Sheet Metal 2007

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Authors: Paolo Bortot, Elisabetta Ceretti, Antonio Fiorentino, Claudio Giardini
Abstract: In the present paper a feasibility study of a funerary vase, made of stainless steel, using the Hydromechanical Deep Drawing process, is presented. The component is currently made of bronze and manufactured by die casting technology in a low volume production environment. To investigate the part feasibility, several FE simulations were implemented using the Aquadraw tool of the explicit FE code Pam Stamp 2G 2005®. The FE simulations showed that HDD process can produce the part in one single step without the requirement of finishing operations such as painting or polishing. Furthermore experimental tests were conducted and the first prototypes were successfully produced.
Authors: Christophe Henrard, Chantal Bouffioux, Laurent Duchêne, Joost R. Duflou, Anne Marie Habraken
Abstract: A new method for modeling the contact between the tool and the metal sheet for the incremental forming process was developed based on a dynamic explicit time integration scheme. The main advantage of this method is that it uses the actual contact location instead of fixed positions, e.g. integration or nodal points. The purpose of this article is to compare the efficiency of the new method, as far as accuracy and computation time are concerned, with finite element simulations using a classic static implicit approach. In addition, a sensitivity analysis of the mesh density will show that bigger elements can be used with the new method compared to those used in classic simulations.
Authors: S. He, J. Gu, Hugo Sol, Albert Van Bael, Paul van Houtte, Yasemin Tunckol, Joost R. Duflou
Abstract: A simplified method to determine the strain distribution during incremental forming of a cone is proposed in this paper. Because of the symmetry of the deformed part, the strain can be derived using the results obtained from a limited number of consecutive tool contours instead of going through the whole process. Comparisons made between the measured and simulated results show that the proposed method can be applied to determine the strain encountered in such kind of incremental forming process where axi-symmetric parts are formed.
Authors: Markus Bambach, M. Todorova, Gerhard Hirt
Abstract: Asymmetric incremental sheet forming (AISF) is a relatively new manufacturing process for the production of low volumes of sheet metal parts. Forming is accomplished by the CNC controlled movements of a simple ball-headed tool that follows a 3D trajectory to gradually shape the sheet metal blank. Due to the local plastic deformation under the tool, there is almost no draw-in from the flange region to avoid thinning in the forming zone. As a consequence, sheet thinning limits the amount of bearable deformation, and thus the range of possible applications. Much attention has been given to the maximum strains that can be attained in AISF. Several authors have found that the forming limits are considerably higher than those obtained using a Nakazima test and that the forming limit curve is approximately a straight line (mostly having a slope of -1) in the stretching region of the FLD. Based on these findings they conclude that the “conventional” forming limit curves cannot be used for AISF and propose dedicated tests to record forming limit diagrams for AISF. Up to now, there is no standardised test and no evaluation procedure for the determination of FLCs for AISF. In the present paper, we start with an analysis of the range of strain states and strain paths that are covered by the various tests that can be found in the literature. This is accomplished by means of on-line deformation measurements using a stereovision system. From these measurements, necking and fracture limits are derived. It is found that the fracture limits can be described consistently by a straight line with negative slope. The necking limits seem to be highly dependent on the test shapes and forming parameters. It is concluded that standardisation in both testing conditions and the evaluation procedures is necessary, and that a forming limit curve does not seem to be an appropriate tool to predict the feasibility of a given part design.
Authors: Wilko C. Emmens, A.H. van den Boogaard
Abstract: This paper discusses some consequences of forming by shear, a situation that is sometimes claimed to occur in incremental forming. The determination of the principal strains and principal directions is discussed in detail. Two methods are presented: using a circular grid (although simulated on the computer), and by deriving formulae from the theory; both yield identical results. The strains assuming forming by shear are found to be (much) higher than in situations of forming by stretch. This affects notably more fundamental studies on material behaviour in incremental forming. The effects are illustrated using experimental data obtained with pre-stressed material.
Authors: Johan Verbert, Joost R. Duflou, Bert Lauwers
Abstract: One of the main issues of the single point incremental forming (SPIF) process is still the achievable accuracy. A number of methods have been suggested to increase this accuracy, but many of these contain a significant drawback. Reprocessing the workpiece can increase the accuracy but also significantly increases the manufacturing time and leads to a worse surface finish of the part. Other methods iteratively correct the toolpath based upon the deviations measured on the previously manufactured parts. This method is not very well suited for one of a kind products, since instead of one part, multiple parts need to be manufactured before the desired accuracy can be reached. Our method proposes to use feature detection to split the workpiece in a configuration of planes, edges, freeform surfaces and other features. For each of these features an optimised toolpath strategy can be determined and the toolpath in that zone can be adjusted for this strategy. The proposed method generates a single pass toolpath that leads to more accurate parts compared to the standard CAM toolpaths. This paper describes the feature based optimised toolpath generation method (FSPIF) and contains the results of experiments performed to validate this method.
Authors: Giuseppina Ambrogio, L. De Napoli, Luigino Filice, M. Muzzupappa
Abstract: It is well known that the geometrical accuracy is a very relevant problem in Incremental Forming operations, since the material is not well sustained and, then, the elastic springback plays a significant role during the process. A number of researches are involved in the study of geometrical precision after the forming stage but considering the sheet clamped to the equipment. However, it is well known that material coupling is carried out after trimming, when it could change its shape after the new equilibrium. In the paper here addressed the above concept is kept in touch and a wide experimental campaign has been set-up in order to acquire experimental information on the effect of unclamping and trimming after incremental forming processes. The obtained results are able to suggest to the process designer some best practices which are accurately discussed in the paper.
Authors: Joost R. Duflou, Yasemin Tunckol, Richard Aerens
Authors: Alexander Szekeres, M. Ham, J. Jeswiet
Abstract: Forces are measured in Single Point Incremental Forming with a spindle mounted sensor. Results for AA3003 aluminum cones and pyramids are shown. Forces are measured for parts with a 75° forming angle, at which shear cracks are expected to occur. Forces in the three directions are measured on the spindle with force spikes being observed when the tool changes direction at pyramid corners, and reductions in force when stepping between contours. There is also a force variation as the forming tool moves along the pyramid wall. A comparison is made between the forces measured for cones and pyramids.
Authors: A. Governale, A. Lo Franco, A. Panzeca, Livan Fratini, Fabrizio Micari
Abstract: In the last decades the scenario of the industrial production is remarkably changed, since new market requirements have to be faced by the industries. The market, actually, more and more, asks for vary models and niches product. The necessity to intercept dynamically and to satisfy the demands for the market, driver of the innovation process, involves the necessity to reduce the Timeto- market introducing to new methodologies of engineering, like the 3D-prototyping, for the qualitative and structural analysis of the final component. For these reasons, at the beginning of the nineties, a new philosophy of sheet metal forming process begins to assert on the industrial scene, whose basic logic is to obtain the shape wished through the progressive action of a tool of simple shape. In this job the application of the simplest process of incremental process on an industrial detail - famous in international field like SPIF (Single Point Incremental Forming) - will be described. The process is intrinsically flexible, and therefore is adapted to the rapid prototyping. The cases are still least, notice in the scientific literature, in which the details of industrial interest have been developed by Incremental Forming process; for this reason, the subject of this job is focused on the evaluation of the possibility to obtain real components of the automotive industry through the SPIF process. The job has been carried out in the R&D laboratory of "Fontana Pietro S.p.A.”, leader in the field of die manufacturing and stamping of component of the automotive industry. In particular, two parts of automotive auto body of aluminium sheets have been considered. It has been lead an analysis of technological and process feasibility, optimizing tool path considering experiences to obtain a product/process for the production of auto body prototypes.

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