Bending Operation Research Articles

Investigation of Digital Light Processing-Based 3D Printing for Optimized Tooling in Automotive and Electronics Sheet Metal Forming

This study addresses the emerging need for efficient and cost-effective solutions in low-volume production by exploring the mechanical performance and industrial feasibility of cutting tools that are fabricated using stereolithography apparatus (SLA) technology. SLA’s high-resolution capabilities make it suitable for creating precise cutting dies, which were tested on aluminum sheets (Al99.5, 0.3 mm, and AlMg3, 1.0 mm) under a 60-ton hydraulic press. Measurements using digital image correlation (DIC) revealed minimal wear and deformation, with tolerances consistently within IT 0.1 mm. The results demonstrated that SLA-printed tools perform comparably to conventional metal tools in cutting and bending operations, achieving similar surface quality and edge precision while significantly reducing the production time and cost. Despite some limitations in wear resistance, the findings highlight SLA technology’s potential for rapid prototyping and short-run manufacturing in the automotive and electronics sectors. This research fills a critical gap in understanding SLA-based tooling applications, offering insights into process optimization to enhance tool durability and broaden material compatibility. These advancements position SLA technology as a transformative tool-making technology for flexible manufacturing.

Oxygen-Doped 2D In2Se3 Nanosheets with Extended In-Plane Lattice Strain for Highly Efficient Piezoelectric Energy Harvesting.

With the emergence of electromechanical devices, considerable efforts have been devoted to improving the piezoelectricity of 2D materials. Herein, an anion-doping approach is proposed as an effective way to enhance the piezoelectricity of α-In2Se3 nanosheets, which has a rare asymmetric structure in both the in-plane and out-of-plane directions. As the O2 plasma treatment gradually substitutes selenium with oxygen, it changes the crystal structure, creating a larger lattice distortion and, thus, an extended dipole moment. Prior to the O2 treatment, the lattice extension is deliberately maximized in the lateral direction by imposing in situ tensile strain during the exfoliation process for preparing the nanosheets. Combining doping and strain engineering substantially enhances the piezoelectric coefficient and electromechanical energy conversion. As a result, the optimal harvester with a 0.9% in situ strain and 10 min plasma exposure achieves the highest piezoelectric energy harvesting values of ≈13.5 nA and ≈420 µW cm-2 under bending operation, outperforming all previously reported 2D materials. Theoretical estimation of the structural changes and polarization with gradual oxygen substitution supports the observed dependence of the electromechanical performance.

Multi-layered morphing soft structure with high-performance embedded electrothermal artificial muscles along with touch and temperature sensors

Abstract In this paper, we present a novel multilayered morphing structure, having similar topology resembling the structures found in nature to grasp delicate objects effectively as well as sense contact force and temperature. The structure consists of two actuation layers, two U-shaped cooling channel layers, piezoelectric based touch sensors and temperature sensors. Employing shape memory alloy (SMA) spring actuators for bending and twisted and coiled polymer fishing line with nichrome (TCPFL NMC) artificial muscles for antagonistic return, the soft silicone-based composite skin exhibits unique capabilities of large bidirectional movement, avoid rigid passive springs for return motion, soft grasping, safe interaction with humans, and ease fabrication. The SMA (0.38 mm wire diameter) serves as relatively fast actuating muscle and the TCPFL NMC (0.8 mm fiber diameter) as a slow actuating (considering mainly heating cycle), which was programmed/designed to mimic the fast and slow twitching muscles found in nature. Bending and return operations of skin samples of length 100 mm and thickness of 9 mm, with three different widths 20 mm, 25 mm, 30 mm, were experimentally studied. The 25 mm wide multilayered soft skin demonstrated cyclic actuation with a maximum bending angle of ∼70°, which was attributed due to the active cooling. The fluidic channels for active cooling were fabricated using 3D printed PVA tubes, casting within the silicone in a mold and subsequently dissolving in a circulating water. The study also included the integration and voltage response of mini-piezodisk sensor PIC255 having a diameter of 2 mm and thickness of 0.15 mm, which was embedded at different depths within the silicone (on the surface, 1 mm depth and 2 mm depth). The multilayered soft skin was also able to detect the temperature of the object during grasping, suggesting its potential application as a soft gripper in robotic systems.

Flattening of bent metal sheets as a remanufacturing operation

The reshaping of end-of-life or scrap sheet metal panels is a potential remanufacturing process, which enables significant environmental benefits over the traditional metal recycling routes. This paper experimentally investigates cold and warm press flattening of waste sheet metal for enabling remanufacturing. Samples of stainless steel, aluminium alloy, and low carbon steel were bent to various internal angles using v-die air bending operations. Then, flattening tests were conducted with a hydraulic press, with tools capable of heating up to 300 °C. The process parameters included dwell force, dwell time, and tool temperature. The target final angle after load release is set at 180°, but the flattening process typically induces springforward, and the final angle is generally larger than 180°. Springforward can be mitigated by using warm flattening conditions with all the tested materials. It can also be reduced if superposing a steel mesh between the top flattening die and the sheet. The paper demonstrates and explains the mechanical effects of the flattening process.

Taguchi Optimization of Screw Flight Bending Operation

The optimizations of screw flight bending operating parameters have been successfully carried out. The optimization of the screw flight bending operation, aims at determining optimal values for key parameters using Taguchi Design and Genetic Algorithm (GA) optimization tools. The parameters investigated include bending radius, diameter of screw, flight thickness, and bending force. Through the systematic application of Taguchi methodology and GA optimization, optimal values of 79.99 mm for bending radius, 69.997 mm for diameter of screw, 5.005 mm for flight thickness, and 232.62 N for bending force were identified. The effectiveness of the optimized parameters was assessed through analysis of variance (ANOVA), revealing an R-squared value of 84.78 % and an adjusted R-squared value of 75.64 %. These results indicate that the developed model explains a significant portion of the variability in the response variable, providing confidence in the reliability and significance of the optimized solutions. Overall, the integration of Taguchi methodology with GA optimization has proven to be a powerful approach for systematically exploring parameter space and identifying optimal solutions in screw flight bending operations. The optimized parameter values offer the potential for enhanced performance, accuracy, and efficiency in the bending process, contributing to improved product quality and manufacturing productivity.

Effects of Bending and Re-bending on Mechanical Properties of Locally-Manufactured Steel Rebars

Steel rebars experience deformation when subjected to bending and re-bending operations. Subsequently, their microstructures are impaired thus affecting the mechanical properties and leading to failure. This study establishes the effects of bending and re-bending the steel rebars on the mechanical properties. Experiments were conducted to determine the effects of bending and re-bending of the steel rebars. Testing was conducted on Ten virgin and Thirty specimens which were bent and re-bent at 45º, 90º, and 180º, and followed by tensile tests. Yield strength, ultimate tensile strength, elongation, and ultimate tensile strength to yield strength ratio (Rm/Re), were recorded. Results showed the yield strength, ultimate tensile strength, elongation, and Rm/Re of virgin steel rebars varied from 553.62 MPa to 618.49 MPa, 634.39 MPa to 745.68 MPa, 17.6 % to 21.67 %, and 1.14 to 1.19. The yield strength, ultimate tensile strength, elongation, and Rm / Re of bent and re-bent steel rebars at angles of 45º, 90º, and 180º varied from 603.67 MPa to 677.38 MPa, 692.82 MPa to 751.76 MPa, 6.88 % to 19 % and 1.09 to 1.21. It was established that bending and re-bending increase strength and reduce the ductility of the rebars proportionally.

Residual Stress Engineering for Wire Drawing of Austenitic Stainless Steel X5CrNi18-10 by Variation in Die Geometries-Effect of Drawing Speed and Process Temperature.

As a result of conventional wire-forming processes, the residual stress distribution in wires is frequently unfavorable for subsequent forming processes such as bending operations. High tensile residual stresses typically occur in the near-surface region of the wires and can limit further application and processability of the semi-finished products. This paper presents an approach for tailoring the residual stress distribution by modifying the forming process, especially with regard to the die geometry and the influence of the drawing velocity as well as the wire temperature. The aim is to mitigate the near-surface tensile residual stresses induced by the drawing process. Preliminary studies have shown that modifications in the forming zone of the dies have a significant impact on the plastic strain and deformation direction, and the approach can be applied to effectively reduce the process-induced near-surface residual stress distributions without affecting the diameter of the product geometry. In this first approach, the process variant using three different drawing die geometries was established for the metastable austenitic stainless steel X5CrNi18-10 (1.4301) using slow (20 mm/s) and fast (2000 mm/s) drawing velocities. The residual stress depth distributions were determined by means of incremental hole drilling. Complementary X-ray stress analysis was carried out to analyze the phase-specific residual stresses since strain-induced martensitic transformations occurred close to the surface as a consequence of the shear deformation and the frictional loading. This paper describes the setup of the drawing tools as well as the results of the experimental tests.

Characterization of Fatigue Crack Growth Behaviour of Alloy 617M Base and Weld Material

Alloy 617M is a Ni-based super-alloy made in the form of tubes which are used in high-temperature boilers and super heaters in Advanced Ultra Super Critical (AUSC) power plants. The high-temperature oxidation and mechanical properties of this material have been derived based on chromium (Cr), cobalt (Co) and molybdenum (Mo) as prime alloying elements which cause solid solution strengthening, carbide precipitation (M23C6, M6C) and formation of intermetallic phase Ni3(Al, Ti) (γʹ-phase). The manufacturing route of these components involve bending and welding operations which are critical locations and potential sites for crack nucleation and growth. Also, the conjoint influence of high temperature and flow-induced vibrations in the tubes further aides to crack nucleation and growth. Thus, fatigue crack growth (FCG) properties are important. Therefore, in this work, detailed experimental studies on the FCG behaviour of Alloy 617M base and weld materials have been carried out at different test temperatures (27 °C, 650 °C, 710 °C and 750 °C). The effect of ageing (1000, 2000, 5000 and 20000 hours) at an operating temperature of 710 °C on FCG has also been evaluated. All the FCG tests have been conducted as per ASTM with a constant load ratio (R = 0.1) and frequency of 15 Hz. From the experimental results, a major trend is observed of decreasing threshold stress intensity factor (ΔKTH) with an increase in ageing time and test temperature. The variations in the ΔKTH with test temperature and ageing time have been discussed and the crack growth mechanism has been established through microstructure and fractographic studies validating from existing literatures.

Giant tridimensional power responses in a T-shaped magneto–mechano–electric energy harvester

We present a T-shaped MME-EH that enables collaborative twisting or bending operation modes for tridimensional responses. The device produces a peak–peak output power of 98.5 mW at 60 Hz, which is 262% higher than the state-of-the-art results.

Bending behavior of structured steel sheets with undercuts for interlocking with Al die-cast metal

Due to the current changes in mobility, lightweight design concepts continue to be of particular interest to the automotive industry. One form is the multi-material design, in which the advantageous properties of different materials are combined in one component. In this work, a component made of a steel sheet with stiffening structures of cast aluminum is considered. The joint is created by channel structures with undercuts on the surface of the steel sheet, into which the molten aluminum can flow. After solidification, an interlocking connection is created. The aim of this work is to investigate the influence of a bending operation on the surface structure before the die casting process. Numerical simulations and experimental validations were performed with different bending angles and radii as well as orientations between the channel structure and the punch. The results show that the undercuts on the outer radius are reduced by up to 75% by the bending operation, thus weakening the resulting joint. On the inner radius, the channel opening width narrows by up to 73% and can thus impede the filling with the melt.

Applicability of a laser pre-treatment for a robust subsequent bending of thin sheet metal

In conventional bending, locally varying residual stress states are one of the main causes for dispersion of bending angle. In this paper, a novel approach is investigated to reduce the dispersion of bending angle by modifying the residual stress state of thin sheets prior to the forming process. For this purpose, steel sheets were pre-treated with a nanosecond-pulsed fiber laser in confined ablation. The deflections were compared to sheets processed with thermal laser bending. It is revealed that the thermal mechanism dominates with respect to the deflection of the sheet because the deflection is in the same direction as that of laser-bent sheets. However, the induced deflection is smaller compared to the laser-bent ones. Moreover, it can be demonstrated that the robustness of subsequent bending operations is increased by the laser pre-treatment. The increase in robustness allows to achieve narrower tolerance windows for thin sheet metal without using cost-intensive tools and high punch forces.

Robust Proton Conduction against Mechanical Stress in Flexible Free‐Standing Membrane Composed of Two‐Dimensional Coordination Polymer

AbstractIntroduction of mechanical flexibility into proton‐conducting coordination polymers (CPs) is in high demand for future protonic applications such as fuel cells and hydrogen sensors. Although such mechanical properties have been primarily investigated in one‐dimensional (1D) CPs, in this study, we successfully fabricated highly flexible free‐standing CP membranes with a high surface‐to‐volume ratio, which is beneficial for enhanced performance in the aforementioned applications. We fabricated a layered CP, Cu2(NiTCPP) (H4(H2TCPP); 5,10,15,20‐tetrakis(4‐carboxyphenyl) porphyrin), in which a two‐dimensional (2D) square grid sheet composed of tetradentate nickel porphyrins and paddlewheel‐type copper dimers was connected to each other by weak van der Waals forces. The mechanical flexibility was evaluated by bending and tensile tests. The flexural and Young's moduli of the membrane were significantly higher than those of conventional Nafion membranes. Electrochemical impedance spectroscopy analysis revealed that the in‐plane proton conductivity of the membrane was maintained even under applied bending stress. Because the X‐ray diffraction analysis indicates that the proton‐conducting pathway through the hydrogen bonding network remains intact during the bending operation, our present study provides a promising strategy for the fabrication of new and advanced 2D CPs without using substrates or additional polymers for protonic devices.

Robust Proton Conduction against Mechanical Stress in Flexible Free-Standing Membrane Composed of Two-Dimensional Coordination Polymer.

Introduction of mechanical flexibility into proton-conducting coordination polymers (CPs) is in high demand for future protonic applications such as fuel cells and hydrogen sensors. Although such mechanical properties have been primarily investigated in one-dimensional (1D) CPs, in this study, we successfully fabricated highly flexible free-standing CP membranes with a high surface-to-volume ratio, which is beneficial for enhanced performance in the aforementioned applications. We fabricated a layered CP, Cu2 (NiTCPP) (H4 (H2 TCPP); 5,10,15,20-tetrakis(4-carboxyphenyl) porphyrin), in which a two-dimensional (2D) square grid sheet composed of tetradentate nickel porphyrins and paddlewheel-type copper dimers was connected to each other by weak van der Waals forces. The mechanical flexibility was evaluated by bending and tensile tests. The flexural and Young's moduli of the membrane were significantly higher than those of conventional Nafion membranes. Electrochemical impedance spectroscopy analysis revealed that the in-plane proton conductivity of the membrane was maintained even under applied bending stress. Because the X-ray diffraction analysis indicates that the proton-conducting pathway through the hydrogen bonding network remains intact during the bending operation, our present study provides a promising strategy for the fabrication of new and advanced 2D CPs without using substrates or additional polymers for protonic devices.

Flexible waveguide integrated thermo-optic switch based on TiO2 platform.

Mechanically flexible photonic devices are critical components of novel bio-integrated optoelectronic and high-end wearable systems, in which thermo-optic switches (TOSs) as optical signal control devices are crucial. In this paper, flexible titanium oxide (TiO2) TOSs based on a Mach-Zehnder interferometer (MZI) structure were demonstrated around 1310 nm for, it is believed, the first time. The insertion loss of flexible passive TiO2 2 × 2 multi-mode interferometers (MMIs) is -3.1 dB per MMI. The demonstrated flexible TOS achieves power consumption (Pπ) of 0.83 mW, compared with its rigid counterpart, for which Pπ is decreased by a factor of 18. The proposed device could withstand 100 consecutive bending operations without noticeable degradation in TOS performance, indicating excellent mechanical stability. These results provide a new perspective for designing and fabricating flexible TOSs for flexible optoelectronic systems in future emerging applications.

Mechanical joining of sheets to tubes by a sheet bending-unbending cycle

The utilization of an axial sheet bending-unbending cycle was previously utilized to produce mechanical joints of sheets to rods at ambient temperature by two subsequent operations. In this research, that joining process is now extended to produce a hidden mechanical joint between a sheet and tube that may not have protrusions both at the sheet surface and at the inner tube wall (if a mandrel is inserted there during the joining operation). The process is performed at ambient temperature and starts with the axial bending of a sheet with a pre-drilled hole of smaller diameter than that of the external diameter of the tube. That hole will be enlarged until a point where its diameter matches the external diameter of the tube to allow for its insertion. In a following operation, the sheet is unbent back to its original form, which will force the sheet material near the adjacent region of the hole to flow into a circular slot previously machined in the tube.Although the joining process is successful, the feasibility of the first axial sheet bending operation can be compromised, since it relies on a predetermined vertical displacement to ensure that its pre-drilled centre hole has the same diameter as the external diameter of the tube or rod that is to be inserted inside that hole, so that the mechanical joint is produced after the unbending of the sheet. To address those limitations, a modification is also proposed to the joining process where a redesigned punch tool allows to calibrate the hole diameter and guarantee that the tube or rod can be inserted correctly inside that hole for every joint to be produced while keeping tight tolerances.The combination of numerical modelling and experimentation allowed to determine the working parameters and their respective influence in the overall mechanics of the process. Unit test cells were utilized to prove the feasibility of the new concept and evaluate its pull-out destructive performance, although the joining process can easily be extended to larger tube and sheet dimensions since the plastic deformation is localized.

Improvement of process control in sheet metal forming by considering the gradual properties of the initial sheet metal

In scientific studies, sheet metal is usually considered as a two-dimensional body. Thus, it is accepted that material properties are in most cases regarded homogeneous in thickness direction. However, a gradation of certain properties becomes apparent when going beyond the standard characterization methods for sheet metals, which can for example, influence the springback behavior and the thinning of the sheet after forming. Thus, the aim of this work is to further improve the prediction accuracy of springback after forming in simulations, by implementing several inhomogeneous properties over the sheet thickness in an existing material model. For this purpose, the entire procedure from the identification of the inhomogeneous properties for describing the gradation to the implementation in a numerical model and its validation by comparing experimental and simulated bending operations is carried out on a DC04 cold-forming steel in order to prove its influence on the springback behavior. It is shown that including graded material properties in simulations does indeed have an impact on the prediction quality of springback and that the information about inhomogeneous properties can be provided by existing characterization methods with a high local resolution like electron backscatter diffraction or X-ray stress analysis. In a further step, it was possible to validate the improvement in numerical accuracy by comparing the prediction of the springback angle from both the existing and the extended model with experimental bending results. Both the initial model as well as the model supplemented with the 3D properties provide a good prediction accuracy in the solution heat treated material state. For the predeformed material, however, the initial numerical model predicts a springback angle of about 13°, which deviates remarkably from the experimentally obtained mean value of about 17°. The extended model delivers a significantly improved accuracy in springback prediction in relation to the initial prediction (deviation of 4°) with a minor deviation of only about 0.8°, which proves the importance of considering the gradation of material properties in thickness direction for an overall higher dimensional accuracy of sheet metal products.

Mosaic Nanocrystalline Graphene Skin Empowers Highly Reversible Zn Metal Anodes.

Constructing a conductive carbon-based artificial interphase layer (AIL) to inhibit dendritic formation and side reaction plays a pivotal role in achieving longevous Zn anodes. Distinct from the previously reported carbonaceous overlayers with singular dopants and thick foreign coatings, a new type of N/O co-doped carbon skin with ultrathin feature (i.e., 20nm thickness) is developed via the direct chemical vapor deposition growth over Zn foil. Throughout fine-tuning the growth conditions, mosaic nanocrystalline graphene can be obtained, which is proven crucial to enable the orientational deposition along Zn (002), thereby inducing a planar Zn texture. Moreover, the abundant heteroatoms help reduce the solvation energy and accelerate the reaction kinetics. As a result, dendrite growth, hydrogen evolution, and side reactions are concurrently mitigated. Symmetric cell harvests durable electrochemical cycling of 3040h at 1.0mA cm-2 /1.0 mAh cm-2 and 136h at 30.0mA cm-2 /30.0 mAh cm-2 . Assembled full battery further realizes elongated lifespans under stringent conditions of fast charging, bending operation, and low N/P ratio. This strategy opens up a new avenue for the in situ construction of conductive AIL toward pragmatic Zn anode.

A new, flexible tool concept for rotary die stretch bending

Mitigating manufacturing risks for profile-type parts formed using stretch bending operations is a considerable challenge in the industry, due to the investments required to manufacture the tooling for these processes. Traditionally such tooling has been made by solid steel blocks machined to the desired shape. This paper introduces a new tool concept for stretch bending processes, utilizing an adjustable multipoint supported flexible spring steel plate as a bend die, applied on a double rotary turntable stretch bender. The capability of the tool is investigated through a proof-of-concept experiment, assessing whether the tool design is capable of creating bends with the same quality as bends made using traditional solid steel dies. Overall, the experiment shows promising results as it allows for creating a large variation of bending shapes with good dimensional quality with low tooling investment, although the interface between the spring steel plate end and the aluminum profile creates some minor scuffing marks. The initial investigation found a pooled standard deviation of 0.25mm over 3 bend shapes with 3 samples for each, which is promising for further development. In industrial applications, the proposed tool would enable cost-efficient experimenting using production-intent tooling in the early product development phase, which could also be utilized for pre-production qualification processes, low volume manufacturing and multi-variant products.

Material Parameters Sensitivity on Springback Modelling of Simple Bending Process

Springback is one of the major defects that continuously concerns the sheet metal experts’ community. It is has long been known that the sheet thickness, the bending angle and the yield stress of the material primarily affect the angle change after the tools’ release. Besides, the consideration of the kinematic hardening (KH) model has powerful influence on the modelling results, too. In this study, we overviewed several possible factors on the springback with finite element modeling of a simple V-die bending operation, highlighting the effect of the material variables on the final shape. AutoForm® R7 software and the built-in theory of kinematic hardening were used for the material characterization, coupled with the Hockett-Sherby isotropic hardening rule as well as the Yld89 yield criterion. The material data for modeling kinematic hardening behavior were obtained by cyclic tension-compression tests, whilst the isotropic hardening and the yield surface parameters were acquired by simple uniaxial tension tests. The simulation results were compared to the experimental springback observations obtained by a CNC bending machine, without using springback compensation. A detailed parametric study was also carried out to highlight the level of criticality of the applied material variables on the final angle change.

DIC Strain Monitoring during Fatigue of Cold-Formed High Strength Steel

Owing to the progressive use of cold-formed high strength steel (HSS) for transportation applications, a characterisation of the fatigue behaviour of HSS has become a focal point for material scientists and design engineers. To mimic the behaviour of cold-formed components, a specimen was adopted from previous research that features multiple bent sections. The geometry was obtained by consecutive bending operations at room temperature. When subsequent tensile cyclic loading is applied to the specimen, the localised damage from forming and stress concentrations cause crack initiation on the inside of the bent area. To investigate the effect of cold-forming on the fatigue behaviour experimentally, the evolution of the strain, displacement or stiffness can be monitored during fatigue testing. The current paper presents an experimental framework for investigating the strain fields of a bent specimen during fatigue. The evolution of the strain fields is then linked with characteristic fatigue mechanisms, such as crack initiation and growth.