Magnetic pulse welded space frame

Magnetic pulse welding (MPW) is a solid state welding process that uses magnetic forces to weld two workpieces together. The welding mechanism is most similar to that of explosion welding.[1] Magnetic pulse welding started in the early 1970s, when the automotive industry began to use solid state welding. The biggest advantage using magnetic pulse welding is that the formation of brittle intermetallic phases is avoided. Therefore, dissimilar metals can be welded, which cannot be effectively joined by fusion welding. With magnetic pulse welding high quality welds in similar and dissimilar metals can be made in microseconds without the need for shielding gases or welding consumables.

Process

Magnetic pulse welded HVAC pressure vessel

Magnetic pulse welding is based on a very short electromagnetic pulse (<100 μs), which is obtained by a fast discharge of capacitors through low inductance switches into a coil. The pulsed current with a very high amplitude and frequency (500 kA and 15 kHz) produces a high-density magnetic field, which creates an eddy current in one of the work pieces. Repulsive Lorentz forces are created and a high magnetic pressure well beyond the material yield strength causing acceleration and one of the work pieces impacts onto the other part with a collision velocity up to 500 m/s (1,100 mph).[2]

During magnetic pulse welding a high plastic deformation is developed along with high shear strain and oxide disruption thanks to the jet and high temperatures near the collision zone. This leads to solid state weld due to the microstructure refinement, dislocation cells, slip bends, micro twins and local recrystallization.[3]

Principles

In order to get a strong weld, several conditions have to be reached:[4]

The main difference between magnetic pulse welding and explosive welding is that the collision angle and the velocity are almost constant during the explosive welding process, while in magnetic pulse welding they continuously vary.

Advantages of MPW

Disadvantages

Numerical simulations of MPW

Various numerical investigations were carried out to predict the interface behavior of the MPW and the in-flight behavior of the flyer to determine the collision conditions. Generally, the flyer velocity prior to the impact governs the interfacial phenomena. This is the characteristic parameter that should be known based on the process and adjustable process parameters. Although, Experimental measurements using laser velocimetry methods provide an accurate assessment of the flyer velocity, (one example of such measurement is Photon Doppler velocimetry (PDV)), numerical computation offers a better description of the flyer velocity in terms of spatial and temporal distribution. Moreover, a multi-physics computation of the MPW process take into account of the electrical current through the coil and compute the physical behavior for an electromagnetic-mechanical coupled problem. Sometime, these simulations also allow to include the thermal effect during the process.[5][6] A 3D example model used for LS-DYNA simulation is also described in [citation needed], and it also provides some details of the physical interactions of the process, the governing equations, the resolution procedure, and both boundary and initial conditions. The model is used to show the capability of 3D computation to predict the process behavior and particularly, the flyer kinematics and macroscopic deformation.[7][8]

References

  1. ^ Weman, Klas (2003), Welding processes handbook, CRC Press, pp. 91–92, ISBN 978-0-8493-1773-6.
  2. ^ Magnetic Pulse Welding Illustration
  3. ^ A. Stern, V. Shribman, A. Ben-Artzy, and M. Aizenshtein, Interface Phenomena and Bonding Mechanism in Magnetic Pulse Welding, Journal of Materials Engineering and Performance, 2014.[page needed]
  4. ^ Magnetic Pulse Welding: J.P. Cuq-Lelandais, S. Ferreira, G. Avrillaud, G. Mazars, B. Rauffet: Welding windows and high velocity impact simulations.[page needed]
  5. ^ Sapanathan, T.; Raoelison, R.N.; Buiron, N.; Rachik, M. (2016). "Magnetic Pulse Welding: An Innovative Joining Technology for Similar and Dissimilar Metal Pairs". Joining Technologies. doi:10.5772/63525. ISBN 978-953-51-2596-9. S2CID 62881653.
  6. ^ Raoelison, R.N.; Sapanathan, T.; Padayodi, E.; Buiron, N.; Rachik, M. (2016). "Interfacial kinematics and governing mechanisms under the influence of high strain rate impact conditions: Numerical computations of experimental observations". Journal of the Mechanics and Physics of Solids. 96: 147–161. Bibcode:2016JMPSo..96..147R. doi:10.1016/j.jmps.2016.07.014.
  7. ^ L'Eplattenier, Pierre; Cook, Grant; Ashcraft, Cleve; Burger, Mike; Imbert, Jose; Worswick, Michael (May 2009). "Introduction of an Electromagnetism Module in LS-DYNA for Coupled Mechanical-Thermal-Electromagnetic Simulations". Steel Research International. 80 (5): 351–8.
  8. ^ I. Çaldichoury and P. L’Eplattenier, EM Theory Manual, Livermore Software Technology Corporation, California, USA, 2012.[page needed]