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Tips for Improving Gas-Tungsten-Arc-Welding Productivity

By: Jack Fulcer

ack Fulcer is marketing and product manager, Weldcraft, Appleton, WI: tel. 920/882-6800, www.weldcraft.com.

Monday, March 01, 2010
 
By its very nature, gas-tungsten-arc welding (GTAW) is a
Tips for Improving Gas-Tungsten-Arc-welding productivity
relatively slow process. But it also is a very versatile one. In fact, it can be used to weld more materials than any other process, even exotic and heavier alloyed metals. It’s also ideal for thin materials, as it results in a relatively low amount of heat input, to prevent burnthrough. Plus, no matter the application, when performed properly GTAW can provide extremely high weld quality.

Achieving such positive results, however, isn’t als easy—success is as much a matter of training and practice as it is simple patience. Fortunately, arming yourself with a few tips along the can help you greatly improve the effectiveness of the process. After all, you don’t want an already slow welding process to become even slower.

Tip #1: Invert the Process

Using an inverter power source is one of the first steps a metalformer can take to improve GTAW efficiency. Inverters operate by switching high-voltage low-amperage alternating current (AC) into direct current (DC) back and forth at a very high

Right  to grind the electrode,and a wrong
Grind the taper on the tungsten-electrode tip to a distance no more than 2.5 times the
electrode diameter (A). For example, using a 1⁄8-in. electrode, grind a surface 1⁄4 to 5⁄16 in. long. This tip design will ease arc starting and help create a more focused arc. And, don’t grind circumferentially (C); grind longitudinally (B).
rate of speed—up to 50,000 times/sec. The overall result is a smooth arc that provides consistent welding performance.

Inverters also have frequency controls that allow the welder to determine the length of time that it takes the unit to complete one full current cycle (the combined time spent on electrode positive and electrode negative), and to adjust the frequency from 20 to 400 Hz. (Note: transformer-based power sources only produce an output of 60 Hz, the same frequency that comes from a wall power receptacle).

The inverter’s frequency feature helps improve welding efficiency by narrowing the focus of the arc, creating a narrow weld bead and minimal heat-affected zone (HAZ). With this feature, welders will spend less time and consume less filler metal completing each weld. And, a smaller HAZ minimizes the likelihood of burnthrough and the need for rework—a definite cost saver in any welding application.

Inverters also feature a balance control, which allows the welder to adjust how long the current spends in each part of the AC cycle—particularly useful when welding aluminum. He can adjust the balance control more toward the electrode-positive portion of the cycle, which helps to remove the oxide layer on the aluminum workpiece (referred to as “cleaning action”), or more toward the electrode-negative portion of the cycle, which increases weld penetration and travel speed.

Tip #2: Stay Cool and Flexible

Selecting the right GTAW torch for the application also can help make the process more efficient. First, select a torch with good insulation. Silicon-rubber insulation, for example, protects against high-frequency leakage and cracking that can lead to premature torch failure and downtime for torch changeover.

Also consider whether an air- or water-cooled GTAW torch is best suited to the application. Air-cooled models prove useful for low-amperage applications, below 200 A, for welding materials less than 3⁄16 in. thick, or for shops where welders tend to move around a lot, since these torches do not require an external cooler. Conversely, consider a water-cooled GTAW torch for applications in excess of 200 A. These torches help prevent overheating and allow welders to achieve faster travel speeds.

When selecting a GTAW torch, also consider the angles at which the welders must weld, since maneuvering around difficult joints can be time-consuming, not to mention uncomfortable. Most GTAW-torch manufacturers offer models with flexible necks that make the job easier in awkward positions.

Some torch-body styles also feature a modular design, which allows the welder to add a flexible neck and different head angles to an existing torch. These kits provide good joint access and can lower downtime associated with changing over different torches for multiple applications. Plus, you can save money on extra inventory.

Tip #3: Cover Yourself

When possible, use a gas lens to replace the collet body of a standard GTAW torch. A gas

Adding gas lens
Adding a gas lens to the GTAW torch (left) provides for an even flow of shielding gas when compared to a torch without a gas lens (right).
lens helps hold the tungsten in place and creates the electrical contact necessary for proper current transfer. It also provides two other functions that can help improve efficiency: It improves shielding-gas coverage (see photos) and improves weld-joint accessibility.

Gas lenses typically consist of a copper or brass body that contains a layered mesh of stainless-steel screens. These screens distribute the shielding gas evenly around the tungsten electrode and along the weld puddle and arc to help prevent oxygen contamination that could lead to weld defects. As in any welding application, minimizing defects and their associated rework ensures that the welder can spend more time in production and less time fixing defects.

Gas lenses also allow the welder to extend the tungsten electrode further out from the nozzle. This additional electrode extension gives the welder a clearer look at the joint and arc, allowing him to have greater torch control and achieve better weld quality, particularly on critical applications or in hard-to-reach areas such as T, K and Y joints.

Gas lenses—which can be used with any shielding gas and are available for air- and water-cooled torches—also prove particularly helpful when welding on alloys highly reactive to atmospheric contaminants or for materials used in high-temperature applications.

Tip #4: Less can be More

Taking steps to prevent overwelding will significantly improve GTAW efficiency, and save money. Overwelding occurs when the welder deposits more weld metal in a joint than is required to obtain the necessary weld strength. It often results from poor joint fitup or preparation, improper welding parameters or from simple overcompensation —the welder believing that he needs more weld metal to fill the joint than is necessary.

Overwelding wastes shielding gas and filler metal, and increases welding time. For example, overwelding a fillet weld by a mere 1⁄16 in. can increase arc-on time by as much as 36 percent for a 3⁄8-in. fillet weld and 125 percent for a 1⁄8-in. weld. In addition, overwelding increases the amount of heat input into the base material, raising the risk of burnthrough or distortion and leading to costly and time-consuming rework. It may even increase the need for grinding and finishing.

To prevent overwelding, avoid over-designing weld joints–do not use a larger joint than is necessary to gain the appropriate strength for the application. A good rule of thumb: Make the leg of a fillet weld no wider than the thickness of the thinnest workpiece, and weld accordingly. For example, when joining a 1⁄8-in. thick plate to a ¼-in. plate, a 1⁄8-in. weld bead suffices.

Also, know the size of the joint being welded. When in doubt, don’t guess—use a fillet gauge.

Lastly, proper joint preparation and tight fitup provide good defenses against overwelding, as does welding in the vertical-down position on thin materials.

Tip #5: Get to the Point

The type of tungsten used—which depends on the kind of power source selected and the type of material being welded—as well as the shape of the electrode tip can significantly impact process efficiency.

For AC and DC welding using an inverter power source and either a ceriated, lanthanated or thoriated tungsten electrode, grind the electrode to create a pointed or truncated tip. This provides the stable arc needed to achieve good welding performance and quality, while preventing contamination or arc wandering. To achieve this shape, grind the tungsten on a borazon or diamond grinding wheel specially designated for the job. Next, grind the taper on the electrode tip to a distance no more than 2.5 times the electrode diameter. For example, using a 1⁄8-in. electrode, grind a surface 1⁄4 to 5⁄16 in. long. This tip design will ease arc starting and help create a more focused arc.

When welding with low amperage on thin materials (0.005 to 0.040 in. thick), grind the tungsten to a point. This allows welding current to transfer in a focused arc and helps prevent distortion. In particular, a pointed, ceriated tungsten electrode works well when welding aluminum, as it provides 30 to 40 percent more amperage capacity than does pure tungsten before it begins to melt. Note: Do not use a balled tungsten-electrode tip for such an application.

On higher-current applications, grinding the tungsten to a truncated tip can help improve welding performance by preventing the tungsten from balling. First grind the tungsten to a taper (as explained above), then grind a 0.010- to 0.030-in. flat land on the end of the tungsten.

Note: When grinding thoriated tungsten, be sure to control and collect any grinding dust, provide operators with an adequate ventilation system at the grinding station, and follow any manufacture’s warnings, instructions and material-safety datasheets. MF

 

See also: Weldcraft

Related Enterprise Zones: Welding


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