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Laser forming is a highly flexible and iterative contactless thermomechanical forming process that utilises a defocused laser beam to induce material shortening and bending. There is a high potential for the use of laser forming in rapid prototyping, small and unique batch production; however, to achieve that potential a certain level of automation is required. The presented work seeks to address this need of automation by proposing an end-to-end sheet-metal manufacturing system utilising laser forming and cutting, where the input for the system is a 3D CAD model and the output is a manufactured product. The contribution of the presented work is interconnected laser forming and cutting framework. The presented framework consists of subsystems for automatic extraction of geometrical information from a CAD model, process planning and generation of manufacturing information, scheduling of tasks and a feedback control loop for laser forming. The framework is experimentally validated and has shown consistent forming and cutting behaviour on two types of parts with variation in cutting features, bend angle and lengths of the bend's free edge. [ABSTRACT FROM AUTHOR]

The use of holding and inspection fixtures is common across many sectors of manufacturing. The concept of a fixture for holding a component, for the purposes of assembly or inspection, is straightforward. The fixture design and the associated clamping strategy can have a significant impact on the process. This paper presents a methodology for investigating the effects of clamping sequence for a production inspection fixture, on the dimensional variability of an automotive production-representative sheet metal sub-assembly, along with experimental findings and analysis of measurement data. The study utilises both a coordinate measuring machine and laser tracker to capture a range of features and surface points, and compares four different clamping sequences, including the manufacturer's defined sequence, to evaluate their effect on the dimensional results from a predetermined measurement plan. The results from the study show that there was significant variation in measurements taken from the four different clamping sequences, and these variations can show the same points and/or features being within tolerance for one clamping sequence and out of tolerance for another. This clearly has major implications for product development and subsequent volume manufacture, so needs to be considered and optimised in the measurement planning process. [ABSTRACT FROM AUTHOR]

In recent years, the application of non-uniform pressure in flexible-die forming, such as viscous pressure forming and magnetorheological pressure forming, has become increasingly prevalent in manufacturing thin-walled components. Non-uniform pressure is primarily employed to change the shape of the sheet, while its effects on thickness reduction and fracture behaviors remain intricate. In this study, the mechanisms of non-uniform pressure to decrease thickness reduction and delay fracture instability in bulge forming are revealed. Non-uniform pressure changes the principal stresses, resulting in distinct deformation behaviors. Numerical simulations indicate that both too large and too small pressure weights lead to severe thickness thinning and increase the risk of fracture instability. Theoretical equations of the polar strain and instability strain are derived to reveal the mechanisms. The characteristics of non-uniform pressure to decrease thickness reduction and delay instability are outlined. Viscous pressure bulge tests are conducted, and the experimental results of bulged shapes, thickness uniformity, polar strains, and instability behaviors validate the theories. The fracture strain under the non-uniform pressure condition shows a 5.6% increase compared with the uniform pressure condition. This study proves that non-uniform pressure can promote sheet formability, suggesting promising applications in sheet metal forming. [ABSTRACT FROM AUTHOR]

The machining trajectory of the irregular contour is usually discretized into straight lines and arcs, and process parameters selection affects the quality and efficiency of irregular sheet metal parts machining. To guide parameters selection of irregular sheet metal parts milling, a multi-objective optimization framework for efficiency and side machining quality is constructed. In the framework, to improve the modeling accuracy and reduce modeling cost, the theory-data coupled models of side roughness for straight line, convex arc and concave arc constructed, respectively. Aiming at the problems of single search method and susceptibility to local optima in the standard multi-objective seagull optimization algorithm (MOSOA), an improved MOSOA (MOSOAimprove) is proposed to solved the multi-objective optimization model of side quality and efficiency developed by the coupled model of side roughness and the empirical formula of the material removal rate. The effectiveness of coupled models and MOSOAimprove in multi-objective optimization of irregular sheet metal parts milling are verified by the actual machining. [ABSTRACT FROM AUTHOR]

The aeronautical industry widely uses the riveting process for metallic sheet metal structure joining processes, mainly when manufactured using aluminum alloys. During riveting operations, some level of geometrical deformation is induced in the airframe structure and such an effect may impact the manufacturing cycle and the product shape. It is important to identify the induced-deformation mechanisms associated with such phenomena and simulation methods capable of foreseeing them numerically or algebraically. The development of simulation methods, even if approximated methodologies, is necessary to assess possible geometrical variations in riveted airframes. Those structures are usually part of wing and fuselage panels. This work presents a general literature review of the riveting process and current modeling techniques aiming to identify modeling methods that could become an adequate baseline approach for riveting-induced deformations. Riveted geometry distortions may produce undesired consequences on manufacturing cycles, aerodynamics performance, and structural efficiency. [ABSTRACT FROM AUTHOR]

Laser shock forming (LSF) is a novel plastic forming process which utilizes a laser-induced shock wave to deform metal sheet to 3D configurations. Quantitative evaluation of the deformation in LSF is of great importance to understand the forming mechanism and achieve the high precision. In this paper, an analytical model was proposed to predict the deformation of a circular plate in laser shock bulging process. Models showed that the deformation is related to material parameters such as the impedance, density, yield strength of the metal target, geometric parameters such as the plate thickness and die radius, and processing parameters such as the energy, radius and pulse duration of the laser beam. The deformation profiles and the maximum deformation height calculated by the analytical model agree with those of experiment, which validate the rationality of the constructed models. The maximum deformation height increases with an increase of laser energy and decreases with increasing plate thickness. [ABSTRACT FROM AUTHOR]

This article presents examples of the use of complex sheet metal in everyday life and the course of modeling a sheet bent simultaneously in two planes. The element selected to describe the modelling process is a fragment of the side wall of a lever hydroelectric power plant that operates on the Bystrzyca River in Lublin. The shape of the element is conditioned by the need to achieve a gentle change in the cross-section of the water stream during the flow between the steering system and the outflow area. The segment through which the water flows is clearly lower and wider than the other modules of the power plant, which is due to the average water level in the Bystrzyca River. Such a shape is necessary because the inflow and outflow parts of the power plant must be submerged under water all the time. This is due to the principle of operation of the power plant, which works by obtaining a vacuum created by pumping air from the inside. The article also presents the results of the strength analysis, which was performed for the segment exposed to the highest loads. The analysis and the entire design were performed in Autodesk Inventor, and the results obtained were as expected and even in the most critical places no values were reached that would require changes to the design. [ABSTRACT FROM AUTHOR]

Incremental sheet forming has emerged as an excellent alternative to other material forming procedures, incrementally deforming flat metal sheets into complex three-dimensional profiles. The main characteristics of this process are its versatility and cost-effectiveness; additionally, it allows for greater formability compared to conventional sheet forming processes. Recently, its application has been extended to polymers and composites. The following review aims to present the current state of the art in the incremental sheet forming of polycarbonate, an outstanding engineering plastic, beginning with initial studies on the feasibility of this process for polymers. Attention is given to the advantages, drawbacks, and main applications of incrementally formed polycarbonate sheets, as well as the influence of process parameters and toolpath strategies on features such as formability, forming forces, deformation and failure mechanisms, geometric accuracy, surface quality, etc. Additionally, new hybrid forming methods for process optimisation are presented. Finally, a discussion is provided on the technical challenges and future research directions for incremental sheet forming of polycarbonate and, more generally, thermoplastics. Thus, this review aims to offer an extensive overview of the incremental forming of polycarbonate sheets, useful to both academic and industrial researchers working on this topic. [ABSTRACT FROM AUTHOR]

Rolling technology with rigid arc rollers presents an innovative approach for the rapid manufacturing of three-dimensional surface components. The unique design generates a variable gap between the rollers, applying lateral bending and uneven compression to sheet metal, thus producing components with complex curvatures. Employing finite element simulation and experimental studies, this research investigates the effects of rotational speed variations on the bending deformation and dimensional accuracy of three-dimensional surface parts. The research findings indicate that as the ratio of rotational speeds between the convex and concave rolls increases from 0.75 to 2, the longitudinal curvature of the saddle-shaped parts gradually increases and then stabilizes, while the transverse curvature decreases. In contrast, for spherical parts, the longitudinal curvature shows an initial decrease followed by stabilization, with minimal changes observed in the transverse curvature. The degree to which the roller rotational speed ratio impacts curvature intensifies with increasing sheet metal compression. These findings suggest that the roll rotational speed ratio can be used as a new process parameter to enhance the curvature range and surface precision of formed parts. [ABSTRACT FROM AUTHOR]

Producing vertical edged parts in sheet metal forming methods can cause tears on the sheet. The incremental forming method can allow sheet forming without tears. Forming can be done multi-stage to prevent this tear. Incremental forming method can be used in prototype production. The most important advantages of incremental forming method are that it is fast and inexpensive. In this study, we applied multi-stage forming to the two-point incremental forming-rolling blank holder method. Thus, we have developed a new way: the multi-stage, two-point incremental forming-rolling blank holder method. Parts with vertical edges are produced, and the wall thickness distribution is examined. The work material is a DC04 sheet with a thickness of 0.98 mm. The workpiece is axially symmetrical with a wall angle of 90°. The effect of four different parameters were researched: increment, feed rate, clamping pressure, and angle increment. Three different levels were determined for each parameter. The wall thickness distribution of the parts obtained from the experiments was measured. [ABSTRACT FROM AUTHOR]

Conventional sheet metal forming processes have problems like low formability, non-uniform strain distribution, spring back, wrinkling, etc. High velocity processes like electrohydraulic forming can deform sheets at high strain rate and have capability to tackle such problems associated with conventional forming operations to a greater extent. Forming limit diagram (FLD) characterizes sheet deformation as measure of formability. Punch stretch test (PST) can assess formability of sheet in conventional low strain rate process, but no standard method is available to determine FLD at high strain rate. So in the present work, an experimental setup has been developed to characterize sheets at high strain rate using hydraulic forming process with a 40 kJ capacitor bank. A similar corresponding standard setup for punch stretch test is also developed for comparative study of formability with respect to dome height, forming limit curve, and strain distribution. Formability of aluminum alloy AA5754 is determined at quasi-static and high strain rates, and comparative analysis is reported for whole state of strain using dog bone samples of width ranging from 10 to 120 mm. An estimate of electrohydraulic forming parameters for high strain test of the Al alloy using the given setup is also determined. Study of comparative strain distribution behavior of samples of different widths is also carried out. Comparative analysis shows that there is an improvement in formability and strain distribution behavior of the alloy deformed using EHF as compared to PST. [ABSTRACT FROM AUTHOR]

Copyright of Automotive Digest is the property of Automotive Digest Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The paper presents research results on the influence of a regular perforation pattern on the modulus of elasticity (Young’s modulus) and on the strength properties of EN AW-5754 aluminium alloy sheet. Square and hexagonal array of cylindrical (in the plane of the sheet metal – round) holes was considered, maintaining a constant hole diameter and pitch value. The reference material was solid sheet metal (without perforation) of the same grade and thickness. It was found that hexagonal perforation pattern reduces the Young’s modulus and strength of the material to a greater extent compared to square array of holes, while maintaining a higher uniformity of the distribution of these parameters in the plane of the sheet metal. The comparative analysis of the elastic and strength properties of sheet metal with straight and hexagonal perforation was also carried out accounting for mass loss ratio. [ABSTRACT FROM AUTHOR]

This paper proposes an innovative electromagnetic forming (EMF) approach for die-forming of sheet metal parts with a low thickness-to-diameter ratio, specifically set at 0.25%. This approach incorporates the use of an auxiliary driver sheet, strategically introduced to refine forming behavior. Numerical simulations reveal that the conventional EMF method fails to prevent wrinkling defects in thin-walled sheet metal forming, with the severity of wrinkles increasing as the voltage rises. These wrinkles reach a maximum height of 11.3 mm and result in inadequate workpiece adherence to the die. To mitigate these issues, the study proposes a novel technique that significantly reduces wrinkle formation through enhanced interaction between the driver sheet and the workpiece. A meticulous evaluation process led to the identification of an optimal driver sheet thickness of 3 mm, effectively reducing the wrinkle height to a mere 0.67 mm. This new method demonstrates superior forming accuracy and a closer adherence to the die contour when juxtaposed with conventional EMF approaches. Furthermore, the process window is defined by analyzing two fundamental process parameters: blank holder force (FBHF) and discharge voltage (Vd). An in-depth investigation into the deformation history associated with the driver sheet EMF technique, particularly under conditions of Vd = 12 kV and FBHF = 8 kN, revealed die-fitting gaps of 1.41 mm. Comparative experimental analysis further validates the effectiveness of this refined EMF method in manufacturing deep-cavity workpieces, evidencing superior forming accuracy with a maximum die-fitting gap of 1.41 mm and a wrinkle height limited to 0.67 mm. Consequently, this innovative driver sheet EMF approach is elucidated as providing notable enhancements in flexibility and efficiency for the manufacturing of extremely thin-walled sheet metal parts. [ABSTRACT FROM AUTHOR]

Introduction: Friction drilling is an innovative method in hole-making for sheet metal applications, thin sheets of conventional structural alloy materials like copper, titanium, steel etc., even though there are other methods, such as thermal distortion for thewelding of nuts, riveting of nuts, and threading. For the last hundred years, researchers have focused on studying the development of this technique to maintain strength, hole roughness, hole geometry, hardness etc. It is interested in finding solutions for wear, tool life, and plastic deformation. Method: Friction drilling is also called a green hole-making process because this process uses the friction between the rotating tool and the workpiece. In this research, instead of regular HSS and Tungsten Carbide tools, the H13 tool steel is used, because the H13 steel tool has unique chemical compositions like chromium and molybdenum, which give high toughness, hot hardness, and wear resistance. Diamond-like-carbon (DLC) coating has been used in this research to enhance tool life and AZ31B magnesium alloy is used as the work material. Initially, in this research, the wear stability of the DLC-coated H13 tool was investigated, and later, the tool surface roughness and hole quality were verified. Results and Discussion: The material loss observed for the DLC-coated H13 steel tool in the pin-on-disk test was 0.05 g. This investigation used two different diameter tools, namely 3 and 7 mm. Research has concluded that the 7mmtool is better for friction drilling by seeing the roughness and hole quality. However, the conditions were that the spindle should rotate at 4,000 rpm and the feed rate of the tool to be at 200 mm/rev. [ABSTRACT FROM AUTHOR]

As vehicle body structures become stronger and part designs more complex for lightweight, controlling frictional properties in automotive press forming has gained critical importance. Friction, a key factor in formability, is influenced by variables such as contact pressure, sliding velocity, sheet strength, and coatings. This study investigates the friction characteristics of steels with tensile strengths of 340 MPa and 980 MPa, under galvanized (GI) and galvannealed (GA) zinc coatings. Experimental results reveal that asperity flattening, a significant factor in determining friction, increases with contact pressure normalized by tensile strength, particularly for GI-coated steels. However, the relationship between friction and surface flattening deviates from conventional expectations, with the friction coefficient initially rising with increased flattening area up to ~20% before decreasing as flattening progresses. These findings suggest that traditional empirical formulas may not fully capture friction behavior under specific conditions. By understanding this inflection point, where friction reduces under high contact pressure, the study provides valuable insights for optimizing formability and improving sheet metal forming processes, especially in scenarios where precise friction control is critical for producing high-quality automotive parts. [ABSTRACT FROM AUTHOR]

This research proposes a complete analysis of the use of physical vapour deposition coated dies in the sheet metal forming process for high‐strength‐steel sheets. The goal of the proposed approach is to investigate how PVD coatings affect die performance and how that affects the formability and quality of the high‐strength‐steel‐sheets that are made. The finite element analyses are used to simulate and evaluate the mechanical behaviour and deformation characteristics during the forming process. Studies to enhance the forming characteristics of these materials, typically denoted by limiting draw ratio and maximum punch force are required. A reduction in punch force required and improved limiting draw ratio is observed that is attributed to the enhanced contact with friction‐conditions in the die‐sheet interfaces. The experimental results are compared with simulation results from DD3IMP, a code used for deep drawing simulations, and it is evident that the experimental outcomes are analysed well with the simulation results. [ABSTRACT FROM AUTHOR]

In the production of hybrid composites made of thermoplast and metal sheets, certain limitations in the linear forming process can be overcome through a free kinematic forming process. This process involves distributing the thermoplast press mass using a tumbling or cyclic rolling movement of the forming tool. Due to this special kinematics, only a small part of the tool is ever in engagement with the workpiece, so the component is formed incrementally. Therefore, the final geometry does not have to be created in one stroke but can be carried out step by step in several partial strokes. In order to determine the optimal trajectory of the forming tool, the kinematic interplay between the workpiece, forming tool, and toolpath should be numerically captured in a mathematical model. The specific toolpath depends on the component being formed, as well as the actual geometry of the forming tool. In this research, the free kinematic forming process is modeled and the optimal toolpath is determined using a genetic algorithm. The optimal toolpath enables a uniform distribution of the thermoplast to a specified thickness and collisions between the upper and lower tool are avoided. This enables key insights into the free kinematic forming process and opens up further avenues of research for this innovative and future‐oriented manufacturing concept. [ABSTRACT FROM AUTHOR]

Damage is an undesirable and progressive process that ultimately leads to complete failure of materials. Obtaining a robust tool to precisely and reliably predict damage evolution behavior in ductile sheet metals is among the most crucial challenges for researchers and engineers. In this paper, first, based on the continuum damage mechanics (CDM) and the original Lemaitre's ductile damage model, a new 2D fast and straightforward version specialized for the plane stress conditions as well as a novel numerical integration algorithm are fully presented. Additionally, a modified numerical approach, founded on the bisection method is suggested for determining the material-dependent ductile damage parameter of the model. Then, an explicit subroutine is developed and implemented to numerically predict damage evolution behavior in different ductile sheet metals and shapes. Finally, the numerical simulation results of damage initiation, growth, and crack onset are attained and validated. The numerical simulation predicted results reveal that the novel offered version of the Lemaitre's ductile damage model in conjunction with the enhanced numerical approach is able to more rapidly predict the material-dependent ductile damage parameter and also the evolution of damage in ductile sheet metals under various loading and boundary conditions. [ABSTRACT FROM AUTHOR]

Reverse roll coating is a high-speed coating process used in many applications. The single largest application for reverse roll coating is applying architectural paint to coils of sheet metal; however, in the converting industry reverse roll coating is used for some thermal coatings, adhesives, color laser paper receivers, wax coatings, magnetic coatings, vinyl dispersions for wallcovering, some specialty light sensitive applications, and many specialty products that require a high precision application process. This work presents a mathematical model for the steady flow of non-isothermal, incompressible, micropolar fluid in the metering nip of a reverse roll coater with velocity slip applied at both roll's surfaces. Lubrication approximation theory (LAT) is utilized to reduce the complexity of the non-dimensional equations. Exact solutions for pressure gradient, velocity, and temperature are achieved. At the same time, numerical techniques (Simpson's 3/8 rule with Newton Raphson method) are used to compute the pressure distribution, coating thickness, flow rate, and separation points. Effects of coupling number, slip parameter, microrotation, and velocity ratio on velocity, pressure, temperature, and pressure gradient are presented in graphs. It is observed from the current analysis that the intrinsic rotations of the fluid particles prove to be the controlling parameter of the pressure gradient, which significantly varies the coating thickness. Also, as a result of velocity slip, the flow rate declines and the coating thickness reduces as the fluid moves faster along the boundary walls. [ABSTRACT FROM AUTHOR]

The predictive capability of an anisotropic yield function highly relies upon the number of the model parameters and its calibration type. Conventional calibration of a plane stress anisotropic yield function considers material behavior in uniaxial and equi-biaxial stress states, whereas it violates shear and plane strain loading conditions. In this study, the direction of the plastic flow in both loading regions was corrected by including shear and plane strain constraint terms to the conventional calibration of the Yld2000 function, and its effect on the sheet metal forming simulations, namely cup drawing and hole expansion tests, was investigated. Two highly anisotropic sheet materials (AA2090-T3 and low-carbon steel) were selected for the investigation, and the anisotropy coefficients were determined. Stress anisotropy was accurately predicted by the conventional method, whereas any decrease in the prediction of the deformation anisotropy could not occur by the applying of the constrained methods. Significant increases in the predicted cup height and differences in the number of the ears were observed by shear constraint identification in the cup drawing. The maximum thinning location in the hole expansion test could be accurately predicted by plane strain constraint identification. [ABSTRACT FROM AUTHOR]

Beam-column (B-C) joints are recognized as critical regions in reinforced concrete (RC) moment-resisting frames when subjected to seismic loads. Furthermore, these joints may be subjected to high temperatures during their lifespan, which might cause severe structural damage. Accordingly, the seismic response of RC beam-column joints that were subjected to heat (i.e., 400 °C and 600 °C) was investigated in the present experimental work. The joint specimens were divided into three categories: Three joints were kept as is (i.e., reference joints; no strengthening is applied), whereas six joints were strengthened with one and two layers of stainless-steel expanded metal sheet mesh (SSEMSM) in order to improve their performance. To investigate the seismic performance of the joints, a quasi-static cyclic load was applied to the joints to simulate a seismic load. Results showed that the average maximum load for joints strengthened with one and two layers of SSEMSM, respectively, was increased by 11% and 21% at ambient temperature and by 2% and 9% at 400 °C, in comparison with the reference joint. In addition, using one and two layers of SSEMSM, respectively, led to achieving an average of 91% and 100% of the full capacity of the reference joint for B-C joints subjected to 600 °C. Furthermore, the experimental findings show a considerable improvement in the cyclic response of non-ductile RC joints that were strengthened with the SSEMSM strategy and subjected to high temperatures (i.e., higher load capacity, greater displacement, higher dissipated energy, higher ductility, and slower degradation in the secant stiffness). [ABSTRACT FROM AUTHOR]

The initial workpiece diameter is one of the most fundamental process parameters in sheet metal forming, as it determines the resistance of the draw-in material flow. In the context of conventional deep drawing, its critical role has been clearly identified. In the context of electromagnetic sheet forming, however, its role has not yet been adequately addressed. This paper aims to clarify its role, by experimentally and numerically investigating the deformation behavior of circular sheet metal in electromagnetic forming. Various combinations of the initial diameter and discharge voltage were established to induce different deformation behaviors. It was found that adjusting the initial diameter can substantially change the forming height, shape, and thickness distribution by altering the draw-in, which suggests a great improvement in deformation controllability. In summary, this study demonstrates that the initial workpiece diameter could play critical role in deformation control in electromagnetic forming. [ABSTRACT FROM AUTHOR]

Copyright of Nachrichten aus der Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

To describe the characteristics of multiphase flow and post-combustion in the converter, two separate 3D models are established in present work. The first model, known as the jet-cavity model, focuses on the interaction between oxygen jet and liquid bath, and discusses the effects of different operating parameters (lance height and operating pressure) on gas-slag-metal behavior. The results show that the impact of oxygen jet on bath surface produces rough surface waves, cavities and some metal sheets on the slag surface. Decreasing lance height or increasing operating pressure may enhance the impact of oxygen jet on molten bath. With the decrease of lance height, the penetration depth increases, while the impact diameter decreases. Increasing the operating pressure increases the penetration depth, but it has little effect on the impact diameter. The second model is called the post-combustion model, which is to describe post-combustion of CO in converter space. It is based on the cavity size (impact diameter and penetration depth) obtained by the above jet-cavity model, and analyzes the post-combustion characteristics with the single-flow post-combustion lance (SF-PCL) under different operating parameters. The results indicate that high-temperature zones and CO2 produced by post-combustion reaction are mainly located in the jet boundaries and the regions among multiple jets. Increasing lance height or operating pressure helps to burn more CO. The post-combustion ratio of converter at the lance height of 1.6 m is 1.08 and 1.04 times than that of H = 1.2 m and H = 1.4 m, respectively. When the operating pressure is 0.89 MPa, it is 1.05 and 1.03 times than that of P = 0.69 MPa and P = 0.79 MPa, respectively. [ABSTRACT FROM AUTHOR]

Springback of sheet metals consists of two components: springback caused by elastic recovery during unloading and time-dependent springback caused by viscoplastic phenomena over time after unloading. While springback can be reduced by punch holding (or bend holding), the influences of bend holding on each of these two springback components are unclear. This study aims to elucidate the effects of bend holding on these two springback components and total springback by conducting L-bending tests on an advanced high-strength steel (SPCN118Y) sheet and an aluminum (A1050-O) sheet. The total springback two days after unloading decreased when bending was held because the springback during unloading decreased due to stress relaxation while holding. The time-dependent springback also tended to decrease with bend holding in most cases, but its amount and reduction were considerably smaller than those in the springback during unloading. The percentage of timedependent springback to total springback was larger for A1050-O than for SPCN118Y. The percentage of SPCN118Y was not much affected by bend holding, while that of A1050-O became larger when bending was held. [ABSTRACT FROM AUTHOR]

Despite advancements in the characterization of forming limit curves (FLCs) with the development of stereoscopic digital image correlation (DIC), there is still uncertainty in the accuracy of the limit strains, especially in forming operations with out-of-plane bending. The ISO12004-2:2008 standard offers a standardized approach to FLC determination but is not without limitations and is not always applicable to new materials and forming processes (e.g., warm forming, hot stamping). In the present work, a physically based limit strain detection technique is developed, termed the Enhanced Curvature Method (ECM), based on the sheet surface curvature evolution at the onset of necking in sheet formability testing. The ECM is applied to the characterization of 1.1 mm AA5182-O sheet using Marciniak, Nakazima, and stretch–bend characterization tests, and its limit strains are compared with those from the linear best-fit (LBF) local strain-rate approach and the ISO-12004 standard. The ECM considers the physical nature of necking in sheet forming with the aid of thresholds defined in terms of an imperfection metric analogous to the well-known Marciniak–Kuczynski (MK) imperfection factor. By quantifying the evolution of necking, FLCs of different safety margins can be readily generated, enabling a more intuitive selection for the factor of safety. For lower and upper ECM thresholds, the Marciniak plane strain limiting strain was determined to lie between 0.173 and 0.198, respectively, which is comparable to the analytical prediction of 0.194 and in general agreement with the published literature for AA5182-O. Similar plane strain limits were obtained using the ISO and LBF methods with values of 0.188 and 0.208, respectively. The same rankings in limit strain values between methods were observed for plane strain loading in Nakazima and stretch–bend tests. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Magnesium alloys, particularly AZ31, are promising materials for the modern automotive industry, offering significant weight savings and environmental benefits. This research focuses on the challenges associated with accurate modelling of multiaxial cyclic plasticity at small strains of AZ31 under low-cycle fatigue conditions. Current modelling approaches, including crystal plasticity and phenomenological plasticity, have been extensively explored. However, the existing models reach their limits when it comes to capturing the complexity of cyclic plasticity in magnesium alloys, especially under multiaxial loading conditions. To address this gap, a cyclically stable elastoplastic model is proposed that integrates elements from existing models with an enhanced algorithm for updating stresses and hardening parameters, using the hyperbolic tangent function to describe hardening and ensure a stabilised response with closed hysteresis loops for both uniaxial and multiaxial loading. The model is based on a von Mises yield surface and includes a kinematic hardening rule that promises a stable simulation of the response of AZ31 sheets under cyclic loading. Using experimental data from previous studies on AZ31 sheets, the proposed model is optimised and validated. The model shows promising capabilities in simulating the response of AZ31 sheet metal under different loading conditions. It has significant potential to improve the accuracy of fatigue simulations, especially in the context of automotive applications. [ABSTRACT FROM AUTHOR]

Additive manufacturing techniques employing laser-based metal melting have garnered significant attention within the scientific community. Despite a decade of comprehensive research on the fundamentals of these techniques, there still remain unexplored facets related to heat flux impact on metallic alloys' properties. Particularly, the effects of point-by-point laser operation on melt pool formation in metallic materials still remain unclear. Thus, this study focuses on the implications of laser metal melting, particularly investigating a point-by-point laser mode operation's influence on melt pool formation and its geometry in the phase-transformation-sensitive material H11 hot work tool steel. To examine the melt pool, singular laser tracks with various laser parameters were scanned across H11 sheet metal, which allowed for the elimination of layer-by-layer heat cycles' influence on the melt pool's microstructure. Samples were examined by means of metallography, revealing significant differences in the melt pool's depth, influenced mostly by exposure time rather than volumetric energy density. Heat-affected zone effects were found to have a limited range and thus potentially marginal effects in layer-by-layer manufacturing conditions. At the same time, retained austenite concentrations near fusion lines have been found within melt pools, suggesting potential micro-segregation of the alloying additions. The results present guidelines towards laser melting processes optimization. [ABSTRACT FROM AUTHOR]

Correct design of the sheet metal forming process requires knowledge of the friction phenomenon occurring in various areas of the drawpiece. Additionally, the friction at the drawbead is decisive to ensure that the sheet flows in the desired direction. This article presents the results of experimental tests enabling the determination of the coefficient of friction at the drawbead and using a specially designed tribometer. The test material was a DC04 carbon steel sheet. The tests were carried out for different orientations of the samples in relation to the sheet rolling direction, different drawbead heights, different lubrication conditions and different average roughnesses of the countersamples. According to the aim of this work, the Features Importance analysis, conducted using the Gradient-Boosted Regression Trees algorithm, was used to find the influence of several parameter features on the coefficient of friction. The advantage of gradient-boosted decision trees is their ability to analyze complex relationships in the data and protect against overfitting. Another advantage is that there is no need for prior data processing. According to the best of the authors' knowledge, the effectiveness of gradient-boosted decision trees in analyzing the friction occurring in the drawbead in sheet metal forming has not been previously studied. To improve the accuracy of the model, five MinLeafs were applied to the regression tree, together with 500 ensembles utilized for learning the previously learned nodes, noting that the MinLeaf indicates the minimum number of leaf node observations. The least-squares-boosting technique, often known as LSBoost, is used to train a group of regression trees. Features Importance analysis has shown that the friction conditions (dry friction of lubricated conditions) had the most significant influence on the coefficient of friction, at 56.98%, followed by the drawbead height, at 23.41%, and the sample width, at 11.95%. The average surface roughness of rollers and sample orientation have the smallest impact on the value of the coefficient of friction at 6.09% and 1.57%, respectively. The dispersion and deviation observed for the testing dataset from the experimental data indicate the model's ability to predict the values of the coefficient of friction at a coefficient of determination of R2 = 0.972 and a mean-squared error of MSE = 0.000048. It was qualitatively found that in order to ensure the optimal (the lowest) coefficient of friction, it is necessary to control the friction conditions (use of lubricant) and the drawbead height. [ABSTRACT FROM AUTHOR]

The classical theory of folded developables suggests that curved crease folding can be applied to sheet metal of high strength to manufacture parts with complex geometries. However, its application has been limited to sheet metals with low strength and requires grooving or perforation of the material at the fold lines. Applying the geometrical concept otherwise remains unexplored despite its potential in sheet metal-intensive industries like automotive, transportation, and construction. The current study introduces a novel sheet metal forming technique called developable forming. The theory of folded developables is applied to design a die tool for flange drawing a developable-shaped steel sheet. A developable connection is produced from high-strength material without resorting to thickness accommodation techniques. Experimental findings establish that the novel process does not follow the premises of the theory of folded developables. New shape effects are observed and the terms curving and coning are introduced to describe these. Additionally, significant redundant strains are identified in the flange, highlighting the different deformation modes in the developable forming process. A higher formability is achieved for a material with limited uniaxial elongation highlighting the need for further investigation on the mechanisms involved in the novel process. [ABSTRACT FROM AUTHOR]

Incremental sheet metal forming is a highly versatile die-less forming process for manufacturing complex sheet metal components. Robot-assisted incremental sheet forming, or roboforming, allows a wider range of tool motion, providing the capability to shape intricate components. This makes roboforming the most flexible variant of the incremental forming method. However, the serial arrangement of links and joints in a robotic manipulator results in low positional accuracy under forming loads due to insufficient structural stiffness. The stiffness of the machine frame and tool directly impacts the accuracy of the final formed profile. The impact of machine compliance on component shape in incremental sheet forming is substantial in roboforming. This work presents a methodology for systematic analysis of the factors contributing to the errors in the geometric shape of robot-based forming. Experimental and numerical methods are used to estimate the material springback, tool/tool holder deflections, and errors due to machine compliance. The CNC machine frame is relatively stiffer than the industrial robots, such that material springback is estimated based on the experimental trials on CNC for cone and variable wall angle cone profiles. Tool and tool holder deflections are estimated using finite element simulations. The analytical method using the Virtual Joint Model is used to model the joint stiffness, and consequently, the robot Cartesian stiffness is estimated to predict path deviation contributing to geometric shape errors. The proportional contribution of each factor in the overall deviation in the Roboforming is also quantified. [ABSTRACT FROM AUTHOR]

The single point incremental forming process (SPIF) is materialized to form the desired shapes in low-cost sheet metal processing and well suited for low batch components and customized designs. Many modifications have been attempted in recent years to maximize the formability, geometric accuracy and quality of the SPIF formed parts. In this work, an attempt has been made to analyse the influence of process parameters namely ball tool diameter, step size, spindle speed and sheet thickness on final wall thickness, forming force and surface roughness. The optimized results exhibit the desirable formability when the roller ball tool diameter of the tool is 12 mm. The results also project that formability of the sheet metal is minimized when the spindle speed is increased and the ball diameter maximizes the accuracy and surface roughness. Also minimizing the step size increases the product quality features. Upon conducting this multi-response optimization by grey based response surface methodology (RSM) technique It is identified that 12 mm ball diameter of the tool, 0.25 mm step size, 2445 rpm spindle speed, and 2 mm sheet thickness are the obtained optimized SPIF process parameters as confirmed through confirmation experiments. [ABSTRACT FROM AUTHOR]

In sheet metal forming, the interaction between virtual models and the real world remains challenging. Process simulations can exhibit significant errors, and reliable measurements are often scarce during early production stages. This study presents a hybrid twin framework that systematically unifies computer-aided design, simulation, and measurement data in an adaptive manner. Central to this framework is a reverse engineering algorithm that reconstructs and transforms the geometry of deep-drawn components from optical scan data into B-spline surfaces. The algorithm demonstrated high precision, indicating its suitability for process control and geometric analysis. The hybrid twin framework integrates virtual data from simulations and real-world data, as evidenced by a sensor concept for inline surface measurement. The framework ensures robust and redundant measurement concepts by estimating complete geometries from a few systematically preselected measuring points. This adaptive approach permits continuous updates and extensions to the database, accommodating both sparse inline signals and offline inspection data. This framework provides a conceptual model for integrating direct feedback interactions between virtual and physical environments, thereby enhancing the precision of analytical and predictive models in sheet metal forming processes. [ABSTRACT FROM AUTHOR]

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Part features, such as dents, holes, and bumps, are integral to the thin-walled sheet metal components used in the automobile and aerospace industries. These features are often required to be suppressed for more agile and reasonably accurate results during the CAE analysis. However, identifying these features is a critical task usually performed by experts. It requires a detailed analysis of the CAD model, which largely depends on the importance of each feature, feature size, and domain boundary conditions. Thus, identifying such features is a challenging task. This work proposes a novel data-driven approach to create an intuitive model that identifies suppressible features on CAD models of sheet metal parts. The dataset to train the supervised learning model is generated by extensive finite element analysis of the part models. The case studies show that the trained Machine learning model gave good test accuracy. [ABSTRACT FROM AUTHOR]

The steel–aluminum hybrid body closure panels can achieve a more balanced and lightweight performance. However, the differences in the physical properties of metal sheets and the complex changes in the properties of the adhesive material result in cumulative deviations in the composite-forming process. This paper proposes a deformation pre-compensation modeling method for the autobody closure panels hemming system oriented towards the process chain, in response to the problem that single-process optimization cannot obtain global optimal results. Taking the car door scaled model as an example, based on surface reconstruction and node compensation, the curing deformation amount is fed back in advance to the gluing and hemming processes. The deformation deviation is corrected through geometric parameter pre-compensation to achieve overall process shape control and optimization. Research shows that this method can significantly reduce the surface differences and gaps of hemming structures with dissimilar materials, and a single iteration can reduce the assembly surface difference by more than 90%. This provides a reference for improving the manufacturing quality of steel–aluminum hybrid body closure panels. [ABSTRACT FROM AUTHOR]

In this paper, a near-net discrete clamp motion path control (SF-CMPC)-based stretch-forming method is proposed as a solution for the low-cost high-quality machining of highly curved surfaces. In this approach, the clamps are discretized, the motion paths are designed to control deformation distribution and avoid forming defects, the stretch-forming transition zone can be effectively reduced, the material utilization rate can be increased, and the near-net formation of large surfaces can be achieved. To investigate this method's feasibility, the conventional stretch-forming (SF-C) and SF-CMPC processes are numerically analyzed. The results indicate that, upon increasing the transition zone length via SF-CMPC, the maximum thickness reduction and strain value are reduced by 0.010 mm and 0.0249, respectively, with the dependence of the forming quality on the transition zone length being significantly reduced compared to SF-C. In the formation of surfaces with large curvatures, SF-CMPC's crack risk is lower than SF-C's crack risk, with better adaptability. Through controlling the contact process with a die, the sheet metals' constraint state is improved, the transverse compressive strain can be effectively reduced via friction, and the wrinkling defects can be suppressed. A stretch-forming experiment was carried out on a spherical surface, using self-developed equipment. The feasibility of achieving surfaces' near-net stretch forming by controlling the clamps' motion paths was hereby proven. [ABSTRACT FROM AUTHOR]

The sheet metal forming of magnesium is challenging due to the material's complex springback behaviour, which is due to the tension/compression yield mismatch. In this study, three different AZ31 grain sizes are produced by a special heat treatment, while maintaining the material strength in uniaxial tension at a similar level. Pure, V-die and channel bending tests are combined with roll forming to compare bending scenarios with and without tension applied transverse and parallel to the bending axis. This is complemented with electron backscatter diffraction to measure the twinning type and twinning area fraction (TAF) in the tension and compression bending zones. Our study shows that, like conventional steel, when bending magnesium, springback reduces with the increasing level of the outer fibre bending strain, i.e., when the bend radius is decreased and the TAF increased. It is further shown that when tension is applied, the TAF increases. However, while in some forming cases, the increase in TAF leads to a clear reduction in springback, in other forming cases the effect of the TAF on springback is less pronounced. Overall, this study provides clear evidence that the twinning behaviour in bending magnesium is influenced by the bend deformation mode and that this influences the springback behaviour. [ABSTRACT FROM AUTHOR]

For prototype design and small batch production, laser forming has more advantages for manufacturing metal sheet products than conventional processes. However, predicting and optimizing the required conditions for the product's final shape is difficult, especially in multi-stage forming, where many governing factors affect the shape intricately. In this study, the convolution neural network (CNN) is proposed to simulate the correlations between the scanning paths and the final deformations of a metal sheet. The imaginary data, which used values to present the distribution of deformation height of metal sheets, was used to examine the feasibility of applying CNN. On the other hand, the simulated images of a structured pattern projected on the sheet surface were used to train and test the CNN. The results demonstrate that CNN can use imaginary data in the training dataset to predict the scanning path determined by two points on the edge of the metal sheet with high accuracy. Although the performance of the test dataset needed to be better to prove the general-purpose ability, this research validates the feasibility of applying CNN for scanning path prediction in laser forming. [ABSTRACT FROM AUTHOR]

Laser drilling cooling holes into turbine components is well established in industries. However, there are drawbacks related to setting and maintaining the appropriate manufacturing conditions, which can be formulated as an inverse problem. The inverse solution of a physical model describing long-pulse laser drilling of sheet metal is learned through an artificial algorithm. The trained feed-forward neural network predicts process parameters of desirable production outcomes. Here, the trained network predicts beam radius and pulse power to drill through getting a hole with specified conicity. The hyperparameters of the neural network are trained using algorithmic differentiation. Using a physical model improves the solvability of the inverse problem, since all trials during training belong to the applicable range of laser drilling and improves the training procedure going in a physically informed direction. [ABSTRACT FROM AUTHOR]