Design of Hybrid Conductors for Electromagnetic Forming Coils
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Date
2018-05-14
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Abstract
The use of hybrid coil turns made of steel (St) and copper (Cu) is originally motivated by the
increased mechanical strength compared to monolithic copper conductors. Due to the
differing electrical conductivities of the two materials, the hybrid design also changes the
current density distribution in the conductor cross section. This affects crucial process
parameters such as the magnetic pressure and the Joule heat losses.
The effect of the hybrid conductor design on the process efficiency is investigated. An
electromagnetic sheet metal forming operation using a one-turn coil with rectangular cross
section is used as reference case. The copper layer (CuCr1Zr) was deposited on a tool steel
substrate (X40CrMoV5-1) using a selective laser melting process. The copper layer
thickness is varied ranging from a monolithic steel conductor to a monolithic copper
conductor. The workpiece (EN AW-5083, t_w = 1 mm) is formed through a drawing ring so
that the final forming height is a qualitative measure for the process efficiency. The
experimental results prove that the efficiency in case of a properly designed hybrid
conductor can exceed the efficiency of a monolithic copper coil. The current density
distribution in the hybrid cross section is investigated by means of numerical simulations.
This way a deeper insight into the physical effects of a varying copper layer thickness is
gained. The results reveal that the optimum layer thickness is not just a function of the coil
cross section and the current frequency. It is also affected by the coil length and the
resistance of the pulse generator.
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Keywords
electromagnetic forming, working coils, coil design, hybrid conductors