinning first decreased and then increased, reaching the lowest point at 250 °C. At 250 °C, the grain size is large and evenly distributed, which is the best forming temperature. The radius of the tool head increases, the forming limit angle increases, the maximum thinning rate decreases, and the overall change of the average grain size is relatively small. However, the grain size is more uniform when the radius is 5 mm, and 5 mm is the best tool radius. The feed rate is inversely proportional to the forming limit angle and directly proportional to the maximum thinning rate. Different feed rates have different degrees of compression and elongation of the grains. The forming quality is better when the feed rate is 2 mm. The initial plate thickness is proportional to the limit angle, the maximum thinning rate, and grain size. And 1 mm is the best plate thickness to ensure the forming quality. This paper is important for developing the forming theory of isothermal local loading that can improve the high-performance forming of alloy parts in advanced manufacturing.

Blades are important parts of aero-engines, and their manufacturing technology directly affects the preparation level and development speed of aero-engines. In view of the many problems existing in the current blade preforming process, this paper proposes a potential way to prepare blade preforms by using cross wedge rolling (CWR). Furthermore, considering the shape characteristics of the blade, a blade preform with an elliptical section formed by CWR was thoroughly investigated. The roll’s profile curve is of significant importance to forming quality, and its equation was deduced based on the plane meshing principle between the roll and the rolling piece and verified by finite element (FE) analysis and CWR experiments on a homemade platform. Meanwhile, the accuracy of the established FE model was quantitatively tested and used to study the forming limit expressed by eccentricity e, and the forming limit was approximately 0.8 (i.e., e ≤ 0.8). Based on this, a blade preform for an aero-engine compressor was designed with two elliptical sections, and it was well formed by the FE model, which verified the feasibility; these research results can also be extended and applied to the preform of other nonrotating parts and other materials.