ADVANCE WELDING TECHNOLOGY

NME-055
ADVANCE WELDING TECHNOLOGY
31-12-2016 RAVI VISHWAKARMA 1

Survey of Welding and Allied Processes
Manufacturing Processes
Shaping Processes
Surface Processing Operation
Particulate Processing
Material Removal
Deformation Processes
Solidification Processes
Processing Operation
Assembly Operation
Property Enhancing Processes
Coating & deposition Pro.
Cleaning & surface Treatm.
Heat Treatment
Adhesive bonding
Mechanical Testing
Permanent Joining Processes
Permanent Fastining
Threaded fasteners
Brazing & Soldering
Welding

WELDING
– Welding is a materials joining process which produces coalescence
of materials by heating them to suitable temperatures with or
without the application of pressure or by the application of pressure
alone, and with or without the use of filler material.
– Welding is used for making permanent joints.
– It is used in the manufacture of automobile bodies, aircraft frames,
railway wagons, machine frames, structural works, tanks, furniture,
boilers, general repair work and ship building.

TYPES
• Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a
plastic state and forced together by external pressure
(Ex) Resistance welding
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and
allowed to solidify
(Ex) Gas welding, Arc welding

Classification of welding processes:
(i). Arc welding
• Carbon arc
• Metal arc
• Metal inert gas
• Tungsten inert gas
• Plasma arc
• Submerged arc
• Electro-slag
(ii). Gas Welding
• Oxy-acetylene
• Air-acetylene
• Oxy-hydrogen
(iii). Resistance Welding
• Butt
• Spot
• Seam
• Projection
• Percussion
(iv)Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Diffusion
Explosive
(vi)Newer Welding
Electron-beam
Laser
(vii)Related Process
Oxy-acetylene cutting
Arc cutting
Hard facing
Brazing
Soldering

Arc welding
• Equipments:
• A welding generator (D.C.) or Transformer (A.C.)
• Two cables- one for work and one for electrode
• Electrode holder
• Electrode
• Protective shield
• Gloves
• Wire brush
• Chipping hammer
• Goggles

Power Source in Arc Welding
• Direct current (DC) vs. Alternating current (AC)
– AC machines less expensive to purchase and operate, but
generally restricted to ferrous metals
– DC equipment can be used on all metals and is generally
noted for better arc control

Arc Welding Equipments

Arc Welding
Uses an electric arc to coalesce
metals
Arc welding is the most common
method of welding metals
Electricity travels from electrode to
base metal to ground

Fusion Welding: Arc Welding (AW)
A fusion welding process in which coalescence of the metals is achieved by the
heat from an electric arc between an electrode and the work
1. Electric energy from the arc produces temperatures ~ 10,000 F (5500 C),
hot enough to melt any metal.
2. Most AW processes add filler metal to increase volume and strength of weld
joint.
3. A pool of molten metal is formed near electrode tip, and as electrode is
moved along joint, molten weld pool solidifies in its wake

Arc and Power Source Characteristics in
Arc Welding
Arc Characteristics
Power Source Characteristics

Two Basic Types of Arc Welding
(Based on Electrodes)
1. Consumable electrodes
 consumed during welding process
 added to weld joint as filler metal
 in the form of rods or spools of wire
2. Non-consumable electrodes
 not consumed during welding process but does get gradually
eroded
 filler metal must be added separately if it is added

Arc welding (AW): Arc Shielding
1. At high temperatures in AW, metals are chemically reactive to
oxygen, nitrogen, and hydrogen in air
 Mechanical properties of joint can be degraded by these
reactions
 Arc must be shielded from surrounding air in AW processes
to prevent reaction
2. Arc shielding is accomplished by
 Shielding gases, e.g., argon, helium, CO2
 Flux

Arc welding (AW): Flux
 A substance that prevents formation of oxides and other
contaminants in welding, which comes from
1. granules that are created from the welded material.
2. a coating on the stick electrode that melts during welding to
cover operation.
3. a core that is within tubular electrodes and is released as
electrode is consumed.
 Melts during welding to be liquid slag that hardens when
cooled. The slag should be removed for a clean look by
brushing or grinding off.

Consumable Electrode AW Processes
 Shielded Metal Arc Welding (or Stick Welding)
 Gas Metal Arc Welding (or Metal Inert Gas Welding)
 Flux-Cored Arc Welding
 Electro-gas Welding
 Submerged Arc Welding

 Uses a consumable electrode consisting of a filler metal rod and coating
around rod.
 Coating composed of chemicals that provide flux and shielding.
 Low cost welding system: Power supply, connecting cables, and electrode
holder available for $300 to $400.
AW: Consumable: Shielded Metal Arc Welding
(SMAW)

SMAW Applications
 Used for steels, stainless steels, cast irons, and certain
nonferrous alloys.
 Not used or rarely used aluminum and its alloys, copper
alloys, and titanium.
 Can be used in windy weather.
 Can be used on dirty metals (i.e. painted or rusted surfaces).
 Good for repair work.
 Makes thick welds.

AR: Consumable: Gas Metal Arc Welding
(GMAW) or Metal Inert Gas (MIG) Welding
Uses a consumable bare metal wire as electrode with shielding by
flooding arc with a gas
1. Wire is fed continuously and automatically from a spool
through the welding gun.
2. Shielding gases include argon and helium for aluminum
welding, and CO2 for steel welding.
3. Bare electrode wire (no flux) plus shielding gases eliminate
slag on weld bead. No need for manual grinding and cleaning
of slag
4. Medium cost welding system: $1000 to $1200

Gas Metal Arc Welding

GMAW Advantages over SMAW
1. Continuous welding because of continuous wire electrode.
Sticks must be periodically changed in SMAW.
2. Higher deposition rates.
3. Eliminates problem of slag removal.
4. Can be readily automated.
5. Has better control to make cleaner & narrower welds than
SMAW.

GMAW Applications
1. Used to weld ferrous and various non-ferrous and metals.
2. Good for fabrications such as frames and farm equipment.
3. Can weld thicker metal (not as thick as SMAW).
4. Metal must be clean to start weld.

Non-consumable Electrode Processes
 Gas Tungsten Arc Welding
 Plasma Arc Welding
 Carbon Arc Welding
 Stud Welding

AW: non-consumable: Gas Tungsten Arc Welding
(GTAW) or Tungsten Inert Gas (TIG) Welding
Uses a non-consumable tungsten electrode and an inert gas for arc
shielding
1. Melting point of tungsten = 3410C (6170F).
2. Used with or without a filler metal. When filler metal used, it is
added to weld pool from separate rod or wire.
3. Applications: aluminum and stainless steel mostly.
4. High cost for welding system: $4000.

Gas Tungsten Arc Welding
Filler rod

Advantages and Disadvantages of GTAW
Advantages:
1. High quality welds for suitable applications
- Welds are cleaner and narrower than MIG
2. No spatter because no filler metal through arc
3. Little or no post-weld cleaning because no flux
Disadvantages:
1. More difficult to use than MIG welding
2. More costly than MIG welding

GTAW Applications
1. Used to weld ferrous and various non-ferrous and metals.
2. Can weld various dissimilar metals together.
3. Good for fabrications such as aircraft or race car frames.
4. Used for welding thinner metal parts (not as thick as MIG).
5. Metal must be very clean to start weld.

Plasma Arc Welding

Advantages and Disadvantages of PAW
Advantages:
• Good arc stability and excellent weld quality
• Better penetration control than other AW processes
• High travel speeds
• Can be used to weld almost any metals
Disadvantages:
• High equipment cost
• Larger torch size than other AW processes
– Tends to restrict access in some joints

Ultrasonic Welding
Friction Welding
Diffusion Welding
Resistance Welding
Solid state welding processes

Friction Welding (Inertia Welding)
• One part rotated, one stationary
• Stationary part forced against
rotating part
• Friction converts kinetic energy to
thermal energy
• Metal at interface melts and is
joined
• When sufficiently hot, rotation
is stopped & axial force
increased
Inertia Welding

Friction Welding (FRW)
SSW process in which coalescence is achieved by frictional heat
combined with pressure
• When properly carried out, no melting occurs at faying
surfaces
• No filler metal, flux, or shielding gases normally used
• Process yields a narrow HAZ
• Can be used to join dissimilar metals
• Widely used commercial process, amenable to automation and
mass production

• (1) Rotating part, no contact; (2) parts brought into contact to
generate friction heat; (3) rotation stopped and axial pressure
applied; and (4) weld created
Friction Welding

Applications and Limitations of Friction Welding
Applications:
• Shafts and tubular parts
• Industries: automotive, aircraft, farm equipment, petroleum
and natural gas
Limitations:
• At least one of the parts must be rotational
• Flash must usually be removed (extra operation)
• Upsetting reduces the part lengths (which must be taken into
consideration in product design)

• Good for dissimilar metals
Diffusion Welding
• Parts forced together at high temperature
(< 0.5Tm absolute) and pressure
• Atoms diffuse across interface
• Heated in furnace or by resistance heating
• Bond can be weakened by surface
impurities
•After sufficient time the interface disappears

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
junction to be welded
• Principal RW process is resistance spot welding (RSW)

Resistance Welding
• Resistance welding,
showing components in
spot welding, the main
process in the RW
group

Components in Resistance Spot Welding
• Parts to be welded (usually sheet metal)
• Two opposing electrodes
• Means of applying pressure to squeeze parts between
electrodes
• Power supply from which a controlled current can be applied
for a specified time duration

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 mass production of automobiles, metal
furniture, appliances, and other sheet metal products
– Typical car body has ~ 10,000 spot welds
– Annual production of automobiles in the world is
measured in tens of millions of units

• (a) Spot welding cycle
• (b) Plot of force and
current
• Cycle: (1) parts
inserted between
electrodes, (2)
electrodes close, (3)
current on, (4) current
off, (5) electrodes
opened
Spot Welding Cycle

Advantages and Drawbacks of Resistance Welding
Advantages:
• No filler metal required
• High production rates possible
• Lends itself to mechanization and automation
• Lower operator skill level than for arc welding
• Good repeatability and reliability
Disadvantages:
• High initial equipment cost
• Limited to lap joints for most RW processes

Resistance Seam Welding (RSEW)
Uses rotating wheel electrodes to produce a series of
overlapping spot welds along lap joint Can produce
air-tight joints.
Applications:
– Gasoline tanks
– Automobile mufflers
– Various sheet metal containers

Resistance Seam Welding

Resistance Projection Welding (RPW)
A resistance welding process in which coalescence occurs at one
or more small contact points on the parts
• Contact points determined by design of parts to be joined
• May consist of projections, embossments, or localized
intersections of parts

(1) Start of operation, contact between parts is at projections;
(2) when current is applied, weld nuggets similar to spot welding
are formed at the projections
Resistance Projection Welding
31-12-2016
RAVI VISHWAKARMA
44

Other Resistance Projection Welding Operations
• (a) Welding of fastener on sheet metal and (b) cross-wire
welding

Arc welding
Advantages
– Most efficient way to join
metals
– Lowest-cost joining
method
– Affords lighter weight
through better utilization
of materials
– Joins all commercial
metals
– Provides design flexibility
Limitations
• Manually applied, therefore
high labor cost.
• Need high energy causing
danger
• Not convenient for
disassembly.
• Defects are hard to detect at
joints.

Comparison of A.C. and D.C. arc welding
Alternating Current (from Transformer)
More efficiency
Power consumption less
Cost of equipment is less
Higher voltage – hence not safe
Not suitable for welding non ferrous metals
Not preferred for welding thin sections
Any terminal can be connected to the work or electrode

Direct Current (from Generator)
Less efficiency
Power consumption more
Cost of equipment is more
Low voltage – safer operation
suitable for both ferrous non ferrous metals
preferred for welding thin sections
Positive terminal connected to the work
Negative terminal connected to the electrode

SMAW - DC Polarity
Straight Polarity Reverse Polarity
Shallow penetration
(thin metal)
(+)
(–)
Deeper weld penetration
(–)
(+)
AC - Gives pulsing arc
- used for welding thick sections
Electric arc welding --Polarity

OXYFUEL WELDING
• OFW is the term to describe the group of fusion operations that
burn various fuels mixed with oxygen to perform welding.
• The OFW processes employ several type of gases, which is the
primary distinction among the members of this group.
• The most important OFW process is oxyacetylene welding. Filler
materials are used to supply additional material to the weld zone.
Flux is often used to clean the surfaces and to retard oxidation by
providing inert gas shield around the weld area. It also helps in
removing oxide and other impurities. Borax, is the most common
flux, but sometimes other substances are added to improve its
effectiveness.

OXYFUEL WELDING
• The heat is obtained by combustion of acetylene and oxygen.
Here primary combustion occurring in the inner zone gives:
C2 H2 + O2 → 2CO + H2 + Heat
and the second reaction in the outer zone gives:
2CO + H2 + 1.5O2 → 2CO2 + H2 O + Heat
• The maximum temperature at the tip of inner cone reaches up
to 3000-3500°C. Therefore, most gas welding is performed by
keeping this inner zone tip just above the metal to be welded
so that maximum temperature is available for welding.

GAS WELDING EQUIPMENT...
1. Gas Cylinders
Pressure
Oxygen – 125 kg/cm2
Acetylene – 16 kg/cm2
2. Regulators
Working pressure of oxygen 1 kg/cm2
Working pressure of acetylene 0.15 kg/cm2
Working pressure varies depends upon the thickness of the work
pieces welded.
3. Pressure Gauges
4. Hoses
5. Welding torch
6. Check valve
7. Non return valve

Oxy-Acetylene welding

TYPES OF FLAMES…
• Oxygen is turned on, flame immediately changes into a long white
inner area (Feather) surrounded by a transparent blue envelope is
called Carburizing flame (30000c)
• Addition of little more oxygen give a bright whitish cone
surrounded by the transparent blue envelope is called Neutral flame
(It has a balance of fuel gas and oxygen) (32000c)
• Used for welding steels, aluminum, copper and cast iron
• If more oxygen is added, the cone becomes darker and more
pointed, while the envelope becomes shorter and more fierce is
called Oxidizing flame
• Has the highest temperature about 34000c
• Used for welding brass and brazing operation

Three basic types of oxyacetylene flames used in oxyfuel-gas
welding and cutting operations: (a) neutral flame; (b) oxidizing
flame; (c) carburizing, or reducing flame.

Three basic types of oxyacetylene flames used in oxyfuel-gas
welding and cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing
flame.31-12-2016 RAVI VISHWAKARMA 58

TEMPERATURE DISTRIBUTION ALONG THE
FLAME

TYPES OF FLAMES…
• A neutral flame is obtained when the ratio of is oxygen and acetylene
is 1. Most gas welding operations are carried out by this flame.
• An oxidizing flame is obtained when this ratio is more than 1. This
type of flame is not suitable for welding of steels since excess oxygen
present reacts with carbon in steel and is generally used for welding of
copper and its alloys.
• When the ratio in mixture is less than 1 a carburizing flame is
obtained. In this type of flame acetylene decomposes into carbon and
hydrogen and the flame temperature gets reduced. Joining operations
such as brazing and soldering which require lower temperature
generally use this flame

Weld defects
Classification of Weld Joint Discontinuities
Geometric
• Misalignment
• Undercut
• Concavity or Convexity
• Excessive Reinforcement
• Improper Reinforcement
• Overlap
• Burn-through
• Backing left on
• Incomplete Penetration
• Lack of Fusion
• Shrinkage
• Surface Irregularities
Other
• Arc Strikes
• Slag Inclusions
• Tungsten Inclusions
• Oxide Films
• Spatter
• Arc Craters

POROSITY
• Porosity is the entrapment of
small volumes of gas in
solidifying weld metal
• Prevention
– Drying consumables
– Cleaning, degreasing
material being welded
– Electrode or filler metals
with higher level of
deoxidants
– Sealing air leaks, reducing
excess shielding gas flow

Molten weld metal is able to hold more gas than solid weld
metal. For this reason, gas bubbles tend to evolve as the liquid
metal solidifies. These gas bubbles trapped within the solid weld
metal are referred to as porosity. Although porosity is sometimes
noted at the surface of a weld, visual inspection cannot detect
internal porosity. Radiography and ultrasonic methods are
required. Localized regions of porosity can be cut from a weld; a
repair is then made. For general porosity throughout a weld, the
entire weld must be gouged out and rewelded.

SLAG INCLUSIONS
• Slag inclusions, as the name
implies, are small pieces of welding
slag which are trapped in the weld
metal. Unlike porosity, which is
usually spherical, slag inclusions are
irregularly shaped. Since these are
internal discontinuities, radiography
or ultrasonic testing is required for
detection. Weld regions containing
slag inclusions must be cut out and
rewelded.
Slag inclusions are irregularly shaped,
not spherical like porosity Prevention
Position work and/or change
electrode/flux to increase slag
control
Better slag removal between passes
Dress weld surface smooth if it is
likely to cause slag traps
Remove heavy mill scale on plate

LACK OF FUSION
• Lack of fusion is caused by
incorrect welding conditions
• Prevention
– Procedure for complete
fusion should be verified
by testing
– Increased energy input
– Correct electrode angle
and work position
• Lack of fusion can occur at
the weld sidewall, root, or
between individual passes.
Magnetic particle and dye or
fluorescent penetrant may
be used to detect this
discontinuity if it reaches
the surface. Otherwise,
radiography or ultrasonic
methods must be used.
Affected regions must be
cut out and rewelded.

INCOMPLETE ROOT PENETRATION
• Incomplete root penetration can
be caused by
– Excessively thick root face,
insufficient root gap
– Incorrect welding conditions
– Misalignment of second weld
• Prevention
– Improved joint preparation
– Test weld verifications for
correct parameters
– Reassessment of back
gouging
• Incomplete root penetration is the
failure of a weld to extend into the
root of a joint. For a double weld,
it is an internal discontinuity and
can be detected only by
radiography or ultrasonic testing.
It can be detected by magnetic
particle, and dye or fluorescent
penetrant methods if the root side
is accessible. A long pipeline
would be an example of when the
weld root (inside the pipe) would
not be accessible. This defect is
repaired by cutting it out and
rewelding.

OVERLAP
• Overlap is an imperfection at
the weld toe or root caused by
metal flowing onto the surface
of the base metal without
fusing to it
• Prevention
– Adjust electrode
manipulation to ensure
fusion of base metal
– Limit size of fillet to 9-
mm leg length
• Overlap is often associated with
horizontal welding; welding in
the flat position can help to
eliminate this problem. Overlap
can be detected visually and can
be supplemented with dye
penetrant. It is corrected by
cutting back to sound weld
metal. Rewelding may be
necessary

UNDERCUT
• Undercut is an irregular
groove at the weld toe in the
parent metal or previous
pass caused by
– excessive weaving
– melting of top edge of fillet
weld with high current
• Prevention
– Weld in flat position
– Change shielding gas to
one which produces better
wetting
– Terminate welds so they
don’t finish at a free edge
• Undercut is another defect that can
be associated with horizontal
welding among other factors such
as high current and excessive
weaving. Flat position welding
can aid in eliminating this
discontinuity. It is detected
visually and measured by a depth
gauge. Deep undercut is ground
out and weld repaired

SPATTER
• Spatter consists of small droplets of
electrode material that land beside the
weld and may or may not fuse to the
base material
• Prevention
– Reduce energy input
– Shorter arc length
– Reposition current return clamp to
reduce magnetic arc blow or switch to
AC current
• As metal drops transfer from the
electrode to the weld pool, some are
blown clear of the weld and form drops
of spatter on the base plate. All open
arc consumable electrode processes
produce some spatter.
• Spatter can occur when the energy input
is too high or when the arc length is
excessive. Arc blow can also cause
spatter, as can insufficient inductance in
GMAW or CO2 welding.
• Spatter can be detected visually. It can
be removed by scraping or by light
grinding. Anti-spatter coatings are
available on the market that prevent
spatter from adhering to the base
material.

GAS CUTTING
• Ferrous metal is heated in to red hot condition and a jet of pure
oxygen is projected onto the surface, which rapidly oxidizes
• Oxides having lower melting point than the metal, melt and are
blown away by the force of the jet, to make a cut
• Fast and efficient method of cutting steel to a high degree of
accuracy
• Torch is different from welding
• Cutting torch has preheat orifice and one central orifice for oxygen
jet
• PIERCING and GOUGING are two important operations
• Piercing, used to cut a hole at the centre of the plate or away from
the edge of the plate
• Gouging, to cut a groove into the steel surface

Flame Cutting
• Metal is merely melted by the
flame of the oxyfuel gas torch
and blown away to form a gap or
kerf.
• When ferrous metal is cut,
actually burning of iron takes
place according to one or more
of the following reactions
Fe+ O Feo+ Q
3Fe+2 O2 Fe3 O4+ Q
4Fe+3 O2 2Fe2 O3 + Q

• Because, these reactions cannot take place below 815°C oxyfuel flame is first used to raise
the metal temperature where burning can be initiated. Then a stream of pure oxygen is
added to the torch (or the oxygen content of the oxyfuel mixture is increased) to oxidize
the iron. The liquid iron and iron oxides are then expelled from the joint by the kinetic
energy of the oxygen gas stream.
• Low rate of heat input, and need of preheating ahead of the cut, oxyfuel produces a
relatively large heat affected zone and thus associated distortion zone.
• The process is suitable when edge finish or tolerance is not critical.
• Theoretically heat generated due to burning of Fe is sufficient to continue cutting however
due to losses additional heat supply is needed. If the work is already hot due from the
other processes, supply of oxygen through a small diameter pipe is needed to continue cut.
This is called Oxygen Lance Cutting. A work piece temperature of 1200°C is needed to
sustain the cutting.
• Low carbon steel from 5 to 75 mm can be cut.

GAS CUTTING…
Manual Gas Cutting

Weld joints

SOLID / LIQUID STATE BONDING
• Low temperature joining methods are used when the metal to
be joined cannot withstand high temperature, or intricate
sections are to be joined, or dissimilar metals are to be joined,
or weldability of material is poor.
• In these methods, the gap between the metal pieces to be
joined is filled with molten filler material after heating the
base metal. Melting point of filler material is much lower than
base metals.
• The bonding is not due to melting of parent metal and fusion.

• Filler material is drawn into the gap between the metal pieces
to be joined by capillary action and the bond formation is
initiated when the molten filer metal comes under intimate
contact with the solid surface as in solid state welding.
• The nature of bond formed is much complex here, and
invariably there is some degree of intersolubility between filler
and base metals.
• This inter-diffusion at the base metal surface and resulting
alloy has a strength which is very close to that the base metal.

• For a good joint strength the liquid filler
metal; must flow into the gap between
the metal pieces to be joined and cover
the entire surface area, without gaps or
blow holes. The following usually
insures good bonding:
– Clean base metal surfaces
– Maintain optimum gap
– Heat the joining area above melting
temperature of the filler material
– Use fluxes for welding of base metal
surfaces.
• Joint strength is sensitive to the gap and
there exists an optimum gap for a filler
material.

Brazing and Soldering
• Brazing
It is a low temperature joining process. It is performed at
temperatures above 840º F and it generally affords strengths
comparable to those of the metal which it joins. It is low
temperature in that it is done below the melting point of the base
metal. It is achieved by diffusion without fusion (melting) of the
base
Brazing can be classified as
Torch brazing
Dip brazing
Furnace brazing
Induction brazing

BRAZING
Brazing methods
(a) Torch and filler rods
(b) Ring of filler metal at
entrance of Gap
(c) Foil of filler metal
between flat part surfaces

• In brazing the joint is made by heating the base
metal red hot and filling the gap with molten
metal whose melting temperature is typically
above 450°C but below melting temperature o
base metal. The filler metals are generally
copper alloys. Cu-Zn and Cu-Ag alloys are
used for brazing because they form alloy with
iron and have good strength.

VARIOUS BRAZING JOINTS
(a) Conventional butt
(b) Scarf joint
(c) Stepped joint
(d) Increased crossest ion
(a)Conventional Lap
(b) Cylindrical part
(c) Sandwiched part
(d) Use of sleeve

Brazing

Advantages & Disadvantages
Advantages
• Dissimilar metals which can not be welded can be joined by brazing
• Very thin metals can be joined
• Metals with different thickness can be joined easily
• In brazing thermal stresses are not produced in the work piece.
Hence there is no distortion
• Using this process, carbides tips are brazed on the steel tool holders
Disadvantages
• Brazed joints have lesser strength compared to welding
• Joint preparation cost is more
• Can be used for thin sheet metal sections

SOLDERING
• Soldering is very similar to brazing except that filler material
is usually a lead-tin based alloy which has much lower
strength and melting temperature around 250°C.
• In this process less alloying action between base metal and
filler material as compared to brazing takes place hence the
strength of joint is lesser.
• It is carried out using electrical resistance heating

Soldering
• It is a low temperature joining
process. It is performed at
temperatures below 840ºF for
joining.
• Soldering is used for,
• Sealing, as in automotive
radiators or tin cans
• Electrical Connections
• Joining thermally
sensitive components
• Joining dissimilar metals

THERMIT WELDING (TW)
FW process in which heat for coalescence is produced by
superheated molten metal from the chemical reaction of
thermite
• Thermite = mixture of Al and Fe3O4 fine powders that produce
an exothermic reaction when ignited
• Also used for incendiary bombs
• Filler metal obtained from liquid metal
• Process used for joining, but has more in common with casting
than welding

• (1) Thermit ignited; (2) crucible tapped, superheated metal
flows into mold; (3) metal solidifies to produce weld joint
Thermit Welding

TW Applications
• Joining of railroad rails
• Repair of cracks in large steel castings and forgings
• Weld surface is often smooth enough that no finishing is
required

WELDING METALLURGY
• In fusion welded joint, where three distinct zones can be
identified:-
• The base metal
• The heat affected Zone
• The fusion Zone

Two major concerns occur in the heat affected zone which
effect weldability these are, a.) changes in structure as a result
of the thermal cycle experienced by the passage of the weld
and the resulting changes in mechanical properties coincident
with these structural changes, and b.) the occurrence of cold or
delayed cracking due to the absorption of hydrogen during
welding.

Heat Affected Zone
• The Heat-Affected Zone (HAZ) is an area of a base metal which, while
not melted, still has had its chemical properties altered by high temperature
heat. This phenomenon primarily occurs during welding or high-heat
cutting. The high temperature from the welding process and eventual re-
cooling causes this change from the weld interface to the end of the
sensitizing temperature in the metal. These areas can be varying sizes and
levels of severity.
• The metallurgical changes that can occur at the HAZ tend to cause stresses
that reduce the strength of the material. The HAZ can also suffer from a
decreased resistance to corrosion and/or cracking (i.e, sensitization). These
metallurgical changes can also lead to the formation of nitrides at the HAZ,
which can affect weldability. In addition, the microstructure at the HAZ can
be altered in a way that increases its hardness compared to the surrounding
material. Hardness, sensitization, and high local stresses in or near the HAZ
may be mitigated by practices such as controlled pre- and post-weld heat
treatment and solution annealing.

How much these changes in metallurgical and physical
properties can affect the HAZ of the material is dependent
on a number of factors, including the base material, the
weld filter metal, and the amount and concentration of heat
input during the welding process.

Hardfacing
Hard facing is a metalworking process where harder or tougher
material is applied to a base metal. It is welded to the base
material, and generally takes the form of specialized electrodes
for arc welding or filler rod for oxyacetylene and TIG welding.
Powder metal alloys are used in (PTA) also called Powder plasma
welding system and Thermal spray processes like HVOF, Plasma
spray, Spray and Fuse, etc.

• Hard facing may be applied to a new part during production to
increase its wear resistance ,or it may be used to restore a worn-
down surface. Hard facing by arc welding is a surfacing operation
to extend the service life of industrial components, pre-emptively
on new components, or as part of a maintenance program. The
result of significant savings in machine down time and production
costs has meant that this process has been adopted across many
industries such as Steel, Cement, Mining, Petro chemical, Power,
Sugar cane and Food. According to the results of an experimental
study, the SMAW (Shielded Metal Arc Welding) and the GMAW
(Gas Metal Arc Welding)hard facing processes were effective in
reducing the wear on the mould board ploughshare. With the
SMAW and GMAW hard facing processes, the life span of the
ploughshare was increased approximately 2 times.

Cladding
Cladding is the bonding together of dissimilar metals. It is
different from fusion welding or gluing as a method to fasten the
metals together. Cladding is often achieved by extruding two
metals through a die as well as pressing or rolling sheets together
under high pressure.

Microstructure Welding
The microstructural studies of friction welding helps in
understanding microstructural changes occurred during
friction welding process. High temperature and strain during
friction welding process changes the microstructure of the
parent material.

Welding Symbols
Representation of welds on drawings requires the use of following
elements-
1. A basic symbol to specify each type of weld.
2. A reference line and an arrow to indicate the location the weld in a
joint.
3. Supplementary symbols to mark weld-all-round, finish of welds
etc.
4. Weld dimensions in cross-section and in length.

Basic Weld Symbols
FILLET
SQUARE BUTT
SINGLE V-BUTT
AND MANY MORE SYMBOLS…..

WELDING DESIGN
Before an arc can be struck on metal, the product must be designed to serve its
purpose, the material chosen and the method of welding determined in more or
less detail.
The weldment design engineer must
I. Know the limitations and specific requirements of the processes as well
as the equipment available on the shop floor.
II. Have a good working knowledge of the shop problems of shrinkage and
distortion.
III. Have accurate knowledge not only of suitability but also of availability of
materials or the costs of extras.
IV. Be able to calculate stresses, strengths and determine weld sizes and put
these together to work out a design that meets all service requirements.

Welding Joint Design
since, welding joins metals, design for welding is chiefly concerned with
joints-when to use a joint, how to weld it, where to place it, what to do and
what not to do.
Selection and preparation of weld joints is an important step in the fabrication
of a weldment.
Selection of correct joint design is very essential if welded members are to
perform within the load service, corrosive atmosphere and safety requirements.

Welding
Fusion Welding (FW)
Solid State Welding (SSW)
Consumable electrodes Non-consumable electrodes
Summary
Shielding
Flux
Various welding processes (AW) are developed to address the two issues: shielding and
flux
Arc weldingOxyfuel welding

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ADVANCE WELDING TECHNOLOGY

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