High Speed TIG Welding
- September 25, 2018
K-TIG, or Keyhole TIG, is a variant of gas tungsten arc welding (GTAW). Developed by the Australian Government’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), K-TIG is a high speed, single pass, full penetration welding technology that eliminates the need for wire, edge bevelling or skilled operators.
According to Neil Le Quesne, K-TIG CEO, “K-TIG operates exceptionally well across a large array of applications, demonstrating a working speed up to 100 times faster than conventional TIG welding in materials up to 16mm in thickness.”
The process is best suited to lower conductivity materials (such as nickel alloys, titanium alloys, stainless steels), as well as exotic and corrosion resistant materials. It can produce clean, high quality welds on these materials with the added
bonus of penetrative capabilities that far outstrip any other plasma, gas metal arc or gas-tungsten-arc process, explains Le Quesne.
“K-TIG makes light work of longitudinal and circumferential welds across many surfaces, from pipe, plate and spooling, to vessels, tanks and more. All this is achieved without compromising on quality: K-TIG meets the most stringent industry standards, from nuclear and aerospace, to defence.”
Customers range from Global 500 companies such as GE and Siemens, as well as advanced manufacturing development centres.
How K-TIG measures up against TIG welding
Conventional TIG welding uses a melt in process, where surface tension creates circulation in the molten metal, so the heat moves to the sides first, before flowing to the bottom of the weld pool, and then returning to the centre. This process creates a shallow, broad and often turbulent weld pool, with currents restricted to below 250 amps to avoid depression and distortion of the weld pool surface.
K-TIG draws on currents from 320 to 600 amps, with higher currents used for thicker materials, and the process can open and maintain a stable ‘keyhole.’ K-TIG keyholes have extremely high stability, due to the high travel speeds and surface tension in the weld pool. As a result, there is no requirement to seek a balance between arc force (plasma column) and surface tension; the nature of the keyhole surface is such that it naturally and dynamically self-corrects for fluctuations in the arc forces.
K-TIG is capable of welding at up to 1,000 mm/min 39.37 in./min), while TIG reaches speeds of just 300 mm/min 11.8 in./mm (depending on the thickness of the material being welded). Preparation times and costs are also reduced thanks to the low-cost, square butt joint that K-TIG requires.
Penetration TIG has a practical upper limit for single pass welding of 2 mm (68 in.). To weld materials any thicker than this, a V-groove root pass is normally applied, followed by filler passes. K-TIG comfortably performs single pass welds in 16 mm (.62 in.) thick titanium, 13 mm (.51 in.) austenitic stainless steels, Hastelloys, Inconels and a wide range of nickel and cobalt alloys, and 9 mm (.35 in.) in conductive materials such as ferritic steels and carbon steels.
Welding Cycle Times The high energy density keyhole allows single pass penetration of thick materials at very high travel speeds. This means fewer weld passes are needed to complete the job, and the weld passes that are required are performed at high speeds. The low energy density arc of TIG welding offers limited penetration capability, and the root and fill passes are performed at a slow travel speed, resulting in numerous weld
passes accomplished in fairly lengthy welding times.
Distortion The low energy density slow travel speeds and multiple weld passes that are characteristic of a TIG weld make shrinkage and distortion a substantial problem. K-TIG’s high travel speeds, high energy density and single pass penetration, result in remarkably low weld distortion and shrinkage.
Process Consistency TIG produces sound welds in a mechanized mode, although root and multiple fill passes are usually required. Erosion of the tungsten tip and the processes’ sensitivity to arc voltage and other parameters can contribute to process drift in a TIG weld. K-TIG uses a high energy density arc to produce a smooth and consistent keyhole through the joint. This significantly reduces the chances of variation throughout the weld. The process is simple enough, and the electrode is large enough, that erosion (and process drift) are negligible.
Duty Cycle TIG welding systems are typically provided with power supplies of 300 amps to 500 amps, and are only rated for 60 per cent duty cycle. K-TIG makes use of a 1,000 amp power supply, more than required for any keyhole processs, and it is rated for 100 per cent duty cycle.
K-TIG and plasma welding
K-TIG and Plasma Arc Welding (PAW) are both arc welding processes which allow full penetration welding. Both create what is referred to as a ‘keyhole’ through the material being welded, and both use higher currents than conventional GTAW welding. But that’s where the similarities end.
Plasma welding is characterized by the need for highly accurate electrode alignment, frequent maintenance, the need for both plasma and shield gases to form the jet and protect the orifice, very accurate determination and maintenance of flow rates, low keyhole stability, highly precise fitup, and a high degree of operator skill to set up, operate and maintain the equipment.
By contrast, K-TIG is simple to operate. The arc structure and keyhole develop spontaneously and are maintained automatically by the controller throughout the weld. There is no plasma nozzle or orifice, no precise electrode alignment is required, only one welding gas is used, flow rate is not critical, and the torches are very robust.
The welding speed, penetration and productivity of K-TIG is typically twice that of PAW. K-TIG delivers consistent, x-ray quality welds and handles tie-ins easily in circumferential welds, overcoming PAW’s well known difficulties with ties in and tendency to entrap gas voids. K-TIG’s high density arc creates a consistent and smooth keyhole through the joint and its long life electrodes make process drift negligible. SMT