International Journal of Material Forming最新文献

Enhanced simulation capability for the cutting process is crucial to making quick evaluations of cutting forces and temperatures, which are significant for assessing the machinability of the workpiece material and predicting tool wear. In this paper, the material flow in orthogonal cutting, including primary and secondary shear zones, is represented by a viscous/viscoplastic model that includes the temperature-sensitive Johnson-Cook flow stress model. A stabilized staggered finite element procedure is developed to handle incompressible Navier-Stokes material flow in combination with convection-dominated hardening and thermomechanical interaction. To handle material flow at tool-workpiece contact, a mixed method is used to reduce spurious oscillations in contact stresses along with simplified heat transfer in the tool-workpiece interface. A novel feature is that the velocity field is resolved as a subscale field to the velocity field of the distributed primary zone deformation model. It appears that the finite element solution to the subscale material flow model is significantly more cost-effective in contrast to directly addressing the velocity field and compared to the chip-forming simulations (DEFORM 2D). The cutting forces, temperature, and stress-strain state of the material in the critical deformation regions can be accurately estimated using the subscale model. The results obtained show that the trend of the estimated forces and temperatures is consistent with our experimental measurements, the DEFORM 2D simulations, and the experimental data from the literature.

Owing to the competitive advantages such as a high strength-to-weight ratio and excellent corrosion resistance, ultra-thin titanium sheets are considered one of the most promising bipolar plate substrates for proton exchange membrane fuel cells and are receiving increasing attention. However, due to their limited formability at room temperature, titanium bipolar plates are challenging to form, especially as the complexity of the flow channels increase continuously. In this study, the flow behavior and mechanical properties of ultra-thin titanium sheets at elevated temperatures were investigated, and their fracture limits were characterized to provide guidance for determining the process window. Finally, a lab-scale titanium bipolar plate was trial-fabricated using hot stamping at 700 ℃ with an on-site electric heating system. The results reveal that both the forming limit and dimensional accuracy of the titanium bipolar plates can be clearly improved, confirming the feasibility of the hot stamping process.

Ultrasonic impact forming (UIF) is an essential cold working process for forming large thin-walled components. Stressing ultrasonic impact forming (SUIF) can produce more deformation than UIF in the prebending direction. In this paper, a four-step numerical model including prestress submodel, impact treatment submodel, data transfer submodel and prestress forming submodel is developed to simulate the SUIF process. The effect of nonuniform residual stress on plate deformation is investigated, the change regulation of residual stress is discussed, the effect of elastic prebending radius on the plate deformation is analyzed. The narrow plate can obtain a nearly single curvature deformation by SUIF. Compared to narrow plate, the square plate can produce smaller deformation in device offset direction. Compared to UIF, SUIF can produce smaller compressive stress in the top surface layer, larger tensile stresses in device moving direction, and smaller tensile stresses in device offset direction; SUIF can produce larger deformation in device offset direction. With the decrease in prebending radius, compressive residual stresses changes little, and the tensile stress increases in the device offset direction, the deformation increases in the device offset direction and decreases in the device moving direction.

Due to the labor-saving one-sided installation and little composite damage, screw type blind rivets are widely used for clinching composite structures in the aerospace field. However, there is a lack of comprehensive understanding of their setting process and the effects of geometric parameters on the large blind head formation and pre-load. In this paper, a 3D finite element model of a typical screw type blind rivet was built and validated by experimental results. According to the simulation results, it was found that the large blind head’s shape and pre-load were highly sensitive to the thickness ratio of insert and sleeve, the height ratio of insert and sleeve, the tapered angle of the nut body nose and the inclining angle, while the tapered angle of sheet and the height ratio of insert and sleeve’s inner stepped surface had relatively little impacts. Specifically, the thickness ratio, height ratio and nose angle had the suitable ranges, not within which an unqualified blind head with minor pre-load, small diameter, or (and) prohibited double flexures would occur. The pre-load is inversely proportional to inclining angle, whose optimum is 0°. In addition, the divided stages revealed the drop of pre-load caused by instability, while no instability took place in large thickness ratio. The accurate and reliable 3D model would build confidence in improving joint integrity and in further studying the failure mechanisms of joints, including loosening and composite damage.

Creasing defects in aluminum profiles post-forming significantly hinder their utilization. This study aimed to mitigate these defects by investigating the causes and mitigating strategies for two types of creases in aluminum profiles formed via flexible stretch bending with roller-type multi-point dies (FSBRD). To achieve dynamic control over the mold surface, magnetorheological elastomers (MREs) were employed to harness their magnetorheological effect, enabling adjustable mold hardness. The adjustable hardness of the mold, enabled by MREs, was investigated under varying magnetic inductions to form T-shaped profiles. The results quantitatively demonstrate that the addition of MREs significantly reduces crease defects, with a minimum value of thick direction strain not exceeding -0.1, and improves moulding quality. Specifically, at a profile thickness of 10mm, an optimal magnetic induction of 200mT minimized crease depth, while for a 66mm thickness, 400mT was most effective. It was also found that increasing the coefficient of friction between the MRE and the contour resulted in a decrease in crease depth and a decrease followed by an increase in crease height. Experimental validation confirmed the simulation accuracy, with thickness trends of the experimentally formed profiles closely matching the simulated ones. The study concludes that the FSBRD-M process is effective in controlling creases and expands the application of MREs in forming technology.

Springback is a critical factor that significantly influences the quality of roll forming. Accurate prediction and control of springback are crucial for the design of process parameters. This paper proposes a technique based on Support Vector Regression (SVR) and Bat Algorithm (BA) to reduce springback. Firstly, based on roll forming experiments, the SVR model optimized by algorithm based on the Simulated Annealing Particle Swarm Optimization algorithm (SAPSO) is used to predict springback and investigate the influence of forming parameters. The considered forming parameters include the mechanical properties of material (e.g. yield strength, Young’s modulus), geometries of metal sheet (e.g. sheet width), and process parameters, such as uphill value, roll gap. Then, using the Bat Algorithm based on Lévy flight disturbance, the process parameters are optimized with the predicted springback as the fitness function. The experimental results show that the springback in roll forming has been reduced by 94.47% after optimizing the process parameters. Therefore, the feasibility of the proposed springback control method is confirmed.

The paper presents a coupled 3D numerical model to understand high-strain rate electromagnetic forming and multi-point perforation of Al6061-T6 tube. This study focuses on a comprehensive exploration of the process by numerically simulating the forming and perforation of Al6061-T6 tubes for two type of punches (concave and pointed) across different configurations (12-holes and 36 -holes), and for two specific hole positions (centrally located and end holes), implemented through LS-DYNA™ software. A detailed analysis of the temporal distributions of various critical process parameters i.e., Lorentz force distribution, velocity on deformation, stress, and strain distribution near the perforated hole has been carried out to elucidate the physics of EMFP. Furthermore, the study compares the numerical simulation with experimental data to evaluate the number of perforated holes and the average hole diameter across different punch configurations and discharge energy ranges. The numerical outcomes are in good agreement with experimental findings, with maximum variations not exceeding 6%. The study also reveals that the non-linearity associated with Lorentz force distributions is not only in circumferential direction but also in axial directions. Higher energy levels increase hole diameter, but for the given tube geometry, maximum 6.2 kJ can be applied without occurrence of crack and rebound. For the given tube thickness, 6.2 kJ discharge energy is optimum to produce clear perforation.

The hole expansion ratio (HER) observed in a standardized hole expansion test (HET) is commonly used to determine the edge fracture of steel sheets. A large variation of the measured HER restricts the practical application of the method. This study presents a systematic investigation on uncertainties in the HER of DP800 sheet material, including the hole-edge quality, pre-strain due to the hole-punching process, the friction coefficient, and the determination of fracture. An artificial neural network was trained to develop a surrogate model using a database gained from a thousand finite element simulations of the HET. Monte-Carlo simulations were performed using the trained surrogate model to characterize the distribution of the HER. Sensitivity analysis via Sobol’s indices is calculated to determine the influence of the input variables on the output. It is found that the pre-strain and pre-damage generated during the hole punching process in the shear-affected zone dominate the variation of the HER. Discussions on reducing the output’s variation are detailed. In general, these findings provide valuable insights for the determination of HER as well as the edge crack behavior of the investigated DP800 steel sheet.

This study considers the Gurson-Tvergaard-Needleman (GTN) micromechanical damage model as a potential alternative to the traditional forming limit curves used in industrial deep drawing applications. In the first step, the parameters of a coupled hardening law with the GTN damage model were identified through parametric identification using inverse analysis. This technique relies on tensile test results obtained from notched specimens cut from cold-rolled steel (DC06EK). The study's originality lies in utilizing both global and local experimental data, focusing principally on the force–displacement curves and the evolution of equivalent plastic strain within two zones of the specimen: rupture and deformation stagnation. The parameter identification demonstrated a good agreement between experimental data and numerical results. In the second step, the determined work hardening law coupled with the GTN damage model was implemented in a numerical simulation of an industrial deep drawing process for a wheelbarrow tray (WBT). The outcomes of the numerical simulation, in terms of thickness reduction in the deep-drawn WBT, were compared with the experimental results, showing very good agreement. A further comparison was made between the numerical results with and without the GTN model, as well as with a previous study (without GTN) on the same numerical simulation. This demonstrated the value of incorporating a hardening law coupled with the GTN model, as it allowed for more accurate determination of wrinkling and necking prior to rupture based on the applied blank holder pressure, helping to prevent those defects during the deep drawing process of the WBT.

The Near Solidus Forming (NSF) process represents a critical method for shaping metallic components under extreme temperature conditions. When metals deform plastically, significant amounts of heat can be generated, which is due to the conversion of plastic deformation energy in the material often known is adiabatic heating. In this study, the influence of the adiabatic heating coefficient (AHC) on temperature distribution and plastic strain during NSF process is investigated. For this purpose, three industrial benchmarks previously fabricated using NSF techniques are selected to serve as representative cases for analysis. To conduct the analysis, sensitivity studies is performed at two key temperatures: 1360 °C and 1370 °C. These temperatures are chosen to capture the range of operating conditions typically encountered in industrial NSF applications. The simulation tool FORGE NXT^® is utilized to investigate the potential effect of AHC on equivalent plastic strain (EPS). The range of potential AHC values considered is between 85% and 100%, as determined from a comprehensive literature survey. The study suggests that the AHC has a minimal effect on the deformation behaviour of 42CrMo4 steel at NSF condition for the studied benchmarks. The findings of this study provide the inside to the importance of AHC in the developing of a reliable Digital Twin (DT) for industrial NSF application.