Electrode classification and wire electrodes

Electrodes for GMAW welding are referred to as wire or wire consumables. The term consumables means that the electrode becomes the weld and gets “consumed.” It starts in wire form but gets transformed into the weld bead by heat in the process. The wire chosen for the weld in this process should match or be extremely similar to the chemical and mechanical properties of the base metal. The welding wire is classified by both a letter and numbering system. The American Welding Society (AWS) created, designed, and maintains this system.

In the photo above, we can see that the numbering system starts with “E,” which simply means “Electrode,” followed by the letter “R,” which means Rod. The R lets the user know that this particular electrode can also be used as a filler electrode in GTAW, aka TIG welding process, which is referred to as a “non-current carrying rod.” The next designation is numbers. In the example, we are presented with the number “70,” which tells the tensile strength of the wire in 1000 lb per square inch (PSI). In this case, 70,000 lbs. This number may change depending on what the welder is working on, and in the case of copper and copper-alloy bare wire, it may be eliminated altogether. Choosing a higher tensile strength weld wire than needed is not always better. Heat, shielding gas, transfer mode, the thickness of material, and joint preparation must also be considered.

The next letter designation in the above image is “S.” In this case, S means the wire being used is solid, sometimes called a hard wire. Flux core arc welding uses tubular wire or T. Other letters in this place may be C for composite. This is used for GMAW metal core wire welding in congruence with spray transfer process.

Lastly, the letter “X” has been placed at the end to act as a placeholder. X will be a number 2 through 7 that refers to the wire’s chemical composition.

Metal-cored wires are tubular wires like that used in the flux cored process. However, unlike the wires used in FCAW, these wires are not filled with flux; instead, they contain

metallic powders such as iron. These wires offer some of the same benefits as their solid wire partners, such as being slag-free, able to weld a multitude of thicknesses, create better fusion on the toes of the welds, and a generally wider root profile. Unlike their solid wire or flux-cored wire counterparts, composite tubular wire is limited to the flat or horizontal weld positions due to the fluidity of the weld puddle.

There are also designations for aluminum, stainless, and low-alloy steel electrodes.

Two examples of these differing classifications would be the electrode ER309L for stainless. Here, the ER still remains the same; however, 309 refers to the grade of stainless steel, and L indicates that it is a low-carbon electrode. The electrode wire ER4043 is an extremely common aluminum welding wire. Again, ER means that this is an Electrode Rod capable of being used in the GTAW process as well. The next number, 4, is an indication that this wire is part of the 4000 series of aluminum alloy, and the 043 refers to the amount of silicone that has been added. All of these wires are manufactured and used in an array of sizes typically ranging from .023” to ⅛” in diameter, and when paired with the appropriate shielding gas, create desirable welds.

Shielding gasses

GMAW can be used in combination with a multitude of shielding gasses such as Argon, CO2, Helium, Hydrogen, Nitrogen, and Oxygen. The most common uses of GMAW are a variation of the three different shielding gasses: Argon, CO2, and Helium.

Not all shielding gasses are the same, and they each have their own effects on the weld in combination with the wire and base metal they are interacting with.

For example, argon and helium are both considered inert gasses. Which means they are non-reactive to chemicals in their environment. Inert or “non-reactive” gasses are also called Noble Gasses. Using these gasses, and others like it is where the term MIG or Metal Inert Gas welding originates from.

However, using active or reactive gasses would change the term to MAG, meaning Metal Active Gas welding. This would be gasses like Helium, CO2, Hydrogen, Nitrogen and Oxygen. When used in combination with heat, the atmosphere, and the base metal, these gasses have a reaction that can change the characteristics of a weld. One or the other (Inert or reactive) gas is not required to be used exclusively. Instead, a combination of these gasses often offers ideal impacts on the weld. It is important for the welder to have an understanding of what type of gas they are using and why. Shielding gas selections can impact the mechanical properties of the weld. Often, a welding job comes with a set of instructions called a welding procedure specification (WPS), which lays out what the welder is supposed to use as far as shielding gas and pressure set at the flow meter. You will learn more about a WPS later in this book.

Referencing Table 10.1, we can see some of the recommendations for different gasses, the attributes they add or take away, and material suggested for that gas selection.

Argon (Ar), for example, is an incredibly common shielding gas in the welding industry.

Using 100% Ar is recommended for gas metal arc welding when welding non-ferrous metals like aluminum or copper. Adding Ar to a mixture may improve arc stability, cut down on spatter, and create better protection for the weld pool, wire electrode, and base metal from contaminants in the atmosphere. Using 100% Ar is not recommended for ferrous metals like steel. Additionally, argon is not very thermally conductive, leading to the outer ranges of the gas coverage being significantly cooler than the middle of the coverage zone.

Welding with hydrogen or nitrogen in a shielding gas will increase penetration control, but the trade off is the weld becomes more susceptible to porosity and embrittlement.

When welding stainless steel, it’s common to use a tri-mix of gas that contains a certain percentage of Helium (He). For example, 90% He +7.5% Ar +2.5% CO2 is a tri-mix gas used to short circuit transfer mode GMAW welding. The Helium allows for a good penetration with a shallow weld bead appearance. Helium is more thermal conductive than argon uses higher heat, which allows for faster travel speeds. However helium is more costly and provides poor cleaning action and, because it is lighter than air, will require a higher setting on the flow meter.

General things to consider when choosing a shielding gas would cost, the effects the gas may have on mechanical properties, heat input, travel speed, increase/decrease spatter, base material, thickness of material, thermal conductivity, bead profile, and rust or oxidation prevention.

Attributions

1. Figure 10.14: Electrode Classification © American Welding Society , illustration by Nicholas Malara (SBCTC Illustrator) Used with permission from the rightsholder, the American Welding Society.