How to Solve 10 Common TIG Welding Problems [Guide] | MillerWelds

How to Solve 10 Common TIG Welding Problems [Guide]

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Learn about common mistakes when TIG welding as well as basic tips on how to prevent these errors.
TIG Welding a bumper

TIG welding mistakes and solutions

Gas tungsten arc welding (GTAW), or TIG, is often specified to meet strict aesthetic, structural or code/standard requirements. The TIG process is complex, and it is undisputedly the most difficult process to learn. This article contains photos and descriptions of common TIG mistakes and basic tips on how to prevent these errors from happening.

1. Poor gas coverage leads to contamination

The weld here shows contamination caused by lack of shielding gas, which can happen when the shielding gas is not turned on, there is either too little or too much gas shielding, or the gas is blown away.

  • To troubleshoot gas contamination issues, check the gas cylinder label to be sure you’re using the right type of gas for TIG welding, generally 100 percent argon (or perhaps an argon/helium blend for thick aluminum). Attempting to weld with an argon/carbon dioxide mix (commonly used for MIG welding) will cause immediate contamination.
  • Set the proper gas flow rate, which should be 15 to 20 cubic feet per hour (cfh). Welders commonly — and incorrectly — assume that a higher gas flow/pressure provides greater protection. In fact, excessive gas flow creates turbulence and swirling currents that pull in unwanted airborne contaminants (and it can cause arc wandering). Generally, err on the lower side of recommended shielding gas rates to ensure proper shielding coverage without turbulence.
  • Check all the fittings and hoses for leaks. Any breach may pull air into the shielding gas stream, which can cause the weld to be contaminated (and you’ll waste money if gas escapes). Rub soapy water over the hose and all fittings. If bubbles form, you have a leak and need to replace the defective components.
  • Assuming you have a full cylinder, the right type of gas and no leaks, consider that you may have a tank contaminated with moisture. Shielding gas cylinder contamination does not happen frequently, but it is possible. Check with your gas supplier to resolve this issue.
Figure 1: Poor gas coverage leads to contamination

2. Welding aluminum in the wrong polarity/adjusting balance

This TIG weld (Figure 2A) was created with the machine’s polarity set on direct current electrode negative (DCEN). As you can see, the weld did not break through the aluminum oxide layer. This created a weld where the filler metal mixed in with the partially melted oxide and created the contaminated bead seen here. To defeat this, always TIG weld aluminum with the polarity set to alternating current (AC). 

TIG welding in AC (Figure 2B) allows the electrode positive (EP) portion of the cycle to blast away the aluminum oxide while the electrode negative (EN) portion melts the base metal. A feature called AC balance control allows operators to tailor the EP to EN ratio. If you notice a brownish oxidation or flakes that look like black pepper in your weld puddle (Figure 2C), increase the cleaning action. However, note that too much EP causes the tungsten to ball excessively (Figure 2D) and provides too much etching. Lastly, when TIG welding aluminum, do not start welding until the puddle has the appearance of a shiny dot. This indicates that the oxide has been removed and it is safe to add filler and move forward. Adding filler to the weld zone before the oxide layer is adequately removed will result in contamination.

Figure 2A: Aluminum welded in DC with argon

Figure 2B: Ideal aluminum weld

Figure 2C: AC balance set too high

Figure 2D: balled tungsten

3. Weld graininess

Figure 2B shows the way an aluminum TIG bead should look. Figure 3 shows a bead with a grainy appearance, which is typically caused by filler metal problems. For instance, a 4043 aluminum filler rod from one manufacturer may have different properties than a 4043 rod from another manufacturer. The welder (if the application permits) may need to adjust filler brand accordingly. The rod may also be defective (too much of a certain ingredient). The welder may even have the wrong type of filler rod, such as 4043 filler instead of 5356 filler.

Prior to welding, always check the filler metal type and remove all grease, oil and moisture from the surface to prevent contamination.

 Figure 3: Grainy aluminum weld

4. Lack of fusion in the root

Lack of fusion at the root of a T-joint or a fillet weld can be caused by a number of factors: improper fit-up, holding the torch too far away from the joint (increasing arc length) and improperly feeding the filler rod, to name a few. This issue may be seen more often with a transformer-based machine, as the arc tends to wander between the two sides of the joint as it seeks the path of least resistance. In this case, reducing arc length will provide better directional control and help increase penetration. It is also important not to under-fill the joint or weld too quickly.

Note that inverter-based machines (especially those with advanced output controls such as adjustable frequency and pulsing controls) offer more control over the arc. These controls create a narrower, more focused arc cone that provides better directional control over the weld puddle and deeper penetration (and often at increased travel speeds).

 Figure 4: Lack of fusion in the root

5. Craters

Craters, such as the one shown in Figure 5A, typically occur at the end of the weld, and they often lead to cracking. Causes include instantly reducing the welding power (which causes the puddle to cool too quickly) and removing the filler rod too quickly at the end of the weld. You can easily fix crater cracking issues by continuing to feed filler rod while slowly reducing current at the end of a weld. Note that some TIG welders feature a crater control function that automatically reduces the current at the end of a weld. The result is a good-looking weld bead, as seen in Figure 5B.

 Figure 5A: Poorly filled weld craters

 Figure 5B: Weld crater filled

6. Dirty base and/or filler metal

One of the first things you should have learned about welding is to clean materials prior to welding. This photo (Figure 6A) shows what happens when you don’t clean the mill scale off hot-rolled mild steel. All base and filler metals need to be cleaned, whether the contaminant is mill scale, oxide on aluminum or dirt and grease on filler metals. Grind, brush and wipe away all potential contaminants. For cleaning aluminum, dedicate a stainless steel brush to the task to prevent contamination from other metals.

Figure 6B shows what happens when a weld on mild steel has been properly cleaned before welding. Figure 6C shows a weld made on chrome-moly tubing that has not been cleaned, while Figure 6D shows a weld made that has been cleaned prior to welding.

Figure 6A: Uncleaned steel weld

Figure 6B: Clean steel weld

Figure 6C: Uncleaned Chrome Moly

Figure 6D: Cleaned chrome moly

7. Poor color on stainless

Figure 7A shows discoloration on a stainless steel weld caused by overheating, which not only affects a material’s color but degrades its corrosion resistance and mechanical properties as well. Unfortunately, once this error is made, there is nothing that can be done to fix it except for scrapping the part and starting over. To prevent overheating, reduce amperage, slightly increase travel speed or shorten the arc length. If your welding equipment features pulsed welding capabilities, now is the time to learn how to use them. Pulsing reduces heat input, and it offers excellent control of the weld puddle. Figure 7B shows proper coloration of stainless.

Figure 7A: Poor color on stainless steel

Figure 7B: Good color on stainless steel

8. Sugaring on stainless steel

Figure 8 shows sugaring on the backside of a stainless steel weld. Sugaring (oxidation) occurs around the weld when it is exposed to oxygen in the air. The best way to prevent sugaring is to back purge the weld with argon shielding gas or reduce welding amperage.

Figure 8: Sugaring on stainless steel

9. Too much amperage on aluminum

Figure 9A shows what a weld bead looks like on aluminum with the amperage set too high. This creates a wider profile, an ill-defined bead and can potentially lead to burn-through. To solve this problem, reduce amperage and/or increase travel speed. Reference back to Figure 2B to identify an ideal weld.

Figure 9: Excessive amperage/heat input

10. Proper arc length control

The color change in the middle of this aluminum weld bead (Figure 10) resulted from an increase in arc length. Arc length, which is the distance between the electrode and the base metal, determines TIG welding voltage. Holding too long of an arc increases overall heat input and the potential for distortion, widens the weld bead while decreasing penetration, and affects weld bead appearance. Practice holding a consistent arc length to improve heat input control and improve weld bead quality.

Figure 10: Change in arc length

This article originally appeared in The Fabricator Magazine and is shared with permission.