Separate flux feed, e.g., submerged arc welding (SAW)
Gas shielding
GTAW (gas tungsten arc welding) - Argon gas
GMAW (gas metal arc welding) - Argon or carbon dioxide
Classification of Fusion Welding Processes by Energy Source
Electrical Resistance
Fusion Welding
Chemical
SMAW
SAW
GMAW
FCAW
EGW
ESW
RSW
OAW
OHW
AAW
Arc
Radiation
EBW
LBW
Consumable Electrode
Non-Consumable Electrode
GTAW
Gas
Consumable Electrode AW Processes
Shielded Metal Arc Welding (SMAW)
Gas Metal Arc Welding (GMAW)
Flux-Cored Arc Welding (FCAW)
Submerged Arc Welding (SAW)
Other Arc Welding Processes
Electrogas Welding (EGW)
Electroslag Welding (ESW)
Arc Stud Welding (SW)
Shielded Metal Arc Welding (SMAW) AKA Metal Manual Arc (MMA) Welding
About 50% of all large-scale industrial-welding operations use this process.
A manual welding process uses a flux-coated consumable electrode.
A welding helmet is a type of personal protective equipment used in performing certain types of welding to protect the eyes, face, and neck from flash burn, sparks, infrared and ultraviolet light and intense heat.
The electric arc forms between the electrode and the workpiece, melting both to create the weld.
Also known as “stick welding.”
Uses consumable electrodes (sticks) consisting of a filler metal long rod that are held manually.
The electrode coating melts to produce shielding gas and slag, which:
Protect the molten weld from atmospheric contamination (oxygen, nitrogen).
Help shape and cool the weld.
The welder must manually feed the electrode and control the arc.
Weld pool: A mixture of materials from base metal and electrode forms the weld when it solidifies. It is protected by shielding gas and solidified slag.
Advantages of SMAW
Can be used in remote locations or places where electricity is not readily available.
Used to weld a wide range of metals (steel, stainless steel, cast iron).
Power supply, connecting cables, and electrode holder available for a few thousand pounds.
High-quality welds.
Disadvantages of SMAW
Consumable electrode. Sticks periodically changed increasing cost, defects, and time reducing productivity.
Skill Requirement. Required welder level of skill is high.
High current levels may melt coating prematurely.
Difficult to weld thin materials as it can lead to excessive heat input, causing the material to warp or distort.
Gas Metal Arc Welding (GMAW) Process AKA Metal Inert/Active Gas (MIG/MAG)
Uses a continuous and consumable bare metal wire electrode and a shielding gas to join two metal pieces.
Shielding gases include inert (argon, helium) and active (CO2 or a blend).
Electrode wire is fed continuously and automatically from a spool through the welding gun.
Used in the automotive, construction, and manufacturing industries.
Advantages of GMAW
GMAW can weld any metal and most commercial alloys.
GMAW can be easily operated or automated.
GMAW is a high-speed welding process that can produce high-quality welds quickly and efficiently. This makes it an ideal choice for applications that require a large amount of welding in a short amount of time.
Better production efficiency versus SMAW since the electrode or filler wire does not need to be continuously replaced.
Produces very little splatter and slag inclusions.
Disadvantages of GMAW
Equipment more expensive and less portable than SMAW.
Torch is heavy and bulky so joint access might be a problem.
Various metal transfer modes add complexity and limitations.
Surface preparation is required.
Flux Cored Arc Welding (FCAW)
Uses a continuously fed electrode coil that has a flux core in its core.
Similar to MIG/MAG welding, but instead of using a solid wire, it uses a tubular wire that is filled with flux.
Self-shielded FCAW - core includes compounds that produce shielding gases making it more portable.
Popular choice as a replacement for GMAW and/or SMAW for welding steels and stainless steels over a wide stock thickness range.
Higher deposition rates than other welding processes, which means that more weld metal can be deposited per unit of time, resulting in faster weld completion.
Self‐shielded version is tolerant to drafty conditions.
More tolerant to weld metal contamination than GMAW.
Disadvantages of FCAW
Filler metal is more expensive than GMAW filler metal.
Requirement to remove slag after welding (self-shielded).
Fume production can be extremely high (especially self‐shielded version).
Limited to steels and nickel‐based alloys only.
Gas‐shielded version is not very tolerant to drafty conditions.
Spatter expelled from the welding arc can sometimes be significant.
More complex and expensive equipment compared to SMAW.
Submerged Arc Welding (SAW)
Uses a continuous, consumable bare wire electrode, with arc shielding by a cover of granular flux.
The arc is submerged under a layer of flux, which prevents spatter, sparks, and fumes from escaping the weld area.
Commonly used in the fabrication of large structures such as ships, pressure vessels, and offshore platforms.
Advantages of SAW
Extremely high weld metal deposition rates, especially when multiple wires are used.
No arc radiation. Minimal smoke and fumes
Significant opportunity to customise weld metal properties through the selection of the flux.
Mechanised process (usually) does not depend on welder skill.
Disadvantages of SAW
Restricted to flat position for groove welds, and flat and horizontal positions for fillet welds.
Flux handling equipment adds complexity.
Not suitable for thin sections.
Non-Consumable Electrode Processes
Gas Tungsten Arc Welding (GTAW)
Plasma Arc Welding
Carbon Arc Welding
Stud Welding
Gas Tungsten Arc Welding (GTAW) AKA Tungsten Inert Gas (TIG)
Uses a non-consumable tungsten or tungsten alloy electrode held in a torch to produce the weld.
Filler wire could be fed into the weld pool to add material to the joint.
Inert shielding gas is used (e.g., argon, helium, or their mixture)
No flux is needed.
Commonly used in aerospace, automotive, and other industries where high-quality welds are required.
Advantages of GTAW
High quality welds and finish.
Minimal post-weld cleaning is required and no possibility for slag defects.
Works well for complex geometries and thin sheets
Disadvantages of GTAW
Expensive due to the use of inert gases.
Possibility of tungsten inclusions in the weld.
Slower and more costly than consumable electrode AW processes.
Requires a high level of welder skill and experience
Resistance Welding (RW)
A group of fusion welding processes that use a combination of heat and pressure to accomplish coalescence
Heat generated by electrical resistance to current flow at the junction to be welded
Principal RW process is resistance spot welding (RSW)
Resistance Spot Welding (RSW)
Resistance welding process in which fusion of faying surfaces of a lap joint is achieved at one location by opposing electrodes
Used to join sheet-metal parts
Widely used in the mass production of automobiles, metal furniture, appliances, and other products
Example: Spot welding car bodies by robots on an automotive assembly line. A typical car body has ~10,000 spot welds. Annual production of automobiles in the world is measured in tens of millions of units
Advantages of Resistance Welding
No filler metal
High production rates possible
Lends itself to mechanisation and automation
Lower operator skill level than for arc welding
Good repeatability and reliability
Disadvantages of Resistance Welding
High initial equipment cost
Limited to lap joints for most RW processes
Summary
In these fusion welding processes, heat is used to bring the joint being welded to a liquid state
Protection of liquid metal in the pool is necessary using shielding gases or fluxes
The metallurgy of the welded joint is important, which will determine the strength and toughness of the joint due to microstructure changes by HAZ
Residual stresses are normally induced in the weld, and it is important to consider this by pre-heating/post heating or post-treatment to relieve the stress, which in turn can lead to distortions of the part.
Concept Questions
Name the principal groups of processes included in fusion welding.
What is an electrical arc?
Name and define the categories in which electrodes in arc welding are divided into.
What is the heat-affected zone (HAZ) in a fusion weld?