6. How can you prevent tungsten contamination and discoloration?
Allowing the tungsten to touch the weld pool is one of the most common causes of contamination. This problem can be resolved by moving your torch farther away from the workpiece, which in turn lengthens the arc. Touching the filler metal to the tungsten also can be a source of contamination, but there is no clear solution to this problem other than practice; trial and error will determine your best technique. If you feel your technique is not the culprit of tungsten contamination or discoloration, check to see that you have adequate gas flow and allow adequate postflow time as well. Permit several seconds of postflow (about 1 second for every 10 amps of weld current). Finally, you may want to consider using a power supply that offers high-frequency starts if you think using the scratch-start method is causing the contamination.

7. What causes porosity in a GTAW bead, and how can you prevent it?
A loose hose or torch component is a primary cause of porosity. It is remedied by tightening the fittings. If you cannot find loose hose connections by doing a visual check, you might want to place the hose in soapy water until you find the leak and tighten the fittings accordingly. Using the wrong shielding gas or one that has impurities also can lead to porosity. This is remedied by using pure argon after using nitrogen to purge the line of air and any condensation that may have accumulated. Drafts from fans or open doors also can lead to porosity, so be sure that your working environment is well isolated from drafts, or use a gas lens to provide better gas coverage. To prevent porosity caused by inadequate shielding gas flow, follow the recommended flow rate, which is approximately 10 to 20 cubic feet per minute (CFM) depending on the application. Doing so helps ensure quality welds.

8. What type of tungsten should you use?
The four main tungsten choices for GTAW are 2 percent thoriated tungsten, pure tungsten, 2 percent ceriated tungsten, and 1.5 percent lanthanum tungsten. Two percent thoriated tungsten is a good choice when using a DC power source because it maintains a pointed shape, resists melting, and has a high current-carrying capacity. When welding thin aluminum (0.09 inch or less) thoriated tungsten is also a good alternative to pure tungsten because it creates a more focused arc. It is recommended that thoriated tungsten be used in a properly ventilated area and measures be taken during preparation to capture dust from grindings. Pure tungsten performs well when welding aluminum, using a conventional AC power source. Two percent ceriated tungsten is a good alternative to thoriated tungsten and provides good arc starts at low currents, along with greater arc stability. This type of tungsten is recommended for aluminum AC welding with an inverter-based power source. Last, 1.5 percent lanthanum tungsten is most commonly used for applications in which long weld times and multiple arc restarts are necessary

9. How do I solve high-frequency interference problems?
Malfunctioning electrical equipment (such as computers, telephones, and radios) is often a sign that you are experiencing high-frequency interference from your welding power source. To remedy such high-frequency interference, start by verifying that the power source is grounded according to the installation instructions provided in the operator's manual. Keep your torch cables and work cables as short as possible, and place them close together. Physically separating your welding equipment from devices that may experience interference is also an option, but doing so can be time-consuming and space-prohibitive. If all else fails, you could switch to an inverter-based power source that provides a high frequency for arc starting only.

10. What are the cause and solution for arc rectification?
Arc rectification occurs when the surface oxide of a nonferrous metal acts as a barrier, making it more difficult for electrons to flow from the workpiece to the tungsten than from the tungsten to the workpiece. Excessive arc noise, unstable weld pools, or a weld pool that appears to dry up are all signs of arc rectification. You can either increase your travel speed or decrease the amperage for the application. Another option is to adjust the balance control on your power source toward electrode negative, which provides more penetration. As a last resort, switch to an inverter power source that offers advanced square-wave technology.

Miller Electric Mfg. Co.