Last updated on January 28th, 2020 at 01:01 am
TIG welding requires three main things; heat, gas, and filler material. Heat is created by the electricity going through the welding tungsten electrode, thus igniting an arc. Gas shielding to protect the weld from contamination provided through a compressed gas cylinder to flow around the weld zone. Lastly, a filler metal is dipped by hand into the melted weld pool to form a bond if required.
Since we are talking about tungsten then it’s good to know a little about it. Tungsten is a very strong, at the same time, delicate and slightly radioactive. It’s not widely used compared to other metals. The tungsten electrode is a non consumable that is used to create the arc. It also allows the arc to maintain a heat level of up to 11,000 degrees Fahrenheit. Providing excellent electrical conductivity and a high melting point keeping the electrode from burning up. Also, the strength of tungsten is extremely high, up to 500,000 pounds of tensile strength per square inch. Which is much higher compared to the filler wire for example. While it is very hard, it’s also delicate which allows you break it with simple hammer tap.
Set the Power Type & Polarities
TIG welding must be operated with a constant current power source, either DC or AC. In TIG, the arc length is associated with the voltage, so with a longer arc the voltage increase, consequently, with a shorter arc the voltage decrease. Current is related to the depth of penetration, the welding speed, and the quality of the weld. While polarity is associated with how much heat is applied to the electrode. These are the polarity types for TIG welding;
- Direct Current Electrode Negative (DCEN). This concentrates most of the heat onto the metal welded. DC (- ve) produces a deep penetration weld as the heat is mainly distributed onto the workpiece.
- Direct Current Electrode Positive (DCEP). This concentrates most of the heat onto the electrode. DC (+ ve) produces a shallow weld and at the same time gives the arc a cleansing effect. More suitable for sheet metal.
- Alternating Current (AC). This current changes direction many times in a second thus provides equal heat distribution. By switching between (+ ve) and (- ve) polarity, the heat periods of electrode positive will also give a cleansing effect. AC must be employed for self oxidising metals such as aluminium.
DC is suitable for all almost all kinds of metals such as steel, stainless, and copper. DC electrode negative helps avoid overheating of the tungsten while DC electrode positive burns the tungsten very quickly. Using AC on the other hand is required for metals such as aluminum and magnesium.
Arc Starting Methods
There are three known methods for starting an arc, scratch, lift, and high frequency.
- Scratch start – The oldest method is scratch start. It works by literally scratching the surface of the workpiece to form a short-circuit to start an arc. However, this technique may cause the tungsten to enter the weld and carries the risk of contamination of the weld.
- Lift start – In lift arc, just like the name suggests, the electrode only touches the workpiece for an instant. The tungsten is short circuited to the surface at a very low current level, but the current will only flow once it’s lifted off the workpiece. In this technique there is less risk of contamination and electrode fusion to the workpiece.
- High Frequency – HF eliminates the need to physically strike an arc by touching the workpiece. The high frequency start can actually create an arc, one inch away from the torch and the workpiece. This happens by creating a short instant of high frequency that has the power to jump this small distance distance. This is very useful to keep the tungsten from getting contaminated and used up, leaving a high quality weld. However HF interferes with control systems and computers near the welding equipment and may actually damage them. When welding is done near sensitive areas, a non high frequency technique should be carried out. HF is also important in stabilising an arc in alternating current AC.
Start an Arc
There are few ways that can allow you to start the arc of the torch. Manually, typically works once the welding unit is turned on and striking the metal with the tungsten to ignite the arc. Automatically, works in two ways, either through a button on the TIG torch or a foot pedal.
- Hand operated – Is a simple button located on the TIG torch. Once you are ready to start an arc, you simply press the button with a finger.
- Foot operated – Controls the arc start and at the same time controls the amperage. It allows you to control the amperage by simply pushing further down the pedal. They are mostly suited when you would need a full control over the heat or when the welder is in a sitting position. As it is difficult to use a foot pedal while standing.
Select the Shielding Gas
GTAW welding incorporate shielding gases to protect the weld zone from any air that can contaminate the weld. The shielding gas is selected according to the material you are planning to weld. The following are some guidelines that may help;
- Argon (Ar): Pure 100% argon can cover almost all your welding needs. It works with steels, stainless steel, titanium and aluminium. It’s the most commonly used shielding gas for TIG welding a wide range of materials.
- Argon (Ar) + Hydrogen (H): The addition of 2% to 5 % hydrogen to argon will allow for the production of a cleaner looking weld without surface oxidation. It also promotes a higher welding speed as the arc gets hotter and more constricted. However, hydrogen may produce blow holes in carbon steels and aluminium alloys.
- Argon (Ar) + Helium (He): The addition of helium to argon raises the temperature of the arc. This also promotes higher welding speeds, as well as, deeper penetration. As a result, this mixture is usually used for thicker metals. This mixture is also used in welding materials that have high thermal conductivity such as aluminum and copper alloys. However, it’s difficult to start an arc with a helium, not to mention it’s high cost.
Set the Gas Flow Rate
Gas flow rates vary depending on the welding conditions, the cup size, and sometimes the position of welding. Gas flow rates for TIG welding of 15 to 25 cubic feet per hour (CFH) will usually cover most applications. The rate may sometimes increase due to using a very large cup size or to compensate poor welding conditions. But a 20 cubic feet per hour is usually sufficient. A flow meter attached to the regulator will give a more precise reading than the gauge of the regulator. Always take safety precautions when dealing with compressed pressure gas cylinders.
Choose the Tungsten Electrode Type
Tungsten is the main ingredient in the electrode. Sometimes the tungsten is alloyed with other materials in a very small percent to achieve different characteristics. The main materials added to the tungsten electrode are cerium, thorium, lanthanum, and zirconium. These tungsten electrodes are color coded by the classification of the American Welding Society (AWS).The following Tungsten electrodes are the most widely used;
- EWP: Has pure Tungsten, with a green color code. Pure Tungsten is used with alternating current (AC) for welding aluminum and magnesium as we discussed in polarity.
- EWLa-1: Has Lanthanum added to the Tungsten, with a black color code. It requires a minimum amount of adjustment of operation conditions and good arc starting and lower electrode consumption.
- EWCe-2: Has Cerium added to the Tungsten, with an orange color code. They provide high current carrying capacity, easy arc starting and stability with lower electrode consumption. Used for steel and stainless steel.
- EWTh-1: Has Thorium added to the Tungsten, with a yellow color code. It’s usually used with direct current (DC) electrode negative (- ve). Thoriated added Tungsten provides high current carrying capacity at a lower temperature. As well as, resistance to weld pool contamination, easy arc starting, and stability. Used for most metals such as steel, stainless steel, nickel, and other ferrous metals.
- EWTh-2: Has Thorium added to the Tungsten, with a red color code. Just like EWTh-1 with a different percent of Thorium. They have a longer lifespan.
- EWZr-1: Has Zirconium added to the Tungsten, with a brown color code. Zirconium added Tungsten has similar properties to pure Tungsten. They provide longer operation for certain types of welding with AC frequency for welding non ferrous metals such as aluminum and magnesium.
Decide on the Tungsten Electrode Diameter and Cup Size
The size of your tungsten electrode mainly depends on the material thickness and the amperage needed to achieve a proper weld. Thicker materials uses a higher current, thus a bigger tungsten is needed. For beginning with TIG welding, practicing with 1/16 to 1/8 inch thickness is a good start.
Gas cups are typically made of ceramic material, they are located in the torch nozzle. They work by directing the flow of the shielding gas to the molten weld pool. They vary in size according to the torch used and the electrode diameter along with the appropriate amperage. Ideally, the cup diameter should be four to six times bigger than the diameter of the electrode in use. These are the common electrode diameters in relationship with the cup size;
- .020 inch: #3 to #5 cup.
- .040 inch: #4 to #5 cup.
- 1/16 inch: #4 to #6 cup.
- 3/32 inch: #6 to #8 cup.
- 1/8 inch: #7 to #10 cup.
- 5/32: #8 to #10 cup.
- 3/16: #8 to #10 cup.
- 1/4: #10 cup.
For controlling the amperage, know that the lower the current the smaller the electrode diameter and tip angle and vice versa.
Set the Amperage
Amperage of a TIG welder vary depending on the type of the metal to be welded and it’s thickness. In this example, it’s set for argon with the three main tungsten sizes you will be starting with.
- 1/16 inch – Amperage rage of 50 to 100 amps. Gas flow rate of 5 to 15 CFH.
- 3/32 inch – Amperage rage of 80 to 130 amps. Gas flow rate of 8 to 20 CFH.
- 1/8 inch – Amperage rage of 90 to 250 amps. Gas flow rate of 8 to 25 CFH.
Using a TIG calculator is very helpful for figuring out the proper tungsten diameter, cup size, gas type and gas flow, and also the current type and amperage range. All you need to do is enter the metal type, thickness, and joint type, then the calculated will do the rest.
Set the Pre-Flow and Post-Flow
TIG welding machines feature a pre-flow and a post-flow option. The pre-flow gives the shielding gas a pre-time to shield the weld zone before the arc is started. No need to have more than half of a second. While the post-flow keeps the shielding gas flow for an extra time after you stop the arc. This enables the tungsten and the weld to cool off which gives more protection to the welded area. As the tungsten take longer to cool from high amps, increasing the post flow by one second every 10 amps is a good start.
Use a Filler Wire
For welding on thin metals no filler material is needed but for welding a thick joint, some filler rods can be added which is then manually fed by the welder’s other hand into weld pool. You can use a solid MIG wire if required. The difference between a GMAW wire and GTAW wire is first TIG doesn’t use any flux and second TIG wires usually come in a 36 inch length packages. In general, the size of the filler depends on what you are trying to weld. As a general rule, for thin metals, use a thin wire and for thick metals, use a thick wire, that simple!
Set the Ground Clamp
Attaching the ground clamp to the table is enough for welding something small. For welding large applications, attaching the clamp directly to the workpiece is better. It’s important to keep the clamp attached to a clean surface that is free of rust and paint to allow for a good connection.
Always take maximum safety precautions when welding and wear the appropriate welding gear. Find an experienced welder to help you in your first arc sticking attempt. This article won’t make you a real TIG welder, it’s only an attempt to make you understand of how is a simple TIG set up. For those interested in learning about TIG welding, a local welding school that offers good training courses will provide you with the required professional skills and give you time to practice. You can also check our list of the best rated TIG welders.