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A Novel Tool Design Strategy for Electromagnetic Forming

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Advanced Materials Research
Authors:
Reimund Neugebauer
Reimund Neugebauer
Reimund Neugebauer
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Verena Psyk at Fraunhofer Institute for Machine Tools and Forming Technology
Verena Psyk
Christian Scheffler at Fraunhofer Institute for Applied Optics and Precision Engineering
Christian Scheffler
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Abstract

To make the advantages of electromagnetic forming applicable for industrial manufacturing, a three step tool design strategy is suggested. At first, simplified decoupled electromagnetic and structural mechanical simulations are used for creating a preliminary design via a systematic iterative optimization process. The selected design is verified in more accurate coupled simulations. A prototypic realization serves for further optimization, if necessary. The applicability of the approach is proved on the basis of an inductor system for magnetic pulse welding of tubes.
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A novel tool design strategy for electromagnetic forming
Reimund Neugebauer
1,a
, Verena Psyk
1,b
and Christian Scheffler
1,c
1Fraunhofer Institute for Machine Tools and Forming Technology IWU, Reichenhainer Strasse 88,
09126 Chemnitz, Germany
areimund.neugebauer@iwu.fraunhofer.de, bverena.psyk@iwu.fraunhofer.de,
cchristian.scheffler@iwu.fraunhofer.de
Keywords: Design method, Metal forming, Electromagnetic forming
Abstract. the advantages ofTo formingmake electromagnetic applicable for industrial
manufacturing, a three step tool design strategy is suggested. At first, simplified decoupled
electromagnetic and structural mechanical simulations are used for creating a preliminary design via
a systematic iterative optimization process. The selected design is verified in more accurate coupled
simulations. A prototypic realization serves for further optimization, if necessary. The applicability
of the approach is proved on the basis of an inductor system for magnetic pulse welding of tubes.
Introduction and motivation
Electromagnetic forming (EMF) is a high-speed forming technology applicable for shaping,
joining and cutting electrically conductive sheet metal or hollow profile components. To do so, a
capacitor is discharged via an inductor system (i.e. a tool coil including a fieldshaper if applicable)
positioned in direct proximity of the workpiece. Thus, a damped sinusoidal current flows through
the inductor inducing a magnetic field and a secondary current in the workpiece. The interactions of
current and magnetic field result in Lorentz forces that can be mathematically transferred to surface
forces, the so-called magnetic pressure. Consequently, workpiece areas are accelerated. [1]
EMF features several technological advantages among which the most important ones are:
• High velocities and strain rates increase the formability of many materials (e.g. [2]).
• Contact-free force application allows forming even parts with sensitive surfaces without
lubricants making the process environmentally friendly and reducing cleaning effort.
• EMF has high potential of interference-fit and form-fit joining and even of metallic
bonding of similar and dissimilar materials (compare e.g. [3]).
• EMF has high potential for cutting thin foils: At Fraunhofer IWU coated aluminum and
of 30 µm and 10 µm, rwithcopper thicknessesfoils espectively, were cut with
significantly higher quality of the cutting edges compared to conventional shearing. The
positioning effort for cutting by EMF was marginal, while for conventional shearing the
effort for guaranteeing the appropriate cutting clearance for such thin foils is challenging.
Although most advantages have been known for a long time, still no industrial breakthrough of
the process is achieved. According to [4], this is due to restrictions considering design and
manufacturing of durable inductors. Knowledge about this is mainly confidential property of
equipment manufactures. An exception is the work by Golovashchenko and his co-authors. Therein
typical failure modes were identified [5] and a coil design was successfully tested in a longterm
series [6]. More details about the state of the art of inductor design are given in [4]. However,
systematic means directly applicable for the process and tool design for specific application cases
are still missing. Therefore, the aim of this paper is contributing to closing this gap.
Design strategy for inductor systems for electromagnetic forming technologies
The major difference between conventional processes and EMF, complicating process and tool
design, is that in EMF mechanical, electromagnetic, and thermal fields interact with each other and
Advanced Materials Research Online: 2014-09-12
ISSN: 1662-8985, Vol. 1018, pp 333-340
doi:10.4028/www.scientific.net/AMR.1018.333
© 2014 Trans Tech Publications Ltd, All Rights Reserved
All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans
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... Based on the previous assumptions and according to Ampere's Circuital Law and Gauss's Magnetism Law (see Eqs. (28) and (29) in Appendix A), B g and B c satisfy the following relationships: ...
... Therefore, these electromagnetic parameters are implicit functions. Before determining the electromagnetic parameters of the model, the angular frequency is determined using the iterative calculation method previously proposed by Neugebauer et al. [29]. This iteration process is illustrated in Fig. 5. Initially, an initial frequency ω (0) is substituted into Eqs. ...
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... Despite these advantages, there are still restraints using this technology in industrial environments (Golovashchenko, 2006). According toNeugebauer et al. (2014), insufficient knowledge about the design of durable and likewise efficient working coils is one of the main reasons for this. The efficiency of the electromagnetic forming process Á is defined by the ratio of plastic strain energy E F to the initial charging energy of the pulse generator E C (Daube and Mattke, 1968). ...
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