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Magnetic pulse welding (MPW) is a solid state
welding Welding is a fabrication (metal), fabrication process that joins materials, usually metals or thermoplastics, primarily by using high temperature to melting, melt the parts together and allow them to cool, causing Fusion welding, fusion. Co ...
process that uses
magnetic Magnetism is the class of physical attributes that occur through a magnetic field, which allows objects to attract or repel each other. Because both electric currents and magnetic moments of elementary particles give rise to a magnetic field, m ...
forces to weld two workpieces together. The welding mechanism is most similar to that of explosion welding. Magnetic pulse welding started in the early 1970s, when the
automotive industry The automotive industry comprises a wide range of company, companies and organizations involved in the design, Business development, development, manufacturing, marketing, selling, Maintenance, repairing, and Custom car, modification of motor ve ...
began to use solid state welding. The primary advantage of using magnetic pulse welding is that the formation of brittle
intermetallic An intermetallic (also called intermetallic compound, intermetallic alloy, ordered intermetallic alloy, long-range-ordered alloy) is a type of metallic alloy that forms an ordered solid-state compound between two or more metallic elements. Inte ...
phases is avoided, allowing the joining of metals which cannot be effectively joined by
fusion welding Fusion welding is a generic term for welding processes that rely on melting to join materials of similar compositions and melting points. Due to the high-temperature phase transitions inherent to these processes, a heat-affected zone is created ...
. Additionally, the process is nearly instantaneous and does not require shielding gas or other welding consumables.


Process

Magnetic pulse welding is based on a very short
electromagnetic pulse An electromagnetic pulse (EMP), also referred to as a transient electromagnetic disturbance (TED), is a brief burst of electromagnetic energy. The origin of an EMP can be natural or artificial, and can occur as an electromagnetic field, as an ...
(<100 μs), which is obtained by a fast discharge of
capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
s through low inductance switches into a coil. The pulsed current with a very high
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
and
frequency Frequency is the number of occurrences of a repeating event per unit of time. Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio ...
(500 kA and 15 kHz) produces a high-density magnetic field, which creates an eddy current in one of the work pieces. Repulsive
Lorentz force In electromagnetism, the Lorentz force is the force exerted on a charged particle by electric and magnetic fields. It determines how charged particles move in electromagnetic environments and underlies many physical phenomena, from the operation ...
s are created and a high magnetic pressure well beyond the material yield strength causes acceleration of one of the work pieces to velocities of up to upon collision. The flying work piece then impacts its target, though different parts will contact at different times. As the line of contact moves, typically a jet of ejected surface material forms ahead of the contact line. This jet is beneficial as it effectively cleans the surfaces by ejecting some surface material (removing oxides or contaminants). During magnetic pulse welding a high
plastic deformation In engineering, deformation (the change in size or shape of an object) may be ''elastic'' or ''plastic''. If the deformation is negligible, the object is said to be ''rigid''. Main concepts Occurrence of deformation in engineering application ...
is developed along with high shear strain and oxide disruption due to the jet and high temperatures near the collision zone. This leads to a solid state weld due to the microstructure refinement ( dislocation cells,
slip bands Slip bands or stretcher-strain marks are localized bands of plastic deformation in metals experiencing stresses. Formation of slip bands indicates a concentrated unidirectional Slip (materials science), slip on certain planes causing a stress conce ...
, micro
twins Twins are two offspring produced by the same pregnancy.MedicineNet > Definition of Twin Last Editorial Review: 19 June 2000 Twins can be either ''monozygotic'' ('identical'), meaning that they develop from one zygote, which splits and forms two e ...
and local recrystallization).


Principles

In order to achieve a strong weld, several conditions have to be reached: *''Jetting condition:'' the collision has to be subsonic compared to the local material's speed of sound to generate a jet. *''High pressure regime:'' the impact velocity has to be sufficient to obtain a hydrodynamic regime, otherwise the parts will only be crimped or formed. *''No fusion during the collision:'' If the pressure is too high, the materials can locally melt and re-solidify. This can cause a weak weld. 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.


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. A multi-physics computation of the MPW process can take into account of the electrical current through the coil and compute the physical behavior for an electromagnetic-mechanical coupled problem. These simulations also allow the thermal effect during the process to be included. A 3D example model used for
LS-DYNA LS-DYNA is an advanced general-purpose multiphysics simulation software package developed by the former Livermore Software Technology Corporation (LSTC), which was acquired by Ansys in 2019. While the package continues to contain more and more p ...
simulation is also used, 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.I. Çaldichoury and P. L’Eplattenier, EM Theory Manual, Livermore Software Technology Corporation, California, USA, 2012.


References


External links


''The Electromagnetic Pulse Technology (EMPT): Forming, Welding, Crimping and Cutting''
by R. Schäfer, P. A. Pasquale and S. W. Kallee
''3D Impacts Modeling of the Magnetic Pulse Welding Process and Comparison to Experimental Data''
by J.-P. Cuq-Lelandais*, G. Avrillaud, S. Ferreira, G. Mazars, A. Nottebaert, G. Teilla, V. Shribman
''Automotive Applications of Electromagnetic Pulse Technology (EMPT)''
by S. W. Kallee, R. Schäfer and P. A. Pasquale.
''Special Issue "Impulse-Based Manufacturing Technologies"''
by Verena Psyk et al., J. Manuf. Mater. Process. 2021, 5(3), 96, ISSN 2504-4494. {{DEFAULTSORT:Magnetic Pulse Welding Welding