Sheet Metal 2005

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Authors: Sami Chatti, Uwe Dirksen, Marco Schikorra, Matthias Kleiner
Abstract: The process chain for the production of lightweight profile structures consists of the design and computation phases, the manufacturing of straight profiles, the manufacturing and further processing of bent profiles, and the joining of single profiles to lightweight structures. A sophisticated lightweight construction design of profile structures is characterised by the use of the correct material at the correct place with the correct dimensions. To design in this way means to purposefully find the technically and economically best solution. This requires a holistic technological approach covering the whole system “design-material-manufacturing”. Furthermore, appropriate experiences in design and the use of calculation software for the determination of several mechanical component properties as well as the simulation of manufacturing processes are necessary. A satisfactory component optimisation and a manufacturing specific design of the components presupposes, however, the integration of design, computation, and manufacturing knowledge into a single system using modern CA technologies to realise simultaneous engineering.
Authors: T.H.M. Nguyen, Joost R. Duflou, Jean Pierre Kruth
Abstract: Sheet metal bending is a metal forming process, in which flat sheets are bent along straight bend lines in a specific bending sequence to form three-dimensional parts. A large number of tools with different characteristics can be used in this process. The task to choose the right tooling for a requested sheet metal part is however one of the bottle necks in process planning. An inefficient tool selection may result in failure of finding a feasible bending sequence. In previous work, methodologies for tool selection and optimization have been proposed. The presented paper describes a framework to implement these methodologies into a system that allows automatic tool selection in consistent consideration of bend sequencing. As a result, automated and optimized tool selection for sheet metal bending is achieved, as illustrated by performance test results for a robust software implementation.
Authors: H. Bley, C. Zenner, M. Bossmann
Abstract: As the quality of manufactured products as well as the quality of the used manufacturing processes has become more and more important for a company in order to stay competitive in the last decades, an integrated quality management leading towards intelligent manufacturing represents a key factor today. Therefore, new methods are required for considering quality information in all phases of the product life cycle. Feature technology and especially the use of so-called measurement and quality features represent an approach towards integrated quality management and the achievement of process-oriented and global quality control loops. Furthermore, feature technology in general also represents a high potential just within the area of sheet metal forming where it can be used to provide additional information for designing manufacturing processes and constructing tools and devices in manufacturing systems.
Authors: M. Prechtl, Andrea Otto, Manfred Geiger
Abstract: The technology of Laminated Object Manufacturing (LOM) is not very new. For hundreds of years wooden parts are built by stacking layers together. Nowadays also paper, plastic, ceramic composite and metal sheets are treated in layers. For the manufacture of prototypes and especially technical tools, e. g. moulds for gravity casting, die casting or injection molding, out of metallic foil however the low self stiffness of this material is a great challenge. In this case it is useful to produce the parts in a two step process. The first subprocess is the stacking of the layers, which can be realised by laser beam spot welding to determine the position of the layer in combination with generating the defined contour by a laser beam cutting process. This procedure is done in a fully automated machine where the CAD-file of the desired part and the building parameters like the laser parameters and the cutting velocity are needed as input. However the stability of the produced green part is insufficient for most kind of application. Hence, a second sub-process to enhance the mechanical properties of the part is necessary. This can for example be realised by high temperature soldering or by diffusion welding in a furnace with inert gas or vacuum. During these kinds of joining processes the green part is homogeneously pressed with the help of a powder bed and at the same time it is tempered for a defined term. In this paper the principle of sheet metal LOM is described as well as the process chain of Laminated Object Manufacturing of metal foil. For each sub-process of metal foil LOM the results of the experimental work for qualifying and optimizing the sub-process are shown. Finally some examples of possible applications especially in the field of Rapid Tooling and Rapid Manufacturing are discussed.
Authors: Massimo Tolazzi, Marion Merklein
Abstract: The finite element analysis of sheet forming processes needs precise and reproducible data of the tribological conditions, which influence the material flow during the process. In this work the friction coefficient and its dependency on the hardness and surface topography of the blank are investigated. The selected materials are four steels with different surface qualities and coatings, FeP04, ZStE340, DP450 and TRIP800, which are joined by laser welding. Moreover, each material both with and without weld seam, was tested at three different values of normal contact pressure in a strip drawing test. The topography of both the base material and the weld line was obtained by measuring the surface roughness and implementing the data in a surface analysis software. Micro-hardness profiles along the tailored welded blanks were also determined. The strip drawing test was used to measure the friction coefficient between sheet metal and tool both in the case of tailored welded blanks and base material. The comparison between the results obtained for base materials and tailored welded blanks shows that the presence of the weld seam causes a clear increase of the friction between blank and tool.
Authors: Bernd Arno Behrens, J.W. Yun, M. Milch
Abstract: In this paper, a concept of a closed-loop-control system for the material flow in deep drawing processes based on a fuzzy-controller is presented. The deep drawing process is influenced by different variables as batch dependent material values, machine parameters as well as variations in the forming tools. Process stability can be improved by continuous process monitoring and process control. The control loop for controlling the material flow consists of an optical sensor, a deep drawing tool with an elastic blank holder, a fuzzy controller and a deep drawing press with a multi point drawing cushion. The controlled variable (material flow) was measured contact-free and on-line by means of an optical sensor developed at the IFUM. As control variable the different lokal blank holder forces were chosen in order to influence the material flow in different areas. In order to combine the controlled variable (material flow) and the control variable (lokal blank holder force) a fuzzy logic controller was designed. The performance of the material flow control was investigated by generating disturbances (e.g. a high blank holder force at the beginning) in the deep drawing process. This procedure shows that the fuzzy-controlled material flow can be compensated for the disturbances by means of changing the blank holder force.
Authors: Branimir Barisic, Tomaz Pepelnjak, Karl Kuzman
Abstract: Deep drawing process, although deceptively simple, involves a complex interplay between material properties, die geometry, process variables and also friction (lubrication) conditions. Numerical and stochastic modeling and simulation of this process means defining the correlation among the variables of the process in order to improve the existing processes. Using the Box-Wilson¢s multi factorial experimental design the stochastic, numerical and experimental investigations on the thinwalled tinplate rings (material: TS 260, TS 275, TH 415, TH 435, TH 520 according to the European Standard EN 10202) were performed. The FEM analysis applying ABAQUS Explicit code as well as stochastic analysis have been used in order to predict the influences of wall thickness and lubrication on reducing drawing force and estimate its influence on process consumed energy. The accuracy of the numerical and stochastic results is confirmed through the comparison with the experimental results.
Authors: C.W. Tai, H.-C. Tsai, Sheng Chi Tsai
Abstract: To promote the competitiveness of 3C industries in Taiwan, the cold forging progressive die technology is still being developed. The technology can rapidly and steadily produce high quality and complex shape products. Moreover, it can reduce manufacturing costs and time, too. The design for the cold forging progressive die process for the slim type spindle motor case consists of three main stages. First, we arrange a reasonable and appropriate process planing for the case. Second, we use computer software to simulate the main forming processes. Third, we perform a simple forming test to check up the results of the simulation. According to the test results, the main forming of the slim type spindle motor case is similar to the results of the simulation. Consequently, we demonstrate that the one-piece slim type spindle motor case can be manufactured with a progressive die. The forming processes include piercing, coining, upsetting, ironing, sizing, and blanking. The results from computer simulation and forming test result indicate that a reasonable effective manufacturing process for the one-piece slim type spindle motor case is possible. The final conclusions will be introduced in the article. In addition, we also discuss the possible problem involving the production of the slim type spindle motor case.
Authors: M. Kerausch, Marion Merklein, Detlev Staud
Abstract: Aluminum alloys, due to their low density compared to steels, are an important group of materials, in particular for light weight construction of transport vehicles. However, aside from their low specific weight, drawing of car body components made from aluminum alloys is limited by an inferior formability. To enable a modern car body design, it is necessary to enhance the formability of aluminum sheet metal. One basic approach to reach this aim is to adapt the mechanical properties of the blank for the drawing process. The general idea is to soften the deformation zone relative to the force transferring zone, which results in an improved material flow and thus to larger drawing depths. In this paper the process sequence consisting of local induction heat treatment followed by deep drawing of precipitation hardenable aluminum alloy is presented. Using an induction system, it is possible to change the mechanical properties of the 6xxx aluminum blanks in a restricted area by influencing the precipitation structure. Tensile tests characterize the conversion from the stable naturally aged condition T4 to reversible solution heat treated W conditions of AA6016 as function of temperature and time. This effect leads to a reduction of flow stress, which is used to design an material property distribution adapted for the subsequent deep drawing process. A process characterization study provides detailed information concerning induction heating parameters, to improve the deep drawing of cylindrical cups, which results in a decisive increase of the limiting drawing ratio. Accompanying the experimental investigations, a finite element analysis approach is realized as a process design and optimization tool. Following the presented strategy, it is possible to enhance the forming capability of aluminum alloys. This leads to advanced manufacturing processes, which extend the field of applications for aluminum car body parts.
Authors: Elisabetta Ceretti, Claudio Giardini, C. Contri, Paolo Bortot
Abstract: Numerical simulation conducted by Finite Element Method is one of the most powerful tools for analyzing metal forming processes. Among them, Hydromechanical Deep Drawing (HDD) is, probably, the process which has gained the major interest in industries in the last few years. In this paper a numerical study of HDD of a can box is presented. The influence of geometrical features of a pressure chamber in terms of the gap with the punch is discussed, together with the main process parameters, such as counter-pressure and Blank Holder Force (BHF). The pressure path was found to be the key parameter for a successful HDD. The pressure, in fact, has to be increased very quickly in the first part of the process in order to obtain a minimum friction between the blank and the die entrance radius. The BHF is determined by the pressure path and so a simple way for understanding the correct force was developed. The results are presented in terms of thinning and wrinkles of the final product. Thickness was found to decrease in the first half of the simulation and then it remains constant; wrinkles take place in the last steps of the simulation and they depend on the BHF and on sheet metal anisotropy. The FEM commercial code Pam Stamp 2000 with Aquadraw function was utilized.

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