One popular way to explain tungsten electrodes is by saying that you could have the best welding equipment in the world, but if you don’t have properly prepared tungsten electrodes to transfer the arc, it’s like driving a Porsche without tyres.
In DC arc welding, the tungsten electrode is one of the most important process variables, but it is also one of the most often forgotten. When choosing and preparing them for welding, there are three important things to keep in mind:
- Electrode geometry.
- Electrode preparation.
- Electrode preparation equipment.
Geometry of Electrodes.
For DC welding, the electrode diameter, the included angle (taper), and the tip make up the full electrode geometry (flat).
The choice of geometry will always affect the life of the electrode, how the arc starts, how deep the weld goes, and the shape of the arc. During the development of a welding procedure, the electrode configuration must be tested, no matter what geometry is chosen. The geometry should be written down as a critical process variable for the weld procedure, and all subsequent welds should be done with close tolerances.
Electrode Diameter. When choosing the electrode diameter, the best place to start is with what the maker of the welding equipment says. Even though it’s easier to start an arc with a small diameter, a large diameter can handle more amperage and lasts longer than a small diameter. But if the current is too high, the tungsten will break down too quickly, fall into the weld pool, and make the weld dirty. On the other hand, if the current is too low for the diameter of the electrode, the arc will start to wobble.
Electrode Was Included (Taper). For DC welding, diamond wheels should be used to grind the electrodes longitudinally and concentrically to an included angle. This should be done at the same time as the tip/flat preparation.
A blunt taper with a large included angle gives the electrode a longer life, better weld penetration, a narrower arc shape, and the ability to handle more amperage without wearing down. With a small included angle and a sharp taper, the arc doesn’t move around as much and is wider and more consistent.
In precision arc welding, the shape of the tungsten electrode tip is an important process variable. This is because the chance of arc wandering and having trouble starting goes up as the size of the flat gets bigger. But increasing the flat also makes weld penetration better and extends the life of the electrode.
If the flat is wrong or uneven, sharp electrode tips can fall into the weld pool. It can also cause the arc to be unstable, the electrodes to wear out faster, and the voltage of the arc to change from one electrode to the next.
The tungsten electrode is the most important part of welding, and it needs to be cut and ground properly. A badly prepared electrode can cause the arc to wander, split, shed, be inconsistent, or lead to costly mistakes. When the electrodes are properly cut and grounded, the arc starts and stays on.
Diamond wheels are the best way to grind and cut tungsten electrodes. Even though tungsten is a very hard material, the surface of a diamond wheel is even harder, which makes for a smoother grind. When you grind with other types of wheels, you can get rough edges, imperfections, or a bad surface finish that you can’t see. All of these things can lead to inconsistent welds and defects.
Preparation for a flat tip.
Depending on how the welding is done, the flat preparation could be done on a new electrode or on an electrode that has already been used. Before making a flat, the end of a used electrode should be cut off if it is very dirty. Place a new or cut-off electrode at a 90-degree angle to the side of the wheel. This will clean it up and get it ready for use again.
Taper Grinding. When grinding an electrode, the most important thing is that it is ground along its length. The molecular structure of the grain in tungsten electrodes is made to run lengthwise. So grinding crosswise is grinding against the grain.
More importantly, electrons flow more quickly on the electrode’s surface. If the electrodes are ground or polished in a crosswise direction, the electrons have to jump over the marks. The arc starts before the tip, spreads out, and often goes in different directions. When the tungsten electrode gets too hot, it wears out faster. When the grain is ground in a straight line, the electrons are steadily led to the very tip of the tungsten electrode. The arc starts out straight and stays straight, narrow, and steady.
Tungsten is the only thing that should be ground with a diamond grinding wheel. This will help make sure that the grinding wheel and tungsten tip don’t get messed up. And it doesn’t transfer foreign material to the weld.
Lengthening or Cutting.
A dirty electrode makes the arc jump around and makes a dirty weld. Cutting off that piece of tungsten is the best way to make sure that all of the dirt is gone from the tip. When the tip is dirty, grinding it may not remove all of the dirt, and the dirt will end up on the grinding wheel, where it will be picked up again the next time the tip is ground.
Since tungsten is a very hard material, the best way to cut it is with a diamond cutting wheel. This makes clean, even cuts. Using one of the following methods, many welders cut their tungsten in the wrong way:
- The electrode can be broken by hand or with wire cutters.
- Two sets of pliers were used to turn the electrode.
- Notching the electrode with the grinding wheel and then breaking it by hand, with a hammer, or with pliers.
- Using a hammer on a sharp metal edge to hit the electrode.
All of these methods can lead to problems with safety and welding. The electrode can break or splinter without anyone noticing. This can make the arc unstable and cause defects in the weld, as well as hurt your eyes or hands. So, it is much easier to cut an electrode with the right cutting tool. Which is made keeping in mind how hard and brittle tungsten is.
By using a diamond cutting wheel, the cut will be clean, smooth, and free of cracks or splinters. The tool should be easy to use and quick to set up. It should also have safety covers and a scale to make sure the right length is measured and cut.
Surface Finish of an Electrode Angle.
Some of the things about the welding process depend on how smooth the finish is on the prepared tip of the electrode. In general, points should be ground as finely as possible to improve how well they weld and to make the electrode last longer. When the electrodes are ground too roughly, the arcs are not stable.
A standard finish of about 20 roughness average (RA), which still shows the longitudinally ground lines to the naked eye, is a good finish for any application. A high-polished, mirror-like finish of about 6 to 8 RA, in which few or no lines can be seen, makes the electrode last longer because it makes it less likely that dirt will “stick” to the electrode point and cause it to wear away. But for welding power supplies that don’t have strong arc-starting features, a finish of about 20 RA is better. This is because longitudinally grounded lines help steadily lead electrons to the end of the electrode. This helps the arc start.
Electrode Preparation Equipment.
Most of the time, it is very important to have a tungsten electrode grinder that is just for that. Most places don’t have the right equipment for longitudinal diamond grinding or for making sure the preparation is the same from one electrode to the next. A machine that isn’t made for welding can also get foreign material on the electrode, which hurts the quality of the weld in a number of ways.
For efficient production of same tungsten electrodes and welds every time, a grinder should have the following features:
- Longitudinal grinding.
- A grinding wheel made of diamond.
- A tool for cutting that has a measuring device and can cut short enough for the job. Especially when orbital welding.
- 20 or better in RA.
- In less than a minute, you can grind tungsten into a fine powder.
- Ability to meet required tolerances for angle, length, and flat.
- Simple and reliable to use, and easy to change to make different shapes.
- Dust collection is important, especially for 2 percent thoriated tungsten electrodes, which are radioactive.