10.3 GMAW Electrodes and Shielding Gasses
Stephanie Oostman
Electrode Classification
Electrodes for GMAW welding are referred to as wire or wire consumables. The term consumables refers to how the electrode becomes part of the weld and gets “consumed” since it starts in wire form but gets transformed into the weld bead by heat during 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 a letter and numbering system. The American Welding Society created, designed, and maintains this classification system.
Figure 10.14 shows the classification. A GMAW electrode starts with E, which simply stands for electrode, followed by the letter R, meaning rod. The R lets the user know that this particular electrode can also be used as a filler electrode in gas tungsten arc welding (GTAW), which is referred to as a “non-current carrying rod.” The GTAW process is covered in Chapter 11.
The next set of characters in the classification is numbers. In Figure 10.14 it is represented by an XX placeholder, but the numbers indicate the tensile strength of the wire in 1,000 pounds per square inch (psi). If a 70 appears, that means the wire’s tensile strength is 70,000 lbs. The recommended tensile strength may change depending on what material the welder is working on, and, in the case of copper and copper-alloy bare wire, it may be eliminated altogether. Note that choosing a higher tensile strength weld wire than needed is not always better, as the heat, shielding gas, transfer mode, thickness of material, and joint preparation must also be considered.
The next letter designation in Figure 10.14 is S, which means the electrode wire is solid. These are sometimes called hard wires. In contrast, FCAW uses tubular wires, indicated by a T. Other letters in this place on GMAW electrodes may be C, for composite. This is used for GMAW metal core wire welding in congruence with the spray transfer process, which will be covered later in this chapter.
Lastly, the letter Y at the end acts as a placeholder. On an electrode, a number between 2 through 7 that refers to the wire’s chemical composition will appear there.
Metal-cored wires are tubular wires like that used in the fluxed-core process. However, unlike the wires used in FCAW, GMAW 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. However, composite tubular wire is limited to use in 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. In th