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 weldingo 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 welding

Air-Acetylene 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

FLAT

HORIZONTAL

VERTICAL

OVERHEAD

INCREASING DIFFICULTY

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..

EQUIPMENTSo Gas Cylinderso Pressure Regulatorso Pressure Gaugeso Welding Torcho Hose and Hose fittingso 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 = Welding rod diameter

t = Thickness of base plate in mm

( / 2) 1d t

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 is used in electronics,

communication and aerospace industry, for

manufacture of medical and 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 flux is

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.

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