Magnetically Impelled Arc Butt Welding Principles

Magnetically impelled arc butt (MIAB) welding (sometimes referred to as rotating arc welding) is a rapid, clean, and reliable arc welding process that employs forging to produce  the finished weld. As such, it is classified as an electric arc welding process since that is the energy source for producing melting or fusion, even though pressure from forging is needed to complete the weld. It is thus a fusion arc pressure welding process, and, in that way, is related to arc stud welding  ( not described in this article. )

The MIAB welding process is well established in Europe (especially Eastern Europe) and the independent  states of  the  former Soviet Union, finding application in  the  automotive  industry for  the fabrication of tubular-section butt welds and, to a lesser extent, tube-to-plate welds. Tubes can have circular or non-circular cross sections, with walls ranging from 0.5 to 5 mm or more (0.020 to 0.200 in.) thick. Steel as well as aluminum alloy has been  welded successfully in mass production, producing welds with exceptional quality even for safety-critical applications.

Magnetically Impelled Arc Butt Welding Principles 

In practice, MIAB welding  is fully automated. An arc drawn between aligned but properly gapped tube ends is impelled to move (rotate) around the joint  line by an interaction of  the arc current  and  an externally  applied magnetic field , hence the name. Once the arc has heated the ends of the tubes to cause localized melting and adjacent softening in the heat-affected zone, the parts are forged together. This expels most of the molten metal present and a solid-phase  bond is formed. The principle of operation is shown  schematically in  Figure 1 ; typical placement of the magnets used to apply the propelling force to the arc is shown in Figure 2

Figure 1 : MIAB principles 

Figure 2 : MIAB schematic 

Benefits of MIAB

The  major benefits of MIAB welding are (1)  no rotation of either  component  (thereby  overcoming  problems  with  asymmetrical  parts  encountered with many friction welding processes), (2) short welding times (e.g., 2-4 s for 2 to 4-mm CO.040-  to 0.080-in.]-thick low-carbon steel tube), (3) low
material loss, (4) low fumes and  spatter, and (5) relatively low required arc current.

As opposed to flash and upset welding , MIAB welding does not use resistance to accomplish heating at the joint, but, rather, an electric arc. This makes  it an arc rather  than a  resistance welding process. The fact that forging  removes  most  molten  metal  suggests that  the  process  could  be considered non-fusion; after  all,  the role of the  liquid is  largely  fluxing . The  process is considered  a  non-consumable electrode arc process because the intent is not to consume the parts being welded and used as electrodes, but to preserve those parts.

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