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The skin-effect in ferromagnetic electrodes for wire-EDM

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Abstract

In wire electrical discharge machining (wire-EDM) material is removed by the thermal energy of an electric spark that has been initiated between two electrodes (the wire and the workpiece), submerged in demineralised water. The use of high frequency current pulses for sparking leads to excellent machining performance, in terms of the work piece roughness, the material integrity of the cut and the material removal rate. To reach the highest frequencies, the wire-EDM generator mostly consists of a voltage source with an as low as possible internal inductance. The working current delivered to the spark and, hence, the material removal rate of the process depends on the total impedance of the electrical circuit. In this article the importance of the wire’s impedance will be shown. Due to the skin-effect, this impedance depends on the frequency of the current signal, especially for ferromagnetic wires, such as steel wire. Coatings will prove to be primordial to prevent the machining speed from dropping significantly.

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Abbreviations

U H ::

Ignition voltage source (V)

U L ::

Burning voltage source (V)

U::

Spark’s voltage signal (V)

I::

Spark’s current signal (A)

S 1, S 2::

Generator switches

D 1, D 2, D h: :

Generator diodes

R H , R w ::

Generator resistors (Ω)

R 0::

Wire’s resistance at D.C. (Ω/m)

R::

Wire’s resistance at 100 kHz (Ω/m)

L s ::

Generator inductance (H)

J::

Current density (A/m2)

r::

Radial co-ordinate

r o: :

Outer radius (m)

r i ::

Inner radius (m)

A::

Current pulse rise time (μs)

t d ::

Pulse ignition delay time (μs)

t e ::

Pulse time (μs)

t o ::

Pulse offtime (μs)

π::

3,1415...

ν::

100 kHz; groundfrequency spark’s current signal (Hz)

μ r ::

Magnetic permeability of the medium

μ 0::

Magnetic susceptibility of vacuum=4π.10−7 (H/m)

μ::

=μ r μ 0

σ::

Electrical conductivity (S/m)

L::

Wire’s inductance at 100 kHz (H/m)

L 0::

Wire’s inductance at D.C. (H/m)

P x: :

Joule Power dissipated in x (W)

References

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Acknowledgements

The authors acknowledge the support of Charmilles Technologies s.a. and Bekaert n.v., and would like to thank them for putting the wire electrical discharge machine and the steel wires at their disposal for scientific research. The authors would also like to thank K. Nijs and M. Persoons for their initial research in this field, described in their master’s thesis [3]. The research was also partially funded by the scholarship of the Flemish Institute for the Promotion of Scientific Technological Research in Industry (IWT), granted to B. Schacht.

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Authors and Affiliations

  1. Division PMA, Katholieke Universiteit Leuven, Celestijnenlaan 300B, 3001, Leuven, Belgium

    B. Schacht, J.-P. Kruth, B. Lauwers & P. Vanherck

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  1. B. Schacht
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  2. J.-P. Kruth
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  3. B. Lauwers
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  4. P. Vanherck
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Correspondence to B. Schacht.

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Schacht, B., Kruth, JP., Lauwers, B. et al. The skin-effect in ferromagnetic electrodes for wire-EDM. Int J Adv Manuf Technol 23, 794–799 (2004). https://doi.org/10.1007/s00170-003-1654-6

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  • DOI: https://doi.org/10.1007/s00170-003-1654-6

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