Welders recognize the significance of having the right tools, from the power source down to the torch and every piece that connects them. Yet, surprisingly, the most overlooked element is also arguably the most vital to the entire welding process: the tungsten electrode. It serves as the final connection that brings the weld to life. Its durability and ability to withstand heat make it an ideal conduit for delivering the welding current to the arc. However, it is puzzling how this crucial component often goes unnoticed and unappreciated. To choose the optimal tungsten electrode, you must consider the tungsten’s material, tip geometry, and tip preparation. Only by focusing on these intricate details can you ensure the highest quality and repeatability of welds.
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Electrodes are made from either pure tungsten or a mixture of tungsten and other rare-earth elements and oxides. Each electrode is assigned a specific color code, which is prominently displayed on its tip. The following is a description of the common tungsten types and their uses.
Pure Tungsten - AWS Classification: EWP; Color Code: Green. Pure tungsten, which is at least 99.5% tungsten, offers stable performance when paired with AC welding, whether it is a balanced wave or continuously high-frequency stabilized. This tungsten retains a neat balled end, ideal for welding aluminum and magnesium.
2% Thoriated Tungsten - AWS Classification: EWTh-2; Color Code: Red. These electrodes comprise a minimum of 97.3% tungsten with 1.7% to 2.2% thorium. These are among the most popular electrodes in use today, renowned for durability and user-friendliness. However, due to its radioactive nature, many welders look for other alternatives. These electrodes are primarily employed for specialized AC welding tasks, like thin-gauge aluminum or materials thinner than 0.06 in., and DC welding. It is suitable for carbon steel, stainless steel, nickel, and titanium, either with electrode negative or straight polarity.
2% Ceriated Tungsten - AWS Classification: EWCe-2; Color Code: Gray. This electrode contains a minimum of 97.3% tungsten and 1.8% to 2.2% cerium. They perform best in DC welding at low current settings. EWCe-2 has excellent arc starts at low amperages, making it essential for orbital tube and pipe fabrication, sheet metal, and applications with small parts. Ceriated electrodes offer similar versatility to thoriated electrodes and often replaces them in low-amperage applications.
2% Lanthanated Tungsten - AWS Classification: EWLa-2; Color Code: Blue. This electrode boasts a wide range of applications and amalgamates some of the finest characteristics observed in other tungsten variants. It is celebrated for its superior arc initiation at minimal amperages, its low wear rate, and its reliable reignition capabilities. Within the industry, lanthanated tungsten is recognized as a versatile substitute for thoriated and ceriated electrodes because it encompasses the best qualities of both.
Zirconiated Tungsten - AWS Classification: EWZr-1; Color Code: Brown. This electrode has 99.1% tungsten with zirconium content ranging between 0.15% and 0.40%. Its balled tip and strong resistance against contamination make it perfectly suited for AC welding. While its current-carrying capacity matches or even surpasses that of thoriated tungsten, the zirconiated electrode is not recommended for DC welding applications.
Tri-Mix Tungsten - AWS Classification: EWG; Color Code: Turquoise. Unlike the radioactive 2% thoriated tungsten, Tri-Mix is a nonradioactive substitute. Infused with a scientifically harmonized blend of three rare-earth oxides, it optimizes migration and evaporation rates, thereby prolonging the life of the tungsten. This tungsten variant delivers a stability and uniformity that is unparalleled by many other tungsten types.
Electrode geometry and preparation play a significant role in determining electrode longevity, arc initiation, arc shape, and welding penetration depth (see Figure 1). Given these factors, it is evident that the geometry of your tungsten electrode is a pivotal aspect of the welding procedure, demanding precise adherence to tight tolerances for every weld.
Electrode Diameter. When selecting an electrode diameter for your needs, you're essentially trying to strike a balance between ease of arc starting and the longevity of the tungsten—two factors that often oppose each other. Although starting with the manufacturer's guidelines is a wise move, it is also beneficial to do your own testing to determine the best fit for your specific tasks.
Tungsten with a smaller diameter provides:
On the other hand, tungsten with a larger diameter offers:
Tungsten Tip. Choosing the right end configuration—balled, pointed, or truncated—is crucial in optimizing results and preventing potential contaminants and additional corrections (see Figure 2).
AC welding electrodes—most commonly pure or zirconiated—necessitate a balled tip. This tip is apt for sine wave and standard square wave GTAW power sources. The diameter of the balled tip shouldn't be more than 1.5 times the electrode's diameter since it can compromise arc stability and may detach, leading to weld contamination.
To achieve a balled tip, no intricate preparation is required. Simply apply an AC current and the ball will naturally form at the electrode's end.
For DC or inverter AC welding—thoriated, ceriated, lanthanated, and Tri-Mix electrodes—a pointed and/or truncated tip is necessary.
Larger flat surfaces can make arc initiation harder and may cause arc wandering. But by optimizing the flat size, you can ensure a stable arc and also extend the electrode's lifespan, especially for high-amperage uses.
A pointed tungsten tip is recommended for welding on thinner materials, between 0.005 and 0.040 in., using a low current. This shape provides a focused arc transfer, which reduces the possibility of warping in sensitive metals like aluminum. However, a pointed tungsten tip isn't suitable for high-current jobs. The strong current can wear down the tip and contaminate the weld puddle.
On the other hand, a truncated tungsten tip is more suitable for tasks requiring high current. To craft this, you'd first shape the tungsten into a taper, then fashion a 0.01- to 0.03-in. flat surface at the end. This design lessens the chances of tungsten contamination in the arc and prevents a ball from forming at the tip.
Included Angle. For DC welding, electrodes should be ground in a longitudinal and concentric manner using a high-quality diamond grinding wheel (see Figure 3). The specific angle at which it is ground influences the arc's shape, the simplicity of arc initiation, the longevity of the tungsten, and the depth of weld penetration.
A blunt taper with a wider included angle provides:
Conversely, a sharp taper with a smaller included angle ensures:
Tungsten Preparation. Properly preparing tungsten electrodes for welding is a meticulous task, and the era of resorting to general shop belt sanders or multipurpose grinders is a thing of the past. It is now imperative to employ a dedicated diamond grinding wheel specifically for tungsten preparation.
Although tungsten is notably hard, a high-quality diamond wheel is even tougher, ensuring a grind that's smooth and devoid of rough edges or any unseen surface flaws that might lead to welding inconsistencies or outright failures.
Reserve the diamond grinding wheel exclusively for tungsten to prevent contaminating the wheel and the electrode tip and potentially introducing foreign materials into the weld.
The most crucial aspect of correctly grinding a tungsten electrode is ensuring it is done longitudinally (see Figure 4). A tungsten electrode's grain structure runs lengthwise; grinding crosswise means you're grinding against this structure. Electrons densely populate the electrode's surface. If ground or polished across, electrons jump over these grinding marks and cause the arc to initiate prematurely, disperse, and often deviate. Longitudinal grinding results in a stable and focused arc.
A diamond cutting wheel ensures the cut remains clean, smooth, and free from splinters or fractures. The tool used should be user-friendly, equipped with safety shields, and incorporate a scale for precise measurements.
Other preparation methods are ill-advised. These include:
These methods can compromise weld quality, and there's also the risk of the electrode fragmenting in ways you can't easily detect, leading to an unstable arc and welding flaws. Such methods can jeopardize your safety, risking hand or eye injuries.
One of the reasons TIG welding is favored for sensitive welding applications is because it gives the welder superlative control. The heat for welding comes from an electric arc that streams from a tungsten electrode in the torch. Over the years, welding engineers have found many ways to tailor these electrodes for specific applications by adding small amounts of exotic elements to the tungsten. The different types of electrodes are identified by a band of color at one end.
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In the early days of TIG welding there were only two types of tungsten that were commonly used. Pure tungsten was favored for aluminum and magnesium, and 2% thoriated tungsten was used for everything else. While these worked well for generations, research and development led to a broad range of tungsten electrodes, each with unique properties. It can be somewhat bewildering for a beginning welder to sort through all the options, so we’ll take a look at the most widely used types of tungsten electrodes. This should help you make an informed decision about which one is best for your welding projects.
Pure tungsten was used as a welding electrode at the beginning of the TIG process, back in the 1940s. TIG welding was developed to efficiently join aluminum and magnesium alloys, and pure tungsten made sense at the time, since it has the highest melting temperature of all metals. In those days power sources were transformer based, and pure tungsten could accommodate welding in the AC mode, which is the standard for aluminum and magnesium. Back then, it was common practice to prepare the tungsten by “balling” the tip. This was done by briefly running a burst of current through the electrode with the power source set to the “reverse polarity” (electrode positive) mode. This would melt the tip of the electrode, and when the current was terminated the tungsten would solidify into a smooth, shiny ball. The shielding gas prevented the electrode from oxidizing, and the size of the ball could be controlled by the amount of current that was run through the electrode in the EP mode. This balled electrode would shape the arc into a wide cone, and the electrode could carry fairly high current without “spitting,” or transferring tiny amounts of tungsten into the weld puddle. Note that with modern inverter power sources, pure tungsten electrodes are not recommended.
For DC welding (used for all metals other than aluminum and magnesium) a small amount of thorium was added to the tungsten electrode, usually 2%. This made arc starts more consistent, and increased the current carrying capacity of the electrode.
Even though these two types of electrodes handled the needs of TIG welders for decades, they are not commonly used with modern welding equipment, for some good reasons. When the industry migrated from transformer to inverter power sources, balling the electrode for AC welding was no longer required, and pure tungsten electrodes gave way to superior blends.
Thorium is slightly radioactive and handling thoriated tungsten electrodes poses health and environmental risks at elevated exposure levels. Consult the AWS Safety and Health Fact Sheet on Thoriated Tungsten Electrodes for more information.
Other elements have proven to be superior to thorium for electrodes in every way. As you’ll see, there are a couple types of tungsten electrodes that are well suited for virtually any TIG welding task, either AC or DC
2% lanthanated tungsten (color-coded blue) is at the top of the list. This is a true all-purpose electrode, with excellent arc starting characteristics and the ability to transmit high current without spitting. It provides a stable arc at both high and low current, and works very well on all metals.
2% Ceriated tungsten (grey) is another good choice for all types of welding; providing good arc start and restart characteristics with no spitting. It is ideal for low- and medium-current welding on all metals.
Rare earth tungsten (chartreuse) has the very best low-current arc starting characteristics, and it can be used on all metals. This type is often preferred for automated welding.
Zirconiated tungsten (white) is good for welding aluminum and magnesium alloys. It has high current-carrying capacity, and it provides better arc starts and stability than pure tungsten.
Tungsten electrodes come in a wide range of diameters — from .020-inch diameter up to ¼-inch. You need to select a diameter large enough to accommodate the maximum current used for each welding job. Smaller diameter electrodes will start the arc more readily at very low amperage settings. For the work I do, which involves a broad range of shapes and sizes, I use a 3/32-inch diameter electrode. I have no problem with arc starts, even for light-gauge sheet metal, and I can weld metals ¼-inch thick, or more.
The most common length for tungsten electrodes is 7 inches. For working in restricted areas, it may be beneficial to cut them down, allowing a shorter back cap to be used on the torch.
Tungsten can be cut with an abrasive cutoff wheel or ground through with the corner of a grinding wheel. Do not cut the electrodes with a wire cutter or break them by bending. This may result in unseen fractures at the cut ends, which can cause an erratic arc.
Tungsten electrodes usually come with blunt ends that need to be sharpened before use. The angle of the point determines the shape of the arc that streams from the electrode. There is an inverse relationship between the electrode point angle and the arc — a sharply pointed electrode will produce a cone-shaped arc with a broad base where it hits the metal, creating a wide puddle. This can be beneficial for edge-welding thin materials.
Conversely, a stubby point on your tungsten will produce a narrow cone with a small base, focusing the energy into a smaller area. This can help you get deep penetration on thicker materials. With some experimentation, you can find the point angle that gives you the characteristics best suited for a particular job.
For very high-amperage welding, it can help to grind a small flat at the tip of the tungsten electrode. This will help prevent the electrode from spitting small particles into the workpiece.
There are lots of tools made specifically for sharpening tungsten electrodes, but you can do a good job with a stone, belt or disc grinder. To avoid contaminating the electrode, use a dedicated grinder for tungsten, and be sure that all of the grinding scratches are parallel with the electrode centerline. If you leave angled or spiral grinding scratches, the arc may be unstable.
It is not uncommon for electrodes to get contaminated. This can happen when the tip is accidentally touched to the molten puddle, or if the filler rod contacts the hot electrode. Sometimes impurities in or on the metal can fly out and contaminate the electrode, too. It is essential that the electrode be absolutely free from any contamination, so be ready to swap it out whenever this happens. It can help to have several pre-sharpened electrodes handy as you weld.
Even though there are many choices for tungsten welding electrodes, after you have selected an appropriate type and diameter for your application, you shouldn’t have to think much about it. A good all-purpose electrode, like a 3/32-inch diameter, 2% lanthanated, should be an excellent choice for most welders.
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