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Hot Wire TIG Welding

Bryan Jones
10 February 2020

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Low deposition rates and slow travel speeds have been the major weaknesses of the TIG welding process. For applications involving the use of filler wires two approaches are available – the cold wire and the hot wire process.

In the cold wire process, the filer metal is melted by the heat of the arc. To melt the wire faster, in the hot wire process the filler metal is preheated by resistive heating while it is being fed into the weld pool. The resistive heat is generated in most cases by a separate AC current, which is supplied to the filler metal that flows from the wire directly into the weld pool. For the hot wire process, AC tends to aid the process because its electromagnetic field deflects the welding arc forward and backward in the weld pool creating a stirring effect. This improves edge wetting and helps break up the surface oxides in the weld pool, minimising inclusions.

The current is properly adjusted so that ideally the temperature of the filler metal can reach its melting point as soon as it enters the weld pool. Because the wire is heated to its melting point it doesn’t chill the weld pool and instead it promotes good wetting.

The microstructure of the weld metal was finer with the hot wire compared to the cold wire process, when similar weld appearances were obtained. The hardness was slightly higher with hot wire process, and good mechanical properties were obtained. In typical applications, the fracture of both cold and hot wire welded joints were all located in the base metal.

In comparison with the cold wire process the hot wire variant is more complicated and has a higher cost because of the additional power supply, but it is capable of achieving 2-3 times faster deposition rates dependent on the application.

The process is widely used in the field of pressure vessel fabrication and shipbuilding.

Hot wire applications extend beyond TIG. In fact processes such as plasma arc and laser can benefit from the use of a heated wire.

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