UNIT—II JOINING PROCESS
WELDING:

Process of joining similar metals with the application
of heat and with or without the application of
pressure.

While welding the edges of metal pieces are either
melted or brought into plastic condition.

Used in the manufacturing of Auto mobiles bodies,
structural work, tanks, and general machine repair
work. In the industries , welding is used in refineries
and pipe line fabrication.
TYPES OF WELDING PROCESS
 Plastic
Welding
(or)
Pressure
Welding:

Metal pieces are heated to plastic state and
pressed together.
Ex: Electric resistance welding
 Fusion
Welding
(or)
Non-pressure
welding:

Metal is heated to molten state.
Ex: Gas welding, Arc welding
CLASSIFICATION OF WELDING PROCESSES:
1: Gas Welding
(a) Air Acetylene
(b) Oxy Acetylene
(c) Oxy Hydrogen Welding
2: Arc Welding
(a) Carbon Arc welding
(b) Plasma Arc welding
(c) Shield Metal Arc Welding
(d) T.I.G. ( Tungsten Inert Gas Welding)
(e) M.I.G. ( Metal Inert Gas Welding)

3: Resistance Welding:
(a) Spot welding
(b) Seam welding
(c) Projection welding
(d) Resistance Butt welding
(e) Flash Butt welding
o
4: Solid State Welding:
(a) Cold welding
(b) Diffusion welding
(c) Forge welding
(d) Fabrication welding
(e) Hot pressure welding
(f) Roll welding

5: Thermo Chemical Welding
(a): Thermit welding
(b): Atomic welding

6: Radiant Energy Welding
(a): Electric Beam Welding
(b): Laser Beam Welding
GAS WELDING

Joining
of
metals
with
the
help
of
high
temperature flame and filler rod.

Flame is generated by mixture of Oxygen and
Acetylene.

Mixture of combustible gases are also be used.
TYPES OF GAS WELDING
 Oxy-Acetylene
 Air-Acetylene
welding
welding
 Hydrogen-Acetylene
welding
OXY-ACETYLENE WELDING


The temperature generated during the process is
33000c
When the metal is fused, oxygen from the atmosphere
and the torch combines with molten metal and forms
oxides, results defective weld.

Fluxes are added to the welded metal to remove
oxides

Common fluxes used are made of sodium, potassium.
Lithium and borax.

Flux can be applied as paste, powder, liquid.solid
coating or gas.
METHODS OF WELDING

Leftward or Forward Welding
Blow pipe 60-70 degrees
Filler rod 30-40 degrees

Rightward or backward welding
Blow pipe 40-50 degrees
Filler rod 40-50 degrees
WELDING POSITIONS
INCREASING DIFFICULTY
FLAT
HORIZONTA
L
VERTICAL
OVERHEAD
TYPES OF FLAMES


NEUTRAL FLAME

Oxygen and Acetylene ratio is equal.

Temperature about 3250° C.

Used to weld carbon steels, Cast iron, Copper, Al etc.
CARBURISING FLAME

Oxygen and Acetylene ratio is 0.95 to 1

Three Zones

Luminus Zone.

Intermediate cone of white colour.

Outer envelope.

Temperature about 3150° C

Used to weld monel metal, high carbon steel, alloy steel.

OXIDISING FLAME

Oxygen and Acetylene ratio is 1.2 to 1.5

Temperature about 3480° C

Used to weld Copper, Bronze, Zinc-Bearing alloys..
EQUIPMENTS
o
o
o
o
o
o
Gas Cylinders
Pressure Regulators
Pressure Gauges
Welding Torch
Hose and Hose fittings
Safety Devices


OXYGEN CYLINDER

12500-14000 kN/m2

Cylinder capacity 6.23m3

Black Or Green
ACETYLENE CYLINDER

1600-2100 kN/m2

Maroon

PRESSURE REGULATORS

Pressure of gas depends
on the thickness of the metal
to be welded

PRESSURE GAUGE

Two Pressure gauges

One to show the cylinder pressure and another one is to
show working pressure

WELDING TORCH

HOSE AND HOSE FITTINGS
FILLER AND FLUX MATERIALS
d  (t / 2)  1

d = Welding rod diameter

t = Thickness of base plate in mm
S.No
Material to be
welded
Welding rod chemical composition
1
L-C Steels
0.08%C, 0.36%Mn, 0.13%Cr, 0.013%Ni,
0.20%P
2
Mn-Steels
0.14%C, 0.12%Si, 0.81%Mn, 0.25%Ni
3
Cr-Steels
0.24%C, 0.21%Si, 0.42%Mn, 0.96%Cr,
0.17%Ni, 0.35%S

FLUX

Except Lead, Zinc all metals require fluxing.

Also needed for Cast iron and Stainless steel.

Fluxes composes of Borates and Boric Acid, Soda ash and
Small amount of other compounds such as Sodium
Chloride, Ammonium Sulphate, Iron Oxide.

Equal amount Boric Acid and Soda Ash, 2% Aluminium
Sulphate and 15% powdered iron makes Flux.
ARC WELDING
Metal pieces are joined melting their edges by an
electric arc.
 Electric Arc produced between Two Conductors
 Elctrode is one conductor and Workpiece is
another conductor.
 Small Air-gap 3mm.

ARC WELDING EQUIPMENTS
ARC WELDING EQUIPMENTS
ARC WELDING ELECTRODES


Non-consumable electrodes

Made of Carbon, Graphite, Tungsten

Carbon and Graphite – D.C Welding

Tungsten – Both

Filler material added separately.
Consumable electrodes

Bare Electrodes

Flux or lightly coated electrodes

Coated or extruded electrodes


Bare Electrodes

Used to weld wrought iron and mild steel.

Hand arc welding – Sticks or rods

Automatic welding – Coil
Flux or lightly coated electrodes
•
1-5% of electrode weight
•
Light coating is given to increase stability and
ionizing coatings.
•
Chalk 80-85 parts and Water glass 15-20 parts
•
Used to weld non critical structures.


Coated electrodes

1-2 mm layer

15-30% of the weight of the electrode rod.
Electrode size

3.2, 4, 5, 6, 8, 9, 12 mm diameter and length 350 or
450 mm.
FUNCTIONS OF COATINGS

Improves arc stability.

Provides gaseous atmosphere to prevent Oxygen,
Hydrogen and Nitrogen.

Provides a protective slag over hot metal.

Provides flux to remove oxides and other
impurities.

Reduces spatter of weld metal.

Slows down the cooling rate of weld.
ELECTRODE COATINGS

Slag formation ingredients: Asbestos, Mica, Silica,
Titanium oxide, iron oxide, calcium carbonate and
aluminium oxide.

Arc stabilizing ingredients: Potassium silicate, Mica,
Calcium oxide, Sodium oxide, magnesium oxide.

Deoxidizing ingredients: Cellulose, Dolomite, Starch,
Dextrin, Wood flour, graphite

Binding Materials: Sodium silicate, Potassium silicate,
asbestos.

Alloying constituents to increase the strength of the
weld.
RESISTANCE WELDING

Uniting two pieces of metal by the passage of a
heavy electric current while the surfaces are
pressed together.

Factors:

Welding current

Welding pressure

Time of application

Contact area of electrodes



Electrodes

Steel with copper

Copper cadmium

Copper chromium
Advantages

No filler material needed.

Requires little skill.

Can weld dissimilar metals.
Disadvantages

High cost of equipment.

Limited to process.
RESISTANCE SPOT WELDING

3000 – 40000 A, depending
on
the
material
and
thickness.

Steel, Copper, Brass and
light alloys can be joined.

Application: Fabrication of
sheet metal products.
RESISTANCE SEAM WELDING

Welding currents range from 2000 – 5000 A.

Welding speed 1.5 m/min.

Application: Pressure tanks, Evaporators,
Condensers.
RESISTANCE BUTT WELDING

Upset Welding
PERCUSSION WELDING

0.5 to 0.38mm
RESISTANCE PROJECTION WELDING

Stud Welding
TIG WELDING

Also called as Gas Tungsten
Arc Welding (GTAW).

Inert Gas – Gas which does
not combine chemically with
the metal being welded.

Argon & Helium

Strond welds

Alloys of Al, SS, Ni, Cu, CS.

Dissimilar metals can be
welded.
MIG WELDING

Tungsten electrode is replaced
with consumable electrode.

Electrode is driven through
same type collet that holds a
tungsten electrode by a set of
drive wheels.
DIFFERENCE BETWEEN TIG AND MIG WELDING
SUBMERGED ARC WELDING

Flux powder is fed into the
hopper.

Arc submerged in the flux
material.

No Spatter or gases.

No reaction with atmosphere.

High strength and ductility.
FLUX CORE WELDING
FLUX CORE WELDING

Flux cored arc welding is similar to a gas metal
arc welding.

Electrode is tubular in shape and is filled with
flux.

Cored electrodes produce more stable arc improve
weld contour and produce better mechanical
properties.

Flux is more flexible than others.
ELECTRO SLAG WELDING (ESW)

Similar to Electro gas welding.

Difference is Arc is started between electrode tip and
bottom part of the part to be welded.

Flux added first and then melted by the heat on the
arc.

Molten slag reaches the tip of the electrode and the
arc is extinguished.

Heat is then continuously produced by electrical
resistance of the molten slag.

Single or multiple solid as well as flux-cored
electrodes may be used.

Applications: Welding of heavy steel forgings, Large
steel castings, Thick steel plates.
ELECTRO GAS WELDING (EGW)

EGW is welding the edges of sections vertically in one pass with
the pieces placed edge to edge.

Weld metal is deposited into weld cavity between the two pieces
to be joined.

Mechanical drives moves shoes upwards.

Single and multiple electrodes are fed through a conduit and a
continuous arc is maintained using flux-cored electrodes at up to
750 A.
Process capabilities :

Weld thickness ranges from 12mm to 75mm

Metals welded are steels, titanium, aluminum alloys

Applications are construction of bridges, pressure vessels, thick
walled and large diameter pipes, storage tanks and ships.
SPECIAL WELDING PROCESSES

Laser beam welding

Electron beam welding

Friction welding

Diffusion welding

Plasma arc welding

Thermit welding

Flame cutting
LASER BEAM WELDING

Solidification of the weld pool surrounded by the
cold metal is as fast as melting.

Since the time when the molten metal is in
contact
with
the
atmosphere
is
short,
no
contamination occurs and therefore no shields
(neutral gas, flux) are required.

Laser
Welding
communication
manufacture
is
and
of
used
in
aerospace
medical
electronics,
industry,
and
for
scientific
instruments, for joining miniature components.
ELECTRON BEAM WELDING

The electrons are emitted by a cathode (electron
gun).

Due to a high voltage (about 150 kV) applied
between the cathode and the anode the electrons
are accelerated up to 30% - 60% of the speed of
light.

Operation done in vacuum to prevent the
reduction of electron velocity.

Kinetic energy of the electrons converted into
heat energy and the metal is fused.

Welding of Automobile, Aerospace and Airplane.
FRICTION WELDING
FRICTION WELDING
Friction Welding is a Solid State Welding
process, in which two cylindrical parts are brought
in contact by a friction pressure when one of them
rotates.
 Friction between the parts results in heating their
ends.
 Forge pressure is then applied to the pieces
providing formation of the joint.
 Carbon steels, Alloy steels, Tool and die steels,
Stainless steels, Aluminum alloys, Copper alloys,
Magnesium alloys, Nickel alloys, Titanium alloys
may be joined by Friction Welding.

DIFFUSION WELDING

Diffusion Welding is a Solid State Welding process, in which
pressure applied to two work pieces with carefully cleaned surfaces
and at an elevated temperature below the melting point of the metals.
Bonding of the materials is a result of mutual diffusion of their
interface atoms.

In order to keep the bonded surfaces clean from oxides and other air
contaminations, the process is often conducted in vacuum.

No appreciable deformation of the work pieces occurs in Diffusion
Welding.

Diffusion Welding is able to bond dissimilar metals, which are difficult
to weld by other welding processes: Steel to tungsten, Steel to
niobium, Stainless steel to titanium, Gold to copper alloys.

Diffusion Welding is used in aerospace and rocketry industries,
electronics, nuclear applications, manufacturing composite materials.

Plasma Arc Welding is the welding process utilizing heat
generated by a constricted arc struck between a tungsten
non-consumable electrode and either the work piece
(transferred arc process) or water cooled constricting
nozzle
(non-transferred
arc
process).
Plasma is a gaseous mixture of positive ions, electrons and
neutral
gas
molecules.
Transferred arc process produces plasma jet of high energy
density and may be used for high speed welding and
cutting of Ceramics, steels, Aluminum alloys, Copper
alloys,
Titanium
alloys,
Nickel
alloys.
Non-transferred arc process produces plasma of relatively
low energy density. It is used for welding of various metals
and for plasma spraying (coating). Since the work piece in
non-transferred plasma arc welding is not a part of electric
circuit, the plasma arc torch may move from one work piece
to other without extinguishing the arc.
FLAME CUTTING
Oxy-fuel
welding
(commonly
called oxyacetylene welding, oxy welding,
or gas welding in the U.S.) and oxy-fuel
cutting are processes that use fuel gases and
oxygen to weld and cut metals, respectively.
 Pure oxygen, instead of air, is used to increase
the flame temperature to allow localized melting
of the workpiece material (e.g. steel) in a room
environment.
A
common propane/air flame burns at
about 2,000 °C (3,630 °F), a propane/oxygen
flame burns at about 2,500 °C(4,530 °F), and an
acetylene/oxygen flame burns at about 3,500
°C (6,330 °F).

WELDING DEFECTS
SOLDERING

Soldering and brazing are adhesive bonds,
whereas welding is a cohesive bond.

Soldering is an operation of two or more parts
together by molten metal.

Soldering should not be used where much
strength is required, where the joint will be
subjected to vibration or heat.
CLASSIFICATION OF SOLDERING METHODS

Soldering iron methods

Torch method

Dip and wave methods

Induction method

Resistance method

Furnace and hot plate method

Spray method

Ultrasonic method

Condensation method
TYPES OF SOLDER
1.
Soft Solder, which is usually a lead-tin
mixture.
2.
Hard solders
1.
Brass solders (Copper-zinc alloy)
2.
Silver solders (Copper-silver alloy)
3.
Copper solders
4.
Nickel-silver solders
FLUX OR SOLDERING FLUID

During soft soldering flux is necessary to cover
the surface of the components and solder with a
film so that the formation of an oxide is
prevented.

Fluxes are of two kinds:

Those which not only protect the surface, but play an
active chemical part in cleaning it.
Ex: Zinc chloride(killed sprits), Ammonium chloride.

Those which protect previously cleaned surface.
Ex: Tallow, resin, vaseline, olive oil. (Fluxite)
ADVANTAGES

Low cost.

Simplicity and cheapness in equipment.

Properties of base metal not affected.
APPLICATIONS

Connection in wireless set(radio), T.V sets.

Wiring joints in electrical connections, battery
and other terminals.
BRAZING

Brazing is a soldering operation using brass as the joining
medium

It is simply a form of hard soldering using a copper-zinc
alloy.

Brass used for making the joint in brazing is called as
“Spelter”

Three brazing alloys are:

Copper-70%, Zinc-30%; Melting point-960˚C

Copper-60%, Zinc-40%; Melting point-910˚C

Copper-50%, Zinc-50%; Melting point-870˚C

The filler penetrates the gap by capillary attraction.
FLUXES

When
hard
soldering,
the
chief
borax(Powder, granulated or stick form).

Action of the flux:

To prevent an oxide forming.

A cleansing medium to remove dirt.

It aids the capillarity of the molten metal.
flux
is
BRAZING METHODS

Torch brazing

Furnace brazing

Resistance brazing

Induction brazing

Dip brazing

Laser brazing and Electron beam brazing
BRAZING PROCEDURE

The surfaces to be joined are thoroughly cleaned.

Then a paste of flux and spelter is kept in the joint.

Flame is directed over the joint.

The flux and spelter will soon melt and fill the recess
between the joint.

When the joint is hot common salt is put to soften the
glossy hard flux.
ADHESIVE BONDING
BONDING PROCEDURE

Preparing the surface


Metals surfaces cleaned by chemical etching and
mechanical abrasion.
Application of adhesive

Spraying, roller or knife coating,
Assembly
 Curing the joint

Apply adequate pressure during curing.
 Curing period 30 mins at 145˚C
 Large components- 1.4 Mpa pressure & 175˚C
