Components

The equipment needed for GTAW include a power source/welding machine, shielding gas, regulator and flow meter, electrode holder known as a torch, tungsten electrode, filler rods, foot pedal or hand-held power control, water cooler when required and always personal protective equipment.

Power source/welding machine:

Most welding machines are capable of GTAW; the machine must be a constant current power source.

Some features included on a power source built for GTAW are

• Direct Current electrode positive (reverse polarity) or electrode negative (Straight polarity).
• Alternating current (AC), often used to weld aluminum and magnesium. Some machines will give the operator the ability to adjust the balance of the AC wave and even control the shape of the wave.
• Solenoid valve that controls shielding gas flow and cooling water (if water cooler is attached).
• A foot pedal or hand held remote control that will not only turn on and off the flow of gas and current but gives the operator the ability to increase or decrease the current while welding. Some machines will have a preflow to make sure your arc is protected from the beginning. Post flow is used once you terminate the weld the shielding gas continues to flow for a set duration of time to protect the weld as it cools. You will not want to move the torch at all during this time or even lift your hood.
• High frequency giving the operator the ability to start an arc without touching the base metal

Direct Current

There are two modes for direct current, direct current electrode positive (DCEP), also known as reverse polarity, and direct current electrode negative (DCEN), known as Straight polarity. When your machine is set to Straight polarity (DCEN) the electrons flow from the electrode to the work. This directs the heat on your workpiece and not your electrode giving you a 70/30 split. This means 70% of the heat being created is on the work, and 30% is on the electrode. This helps to minimize the wear and tear on your electrode, making this the most common way to set up a GTAW machine.

When the welding machine is set up for Reverse polarity (DCEP), the electrons flow from the work to the electrode. This will put 70% of the heat on your electrode and 30% of the heat on the workpiece. When you have a non-consumable electrode as you do with GTAW, this can be detrimental. There are benefits to this; as the electrons flow up from the workpiece, positively charged ions strike the metal, breaking up the oxides on the surface of your work. This is a wonderful cleaning action. Setting the machine up this way will give you a very wide, shallow puddle. A fun thing to practice once or twice is to get a very thin sheet of aluminum and try to weld it with Reverse polarity (DCEP). A thicker tungsten is recommended, and it will still take a lot of wear and tear.

Alternating Current

Alternating Current (AC) is continuously switching from DCEP to DCEN at 60hz this switch happens 60 times a second. The purpose of using AC while GTAW is to take advantage of the benefits of Straight (DCEN) and Reverse (DCEP) at the same time. This is extremely useful when welding aluminum; you can break up the oxide on the surface and direct enough heat to the workpiece to weld. There are three main factors to consider when using AC: Balance, frequency, and waveform. Not all machines will have the ability to manipulate all of these.

Balance gives you the ability to favor DCEP or DCEN. If you are set to 75/25 in favor of DCEN, the arc will be on DCEN for 75% of the time. Imagine 0.1 of a second drawn with a 50/50 AC wave, positive on top, negative on the bottom, and 0 in the middle. You would get six equal humps on both sides. The wave will stay on the negative side of the 0 three times as long as on the positive.

This would give you more penetration and less cleaning. Set the machine to 25/75 favoring DCEP now, the wave would stay on the positive side of 0 for longer. This would give the arc more cleaning action and less penetration. This also puts much more heat on your tungsten. The goal here should be to use as little cleaning action as possible.

Frequency. This setting affects how often the arc switches from DCEP to DCEN per second. The ability for machines to adjust the frequency will vary (not all machines have this feature) from as low as 20hz and as high as 350hz. At lower frequencies, the arc cone is wider, and at higher frequencies, the arc cone will be tighter, this can help to get into tight corners. If you have a machine with this setting, it is highly recommended to experiment with both extremes. A great generic setting for everyday welding is 110hz.

High Frequency is a separate function from your frequency adjustment. This function is to jump the gap between your tungsten and work to initiate your arc without contaminating your tungsten. It is also to maintain a stable arc during AC welding.

AC Waveforms

The original AC wave for GTAW was a sine wave. This produces a smooth arc that is good for welding but does require continuous High frequency to maintain the arc stability.

For a brief second, the sine wave passes through zero, and this can cause the arc to break or stutter. By adding high frequency, the amount of time the ace is at zero is reduced to almost nothing.

With the technology of inverter machines, the square wave was developed. This removes the need for continuous high frequency. Square wave switches instantaneously from reverse polarity (DCEP) to Straight polarity (DCEN) without spending any time at zero amperage. This also increases the heat input allowing for faster travel speeds.

Soft Square Wave is a mix between Sine Wave and Square Wave, giving the benefit of both. This is a good standard setting for most AC welding.

Triangle Wave is used for reduction in heat on the base metal. This is great for thin material to reduce distortion.

Torches

The torch is a critical part of GTAW, these are designed to conduct the welding current and carry the inert gas to the weld zone. Torches are either air or water-cooled. Air-cooled touches are typically used for lighter gauge materials requiring less amperage (current). Water-cooled torches will typically have an amperage (current) rating of over 200 amps. Water is pumped in from a cooler to cool the touch and as it travels back it will cool the lead as well. It’s very important to maintain the water in the cooler to prevent overheating (See the owner’s manual on the machine you use for details).

Most GTAW torches are going to be relatively the same though they do come in a variation of sizes. Here are the basic parts of the torch and what they do:

• Backing cap: This pushes the collect forward and caps the back of the torch. The interior of this cap is hollow for the excess tungsten.
• O ring: The O ring seals the backing cap to the torch body to ensure there is no gas leakage and a vacuum is not created pulling in the atmosphere to the weld zone.
• Electrode: Tungsten electrodes come in a variety of sizes and alloys. This will be the most commonly altered, replaced, or sharpened piece of your torch. If at any time this becomes contaminated you should address it immediately.
• Collet: As the backing cap is tightened the collet is pushed forward locking the tungsten electrode in place.
• Torch Body: Creating a base for everything to come together, the whip for your gas, current, and water (if water cooled) to come in at the handle. The back cap, electrode, and collet go on the back. The collet body and nozzle go on the front of the torch body.
• Collet Body/Gas lens: Attached to the front of the torch body (do not over-tighten). It’s important to make sure this is tightened before the backing cap as this can create a vacuum in the torch leading to contamination in the weld. There are also gas lenses to replace this part, this is a diffuser to create a laminar flow of gas. The advantage is to get a more even gas coverage with less likelihood of contamination. This also enables you to extend your tungsten slightly farther out of your nozzle/cup. If you want to see a visual example of this, take the screen out of your kitchen sink and watch the difference in the flow as you put it back.
• Nozzle/cup: The last piece of the torch and the second most changed out, these come in an assortment of sizes. The numbers represent 1/6” exit diameter. A number 5 nozzle has a 5/16 exit diameter. The nozzle directs the argon or helium to the area in which you are welding. A good rule of thumb for how far your electrode can stick out is equal to your exit diameter.

Regulators and flow meters

The regulator flow meter combinations will be most commonly used in GTAW. The regulator shows how much pressure is in the high-pressure bottle and has a set pressure on the flowmeter for a consistent flow of shielding gas. The flow meter will control the amount of gas flowing in cubic feet per hour (CFH).

As Figure 11.10 depicts, the gasses flow in and will float a ball in a plastic or glass tube and then out of the welding machine or directly to our torch, depending on the set up you are running. The top of the ball is where you take the reading on how gas is following. This can be adjusted depending on your requirements for what you are welding. It’s very important to ensure the flow meter is positioned at 90 degrees to ensure an accurate reading

Shielding gasses

It is very important to understand the dynamics of the shielding gasses used in GTAW. There are two gasses used, both inert (non-reactive) to protect the molten weld pool and tungsten during welding. Argon and Helium are used separately or as a mixture.

• Argon is by far the most commonly used gas for its cost and availability. The atomic weight of Argon is 39.948, making it heavier than air. This helps create a blanket over a flat weld to protect it from contamination. Argon also produces a very smooth arc.
• Helium was the first inert gas used for GTAW, now less commonly used because of the increased cost. The need for a higher flow rate when using helium also increased cost. The atomic weight of helium is 4.0026, this makes it much lighter than air so it will not pool in a valley when welding in the flat position. The advantages of welding with helium are a hotter arc creating deeper penetration and faster welding speeds. Being lighter than air also makes it good for overhead welding.

Flow rate: This should be enough to protect your molten puddle. You do not want to turn your flow rate up too high, this can cause turbulence and lead to contamination. A good range to stay in is 11 c.f.m. to 25 c.f.m. The smaller your nozzle/cup, the less gas you will need. This is adjusted on the flowmeter.

Setting up the welding system

Always read the owner’s manual. They will have detailed instructions specific to your machine. The first thing you will want to check is the power to the machine. Is it three-phase or single-phase, 110v, 220, or 480? This information will be labeled directly on the machine 90% of the time.

The next step will be to connect your ground. Depending on your machine, this will either go in the positive terminal or the terminal label ground.

Connect your whip to the negative terminal and attach your torch.

Connect the gas to the back of your machine if it has a solenoid. If not, there are options to connect directly to your torch and have an on-off valve on your torch. Don’t forget to turn this off after every weld. The gasses are not free.

Specific safety concerns associated with GTAW

Electric shock

Always insulate yourself from electric shock. Make sure your gloves and clothing are dry. Electricity will follow the easiest path. Make sure you are not part of that path.

High frequency

This has been known to ruin electronics in the weld booth (cell phones). If you have a pacemaker you should definitely do more research.

Radioactive dust from thoriated tungsten

Thoriated tungsten will produce radioactive dust when sharpened by grinding. Follow the precautions on the SDS. These will include but are not limited to avoiding ingesting, washing hands after handling, and wearing a mask that covers the nose and mouth.

Hexavalent chromium

This is a cancer-causing fume that is produced during hot work of chromium-containing alloys mostly stainless steel. GTAW is going to have lower exposure than SMAW or PAC, but a respirator with properly rated filters is highly recommended.

Burns

When welding, you are elevating the metal to extreme temperatures. This makes burns the most common injury in welding. Always wear your PPE and be aware of your surroundings. When welding, if it hurts, stop. Let’s say that together. If it hurts, stop.

Ultraviolet and infrared rays

These rays can cause burns and irritation to the skin and eyes. Cover all skin and never expose your eyes to the arc. At minimum use a shade 9 when welding, and if you are having trouble seeing, go darker before you go lighter.

Argon

Higher levels can cause nausea, vomiting, unconsciousness, coma and death. No occupational exposure limits have been established for Argon. However, it may pose a health risk. Always follow safe work practices (NJ Health, 2016).

Attributions

1. Figure 11.4: AC Sine Wave by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
2. Figure 11.5: AC Square Wave by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
3. Figure 11.6: AC Soft Square Wave by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
4. Figure 11.7: Triangle Wave by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
5. Figure 11.8: GTAW Torch Exploded View by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
6. Figure 11.9: Combination regulator and flowmeter by Nicholas Malara, for WA Open ProfTech, © SBCTC, CC BY 4.0
7. Figure 11.10: Cross section of flowmeter by Naval Education and Training Professional Development and Technology Center in the Public Domain; United States government work