Gun Control: GTAW torch design innovations enhance productivity, quality

THE FABRICATOR® NOVEMBER 2001

November 15, 2001

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This article discusses improvements to the GTAW torch that should enhance the productivity and quality of welding operations. It specifically discusses the welding gun's affect on ergonomics and cooling capacity.

Gas tungsten arc welding was developed during World War II to join hard-to-weld alloys such as zirconium, titanium, and aluminum. Later it proved to be equally successful on carbon, alloys, stainless steel, and other ferrous and nonferrous metals. Today GTAW is used heavily in the military, nuclear, aerospace, chemical processing, medical, motorsports, commercial aircraft, and decorative fabricating industries.

While GTAW can be used to weld a range of metal thicknesses, it is best-suited for welding thin metals in applications with exacting requirements for quality and finish. Although filler metal typically is not added in GTAW of thin materials, it may be added either manually or automatically.

In the GTAW process, an electric arc is struck between a nearly unconsumable tungsten or tungsten-alloy electrode and the workpiece. The heat of the arc causes the edges of the metals being welded to flow together. During the welding cycle, the weld area is shielded by a blanket of chemically inert helium or argon gas. A steady stream of this gas pushes the air away from the welding area and prevents oxidation of the electrode, weld puddle, and heat-affected zone.

The Impact of Torch Design

The main drawback with GTAW is its high labor cost, particularly when compared to gas metal arc welding. The average training period for a gas metal arc welder generally is 30 hours or less, whereas a gas tungsten arc welder commonly requires 70 to 80 hours of training.

Therefore, a major element of controlling GTAW costs is to improve the welder's productivity. The key is to improve time usage, often achieved by increasing convenience and reducing human fatigue. The welding torch's design can have a major impact on these areas.

Until recently the commonly used water-cooled 20-style (250-amp) and 18-style (350-amp) torch designs had changed little. Recent changes in GTAW torches have taken three main paths:

1. Redesign of the conventional torch

2. Upgrade of the components and construction materials

3. New torch designs to create new GTAW applications

Redesigned Torches

The first path redesign has focused on improving the torch's ergonomics and increasing the torch's cooling capacity to handle higher arc current without changing torch size.

Ergonomics. An ergonomic design provides comfort for the welder, reducing fatigue and rework and thus helping to improve weld quality. For example, some redesigned torches with higher cooling capacities have a noncylindrical handle, which is a departure from the traditional cylindrical style. The handle has a flat top where the welder grasps it, which means the welder may know arc direction at all times solely by feel. This design change can help prevent misdirected arcs, which produce weld defects such as undercut and can cause even more serious defects if they miss the root entirely.

Although the new design has a traditional friction fit, it is fixed and cannot rotate, unlike many traditional torches. This fixed torch eliminates any downtime or manual injury that might be caused by the rotation.

Cooling Capacity. Arc current is limited mainly by the inability to remove heat from the torch components. Because higher currents are more likely to provide full-penetration welds, which are a necessity in quality welding, the ability to remove the heat generated by these higher currents is a key operational issue.

Figure 1:
This torch, with a 90-degree, low-profile torch head and a 5-degree extension, works the bottoms of engine ports in a 900-cc motorcycle engine.

Inadequate heat removal may reduce or limit weld quality. This issue is particularly important when using alternating current power to weld aluminum — a common GTAW application — because AC transfers half the heat to the torch and half to the work. This generates more heat in the torch than during traditional direct-current straight-polarity welding. To address this problem, newer power supplies offer AC balance and arc-controlling characteristics that reduce heat input to the torch, thus increasing overall torch efficiency.

When a torch exceeds its amperage rating and overheats, the operator experiences discomfort and risk. It also can damage the torch's seals, insulation, and other key components.

Two of the new torch designs, no larger than traditional 20- or 18-style models, have cooling systems and water chambers that allow them to achieve a maximum current of 310 and 410 amps, respectively, at 100 percent duty cycle.

Most designs on the market today fight heat by employing silicon rubber as insulation material rather than the traditional glass-reinforced phenolic insulation, as well as Teflon® gaskets for tight, easily replaceable seals.

Silicon rubber is temperature-resistant to 500 degrees F. It is highly resistant to ozone, corona, radiation, moisture, flame, and chemicals. In addition, both silicon rubber and Teflon have excellent dielectric strength and arc resistance. Silicon rubber is also resilient. It does not readily chip or crack, and it allows operators to bend the torch neck occasionally to fit the application. However, bending the torch too often can weaken and break its internal copper tubes.

Figure 2:
Flexible-head GTAW torches allow welding in hard-to-reach places, such as the underside of a car.

Upgraded Torches

Some existing GTAW torch models have been upgraded with new components. Integrated switches for controlling welding current, for instance, have been common in Europe and Asia, and they now are appearing in the U.S. as more digital power supplies are put into service. Handles with integrated switches locate arc adjustment at the welder's fingertip. Simple one- or two-button, low- and high-voltage switch handles are available for both international and domestic power supplies.

New Torch Designs

All-new torch designs also are available. For instance, microsize, pencil-shaped GTAW torches can fit into small areas and deposit very small amounts of material. In one application, one of these torches configured with a 90-degree head and a 5-in. extension was used to reach into a small cylinder opening and weld-deposit 0.3 in. of aluminum (see Figure 1).

Another new design is the flexible-head torch (see Figure 2). This design was used to reduce the depth of a 4-in.-dia., 7-in.-deep cavity in an H13 steel mold that could be accessed only by a torch that could reach around a corner. With the flexible-head configuration, the torch reached easily to the bottom of the mold cavity, allowing accurate application of additional H13 hot-work tool steel to reduce the dimension by the required 1/8 in.

The Bottom Line

Many factors influence a welder's productivity. These often are specific to the company and the application. However, today's efficient, welder-friendly GTAW torches also can have an impact on a welder's productivity and, thus, a shop's bottom line.



Harshad Shah

Contributing Writer

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