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Project summary

Conceptual design and Finite-element simulations

After the study of the literature and definition of the state-of-the-art, an initial conceptual coil design was developed. Numerical simulations were used both as a design tool and for understanding the complex device behaviour. The analytical problem is formulated in terms of the electrical problem as a circuit with lumped parameters. To analyse the complex 2D/3D problem the commercial product ANSYS Emag was used.

mechanical stress

Figure 1: Mechanical stress (von Mises) in N/m2 on the field shaper of the “Coil100” at 8kV/10.6kJ. On the left side of the field shaper is the field shaper slot (© Fraunhofer IWU)

   

Prototyping of new coils and experimental testing

Four different coil prototypes were built based on the results of the conceptual design process and the FE simulations.

Design of Bitter coils for flat forming and cutting

In order to demonstrate possible applications of inductors of the Bitter coil type for flat forming and cutting applications, two of these coils were developed. The developed “Coil50” is highly efficient for the diameter range of 35 mm up to 55 mm and the “Coil100” was designed for the range of 70 mm up to 100 mm. The principle coil design will probably be applicable also for slightly smaller and for larger diameters. In those cases an adaptation of the coil measurement will be necessary.

flat Bitter coil

Figure 2: Assembly of a cutting coil with feedings (© Fraunhofer IWU)

Design of flat coils

For flat forming a uniform pressure actuator was developed. Different kinds of coil types were investigated and a development method for the dimensioning of different coil types was worked out. Based on the patents DE 10 2005 013 539 A1 and US 2005/0217333 A1 of Glenn Daehn from Ohio State university the Fraunhofer IWU developed an actuator with a relatively uniform pressure distribution. This actuator design is based on rectangular windings (7 turns) and insulated with Kapton film and Nomex paper.

flat coil (1)flat coil (2)

Figure 3: Assembly of the uniform pressure actuator: Coil with core (left), complete coil with housing and conductive channel (right) (© Fraunhofer IWU)

Cylindrical Bitter coil prototype

A new Bitter coil has been designed and constructed. A Bitter coil is formed by stacking the alternating conductors and insulating discs, each foreseen with a radial cut. The neighbouring conductor parts form a spiral conducting path. The contact between the disks is realised due to their overlap. A simple assembly jig can be used to assemble the coil.

cylindrical Bitter coil (1)cylindrical Bitter coil (2)

Figure 4: Principle drawing of the designed coil (left) and new designed prototype coil (right)

Cylindrical helix coil prototype

The building of a helix coil prototype starts with the preparation of the coil former (the base) on which the conductors are wound. The following step is the winding of the conductors with a rectangular cross section. A layer of polyester resin with glass fibre filler is used for equalizing the level for the glass fibre reinforcement material. After the curing process the filling factor between the glass fibre and the resin is calculated by the weight and the volume.

cylindrical helix coil

Figure 5: Helix prototype coil

   

Manufacturing of demonstration work pieces with the obtained coils

Demonstation work pieces for flat forming were selected to set up a feasible equipment for the realisation of the embossing process by electromagnetic forming. In Figure 6, results of individual tests are presented. It can be observed that as expected the incisiveness and quality increases with increasing capacitor charging energy. Furthermore, it is obvious that a minimal size of the embossing element is necessary.

shaping demonstrator

Figure 6: Series of embossing tests with different charging energies. (© Fraunhofer IWU)

For the experimental investigations a complex cutting demonstrator with a scope of different practical design elements was used together with a helical flat coil (Figure 7). The objective was to show the characteristic of cutting multiple cut-offs within one single pulse. The results clearly show that in principle it is possible to cut multiple elements including the outer contour of the component.

cutting demonstrator

Figure 7: Technology oriented cutting demonstrator. (© Fraunhofer IWU)

  

Literature

Psyk, Verena; Scheffler, Christian; Drossel, Welf-Guntram; Kolchuzhin, Vladimir; Mehner, Jan; Faes, Koen et al. (2014): Advanced Coil Design for Electromagnetic Pulse Technology. Report on the methodology of coil design. [Ergebnisse des Vorhabens der industriellen Gemeinschaftsforschung (IGF) gefördert über die Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V.]. 1., Aufl. Hannover: Europäische Forschungsgesellschaft für Blechverarbeitung e.V. (EFB) (EFB-Forschungsbericht, 397).

 



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