Welding Processes

• Types of Welding Processes:

o Welding processes are divided into two major groups: Fusion welding
and solid-state welding.
o Fusion welding involves melting the base metals, with examples like arc
welding, oxyfuel gas welding, and laser welding.
o Solid-state welding processes, such as diffusion welding, friction
welding, and ultrasonic welding, do not involve melting.
• Arc Welding:

o Arc welding refers to a group of welding processes where metals are

heated by an electric arc.
o It involves dangerous radiation harmful to human vision, requiring
welders to wear special helmets with dark viewing windows.
o Arc welding is commonly used in various industries like construction,
shipbuilding, and automotive, and is usually performed manually by
skilled workers.
• Oxyfuel Gas Welding (OFW):

o OFW uses an oxyfuel gas mixture like oxygen and acetylene to produce
a hot flame for melting base and filler metals.
o It is a fusion-welding process that involves melting the metals being
joined.
Arc Welding (AW)

• is a fusion-welding process where metals are joined by the heat of an electric

arc between an electrode and the workpiece.
• The process involves creating temperatures of 5500 °C or higher to melt the
metal, forming a molten pool near the electrode tip.
• Filler metal is often added during welding to strengthen the joint, and
different techniques for flux application and power sources (DC and AC) are
used in various AW processes.

Electrodes
• in arc welding can be consumable or non-consumable, providing filler metal
for the welding process.
• Consumable electrodes come in forms of rods or wires, with wires offering
continuous feeding advantages over rods.

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 • Non-consumable electrodes, typically made of tungsten, are used in
processes like Gas Tungsten Arc Welding (GTAW) with separate filler metal
supply.

Power Source
• in Arc Welding Both direct current (DC) and alternating current (AC) are used
in arc welding.
• AC machines are less expensive, but are generally restricted to welding of
ferrous metals.
• DC equipment can be used on all metals with good results and is generally
noted for better arc control.

Shielded Metal Arc Welding (SMAW)

• is a manual arc welding process commonly used in construction, shipbuilding,
and repair work.
• It is preferred for thicker sections above 5 mm due to its higher power density
and versatility.
• SMAW uses a consumable electrode coated with flux to shield the arc and
molten weld pool, making it one of the most widely used arc welding
processes.
• SMAW is also known as stick welding, where the electrode is manually fed
into the weld pool.
• The flux coating on the electrode vaporizes, creating a shielding gas to protect
the weld from atmospheric contamination.
• This process is versatile, portable, and can be used in various positions,
making it a popular choice for field welding and maintenance applications.
• SMAW is suitable for welding a wide range of materials, including carbon
steel, stainless steel, and cast iron.
• It is a cost-effective method due to its simplicity and minimal equipment
requirements.
• SMAW produces strong and durable welds, making it a reliable choice for
many welding applications.

Gas Metal Arc Welding (GMAW)

• is an arc welding process that uses a consumable bare metal wire electrode
and a shielding gas to protect the weld pool.
• Initially known as Metal Inert Gas (MIG) welding when used with inert gases
like argon for aluminum welding, and as CO2 welding when CO2 was used for
steel welding.
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 • GMAW is versatile, efficient, and commonly used for welding aluminum,
steel, and stainless steel due to its high deposition rates and clean welds.
• GMAW is suitable for both manual and automated welding processes,
making it widely used in various industries.
• It offers advantages such as high welding speeds, minimal post-weld cleanup,
and good control over the welding parameters.
• The continuous wire feed feature of GMAW results in higher productivity and
reduced downtime compared to other welding processes.
• GMAW eliminates the need for flux, reducing the need for slag removal and
resulting in cleaner welds.
• The process is known for its high deposition rates, making it efficient for
welding thicker materials.
• GMAW is commonly used in fabrication operations due to its versatility and
ability to weld a wide range of ferrous and nonferrous metals.

Flux-Cored Arc Welding (FCAW)

• is an arc-welding process where the electrode is a continuous consumable
tubing containing flux and other ingredients in its core.
• There are two versions of FCAW: self-shielded, where arc shielding is provided
by the flux core, and gas shielded, where external shielding gases are used.
• FCAW is known for its versatility, continuous electrode feeding, and suitability
for welding steels and stainless steels over a wide stock thickness range.
• FCAW is capable of producing high-quality weld joints that are smooth and
uniform due to the continuous feeding of the electrode.
• The process is efficient and commonly used in various industries for welding
applications.
• FCAW eliminates the need for flux removal and produces clean welds, making
it a preferred choice for many welding operations.
• In Flux-Cored Arc Welding (FCAW), shielding gases are not always required
due to the flux core in the electrode providing the necessary protection.
• However, when gas shielding is used in FCAW, common shielding gases
include carbon dioxide (CO2) and mixtures of argon and carbon dioxide.
• The choice of shielding gas in FCAW depends on the material being welded
and the desired welding characteristics.

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Electrogas Welding (EGW)
• is an arc welding process primarily used for vertical butt welding of steels,
including low- and medium-carbon, low-alloy, and certain stainless steels.
• EGW utilizes a continuous consumable electrode, either flux-cored wire or
bare wire with externally supplied shielding gases, along with molding shoes
to contain the molten metal during welding.
• It is commonly applied in the construction of large storage tanks,
shipbuilding, and other industries requiring vertical welding of thick materials
ranging from 12 to 75 mm (0.5–3.0 in).
• Electrogas Welding (EGW) is an automated process where the weld head
moves vertically upward to fill a cavity formed by the molding shoes and the
edges of the parts being welded.
• EGW is known for its ability to produce high-quality weld joints with minimal
defects, making it suitable for critical applications.
• The process does not require filler metal, flux, or shielding gas, contributing
to its efficiency and cost-effectiveness in welding thick materials.

Submerged Arc Welding (SAW)

• is an arc welding process that uses a continuous, consumable bare wire
electrode and granular flux to shield the arc and weld pool.
• Widely used in steel fabrication for structural shapes, large pipes, tanks, and
heavy machinery components, SAW is suitable for welding steel plates of 25
mm (1.0 in) thickness and heavier.
• SAW is not suitable for high-carbon steels, tool steels, or nonferrous metals,
and requires horizontal orientation due to gravity feed of flux, often
necessitating a backup plate during welding.
• Submerged Arc Welding (SAW) is characterized by high deposition rates and
deep weld penetration, making it efficient for welding thick materials.
• The process is mechanized or automated, enhancing productivity and
ensuring consistent weld quality.
• SAW is commonly used in industries such as shipbuilding, pressure vessel
fabrication, and the production of large structural components due to its
ability to produce high-quality, uniform welds efficiently.

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Gas Tungsten Arc Welding (GTAW)
• known as Tungsten Inert Gas (TIG) welding, uses a nonconsumable tungsten
electrode and inert gas for arc shielding.
• GTAW is versatile, applicable to various metals and thicknesses, commonly
used for aluminum and stainless steel welding.
• The process can be performed with or without filler metal, offering high-
quality welds with minimal post-weld cleaning required.
• GTAW provides precise control over the welding arc, resulting in high-quality,
clean welds suitable for critical applications like aerospace and nuclear
industries.
• GTAW requires a skilled operator due to the manual control of the torch and
filler metal, making it a slower process compared to other welding methods.
• The use of inert gas shielding in GTAW prevents atmospheric contamination
of the weld pool, contributing to the high quality and integrity of the weld
joint.

Plasma Arc Welding (PAW)

• is a specialized form of gas tungsten arc welding that uses a constricted
plasma arc directed at the weld area.
• PAW utilizes a tungsten electrode in a specially designed nozzle to focus a
high-velocity stream of inert gas (e.g., argon) to create a high-temperature
plasma arc stream.
• With temperatures exceeding 17,000 °C, PAW can melt any known metal,
offering advantages like good arc stability, high travel speeds, and excellent
weld quality in applications such as automobile subassemblies and home
appliances.
• PAW is known for producing high-quality welds with deep penetration and
minimal weld defects, making it a preferred choice for industries requiring
high precision and quality welds.
• PAW offers high energy density, allowing for deep weld penetration and
narrow heat-affected zones.
• The process is versatile, capable of welding a wide range of materials,
including stainless steel, aluminum, and titanium.
• PAW is commonly used in industries such as aerospace, automotive, and
electronics due to its ability to produce high-quality, precise welds.

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 • in Plasma Arc Welding (PAW), inert gases like argon or helium are commonly
used as shielding gases to protect the weld pool from atmospheric
contamination.
• The choice of shielding gas depends on the material being welded and the
desired welding characteristics.
• These gases help maintain a stable arc, prevent oxidation of the weld pool,
and contribute to the overall quality of the weld.

Oxyacetylene welding (OAW)

• is a fusion-welding process that uses a high-temperature flame generated by
the combustion of acetylene and oxygen.
• The process involves directing the flame with a welding torch and adjusting
the gas mixture to achieve different types of flames: neutral, oxidizing, and
reducing.
• OAW is commonly used for welding various metals, with acetylene being the
preferred fuel due to its high temperatures and versatility in creating quality
weld joints.
• Oxyacetylene welding is versatile and can be used for various applications,
including cutting, brazing, and heating metals.
• The process requires skill and control to manage the flame temperature and
welding speed effectively.
• OAW is popular in metalworking industries for its portability, affordability, and
ability to weld both ferrous and non-ferrous metals effectively.
• Oxyacetylene welding is suitable for both thin and thick materials, making it a
versatile choice for a wide range of metal thicknesses.
• The equipment for OAW is relatively simple and portable, allowing for
flexibility in various work environments.

Electron-beam welding (EBW)

• uses high-velocity narrow-beam electrons to generate heat that is converted
into welds upon striking the workpiece.
• EBW requires special equipment to focus the beam, typically in a vacuum,
and can weld almost any metal with thicknesses ranging from foil to plate.
• The process produces high-quality welds with deep penetration, minimal
distortion, and small heat-affected zones, making it suitable for applications
in aerospace, automotive, and electronics industries.

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 • Electron-beam welding typically requires a vacuum environment for optimal
performance.
• The level of vacuum affects the penetration depth of the electron beam, with
higher vacuums allowing for greater penetration.
• Different vacuum levels are used in electron-beam welding processes, such as
high vacuum (EBW-HV), medium vacuum (EBW-MV), and even no vacuum
(EBW-NV) for certain materials.

Laser-beam welding (LBW)

• uses a high-power laser beam to generate heat for fusion welding, offering
high energy density and deep penetration capabilities.
• LBW is suitable for welding deep and narrow joints with depth-to-width ratios
typically ranging from 4 to 10, making it ideal for various applications,
including welding transmission components in the automotive industry.
• The process produces high-quality welds with minimal shrinkage or
distortion, good strength, and ductility, and can be automated for precise
control over the welding process on a variety of materials up to 25 mm thick.
• LBW is commonly used in industries such as automotive, aerospace,
electronics, and medical devices for its versatility, efficiency, and ability to
produce high-quality welds.
• Laser-beam welding produces welds of good quality with minimum shrinkage
or distortion. Laser welds have good strength and generally are ductile and
free of porosity.

The major advantages of LBW over EBW are the following:

• A vacuum is not required, and the beam can be transmitted through air.
• Laser beams can be shaped, manipulated, and focused optically (by means of fiber
optics), so the process can be automated easily.
• The beams do not generate X-rays • The quality of the weld is better than in EBW;
the weld has less tendency toward incomplete fusion, spatter, and porosity; and
there is less distortion.

Solid-state bonding
• utilizes diffusion, pressure, and relative interfacial movements to create
strong bonds without melting the materials.
• Techniques like friction welding, resistance welding, and ultrasonic welding
are examples of solid-state welding processes.
• Automation of these processes with robotics, vision systems, sensors, and
computer controls is common for cost reduction, consistency, and increased
productivity.
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Friction Welding
• In the joining processes described thus far, the energy required for welding
(typically chemical, electrical, or ultrasonic energy) is supplied from external
sources.
• in friction welding (FRW), the heat required for welding is generated through
(as the name implies) friction at the interface of the two components being
joined.

Friction Stir Welding (FSW)

• Friction Stir Welding (FSW) is a solid-state welding process developed in 1991,
involving a rotating non-consumable probe.
• The process uses frictional heating to join materials without melting them,
typically achieving temperatures between 230°C and 260°C.
• FSW is versatile, suitable for materials like aluminum, copper, steel, and
titanium, with applications in aerospace, automotive, shipbuilding, and
military industries.
• Welds produced by FSW are of high quality, with minimal pores and uniform
material structure, requiring low heat input and resulting in little distortion.
• FSW is environmentally friendly, as it does not require shielding gas or surface
cleaning, making it a preferred choice for sustainable welding practices.
• The process is known for joining dissimilar materials effectively, producing
high-strength welds with excellent fatigue and corrosion resistance
properties.

• Resistance Spot Welding (RSW)

• is a commonly used process in sheet-metal fabrication and automotive body
assembly.
• In RSW, two opposing solid, cylindrical electrodes apply pressure to a lap joint
of two sheet metals to produce a spot weld.
• The strength of the bond in RSW depends on surface roughness and
cleanliness of mating surfaces.
• The weld nugget in RSW is typically 6 to 10 mm in diameter with a slightly
discolored indentation on the surface.
• Current levels in RSW range from 3000 to 40,000 A, depending on the
materials and thicknesses being welded.

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 • Electrodes in RSW are usually made of copper alloys with sufficient electrical
conductivity and hot strength.
• RSW is suitable for use in manufacturing plants and machine shops, operated
by programmable computer control.
• The process requires accurate control and timing of alternating electric
current and pressure for successful welding.
• RSW is a simple and widely used resistance-welding process, suitable for
various applications in different industries.

Resistance Seam Welding (RSEW)

• is a modification of spot welding where rotating wheels or rollers replace
electrodes.
• RSEW uses continuous AC power supply to produce spot welds that overlap
into a continuous seam for liquid-tight and gas-tight joints.
• Roll spot welding and mash seam welding are variations of RSEW, producing
spot welds at intervals and overlapping welds about one to two times the
sheet thickness, respectively.
• RSEW is used in manufacturing cans, mufflers, gasoline tanks, and tailor-
welded sheet-metal blanks.
• The process requires specialized machinery and is suitable for use in
manufacturing plants and machine shops.
• Operator skill required for RSEW is minimal, especially with modern
machinery controlled by programmable computers.

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