Sheet Metal 2007

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Authors: Taylan Altan, Serhat Kaya, Yingyot Aue-u-Ian
Abstract: Experimental investigation on the formability limits of aluminum and magnesium alloys are conducted through hydraulic bulging and deep drawing. New tube hydroforming tooling was designed and the submerged tool concept is introduced. Tube hydroforming experiments were conducted with and without axial feed by using AA6061 tubes. The formability of Mg AZ31-O sheets are determined by hydraulic bulging using similar submerged tool. Finally the effect of temperature and initial blank size on the attainable highest punch velocity is investigated and round cups from Mg AZ31-O were successfully formed in a heated tool with punch speeds up to 300 mm/s.
Authors: S. Guarino, Nadia Ucciardello, Vincenzo Tagliaferri
Abstract: In this paper a neural network approach is used to model the diode laser assisted forming process. In particular thin sheets of Aluminum alloy AA 6082 were bended in the elastic range and then treated with a diode laser with the aim to reduce the spring back phenomenon. Experimental tests were performed to study the influence of the process parameters such as laser power, laser speed and starting elastic deformation on the evolution of forming process. In particular the heating effects on the elastic properties of the material was studied. A statistical approach is used to define the experimental plan and discuss the experimental results. Interesting trend of the effects of the diode laser on the forming process were found. Subsequently in order to predict the residual inflexion, during the laser forming, a multilayer feedforward artificial neural network has been implemented. A sensitivity analysis on the artificial neural network model is used to show the significance of all the input data employed. As a result of sensitivity analysis, a check between experimental and calculated trends for each investigated variables was performed, which revealed an appreciable fit between data displayed.
Authors: W.T. Zheng, Donato Sorgente, G. Palumbo, Luigi Tricarico, Li Mei Ren, L.X. Zhou, Shi Hong Zhang
Abstract: Using the optimum blank in sheet metal forming process not only can decrease the material wasting but also avoid possible defects such as local severe thinning, wrinkling and fracture. Since it is practical technology for industrial production, many blank optimization methods have been proposed and their validity was verified by some forming tests of typical or complicated components. However, all the forming tests were carried out at room temperature or under isothermal condition. In present work, a blank optimization method was employed to evaluate its efficiency in deep drawing of rectangular magnesium alloy cups under non-isothermal condition. It is proved by experiment that the employed blank optimization method can predict successfully the optimum initial blank shape for the component with specified shape and dimension.
Authors: Mehmet Ali Pişkin, Bilgin Kaftanoğlu
Abstract: Deep-drawing operations are performed widely in industrial applications. It is very important for efficiency to achieve parts with no defects. In this work, a finite element method is developed to simulate deep-drawing operation including wrinkling. A four nodded five degree of freedom shell element is formulated. Isotropic elasto-plastic material model with Von Mises yield criterion is used. By using this shell element, the developed code can predict the bending behavior of workpiece besides membrane behavior. Simulations are carried out with four different element sizes. The thickness strain and nodal displacement values obtained are compared with results of a commercial finite element program and results of previously conducted experiments.
Authors: Piotr Lacki
Abstract: Demand for an increase in the useable properties of a drawn-part made of stainless steel has been the inspiration for the work. The use of 4H13 steel instead of 3H13 has resulted in the higher strength of the drawn-part but also a decrease in drawability. Therefore, some modifications to the original design of the sheet-metal forming process were necessary. A numerical simulation was applied to optimise of the stamping process. The ADINA System based on the finite element method (MES) was used. Frictional conditions on the contact surfaces, blank diameter and the course of the blank holding force versus time were analysed. In this paper, the test results of the mechanical properties of the analysed sheets (3H13 and 4H13 stainless steel) are given, some differences in the way of stamping drawn-parts made of these materials are discussed and the results of the numerical simulation are presented. A 3D model and perfectly rigid tool were assumed in the numerical model. The sheet was modelled using shell elements. The elastic and plastic properties of the sheet material were assumed and the frictional conditions on the contact surfaces were taken into consideration during the numerical simulation. Based on the numerical simulation the stamping process was optimised. A comparison between the numerical calculation and test results shows good convergence. Thanks to the MES analysis and the application of the new technological parameters, the desired drawn-part with the better useable properties was obtained.
Authors: Elisabetta Ceretti, Aldo Attanasio, Antonio Fiorentino, Claudio Giardini
Abstract: The present paper is the continuation of a research conducted on hemming operations by using rolling tools. Sheet hemming is a joining operation widely used in automotive industry when it is necessary to join two sheet parts (such as the engine hood or the door panels with their internal frame) by plastic deformation of the edge of the outer part. The whole process is characterised by a 90° sheet flanging, a pre-hemming (up to approximately 135°) and the final hemming where the outer sheet edge is bended up to 180° clamping the inner sheet. Hemming processes are normally performed using rigid dies in series production and manually in pre-series and small batch production, due to the high cost of the dies. Nowadays, rollers moved by robots are becoming an interesting alternative to the manual operations especially when flexible productions are required. Even if the process time is higher, this solution can help in minimizing set-up times and costs. The required equipments are a support and a blocking system for the sheets together with the rollers mounted on a CNC machine or on a robot. The production flexibility is guaranteed by changing the 3D tool path using a CAD/CAM system. Authors are dealing with this technique having conducted many experiments studying the influence of the hemming process parameters such as flange geometry (edge height, fillet radius), distance of the inner panel from the flange, tool path sequence, along straight paths on steel sheets. The goal of the present research is to study the material behaviour and the produced parts quality when working on aluminium sheets. In particular, both experimental tests and simulations will be carried out in order to optimize the process.
Authors: P. Jimbert, I. Perez, I. Eguia, Glenn S. Daehn
Abstract: Hemming is the last or one of the latest stage operations for the stamped parts. For this reason it has a critical importance on the performance and perceived quality of assembled vehicles. It is used to attach two sheet metal parts together or to improve appearance creating a smooth edge rather than a razor edge with burrs. However, designing the hemmed union is not always easy and is deeply influenced by the mechanical properties of the material of the bended part. Main problems for the automotive industry arise when bending aluminum alloys. Aluminum sheet is more difficult to hem due to its susceptibility to strain localization during the hemming process. This phenomenon produces cracking on the hemmed edge [1]. In order to avoid this problem and due to the limitations of conventional flanging and hemming technologies, the flange radii must be increased and a rope hem used (instead of the flat hem used with steels) when working with aluminum alloys. These changes on the design of the hem union give as a result a lower quality final product [2]. Dies and tools used for the hemming process are designed based on experience and on lengthy and costly die tryouts. Continuing with the development of new applications for the Electromagnetic Forming (EMF) technology, LABEIN-Tecnalia and Professor Glenn Daehn’s group from The Ohio State University carried out some first straight flat hemming experiments using the AA 6016 T4 aluminum alloy. The results obtained from these first trials are presented in this paper giving a first sight of the possibilities, advantages and disadvantages of using the Electromagnetic Forming technology for the hemming of aluminum sheet panels. Using a non-clouped FEM simulation method, the experimental results are compared to the ones obtained with the simulations. The future working line in developing this new application for the Electromagnetic Forming technology will be based on the results obtained by this study.
Authors: A.A. Zadpoor, J. Sinke, R. Benedictus
Abstract: Taking advantage of high-tech welding methods, a concept is formed in sheet metal forming community. The so-called tailor-welded blanks (TWBs) are sheet metals that are welded together prior to forming. This technology dates back to the 80’s, and numerous studies are conducted in order to explore different aspects of it. This review paper concerns with mechanics of TWBs. The paper is divided into three major chapters. The first chapter is devoted to mechanical properties of TWBs. Tensile testing, tensile properties, and hardness of TWBs are covered in this chapter. The second chapter deals with the formability of TWBs. The formability testing methods, effect of different parameters on the formability of TWBs, material flow phenomena, control of material flow, stress and strain distributions, and springback behavior are covered in the second chapter. The third chapter is focused on failure and fracture of TWBs. Failure modes and failure criteria are the principal topics of this chapter.
Authors: Marion Merklein, Uwe Vogt
Abstract: Tailored Heat Treated Blanks (THTB) are blanks that exhibit locally different strength specifically optimized for the succeeding forming process. The strength distribution is set by a local, short-term heat treatment modifying the mechanical properties of the material. Hence, THTB allow enhancing forming limits significantly leading to shorter and more robust manufacture process chains. In order to qualify the use of THTB under quasi series conditions, the interdependencies of the blank’s local heat treatment and the entire process chain of the car body manufacture have to be analyzed. In this respect, the impact of a short-term heat treatment on the mechanical properties of AA6181PX, a commonly used aluminum alloy in today’s car bodies, was studied. Also the influence of a short-term heat treatment on the coil lubricant, usually already applied by the material supplier, was given a closer look. Based on these experiments process restrictions for the application of THTB in an industrial automotive environment were derived and a process window for the THTB design was set up. In conclusion, strategies were defined how to enhance the found process boundaries leading to a more robust process window.
Authors: Robert McMurray, Alan G. Leacock, Desmond Brown
Abstract: A test rig was developed to investigate springback in stretch draw forming processes, which are considered to be nominally uniaxial. An interchangeable tool allows the examination of both single and double curvature surfaces. Two double curvature tools with the following radii were used in the experiments, (A) 200mm by 450mm and (B) 450mm by 200mm. The first radius in each case corresponds to the direction of stretch. Obviously the smaller radius results in a larger moment, which creates a negative springback in the orthogonal direction. This effect is more pronounced in tool (A) due to the higher tensile strain levels in the direction of stretch directly affecting the strains in the orthogonal direction. By considering the resultant moment in each axis of the sheet independently, an analytical method was devised to give an approximation of the springback profile. Overall the analytical data correlates well with both experimental and Finite Element (FE) results.

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