Sheet Metal 2007

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Authors: Antonio del Prete, Teresa Primo, Antonio A. De Vitis
Abstract: An uncertain approach has been evaluated to analyze the finite element analysis responses for the springback evaluation on a stamped part. In the Metal Forming and Springback simulations a deterministic approach does not take in account uncertain physical variations related to material characteristics, friction conditions, tools active surfaces status, etc. Then, if one of the purposes of the process design it is its reliability, a CAE study in aleatory conditions is the only way to evaluate the process robustness. A study case has been defined and the explicit simulation was performed for the forming stage while, the implicit simulation was performed for the springback phase. Subsequently, a stochastic problem was solved to found the aleatory influence of process parameters such as: anisotropy coefficient, Young modulus and friction between blank and tools to evaluate their effect on the component springback. The evaluation of finite element models in uncertain conditions can be considered like a CAE usage in order to obtain a “Robust Design” for the examinated problem.
Authors: Isamu Aoki, Sasada Masahiro, Tadao Fuchiwaki
Abstract: Medical examinations and treatments using endoscopes are becoming increasing common due to their minimally invasive nature. Many types of medical devices for endoscopic therapy are available, and of these, forceps are most frequently used. Forceps prices are on the whole high, and one of the reasons for this can be attributed to the manufacturing method. Currently forceps parts are made by cutting or metal removal process. By replacing these methods with die forming, stable supply at low costs should be possible. This paper describes a study proposing and developing a forceps manufacturing method by die forming, and describes the successful results. It also reports the evaluation carried out on functions of the prototyped forceps and the proposed method of changing the shape of products for which die forming is not suitable.
Authors: Branimir Barisic, Miljenko Dino Math, Branko Grizelj
Abstract: In order to determine the forming force in deep drawing and backward extrusion processes (on Al 99.5F7 specimens) the analytical, numerical and stochastic modeling and analysis of forming force on the basis of the Box-Wilson’s multi factorial experimental designs by use of rotatable experimental design were carried out. The goal of the paper is to predict the force in these different forming processes giving identical parts by means of different modeling approaches. This study will seek to compare the results of these modeling solutions with experimental results serving to check the correction and the verification of analytic, stochastic and numerically obtained results. Also, the scope of the present paper is to evaluate different parameters affecting these processes and to examine some experimental procedures in laboratory scale for the listed material in order to give more useful information in numerical and stochastic computations and also, to define the correlation among the parameters of these processes in order to improve the existing one and to raise it to a higher techno economic level. The increasing tendency for industrial parts cost reduction, quality improvement, materials savings, and the shortening of design and manufacturing time is more focused on this way of analysis of processes. These investigations are a basis for general conclusions about the forming force and they have a direct application in the projecting of these processes, tools and forming systems.
Authors: Y. Abe, J. Watanabe, Kenichiro Mori
Abstract: A multi-stage stamping process of one-piece automobile steel wheels from tubes was developed to decrease the loss of material for the blanking. In this process, the tube is nosed into a cup with a central hole, and then the taper bottom and side wall of the cup are formed into disk and rim portions of the wheel, respectively. The tube is produced by bending a rectangular sheet into a tube and by welding both edges of the bent sheet to prevent the loss of material for the blanking. The stamping sequence of the one-piece wheels was designed by finite element simulation. The central hole of the cup was decreased to a desired diameter of the hub hole without buckling and wrinkling by a 5-stages nosing operation. The taper bottom of the cup was reversely drawn, and then was flared without folding by 2 stages. The wall thickness of the formed wheel was thick and thin in the disk and rim portions, receptively, and thus the requirement of strength of wheels is satisfied. A one-piece wheel having a hub hole was successfully formed by the designed sequence in a miniature experiment.
Authors: Verena Psyk, C. Beerwald, A. Henselek, Werner Homberg, Alexander Brosius, Matthias Kleiner
Abstract: In recent years a steadily growing interest in applying lightweight construction concepts could be observed. This development is accompanied by an increasing demand for innovative forming strategies suitable for extending the forming limits of the typical lightweight materials. Deep drawing combined with an integrated electromagnetic calibration step is an example of such a technology. The feasibility and potential of this process combination is analyzed on the basis of a demonstrator part from the automotive industry. Thereby, aspects related to the practicability of the electromagnetic forming process itself are regarded as well as points related to the deep drawn preform. The concept of a 3D-coil insert, integrated into a deep drawing punch in order to realize the calibration in the deep drawing process, is introduced and based on the experimental results, conclusions regarding the applicability of the process combination are drawn.
Authors: Jean Savoie, Melinda Bissinger
Abstract: Aircraft engine components are assemblies of several parts that are manufactured using various processes: deep drawing and machining, among others. Deep drawing cannot control accurately wall thicknesses and is performed in numerous steps. Machining parts from solids is less and less cost effective as prices for raw materials increase. Hence, the use of near net shape manufacturing methods is becoming more appealing. An alternative forming process is here investigated: flowforming, process well adapted to axisymmetric parts. The amount of forming steps, welding and machining could be significantly reduced, reducing lead-times and manufacturing costs. Examples are presented for the forming of selected parts (gas generator cases, fan cases and diverter ducts), together with their metallurgical and mechanical properties. Flowforming, however, can only generate shells with some hollow details: most flanges, bosses, stiffeners or weld lips cannot be obtained. Hence, methods of adding material are explored.
Authors: Antonio del Prete, Gabriele Papadia, Barbara Manisi
Abstract: In order to value the process of variables influence in sheet metal hydroforming, a special hydroforming cell has been developed. Generally, sheet hydroforming is obtained using appropriate press tooling. This option requires large investments completely dedicated to this technology of production. As an alternative, conventional hydraulic presses can be used for sheet hydroforming in combination with special hydraulic tooling named “hydroforming cells”. A special “hydroforming cell” concept has been developed to perform experimental analysis for different shapes using the same tooling set up. CAE tools had a strategic role just to develop the best layout and to find the optimum solutions for the process variables. FEA has been used to define the distribution of the blank holder variable forces: a solution which implies the use of twelve independent actuators have been implemented. The position and the load path of each one of them has been chosen for each formed shape, in accordance with the FEA results. Customized actuators have been used to solve interferences between mechanical parts of the hydroforming cell. For this specific aspects the virtual 3D design was necessary for the appropriate decisions. The developed process system is very effective so that is possible to set up experimental campaigns for sheet hydroformed components.
Authors: M. Loh-Mousavi, Kenichiro Mori, K. Hayashi, M. Bakhshi
Abstract: The filling of the die corner in hydroforming of a tube with a box die was improved by controlling wrinkling under oscillation of internal pressure. In this process, a small wrinkle occurs near the die corner in the former stage, and then the wrinkle is eliminated in the latter stage because the flat bulge appears in the former stage due to the oscillation of internal pressure. A hydroforming process of steel tubes with a box die was performed in both three dimensional finite element simulation and experiment. The filling of the die corner for the mean linear pressure was not sufficient due to large wrinkles appearing in the former stage, whereas bursting occurs for the peak linear pressure due to round bulging. On the other hand, the uniformity of wall thickness of the formed tube was improved by the pulsating pressure.
Authors: H. Ali Hatipoğlu, Naki Polat, Arif Koksal, A. Erman Tekkaya
Abstract: In this paper, the flexforming process is modeled by finite element method in order to investigate the operation window of the problem. Various models are established using explicit approach for the forming operation and implicit approach for the unloading one. In all analyses the rubber diaphragm has been modeled revealing that the modeling of this diaphragm is essential. Using the material Aluminum 2024 T3 alclad sheet alloy, three basic experiments are conducted: Bending of a straight flange specimen, bending of a contoured flange specimen and bulging of a circular specimen. By these experiments the effects of blank thickness, die bend radius, flange length and orientation of the rolling direction of the part have been investigated. Experimental results are compared with finite element results to verify the computational models.
Authors: Manfred Geiger, Marion Merklein, Massimo Cojutti
Abstract: The possibility to produce lightweight components with a complex geometry enhanced, in the last decades, the industrial application of the tube hydroforming and, more recently and restricted to specific industrial fields, of the sheet hydroforming technology. The integration in one tool of a tube and a double sheet hydroforming process represents an innovative technology which further emphasises the advantages offered by hydroforming in terms of costs reduction and complexity of the manufactured part. This paper describes the design and the construction of a complex hollow part resulting from the simultaneous hydroforming of two sheets and a tubular component in one tool. The focus is set in particular on the optimisation of the joining zone between tube and sheet pair, whose geometry allows a “metallic” sealing of the gap between the sheets and the tube, i.e. without using sealing components. The contact between tube and sheet pair allows the transmission of the axial force used to support the bulging of the tube to the sheet blanks, thus increasing their draw-in in the die and, consequently, avoiding the occurrence of tearing on the part. The paper describes the optimisation of different process parameters like the shape and the dimension of the blanks, their initial positioning in the tool, the value of the axial force applied to the tubular component and the blankholder force during the preforming and the calibrating stages.

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