Sheet Metal

SUMMARY: Springback is one of the major causes for fabrication parts rejection in sheet metal forming. This is a geometrical defect that occurs on the drawn part after removing all the stamping tools, and is caused by elastic strain recovery of the material. In this work, springback is evaluated with a benchmark test that consists on cutting a ring specimen from a drawn cup and then splitting it longitudinally along a radial plan. Numerical simulation results were obtained using the finite element code DD3IMP with the package DD3TRIM to perform the ring cuts and splitting. Finite element mesh sensitivity tests were done and results were post-processed with GID software.

This article demonstrates the optimum working areas and cutting conditions for the laser cutting of a series of advanced high strength steels (AHSS). The parameters that most influence the cutting of sheet metal have been studied and the results have been divided into two large groups with thickness of more and less than 1 mm. The influence of the material and, more important, the effect of coating have been taken into account. The results, have demonstrate very different behaviours between the thinnest and thickest sheets, whilst the variation of the cutting parameters due to the influence of the material is less relevant. The optimum cutting areas and the quality of the cut evaluated with different criteria are presented. Finally, the best position for the laser beam has been observed to be underneath the sheet.

Ti-6Al-4V ELI (extra low interstitials) grade alloy provides improved ductility and fracture toughness comparing to grade 5 Ti-6Al-4V alloy. In order to find the optimum superplastic forming and diffusion bonding (SPF/DB) condition, a series of tensile tests was carried out at the strain rate range of 10 −4 to 10 −2 s −1 and temperature range of 1073-1223 K. The maximum elongation of 1898% was obtained at the strain rate of 10 −3 s −1 at 850 • C. It was shown that the ELI grade alloy performs better than the grade 5 alloy in terms of the optimum superplastic condition for Ti-6Al-4V. Based on this result, diffusion bonding process of superplastic Ti-6Al-4V ELI sheet metals was developed. Bonding was completed by means of inert gas pressure applied in a bonding tool at high temperature. The microstructure of the bonding area was investigated and the bonding interface was microscopically undetectable. The evidence of nucleation of new grains and migration of grain boundaries at the interface proves the diffusion bonding process is successful. It is shown that the superplastic forming and diffusion bonding of Ti-6Al-4V ELI grade is possible at the temperature lower than those of conventional Ti-6Al-4V.

Over the past ten years, a novel cellular solid, Trabecular Metal TM , has been developed for use in the orthopaedics industry as an ingrowth scaffold. Manufactured using chemical vapour deposition (CVD) on top of a graphite foam substrate, this material has a regular matrix of interconnecting pores, high strength, and high porosity. Manufacturing difficulties encourage the application of bending, stamping and forming technologies to increase CVD reactor throughput and reduce material wastes. In this study, the bending and forming behaviour of Trabecular Metal TM was evaluated using a novel camera-based system for measuring surface strains, since the conventional approach of printing or etching gridded patterns was not feasible. A forming limit diagram was obtained using specially fabricated 1.65 mm thick sheets. A springback coefficient was measured and modeled using effective hexagonal cell arrangements.

For preparation of a proper offer in tool-making industry the most frequently the values of total cost for manufacture are needed. Because of lack of time for making a detailed analysis the total costs of tool manufacture are predicted by the expert on the basis of the experience gathered during several years of work in this area. In our work we conceived an intelligent system for predicting of total cost of the tool manufacture. The system is based on the concept of case-based reasoning; on the basis of target and source cases the system prepares the prediction of cost. The target case is the CAD-model in whose certain production costs we are interested, whereas the source cases are the CAD-model of products, for which the tools had already been made, and the relevant total costs are known. The system first abstracts from CAD-models the geometrical features, and then it calculates the similarities between the source cases and target case. Then the most similar cases are used for preparation of prediction by genetic programming method. The genetic programming method provides the model connecting the individual geometrical features with total costs searched for.

Geometrical optimization of structural components is a topic of high interest for engineers involved with design activities mainly related to mass reduction. The study described in these pages focuses on the optimization of plates subjected to bending for which stiffness is obtained by a pattern of ribs. Although stiffening by means of ribs is a well-known and old technique, the design of ribs for maximum stiffness is often based on practice and experience. Classical optimization methods such as topological, topographical and parametric optimization fail to give an efficient design with a reasonable programming effort, especially when dealing with many and complex constraints. These constraints are both technical and technological. A most promising technique to obtain optimal rib patterns was to define a set of feasible rib trajectories and then to select the subset with the most efficient combinations. The result is not unique and a method to select the optimal patterns is required. In fact, the stiffening effect increases with increasing rib length, but at a greater cost. A trade-off must be found between structural performance and cost: The tools to guide this selection process is the main objective of the paper, with particular attention in evaluating the stiffening due to the presence of beads on the plate with a close link with the production system and possible technological constraints which can occur during manufacturing processes, such as minimum rib distance or the presence of discontinuities or the presence of holes or other elements on the plate. A special tool with enforced rib cross section is considered, and optimal rib deployment has to be found. Numerical examples attached show the methodology and obtainable results.

Optimization of process parameters in sheet metal forming is an important task to reduce manufacturing cost. To determine the optimum values of the process parameters, it is essential to find their influence on the deformation behaviour of the sheet metal. The significance of three important process parameters namely, die radius, blank holder force and friction coefficient on the deep-drawing characteristics of a stainless steel axi-symmetric cup was determined. Finite element method combined with Taguchi technique form a refined predictive tool to determine the influence of forming process parameters. The Taguchi method was employed to identify the relative influence of each process parameter considered in this study. A reduced set of finite element simulations were carried out as per the Taguchi orthogonal array. Based on the predicted thickness distribution of the deep drawn circular cup and analysis of variance test, it is evident that die radius has the greatest influence on the deep drawing of stainless steel blank sheet followed by the blank holder force and the friction coefficient. Further, it is shown that a blank holder force application and local lubrication scheme improved the quality of the formed part.

Transfer and accumulation of adhered sheet material, generally referred to as galling, is the major cause for tool failure in sheet metal forming. In this study, the galling resistances of several tool steels were evaluated against dual-phase high-strength carbon steel using a SOFS tribometer, in which disc-shaped tools were slid against a real sheet surface in dry sliding test conditions. Three different frictional regimes were identified and characterized during sliding, and any transition in friction corresponded to a transition in wear mechanisms of the sheets. The performance of the tools depended on load, material and the particular frictional regime. Best overall performance was obtained by nitrogen-alloyed powder metallurgy tool steel.

Sheet Metal Spinning is a flexible manufacturing process for axially-symmetric hollow components. While the process itself is already known for centuries, process planning is still based on undocumented expertise, thus requiring specialized craftsmen for new process layouts. Current process descriptions indicate a vast scope of different dynamic influences while the underlying mechanical model uses a simple static approach. Thus, a 3D Finite Element Model of the process has been set up at IUL in order to analyze the process in detail, providing online as well as cross sectional data of the specimen formed. Within the scope of this article, the results of the above mentioned Finite Element Analysis (FEA) are presented and discussed with respect to the qualitative stress distributions introduced in the existing theoretical models. Main emphasis of this paper is set on a discussion of the qualitative stress distribution, which is, to the current state, only known in theory.

Spot welding used in four wheeler fabrication and repair works. It is one of the essential area where the design plays a
vital role in identifying the mechanical behavior of different structures which are joint together and to impose the static, fatigue
and impact strength of this joints at computer aided engineering technique by identifying the works which are to be concentrated
during fabrication. This work is about determining the fatigue life of spot welded joint which are introduced which some boundary
condition which could be used in mechanical structural analysis using CAE. Here the life of nugget which is subjected to fatigue
loading is determined. In order to carry out analysis of sheet thickness and spot diameter geometry is considered to be essential
parameter for proceeding the above suggested research work. Here ANSYS workbench is used to solve the required problem by
using finite element analysis technique. Static structural works space is used to carry out the basic structural analysis of the rigid
member which is joint together. Workbench is considered to be a user friendly tool compared with that of ADPL. In order to
determine the fatigue life of spot welded joints before undergoing fabrication works this kinds of studies are carried out over here.
The results acquired can be plotted in stress strain graphs where the characteristic curve helps as in solving our engineering
constrains. The modeling of the part work are carried out the CREO software

Surface texturing, which fabricates micro dimples or micro channels on the surface of parts, is a growing technique for improving tribological characteristics of materials. Currently, electrical discharge texturing (EDT) technique, one surface texturing method suitable for mass production, is being used to texture aluminum sheets for the applications in automotive industry. It has been widely accepted in industry that EDT improves the forming behavior of aluminum sheets due to better friction behavior. However, how the textures on the surface of sheet metal change the friction behavior has not been investigated. In this paper, the influence of EDT on the friction behavior of aluminum automotive sheet at different contact pressures and sliding speeds is investigated based on both experimental studies and numerical simulations. To fully investigate the tribological behaviors, a flat-on-flat friction test device was built and a numerical code based on mixed lubrication theory was developed. It was found that EDT texturing can reduce the friction coefficient of contacting pair at high contact pressure, however, increase friction coefficient at low contact pressure. Numerical simulations confirmed this finding. Furthermore, the model provides valuable information for the prediction of friction behavior of EDT sheets and helps to optimize processing parameters for various forming processes using EDT aluminum sheets.

The blanking of thin sheet (0.1±1 mm) of mild steel has been analysed using an elastic±plastic ®nite element method based on the incremental theory of plasticity. The blank diameters are considered in the range 1±4 mm. The study has helped to evaluate the in¯uence of tool clearance, friction, sheet thickness, punch/die size and blanking layout on the sheet deformation. The punch load variation with tool travel and stress distribution in the sheet have been obtained. The results indicate that a reduction in the tool clearance increases the blanking load. The blanking load increases with an increase in the coef®cient of friction. These observations are very similar to the case of blanking of component of large size. Further, these effects are very similar in the case of both single and double blanking. An interblanking site distance of about twice the sheet thickness is good to reduce the thinning of sheet at the intermediate regions between the two blanking sites. For a particular sheet thickness, the blanking load requirement reduces as the blank diameter increases. # 2000 Elsevier Science S.A. All rights reserved.

Laser cutting of hole in a mild steel thick sheet metal is investigated. Temperature and stress fields developed around the cutting section are simulated using the finite element method. An experimental is carried out accommodating the simulation parameters. The residual stress developed in the cutting section is measured using the XRD technique and findings are compared with the predictions. Optical microscopy and SEM are carried out to examine the morphological changes in the cutting sections. It is found that temperature decays sharply in the region of the laser heat source, which results in high temperature gradient in this region. This causes the development of high stress levels around the cut edges. The residual stresses predicted are in agreement with the measured results.

A process design technique is presented for the formability assessment of sheet metal stamping parts and feasibility analysis of process conditions. The proposed approach is based on numerical simulation of stamping processes by using explicit -incremental and implicit -iterative finite element techniques. The influence of the numeric model parameters are investigated with factor analysis and described with response surfaces obtained by multi-linear regression. A forming process leading to springback-critic channel geometry is selected for the application of the proposed methodology. The effects of modeling parameters are determined by evaluating influences of the punch velocity and the element size, in order to obtain a numerically calibrated simulation model. Then the sensitivity of the springback deformations to the contact interface friction and the blankholder force is predicted, and a set of response surfaces is generated. Comparisons with the experimental data indicated the suitability of the proposed approach in springback predictions. The proposed technique is employed in the stamping analysis of an engine suspension bracket made of high-strength steel. The process conditions are investigated in terms of drawbead penetration and blankholder force setting, and the predicted part shapes are compared with CMM measurements of the manufactured parts. An evaluation of computed springback distortions shows a good correlation with experiment results and confirms the use of process parameters estimated with the proposed design.

Hole-flanging is a manufacturing process which is used to form flanges around holes by using sheet metal. A brief and concise review of the contributions made by the previous researchers in the area of hole-flanging process has been presented. Steel sheet material and aluminum alloys are used by researchers for hole flange forming. FEM modelling of hole-flanging is carried out by employing axisymmetric conditions. Meshing of the work piece is done by using axisymmetric quadrilateral elements. Experimental setup and tools utilized in formation of hole flanges are presented and discussed. Results are presented in terms of variation of distribution of thickness along flange wall through conventional hole-flanging and incremental forming technique. Incremental forming techniques with different forming strategies is found to be more accurate, less complicated and better means of hole flanging in comparison to conventional forming techniques.

This paper presents a closed-form theoretical analysis modelling the fundamentals of single point incremental forming and explaining the experimental and numerical results available in the literature for the past couple of years. The model is based on membrane analysis with bi-directional in-plane contact friction and is focused on the extreme modes of deformation that are likely to be found in single point incremental forming processes. The overall investigation is supported by experimental work performed by the authors and data retrieved from the literature.

The idea of incremental forming technique has been investigated for production of sheet metal components. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. In the present study, the formability of an aluminum sheet under various forming conditions was assessed and difficult-to-form shapes were produced with the technique. By utilizing knowledge and experience obtained during the present study, it became possible to produce some free surfaces.

Importance of bending dies is very wide in sheet metal industry. Knowing that springback amount of bending material in bending dies is as important as the die itself, because the material leaving the die should be within the allowed tolerance limits. Therefore, in this study the subject of bending dies and springback in bending process has been researched. In order to find springback in bending, a ''V'' shaped die is designed and it has been aimed to find out how much can steel sheet metal materials resile in various angles and to bring forward springback graphics to add literature. There is little satisfying information in the literature regarding this issue. In order to reach a conclusion, 15 different dies have been prepared, more than 150 samples, each of which has been bent at least 10 times, have been bent and the obtained angles have been measured with profile meter. The acquired results have been statistically evaluated in a computer media and converted to graphics.

This paper describes the development of an expert system for both process planning and die design of sheet metal cutting and piercing operations. Knowledge for the system is acquired from practical handbooks, theory and empirical knowledge from industrial partners and is expressed as 'crude' rules, transformed by the knowledge engineer into production rules. These are then coded into constructs of the CLIPS expert system development environment. This process is explained using a number of examples. The expert system comprises of five modules: initial calculations (including data input), process planning, finishing operation, die and press selection, and tools selection. Each module draws upon one or more among 18 rule pools defined around the important notions characterising the problem studied. The results of the expert system can be used by both the designer deciding on the production feasibility (manufacturability) for a sheet metal component and by the manufacturer receiving advice either on the hardware needed, or on the process plan.

Au sud de la Loire, la cathédrale de Clermont-Ferrand est l’unique témoin connu et conservé qui ait été couvert d’une toiture en plomb sur le modèle des cathédrales de Chartres, Paris, Rouen, Beauvais, Reims, Saint-Denis ou Senlis (chœur). Ce constat confine à hypostasier les fins politiques d’un tel choix qui suggère la volonté de hisser l’édifice auvergnat au rang de ceux qui, au cœur du royaume, sont les vitrines de grands évêchés. Le langage politique de l’architecture gothique n’est certes pas un sujet nouveau et nous savons qu’il mérite parfois quelques réserves mais la question doit se poser du rôle des couvertures en plomb, lourdes, onéreuses, fragiles qui couvrent les édifices de blancs manteaux prestigieux. A Clermont,  ce choix s’entend par son illustre commanditaire : l’évêque Jacques d’Amboise, qui en projette la construction dès 1496, et dont nous savons combien la famille, dans la seconde moitié du XVe siècle, accompagne le renouveau de l’entourage royal et joue un rôle politique, artistique et économique à l’orée de la Renaissance. Sur le fondement de comptes de construction inédits de la fin du XVe et de la première moitié du XVIe siècle, le chantier se dessine, sa composition humaine, la provenance, le coût et le poids des matériaux, les techniques mises en œuvre et la richesse du décor disparu. La couverture médiévale, maintes fois altérées, a jusqu’au XIXe siècle impliqué de constantes réflexions sur sa conservation et son étanchéité. Entièrement restaurée entre 1870 et 1896 par l’entreprise Monduit, Gaget, Gauthier et Compagnie, partenaire privilégié d’Eugène-Emmanuel Viollet-le-Duc, elle témoigne d’un savoir-faire qui, bien qu’introduisant de nouvelles techniques (fixations, voligeages, orientation des tables modifiés), semble révéler en pleine révolution industrielle une anamnèse évidente des gestes médiévaux.

This paper discusses the results of the numerical study of rectangular cup drawing of steel sheets using finite element methods. To be able to verify the results of the numerical solutions, an experimental study was done where the material behavior under deformation was analyzed. A 3D parametric finite element (FE) model was built using the commercial FE-package ABAQUS/Standard. ABAQUS allows analyzing physical models of real processes putting special emphasis on geometrical non-linearities caused by large deformations, material non-linearities and complex friction conditions. Friction properties of the deep drawing quality steel sheet were determined by using the pin-on-disc tribometer. The results show that the friction coefficient depends on the measured angle from the rolling direction and corresponds to the surface topography. A quadratic Hill anisotropic yield criterion was compared with von Mises yield criterion having isotropic hardening. The sensitivity of constitutive laws to the initial data characterizing material behavior is also presented. It is found out that plastic anisotropy of the matrix in ductile sheet metal has influence on deformation behavior of the material. When the material and friction anisotropy are taken into account in the finite element analysis, this approach gives better approximate numerical results for real processes.

The electrical contact resistance at the interface between two materials is often an unknown when modelling certain processes, such as the anodes and cathodes in Hall-Héroult cells or the spot welding of sheet metal. In this paper, a 2D axisymmetric weakly coupled thermoelectro-mechanical finite element methodology built in the commercial code ANSYS is presented. It allows the generation of Joule heat directly at the interface, the precise representation of the contact areas as well as the testing of different contact resistance models. Using existing experimental results of industrial carbon and steel cylinders in contact at different temperatures, a novel phenomenological constitutive law for electrical contact resistance was developed. This experiment was repeated at room temperature with Alcoa-Lauralco carbon and cast iron cylinders, and the 2D finite element model was used to validate and calibrate the constitutive law. An excellent agreement was found between the model predictions and the new experimental data. #

Springback remains a major concern in sheet metal forming process. Springback, shape discrepancy between fully loaded and unloaded configuration due to elastic recovery of material, is mainly affected by geometrical parameters, material properties of sheet and lubrication condition between the blank and the tool. A total-elastic-incremental-plastic (TEIP) algorithm, for large deformation and large rotational problems, was incorporated in indigenous Finite Element software. This software was used to predict the springback in a typical sheet metal bending process and to investigate the influence of these parameters on springback. The results of simulation are validated with own experiments and published experimental results.

The perceived wisdom about thin sheet fracture is that (i) the crack propagates under mixed mode I & III giving rise to a slant through-thickness fracture proÿle and (ii) the fracture toughness remains constant at low thickness and eventually decreases with increasing thickness. In the present study, fracture tests performed on thin DENT plates of various thicknesses made of stainless steel, mild steel, 6082-O and NS4 aluminium alloys, brass, bronze, lead, and zinc systematically exhibit (i) mode I "bath-tub", i.e. "cup & cup", fracture proÿles with limited shear lips and signiÿcant localized necking (more than 50% thickness reduction), (ii) a fracture toughness that linearly increases with increasing thickness (in the range of 0.5 -5 mm). The di erent contributions to the work expended during fracture of these materials are separated based on dimensional considerations. The paper emphasises the two parts of the work spent in the fracture process zone: the necking work and the "fracture" work. Experiments show that, as expected, the work of necking per unit area linearly increases with thickness. For a typical thickness of 1 mm, both fracture and necking contributions have the same order of magnitude in most of the metals investigated.

The paper starts with a brief historical overview to the attempts of numerical simulation of sheet metal forming. Comparison between bulk and sheet metal forming processes from the simulation point of view is given. Basic requirements of the applier to the simulation tools are summarized. Various possible methodologies are brie¯y discussed. Special emphasis is given to the static explicit and dynamic implicit ®nite element procedures. Also different element types are overviewed. Available important commercial ®nite element packages are given. The current state of the application of the simulation tools is discussed. Some typical industrial applications are reviewed to demonstrate the current abilities of analysis. Finally, an attempt to prognosticate some future developments is made. #

Formability of sheet metal is usually assessed by the useful concept of forming limit diagrams (FLD) and forming limit curves (FLC) represent a first safety criterion for deep drawing operations. The level of FLC is strongly strain path dependent as observed by experimental and numerical results and therefore nonproportional strain paths need to be incorporated when analyzing formability of sheet metal components. Simulations using finite element method allow accurate predictions of stress and strain distributions in complex stamped parts. However, the prediction of localized necking is a difficult task and the combination of forming limit diagram analysis with finite element simulations often fail to give the right answer, if complex strain paths are not included in these predictions.

The importance of hydromechanical deep drawing is due to certain advantages over conventional deep drawing such as better formability, reduced number of manufacturing steps, improved surface finish, etc. Due to this, the potential applications of hydromechanical deep drawing have increased in the recent years. In this process, sheet metal parts are formed with the assistance of fluid pressure. The present work addresses the effect of sheet thickness and punch roughness on the formability of interstitial-free steel sheets in hydromechanical deep drawing. Experimental work has been done to study the influence of counter pressure on drawability by varying the sheet thickness and punch roughness. Finite element method has been used to simulate the process, and the results have been found to be in good agreement with the experimental results. It has been found out that the minimum required counter pressure for successful drawing increases with increase in sheet thickness. Drawability of 1.2 mm thick sheet improved with increase in punch roughness. As the punch roughness increases, the minimum required counter pressure decreases because of improved friction holding effect. For the same punch roughness, the minimum required counter pressure increases with increase in draw ratio.

Sheet metal forming Springback Bauschinger effect Finite element method Kinematic hardening a b s t r a c t An accurate modeling of the sheet metal deformations including the springback is one of the key factors in the efficient utilization of FE process simulation in the industrial setting. In this paper, a rate-independent anisotropic plasticity model accounting the Bauschinger effect is presented and applied in the FE forming and springback analyses. The proposed model uses the Hill's quadratic yield function in the description of the anisotropic yield loci of planar and transversely anisotropic sheets. The material strain-hardening behavior is simulated by an additive backstress form of the nonlinear kinematic hardening rule and the model parameters are computed explicitly based on the stress-strain curve in the sheet rolling direction. The proposed model is employed in the FE analysis of Numisheet'93 U-channel benchmark, and a performance comparison in terms of the predicted springback indicated an enhanced correlation with the average of measurements. In addition, the stamping analyses of an automotive part are conducted, and comparisons of the FE results using both the isotropic hardening plasticity model and the proposed model are presented in terms of the calculated strain, thickness, residual stress and bending moment

Paper, sheet metal, and many other materials are approximately unstretchable. The surfaces obtained by bending these materials can be flattened onto a plane without stretching or tearing. More precisely, there exists a transformation that maps the surface onto the plane, after which the length of any curve drawn on the surface remains the same. Such surfaces, when sufficiently regular, are well known to mathematicians as developable surfaces. While developable surfaces have been widely used in engineering, design and manufacture, they have been less popular in computer graphics, despite the fact that their isometric properties make them ideal primitives for texture mapping, some kinds of surface modelling, and computer animation. Unfortunately, their constrained isometric behaviour cuts across common surface formulations. We formulate a new developable surface representation technique suitable for use in interactive computer graphics. The feasibility of our model is demonstrated by applying it to the modelling of a hanging scarf and ribbons and bows. Possible extensions and interesting areas of further research are discussed.

This paper presents a new yield criterion for orthotropic sheet metals and its implementation in a theoretical model of the forming limit diagrams. The equivalent stress equation shows that the shape of the yield surface is defined by eight material parameters. The minimisation of an error-function has been used for the numerical identification of these coefficients. The parameters are established in such a way that the constitutive equation associated to the yield surface reproduces the plastic behaviour of the actual material. The uniaxial yield stresses (σ 0 ,  σ 45 , σ 90 ), biaxial yield stress (σ b ), uniaxial anisotropy coefficients (r 0 , r 45 , r 90 ) have been used in identification. The new yield criterion has been implemented in the Marciniak-Kuczynski theory in order to predict the limit strains. The theoretical forming limit curves have been compared with the experimental ones. The friction free tests, the hydraulic bulge test (for the positive minor strains) and the tensile test for plane strain and for uniaxial tensile test (for the negative minor strains) are used. The predicted yield surface and forming limit diagrams for AA5182-0 aluminium alloy sheets are in good agreement with the experimental ones.

Surface distortions in the form of wrinkles are often observed in sheet metals during stamping and other forming operations. Because of the trend in recent years towards thinner, higher-strength sheet metals, wrinkling is increasingly becoming a more common and troublesome mode of failure in sheet metal forming. The prediction and prevention of wrinkling during a sheet forming process are important issues for the design of part geometry and processing parameters. This paper treats the phenomenon of flange wrinkling as a bifurcated solution of the equations governing the deep drawing problem when the flat position of the flange becomes unstable. Hill's bifurcation criterion is used to predict the onset of flange wrinkling in circular and square cup drawing. In particular, the maximum cup height that can be drawn without the onset of flange wrinkling is predicted for the given set of process parameters. A parametric study of the maximum cup height is also carried out with respect to various geometric, material and process parameters. Finite element formulation, based on the updated Lagrangian approach, is employed for the analysis. The incremental logarithmic strain measure, which allows the use of a large incremental deformation, is used. The stresses are updated in a material frame. The material is assumed to be elastic-plastic, strain hardening, yielding according to an anisotropic yield criterion of [23] (named as Yld2004-18p). Isotropic power law hardening is assumed. Inertia forces are neglected due to small accelerations. Modified Newton-Raphson iterative technique is used to solve the nonlinear incremental equations.

At the present time a number of experimental methods are widely used for both qualitative and quantitative estimation of the sheet metal behaviour under processing by forming. There exist some special features of sheet metal deformation and, therefore, it is not possible yet to apply one and only testing procedure for all types of forming operations. The paper gives a brief description of the bulge testing of planar isotropic sheet metals and also presents some preliminary results about the applicability of this method for work hardening curves evaluation using data for specimen areas out of pole and for strength estimation under hydrostatic or hydrodynamic loading.

We explore the following problem: given a collection of creases on a piece of paper, each assigned a folding direction of mountain or valley, is there a flat folding by a sequence of simple folds? There are several models of simple folds; the simplest one-layer simple fold rotates a portion of paper about a crease in the paper by ±180 • . We first consider the analogous questions in one dimension lower-bending a segment into a flat object-which lead to interesting problems on strings. We develop efficient algorithms for the recognition of simply foldable 1D crease patterns, and reconstruction of a sequence of simple folds. Indeed, we prove that a 1D crease pattern is flat-foldable by any means precisely if it is by a sequence of one-layer simple folds.

In this paper, approaches to apply DFM(A) (Design for Manufacturing and Assembly) in practice are reviewed based on both the research results of the areas of MW mechanics and sheet metal work achieved at Lappeenranta University of Technology. These results are supported by a literature review. In this paper, we present five view-points on how to apply DFM(A) in practise in the previously mentioned research areas. The view-points are as follows: applied DFM(A) rules for sheet metal work, utilization of lists and forms to analyze MW constructions, development of traditional design methodologies, development of manufacturing technologies for easy production, integrated DFM(A) approaches which aim to control and manage both the product design process and its costs.

The ferromagnetic sheet metal blanking is widely used for the manufacturing of rotating electrical machines. However, the optimization of the designed machines depends on full understanding of the shearing process. The material mechanical state and magnetic properties near the cut edge depend on various parameters like geometric configuration (shape of the tools, punch blade radius), clearance, frictional contact at the interfaces and the punch speed. Several studies of the blanking process have been proposed to assess the influence of these parameters, but only a few are concerned with the punch velocity. In this paper we use a rate dependent constitutive model for the blanking process investigation to improve the accuracy of the predictions. A 0.65 mm thickness sheet of a non-oriented full-process FeSi (3 wt.%) steel is used. The material testing and the characterization are carried out in order to fit the constitutive model parameters to the experimental data. Classical tensile tests and video-tensile tests are combined to establish the sheet metal constitutive law. The identified model is, then, used for numerical simulations (which are performed using ABAQUS/Explicit software) of various blanking tests: the clearance is ranging from 3.8% to 23%, punch velocity of 23 mm/s and 123 mm/s. In order to validate this work the numerical results obtained are compared to the measurement. The comparisons relate to the punch force and the punch penetration at fracture that are affected by the clearance and the strain rate.

The advances achieved in phenomenological constitutive laws and their implementation in finite element codes for predicting material behavior during forming processes have motivated the research on material identification parameters in order to ensure prediction accuracy. New models require experimental points describing a bi-axial stress state for proper calibration, and the features of the plane strain tensile test have made it one of the most used. The test's principal inconvenience is the influence of the free edges on strain field homogeneity and stress computation.

The conventional welding method for joining dissimilar steels is the manual tungsten inert gas (TIG) method. Nevertheless, recently the benefits of solid-state welding have been attracted the attention of industrial manufacturers. In this article, TIG and friction stir welding method are compared based on the formability and mechanical properties of the welded sheets. Experimental evaluation of mechanical properties and forming limit curves have been carried out using uniaxial tensile test and Nakazima test, respectively. Results of experimental tests illustrated that formability of friction stir welded sheets was about 38% higher than the TIG-welded sheets. The microstructure analysis of TIG welded blanks revealed that grain growth in the heat-affected zone on the St37 steel, reduced the formability of welded joints in this method. Finite element simulation was used to estimate the forming limit diagram of the joints without considering the effects of welding heat on the material properties. The difference between the results of the FSW and finite element simulations was about 6%. While in the TIG welded blanks formability reduces significantly and the difference between the result of the experiment and simulation is about 33%. These results show that friction stir welding could more effectively preserve the sheets' formability after welding.