Sheet Metal 2011

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Authors: Frank Vollertsen
Abstract: Size effects are effects which might occur, if the dimensions of a forming process are scaled up or down. They might enable or disable the application of a process in the micro range. Based on the systematic order of size effects, which defines density, shape and structure effects, one example for each group is given. A density effect, which occurs in Tiffany structures, explains the changes in forming behavior of foils with respect to the forming limit diagram. The feasibility of a new heading process only in the micro range is due to a shape effect, driven by the surface energy. The changes in the tribology in deep drawing by a structure effect, known as closed an open lubricant pocket model, can be explained only if one takes the temperature dependence of the viscosity of the lubricant into account.
Authors: Wim Serruys
Abstract: Three different and complementary ways of adaptive control are presented, each working on a different time scale. All three of them are made possible due to evolutions and developments in CNC controls. The first and most popular way of adaptive control is adaptive process control. Since the process variables in sheet metal equipment change significantly in milliseconds, the control loop must also perform on a sub second time scale. The second adaptive loop is adaptive production control. Modern CNC controls know what they are manufacturing and talk with higher production software. Instead of just executing a planning that came top down, the CNC has enough knowledge of its environment that it can propose an intelligent job sequence and hence react more effectively on unforeseen situations. These adaptive loops perform on a time scale of hours and days. The third adaptive loop is adaptive resource control. To produce sheet metal parts, we need several kinds of resources: human resources, material, consumables, energy and equipment. CNC sheet metal equipment is a considerable investment. However most production managers do not know how effective their resources are being used. By applying the principles of overall equipment effectiveness, we can close the resource control loop. This loop performs on a time scale of weeks and months.
Authors: Joost R. Duflou, Karel Kellens, Renaldi, Wim Dewulf
Authors: Kenichiro Mori
Abstract: Mechanical AC servo presses having high flexibility for control of motion have been recently developed. In these presses driven by servo motors, the slide motion is accurately controlled by real-time feedback of ram position measured with sensors like the conventional machine tools, and thus complicated motion is attainable. The application of servo presses to sheet metal forming processes is reviewed in the present paper. The springback in bending was reduced by bottoming and re-striking. In deep drawing, the forming limit of high strength steel sheets was improved by detaching tools from the sheet, and the wrinkling was prevented by applying a stepwise motion. A hot stamping process using rapid resistance heating and a servo press was developed to produce ultra-high strength steel parts.
Authors: Matthias Hermes, Daniel Staupendahl, Christoph Becker, A. Erman Tekkaya
Abstract: The paper deals with two new processes and developed special machines for profile and tube bending. The first process is a new roll-based machine for three-dimensional bending of profiles with symmetrical and asymmetrical cross-sections that has been developed. Compared to conventional processes like stretch bending, the advantage of Torque Superposed Spatial (TSS) Bending is the kinematic adjustment of the bending contour, leading to higher flexibility and cost efficiency especially in small batch production. The second process is the new process of Incremental Tube Forming (ITF). This process is based on a combination of a spinning process and kinematic free form bending of tubular semi-finished products. It is suitable for bending tubes two- and three-dimensionally to arbitrary contours and for manufacturing tailored tubes. The combined spinning and bending process leads to low bending forces with the possibility of a significant springback reduction.
Authors: Philip Beiter, Peter Groche
Abstract: Due to continuously increasing demands on safety, comfort and ecological performance, different lightweight construction concepts have been searched for and applied by the automotive industry lately. This paper focuses on the development of novel light weight profiles by roll forming of tailor rolled blanks (TRBs). It covers analytics, experiments and FE analysis. At the beginning, state of the art tools were used for a fundamental process layout. The results show, that their application with respect to the varying sheet thicknesses within the blanks is generally acceptable. However, it may be concluded that TRBs as semi-finished products for roll forming operations call for a well adapted pre-cut of the blank. In a second step, roll forming of TRBs to a symmetrical U-profile with constant roll gap was investigated. For this purpose, experiments on a conventional roll forming line and corresponding FE simulations were conducted. Both show very similar results for the final bending angle of the part. Nevertheless, variability in bending angle of up to 14.3° is witnessed between the areas of different sheet thickness on one part. Thus, one may conclude, that a sheet thickness dependent adaptation of the roll gap is necessary for closer tolerances. A vertical and horizontal adjustability of the rolls seems appropriate to meet this purpose. With respect to these findings, two different tool kit concepts were developed and investigated by means of FE analysis. Both aim at a real-time adjustment of the roll gap to the actual sheet thickness within the stand. On the one hand, a force-driven self-positioning of the rolls was simulated. On the other hand the positioning of the rolls was preset in accordance to the feed of the sheet and its thickness distribution. Both concepts are discussed by their effect on the final bending angle of the roll formed U-profile.
Authors: Antti Määttä, Kari Mäntyjärvi, Jussi A. Karjalainen
Abstract: Utilisation of ultra-high-strength steels (UHS) has increased, particularly in the automotive industry. By using these materials vehicle structures can be lightened. However, one of the problems of UHS is weak formability. Materials fracture easily with small bending radii and the minimum bending radii are rather large. In this study, the tested materials were complex phase (CP) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). The steels were incrementally bent with a press brake in the rolling direction and perpendicular to it, and the final bending angle was 90 degrees. The incremental bending angles were 150°, 130°, 110° and 90°. The punch was unloaded after every incremental bending step. The test materials were bent with different bending radii. The aim was to find the minimum bending radius which produces an acceptable bend. Every incremental bend was compared with a bending performed in the traditional manner. The aim of this study was to examine how well the results of incremental bending compare to roll forming. In addition, clarification studies of when the bend started to fracture were made. It is well known that steels are more efficiently bent by roll forming compared with traditional bending. The results presented in this study demonstrate that incremental bending does not produce better results than traditional bending. Nevertheless, it has been shown that the examined steels can be bent incrementally against manufacturer’s recommendations.
Authors: Ralph Schäfer, Pablo Pasquale, Alexander Elsen
Abstract: Adhesively joining metals of dissimilar melting point represents one of the most sophisticated tasks in joining technique. However, due to light weight considerations this type of joint, for example the connection between an aluminum flange and a high strength steel crash element, is of prior interest. The electromagnetic pulse technology is a proven process to accomplish adhesive joints between tubes made of dissimilar metals. Recent developments of the technique now allow welding even dissimilar and similar sheet metals under industrial conditions. This paper details the underlying mechanisms and shows a variety of samples, depicting for the potential of this new process.
Authors: Tomoyoshi Maeno, Kenichiro Mori, Chihiro Unou
Abstract: A hot gas bulging process of an aluminium alloy tube using resistance heating set into a die was developed. In the developed process, the tube was heated during the forming, and thus the drop in temperature was prevented. The control of the hot gas bulging was simplified by sealing air in the tube. The tube was bulged by thermal expansion of the air sealed in the tube without control of internal pressure during the forming. Hot gas bulging of an aluminium alloy tube without and with the axial feeding was performed. The deformation behaviour of the tube in the die was observed by a heatproof glass plate inserted in the die. The timing of the axial feeding, the feeding velocity and the amount of the axial feeding were optimised.

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