Tungsten has the hardness and high-temperature resistance that make it ideal for carrying the welding current to the arc. Here’s what you need to know to gain top TIG welding performance.
Like any other welding process, TIG welding relies on the right equipment to get the job done properly, and from the power source to the TIG torch and cables, each component plays a critical role. But at the core of the TIG welding process is something unique: the tungsten electrode. This non-consumable metallic element has the highest melting point of any metal (3,410 degrees Celsius), making its hardness and high-temperature resistance the ideal option for carrying the welding current to the arc.
Choosing a specific type of tungsten for your TIG welding application doesn’t have to be difficult, but it depends on you having a little know-how. To begin, tungsten electrodes come in a variety of diameters — typically ranging from 0.040- to 5/32-inch — and they are available in industry-standard lengths of seven inches. Custom lengths are available, too, but they tend to cost more. The electrodes are composed either of pure tungsten or a hybrid of tungsten and other rare earth elements and oxides (all discussed below.) To eliminate confusion between the various types, each electrode is color-coded, with the color appearing at the tip of each electrode.
Following here is a description of the various types of tungsten electrodes, including their characteristics, typical applications and most appropriate weld settings, along with recommendations for proper preparation.
Pure tungsten (color code: green)
Pure tungsten electrodes have an AWS (American Welding Society) classification of EWP and typically are less expensive than their “alloyed” counterparts. They contain 99.50% tungsten and have the highest consumption rate of all electrodes, and provide a clean, balled tip when heated. This shape offers especially good arc stability for AC welding with a balanced waveform. Pure tungsten electrodes also provide good arc stability for AC sine wave welding on aluminum and magnesium. They are not, however, used for DC welding.
2% Ceriated (color code: orange)
Containing a minimum of 97.30% tungsten and 1.80 to 2.20% cerium, 2% ceriated tungsten electrodes perform best in DC welding, but they can be used proficiently in AC, too. These electrodes have an AWS classification of EWCe-2 and offer excellent arc starts at low amperages, making them popular in orbital tube and pipe manufacturing, thin sheet metal work or jobs that require the welding of small and delicate parts. 2% ceriated tungsten works well for welding carbon and stainless steels, nickel alloys and titanium.
In recent years, pointed 2% ceriated tungsten has replaced balled pure tungsten for AC welding on aluminum, as it provides approximately 30-40% more current-carrying capacity than the pure tungsten at the same diameter.
1.5% Lanthanated (color code: gold)
1.5% lanthanated tungsten electrodes have excellent arc starting, low-burn-off rate, good arc stability, and excellent re-ignition characteristics — many of the same advantages as ceriated electrodes. 1.5% lanthanated electrodes also closely resemble the conductivity characteristics of 2% thoriated tungsten (discussed later), meaning, in some cases, it can replace 2% thoriated without having to make significant welding program changes. These electrodes have an AWS classification of EWLa-1.5 and contain a minimum of 97.80% tungsten and 1.30 to 1.70% lanthanum, or lanthana.
1.5% lanthanated electrodes work well on AC or DC electrode negative with a pointed end, or they can be balled for use with AC sine wave power sources. They also maintain a sharpened point well, which is an advantage when welding steel and stainless steel on DC or the AC from squarewave power sources.
These electrodes are suitable for AC welding and, like ceriated electrodes, allow the arc to be started and maintained at lower voltages AC. Compared to pure tungsten, the addition of 1.5% lanthana increases the maximum carrying capacity by approximately 50% for a given-size electrode.
Rare earth (color code: gray)
Rare earth tungsten electrodes contain unspecified additives of rare earth oxides or hybrid combinations of different oxides that manufacturers must identify on all packaging by both additive and percentage. Depending on the type of additives, rare earth tungsten can provide benefits that include: a stable arc in both AC and DC processes; greater longevity than thoriated tungsten; the ability to use a smaller-sized diameter tungsten for the same job; use of a higher current for similar-sized tungsten; and less tungsten spitting. Rare earth tungsten has an AWS classification of EWG.
2% Thoriated (color code: red)
Preferred for their longevity and ease of use, 2% thoriated tungsten electrodes are the most commonly used electrodes today. They contain a minimum of 97.30% tungsten and 1.70% to 2.20% thorium, and they have an AWS classification of EWTh-2.
These electrodes offer good arc starts and provide a higher current-carrying capacity than many other types. 2% thoriated tungsten also operates far below its melting temperature, which results in a considerably lower rate of consumption, minimizes arc wandering and lessens instances of weld contamination.
These electrodes can be used for AC welding, and they are exceptional for DC electrode negative (straight polarity) on carbon and stainless steel, nickel and titanium applications.
During manufacturing, thorium is evenly dispersed throughout the electrode. This evenness allows the electrode to maintain a sharpened edge — the ideal electrode shape for welding thin steel. Sharpening the electrode’s point, however, should be done with great care. Thoriated tungsten contains low levels of radioactivity. Therefore, operators must always follow manufacture’s warnings, instructions, and the MSDS (Material Safety Data Sheet) for its use.
Proper tungsten preparation
There are three main ways to prepare tungsten electrodes for welding — balled, pointed or truncated — each of which depends on the type of tungsten electrode you choose to use. For example, pure tungsten generally requires a balled tip and works well when using the AC process on sine wave and conventional squarewave TIG welders.
To ball the end of the tungsten, apply the AC amperage recommended for a given electrode diameter (see Figure 1); the ball on the end of the tungsten will form itself. As a rule of thumb, the diameter of the balled end should not exceed 1.5 times the diameter of the electrode, as having a larger sphere at the tip of the electrode can reduce arc stability and/or can fall off and contaminate the weld. As an example, a 1/8-in. electrode should form a 3/16-in. diameter end maximum.
You should use a pointed and/or truncated tip (for pure tungsten, ceriated, lanthanated and thoriated types) for inverter AC and DC welding processes, and also when welding with lower currents on thinner materials (those ranging from .005- to .040-in). A pointed tungsten allows the welding current to transfer in a focused arc and helps prevent thinner metals, such as aluminum, from becoming distorted. As a note, using pointed tungsten for higher-current applications is not recommended, as the higher current can blow off the tip of the tungsten and cause weld puddle contamination.
To grind the tungsten to a point, use a grinding wheel specially designated for tungsten grinding, to help prevent contamination. A grinding wheel made of borazon or diamond works well to resist tungsten’s hardness. Note: iIf you are grinding thoriated tungsten, make certain you control and collect the dust, have an adequate ventilation system at the grinding station, and follow manufacture’s warnings, instructions, and MSDS.
Grind the tungsten straight on the wheel (not at a 90-degree angle) to ensure that the grind marks run the length of the electrode. Doing so reduces ridges on the tungsten that can lead to arc wandering or melt into the weld puddle. Grind the taper on the tungsten to a distance of no more than 2.5 times the electrode diameter (for example, with a 1/8-in. electrode you would grind a surface 1/4 to 5/16-in. long). Grinding the tungsten to a taper eases arc starting and creates a more focused arc for better welding performance.
For higher-current applications, grind your tungsten to a truncated tip by first grinding the tungsten to a taper (as explained above) and then grinding a 0.010- to 0.030-in. flat land on the end of the tungsten. This flat land helps prevent the tungsten from being transferred across the arc and/or from balling.
In any application, the type and shape of tungsten you use helps to determine the arc quality and welding performance you will achieve. Each of the five types of tungsten discussed here brings with it distinct advantages and disadvantages. That’s why, regardless of type of material you are TIG welding or whether you are using an AC or DC process, it is always important to choose your tungsten carefully for each application. Doing so can maximize your TIG welding success and is one of the best defenses against contamination and rework.
Joshua Sprinkle is a regional sales manager for Weldcraft, a full-spectrum supplier of TIG welding products and accessories.