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The transfer mechanism of a toner pattern printed on a soft film using a laser printer to a metal surface in compression was investigated by experiment and computer simulations. The toner pattern can be transferred successfully to the workpiece surface under the conditions that the entire soft film continues to be squeezed out smoothly from the workpiece edge until the transfer process is completed. The results indicate that the average tool pressure needed for the complete transfer of the toner pattern to the workpiece surface can be predicted by the average compression pressure calculated with slab method [ABSTRACT FROM AUTHOR]

Metal forming processes and formed components can be enhanced by stress superposition. Stress superposition is defined here as adding stresses on an existing (primary) forming process acting simultaneously with the core stress state. An extensive analysis of existing applications leads to a systematic classification of current stress superposition methods. The mechanisms of stress superposition and the modelling are provided. Achievable improvements in the reduction of forming force, increase in formability, and tailoring physical properties are presented. The limits of stress superposition and future opportunities of designing new forming processes through utilization of stress superposition are proposed. [ABSTRACT FROM AUTHOR]

This paper presents an upset geometry sequence capable of providing strain loading paths from uniaxial compression to biaxial stretching. Combination of digital image correlation and experimental force vs. time evolutions allows determining the fracture strains and the instantaneous slope of the strain loading paths at the instant of cracking in principal strain space. Fractography using scanning electron microscopy helps identifying the crack opening modes corresponding to the different fracture strains. Results show that the proposed upset geometry sequence allows creating a new testing methodology for bulk forming similar to that of sheet forming with the widely used Nakajima test. [ABSTRACT FROM AUTHOR]

We developed 3D scanning and rapid prototyping-based approach for an easier design of high precision, single pass tube drawing technology dedicated to the manufacturing of high-quality internally helically ribbed tubes. The major difficulty in the currently used process design is the identification of floating plug stability criterion allowing manufacturing of high precision helical ribs. The novelty of the proposed approach is therefore to use a combination of 3D scanning and rapid prototyping processes to design a complex floating plug geometry based on minimizing membrane energy. It was combined with computer-aided design of drawing die geometry and process parameters of the optimal tube drawing. [ABSTRACT FROM AUTHOR]

A new tool concept is presented. It reduces galling and tool wear by lowering the interface pressure between workpiece and tool during retraction. The work performed during retraction of a prototype ironing punch is reduced by more than 50% compared to a conventional punch. This is achieved by a hollow punch with an internal mandrel, which provides stiffness during ironing through a conical interface, while the punch contracts during retraction when the mandrel is released. Adjustability of the punch diameter by the mandrel position enables adaptation to variable external factors, e.g. variation of strip thickness in progressive die forming. [ABSTRACT FROM AUTHOR]

• Ductile fracture of thin-walled structures requires computationally efficient simulation tools that also captures sub-thickness scale. • Classical shell elements cannot capture the through-thickness stresses, leading to discrepancies in fracture prediction in bending vs. in-plane tension. • An extension of the GISSMO model is presented by introducing a separate fracture criterion based on stress-dependent fracture locus for bending. • Fracture occurs when the equivalent plastic strain reaches its critical level, interpolated between the bending and in-plane fracture loci. Ductile fracture prediction for thin-walled structures requires computationally efficient simulation tools able to approximately represent the key effects that occur on the sub-thickness scale. Unfortunately, classical shell elements, typically used to model deformation and failure of thin components, are inherently in a state of plane stress and therefore unable to capture the through-thickness stress distribution. This is consequential considering recent studies that demonstrated the differences between fracture in bending vs. in-plane tension. A laterally constrained thin metal plate under in-plane tension is likely to fracture under significantly lower plastic strain than the same plate under bending (with fracture initiating on the tensile side), even though both these conditions are examples of plane strain tension. Under in-plane tension fracture is preceded by a through-thickness neck, and therefore higher stress triaxiality than in the case of plane strain bending, where necking is absent. To account for these differences, we propose an extension of the GISSMO model, which relies on a simple fracture criterion based on stress-dependent fracture strain defined by the user (i.e. fracture locus). The fracture strain is typically determined experimentally using a combination of in-plane tensile tests under varying degree of lateral constraint and shear tests. The proposed extension involves defining a separate fracture locus for bending, also determined experimentally using bending tests. Fracture occurs when the equivalent plastic strain reaches its critical level represented by interpolation between the two bounding cases, i.e. bending and in-plane tension, with a bending index Ω used as an interpolation parameter. [ABSTRACT FROM AUTHOR]

Post Forming Electro Plastic Effect (PFEPE) has been proposed as a promising technology for mitigating forming forces and addressing springback challenges in the metal forming industry. However, several research gaps remain unaddressed for the industrialization of this technology. Firstly, there is a lack of experimental validation regarding the impact of stress reduction on springback. Secondly, the potential effect of the skin-effect on the current metrics of stress reduction needs to be evaluated. Additionally, a post-forming electrically assisted elastoplastic material model is necessary for further technology development in stamping processes. This study tackles these challenges by utilizing AA5754H22 as a reference material and integrating a comprehensive experimental campaign with finite element numerical models and empirical material model developments. Our findings confirm that PFEPE facilitates a significant reduction in springback, achieving approximately a 100% reduction. Although the skin-effect introduces non-uniform current flux density distribution, its impact at the macroscopic level is negligible for the studied thin samples. While the numerical results of springback fails to accurately replicate experimental results, the developed material model aligns well with experimental trends. [Display omitted] • PFEPE effectively reduces springback by approximately 40%–100%. • The skin-effect generates minimal heterogeneity. • An initial shock impact effect that results in a 40%–60% reduction in springback. [ABSTRACT FROM AUTHOR]

Friction in sheet metal forming is largely governed by the flattening of surface asperities. Liquid lubricants can reduce flattening and friction by filling the surface valleys and carry a substantial amount of the pressure. Experimental and numerical work is presented for investigating the influence of the compressibility of the lubricant and the material strength on the deformation of a simple cylinder with an enlarged surface pocket filled with oil. Results show that deformation is not sensitive to differences in compressibility of typical lubrication oils under hydrostatic pressure conditions. This was observed independent of the material strength. [ABSTRACT FROM AUTHOR]

The simulation of manufacturing processes has significant importance. The research and development of metal forming simulation started in the 1960s from the elastoplastic analysis of a simple plastic deformation, and it now covers a wide range of forming processes. The accuracy and applicability of metal forming simulation have significantly progressed, driven by the development of plasticity theory and numerical methods such as the remeshing technique and contact analysis algorithm. Now the targets of metal forming simulations are undergoing a transition from the macroscale analysis of deforming bodies to coupled analyses of deformations of deforming bodies and tools, and multiscale analyses of microstructure and texture. Past achievements of metal forming simulation show that it has reached the level of 'visualizing forming phenomena', but it will continue to evolve in the digital era, impacting the digital society and factories of the future, where machines work autonomously without human intervention. Emergent technologies require advanced materials, augmented reality, and, of course, metal forming simulation. In this paper, we reinforce the role of simulation as a means of performing computational (virtual) experiments and as a tool for the high-fidelity numerical visualization and quantification of unknown, unmeasurable, and invisible phenomena in formed components and their assembly. We will also discuss simulation–machine interactions, such as online simulation with process operation, to realize the triad of 'process operation – data – simulation' in the near future. [ABSTRACT FROM AUTHOR]

[Display omitted] • The original and shear-modified GTN ductile fracture criteria are utilized during the stretch bending process. • The original GTN model can be used only in processes where the stress state is the same as the calibration test stress state. • The evolution of damage, principal strains, and displacement of fractures under different forming conditions are investigated. In this paper, the original and shear-modified GTN ductile fracture criteria are utilized to investigate the fracture behavior of the AA6061-T6 aluminum alloy sheet during the stretch bending process. An appropriate calibration strategy is presented to find the unknown coefficients of the fracture models. In this way, different tension tests such as uniaxial tension, plane strain, notched tension, and shear tension specimens are utilized. Results show that the shear-modified GTN model calibrated by the mentioned tension tests is able to predict the onset of fracture of the stretch bending process with a 5% error, while the original GTN model, calibrated by the uniaxial tension is unable to predict the fracture properly. Since the accuracy of fracture prediction depends on the stress state, the effects of the calibration test on onset of fracture were investigated. It is shown that using the original GTN model with a proper calibration test (plane strain tension) can achieve a good accuracy with 3.5% error in the stretch bending process. In addition, results show that any change in the friction coefficient and bending radius in the stretch bending process can lead to different fracture behavior. Several investigations are carried out to examine the evolution of damage and displacement of fractures in the stretch bending process under different forming conditions. [ABSTRACT FROM AUTHOR]

Especially for safety-relevant components local characterization of the mechanical properties is necessary for product testing. For sheet metal parts with a complicated geometry conventional specimens for standardized tests cannot be extracted due to size limitations. Thus, a novel extraction procedure of miniaturized upsetting specimens is investigated. Taking a miniaturized upsetting specimen out of the sheet component allows for the first time the characterization of sheet metals in a standardized upsetting test under uniaxial compression stresses. Furthermore, this enables the analysis of strain hardening behavior of components and a direct validation of finite element simulations based on the true stress. [ABSTRACT FROM AUTHOR]

Screens made of drawn and spot-welded stainless steel precise profile wires are widely used to separate particles from fluids during various industrial applications. Increased durability and surface quality of these products are critical in maximising their wear resistance and extending the screen service life. Therefore, the paper discusses the development of metal forming technology considering the surface quality and residual stress level of austenitic and lean-duplex steel profile wires for the production of high-quality industrial screens. It is shown that surface engineering driven by metal forming is a key factor in extending the life and performance of these products. [ABSTRACT FROM AUTHOR]

The last decades have seen several attempts to develop Severe Plastic Deformation (SPD) processes to manufacture parts with Ultra-Fine Grained (UFG) microstructure without additional thermal processing. However, they remained mostly focused on producing small components, often in the micro-scale range, thus limiting the technological and environmental impact of SPD techniques. The paper introduces a new approach to produce large size UFG metal sheets which main innovation lies in a constrained flowforming process that allows obtaining large deformations under high hydrostatic pressure. Metal sheets with isotropic grain distribution and average grain size of 4 μm were manufactured by this process chain and their mechanical properties assessed. [ABSTRACT FROM AUTHOR]

The work concerns the possibility of producing B-pillars from the 7075 aluminum alloy. First, extensive material tests were carried out. The as-delivered sheets (T6 temper) were heated up to 500 °C and solution heat-treated to dissolve the phases in the aluminum matrix. Then, the foot of the B-pillar was stamped from water-cooled and conductively-cooled blanks. When the initial process parameters were established, stamping tests of B-pillars were carried out. The strength and hardness of the manufactured elements were tested. The selection of process parameters allowed to obtain a product with an appropriate strength, similar to the strength of the T6 temper. [ABSTRACT FROM AUTHOR]

The load bearing capacity of entrapped lubricant and resulting diminished asperity flattening are studied with a new specimen design that allows for both compression and biaxial bulk deformation of the subsurface material. Numerical simulations considering the experimental compressibility curve for the trapped oil support the analysis and show how incomplete filling of the valleys affect asperity flattening depending on the asperity flank angle. Finally, the new specimen design also allows quantifying the differences in friction when bulk deformation of the subsurface material is carried out with and without trapped oil in the valleys between asperities. [ABSTRACT FROM AUTHOR]

This study conducts numerical and experimental analyses to study the parameters affecting deep drawing of symmetric low-depth products, such as die geometry, punch movement, and cushioning. The methodology proposed in this paper is applied on the deep drawing of a frying pan manufactured out of AL99.9%. The finite element model (FE-model) is developed using LS-Dyna© and an experiment is carried out to validate the FE-model. The numerical and experimental results have shown minor deviation of 3.5% and 0.92% for maximum pressing load and maximum thickness, respectively. The validated FE-model is then employed to study the parameters affecting the maximum pressing load and maximum thinning. It is proved that the cushion stiffness and the initial blank thickness have the major influence, while the punch speed shows an insignificant impact. The results are justified and hence the FE-model proves to be reliable for further analyses. [ABSTRACT FROM AUTHOR]

The energy demand and CO 2 emissions of the steel processing industry are a global challenge. During conventional steel processing, the treatment of iron ore and steel in a molten state heavily contributes to this problem. This paper provides an in-depth investigation of the benefits and technical requirements of an alternative processing pathway with minimal energy and CO 2 burdens. Our proposed method, scrap metal consolidation (SMC) by rolling , is adapted from roll bonding, a scalable metal bonding technique, commonly used for niche composite applications to achieve material properties unattainable by monolithic alloy design. SMC transforms steel scrap into hot rolled steel in solid state without melting. Based on pre-published high-fidelity industrial data, we determined that processing hot rolled steel from scrap in the solid state would consume 94% less energy compared to the primary steel processing route with 94% less CO 2 burden. Compared to conventional recycling methods, the energy savings of SMC would be 86%, with an 84% decrease in CO 2 emissions. The proposed method is described in detail, and the process windows for AISI 1008 mild steel and SS304 stainless steel were determined in terms of rolling temperature and reduction using a lab-scale rolling mill at a temperature range of 700–1100 °C. The formability of the consolidated mild steel is also evaluated via the hemisphere punch test, a standard industrial test for assessing the formability of sheet metals. While the fracture height of consolidated specimens is in the 9.27–10.62 mm range, the monolithic sample has a fracture height of 10.34 mm. The test results show that the consolidated sheets have comparable formability to monolithic specimens. These investigations altogether demonstrate that SMC-by-rolling is a feasible and environmentally sustainable alternative for conventional steelmaking or recycling processes. [Display omitted] • Solid-state consolidation of steel scrap uses 94% less energy than primary processing. • Compared to recycling, scrap metal consolidation saves 84% of process CO 2 emissions. • Process boundaries for mild and stainless steel follow a reverse S-curve trend. • Test results exhibit comparable formability for roll-bonded and monolithic samples. • Most sheet metal forming operations don't cause opening stress, reducing failure risk. [ABSTRACT FROM AUTHOR]

A novel criterion for microcrack resistance of multi-phase steels based on property gradient maps is proposed. Two industrial sheets of steel were processed to obtain dual-phase and complex-phase microstructures with exactly the same chemical composition. Experimental investigations showed characteristic differences for the tensile tests, hole expansion and the local plastic behavior during deformation. An innovative full-field modeling approach that explicitly predicts mechanical property gradients as a function of microstructural gradients during forming was developed and validated. This allowed to form a new criterion for evaluation of structure–property relationship in nano-structured multi-phase steels and can reveal the formability limitations. [ABSTRACT FROM AUTHOR]

Models for the evolution of hidden microstructural states are needed for fast prediction and closed-loop control of workpiece properties. Machine learning allows to obtain models by learning from experimental data, avoiding the limitations of explicitly defined physics-based models. However, the identification of the parameters of deep network structures, reliable extrapolation and fast online assimilation to new measurements are open problems. At the example of titanium forging, a new approach is investigated that combines a hybrid physics-informed microstructure and flow stress model that draws upon a long short-term memory network with a particle filter for online data assimilation to new measurements. [ABSTRACT FROM AUTHOR]

This paper presents a new bending method of sheet metal for forming diversified shapes and enhancing operability. The method, "asymmetric bending", uses a punch and a pair of front and back dies. While the punch moves down for bending, the two dies move at different velocities so that the movement of the front side of the sheet metal can severely be restricted. The front side of the metal can be deformed with diversity in advance as it can escape from geometric interference with the bending tools. The method also improves operability and safety for operators due to the movement restriction. [ABSTRACT FROM AUTHOR]

Scaled experimentation continues to play a significant role in process, product design and testing for metallic components and products but for hot forging in particular is recognized to suffer pronounced scale effects with physical behaviour changing with scale. This paper is concerned with an assessment of a new scaling approach called finite similitude that has appeared in the recent literature and a new methodology for exact and inexact experimentation involving scaled experiments. Finite similitude is founded on the scaling of space itself and on a formulation that ensures that the governing physics (in transport form) remain invariant up to proportionality. Unfortunately, proportionality breaks down with scale and to account for this careful experimental design is needed. A question of some importance, which is addressed in this paper, is whether it is possible that physically different materials can exhibit similar mechanical behaviour at certain conditions? These are termed "scaled-material twins" if they are able to match the required material response to some degree of accuracy for those ranges of temperature and strain rates that are representative of forging processes. Presented in the paper is a methodology for selecting scaled-material twins and the quantification of errors involved and its effect on scaled experimentation. Trials with hot disc forgings of different materials and sizes are performed to highlight the difficulties associated with scaling but also to demonstrate that scaled experimentation is possible and if correctly designed offers measurable advantages. [ABSTRACT FROM AUTHOR]

Sheet metals exhibits plastic anisotropy due to the rolling process. This article focuses on the particular case of an 2024T351 Aluminium alloy thick sheet which showed in addition to the anisotropy of mechanical properties an important evolution of the these properties along the thickness. A large series of tension tests performed is carried out using samples machined varying the position along the thickness and the orientation in the rolling plane. Strong variation in terms of elastic limit and ultimate tensile stress are observed. The heterogeneity of the miscrostructure is studied by EBSD along the plate thickness and correlated with the mechanical properties variations; 4 main zones are identified. The constitutive behaviour of the material is model using an anisotropic yield criterion combined to a non-linear hardening rule and one set of parameters is identified for each material layer. The predictive capabilities of the model are illustrated by simulations of notched tension tests with three notch radii. Finally a large structure panel bending test representative of cold forming industrial operations is simulated using the identified model parameters. A very good agreement between the FE results and the experimental strain gauge signals from a scale 1 experiment is observed. This shows the thickness-based identification accurately account for the property gradient for large structure panel simulations. [ABSTRACT FROM AUTHOR]

The present study investigates the effects of the process parameters on cold forming process of an automotive component in AISI 1006 low carbon steel. The material formability was characterised up to 250°C. The material flow behaviour and the related thermal distributions during the geometrical transformations were analyzed. Coining and forming operations were investigated by using a coupled 3D Thermo-mechanical FEM with different die geometries and friction conditions in order to optimize the final die geometry and to reduce the energy consumption. FEM simulation results were validated by comparison with the experimental trials. The detailed study of the component allowed defining the energy required by the severe bending of the initial thick plate. The FEM predictions led to a reduction of deformation energy of about 20%, a mass reduction of 28% on the final product and permitted avoiding secondary machining operations. [ABSTRACT FROM AUTHOR]

Physical mechanisms of ductile damage in metal forming, experimental characterization methods for damage, and models predicting the damage level in formed components are reviewed. Applications of damage analysis in metal forming processes reveal that damage in metal formed parts is not failure, but a product property that accumulates between processes. Various metal forming process designs demonstrate that damage in formed products can be reduced and their performance can be increased. Static and fatigue strength, impact toughness, stiffness, and formability are typical examples of performance indicators that can be improved by damage-based process design. Potential scientific and technological challenges are addressed to realize damage-controlled metal forming processes. [ABSTRACT FROM AUTHOR]

A locally heat-assisted torsion forming process for metal tubes is proposed and integrated in the conventional dieless drawing process. The part of the tube heated by a laser is subjected to torsion deformation due to the difference in the rotation speed of chucks. Pure aluminum tubes A1050 are used in the experiments, and excessive torsional deformation causes unstable deformation. The microstructure is controlled by the amount of torsion. The strength, ductility, and Lankford value are enhanced by the microstructure control in the proposed process. The process can be applied to the continuous mass manufacturing of metal tubes with high performance. [ABSTRACT FROM AUTHOR]

Machine tools with multiple degrees of freedom and parallel kinematics offer tremendous opportunities for new kind of processes but at the same time also a lot of control challenges. They are subject to uncertainties in the form of kinematic errors, elasticities and thermal deflections. Their kinematic non-linearity requires the application of model-based control concepts whose full effectiveness can only be unlocked through controls in the task space. In particular, kinematic singularities occur in forming machines such as presses, which make closed-loop control at corresponding operating points considerably more difficult. In this paper, we use the example of a servo-driven press with three ram degrees of freedom to show how parallel kinematic machine tools can be controlled via inverse differential kinematics models in task space and to what extent the controls can benefit from scheduled gain factors. The results are validated both simulatively and experimentally. In the experimental tests, three-dimensional tool paths are traced that can be used to carry out orbital forging processes. Furthermore, the example of a punch hole rolling process demonstrates that the ram pose is controlled more accurately, which also has positive effects on the resulting workpiece geometry. The performance of the developed gain scheduling task space control is compared with that of a robust and non-robust control with static gains. • Parallel kinematic machine tools are hard to control in task space • Task space control requires integration of sensors in the vicinity of the TCP • Controlling the bearing position of the TCP platform allows gain scheduled control • Gain scheduled control with better performance than conventional control • Superiority of the control also visible in produced workpiece geometries [ABSTRACT FROM AUTHOR]

The deep drawing process is utilized for the manufacturing of sheet metal components in the automobile and aerospace industries. The present study briefs about the current developments in the deep drawing process at the elevated temperature. The comparative study is carried out on the utilization of different approaches and techniques for deep drawing of various sheet metals. The effects of geometrical and process parameters are considered for the elimination of defects like tearing, wrinkling, earing, and spring-back. The study also focuses on deep drawing of the sandwich composite materials at elevated temperatures. The different behaviors and formability are observed from the result for different materials at the elevated temperatures, which indicates the positivity in drawing of complex profile components as per the industry requirements. [ABSTRACT FROM AUTHOR]

Forming is widely used due to its high efficiency in material utilization and its high production rate in general. Most forming processes control the geometry of final products through a set of tooling. The increasing demands on lightweight products have challenged the performances and functionalities of tooling. This paper provides a systematic review of recent advancements related to tooling performance and functionalities, including tool materials, tooling fabrication processes (e.g., machining, heat treatment, coating, surface texturing, and additive manufacturing), sensing, and data analytics. Finally, recommendations on future research directions for metal forming tooling are provided. [ABSTRACT FROM AUTHOR]

Abstract Due to the texture formed in cold/hot rolled forming process, anisotropy is a key issue not only in modeling of plastic deformation but also in characterization of fracture behavior. In this study, an anisotropic ductile fracture criterion is developed by introducing anisotropic parameters into the weight function of an uncoupled shear ductile fracture criterion. The proposed anisotropic ductile fracture is applied to describe the anisotropic characteristics in the ductile fracture of AA6082-T6. Ductile fracture behavior of AA6082 is experimentally investigated at the different loading conditions: shear by in-plane torsion test, uniaxial tension by specimens with a central hole, plane strain tension by notched specimens, and the balanced biaxial tension by the Nakajima test. In-plane torsion and tension tests with a central hole and notch are conducted along three directions: rolling direction, diagonal direction and transverse direction. Specimen deformations during the tests are recorded and fracture strains are measured by digital image correlation approach. The measured fracture strains are then utilized to calibrate the parameters in the proposed ductile fracture criterion. With the calibrated ductile fracture criterion, the fracture locus and anisotropic ductile fracture in various loading conditions are predicted and compared with experimental measurement and those predicted by linearly transformed anisotropic fracture model to investigate the predictability of the proposed ductile fracture criterion. The comparison demonstrates that the anisotropic fracture of AA6082 is predicted by the proposed criterion with good agreement in the different loading directions of shear, uniaxial tension, plane strain tension, and the balanced biaxial tension. Considering the high accuracy of the proposed ductile fracture criterion, it is expected that the proposed anisotropic ductile fracture criterion can improve the reliability of failure prediction in metal forming for materials with strong directionality in fracture. [ABSTRACT FROM AUTHOR]

Abstract In aluminum forming processes, it is observed that the coefficient of friction increases and a transfer layer is formed on the tool surfaces. In the current paper, this phenomenon is studied via pin-on-disc dry sliding tests with aluminum alloy 6082 sliding against cast iron G3500. The results showed that the aluminum transfer layers generated at the sliding interface were identified as the origin of this behaviour that affects both friction and wear. To model this phenomenon, an interactive friction model was developed enabling the prediction of friction and the evolution of the transfer layer from the running in to the steady state. This mechanism based model can be used for representing friction variations and material transfer in sliding systems. Highlights • Observe the interaction between friction, wear and transfer in an aluminium-cast iron contact. • Interactive modelling combining friction, wear and aluminium transfer. • Enable the prediction of sliding distance and contact load dependency of galling. [ABSTRACT FROM AUTHOR]

Abstract Tribological conditions in forming operations depend on several parameters such as tool-workpiece interface pressure, surface expansion, sliding length, sliding speed, tool and workpiece materials and the roughness of the parts. Among indirect parameters, the most influential one is the tool-workpiece interface temperature, which directly influences the lubricant performance. Prior to testing new tribo-systems to determine their limits of lubrication, it is therefore important to find the interface temperature. However, measurement of the interface temperature in metal forming is difficult. The present work investigates the determination of the interface temperature in an industrial ironing operation, where severe process parameters lead to lubricant film breakdown and galling after several strokes. The methodology combines finite element simulations and experimental measurements. The overall procedure is based on a steady-state thermal analysis to determine the temperature distribution within the tool and a transient thermo-mechanical analysis of the ironing process when steady-state conditions are achieved. Results show that the proposed methodology applied to a single stroke can effectively and accurately predict the interface temperature in the test tool, thus avoiding the otherwise required thermo-mechanical FEM analyses of hundreds of strokes to reach steady-state. Furthermore, the influence of parameters, such as the predicted steady-state tool temperature, the friction coefficient and the heat transfer coefficient on the contact temperature, is analysed. It is concluded that the frictional heating is the primary cause for the peak temperature. By calibration of the friction coefficient and the heat transfer coefficient to ensure matching of the numerical results and the experimental measurements, a maximum tool-workpiece interface temperature of 158 °C was determined during the forward stroke and 150 °C during the backward stroke. [ABSTRACT FROM AUTHOR]

Abstract The high tendency of aluminum to adhere to steel has led to extensive research into the application of lubricants to reduce adhesion and friction during forming processes. The behavior of lubricants like tungsten disulfide (WS 2) and graphene oxide (GO) are sensitive to their deposition method. WS 2 applied through aerosol spray has been observed to increase its working temperature range. This research aims to evaluate the tribological and durability properties of WS 2 and GO (deposited as an aerosol spray coating) at temperatures between 25 °C and 450 °C, using ball-on-disc sliding tests. The spray coatings displayed low COF during sliding contact which has been attributed to the formation of transfer layers on the steel counter-faces and tribolayers on the coated Al-Mg surfaces, while their durability was observed to be related to the stability of the tribolayers. The WS 2 spray coating was noted to possess more durable tribolayers, which could be a result of the superior adhesion properties of the carbon-bonded WS 2 platelets to each other and the Al Mg substrate. Highlights • WS 2 and GO spray coatings applied on Al Mg alloys were examined. • Both coatings displayed low COF between 25 °C and 350 °C. • At 450 °C the WS 2 coating displayed low COF while the GO coating failed. • The WS 2 coating displayed greater durability than the GO coating. • The durability of the coatings was related to the stability of the tribolayers. [ABSTRACT FROM AUTHOR]

Abstract The paper gives a view on perspectives for metal forming processes rising due to the industry 4.0 discussion and its consequences. The discussion starts with a view at aims pursued by introducing 4.0 into metal forming. From the results of this the needed data and required sensors are discussed as well as the potential of their introduction into current processes. At this point the processes in metal forming and their respective demands have to be taken into account as well. From here the step to the specific challenges, e.g. originating from the machine tools at hand, can be elaborated on. [ABSTRACT FROM AUTHOR]

Laser bending by means of the temperature gradient mechanism (TGM) has so far been limited to bending the free end of a sheet metal strip toward the irradiating laser beam. This investigation aims to present a new approach which, despite one-sided accessibility, allows targeted incremental laser bending in both directions by the TGM and the upsetting deformation mechanism (UM). The method is based on blind holes along the bending line, whereby the bend direction can be determined by irradiating either the blind hole bottoms or the bridges between the holes. The possibility of bidirectional and alternating laser bending is demonstrated. [ABSTRACT FROM AUTHOR]

Thixoforging allows one-step forming processes of near-net shape components having excellent mechanical properties. However, the high sensitivity of thixoforging regarding process conditions requires precise modelling and determination of process related parameters. At the same time, simple numerical design proves challenging because of the inaccuracy of existing one-phase material models regarding the shear thinning flow behaviour of semi solid metals. Consequently, this paper deals with the development of a new one-phase material model providing a more precise simulation of materials' shear rate dependency. By using this model, simulations could be performed, which allowed the prediction of solidification and flow-related component defects. [ABSTRACT FROM AUTHOR]

This paper presents a new shear bending method of tubes for controlling bending radius, of which the target value at the neutral plane is 0.5 times the tube diameter. The method consists of two steps using a pair of mandrels. The first step makes a space inside the tube, and the second step inserts a new mandrel into the space for transferring the mandrel shape to the bent part. As a result, the bending radius becomes a target radius, which has never been achieved by conventional shear bending, the bending radius of which has always been zero. [ABSTRACT FROM AUTHOR]

• Design and development of an automatic thermo-mechanical testing apparatus. • Three materials were tested at varying strain rates and temperatures. • The device was validated with Hopkinson bar experiments on S235JR steel. • Numerical simulations were performed to analyse the experimental observations. Dynamic testing of materials is necessary to model high-speed forming processes (e.g. hammer forging, blanking, forming, etc.) and crash/impact behaviour of structures, amongst others. The most common machines to perform medium to high-speed tests are the servo-hydraulic high-speed tensile and compression machines and the Hopkinson bars. The paper analyses the use of a newly-developed laboratory testing facility, named the Automatic Thermo-Mechanical Tester (ATMT). This testing machine is equipped with a pneumatically accelerated Direct Impact Drop Hammer (DIDH), a furnace and automatised robotic arm, capable of characterising materials at intermediate strain rates, ranging from 100 to 300 s−1 in combination with temperatures up to 1350 °C. The hammer has been designed and constructed to conduct a variety of material characterisation tests, such as, upsetting or plane strain compression tests as well as component tests for validation purposes. The DIDH allows testing standard compression specimens at average strain rates in the order of 100 s−1 that decrease progressively until the it is fully stopped. It is, in combination with universal testing machines and Hopkinson bar systems, particularly suitable for experimental validation of loading-rate dependant material models. Compression tests were conducted with different hammer impact velocities generating a variety of strain rates at varying temperatures on S235JR structural steel, OFHC copper and wrought Inconel 625 nickel-based superalloy to assess the potential of the novel apparatus. A detailed finite element numerical study of the system was performed to assess several aspects such as the effect of the specimen geometry or its capability as an intermediate testing device, simulating a simplified system and the full Direct Impact Drop Hammer apparatus. [ABSTRACT FROM AUTHOR]

• Uncovering the fracture behavior of two Mg-RE alloys in the wide stress triaxiality; • Calibrating the fracture-related variables through inverse method; • Establishing the two-component DF2016 fracture criterion; • Predicting the fracture occurrence with high accuracy. Stress state has a significant influence on the fracture behavior of materials, especially for the lightweight-high strength metals. The research is carried out to uncover and characterize the stress state-dependent fracture behavior of two Mg alloys containing rare-earth (RE) elements. A two-component DF2016 fracture criterion is constructed by coupling two DF2016 models with the form of addition. The mechanical experiments in wide stress triaxiality were performed for WE43 and Mg-Gd-Y alloys, and the loading process was recorded by adopting digital image correlation technology. Based on the experiment-inverse engineering method, the deformation behavior of each specimen is captured by the numerical simulation with high accuracy. The fracture-related variables in the key element are extracted to present the strong dependence of fracture strain on the stress triaxiality and Lode parameter. Experimental results are used to calibrate the fracture parameters of the two-component DF2016, two-component DF2014 and DF2016 fracture criteria, respectively. The comparative result intuitively shows that the prediction performance of the two-component DF2016 criterion is prior to the other two models. This implies that the established fracture model is more suitable to characterize the fracture behavior of the two Mg-RE alloys. The research provides a comprehensive experimental database and numerical model for the fracture behavior of Mg-RE alloys under a pretty broad range of loading conditions, and is helpful in the engineering application. [ABSTRACT FROM AUTHOR]

Applied in this paper is a new technique for scaling metal forming processes, founded on the idea that scaling can be achieved by scaling space itself. With this approach, the physics in two spaces is described using transport equations and are deemed to possess finite similitude if found to be proportional. Finite similitude can be shown to always exist in continuum mechanics for isotropic scaling and it is demonstrated here how the concept can be used to design experiments. Validation of the approach is achieved by means of scaled experimental, numerical and analytical solutions of scaled upsetting tests for cylindrical and ring samples. Three trial materials are tested and distinguished by the degree of strain softening, strain hardening and near perfect-plastic behaviour. Finite similitude results confirm that any discrepancies between the maximum loads are substantially reduced when the new scaling theory is applied. Best results are obtained when the same material is adopted for both full and small-scale experimentation. [ABSTRACT FROM AUTHOR]

Abstract The design of a product component may require complex processing steps such as metal forming followed by a thermal treatment. The thermal treatment may improve the functional performance of the material itself, but may result in rather unwanted changes in the shape of the product. Here it is shown that Finite Element modeling of the various processes can assist in the design of a robust and accurate production process. The modeling approach presented allows a coupling between various complex material models, in such a way that full cold forming and thermal treatment processes are calculated. This coupling of material models is key for the design and concerns the novelty of the proposed approach. Cold forming by deep drawing is calculated whereby planar anisotropy is implemented. The thermal hardening treatment consists of three contributions: creep, thermal expansion and phase transformation. All models are based on experimental data, acquired from tensile and dilatometer tests, and are implemented into the material model either directly or by a simple fit. It is shown that the effects of a complete forming and heat treatment of a cup could be successfully calculated. The predicted cup shape change was compared to experiments, and shows excellent agreement. Graphical abstract Unlabelled Image Highlights • The predictability and accuracy of the shape changes in the product design • Coupling between forming and thermal treatment • Processing steps of forming and thermal treatment are successfully implemented in the Finite Element computer code. [ABSTRACT FROM AUTHOR]

Many high temperature (HT) forming processes require the use of solid lubricants in order to control friction and reduce wear. In an attempt to eliminate the need for solid lubrication in high temperature sliding applications, nickel-based self-lubricating coatings with the addition of Ag and MoS 2 were prepared by means of laser cladding on stainless steel substrates. The behaviour of the resulting laser claddings was thoroughly evaluated up to 600 °C, including the oxidation behaviour and reciprocating tribotesting using different counter body geometries (ball and flat pin). The self-lubricating coatings showed lower friction than the unmodified reference alloy at all tested temperatures, in addition to a significant microstructural stability after prolonged exposure at high temperatures. The addition of solid lubricants to the claddings was also found to be beneficial in terms of the counter body wear at HT, as no material loss could be measured for the bearing balls after testing at 600 °C against the self-lubricating claddings, despite the significant softening experienced by AISI 52100 bearing steel at HT. [ABSTRACT FROM AUTHOR]

Recently, various methods for the metal spinning of noncircular shapes have been proposed to overcome the limitation of its application range. In this study, a metal spinning method for noncircular shapes with oblique bottoms is proposed. This method is a combination of synchronous spinning and multipass spinning, in which the roller is synchronized with the mandrel rotation to track a noncircular cross section while the workpiece is gradually deformed without much thinning through some paths of the roller. The roller trajectory is calculated by linear interpolation in the radial direction and axial direction between the inclined blank shape and the inclined cross section of the product. A circular cup and square cup with an oblique bottom and vertical side walls are successfully spun using this method. As the wall thickness locally increases at the side edges of the square cup, the thickness distribution is equalized by using an intermediate circular shape. This method interpolates the roller trajectory between the blank shape and intermediate shape and between the intermediate shape and the product. The difference in the wall thickness is reduced since the square shape is formed via a cylindrical shape. In addition, the effect of the process parameters on the forming results is experimentally investigated. [ABSTRACT FROM AUTHOR]

Highlights • Mechanisms of ductile fracture is investigated experimentally in the wide range of loading conditions from compressive upsetting to the tension of notched specimens for two lightweight metals of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. • All the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension and plane strain tension. • Fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from negative in compression to 0.57 in the plane strain tension. • The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, and plane strain tension with stress triaxiality below 0.6. • Effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions. Abstract Mechanisms of ductile fracture are investigated experimentally in a wide range of loading conditions from compressive upsetting to the balanced biaxial tension for two metals with high strength-to-density ratio of DP980 (t1.2) steel sheets and a bulk aluminum alloy of AA7075. Specimens are carefully designed to achieve various loading conditions from shear at low stress triaxiality to the balanced biaxial tension at high stress triaxiality for DP980, while both tensile and compressive tests are conducted for AA7075. Fractured specimen surfaces are analyzed macroscopically focusing on their relations with the maximum shear stress. It is observed that all the specimens tend to fail along the direction of the maximum shear stress in various loading states of plane strain compression, uniaxial compression, shear, uniaxial tension, plane strain tension and the balanced biaxial tension. Scanning electron microscope analyses of fracture surfaces are also conducted to explore the underlying mechanism of void coalescence since coalescence of voids is viewed as the last step of ductile fracture after nucleation and growth of voids. It is noted that fractured voids elongate along the direction of the maximum shear stress for all specimens with the stress triaxiality ranging from about −0.57 in compression to 0.67 in the balanced biaxial tension. The experiments of DP980 and AA7075 reveal that ductile fracture takes place along the direction of the maximum shear stress in the wide loading conditions of compressive upsetting, shear, uniaxial tension, plane strain tension and the balanced biaxial tension with stress triaxiality below 0.67. Thus, ductile fracture is expected to be governed by the maximum shear stress in these wide loading conditions of compression, shear and tension. It is suggested that effect of the maximum shear stress must be correctly coupled in modeling of ductile fracture in these loading conditions with uncoupled and coupled ductile fracture criteria. Graphical abstract Shear fracture takes place in wide loading conditions of tension, shear and compression. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In recent years, due to the introduction of higher resistance materials in the automotive sector, sheet metal-forming tool-makers have been forced to deal with more challenging process designs. Therefore, the optimisation of the manufacturing process has become a key factor in obtaining a part which fits the required tolerances, and the finite element method (FEM) is the most widely used technique to speed up that optimisation time. However, to obtain a numerical result as close as possible to those of industrial conditions, the FEM software inputs must be highly accurate. The present work is focused on the hardening extension of the currently available reduced-formability materials, as it is a key factor in the correct prediction of the stress state and hence, of the springback during a sheet metal-forming process. The objective in this work was the selection of the most appropriate hardening model to extend the flow curve beyond the necking limit for a wide variety of material families currently utilised in the industrial environment. To carry out that analysis, a digital image correlation (DIC) technique was utilised during conventional tensile tests to extend the experimental flow curves of the analysed materials. Commonly used hardening models were fitted to the experimental tensile flow curves with the aim of selecting the model that best predicts the hardening behaviour of each analysed material family. The results showed that the DIC technique was valid for the extension of the hardening curve of the analysed materials and for the final selection of the most suitable hardening model for each analysed material family. [ABSTRACT FROM AUTHOR]

Zinc and its alloys are important industrial materials due to their high corrosion resistance, low cost and good ductility. However, the characterization of these materials remains a difficult task due to their highly anisotropic behavior, the latter being due to the influence of microstructural effects, i.e. loading orientation-dependent activation of different families of slip systems and subsequent texture evolution, rendering the development of a reliable material model considerably difficult. A micro-mechanical approach based on polycrystal plasticity would better describe the physical mechanisms underlying the macroscopic behavior. This improved model should ostensibly improve the comprehension of the mechanical behavior, compared to the macroscopic approach using solely phenomenological anisotropy models along with a prohibitively large number of experiments required to identify the material parameters. In this paper, a multi-scale Visco-Plastic Self-Consistent (VPSC) approach is used. It is based on a micro-scale model calibrated by microstructural and deformation mechanism information based on Electron Back-Scattered Diffraction (EBSD) to describe the macroscopic anisotropic mechanical response during sheet metal deformation. The critical resolved shear stress (CRSS) as well as the micro-scale crystal parameters are obtained by an inverse analysis comparing the simulated and experimental results in terms of obtained tensile curves along three different directions. In order to obtain a global solution for the identification, we then use the Covariance Matrix Adaptation-Evolution Strategy (CMA-ES) genetic algorithm to the inverse problem. We validate our approach by comparing the simulated and experimental textures and activated slip systems. Finally, the identified mechanical parameters are used to investigate the anisotropy of the alloy and predict its formability by determining the corresponding R-values and Hill yield coefficients. [ABSTRACT FROM AUTHOR]

Titanium and its alloys have been widely used in aerospace and biomedical industries, however, they are classified as difficult-to-machine materials. In this paper, ultrasonic vibration is imposed on the die to overcome the difficulties during conventional titanium wire drawing processes at the room temperature. Numerical simulations were performed to investigate the variation of axial stress within the contacting region and study the change of the drawing stress with several factors in terms of the longitudinal amplitude and frequency of the applied ultrasonic vibration, the diameter reduction ratio, and the drawing force. An experimental testing equipment was established to measure the drawing torque and rotational velocity of the coiler drum during the wire drawing process. The result indicates the drawing force increases with the growth of the drawing velocity and the reduction ratio, whether with or without vibrations. Application of either form of ultrasonic vibrations contributes to the further decrease of the drawing force, especially the longitudinal vibration with larger amplitude. SEM was employed to detect the surface morphology of the processed wires drawn under the three circumstances. The surface quality of the drawn wires with ultrasonic vibrations was apparently improved compared with those using conventional method. In addition, the longitudinal and torsional composite vibration was more effective for surface quality improvement than pure longitudinal vibration, however, at the cost of weakened drawing force reduction effect. [ABSTRACT FROM AUTHOR]

It is essential to accurately model the anisotropic plastic deformation and ductile fracture of metals in order to guarantee the reliable numerical analysis and optimization of metal forming. For this purpose, the Drucker function is revisited. Effect of the third stress invariant in the Drucker function is analyzed and calibrated for metals with body-centered cubic (BCC) and face-centered cubic (FCC) crystal systems based on the yielding and plastic flow of both crystal plasticity and biaxial tensile experiments. The calibrated Drucker function is extended into an anisotropic form using a fourth order linear transformation tensor. The anisotropic flexibility is enhanced by two approaches: non-associate flow rule (non-AFR) and the sum of n-components of the anisotropic Drucker function. The proposed anisotropic Drucker function is applied to model the anisotropic behavior of both BCC and FCC metals. The predicted anisotropic behavior is compared with experimental results. The comparison demonstrates that the anisotropy is accurately modeled for both BCC and FCC metals by the anisotropic Drucker function. The anisotropic Drucker function is also implemented into numerical analysis of tension of specimens with a central hole to investigate its computation efficiency under spatial loading compared with the Yld2000-18p function. It is found that the proposed anisotropic Drucker function can reduce about 60% of computation time in case that the Yld2000-18p function is substituted by the anisotropic Drucker function in numerical computation due to its simplicity compared to the Yld2000-18p function. A ductile fracture criterion is also developed by coupling the Drucker function with the first stress invariant. The modified Drucker function is reformulated to investigate the effect of the stress triaxiality and the normalized third invariant on ductile fracture. Comparison of the modified Drucker fracture locus with the experimental results of AA2024-T351 demonstrates that the modified Drucker criterion accurately illustrates the fracture stress of the alloy in wide stress states with the stress triaxiality ranging from −0.5 in plane strain compression to 0.6 in tension of notched specimens. The modified Drucker fracture criterion is expected to be less sensitive to the change of strain path considering that the criterion describes fracture in the stress space. Accordingly, the anisotropic Drucker yield function and the pressure-coupled Drucker fracture criterion are suggested to model anisotropic plastic deformation and to predict the onset of failure for both BCC and FCC metals due to simple implementation in numerical analysis under spatial loading and computation efficiency with brick elements. [ABSTRACT FROM AUTHOR]

Central damage is a serious defect in the solid products of cross wedge rolling. A combined experimental and modelling approach was used to study the micro-mechanism of central damage. The evolution process of the micro-voids initiation, growth and coalescence during cross wedge rolling of steel was observed, and the micro-damage morphology was linked to the stress-strain state to reveal the mechanism of central damage. The influences of process parameters on the central damage were investigated on the basis of analyzing the characteristics of stress and strain in the center of the workpiece. It is found that the micro-voids in the center of the workpiece initiate around non-metallic inclusions and develop into macroscopic damage in the directions of shear stress and tensile stress by growth and coalescence; the shear stress and tensile stress cause significant alternating shear and tensile deformation with the rotation of the workpiece, leading to the central damage. The larger the shear deformation and tensile deformation coefficient, the more the cyclic numbers, the greater the degree of damage; among the process parameters of cross wedge rolling, the forming angle has the greatest influence on the central damage. [ABSTRACT FROM AUTHOR]

This paper presents a new extrusion method for fabrication of a tube with spiral inner fins. The spiral fins are formed by utilizing the generation of spiral outer fins or grooves, which drive the metal to circumferentially move with twist deformation. The effect of the outer fins/grooves is examined for realizing the circumferential metal flow. The position of the mandrel has an ability to flexibly control the spiral angle. This method would drastically enhance the productivity and reduce the manufacturing cost, as the tube would be manufactured directly from a billet through only one process. [ABSTRACT FROM AUTHOR]