International Journal of Material Forming最新文献

Lightweight automotive extrusions are increasingly complex, thin-walled, multi-hollow profiles made from quench-sensitive alloys like AA6082. These profiles require rapid (water) quenching as they leave the press in preparation for age-hardening. Conventional rapid quenching, which only directly cools the profile’s extremity, can distort the part. Lower quenching rates reduce distortion but may compromise the mechanical properties. We test three hypotheses: (1) That the different cooling rates across the section during quenching induce varying mechanical properties as well as distortion; (2) That this temperature differential can be minimized by combining novel internal profile quenching with conventional quenching; and (3) That internal quenching can be achieved using insulated channels in the extrusion die to convey the quenchant to the profile’s interior. The first hypothesis is tested experimentally by taking tensile specimens from a AA6082 multi-hollow profile. The second is examined experimentally using a lab-built quench box and theoretically using thermo-mechanical finite element simulations. The third hypothesis is tested by conducting a hollow profile extrusion trial using a specially designed porthole die. The testing shows that conventional quenching results in reduced mechanical properties in the profile’s internal walls but that combined external/internal quenching alleviates this problem and reduces distortion. The extrusion trial on internal quenching demonstrates die survivability, an acceptable die temperature drop during quenchant flow, and effective quenchant disposal via evaporation and capture of liquid at the end of the profile. This study suggests that internal quenching is a promising technology option for reducing scrap and improving mechanical properties of hard-to-quench aluminum profiles.

The general ({I}_{1}{J}_{2}{J}_{3}) yield function (Lou et al. in Int J Plast 158:103414, 33) is extended to an analytically anisotropic form by using a newly proposed five-parameter linear transformation tensor based on the work of Barlat et al. Int J Plast 7:693–712, 7). The anisotropic parameters are analytically calculated so that the proposed yield function can model both differential hardening at various stress states and anisotropic hardening along different loading directions. The extended anisotropic form is applied to characterize the strain hardening behavior of metals of three different polycrystal structures, including AA7075 T6 aluminium, QP1180 steel, and AZ31 magnesium. The results show that the extended anisotropic form is capable of precisely modelling both the differential and anisotropic hardening for the studied metals under various stress states. The proposed function is also applied to a high strength steel QP980 (Hou et al. J Mater Process Technol 290:116979, 17) to validate the capability of the proposed model for the modeling of strength differential (SD) effect between uniaxial tension and compression and its evolution with respect to plastic strain. The results show that the proposed function is capable of predicting the SD effect between uniaxial tension and compression with very high accuracy along RD, DD and TD. Convexity analysis is conducted during yield surface evolution by a newly proposed geometry-inspired numerical convex analysis method to ensure the yield surface convexity during significant change of yield surfaces.

Aluminum alloy forged wheel hubs are lightweight materials for electric vehicles. However, forming high-ribbed spokes is challenging due to potential shrinkage during high rib extrusion with plane strain characteristics. This study utilizes the finite element method to analyze the high-rib extrusion process with plane-strain characteristics. It is found that a region of tensile stress exists near the bottom fillet of the rib persisting until the high rib contour is fully filled. The position and size of this region remain largely unchanged during extrusion. Defining the occurrence of shrinkage defects as a critical state, the thickness is defined as the critical residual thickness. By constructing a stress state slip line field for plane-strain extrusion, a prediction formula for the critical residual thickness of high-rib extrusion is proposed. The proposed critical residual thickness is evaluated through finite element calculations and high-rib extrusion experiments. The results show that the critical residual thickness is linearly positively correlated with the half-width of the rib root and negatively correlated with the fillet radius of the rib root, taper angle, and shear friction coefficient. The initial blank thickness does not affect the critical residual thickness. The depth of the shrinkage increases linearly with the decrease in residual thickness. The experimental critical residual thickness can be determined by combining finite element calculations and extrusion experiments. The proposed theoretical formula for the critical residual thickness has an error of + 8.14% compared to the experimental critical residual thickness. This theoretical prediction is relatively conservative and can guide the design of high-rib extrusion forming billets to ensure defect-free high-rib forming.

In the light of recent developments in the design of structural materials, micro-architected heterogenous-structure metals are considered among most structurally efficient. In this work, a new technique for Local High Pressure Torsion (L-HPT) enabling the creation of heterogeneous structures through localised deformation processing in sheet metals by impeding a rotating punch is proposed. Using AA5083 aluminium alloy as an example, we show experimentally that the rotation of the punch sets adjacent material layers in motion. This results in more than two-fold increase in material hardness over initial level in the workpiece bulk with rather sharp gradients in hardness level transition. The maximum hardness is observed at the peripheral edge of a punch tip. Finite-element modelling of the L-HPT process confirmed that the rotational flow of workpiece material leads to the accumulation of shear strain. The level of accumulated strain increases with an increase in friction at the contact surface. Further analysis based on dimensionality theory revealed that for such an L-HPT configuration the level of equivalent strain is directly proportional to the ratio of rotation-to-translation speeds at the punch.

The Sheet Molding Compound (SMC) process is essential in high-volume manufacturing of composite structures due to its scalability and efficiency. A primary challenge, however, lies in determining the initial charge shape that ensures complete mold filling without excessive overflow, typically resolved through labor-intensive trial and error. While simulations can anticipate the mold filling outcome, they often lack the capability to fine-tune the initial preform configuration, leading to inefficiencies in both time and material. This study presents an innovative, simulation-driven approach for accurately predicting initial charge shapes for two-dimensional (2D) mold designs. By employing Darcy’s Law and a fixed mesh grid framework, the methodology simulates a reverse material flow to trace the optimal preform shape. A complementary machine learning (ML) model was then developed to predict the preform shapes based on mold geometry, final thickness, and initial charge thickness. Serving as a digital twin of the SMC process, this ML model delivers results with comparable accuracy to simulations, significantly enhancing computational efficiency and avoiding common convergence issues in traditional simulations. This ML-driven digital twin approach also provides a robust proof of concept for addressing initial charge shapes in complex three-dimensional (3D) molds, where the computational demands of reverse flow simulations may present challenges. This combined simulation and ML framework equips manufacturers with a more precise and efficient tool for optimizing SMC processes, minimizing material waste, and reducing production time.

Explosive welding (EXW) is a high-speed process used to join dissimilar materials and produce large surface sheet products. While traditionally reliant on experimental observations of welded interfaces, this approach offers limited insight into the dynamic phenomena during flyer and base plate collisions, hindering the development of closed-loop control systems. Therefore, numerical modeling has emerged as a critical tool to optimize welding parameters and predict product properties more effectively. This research presents a novel physics-based numerical model for EXW, developed using a refined Smooth Particle Hydrodynamics (SPH) framework. Unlike existing models that simplify or exclude the explosive material’s dynamics, this approach explicitly simulates explosive detonation, flyer plate response, and the resulting welding process. The model integrates comprehensive equations of state and constitutive laws to capture both macroscale and microscale phenomena observed in experiments. The key novelty lies in bridging microscale interface behavior with macroscale process outcomes, offering a detailed representation of vortex formation and weld quality. Validation against analytical solutions and experimental data demonstrates the model’s accuracy and ability to resolve critical features of the EXW process, providing a foundation for future optimization and control strategies.

Sheet metal forming is essential in automotive and aerospace industries, where accurate simulations are crucial for optimizing material deformation and tool design. Finite Element Analysis (FEA) is a key tool for predicting stresses, strains, and material flow in these processes. Recent advancements in artificial intelligence (AI) and machine learning have further enhanced these simulations, improving toolpath planning and overall process efficiency Appl Mech 1:97-110, 2020, ASME J Manuf Sci Eng 144(2):021012, 2021. A critical aspect of sheet metal forming is the development of forming tools, which must withstand high forces and ensure precision. Traditionally, tool design has relied on a trial-and-error approach, heavily dependent on manufacturer expertise. This paper introduces an innovative methodology that integrates sheet metal forming simulations with the structural analysis of forming tools, facilitated by a specialized connector. The connector enables integrated analysis of the forming process and tool structural behaviour, providing feedback on tool performance under operational loads. The output of the forming simulation (contact pressures between workpiece and tools) feeds the structural model. Additionally, the methodology incorporates AI-driven what-if analysis to streamline decision-making in the early design stages. This modular solution is designed to integrate with a Digital Twin framework, offering continuous optimization. The proposed methodology enhances manufacturing efficiency by reducing simulation time and improving tool structural behaviour predictions, enabling faster, more accurate tool development and ultimately minimizing trial-and-error in tool design.

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.