The hot wire concept
Hot wire GTAW welding is a further development of the Gas Tungsten Arc Welding or Tungsten Inert Gas process. GTAW was invented by Russell Meredith working at Northrop Aircraft Company in 1939-1941. The GTAW process was initially called "Heliarc" as it used an electric arc to melt the base material and helium to shield the molten puddle. The patents were sold to the Linde Division of Union Carbide who developed a number of torches for different applications and sold them under the brand name Heliarc. Linde also developed procedures for using argon which was more readily available and less expensive than helium. Hot wire GTAW technology was invented in 1964 by A.F. Manz and developed by Linde. Filler metal in the form of wire is commonly added to welds in the GTA welding process, particularly when heavy wall thicknesses are being welded. With conventional GTAW the filler wire is introduced into the leading edge of the weld puddle in the cold state (ambient temperature). Energy from the arc is required to melt the wire reducing the efficiency of the process. In hot wire welding, filler wire is resistance heated until close to the melting point and added to the weld puddle behind the tungsten. This prevents the wire from chilling the weld pool and allows the filler metal to flow out across the weld puddle resulting in a smooth, attractive weld bead. Since nearly all of the full energy of the welding arc is available for penetration or to generate the weld pool and fusion, a two to three times faster travel speed is realized. More wire can be deposited and fill rates are increased with the added benefit of weld quality as good as or in some cases better than with cold wire GTAW (see Figure 1).