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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]

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]

Reconfigurable multipoint forming is a flexible sheet forming technique aimed at customised sheet metal products. However, one drawback of multipoint forming is the cost and time needed to set up and align the upper and lower pin matrices. This study introduces an optimisation study of a novel hole-type rubber punch replacing the top pin matrix of multipoint incremental forming, aiming to reduce pins setting up and alignment complexity and time. Finite element modelling and design of experiments were used to investigate the effect of hole-type rubber punch configuration such as hole size, hole type, and the compression ratio on the wrinkling, thickness variation, and shape deviation. This research shows that the most significant process parameter in all responses was the hole size. The compression ratio of the material was found to be insignificant in wrinkling and shape deviation. The hole-type rubber punch parameters were found to be a hole size of 9 mm, circular hole type, and a compression ratio of 75%. This experimentally resulted in an improved parts wrinkling of 80%, when compared to using solid rubber punch, with the added benefits of reduction of the cost and time needed to set up and align the pin matrices. [ABSTRACT FROM AUTHOR]

Because the forming area involved in traditional reverse multistage incremental forming is only located inside the model, the sheet-metal thinning rate is relatively large. Particularly, the straight-wall parts with a narrow internal space cannot be formed using traditional multistage incremental forming. Therefore, a negative multistage incremental forming that extrudes the sheet from the forward and the reverse side of the straight-wall part is proposed in this paper. In this method, firstly, the auxiliary surface is generated to divide the straight-wall part model into three forming regions; secondly, the first- and second-stage forming are carried out from the forward side of the straight-wall part with support, respectively; Thirdly, the third-stage forming is carried out from the forward side of the straight-wall part without support. The software system for auxiliary-surface generation, the straight-wall parts partition, each intermediate-stage-forming model, and each stage-forming toolpath generation was developed by using C++, VC++, and OpenGL library. In order to verify the feasibility of the proposed method in this paper, the forming experiments of a 1060 aluminum sheet were conducted using traditional reverse multistage forming and the proposed method in this paper, and the forming effects were compared and analyzed. The results show that compared with traditional reverse multistage incremental forming with forward-side extrusion, the multistage incremental forming method with the forward and the reverse-sided extrusion proposed in this paper can increase the area of the sheet participating in the deformation and avoid the problem of excessive thinning of sheet thickness, especially suitable for the straight-wall part model with narrow internal space. [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]

Many forming failures such as tearing and wrinkling are encountered during sheet metal forming operations, and it is important for manufacturers to find a quick solution for these failures that hinder the production of a desired part. The theory of inventive problem-solving (TRIZ) is a problem-solving method that considers the patents issued in the past that have been useful in solving problems across a variety of industries. In this paper, TRIZ methodology was utilized to solve the tearing problem occurring during the forming of the lower control arm (automotive suspension part) without altering the desired shape and material of the part. For this purpose, a contradiction matrix was developed and the four different TRIZ principles of "segmentation," "taking out," "the other way around," and "parameter change" were implemented in four different experiments. Of the conducted experiments, the experiment in which the TRIZ principles of "segmentation," "taking out," and "parameter change" were implemented together resolved the problem in a way that was acceptable and feasible for mass production of the lower control arm. [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]

To simulate sheet metal forming processes precisely, an in-house dynamic explicit code was developed to apply a new solid-shell element to sheet metal forming analyses, with a corotational coordinate system utilized to simplify the nonlinearity and to integrate the element with anisotropic constitutive laws. The enhancing parameter of the solid-shell element, implemented to circumvent the volumetric and thickness locking phenomena, was condensed into an explicit form. To avoid the rank deficiency, a modified physical stabilization involving the B-bar method and reconstruction of transverse shear components was adopted. For computational efficiency of the solid-shell element in numerical applications, an adaptive mesh subdivision scheme was developed, with element geometry and contact condition taken as subdivision criteria. To accurately capture the anisotropic behavior of sheet metals, material models with three different anisotropic yield functions were incorporated. Several numerical examples were carried out to validate the accuracy of the proposed element and the efficiency of the adaptive mesh subdivision. [ABSTRACT FROM AUTHOR]

The article presents the results of friction tests of a 0.8 mm-thick DC04 deep-drawing quality steel sheet. A special friction simulator was used in the tests, reflecting friction conditions occurring while pulling a sheet strip through a drawbead in sheet metal forming. The variable parameters in the experimental tests were as follows: surface roughness of countersamples, lubrication conditions, sample orientation in relation to the sheet rolling direction as well as the sample width and height of the drawbead. Due to many factors that affect the value of the coefficient of friction coefficient, artificial neural networks (ANNs) were used to build and analyse the friction model. Four training algorithms were used to train the ANNs: back propagation, conjugate gradients, quasi-Newton and Levenberg–Marquardt. It was found that for all analysed friction conditions and sheet strip widths, increasing the drawbead height increases the COF value. The chlorine-based Heavy Draw 1150 compound provides a more effective friction reduction compared to a LAN-46 machine oil. [ABSTRACT FROM AUTHOR]

Heat-assisted forming processes are becoming increasingly important in the manufacturing of sheet metal parts for body-in-white applications. However, the non-isothermal nature of these processes leads to challenges in evaluating the forming limits, since established methods such as Forming Limit Curves (FLCs) only allow the assessment of critical forming strains for steady temperatures. For this reason, a temperature-dependent extension of the well-established GISSMO (Generalized Incremental Stress State Dependent Damage Model) fracture indicator framework is developed by the authors to predict forming failures under non-isothermal conditions. In this paper, a general approach to combine several isothermal FLCs within the temperature-extended GISSMO model into a temperature-dependent forming limit surface is investigated. The general capabilities of the model are tested in a coupled thermo-mechanical FEA using the example of warm forming of an AA5182-O sheet metal cross-die cup. The obtained results are then compared with state of the art of evaluation methods. By taking the strain and temperature path into account, GISSMO predicts greater drawing depths by up to 20 % than established methods. In this way the forming and so the lightweight potential of sheet metal parts can by fully exploited. Moreover, the risk and locus of failure can be evaluated directly on the part geometry by a contour plot. An additional advantage of the GISSMO model is the applicability for low triaxialities as well as the possibility to predict the materials behavior beyond necking up to ductile fracture. [ABSTRACT FROM AUTHOR]

• An Eulerian formulation based on microstructural vectors is used to model orthotropic inelasticity in sheet metal. • A new functional form for inelastic spin is proposed. • A single material constant controlling inelastic spin is calibrated by measured data. • The Eulerian model is insensitive to arbitrariness of a reference configuration. • Simple shear is used to show that a common Lagrangian model predicts unphysical dependence on the reference configuration. This paper develops a new functional form for the inelastic spin that influences the orientation of microstructural vectors during large inelastic deformations in a recently developed Eulerian formulation of sheet metal. For the problems under consideration, a single constant determines the inelastic spin, and the results of the New model are compared to those of a common Lagrangian sheet metal model. It is shown that the same value of this constant causes the New model to predict good results relative to measured data for uniaxial stress at angles relative to the RD, equibiaxial stress and the R-value distribution for AA6022-T4 sheet metal. In contrast, the Lagrangian model predicts zero inelastic spin, which is inconsistent with the measured data. The example of large deformation simple shear is used to further examine the influence of inelastic spin predicted by the New model and the Lagrangian model. The results show that the predictions of the New model, which is insensitive to arbitrariness of a reference configuration, are reasonable, while those of the Lagrangian model exhibit an unphysical dependence on the reference configuration. [ABSTRACT FROM AUTHOR]