11.4 GTAW Operation and Welding Techniques
Karl Fulton
Cleaning and fit up
Cleaning and proper fit up are critical for all welding but it is accentuated with GTAW. Here are the tools and techniques recommended for cleaning.
Sanding disk or belt sander: his is great for removing mill scale from mild steel. Not recommended for aluminum or stainless.
Stainless steel wire brush: You will want to have one of these for each type of metal you weld. Label them with the material you have designated them for and only use them on that material. This will prevent cross-contamination.
When wire brushing your material, only brush in one direction and all the way off the material if possible. When brushing aluminum, you will want to break through the oxide layer. You will know when you have done this when it starts to feel gummy as you brush the material.
Acetone: Wipe down parts to be welded with acetone and a lint free rag to remove any oil or other unknown contaminates from the surface of the metal. You may also want to wipe down your filler rod. It may be surprising how dirty your filler will be.
Fit-up: As with all welding processes, the fit-up is critical. Most of the time, you will want the joints to be as tight as possible. The exception to this rule would be for an open root butt weld where 100% penetration is required. You will want to refer to your WPS for restrictions but to practice, you can adjust this in a few ways. You can bevel your parts to a knife edge that is where the bevel continues all the way to the edge. When using this technique, you will want the joints to be very close. You can also put a landing on the end of your bevel. This end of the bevel has a small flat spot to create a little thicker material for you to weld with a gap. The land and the gap between your parts should be about the same size as your filler rod.
Make sure your parts are tacked up in multiple spots before welding to reduce the possibility of the joint separating as you introduce heat and tension from the weld. This is very important, no matter the weld joint you are doing. The tension will increase in the direction you are welding.
For a fun experiment, weld a butt joint from one side to the other without tacking the side you are welding to. You will probably see the two parts pull themselves together or even overlap.
Feeding the filler rod.
Here are three options to try but find a technique that works best for you. The idea is to keep your hand the same distance from the molten puddle the entire time you weld as you feed the filler through your hand.
Push with your thumb: Good for slower ace welding.: Set your hand on the table, palm facing up. Put the filler rod in the crux between your palm and thumb and between your ring and middle finger. Use your thumb to push the rod forward.
Pulling forward with your Fingers: Gives you a longer stroke for faster welding.
Palm up, rod between thumb and palm, and ring and middle fingers. Squeeze the rod with your thumb to hold it in place. Collapse your fingers to make a fist then with your fingers, pull the rod forward as you release with your thumb. Repeat.
The bunny ears: Great for vertical welding. Hold filler with pinky, ring finger, and thumb. Then, push the filler down with your middle and index fingers.
GTAW welding fundamentals for ferrous metals
Mild steel
Using sharp tungsten, set the power source to DCEN (straight polarity). Current (amps) should be set high enough to establish a puddle within two to three seconds of striking your arc. Dip the tip of the filler rod into the puddle and move the arc forward. It is very important to remember to use the molten puddle to melt the filler rod and not the arc.
The puddle is what melts your filler. When you terminate your weld, you will want to ease off the pedal slowly and fill your crater. Once the arc is extinguished, hold the torch where it is for the duration of your post flow. Do not move or even lift up your welding hood. This will disrupt your post flow as the weld is cooling.
The end result should be a uniform weld with slight convex reinforcement. You do not want a concave weld.
Stainless steel (S.S.)
| Metal Gauge | Joint Type | Tungsten Size | Filler Rod Size | Cup Size | Shield Gas Flow: Type, CFH,
(L/MN) PSI |
Welding Amperes | Travel Speed |
|---|---|---|---|---|---|---|---|
| 1/16”
(1.6mm) |
Butt | 1/16”
(1.6mm) |
1/16”
(1.6mm) |
4, 5, 6 | Argon, 11 (5.5), 20 | 80-100 | 12”
(307.2mm) |
| 1/16”
(1.6mm) |
Fillet | 1/16”
(1.6mm) |
1/16”
(1.6mm) |
4, 5, 6 | Argon, 11 (5.5), 20 | 90-100 | 12”
(307.2mm) |
| 1/8”
(3.2mm) |
Butt | 1/16”
(1.6mm) |
3/32”
(2.4mm) |
4, 5, 6 | Argon, 11 (5.5), 20 | 120-140 | 12”
(307.2mm) |
| 1/8”
(3.2mm) |
Fillet | 1/16”
(1.6mm) |
3/32”
(2.4mm) |
4, 5, 6 | Argon, 11 (5.5), 20 | 130-150 | 10”
(256mm) |
| 3/16”
(4.8mm) |
Butt | 3/32”
(2.4mm) |
1/8” (3.2mm) | 5, 6, 7 | Argon, 13(6) , 20 | 200-250 | 12”
(307.2mm) |
| 3/16”
(4.8mm) |
Fillet | 3/32”
(2.4mm) 1/8” (3.2mm) |
1/8” (3.2mm) | 5, 6, 7 | Argon, 13(6) , 20 | 225-275 | 10”
(256mm) |
| 1/4”
(6.4mm) |
Butt | 1/8” (3.2mm) | 3/16”
(4.8mm) |
8, 10 | Argon, 13(6) , 20 | 275-350 | 10”
(256mm) |
| 1/4”
(6.4mm) |
Fillet | 1/8” (3.2mm) | 3/16”
(4.8mm) |
8, 10 | Argon, 13(6) , 20 | 300-375 | 8”
(204.8mm) |
Note: This table is directly excerpted from The Standard in TIG Welding, CK Worldwide (Page 11). The format has been slightly modified to enhance accessibility.
Begin with sharp tungsten and straight polarity (DCEN).
There are many different alloys of stainless steel. You will want to be sure you select the correct filler rod for your base materials. Whether you are welding to like materials or two different materials you can normally find a good match on a list like this one at Washington Alloy, STAINLESS Filler Metal Selector Guide.
Stainless Steel welds similar to mild steel but it is much more sensitive and will give you lots of feedback. It has a high coefficient of thermal expansion and a low coefficient of thermal conductivity.
What does that mean for welding? The base metal will be more susceptible to distortion. The weld itself has a higher likelihood of overheating as the heat is not being sucked away from the weld by the rest of the base metal. As much as possible you will want to reduce your heat input. The oxidation on the weld will let you know how much heat you have been putting into the weld. You will want a gold or straw color. Blue and purple indicate higher heat. If your weld comes out gray it has been overheated. This will reduce its ability to resist corrosion and the weld will be more susceptible to entitlements.
Pictured below are some examples:
A gold or straw color is what you are looking for
Purples and blues are indications that you are getting too hot
Gray is definitely too hot. (tighten your arc and increase your travel speed)
Autogenous welds are commonly used with SS in applications where it is desirable.
GTAW welding fundamentals for non-ferrous metals
| Metal Gauge | Joint Type | Tungsten Size | Filler Rod Size | Cup Size | Shield Gas Flow: Type, CFH,
(L/MN) PSI |
Welding Amperes | Travel Speed |
|---|---|---|---|---|---|---|---|
| 1/16”
(1.6mm) |
Butt | 1/16”
(1.6mm) |
1/16”
(1.6mm) |
4, 5, 6 | Argon, 15 (7), 20 | 60-80 | 12”
(307.2mm) |
| 1/16”
(1.6mm) |
Fillet | 1/16”
(1.6mm) |
1/16”
(1.6mm) |
4, 5, 6 | Argon, 15 (7), 20 | 70-90 | 10”
(256 mm) |
| 1/8”
(3.2mm) |
Butt | 3/32”
(2.4mm) |
3/32”
(2.4mm) 1/8” (3.2mm) |
6,7 | Argon, 17 (8), 20 | 125-145 | 12”
(307.2mm) |
| 1/8”
(3.2mm) |
Fillet | 3/32”
(2.4mm) |
3/32”
(2.4mm) 1/16” (1.6mm) |
6,7 | Argon, 17 (8), 20 | 140-160 | 10”
(256mm) |
| 3/16”
(4.8mm) |
Butt | 1/8” (3.2mm) | 1/8” (3.2mm) | 7,8 | Argon, 21(10) , 20 | 195-220 | 11”
(258.6mm) |
| 3/16”
(4.8mm) |
Fillet | 1/8” (3.2mm) | 1/8” (3.2mm) | 7,8 | Argon, 21(10) , 20 | 210-241 | 9”
(230.4mm) |
| 1/4”
(6.4mm) |
Butt | 1/8” (3.2mm) | 3/16”
(4.8mm) |
8, 10 | Argon, 25(10) , 20 | 260-300 | 10”
(256mm) |
| 1/4”
(6.4mm) |
Fillet | 1/8” (3.2mm) | 3/16”
(4.8mm) |
8, 10 | Argon, 25(12) , 20 | 290-320 | 8”
(204.8mm) |
Note: This table is directly excerpted from The Standard in TIG Welding, CK Worldwide (Page 10). The format has been slightly modified to enhance accessibility.
Your materials will change, depending on the type of power supply you are using. For a Transformer power supply use Green tungsten and be sure to ball the end as discussed earlier in this chapter. For an Inverter power supply you can use more tungsten options, but be sure to sharpen and then blunt the tip.
Use alternating current (AC) with your balance 70% Electrode Negative and 30% electrode Positive. This is just a starting point. Adjust as needed. Why use AC? Aluminum is known as a self-healing metal. An oxide layer forms on the surface of the metal rapidly when exposed to oxygen. This oxide layer acts as an armored skin for the aluminum.
Pure aluminum melts at approximately 1200 degrees F and aluminum oxide melts at approximately 3700 degrees F. This poses a problem when welding. The aluminum will melt long before the oxide layer and be incredibly difficult to penetrate.
During the reverse polarity cycle (Electrode Positive) of the AC wave the oxide layer is broken up. This is considered a cleaning action. You can adjust the balance on your machine to have more time spent on the reverse polarity (electrode positive) side of the wave but you will sacrifice penetration and put more strain on your tungsten. Do not mistake this cleaning action for a replacement of material preparation.
Select the appropriate filler rod for the base metals you are joining. Reference a material chart for this such as the Aluminum selection chart from Washington Alloy.
Aluminum does not change color when heated. The puddle will appear as a tiny mirror.
Amp- a good starting point is one amp for every thousandth of an inch of thickness of your material. ⅛ (0.125) equals 125 amps. Slightly more for a fillet weld. You should be able to establish a puddle in two to three seconds.
If you are using a foot pedal, set your amps to 120% of what you need. This way you can establish the puddle very quickly and then immediately start to ease off. This will give you more control.
Dip the filler into the puddle ensuring that the puddle is what is melting your filler metal. Dip move, dip move. Once you start you will want to move pretty quickly. You will also want to feed your filler metal through your hand every time you dip.
As you establish your puddle do not hold your filler too close. The end will ball up and give you issues.
Terminating the weld!
Fill your crater!
Aluminum will get heat shrinkage as you weld it and at the end of your weld, there will be a crater if you do not take steps to fill it. This will leave it susceptible to hot shortness and you will get cracks that will start in the crater. These may be tiny and seem insignificant but imagine the rock chip on your windshield, it will eventually spread if not dealt with.
To prevent this as you come to the end of your weld (dip move, dip move) stop moving the puddle, dip twice, ease off the peddle, and back the arc to where you were two or three dips ago. This will take some practice but with time it will become natural.
Attributions
- Figure 11.14: Stainless steel wire brush by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 11.15: S.S. Weld with Proper Heat Input by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 11.16: S.S. Weld Getting a Little Hot, But Still Okay by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
- Figure 11.17: S.S. Weld Too Hot by Karl Fulton, for WA Open ProfTech, © SBCTC, CC BY 4.0
