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Aiming at the problem that large sheet metal bending parts cannot be processed by single robot, and the manual assisted bending method has high labor intensity and low work efficiency; double robots work together to complete the handling of the plate; Firstly, according to the actual production requirements of sheet metal bending, the process planning and three-dimensional modeling of the production line are completed. Secondly, the kinematics analysis and base coordinate system calibration of the dual robot are completed. Then, by establishing the mathematical model of each unit, the end pose matrix in the local coordinate system of the robot is finally obtained, and the joint angles of the robot machine are obtained by inverse kinematics. Finally, the production line simulation is completed by Rapid offline programming. The research results show that the kinematics model is correct, and the production line can complete the sheet metal bending work without collision, which can provide reference for the research of large sheet metal bending. [ABSTRACT FROM AUTHOR]

In the deformation machining (DM) approach, the machining and incremental forming operations are combined to utilize the strengths of the two processes to produce monolithic components with thin structures using a single setup. DM offers a high degree of flexibility to manufacture monolithic components in comparison to conventional techniques. Some freeform monolithic products are difficult to machine with the 3-axis machining approach due to restricted entry of the tool in certain portions of the geometry. This paper presents a novel double-sided deformation machining (DSDM) technique to manufacture freeform double-sided monolithic components. As a test case, a double-sided monolithic impeller-shaped structure with freeform blades is manufactured with the proposed technique. For this, first, a blank is machined to create the required structure and blades of desired thickness. These machined structures are used as preforms for the incremental forming (bending) of the blades to the final shape. As the existing commercial toolpath development packages are not compatible with the DM process, a novel feature-based double-sided combined machining-forming toolpath is developed for the DSDM operation. Here, the blades are deformed separately and sequentially. This avoids the collision issue and achieves a faster forming operation. To evaluate the quality of the monolithic components developed, a few response parameters, like the process forces, the geometrical accuracy in terms of springback, and the surface roughness, are reported. [ABSTRACT FROM AUTHOR]

Based on the analysis of the advantages and disadvantages of existing surface flattening algorithms, this paper proposes a free‐form surface flattening algorithm that minimizes geometric deformation by combining the advantages of the geometric flattening method and the mechanical energy flattening method to address the problems of many iterations, large changes in convergence, and weak visualization of deformation. The point cloud surface is meshed using the triangular slice search method, and the 3D surface mesh is wrapped around the surface using geometric mapping relationships. The initial correction and deformation analysis of the ring flatten graphic are carried out according to the average flattening error, and a global geometric deformation energy model is established to obtain the energy‐minimizing unfolding conditions and optimize the initial flattening graph by iterative optimization. The verification of the algorithm shows that the algorithm is general, has good robustness, high flattening accuracy, and visualizes the flattening deformation. The method is suitable for some design occasions of machining, such as the flattening calculation of automobile outer cladding parts and sheet metal parts. It is especially suitable for the flattening calculation of ring‐like parts, and is a good guide for the design calculation and stamping process of sheet‐metal‐like parts. [ABSTRACT FROM AUTHOR]

Some industrial sheet metal parts have sharp-corner features for specific function, which are difficult to be formed by conventional forming process. In the present work, a novel double-surface incremental sheet forming (DSISF) method with single forming tool is developed to fabricate such kind of parts. Besides, a new compensation method of tool path is developed to improve the geometric accuracy of the inclined wall and transition corner. To better characterize the forming quality, the effects of process parameters on the geometric accuracy of parts formed by this new method are investigated based on the orthogonal experiments with five levels. Besides, the optimized combination of process parameters is also provided by the range analysis. The results demonstrate that the tool diameter and step down have ignorable effect on geometric accuracy of the inclined wall, while the compensation value and feature dimension have significant influences. This research shows its enlightening significance for the fast-fabrication of unconventional characteristics, such as sharp-corner feature. [ABSTRACT FROM AUTHOR]

This paper presents the use of a computational design algorithm in combination with robotic fabrication and sensing to augment the design and construction process for non-standardized material. Although reusing reclaimed material can significantly reduce the environmental impact in building construction, current design processes are not set up for this shift in thinking. Contrary to conventional practices, designing within the constraints of available material means that geometry and topology cannot be fully pre-determined. This paper introduces a design methodology for corrugated shell structures from folded sheet metal of variable geometries and properties, in which the design goal adapts to available material. It follows a two-fold approach of digital algorithm development and scanning and physical prototyping for robotic fabrication. The scanned materials database is classified based on object geometry data and material properties; such as thickness, type of metal, and spring-back values for fabrication purposes. Together with a target surface, it is an input for a generative design algorithm consisting of surface generation and optimization. The surface generation tries to approximate the target through a translation of search algorithm results for object placement into a 2D mesh graph which is then linked to 3D particle spring based form-finding. The optimization consists of evaluation of structural, fabrication, and design criteria, with finally user selection. Robotic fabrication included object recognition, metal sheet folding and consideration of different metal spring back behavior. These methods were tested on a single curved arch surface and applied to a double curved cantilever canopy as a final demonstrator. The algorithm results showed a generation of different corrugated shell topologies based on iterated object placement. As a demonstrator, a part of the selected canopy was robotically fabricated from local industrial leftovers. [ABSTRACT FROM AUTHOR]

This paper proposed a novel electromagnetic actuator to produce an adaptive pulsed Lorentz force and use it to shape sheet metal workpieces. Such an adaptive pulsed Lorentz force can adapt its spatial distribution with respect to the sheet profile, which may stimulate a wide group of process variant. Herein, we shall introduce this adaptive pulsed Lorentz force to realize an energy-efficient and flexible multi-step electromagnetic forming process. And we shall validate the feasibility and advantages of the proposal by a combination of simulation and experimentation. Our simulation and experimental results suggested that the proposed multi-step process may resolve two critical issues (that is, the limited forming capability and the limited deformation control) for electromagnetic forming process. For the forming capability issue, our proposed process can successfully realize a forming mission which cannot be realized by conventional electromagnetic forming process for the relatively high mechanical strength of the workpiece; in addition, the proposed process has been successfully applied for shaping a sheet metal with 1000 mm length-scale, and compared with a previous work on a similar manufacturing case, the energy capacity required for the proposed process is only 25% of that for the former. For the deformation control issues, the proposed process can substantially reduce or even eliminate the forming defects of the wrinkling and rebounding by using a multi-step calibration process, thus substantially improving the forming quality. In summary, the proposed electromagnetic actuator and process are expected to break through several existing technical bottlenecks, and thus facilitate the advances for electromagnetic forming. [ABSTRACT FROM AUTHOR]

Lightweight structures made of thin sheet metal For many years, the use of steel in the construction industry was characterized by strict specifications regarding the semi‐finished products that could be used and often gave steel structures the character of "modular systems". The modernization of processing methods changed and improved these conditions. In the digital era, it is now possible to create a process chain not only on the production end, but also on the design, presentation, planning and construction end, with the support of which highly individualized steel components can be produced, which in return form part of individualized structures. With these means, lightweight sheet metal structures with individual design can be created, as impressively demonstrated by two prototypes that were created at RWTH Aachen University in cooperation between the Chair of Structures and Structural Design and the Institute of Metal Forming. The novel construction method using thin sheet metal opens up a canon of shapes that was previously rather inaccessible to steel construction and proves to be extremely material saving, thus being in line with the trend of sustainable construction of our time. [ABSTRACT FROM AUTHOR]

Single point incremental forming (SPIF) is one of the most promising technologies for the manufacturing of sheet metal prototypes and parts in small quantities. Similar to other forming processes, the design of the SPIF process is a demanding task. Nowadays, the design process is usually performed using numerical simulations and virtual models. The modelling of the SPIF process faces several challenges, including extremely long computational times caused by long tool paths and the complexity of the problem. Path determination is also a demanding task. This paper presents a finite element (FE) analysis of an incrementally formed truncated pyramid compared to experimental validation. Focus was placed on a possible simplification of the FE process modelling and its impact on the reliability of the results obtained, especially on the geometric accuracy of the part and bottom pillowing effect. The FE modelling of SPIF process was performed with the software ABAQUS, while the experiment was performed on a conventional milling machine. Low-carbon steel DC04 was used. The results confirm that by implementing mass scaling and/or time scaling, the required calculation time can be significantly reduced without substantially affecting the pillowing accuracy. An innovative artificial neural network (ANN) approach was selected to find the optimal values of mesh size and mass scaling in term of minimal bottom pillowing error. However, care should be taken when increasing the element size, as it has a significant impact on the pillow effect at the bottom of the formed part. In the range of selected mass scaling and element size, the smallest geometrical error regarding the experimental part was obtained by mass scaling of 19.01 and tool velocity of 16.49 m/s at the mesh size of 1 × 1 mm. The obtained results enable significant reduction of the computational time and can be applied in the future for other incrementally formed shapes as well. [ABSTRACT FROM AUTHOR]

Plastic deformation of the sheet metal occurs synchronously with elastic deformation of the elastomer in flexible die forming process using elastic die. Thus, adjusting elastic deformation state of the elastomer to adapt to stress state of the sheet metal may be a potential way to improve sheet-forming capability. In this work, various deformation modes of the flexible dies were established using elastomers with different structures, which aims at developing a new way to improve sheet-forming capability through controlling in-plane stress state of the sheet metal. Digital image correlation (DIC) technique was used to capture the displacement and strain field of the sheet metal in bulge tests. Finite element analysis (FEA) was conducted to obtain pressure field of the flexible die and in-plane stresses of the sheet metal. The results showed that forming load, bulged height, and bulge strain could be adjusted by using flexible dies with different structures. The sharp increase of normal pressure in local region at the flexible die/sheet interface leads to non-uniform distribution of radial and circumferential stresses of the sheet metal. A design strategy of flexible die with a hollow structure (i.e., type 6) was proposed to reduce localization of interfacial normal pressure. Due to evenly-distributed normal pressure and beneficial friction at the flexible die/sheet interface, radial and circumferential stresses subjected by the sheet metal were relieved effectively. And the consequent increase of bulge height and bulge strain indicates the improvement of sheet-forming capability. [ABSTRACT FROM AUTHOR]

Advanced high strength steels (AHSS) are multiphase steels that contain various concentrations of ferrite, bainite, martensite, and retained austenite phases. The unique physical characteristics of AHSS present some challenges to welding and bonding processes. AHSS have tendency to change microstructure and mechanical properties by any welding process like other steels. Based on the significant applications in various industries, the experimental works are carried out on one of AHSS materials, EN-10149-2 S700MC, with thickness of 2 mm steel sheet metal by MIG welding process parameters such as current, voltage, and welding speed. For all combinations of process parameters, the butt joints are fabricated. The butt joints are inspected through different nondestructive testing for defects detection. All the defect-free joints are characterized through microstructure (at different zones of joint), hardness, and tensile tests. From the obtained mechanical test results, the process parameters are optimized through design of experiment techniques (DoE). The analysis from DoE method is used to identify which parameter is the most significant among all parameters. Confirmatory test is also done by taking the optimal parameters and the result shows that the improvement of the response variables is acceptable and also shows that the method that is used for optimization was valid. [ABSTRACT FROM AUTHOR]

Automated clamping for post-processing of mass-customized parts is a challenging step in the laser powder bed fusion (LPBF) process chain. In this study, a novel modular sheet metal clamping system was developed that uses disposable sheet metal profiles as a universal interface for the LPBF, robotic handling, and milling processes. Based on a fundamental investigation of hybrid additive manufacturing, the sheet metal clamping system was designed to use the same interface for the LPBF and milling processes. Subsequent an end-to-end validation was performed for the entire process chain. The concept of the sheet metal clamping system gives milling tools access to a part on five to six sides. Further, the part can be accessed from the top and bottom sides, and simplifying the removal of LPBF supports. No clamping forces are induced in the LPBF part, which is especially important for filigree structures. The sheet metal clamping system's underlying concept could be adapted to automating the LPBF process chain for applications such as prosthetic dentistry. [ABSTRACT FROM AUTHOR]

Origami-based sheet metal (OSM) bending is a promising new die-free folding technique for sheet metal. OSM bending principle is based on deforming the material along a pre-defined fold line, which is determined using material discontinuity (MD) produced by laser or waterjet cutting. The objective of this work is to study and evaluate the fracture in OSM bending under the influence of various MD types, kerf-to-thickness (k/t) ratios, and sheet thicknesses. The research goal is to provide information on selecting an optimized k/t ratio and type of MD that allows for fracture-free bending. Four different ductile fracture criteria (DFC) are used and calibrated from experimental data to forecast fracture. The DFC calibration is used to produce a set of critical damage values (CDV) for assessing the possibility of fracture in the OSM bending. In addition, the study provides fracture evaluation using finite element analysis (FEA) integrated with experimental cases for a broader range of OSM bending parameters and MDs. The results demonstrated that an MD with a higher k/t ratio is less likely to fracture during the OSM bending, whereas a higher sheet thickness increases the possibility of fracture. Furthermore, the study identifies the k/t ratio limit that ensures successful bending without fracture and categorizes MD types into two groups based on fracture likelihood. The fracture in the first group is dependent on the limiting k/t ratio, whereas the possibility of fracture in the second group is independent of the k/t ratio due to its topology. [ABSTRACT FROM AUTHOR]

Nowadays the development of innovative processes is a major challenge for industries which want to prototype functional workpieces. Incremental sheet forming (ISF) is a good alternative for sheet metal prototyping to ensure flexibility, accuracy of the part produced, and cost effectiveness. A derived process, the Water Jet Incremental Sheet Forming (WJISF), has been undergoing development since 2001 and this paper purpose to give its state of the art. Different eclectic industrial fields could be concerned by WJISF process: automotive, micro-electronics, medical, and aerospace industry, for example. As the ISF process, the WJISF device needs a multi-axial machine, but it also needs a pressure pump with a sufficient flow rate and pressure. In an environmental point of view, this process can be seen as a "green" one giving that the water can be recycled and there is no lubricant. A general methodology has been defined to rigorously investigate this process and focus on researchers' teams, technological feasibility, numerical simulations, machine-tool uses, and real parts manufacturing. The study presented here provides summarizing evidence, especially technological windows, which give quick view of the actual knowledges and will help scientists and industrials to find WJISF parameters related to their needs. A lot of simple tests have been carried out with numerical and experimental comparisons. Nevertheless, few real parts have been manufactured, and the complex shape obtained by WJISF remains a scientific field to explore. [ABSTRACT FROM AUTHOR]

The clinched process of heterogeneous materials is increasingly used in automobile, aerospace, and household appliances manufacturing. To investigate the forming quality of clinched joint for dissimilar sheet metal, the clinching experiments are carried out, and the cross-section morphology of clinched joints is observed. The finite element model for forming steel-aluminum clinched joint is established. The influence of process parameters (forming process parameters, geometry parameters, and concave die structural parameters) on the forming quality of steel-aluminum clinched joint is analyzed. The evaluation of the joint after forming includes the critical dimension, deformation, and neck-lock ratio. Then, the strength of the joint is measured by the tensile shear test. The changing law of strength and the neck-lock ratio is analyzed. The design strategy of different process parameters is proposed. The results show that the forming process of the joint is well predicted by numerical simulation, and the joint quality is good. The neck lock ratio of the joint with the highest tensile and shear strength is close to 1 when the forming force is 40 kN. The tensile strength and shear strength of the joint are increased by 125% and 62.35%. The design strategy is verified by experiments. The shear strength of the joint is increased by 16.49%. [ABSTRACT FROM AUTHOR]

The article covers experimental research on the forming of products made of 7075 aluminum alloy. This aluminum alloy grade is characterized by high strength, but due to its low formability in T6 temper, its use in the stamping processes of complex structural elements is limited. The authors have manufactured a U-shaped element at an elevated temperature and determined the optimal parameters of the process. Conventional heating of the sheet and shaping it at the temperature of 100 and 150 °C allowed to obtain a product of high strength similar to the T6 state, above 540 MPa. Due to the excessive springback of the sheet during forming, these products were characterized by a large deviation of the shape geometry, exceeding the allowable values of + / − 1 mm. Only the use of an alternative method of heating the sheet to temperatures of 200 and 240 °C (between plates at 350 °C, heating time 2 min, heating rate 1.8 °C/s) allowed to obtain a product that meets both the strength and geometric requirements. The determined optimal process' parameters were later transferred to the stamping process of elements of a more complex shape (lower part of the B-pillar). The sheet was heated up and formed in the previously pre-heated tools. In the subsequent series of tests, the heating method and the blank's temperature were being analyzed. In the case of the foot of the B-pillar, it was necessary to lower the initial blank temperature to 200 °C (heating in a furnace with a temperature of 340 °C, heating speed 0.5 °C/s). The appropriate combination of the process parameters resulted in the satisfactory shape deviation and reaching the product's strength comparable to the strength of the material in as-delivered T6 temper. Using electron microscopy, it was verified that the structure of the finished product contained particles MgZn2 that strongly strengthen the alloy. The obtained results complement the data on the possibility of using 7075 aluminum alloy to produce energy-absorbing elements of motor vehicles. [ABSTRACT FROM AUTHOR]

The construction industry involves a variety of construction works, all of which differ in terms of the frequency and probability of fatal incidents and types of accidents. Accordingly, the risk level of various construction works should be defined for effective safety management at the design and construction phases. This study proposes an approach for quantifying the risk level of fatal incidents in construction works based on frequency and probability analysis using estimation and clustering methods. The main study objective is accomplished in four steps. It was found that the average normalized ranking (ANR) ranged from 2.51 to 26.88, with the most dangerous construction works being scaffolding and demolition works (2.51). Based on the ANR, 27 construction works were categorized into five groups with risk levels ranked from 1 to 5. Risk level 5, the most dangerous group of construction works, was composed of scaffolding and demolition works and roofing and sheet metal construction works, both of which were higher than other construction works considering the frequency and probability of fatal incidents. [ABSTRACT FROM AUTHOR]

Single point incremental forming (SPIF) is a highly flexible forming process for sheet metal. It has low production costs be-cause the process does not use a die. It is suitable for prototyping and made-to-order production. Currently, the SPIF process employs the concept of heat to increase formability. The idea is to generate heat from friction caused by sliding the tool against the workpiece, called "friction stir". This research proposed to study the behavior of temperature that occurs when affected by the tool rotation speed and the feed rate, which are both variables affecting friction stir. This research adopted the method of detecting temperature with infrared cameras and online recording data. The camera sensor received data as 8-bit images containing data from 0 to 255. The value of each position represented the temperature level. In this research, the mini-mum-maximum temperature range was set at 80–300 degrees Celsius for forming the hot dipped zinc coat roll steel sheet at a thickness of 0.2 mm using the SPIF process. The variable parameters were the tool rotation speed and feed rate. The tool rotation speed was categorized as high and used no sliding friction with feed rates of 500, 1000, 1500 mm/min. Concerning the results analysis, this study used the relationships between tool rotational speed and feed rate, shown as relative sliding velocity. The results showed with significance that the increase of the maximum temperature in the process corresponded to an increase in relative sliding velocity using a tool rotational speed and feed rate with no relative sliding velocity. The process temperature was close to room temperature. Relative sliding velocity at approximately 6000 and 10000 mm/min caused a maximum temperature of approximately 160–180 and 200–250 degrees Celsius, respectively. Another issue found in the experiment was that not turning the tool reduced the formability of the process. [ABSTRACT FROM AUTHOR]

Parts or products can be considered as the carrier of energy consumption during manufacturing since they are the final output of workshops. The concept of "embodied energy" is presented as a feasible indicator to characterize the energy consumption of a part or a product. Previous work mainly discussed methods and technologies to apply the embodied energy of parts for selecting materials and processes in product design; the role that embodied energy of parts can play in production optimization was seldom investigated. In addition, different from machining workshops, which has been widely discussed, there is less research on energy saving in the sheet metal forming workshop. In this paper, modeling and application of embodied energy for energy saving in the sheet metal forming workshop is presented. The embodied energy of parts during the manufacturing phase (EEPM) is modeled. The EEPM is evaluated by discrete event simulation to identify energy distribution, energy-intensive processes, and bottlenecks (e.g., processes with feed blocking, machines with low utilization, and others) during production. Energy-oriented scheduling in the workshop is implemented, and a two-stage approach based on ranks of EEPM that can quickly select more efficient production solutions is proposed. A case in a stamping workshop of a partner company validates the proposed methods. This study provides a practical approach to seek a trade-off between energy saving and high production efficiency for energy-intensive discrete workshops. [ABSTRACT FROM AUTHOR]

To reduce the springback after sheet stamping, two forming processes which include electromagnetic forming (EMF) were designed. Compared with traditional electromagnetic-assisted stamping (EMAS), the new methods use the same mold structure and control springback without obvious plastic deformation. The ANSYS and ABAQUS software were used to analyze the influence of different discharge voltages on springback in the two forming processes. The simulation results accurately predict the deformation and springback of sheet metal after quasi-static stamping and subsequent EMF. After coil discharge, the sheet oscillates with high frequency and small amplitude and only exhibits insignificant deformation. With the increase of the discharge voltage, the sheet springback angle decreases. The springback inhibition effect of process 1, in which the sheet corners merely touch the coil surface, is greater than that of process 2, where the sheet was pressed close to the coil surface. [ABSTRACT FROM AUTHOR]

Electromagnetic forming (EMF) can greatly improve the materials forming limit, but how to improve the energy utilization of EMF is an urgent problem to be solved. In this paper, the method of current assisted electromagnetic forming (CA-EMF) was proposed and compared the deformation process with traditional EMF. Three forming schemes were carried out to analyze the effects of steel die and bridge structure on current distribution and deformation result of sheet metal. The results show that steel die which is commonly used in traditional EMF was not suitable for CA-EMF. Then, the epoxy plate die with good insulation is used to replace steel die, and a bridge structure is used to form a current loop with the sheet during CA-EMF process. Thus, the current density and electromagnetic force in the deformation area of the sheet were significantly increased. Therefore, CA-EMF is an effective means of improving the plastic deformation effect of metals. The sheet-deformed profile and forming height obtained from experiment and simulation were compared, and the correctness of simulation was proved. [ABSTRACT FROM AUTHOR]

In order to reduce fuel consumption and thus pollutant emissions, the automotive industry is increasingly developing lightweight construction concepts that are accompanied by an increasing usage of aluminum materials. Due to poor weldability of aluminum in combination with other materials, mechanical joining methods such as clinching were developed and established in series production. In order to predict the relevant characteristics of clinched joints and to ensure the reliability of the process, it is simulated numerically during product development processes. In this regard, the predictive accuracy of the simulated process highly depends on the implemented friction model. In particular, the frictional behavior between the sheet metals as well as between the sheet metal and clinching tools has a significant impact on the geometrical formation of the clinched joint. No testing methods exist that can sufficiently investigate the frictional behavior in sheet materials, especially under high interface pressures, different relative velocities, and long friction paths, while allowing a decoupled consideration of the test parameters. This paper describes the development of further testing concepts based on a proven tribo-torsion test method for determining friction coefficients between sheet metal materials for the simulation of clinching processes. For this purpose, the correlation of interface pressure and the relative velocity between aluminum and steel sheet material in clinching processes is investigated using numerical simulation. Based on these findings, the developed concepts focus on determining friction coefficients at interface pressures of the above materials, yield stress, as well as the reproduction of the occurring friction conditions between sheet metal materials and tool surfaces in clinching processes using tool substitutes. Furthermore, wear investigations between sheet metal material and tool surface were carried out in the friction tests with subsequent EDX analyses of the frictioned tool surfaces. The developed method also allows an optical deformation measurement of the sheet metal material specimen by means of digital image correlation (DIC). Based on a methodological approach, the test setups and the test systems used are explained, and the functionality of the concepts is proven by experimental tests using different sheet metal materials. [ABSTRACT FROM AUTHOR]

The discrete clamp is used to replace the integral clamp in the traditional stretch forming process, and the stretch forming process of complex curved parts is studied. With the trapezoidal profile part and the double curved top part as the research objects, numerical simulation of the stretch forming process with the integral clamp and the discrete clamp is carried out respectively. The numerical simulation results show that: compared with the integral clamp, it is easier for the trapezoidal profile part to fit the die during stretch forming with the discrete clamp, and the distribution of strain and thickness of the formed part is more uniform; during forming of the double curved top part, with the same forming force, the sheet metal cannot fit the die completely with the integral clamp forming, while it can completely fit the die during stretch forming with the discrete clamp. When the forming force of the integral clamp is increased, the sheet metal still cannot fit the die completely, and the sheet metal is more likely to crack. Stretch forming tests are conducted for the trapezoidal profile part and the double curved top part with the discrete clamp stretch forming device, and good forming effect is realized, which is consistent with the numerical simulation results. [ABSTRACT FROM AUTHOR]

Metal forming or shaping processes, such as sheet metal forming and bulk forming, are widely used in many industries including automotive industry. Before computational simulations were widely used in the field of metal forming industry, the trial-and-error based empirical approach was conventionally applied to the optimization of the metal forming process and product. The most commonly employed numerical approach in the metal forming process for robust process optimization is the finite element analysis. Friction, one of the parameters that significantly affect the accuracy of numerical analysis, depends on several variants such as surface quality, contact pressure, lubrication, deformation, and the forming environment. Despite the complexity and difficulty of identifying friction mechanisms, accurate friction models are essential and hence have been proposed by numerous researchers. In this paper, the friction models in the previous studies are reviewed by categorizing them into the boundary lubrication condition and mixed-boundary lubrication condition according to their evaluative influences on friction. Since friction models have been proposed based on the contact theories, an overview on the contact models is also included in this paper. In addition, the contribution of several parameters on the friction such as surface roughness and material properties of the tool, adhesion, contact pressure, sliding speed, bulk deformation is also discussed. This review paper aims to provide an understanding and insight into the friction modeling and simulation along with associated friction experiments. [ABSTRACT FROM AUTHOR]

Extrusion connection is a new method of forming and manufacturing heterogeneous welded sheets. The factors that affected the bonding quality are the forming temperature, the extrusion ratio, and the guiding angle of the die, which has brought trouble to the evaluation of bonding strength and quality. A method to establish a predicted model for the bonding strength of welded sheets by integrating finite element simulations, process experiments, and artificial neural networks was developed. Finite element simulations were used to verify the process experiments and provided training data sets for the artificial neural networks. The BP neural network was used to predict the bonding strength. Due to the randomness of the weight and threshold of the BP neural network, its predicted accuracy needs to be improved, in which genetic algorithms were used to optimize consequently. The results showed that the genetic algorithm neural network model had higher reliability, and the predicted accuracy was 99.5%. Compared with the traditional BP neural network, the predicted accuracy was improved by 5.78%, and the error was reduced to 0.5%. It has good generalization ability and provides a new way for intelligent reliability evaluation of high performance heterogeneous welded sheets via extrusion. [ABSTRACT FROM AUTHOR]

In the sheet metal forming processes, the transformed induced plasticity (TRIP) steel of RAK 40/70 grade exhibits a so-called springback effect, which is governed by strain recovery of material after the load removal. In this study, the numerical simulation of the bending process was performed and compared with experimental data. Springback can be related to many parameters, including forming conditions, tool geometry, sheet thickness, yield stress, work hardening, strain rate sensitivity, and elastic modulus. The effects of the above parameters on the springback effect were evaluated for the V-shaped sheet metal part made of TRIP steel with a thickness of 0.75 mm and a bending angle of 90°. In the numerical simulation, Hill's and Barlat's yield criterions were used in combination with Ludwik's and Swift's hardening models. The numerical simulation data were compared with the experimental results, showing their close correlation. [ABSTRACT FROM AUTHOR]

Sheet springback and structural deformation of the folding mechanism are key issues in the sheet metal–forming process. Elastic-plastic bending theory and numerical simulation are applied to study the forming performance of sheet metal. First, a springback prediction model under general assumptions is established, based on the constitutive relationship of the elastic-plastic linear hardening material. In addition, the influences of processing parameters, such as sheet thickness and forming angle on springback, are analysed according to the theoretical model and verified by experiments. Then, a laser tracker is used to acquire the folding trajectory, and the structural deformation of the folding mechanism is confirmed by trajectory comparison. On this basis, numerical simulations are performed to collect deformation parameters, and a formula for mechanical compensation is obtained by linear fitting to the simulation data. Finally, experimental tests are carried out to verify the accuracy of the compensation model. The results show that the forming precision of the sheet metal can be controlled in the range of ± 1 0 ′ . The proposed method is generally applicable to linear hardening materials and operation conditions where the sheet thickness ranges from 0.8 to 3 mm. [ABSTRACT FROM AUTHOR]

To improve the thickness uniformity of sheet metal parts in incremental forming method based on a virtual auxiliary body, the effect of relevant parameters on the thickness uniformity was studied from both overall and local perspectives. Finite element (FE) method was used to carry out the single-factor and two-level factorial experiments, in which standard deviation of the thickness of section nodes was used as a response to analyzing the effect of factors on the thickness uniformity. First, the mean effects of each factor were obtained and the factor levels of factorial experiments were determined through a single-factor experiment. Then, the interaction effect between factors was analyzed and the optimal combination of parameters was determined through factorial experiments. From the FE analysis, it was found that the desired forming angle and the gap at the bottom have obvious mean effects and interactional effects on the thickness uniformity. Finally, the initial and optimal parameters were used for forming experiments. In the forming experiments, the overall and local thickness standard deviations of section nodes were reduced from 0.194 to 0.088 mm and from 0.149 to 0.081 mm, respectively, which means that the optimized parameters can effectively improve the thickness uniformity of sheet metal parts. [ABSTRACT FROM AUTHOR]

Process-induced residual stresses significantly influence the mechanical properties of a formed component. A polymer pad is used as a flexible die in two-point incremental forming to induce compressive residual stresses in the component during the forming process. Experimental and numerical results illustrate the influence of compressive stress superposition on the component properties. It is shown that the active support, using a geometry-independent polyurethane die, causes beneficial compressive residual stresses on the tool side compared to the tensile residual stresses induced by the single-point incremental forming process without such a supporting die. [ABSTRACT FROM AUTHOR]

Due to the change from mass production to mass personalized production and the resulting intrinsic product flexibility, the automotive industry, among others, is looking for cost-efficient and resource-saving production methods to combining global just-in-time production. In addition to geometric manufacturing flexibility, additive manufacturing offers a resource-saving application for rapid prototyping and small series in predevelopment. In this study, the FDM process is utilized to manufacture the tooling to draw a small series of sheet metal parts in combination with the rubber pad forming process. Therefore, a variety of common AM polymer materials (PETG, PLA, and ABS) is compared in compression tests, from which PLA is selected to be applied as sheet metal forming die. For the rubber pad forming process, relevant processing parameters, i.e., press force and rubber cushion hardness, are studied with respect to forming depth. The product batch is examined by optical evaluation using a metrological system. The scans of the tool and sheet metal parts confirm the mechanical integrity of the additively manufactured die from polymer and thus the suitability of this approach for small series in sheet metal drawing processes, e.g., for automotive applications. [ABSTRACT FROM AUTHOR]

The Lorentz-force-driven stamping process is a newly developed forming process, which combines the advantages of the quasi-static stamping and electromagnetic forming to a certain extent. It involves complex physical problems such as strong electro-magneto-mechanical interactions and considerable deformation. Therefore, it is still a challenge to accurately predict the electromagnetic parameters (coil current and Lorentz force, etc.) and workpiece deformation (forming height and material flow) during the stamping process for different forming conditions. To solve this problem, taking the cylindrical cup forming of 5052-O aluminum alloy sheet metal as an example, a numerical method based on the iterative calculation of a circuit-electromagnetic model and an electromagnetic-mechanical model is developed and systematically validated. Numerical tests show that, compared with the non-iterative model, the proposed iterative mode can significantly improve the simulation accuracy for different forming conditions (such as varied discharge voltages and initial gaps between the coil and the punch). It has been confirmed that the iterative procedure can well consider the effect of the increased distance between the coil and the punch on the calculations of electromagnetic and mechanical parameters. Furthermore, numerical and experimental investigations for a Lorentz-force-driven stamping system using a discharge circuit with an additional crowbar branch are carried out, showing the simulation data of discharge current and workpiece deformation agree well with that of experiment measurement. This confirms the applicability of the proposed method to different discharge circuits. [ABSTRACT FROM AUTHOR]

For sheet metal parts with the vertical-wall partially and irregularly distributed on the sides (VWPIS) that contains both the difficult-form-surface (i.e., vertical-wall) with large forming angle and easy-to-form surface (i.e., gently tilted surface) with small forming angle, a selective multi-stage two point incremental forming (SMTPIF) on the basis of the forming angle was proposed. This SMTPIF method performs multi-stage forming only for the difficult-form-surface and gives different forming strategies and forming parameters to the different surface regions according to the forming angle. The algorithms for surface zoning, generation of the small forming angle surface for vertical-wall, generation of one-stage forming model by combining the easy-form-surface and small forming angle surface were presented. Meanwhile, the algorithm for the generation of the toolpath that is suitable to the SMTPIF was also given. The effectiveness of the proposed algorithm and the SMTPIF was verified by using the case studies, the finite element analysis, and the forming experiments. The results indicate that the SMTPIF can fabricate the VWPIS with short forming time and no sinking phenomenon. [ABSTRACT FROM AUTHOR]

Drucker's sixth-order yield function for isotropic materials (J Appl Mech 16:349–357, 1949) was extended by Cazacu and Barlat (Math Mech Solids 6:613–630, 2001) for modeling orthotropic sheet metals via a generalization of the two stress invariants according to the theory of representation. The constant c in the original Drucker's isotropic yield function was found by Dodd and Naruse (Int J Mech Sci 31:511–519, 1989) to be bound between –27/8 and 9/4 per the convexity requirement. In many subsequent modeling applications of orthotropic sheets, the same bound is also tacitly assumed for the constant c used in this class of the generalized Drucker's yield function CB2001. No actual proof has, however, been presented in the literature that such a bound is indeed absolutely necessary if not sufficient to guarantee the convexity of the orthotropic CB2001 yield function. In this study, the validity of assuming such a convexity bound on the adjustable constant c is examined using a recently proposed numerical convexity certification algorithm. Representative orthotropic CB2001 yield functions whose material parameters have been calibrated and reported in the literature for some 12 FCC, BCC, and HCP sheet metals are evaluated. It is found that a single convexity bound between - 27 / 8 and 9/4 on the constant c does not hold at all for any of those yield functions. This is in contrast to another class of generalized Drucker's yield function based on linearly transformed stresses where the original convexity bound on the constant c does still hold. [ABSTRACT FROM AUTHOR]

Spring-back is one of the vital problems associated with sheet metal forming. To satisfy the customer with a high-quality product at a low cost and quick delivery, the awareness, and proper control of the spring-back after forming is a primary aspect in achieving near-net-shape products. This work aims at developing empirical models using techniques such as the Taguchi design of experiments to predict spring-back in air-bending process of the Interstitial Free (IF) steel sheet. Using the five identified independent predominant bending parameters such as punch travel, strain hardening exponent, punch radius, punch velocity and width of the sheet that has greater influences on the spring-back is used to establish the prediction models, using MINITAB v13 with the help of the experimental data. It is used effectively to analyze the cause and effect of process parameters on response and provides insights for the selection of process variables to achieve minimum spring-back. [ABSTRACT FROM AUTHOR]

Putting in place circular economy strategies is an urgent challenge to face. In this scenario, manufacturing processes play a relevant role as efficient material reuse enabler. Scientists have to make an effort either to find new process or to rethink old process to reprocess end-of-life (EoL) component to recover both material and functions. In this paper, single point incremental forming (SPIF) process is used for reshaping sheet metal EoL components. The entire process chain was replicated including both deep drawing process (to imitate the end-of-life component) as well as SPIF operations (to obtain the reshaped components). The geometrical deviation as a consequence of SPIF operations was studied; two different SPIF directions (named inwards and outwards) were analyzed. A wide experimental campaign along with statistical analyses was developed to analyze effects of some geometrical parameters on the observed geometrical deviation. The results are promising as limited distortions were observed and sound components were obtained in all the analyzed process configurations. Despite that, some research is still needed to better standardize the reshaping process and bring it closer to an industrial applicability. [ABSTRACT FROM AUTHOR]

The flaring process of thin-walled tubes from light metal alloys such as titanium is very important in automotive and aerospace industries, which is usually carried out at high temperatures. As compared to conventional flaring processes of the tube end, the single-point incremental forming (SPIF) process has a great potential to form symmetric and asymmetric shapes without needing dedicated dies. In this research, the end flaring of the commercially pure grade 2 titanium (Ti-grade 2) tube is experimentally and numerically investigated at room and high temperatures. To this end, firstly, an appropriate fixture was designed and manufactured for the high-temperature SPIF of tubes. Effects of the angular step of the multistage deformation strategy and the forming temperature on the formability limit and surface defects are studied. Results of the conical flaring at room temperature show that the maximum expansion ratio at the tube edge is greatly dependent on the angular step, such that by increasing the angular step from 5° to 10°, the maximum expansion ratio increases by 63%. At the temperature of 400 °C, the expansion of the tube end into the vertical wall relative to the tube axis (i.e., the semi-angle of 90°) was successfully performed. While at room temperature, the conical flaring is limited to the semi-angle of 40° and 70° for the flange length of 33 mm using the angular steps of 5° and 10°, respectively. To extend the process capability of the tube end flaring, it is shown that the cylindrical, elliptical, and square flaring with specified dimensions, which are not possible at room temperature, can be successfully carried out at the temperature of 400 °C. The above results are analyzed in detail by investigating the deformation mechanics using the finite element modeling. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation on the incremental sheet metal forming assisted by ultrasonic vibration (UV). With the aid of a new acoustoplasticity constitutive model which can accurately capture the deformation response to ultra-high strain rates, extensive numerical analyses on incremental sheet metal forming under UV were conducted by using the finite element method. Corresponding experimental investigations were also carried out to examine the capacity of the constitutive and numerical models. The effects of critical parameters, such as tool size, tool revolution speed, feed rate, pitch and tool vibration amplitude, on the forming force, maximum sheet thickness reduction and springback, were investigated in detail. It was found that the models can realistically predict the incremental sheet metal forming under UV. It is expected that this research can facilitate the development of ultrasonic vibration–assisted forming techniques. [ABSTRACT FROM AUTHOR]

The design of the progressive die stamping process is optimized through minimizing the number of die stamping stations in the strip layout to reduce the die cost. In order to accomplish such end, in this study, a graph-theoretic based method is implemented to model and optimize the strip layout design. This method starts with mapping stamping features into stamping operations. This step is followed by constructing two graphs to model the precedence and adjacency constraints among stamping operations based on a set of manufacturing rules. These two graphs are called: operation precedence graph and operation adjacency graph. In the next step, a topological sorting algorithm clusters the operations into partially ordered sets. Then, a graph coloring algorithm clusters the partially ordered operations sets into final sequence of operations. The graph-theoretic technique has been implemented on a part currently manufactured by laser cutting process technology in some Egyptian factory in Cairo. This study indicated that the graph-theoretic technique offers several advantages including the ease of programming and transparency in understanding the obtained strip layout design. This is besides being a systematic and logically approach to obtain an optimized strip layout design. In general, the progressive die manufacturing can increase productivity of sheet metal works in Egypt, only in situations of mass production. The limitation is that it requires considerable skill level and training for labor to conduct die strip layout design. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) films produced by rolling and tentering have biaxial orientation and thus exhibit anisotropic mechanical properties such as yielding, hardening, and fracture. The anisotropy of film makes it difficult to analyze deformation and failures occurring during processing such as metal forming of polymer-coated sheet metals. In this work, the anisotropic yielding and hardening of the PET film were measured and an anisotropic constitutive model is developed to represent the anisotropic behavior. In addition, fracture limits of the PET film were measured using the Nakajima test. To describe anisotropic fracture behavior of the film, an anisotropic fracture criterion based on the strain energy density and the theory of isotropic equivalent material was proposed. For validation of the developed constitutive model and the fracture criterion, a deep drawing test of the PET-coated sheet metal was conducted. The film cracking predicted by the anisotropic fracture criterion agreed well with measurements. [ABSTRACT FROM AUTHOR]

Springback is adversely affected by mechanical anisotropy in the process of sheet metal forming. In this work, an analytical method was proposed to predict the springback of the double-curved workpiece in multi-point forming process. To characterize the anisotropy of the AA7B04 aluminum plate, the plate was divided into several layers along thickness direction. And in each layer, the calculation of bending moment was done respectively based on von Mises, Hill's 48 and Yld2004-18p yield criterion. After springback, the neutral surface curvature was calculated and the profile of the neutral surface was constructed by the Bezier surface blending method. To verify the prediction method, finite element simulation and bending experiment were performed. The results show that the predictive accuracy of the method was more accurate than that with the isotropy model. Additionally, the most accurate constitutive model to describe the in-plane anisotropy of AA7B04 aluminum was the Yld2004-18p yield criterion. [ABSTRACT FROM AUTHOR]

Polyethylene terephthalate (PET) films produced by rolling and tentering have biaxial orientation and thus exhibit anisotropic mechanical properties such as yielding, hardening, and fracture. The anisotropy of film makes it difficult to analyze deformation and failures occurring during processing such as metal forming of polymer-coated sheet metals. In this work, the anisotropic yielding and hardening of the PET film were measured and an anisotropic constitutive model is developed to represent the anisotropic behavior. In addition, fracture limits of the PET film were measured using the Nakajima test. To describe anisotropic fracture behavior of the film, an anisotropic fracture criterion based on the strain energy density and the theory of isotropic equivalent material was proposed. For validation of the developed constitutive model and the fracture criterion, a deep drawing test of the PET-coated sheet metal was conducted. The film cracking predicted by the anisotropic fracture criterion agreed well with measurements. [ABSTRACT FROM AUTHOR]

Anisotropic ductile fracture is of special importance for accurate modeling of failure in plastic forming of lightweight sheet metals. This research introduces a user-friendly approach to model loading direction effect on fracture limits of sheet metals. The approach is combined with a newly developed fracture criterion (DF2016) to illustrate anisotropic fracture in shear, uniaxial tension and plane strain tension as well as fracture under balanced biaxial tension. The anisotropic DF2016 criterion is applied to describe loading direction effect on the fracture limits of two sheet metals: 6k21 aluminum alloy and a steel sheet of DP980. The predicted loading direction effect is observed to agree with the experimental results with high accuracy. The applications demonstrate that there are three advantages of the proposed approach: high accuracy, good flexibility and being very user-friendly in the calibration of anisotropic parameters. Therefore, we recommend the proposed anisotropic DF2016 criterion for numerical failure prediction in stamping of strong anisotropic metals. [ABSTRACT FROM AUTHOR]

The Lorentz force distribution on a tube is the dominant factor that determines the tube deformation behavior in the electromagnetic forming process. However, the existing forming technologies in this field are mainly based on a single-coil system, which results in a relatively fixed Lorentz force distribution and makes it difficult to control the forming process or the final tube shape. To solve this problem, a three-coil forming system composed of three sub-coils and two pulsed power supplies is developed for tube forming in this work. Both numerical simulation and experimental results show that the three-coil system can be easily applied to alter the Lorentz force distribution through adjusting the discharge voltage of sub-coils, providing an effective way to improve the deformation uniformity and control the deformation shape. It is found that an AA6061-O aluminum alloy tube with an inner diameter of 76 mm and a thickness of 2 mm can be deformed with a homogeneous deformation range of about 23.56 mm via the three-coil system in the experiments, while the range is only about 11.48 mm under the same conditions when using the conventional single-coil system. Meanwhile, it is demonstrated that the three-coil system can achieve a variety of tube shapes including concave and convex profiles with different uniformity. The developed method and obtained results are of good value for expanding the application of electromagnetic tube forming. [ABSTRACT FROM AUTHOR]

Aluminum alloys are characterized by low formability limits under cold forming conditions. The accurate prediction of deformation and failure in sheet metal forming allows for the optimization of forming process parameters and reduces tooling modifications and materials costs. Several models for ductile damage have been developed in the past decades to quantify and predict forming and damage response of sheet metal under complex-forming conditions. However, there is a need to identify a robust model which can provide realistic predictions for the behavior of aluminum sheet metal under the cold forming condition and different loading conditions. This work aims to investigate the prediction capabilities of different damage models for AA-5754 during the cold forming process. The experimental tensile and forming limit diagram (FLD) data of AA-5754 sheet metal used for the damage models' calibration were obtained from literature. In this article, four damage models available in two broadly used the FE software; namely, LS-DYNA and PAM-STAMP were investigated. The models utilized from LS-DYNA material library were MAT_JOHNSON_COOK, MAT_GURSON, and MAT_GISSMO; while from the PAM-STAMP software, the novel CDM model was used. The cross-die formability tests for AA-5754 sheets were performed to validate these damage models. The predictions of the novel CDM model were found to give a good agreement with the experimental results obtained from the formability tests. [ABSTRACT FROM AUTHOR]

This paper presents an iterative finite element (FE)–based method to calculate the gravity-free shape of nonrigid parts from an optical measurement performed on a non-over-constrained fixture. Measuring these kinds of parts in a stress-free state is almost impossible because deflections caused by their weight occur. To solve this problem, a simulation model of the measurement is created using available methods of reverse engineering. Then, an iterative algorithm calculates the gravity-free shape. The approach does not require a CAD model of the measured part, implying the whole part can be fully scanned. The application of this method mainly addresses thin, unstable sheet metal parts, like those commonly used in the automotive or aerospace industry. To show the performance of the proposed method, validations with simulation and experimental data are presented. The shown results meet the predefined quality goal to predict shapes within a tolerance of ± 0.05 mm measured in surface normal direction. [ABSTRACT FROM AUTHOR]

In this paper, experimental and numerical simulation studies on the forming limit diagram of single-point incremental forming (SPIF) were described. We proposed a novel method for evaluating the forming limit in incremental forming. The proposed method utilizes the forming limit angle and the maximum thinning rate. The effects of the forming and processing parameters on the forming limit of an aluminum sheet during incremental forming were investigated using a combination of simulation analysis and experimental verification. The obtained results show that the forming limit is large for 1060Al and 6061Al when the initial thickness is 1.5 mm for a single parameter change for SPIF. For 1060Al, the step size is in the range of 0.8–1.5 mm. When the step size is 0.8 mm, the incremental forming limit is large and the forming precision is high. For 1060Al and 6061Al, the incremental forming limit is at the maximum level when the tool radius is 6.0 mm, and when the tool radius is 5.0 mm, the best forming precision can be achieved. It is of great theoretical significance and practical engineering value to study the effects of various forming parameters on the forming limit of metal sheet SPIF. [ABSTRACT FROM AUTHOR]

The market of consumer goods requires nowadays quick response to customer needs. As a consequence, this is transferred to the time restrictions that the semi-finished product manufacturer must meet. Therefore the cost of manufacturing cannot determine how production processes are designed, and the main evaluation function of manufacturing processes is the response time to customers' orders. One of the ideas for implementing this idea is the QRM (Quick Response Manufacturing) production organization system. The purpose of the research undertaken by the authors was to develop an innovative solution in the field of production structure, allowing for the implementation of the QRM concept in a Contract Manufacturer, which realizes its tasks according to engineering-to-order (ETO) system in conditions defined as High Mix, Low Volume, High Complexity. The object of the research was to select appropriate methods for grouping products assuming that certain operations will be carried out in traditional but well-organized technological and/or linear cells. The research was carried out in one of the largest producers of sheet metal components in Europe. Pre-completed groupings for data obtained from the company had indicated that -- among the classical methods -- the best results had been given by the following methods: King's Algorithm (otherwise called: Binary Ordering, Rank Order Clustering), k-means, and Kohonen's neural networks. The results of the tests and preliminary simulations based on the data from the company proved that the implementation of the QRM concept does not have to be associated with the absolute formation of multi-purpose cells. It turned out that the effect of reducing the response time to customer needs can be obtained by using hybrid structures that combine solutions characteristic of cellular systems with traditional systems such as a technological, linear, or mixed structure. However, this requires the application of technological solutions with the highest level of organization. [ABSTRACT FROM AUTHOR]