Sheet Metal 2007

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Authors: Raoul Plettke, Hinnerk Hagenah, Manfred Geiger
Abstract: The adjustment of micro system components with laser forming using especially designed sheet metal actuator systems is a new and promising technology. However, due to the complexity of the design challenge and the contradicting targets that have to be considered computer assistance for the design of the actuator systems is needed. In order to build such a system several steps have to be taken. First, the actuators have to be modeled with all necessary data. Second, quality criteria have to be defined and fully automated assessment modules for every single objective have to be implemented. And third, an optimization system which utilizes the assessment modules must be developed to improve an initial design. This paper presents a solution for each of these steps. It closes with first results of a reduced version of the system as well as an outlook on the next development steps.
Authors: Matteo Strano, Andrea Burdi
Abstract: During sheet metal forming operations, many different sources of non-controllable process variations usually display their effect, leading to a degree of uncertainty in the final parts’ quality. For this reason, statistical tools are increasingly used in combination with FEM numerical simulation. The focus is moving in recent times beyond mere feasibility to robustness of the product and process being engineered. Ensuring robustness is the next big challenge for the virtual tryout / simulation technology. In this paper, some of the numerous applications of statistical analysis combined with simulation of sheet forming processes are presented and discussed: 1) sensitivity analysis under uncertainty, 2) process capability studies, 3) reliability assessment, 4) reliability optimization, 5) process design optimization under uncertainty. Problems of type 2) and 5) will be particularly addressed, by giving the description of some innovative methods and applications.
Authors: Augusto Barata da Rocha, Abel D. Santos, Pedro Teixeira
Abstract: The use of Finite Element Simulation allows accurate predictions of stress and strain distributions in complex stamped parts. The onset of necking is strongly dependent on the strain paths imposed to the parts and therefore the prediction of localized necking can be a difficult task. Numerical models of plastic instability have been used to predict such behavior and recent and more accurate constitutive models have been applied in these calculations. In many manufacturing areas such as automotive, aerospace, building, packaging and electronic industries, the optimization of sheet metal processes, through the use of numerical simulations, has become a key factor to a continuously increasing requirement for time and cost efficiency, for quality improvement and materials saving. This paper makes an analysis of the evolution of strain gradients in stamped parts. The combination of Finite Element Analysis with a Plastic Instability Model, developed to predict localized necking under complex strain paths, shows that it is possible to predict failure with precision. Several constitutive laws are used and comparisons are made with experiments in stamped benchmark parts. Considering non linear strain paths, as detected in stamped parts, more accurate failure predictions are achieved. The work described in this paper shows the need to include a post processor analysis of failure, capable of predicting the behavior of the material under non linear strain paths. Taking this phenomenon into account, it is shown that it is possible to increase the accuracy of the onset of localized necking prediction.
Authors: Dan Sorin Comsa, Dorel Banabic
Abstract: The paper is focused on the development of a new phenomenological yield criterion able to describe the inelastic response of sheet metals subjected to cold forming. The model consists in two components: the equivalent stress and the hardening law. The equivalent stress is a function incorporating 8 material parameters. Due to these parameters, the new formulation is able to describe four normalized yield stresses (y0, y45, y90, yb) and four coefficients of plastic anisotropy (r0, r45, r90, rb). The hardening law is defined as a linearly asymptotic function containing 4 material parameters. The numerical tests presented in the last section of the paper prove the capability of the elastoplastic constitutive models based on the new yield criterion to model the earing as well as the wrinkling phenomena accompanying the deep-drawing process.
Authors: Rosanna Di Lorenzo, Giuseppe Ingarao, Fabrizio Micari
Abstract: One of the main issues in sheet metal forming operations design is the determination of formability limits in order to prevent necking and fracture. In fact, the ability to predict fracture represents a powerful tool to improve the production quality in mechanical industry. Many researchers investigated the problem here addressed, mainly studying forming limit diagrams (FLD) or developing fracture criteria which are able to foresee fracture defects for different processes. In this paper, the author present some early results of a research project focused on the application of artificial intelligence (AI) for ductile fracture prediction in sheet metal forming operations. The main advantage of the application of AI tools and in particular, of artificial neural networks (ANN), is the possibility to obtain a predictive tool with a wide applicability. The prediction results obtained in this paper fully demonstrate the usefulness of the proposed approach.
Authors: J. Hecht, K. Lamprecht, Marion Merklein, Konstantin Galanulis, J. Steinbeck
Abstract: The dynamic development of highly accurate optical measuring machines within the last years pushed the introduction of digitizing techniques to many applications in the fields of quality control, reverse engineering and rapid prototyping. By projecting fringe patterns onto the object's surface and recording pictures of the curvature dependant deformation of the pattern, 3D coordinates for each camera pixel are calculated on the basis of the principle of triangulation. The generation of a polygon mesh can be used for the analysis of the deviation of a die or a formed part to the initial CAD data, i.e. by means of full field or section based comparison. This paper presents the application of the above mentioned techniques on a double sheet hydroforming process. The gathered 3D data of the clam-shell part as well as of the tooling dies served for the calculation of the deviation to the respective reference geometry. With respect to the utilization of digitized tooling data within the finite element analysis, further investigations were performed on the impact of data reduction strategies. Aiming on the minimization of the necessary number of elements, representing the tooling surface in a discrete state, and on the request for a sufficient degree of accuracy, these strategies have to be considered of high priority.
Authors: Shankar Kalyanasundaram, Paul Compston, Joel Gresham
Abstract: The quality of stamp formed parts depends on a number of variables. Numerical studies based on finite element analysis can provide evolution of strain during forming and correlate with different failures of the formed parts. This study presents a methodology of capturing the evolution of strain during forming through a photogrammetric method. An open die was used to monitor the strain evolution of domed parts. The forming characteristic of a fibre-metal laminate system was compared to a monolithic aluminum alloy to elucidate the differences in the strain evolution during forming. It was found that the two materials exhibited different strain evolution during forming and this affected the failure behavior of the formed parts.
Authors: Dominik T. Matt
Abstract: The complexity of a manufacturing system is determined by the uncertainty in achieving the system’s functional requirements and is caused by two factors: by a time-independent poor design that causes a system-inherent low efficiency (system design), and by a time-dependent reduction of system performance due to system deterioration or to market or technology changes (system dynamics). To maximize the productivity of a manufacturing system, its entire complexity must be reduced. Many valid methods have been developed so far addressing different single manufacturing and quality issues. But to continuously increase the productivity of a manufacturing system within a turbulent environment its entire complexity must be reduced. This requires a holistic understanding and knowledge about the system. To reduce a system’s complexity, its subsystems should not overlap in their contribution to the overall system’s functionality, they must be mutually exclusive. On the other hand, the interplay of system’s components must be collectively exhaustive in order to include every issue relevant to the entire system’s functionality. This paper introduces a concept for complexity reduction in manufacturing systems with the help of Nam P. Suh’s Axiomatic Design principles. In a first step, time-dependent elements are separated from time-independent elements. To eliminate the real complexity of the time-independent elements (so called manufacturing modules), a set of alternative design parameters are defined that fit the system range of the manufacturing module’s set of functional requirements. To reduce the time-dependent combinatorial complexity, a methodology is proposed to systematically define an entire manufacturing system’s functional requirements within very short times in order to guarantee a fast reconfiguration of the system considering internal and external system dynamics. With the help of practical examples and the obtained results, the validity of the approach is illustrated.
Authors: S. Kumar, R. Singh
Abstract: This paper presents an intelligent system for modeling and material selection for progressive die components. The proposed system comprises of two modules, namely INTPMOD and MATSEL. The first module INTPMOD is constructed for modeling of die block, stripper plate, punch plate, back-up plate, die-set and die assembly of progressive die automatically in the drawing editor of AutoCAD. The second module MATSEL is developed for material selection for progressive die components. Both the modules are coded in AutoLISP language and designed to be loaded into the prompt area of AutoCAD. An illustrative example is included to demonstrate the usefulness of the system modules. The proposed system is implemented on a PC having AutoCAD software and its low cost of implementation makes it affordable for small and medium-size sheet metal industries.
Authors: Hartmut Hoffmann, Michael F. Zäh, Ingo Faass, Roland Mork, Matthias Golle, Bernd Griesbach, Matthias Kerschner
Abstract: The manufacturing of automotive body components in press lines is a sensitive process. The quality characteristics of body components vary. These fluctuations are rooted in the fact that the factors influencing the component quality are varying, e.g., fluctuations of batches regarding material quality, abrasion or heating of the tool during the production cycle. If a certain quality characteristic exceeds a predefined range an intervention in the process is necessary. This intervention is based upon the subjective know-how of the machine operator. Objective information about the state of the process, like tool temperature or the material quality of the semi-finished product is not available. Therefore, a lack of knowledge emerges in the interrelations between the tuning parameters of the system press-tool and the component quality during different stages of the process (material quality, temperature…). In this paper a complete concept for an automatic process control in press shops is described. The concept will be realized in a pilot plant for mass production in the press shop of AUDI AG. The mechanisms of occurrence of quality defects are shown in the paper, as well as the essential factors influencing the quality during the mass production of body components in the automotive industry and their variation. A sensor-system for continuous measurement of influencing variables during the mass production is presented. The key element of the concept is the non-destructive identification of material-properties for every single blank. By associating the sensor-data with the respective quality, a knowledge-based process control can be realized. The purpose is to create a failure prediction algorithm and make optimal adjustments for each stroke of the moulding press, respectively. The potential of existing actuators in modern press lines as well as new, tool integrated proposals for actuators are highlighted.

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