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What is magnetically impelled arc fusion (MIAF) welding?

 

Magnetically impelled arc fusion (MIAF) welding is a variation on MIAB (magnetically impelled arc butt welding) which is widely used to join steel pipes and tubes. In MIAB, an arc is struck between the two components to be joined, MIAF uses a non-consumable electrode as an arc initiator. Illustrations A and B show a MIAF set-up for edge-welding the periphery of a flat, circular component.

a) MIAF welding set-up, cross-sectional view
a) MIAF welding set-up, cross-sectional view
b) MIAF welding set-up, plan view
b) MIAF welding set-up, plan view

The component to be welded is located on a central spigot which is connected to a pulsed arc welding power supply, similar to that used for micro-TIG welding. The annular electrode completes the electrical circuit.

When the power supply is activated, an arc is struck between a point on the annular electrode and the edge of the component. The arc is then propelled around the annular electrode by a series of electro-magnets (see illustration B) which are switched on and off in a high-speed sequence.

Rotation of the arc continues for a pre-set period until the edge of the component is fusion welded. No additional filler material is used.

Applications

Pressure or temperature (as used in thermostatic heating controls) transducer bellows are typical applications of MIAF welding. Formed (dished) washers have been edge welded to form a compressible assembly for pressure measurement. The capping of tubes is also feasible.

Candidate applications need to incorporate a defined point for the arc to target, otherwise arc wander can cause melting adjacent to the joint line.

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