WELDING PROCESSES
Production Technology
EDPT 201
A. Prof. Dr. Yasser Fouad
A Brief History of Welding
• Late 19th Century
• Scientists/engineers apply advances in electricity to heat
and/or join metals (Le Chatelier, Joule, etc.)
• Early 20th Century
• Prior to WWI welding was not trusted as a method to join two
metals due to crack issues
• 1930’s and 40’s
• Industrial welding gains acceptance and is used extensively in
the war effort to build tanks, aircraft, ships, etc.
• Modern Welding
• the nuclear/space age helps bring welding from an art to a
science
Types of Welding
Fusion Welding Pressure Welding
Homogeneous Heterogeneous Friction Welding
Gas Welding Brazing Soldering
Electroslag MIG
High Energy Beam TIG
Electric Arc Shielded Metal Arc – “Stick”
Weldability of a Metal
• Metallurgical Capacity
• Parent metal will join with the weld metal without
formation of deleterious constituents or alloys
• Mechanical Soundness
• Joint will be free from discontinuities, gas porosity,
shrinkage, slag, or cracks
• Serviceability
• Weld is able to perform under varying conditions or
service (e.g., extreme temperatures, corrosive
environments, fatigue, high pressures, etc.)
Fusion Welding Principles
• Base metal is melted
• Filler metal may be added
• Heat is supplied by various means
• Oxyacetylene gas
• Electric Arc
• Plasma Arc
• Laser
Fusion Welding
ELECTRODE COATING
CORE WIRE
WELDING ATMOSPHERE
ARC STREAM
ARC POOL
SOLIDIFIED SLAG
PENETRATION
DEPTH
WELD
BASE METAL
Weld Metal Protection
• During fusion welding, the molten metal in the
weld “puddle” is susceptible to oxidation
• Must protect weld puddle (arc pool) from the
atmosphere
• Methods
• Weld Fluxes
• Inert Gases
• Vacuum
Weld Fluxes
• Typical fluxes
• SiO2, TiO2, FeO, MgO, Al2O3
• Produces a gaseous shield to prevent contamination
• Act as scavengers to reduce oxides
• Add alloying elements to the weld
• Influence shape of weld bead during solidification
Inert Gases
• Argon, helium, nitrogen, and carbon dioxide
• Form a protective envelope around the weld area
• Used in
• MIG
• TIG
• Shield Metal Arc
Vacuum
• Produce high-quality welds
• Used in electron beam welding
• Nuclear/special metal applications
• Zr, Hf, Ti
• Reduces impurities by a factor of 20% versus other
methods
• Expensive and time-consuming
Types of Fusion Welding
• Oxyacetylene Cutting/Welding
• Shielded Metal Arc (“Stick”)
• Metal Inert Gas (MIG)
• Tungsten Inert Gas (TIG)
Oxyacetylene Welding
• Flame formed by burning a mix of acetylene
(C2H2) and oxygen
TORCH TIP 2300 deg F
Inner Cone: 5000-6300 deg F Combustion Envelope 3800 deg F
• Fusion of metal is achieved by passing the
inner cone of the flame over the metal
• Oxyacetylene can also be used for cutting
metals
Shielded Metal Arc Welding(Stick)-
(SMAW)
• An electric arc is generated between a coated
electrode and the parent metal
• The coated electrode carries the electric current
to form the arc, produces a gas to control the
atmosphere and provides filler metal for the weld
bead
• Electric current may be AC or DC. If the current
is DC, the polarity will affect the weld size and
application
Shielded Metal Arc Welding (SMAW) (con’t)
• Process:
• Intense heat at the arc melts the tip of the electrode
• Tiny drops of metal enter the arc stream and are
deposited on the parent metal
• As molten metal is deposited, a slag forms over the
bead which serves as an insulation against air
contaminants during cooling
• After a weld ‘pass’ is allowed the cool, the oxide layer is
removed by a chipping hammer and then cleaned with a
wire brush before the next pass.
Inert Gas Welding
• For materials such as Al or Ti which quickly form oxide
layers, a method to place an inert atmosphere around the
weld puddle had to be developed
Metal Inert Gas (MIG)
• Uses a consumable electrode (filler wire made of the base
metal)
• Inert gas is typically Argon
DRIVE WHEELS
CONSUMABLE
ELECTRODE
POWER
SOURCE
SHIELDING
ARC COLUMN
GAS
BASE METAL PUDDLE
Tungsten Inert Gas (TIG)
• Tungsten electrode acts as a cathode
• A plasma is produced between the tungsten cathode and the base metal
which heats the base metal to its melting point
• Filler metal can be added to the weld pool
TUNGSTEN
ELECTROD
POWE E
TUNGSTEN
R (CATHODE)
ELECTROD
SOUR
E
CE
++ ++
SHIELDING GAS ARC ---
COLUMN
BASE METAL PUDDLE BASE METAL
(ANODE)
Welding Positions
INCREASING DIFFICULTY
FLAT
HORIZONTAL
OVERHEAD
VERTICAL
Weld Defects
• Undercuts/Overlaps
• Grain Growth
• A wide T will exist between base metal and HAZ. Preheating and
cooling methods will affect the brittleness of the metal in this region
• Blowholes
• Are cavities caused by gas entrapment during the solidification of
the weld puddle. Prevented by proper weld technique (even
temperature and speed)
Weld Defects
• Inclusions
• Impurities or foreign substances which are forced into the weld puddle
during the welding process. Has the same effect as a crack. Prevented by
proper technique/cleanliness.
• Segregation
• Condition where some regions of the metal are enriched with an alloy
ingredient and others aren’t. Can be prevented by proper heat treatment
and cooling.
• Porosity
• The formation of tiny pinholes generated by atmospheric contamination.
Prevented by keeping a protective shield over the molten weld puddle.
Welding Cracks
Residual Stresses
• Rapid heating and cooling results in thermal stresses
detrimental to joint strength.
• Prevention
• Edge Preparation/Alignment – beveled edges and space
between components to allow movement
• Control of heat input – skip or intermittent weld technique
• Preheating – reduces expansion/contraction forces (alloys) and
removes moisture from the surface
• Peening – help metal stretch as it cools by hitting with a
hammer. Use with care since it may work harden the metal
• Heat Treatment – “soak” the metal at a high temperature to
relieve stresses
• Jigs and Fixtures – prevent distortion by holding metal fixed
• Number of Passes – the fewer the better.
Joint Design
BUTT JOINT
FILLET JOINT
STRAP JOINT
CORNER JOINT
LAP JOINT
Generalized Welding Symbol
FAR SIDE DETAILS Field weld symbol
Weld Geometry
D L1-L2
Electrode Weld all-around for
pipes, etc.
Material D L1-L2
ARROW SIDE DETAILS D = Weld Depth (usually equal to plate thickness)
L1 = Weld Length
L2 = Distance between centers for stitched welds
The Field Weld Symbol is a guide for installation. Shipyards
normally do not use it, except in modular construction.
Example Welding Symbol
Geometry symbol for V-groove
One-sided welds are max 80% efficient
Two sided are 100% efficient
1/2
1/2
1/2” 1/2”
Weld Symbols (Butt Joints)
Backing
Weld Symbol (Fillet Joints)
Weld Symbol (Corner Joints)
