Welding Process

By Rahmat Azis Nabawi

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According to the definition of the Deutsche Industrie Normen (DIN) as cited by Harsono and Toshie (2000), welding is defined as "a metallurgical bond produced between metallic materials in the molten or liquid state." In other words, welding is a metal joining process in which the base materials are locally heated until they melt, allowing a permanent metallurgical bond to be formed after solidification (Harsono & Toshie, 2000).

Before welding operations are carried out, a comprehensive welding procedure should be prepared. The procedure includes selecting the appropriate welding process, determining the required equipment, and establishing production quality requirements. The quality of a welded joint depends not only on the welding operation itself but also on the preparation performed before welding begins (Cary & Helzer, 2005).

Proper welding preparation generally consists of selecting the appropriate welding process, preparing the joint edges, and determining the most suitable welding position for the intended application.

a. Types of Welding Processes

According to Harsono and Toshie (2000), steel fabrication commonly employs three principal welding processes: Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (MIG/GMAW), and Submerged Arc Welding (SAW). Each process possesses its own advantages and limitations; therefore, careful consideration should be given before selecting the most appropriate welding method for a particular fabrication project.

1. Shielded Metal Arc Welding (SMAW)

Shielded Metal Arc Welding (SMAW), commonly referred to as manual metal arc welding or stick welding, is a fusion welding process in which heat generated by an electric arc melts both the base metal and a consumable covered electrode. During welding, the electrode coating melts simultaneously to produce shielding gas and slag, protecting the molten weld pool from atmospheric contamination (Jeffus, 2012).

Figure 1. Shielded Metal Arc Welding (SMAW) process.

In the SMAW process, an electric arc is generated between the tip of the covered electrode and the base metal. The intense heat produced by the arc melts both the electrode and the parent material locally. Molten metal from the electrode fills the weld groove and combines with the molten base metal to form a weld pool. As the weld pool solidifies, it produces a permanent welded joint (weldment), while the molten flux solidifies into a protective slag layer that must be removed after welding (Cary & Helzer, 2005).

One of the most important components in SMAW is the electrode itself. The type of electrode selected significantly influences weld quality, penetration, mechanical properties, and overall welding performance.

Advantages of SMAW

• Can be used in workshops, outdoor environments, and even underwater applications.
• Suitable for welding a wide variety of ferrous materials.
• Simple and fast equipment setup.
• Can be performed in all welding positions.
• Electrodes are readily available in various types and diameters.
• Equipment is relatively inexpensive, portable, and easy to operate.
• Produces relatively low operating noise when using rectifier power sources.
• Less sensitive to light surface contamination such as rust, oil, and grease than several other welding processes.

Limitations of SMAW

• Welding length is limited by the length of the consumable electrode, requiring frequent electrode replacement.
• Slag must be removed before depositing the next weld pass.
• Not suitable for welding many non-ferrous metals.
• The molten weld pool is susceptible to oxidation if shielding is inadequate.
• The electrode diameter must be selected according to the plate thickness and welding position.

2. Gas Metal Arc Welding (GMAW/MIG)

Gas Metal Arc Welding (GMAW), commonly known as Metal Inert Gas (MIG) welding, is a fusion welding process in which two or more metallic materials are joined by localized melting. The process employs a continuously fed consumable wire electrode (filler metal) together with an externally supplied shielding gas, typically argon or helium, to protect the molten weld pool from atmospheric contamination (Jeffus, 2012).

In MIG welding, the wire electrode is supplied from a spool and is automatically fed through a welding gun by an electric wire feeder. During welding, an electric arc is established between the continuously fed wire electrode and the base metal. The heat generated by the arc melts both the wire electrode and the base material, producing molten weld metal that solidifies to form a sound welded joint (Cary & Helzer, 2005).

The shielding gas plays a critical role in protecting the molten weld pool during solidification by preventing oxidation and contamination from the surrounding atmosphere. MIG welding normally operates using direct current with reverse polarity (electrode positive), which provides stable metal transfer and improved weld quality. Welding currents generally range from approximately 50 A to 600 A, while arc voltages typically vary between 15 V and 32 V, depending on the material thickness and welding application (Jeffus, 2012).

Figure 2. Gas Metal Arc Welding (MIG) process.

Advantages of MIG Welding

• Provides high welding productivity because the wire electrode is continuously fed.
• Produces smooth weld beads with excellent appearance.
• High deposition rate compared with manual arc welding.
• Suitable for welding both thin and thick steel plates.
• Produces minimal slag, reducing post-weld cleaning time.
• Can be readily automated for large-scale fabrication.
• Widely used for structural steel fabrication and industrial manufacturing.

Limitations of MIG Welding

• Equipment is more expensive than Shielded Metal Arc Welding (SMAW).
• Requires shielding gas cylinders and additional gas supply equipment.
• Less suitable for outdoor applications because wind may disperse the shielding gas.
• Requires clean joint surfaces to achieve high-quality welds.
• Equipment is generally less portable than SMAW systems.

3. Flux Cored Arc Welding (FCAW)

Flux Cored Arc Welding (FCAW) is an arc welding process that utilizes a continuously fed tubular electrode containing flux at its core. FCAW combines several characteristics of Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW), and Submerged Arc Welding (SAW). The welding power source may employ either alternating current (AC) or direct current (DC) supplied through a transformer or rectifier, operating with either electrode-positive (DCRP) or electrode-negative (DCSP) polarity depending on the required welding application (Cary & Helzer, 2005).

In the FCAW process, the filler electrode is supplied mechanically and continuously into the electric arc formed between the wire electrode and the base metal. The electrode itself is manufactured from a thin steel strip that is rolled into a tubular shape and filled with flux specifically formulated for the intended welding application. The flux performs several important metallurgical functions, including shielding the molten weld pool, stabilizing the welding arc, and improving the mechanical properties of the deposited weld metal (Jeffus, 2012).

Protection of the molten weld pool against atmospheric contamination may be achieved using two different methods:

• Self-shielded FCAW, in which shielding gases are generated by the decomposition of the flux contained within the tubular electrode.
• Gas-shielded FCAW, which combines internally generated shielding gases with an externally supplied shielding gas to provide enhanced weld protection.

Both shielding methods produce sufficient slag to protect the molten weld metal during solidification. The principal difference lies in the use of an external shielding gas supply and a welding gun for gas-shielded FCAW (Jeffus, 2012).

Based on the operating method, FCAW systems are classified into:

• Semi-automatic FCAW
• Automatic FCAW

Principal Features of FCAW

• Continuous electrode feeding provides high welding productivity.
• The metallurgical properties of the weld deposit can be controlled through appropriate flux selection.
• Excellent deposition efficiency and high metal recovery.
• When welding voltage and current are properly controlled, deposition rates increase significantly, thereby improving productivity.
• Weld penetration can be adjusted according to the selected welding current and polarity.

Automatic FCAW systems generally operate using constant-voltage direct current power sources. External shielding gases are commonly employed for narrow groove welding, deep penetration applications, and the reduction of weld spatter. For high-current operations exceeding approximately 600 A, water-cooled welding guns are frequently used to prevent overheating and ensure continuous operation (ASM International, 1993).

Carbon dioxide (CO₂) is the shielding gas most commonly used in FCAW because of its relatively low cost, good penetration characteristics, and suitability for structural steel fabrication. In addition, tandem torch arrangements may be employed to achieve exceptionally high deposition rates in heavy fabrication work (Cary & Helzer, 2005).

FCAW is widely applied in shipbuilding, bridge construction, pressure vessels, heavy machinery, structural steel fabrication, surfacing, hard-facing, and cladding operations. In general, the base metals that can be welded using SMAW, GMAW, or SAW can also be successfully welded using FCAW (Jeffus, 2012).

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Conclusion

Welding is one of the most important joining processes in steel fabrication because it provides permanent metallurgical bonding between structural components. The quality of a welded structure depends not only on the welding process itself but also on proper joint preparation, material selection, welding procedures, and the qualifications of the welder. Appropriate process selection and strict adherence to established welding standards contribute significantly to the strength, reliability, and service life of fabricated structures.

Among the welding processes commonly used in fabrication industries, Shielded Metal Arc Welding (SMAW), Gas Metal Arc Welding (GMAW/MIG), Flux Cored Arc Welding (FCAW), and Submerged Arc Welding (SAW) each offer distinct advantages and limitations. Therefore, selecting the appropriate welding method should be based on the material properties, joint configuration, production requirements, welding position, and the desired quality of the final product. A thorough understanding of these welding processes enables engineers and fabricators to produce safe, efficient, and high-quality welded structures.

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References

1. American Welding Society. (2010). AWS Welding Handbook (9th ed., Vol. 2: Welding Processes). Miami, FL: American Welding Society.
2. ASM International. (1993). ASM Handbook, Volume 6: Welding, Brazing, and Soldering. Materials Park, OH: ASM International.
3. Cary, H. B., & Helzer, S. C. (2005). Modern Welding Technology (6th ed.). Upper Saddle River, NJ: Pearson Prentice Hall.
4. DeGarmo, E. P., Black, J. T., & Kohser, R. A. (2012). DeGarmo's Materials and Processes in Manufacturing (11th ed.). Hoboken, NJ: John Wiley & Sons.
5. Harsono, W., & Toshie, O. (2000). Teknologi Pengelasan Logam. Jakarta: Pradnya Paramita.
6. Jeffus, L. (2012). Welding: Principles and Applications (7th ed.). Clifton Park, NY: Delmar Cengage Learning.