Sheet Metal 2009

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Authors: Marion Merklein, Markus Kaupper
Abstract: Nowadays advanced high strength steel sheets and related forming technologies play an important role in lightweight construction in the transportation sector. Since especially car seat components are subject to very strict safety demands, the application of these modern steel grades, which provide enhanced strength levels, seems to be a promising strategy to meet the challenge of reducing the sheet metal thickness while maintaining the crash energy absorption capacity. Concerning the high required level of part complexity and accuracy both the reduced formability and the increased springback tendency of advanced high strength steels are challenges for forming technologies compared to conventional steel grades. Against this background the forming potentials of advanced high strength steels are investigated and are made accessible for an application in structural car seat components. The analysis is to be done both experimentally and numerically, focusing on the finite element method (FEM) regarding a reliable process design.
Authors: Antonio Fiorentino, Elisabetta Ceretti, Aldo Attanasio, Dario Braga, Claudio Giardini
Abstract: THF process is a forming technique that consists of tube deformation by means of hydraulic pressure and punches which guarantee the tube ends feeding and sealing. In the last years, this technique found a large and rapid diffusion thanks to its many advantages with respect to conventional processes: parts weight reduction, tighter dimensional tolerances, lower costs or fewer secondary assembly operations. Besides, many lacks in the process knowledge still represent an obstacle and they are usually bypassed by trial and error methods. Therefore, lot of studies were conducted to better understand the influence of the process parameters, such as pressure path, punch stroke or material behaviour. In this paper, an experimental study of tubular T-joints made of copper manufactured by means of THF process is described. The aim of this work is to analyze the tube-die interface friction condition effects on the final part. In fact, material flow during the process is greatly influenced by the friction conditions between tube and die especially due to the high pressure acting inside the tube. Different lubrication types were considered: dry, oil, Teflon, Teflon with oil, Teflon spray and Graphitic oil. Two different experimental campaigns were performed in this investigation. The first one was carried out in order to estimate the lubricant friction coefficients using a Pin on Disk tribometer. The second one was performed to study the effects of the lubrication on the process and the tests were conducted hydroforming T-joints under the different lubrication conditions considered. The collected data allowed to identify how the different lubrication conditions affect the final workpiece geometry. Moreover, a critical aspect of the process related to the tube wrinkling was identified and a solution was proposed.
Authors: Antonio del Prete, Teresa Primo, Gabriele Papadia, Barbara Manisi
Abstract: Sheet hydroforming has gained increasing interest in the automotive and aerospace industries because of its many advantages such as higher forming potentiality, good quality of the formed parts which may have complex geometry. The main advantage is that the uniform pressure can be transferred to any part of the formed blank at the same time [1]. In this paper, a “shape factors” set has been defined with the proper goal to understand if it can be used to help engineers to define “process rules” for the studied non conventional technology [2]. A specific prediction model, obtained thanks to a numerical factorial fractional plane, has been used in order to preview the process responses vs each defined shape factor. These shape factors have been used to track the process performances through their variation thanks to the usage of the numerical simulation that has been validated with an appropriate experimental campaign executed thanks to the usage of a specific equipment properly designed.
Authors: W. Homberg, A. Erman Tekkaya, Charlotte Beerwald, Alexander Brosius, J. Dau, Michael Trompeter
Abstract: In this paper, the use of partially or tailored cladded blanks is proposed for the production of multifunctional lightweight components. Therefore, the non-joined sheet areas will be formed to hollow structures by hydroforming subsequent to the partial cladding operation. The paper presents results of research work on the production processes and potential applications of partially cladded blanks in the field of thermal engineering and automotive engineering. Furthermore, it is focused on possible developments regarding the use of multiple materials and process combinations for sophisticated applications e.g. in the field of lightweight constructions.
Authors: Antonio del Prete, Gabriele Papadia, Alfredo Anglani
Abstract: The increasing application of numerical simulation in metal forming field has helped engineers to solve problems one after another to manufacture a qualified formed product reducing the time required. Accurate simulation results are fundamental for the tooling and the product designs. Many factors can influence the final simulation result like for example a suitable yield criterion [1]. The wide application of numerical simulation is encouraging the development of highly accurate simulation procedures to meet industrial requirements. Currently, industrial goals of the forming simulation can be summarized in three main groups [2]: time reduction, costs reduction, increase of product quality. Many studies have been carried out about: materials, yield criteria [3, 4, 5] and plastic deformation [6, 7, 8], process parameters [9, 10, 11] and their optimization, geometry modification of the stamped part to evaluate if process responses modifications are required, reaching the goal to perform a virtual tryout of the whole deformation process [12]. In this paper proper metal forming numerical model and experimental analysis have been developed in order to foresee process responses in the case of sheet hydroforming technology. The interactions among the process performances and its variables are the most interesting aspects of the research because their knowledge means the possibility to drive the process feasibility which can be represented by the absence of ruptures and/or wrinkles in the stamped component. This paper analyzes the sheet thickness variation during the hydroforming process, according to a specifically defined “shape ratio”, useful to characterize product’s geometry. The latter is an hydroformed product characterized by a rectangular characteristic section with a drawing depth of 150mm, obtained by a hydroforming operation on a blank having a hexagonal shape. The physical and numerical experimentations were carried out on multiple geometries, different each others in punch radius and die radius, and on multiple materials, steel FeP04 (with a thickness of 1mm and 0,7mm) and Aluminum Al6061 (with a thickness of 0,7mm). The numerical simulation, validated by the experimental investigations [13,14], allowed to define a relationship, specific for sheet metal hydroforming, between the defined shape ratio and the key performance indicator, that is the percentage reduction thickness measured on specific areas of the formed part. The development of numerical models with an high level accuracy could give the real possibility to evaluate process feasibility with different combinations of geometrical and materials parameters without, at the first glance, simulation but only analyzing the specific curves (y = percentage reduction thickness, x = shape ratio).
Authors: Michael Trompeter, Boris Rauscher, Hossein Karbasian, A. Erman Tekkaya, W. Homberg
Abstract: This paper presents a sectionwise hydroforming technique for manufacturing of large-area multi-cell sheet metal structures in terms of hump plates. The sectionwise hydroforming technique allows production of hump sheets with variable width and length. The hump plates are based on hexagonal hump geometry. The hump height is optimized for the application as a partition wall in light utility vehicles. Manufactured hump sheets feature a high contour accuracy which allows joining of two hump sheets to a large-area hump plate (up to 1,800 x 2,000 mm). The hump plates have been successfully tested in a load test which proves their potential for light utility vehicles.

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