When to use FCAW-G over GMAW for manufacturing applicationsShawn Martin | June 30, 2019
Gas shielded flux core arc welding (FCAW-G) and gas metal arc welding (GMAW) are the two most common welding techniques in manufacturing. Both techniques utilize a wire feed that provides for increased productivity over stick electrode techniques, minimizing weld discontinuities and maximizing throughput. While FCAW-G is often viewed as the preferred alternative to shielded metal arc welding in field operations, both processes carry their own advantages and disadvantages in the manufacturing industry.
GMAW provides numerous advantages in manufacturing operations. Although setup can be slightly more involved, it is widely considered one of the easiest welding techniques to learn. Compared to other welding techniques, GMAW produces a cleaner weld, emits less fumes, provides for higher deposition rates and is the preferred welding technique for most manufacturing operations.
Limitations of GMAW include environmental susceptibility, fewer electrode options and difficulty performing out-of-position welds. In most manufacturing operations, the work piece can be manipulated to provide either a flat or horizontal welding position. In instances where vertical or overhead welds, also referred to as out-of-position welds, are required, GMAW begins to exhibit some of its limitations.
GMAW shielding of the weld pool is solely accomplished by a shielding gas. Weld pool contamination is typically associated with either incorrect setup or environmental influences. Consequently, GMAW is limited to indoor environments, as even in a controlled environment inadvertent airflow can jeopardize the gas shield.
Gas mixtures are typically selected based on electrode material and weld position with pure argon and helium solely used for nonferrous metals. In most cases, a gas mixture is required. The introduction of a lighter semi-inert gas such as carbon dioxide can help improve GMAW performance when making out-of-position welds, although the addition of these gases may induce undesired side-effects including increased weld spatter, arc stability issues or excessive heat input and loss of puddle control.
There are a number of GMAW electrodes available for welding low-carbon steels, stainless steels, aluminum alloys and copper alloys. Ferrous electrodes generally contain deoxidizers that act to limit any amount of porosity in the weld joint that gets introduced by semi-inert gas mixtures. There is, however, limited availability of GMAW electrodes for low-alloy, high-tensile strength steels.
FCAW was developed as a self-shielding welding technique that provides for higher deposition rates than shielded metal arc welding. The wire-fed consumable is basically an inside-out stick electrode. The technique was developed in the 1950s and has been widely used in structural steel and other field operations that benefit from an increased deposition rate and when environmental influences render other welding techniques useless.
Currently, there are two basic types of FCAW welding techniques: self-shielded flux cored arc welding (FCAW-S) and FCAW-G. While FCAW-S is primarily used in field operations, FCAW-G has found applications in manufacturing where it addresses deficiencies of GMAW processes, producing a smoother arc and less spatter when compared to FCAW-S.
FCAW-G is also referenced as a dual-shield welding technique. The fluxed core produces a protective slag that quickly solidifies over the weld pool, holding molten metal in place when welding out of position while a shielding gas is introduced via the welding torch to isolate the arc and prevent any atmospheric gases from contaminating the weld pool.
The main benefits of FCAW-G over GMAW include improved out-of-position weld quality, deeper penetration, ability to join plates in the presence of contaminants and a wider selection of electrode materials.
The increased electrode availability for FCAW-G includes a range of application-targeted consumables. The fluxed-core provides another pathway for introducing deoxidizers, which allows for more freedom in base metal composition. This also allows for the introduction of a fast-freezing slag system that works to improve deposition rates when performing out-of-position welds. FCAW-G electrodes can also be engineered for use with specific shielding gases, to join higher strength steels, to provide for improved low-temperature toughness, for stress relief applications, for pipe welding applications and for joining chromium-molybdenum (Cr-Mo) steels. This has created several niche roles where FCAW-G provides for a clear advantage over GMAW.