By Clare Goldsberry, Associate Editor

Hot-wire TIG welding combines the repeatability of machine tools with the ability to lay down a large volume of weld metal.

Hot wire TIG welding has been around since the mid-1960s, but it’s just one of those technologies that doesn’t have wide-spread appeal, according to Oszkar Santa, product manager for Jetline Engineering (www.jetline.com). “People usually think hot wire TIG is very unique, probably because it’s not well-known. However, a lot of people in the industry could use it, or they are using it without reaching its full potential and using it in the wrong way.”

Santa explained that hot wire TIG is a good process for increased productivity. It competes with sub-arc welding, and can deposit as much or more material than the MIG process.

“It’s one of those hidden secrets,” said Santa, adding that the quality of the weld it produces is excellent. The biggest advantages are for V-groove or J-groove welds at thicknesses of … in. or more.

“If you have to do more than one pass with cold wire TIG you might benefit from using hot wire,” Santa said, adding that hot wire TIG can weld in three or four passes welds that would require 10 passes to 12 passes with normal TIG or MIG welding.

“Certainly if you’re doing more than three passes. you can benefit from hot wire,” Santa said.

A separate power supply is required to melt the wire, and one for the TIG arc to produce the puddle, so the wire is at its melting point when it reaches the puddle. That reduces the heat input to the base metal.

“Heating up the wire rids it of moisture, so when it enters the puddle it’s free of porosity, clean and the quality is significantly better than cold wire,” Santa said.

The use of hot wire TIG tends to be more part related and industry related. For example, hot wire TIG is used extensively in the transportation and power generation industries. It’s big in shipbuilding, and for rebuilding turbine shafts for large power plants. Hot wire TIG also is used in cladding very large valve welds such as those for oil industry in which welders clad the inside of the valve weld with high-performance alloys.

“It’s easier to put a .125 in. layer of high-performance alloy and to use hot wire TIG to lay this cladding. Most of the time it is used for circumferential joining as it makes for a better fit,” Santa said.

Jetline Engineering has supplied multiple hot wire TIG systems to various turbine manufacturers and nuclear shipbuilding yards worldwide. In shipyards, hot wire TIG has been used for surfacing as well as narrow groove welding. “Using hot wire with a narrow groove –1 in. on pipe that has 1 in. to 3 in. wall thickness – enables the welders there to cut back on their welding time and to increase the inspection passing rate. Instead of opening the groove 45 degrees or 60 degrees, they used a 3 degree to 5 degree angle,” Santa said.

Santa said that hot wire is underutilized because of some of the disadvantages associated with it. “Maybe one of the disadvantages is that you need a welding controller for this process, which has to be more sophisticated than a basic controller. There is the need to precisely control the process when ramping up the wire feed speed while ramping the hot wire volts at the same time from the hot wire power supply. As we’re increasing the hot wire volts, the wire feed speed increases and brings it to its melting point so that it flows into the puddle,” said Santa.

Another company that specializes in hot wire TIG is ARC Specialties (www.arcspecialties.com), which has its niche in the more unusual welding jobs that often require hot wire TIG. The largest portion of the company’s business is the design and fabrication of automatic bore welding machines for valves and fittings that are used in high corrosion environments, said Trey Hoover, technical sales manager for ARC Specialties.

“We have more than 100 machines running in six different countries. With ARC Specialties’ advanced computer control, hot wire TIG is an appealing solution in a number of overlay applications. Our ARC-5P PLC GTAW Vertical Bore Cladding machine is very popular and has several unique features. It comes in different configurations, such as a standard vertical machine, a vertical machine with rotating torch, horizontal machine, or a vertical/ horizontal machine that utilizes an adjustable torch,” Hoover said. All of these GTAW systems use a hot wire power supply designed by ARC Specialties.

“The ARC-5P can weld bores as small as 1 in. and up to 36 in. deep. Our machines also can weld 2.5 in. bores up to 12 ft. deep,” he said. The company uses ESAB and Miller power supplies on most of its ARC-5P units along with a solid state hot wire power supply – the ARC ‘Hot One’ – that is specifically designed by ARC Specialties for this process. The ARC ‘Hot One’ is an independent AC constant voltage power supply that preheats the welding wire before it enters the puddle. That reduces dilution of the weld deposit and increases productivity, Hoover said.

“The CNC version of the ARC- 5P is the ARC-6G that features full automatic welding of ‘racetrack’ and non-cylindrical part shapes including stepped bores and intersecting bores. These machines allow us the opportunity to refine our torches, mechanisms and control systems. Our ARC-5P and ARC- 6G machines have the option to include data,” Hoover said. The data the machine can record includes logging specific welding parameters to providing spread sheet information for quality control.

ARC Specialties has built cladding machines for more than 15 years, and through its research and development lab, it tests new applications and ways to use hot wire TIG and other processes. “We are looking to expand applications for hot wire TIG, and for improvements in the process itself,” Hoover said.

Information Advantages of Hot Wire TIG: High deposition rate (16 pounds per hour has been achieved in flat position and 3 pounds per hour has been achieved in horizontal positions.) Better control of heat input Reduced dilution How It Works: AC Constant Voltage Power Supply is connected between the wire contact tube and the work piece. Using the AC Power Supply minimizes magnetic interference of the main arc. The power supply electrically heats the wire before it reaches the puddle. Wire is fed into the weld puddle immediately behind the arc. Information supplied by ARC Specialties.