The beauty of TIG

A close up of a TIG torch melting the base element and the filler material. PHOTO COURTESY OF MILLER ELECTRIC MFG. CO.

If you have ever welded using the TIG welding process you will know of the elegance of the technique. The process involves using a special tungsten needle to focus heat energy onto the work piece while a slender piece of filler metal is dabbed into the weld puddle. It is properly known as Gas Tungsten Arc Welding (GTAW) and colloquially as Tungsten Inert Gas (TIG). “TIG welding is accomplished through constant current power sources that maintain a relatively constant welding output (heat) that is emitted from a tungsten electrode that is contained in a TIG torch connected to the power source,” says Ivan Gracic, product manager – TIG Process Solutions from The Lincoln Electric Company.

“DC TIG welding emits a majority of the current away from the tungsten towards the work piece, whereas AC TIG welding applications have the current shift directions during every one cycle of the wave, helping break away surface oxide layers on Aluminum and Magnesium base materials.”

It’s a very precise process able to accurately weld tiny and thin objects as well as very large parts. “The TIG welding process is able to produce the highest quality welds—clean and sound—and it’s also a very versatile process in terms of application because it can be used for virtually any metal and in a range of metal thicknesses, with or without a filler metal,” says Jay Ginder, Sr. application engineer/CWI, CWE at ESAB Welding & Cutting Products.

“As a result, TIG welding is used in a broad scope of industries from aerospace to nuclear/power plant construction to automotive for jobs that demand a high integrity weld and/or an aesthetic surface finish that doesn’t need grinding. Aluminum and stainless steel applications are the most common for this process. Because the TIG process gives you more control over the weld, it is also ideal for welding more challenging materials such as titanium and Inconel.”

The precision and quality offered by TIG welding is the main reason why a manufacturer would choose to use this process in its facility. “If the application demands the absolute highest degree of weld quality, to be proven through non-destructive evaluation, TIG is often the best choice,” notes Devan DePauw, welding engineer, TIG System Solutions at Miller Electric Mfg. Co.

“When equipped with a modern, high-quality TIG power source, an experienced welding operator can work on nearly any weldable metal using only a single variety of tungsten electrode and pure argon as a shielding gas. All they must acquire is the appropriate filler metal.”

Suppliers offer a wide variety of filler materials available to them and exotic metal alloys can be welded without too much fuss by an experienced welder by using the base metal as filler.

“Another advantage to TIG welding is that it can be accomplished with or without a filler metal (this is known as autogenous welding),” says Ginder. “Autogenous welds melt one part to the other, usually used in thinner materials and for smaller-scale applications (like medical devices, electrical components).

“Modern TIG welding machines also take the versatility and capability of TIG a step further, providing more control over weld parameters. Today’s inverter-based TIG machines are lighter and more portable than SCR technology, making them suitable for onsite and offsite use. If the goal is a high quality weld with no contaminant and/or if you have an application that can’t handle any extra oxygen in the weld, then the TIG process is the cleanest process.”

The heat input from the welding torch is precisely controlled by the operator, usually using a foot controller that operates like the clutch on a car. Hand controls are also available. The heat and the position of the weld can be accurately manipulated. “As the operator has a greater degree of control over the weld, precision welding applications that require minimal material distortion, high cosmetic properties, and the elimination of welding spatter, rely upon TIG welding,” says Gracic. “Other processes such as MIG, or even Stick, often can require post welding clean-up and also more challenges with respect to managing heat input in comparison to TIG.”

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The aesthetics of a finished TIG weld are quite beautiful—as far as welds go. “There is just no mistaking the pleasing uniformity of a well-executed TIG weld,” says DePauw. “This process not only creates the appearance of high weld quality, but also can be used successfully to enhance the visual appeal of a precision part or assembly.”

One can use the saying, “if it looks right—it is right” to describe TIG welding in this case. The neat appearance does signify a high quality weld. “The high surface finish that’s achieved with TIG makes it the process of choice for the auto racing industry and for architectural fabrications,” notes Ginder. “Beyond the procedures and codes that dictate using the TIG process, choosing to use this process depends largely on the material you are welding and the speed at which you’re welding.”

Generally speaking, TIG is known as a handheld process, with a highly skilled operator working the torch, filler material and foot control in a welding ballet. “The GTAW process has been automated for quite some time,” says Ginder. “Automated TIG welding has received more attention of late because shops are looking for ways to increase productivity and address the shortage of skilled welders.

Cold wire TIG—feeding the wire from a wire feeder—is a process that can be semi-automatic (or, handled manually). Recently, we are also seeing more hot wire TIG welding. In this process, the wire is heated before it goes into the weld. This increases productivity because of the higher burn-off rate and subsequent higher speed that can be achieved. Hot wire TIG is usually automated, and the development of automated and specialized equipment for hot wire TIG has helped give it more visibility.”

The weld process can be automated using seamers and multi-axis robots. “TIG Welding can be automated, where a robotic arm manages the TIG Torch and a separate wire feeder unit deposits filler metal into the weld puddle,” says Gracic. “This results in increased throughput, while at the same time managing quality standards that are often required when TIG welding.”

Manufacturers are creating power sources to adapt to different types of TIG welding and incorporating features that will make them adaptable to automation.

There is a bit of price to pay for having a welding process that is simultaneously of high quality and aesthetically pleasing. A high skill set is needed to consistently lay down proper TIG welds. “TIG has often been known to be considered one of the most challenging welding applications to manage from a skill level perspective,” says Gracic. “It is for this reason, that manufactures often have difficulty finding skilled and experienced TIG welders in industry.”

Not just high skill is needed. Proper TIG welding takes time. “The manufacturer integrating TIG welding into his production facility has to know that there is a productivity trade off. The high quality weld that results from TIG welding takes more process time and this impacts the cost of manufacturing,” explains Ginder. “The TIG process is much slower than other welding processes and could even be slower than Stick welding, depending on the stick electrodes.”

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TIG welding is a very specialized process and should be only used where the benefits of this type of welding are appropriate. “Successful implementation of the TIG process requires an understanding of its advantages and limitations. The ideal TIG welding operator will be knowledgeable regarding the many adjustable machine parameters that are within his or her control, especially on modern inverter equipment,” says DePauw. “Of course, a high quality TIG power source is critical, but so too is the quality and integrity of the consumables that are used along with it. Production losses tracing back to a faulty collet or missing O-ring can be costly and frustrating. Providing the appropriate training, when necessary, is also critical.”Due to its process, TIG welding gives the welder the most control over the weld. “Inverter-based welding equipment gives the welder greater control over the process with better control over the AC arc and heat, more programmability through advanced controls, faster travel speeds,” says Ginder. “This translates to more consistent welding results, less time to weld, less weld clean up. Where this is especially impactful is in challenging aluminum welding applications because more capable TIG welding equipment makes it easier and more cost effective to weld aluminum.”

The inverter based TIG welding power sources are more prominent and are the result of higher powered semiconductors. The net result is the power sources have become smaller and quite portable because of the smaller step down transformer needed in these machines. “In the past few years, the industry has witnessed the continued advancement of inverter TIG power sources and peripheral accessories. The best of these power sources offer vast out-of-the-box feature sets, which can include independent adjustment of the AC wave and DC pulsing frequencies up to 5kHz, as well as software that is easily updated and expanded through the use of a common SD card,” said DePauw. “Advances in TIG torch design have also allowed for the manufacture of 375A water-cooled torches that are only marginally larger than those rated for only 250 amps, thereby providing optimal cooling for longer, more comfortable welding and increased productivity.”