Magnetic-Pulse-Welding

for the right applications.

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Magnetic-Pulse-Welding is one more example of solid state welding.

It is performed cold, without heating of any sort, producing true metallurgical atomic bonding.

In that it is similar to ultrasonic- and explosion-welding.

Its origins are pushed back to more than a century ago when essentially similar processes were used for metal forming.

The renewed interest and development for welded applications is much more recent, supported in large measure by the needs of the automotive industry.

Short notes referring to Magnetic-Pulse-Welding were published in the past Issues PWL#018,
PWL#043
and PWL#046
of Practical Welding Letter, mentioning a few applications.

Magnetic-Pulse-Welding, a high speed, single pulse welding process, is suitable for cold welding together electrically conductive metals.

The absence of fusion makes the bonding between dissimilar metals possible, without producing brittle intermetallic compounds.

One of the most common configurations consists of a lap joint where a tubular exterior element surrounds an inner one, either tubular or solid.

Magnetic-Pulse-Welding: Rapid, Effective, Safe

Before welding, a measurable gap is present between the two elements.

Due to the collision generated, one of the elements looks deformed by the process after joining took place.

A less common joint geometry consisting in overlapping sheet metal sections.

This is aggressively pursued by automakers because of the intrinsic capabilities of this cold weld and applicability to dissimilar materials.

Magnetic-Pulse-Welding is performed by accelerating a definite region of one of the parts to impact at high speed with much force against the other.

This movement is the result of a high repulsive force generated into the workpiece by the opposing transient magnetic fields.

One is associated with the current flowing in the primary coil.

The other is produced by eddy currents induced in the opposite direction in the conductive material nearby.

The powerful current is generated by the sudden discharge of energy, from a bank of capacitors storing the charge at high voltage.

The discharge occurs through the primary coil designed to exhibit low inductance and high conductivity.

The peak current can reach a very high level of amperes, measured in the millions.

The pulse width is limited to tens of microseconds.

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Magnetic-Pulse-Welding has some features in common with Explosion Welding.

The gap through which the material of one element impacts at an angle with the surface of the second element,
the local plastic deformation of one of the parts,
and the formation of a powerful jet at the point of collision, that cleans the surfaces by effectively removing all contaminants.

As a consequence also the appearance of the wavy interface after welding, in metallographic sections across the welds is very similar for both processes as seen under a microscope.

Magnetic-Pulse-Welding has therefore all the advantages that promote its application for mass production of welds in repetitive parts:

Very short cycle time
Suitable for automation
Cold process, applicable to dissimilar materials
Does not degrade (by heating) the mechanical properties
No need for filler metal or shielding gases
No heat affected zone and almost no distortion
Does not require skilled workforce
Does not require expensive inspection because of its highest weld quality
No need for post weld cleaning and finishing or heat treatment operations
No dangerous impact on the environment.

The limitations include:

Expensive equipment, justifiable only by important mass production
Limited possible joint configurations
Excessive power required for less conductive materials

Aluminum and Copper, because of their high conductivity, are among the most used materials, joined by Magnetic-Pulse-Welding.

All other commercial metals can be welded to, for ever expanding applications in all industries.

Designers of tubular joints intended for parts to be mass produced are urged to explore Magnetic-Pulse-Welding for its low cost high productivity.

Links to online resources can be found in our Mid January 2013 - Bulletin_81-MPW-Resources.
Click on Bulletin 81 MPW-Resources to see it.

Watch the following Video (in German)

EMPT Sheet Metal Welding:
Welding of Aluminum to Steel

https://www.youtube.com/watch?v=Ad1Fyweoa9s&feature=endscreen&NR=1

EMPT = Electro-Magnetic Pulse Technology

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