Page 17 - MetalForming March 2010

A Right Way to Grind the Electrode,
and a Wrong Way
1
2
21⁄2 times Electrode diameter
A
B
C
1. Tungsten Electrode
2. Tapered End
Grind the end of tungsten on a fine grit, hard abrasive wheel before the welding. Do not use the wheel for other jobs or the tungsten can become contaminated, causing lower weld quality.
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).
require an external cooler. Con- versely, 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 pro- vide 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
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).
electrode extension gives the welder a clearer look at the joint and arc, allow- ing him to have greater torch control and achieve better weld quality, partic- ularly 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 effi- ciency, 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 param- eters 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
(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, pro- tects 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 suit- ed to the application. Air-cooled mod- els prove useful for low-amperage appli- cations, 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
When possible, use a gas lens to replace the collet body of a stan- dard GTAW torch. A gas 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 cop-
per or brass body that contains a layered mesh of stainless-steel screens. These screens distribute the shielding gas even- ly 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
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