welding an its types

8/11/2019 Welding an Its Types

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What is WeldingJoin together (metal parts) by heating the surfaces to the

point of melting with a blowpipe, electric arc, or othermeans, and uniting them by pressing, hammering, etc


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WeldingParts are joined together by Fusion. Fusion is

brought about by a combination of heat and

pressure between parts being joined. In normal

welding processes very high temperatures andlittle or no pressure is used.

Welding conditions Smooth joint surfaces that match each other

Surfaces clean and free from oxides, grease and dirt.

Metals to be joined have same microstructure


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The metals should be good quality (no internal

impurities)

Welding Preparation

Before starting a weld, the joint edges should be

carefully prepared. Beveling large edges

Cleaning (Chemical/Mechanical)

Weld Joints

Welding Symboles Welding Techniques


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Weld Joints - Parts of a Weld Joint

Joint root

Groove face, Root face and Root edge

Root opening and Bevel

Bevel angle, Groove angle and Groove radius

Weld Joints - Types of Weld Joint

Butt Joint

Lap Joint

T Joint

Corner joint

Edge Joint

Splice Member


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Joint Root

is that portion of a joint to be welded where the membersare closest to each other

The joint root may be

either a point, line, or

an area

The joint roots are

shown as shaded areas

in (A)-(D) and lines in

(E) (F)


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Groove face, Root face and Root edge

Groove face is thatsurface of a member

included in the

groove

Root face (land) is

that portion of the

groove face within

the joint root

Root edge is a root

face of zero width


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Bevel angle, Groove angle and Groove

Radius


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Welding Joints

Butt Joint

A joint between two

members aligned

approximately in the

same plane


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Lap Joint

A joint between two

overlapping members


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T Joint

A joint between twomembers located

approximately at right

angles to each other


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Corner Joint

A joint between twomembers located at

right angles to each

other


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Edge Joint

A joint between the

edges of two or

more parallel or

nearly parallelmembers


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Splice member

is the work piece that spans the joint in a spliced joint

Single-

spliced

butt joint

Double-spliced

butt joint with

joint filler


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Basic components of awelding symbol

Reference Line (Required element)

ArrowTail

Reference Line must always be horizontal,

Arrow points to the line or lines on drawing

which clearly identify the proposed joint or weld

area.


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Weld Symbol Terminology

ARROW SIDE

OTHER SIDE

Work

Fillet Weld (Arrow Side Only) Fillet Weld (Both sides)


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Welding Techniques

There are many different methods of welding. The difference

between them is outlined by two important features

The way the metal is heated

The way additional filler metal if any is fedinto the weld

Types of Welding

Electric arc welding

Gas Welding

Resistance Welding

Friction Welding

Robotic Welding


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Electric Arc Welding

The heat for fusionis supplied by an electric arc

Arc is formed between electrode and work this melts

and fuses the joint edges


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Manual Metal Arc (MMA)

Most widely used of all

the arc welding processes

Commonly called stick

welding

Applications

repair work, structural steelwork,


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In arc welding an electrode is used to conduct currentthrough a workpiece to fuse two pieces together.,


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The Electrode and

Coating

Coating is a combination of chemicals

Cellulosic electrodescontain

cellulose

Rutile electrodestitanium oxide

(rutile)

Basic electrodescontain calciumcarbonate (limestone) and calcium

fluoride (fluorspar)


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Advantages of Electric arc welding

Dis-advantages

Used with many electrode types & sizes Used in all positions

Used on great variety of materials

Flexibility in operator control makes it the

most versatile of all welding processes

Low cost of equipment

Rod becomes shorter & periodically needs replacing

Slows production rate (% time welder welding)


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MIG is similar to MMA in that heat

for welding is produced by forming

an arc between a metal electrode and

the workpiece.But we use very long

electrode wire rolled on pulley.

Metal Arc Gas Shielded (MAGS)

MIG

ApplicationsWelding Sheets and Heavy plates, production

welding by robots on cars


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MIG is similar to

MMA in that heat for

welding is producedby forming an arc

between a metal

electrode and the

workpiece; theelectrode melts to

form the weld bead.

The main difference

is that the metal electrode is a small diameter wire fed from aspool and a sheilding gas is used. As the wire is continuously

fed, the process is often referred to as semi-automatic welding.


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Advantages

Large gaps filled or bridged easily Welding can be done in all positions

No slag removal required

High welding speeds

High weld quality

Less distortion of work piece


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Equipmnt used in MAGS

Three major elements are :

Welding torch and accessories

Welding control & Wire feed motor

Power Source is Transformer

Shielding Gas


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Welding torch and accessories

The welding torch guides the wire and shielding gas to the

weld zone.

Brings welding power to the wire also

Major components/parts of the torch are the contact tip,

shielding gas nozzle, gas diffuser, and the wire conduit

NOZZLE

CONTACT TIP

GAS DIFFUSER


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Welding control and wire feed motor

Main function is to pull

the wire from the spooland feed it to the arc

Controls wire feed speed

and regulates the starting

and stopping of wire feed


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Sheilding Gas

Purpose of shielding gas is toprotect the weld area from thecontaminants in the atmosphere

Gas can be Inert, Reactive, or

Mixtures of both Argon, Helium, and Carbon

Dioxide are the main three gasesused in MAGS


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Tungsten Arc Gas Shielded (TAGS)

TIGTIG is similar to MMA in that

heat for welding is produced

by forming an arc between a

metal electrode and the

workpiece

ApplicationsUsed in joining magnesium and

Aluminium, stainless steels

for high quality welding

Thin sheet material


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In the TIG process the arc

is formed between a

pointed tungsten

electrode and the work

piece in an inert

atmosphere of argon or

helium. The small intense

arc provided by thepointed electrode is ideal

for high quality and

precision welding.

The electrode is not consumed during welding. When filler metalis required, it must be added separately to the weldpool. There

are two currents one for starting the arc the other switched on

using a trigger or foot pedal, this is a high frequency current

to maintain the arc, this is generated by a separte unit.


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Advantages

Superior quality welding

Can be used in mechanised systems

Used to weld aluminium and stainless

steels

Low distortion


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Equipment used in TAGS

Power source

Electrodes

TIG must be operated with a

constant current power source -

either DC or AC

Electrodes for DC welding are normally pure

tungsten. In AC welding, as the electrode will be

operating at a much higher temperature, It should

be noted that because of the large amount of heatgenerated at the electrode, it is difficult to

maintain a pointed tip and the end of the

electrode assumes a spherical or 'ball' profile.


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Sheilding Gas

Argon

Argon + Hydrogen

Argon/Helium

Helium is generally added to increase heat

input (increase welding speed or weld

penetration). Hydrogen will result in cleaner

looking welds and also increase heat input,however, Hydrogen may promote porosity

or hydrogen cracking.

Shielding gas is selected according to the material being welded.


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Gas Welding (Oxy-acetylene)

Separate cylinders and

a hose pipe from each

cylinder transports the

gases to a torch.

Gas and fuel mix inthe torch

burns @ 3100C.

A number of welding processes use a flameproduced by burning a mixture offuel gasand

oxygen. The gas usually used isAcetylenebut other

gases are also used.


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During the welding heat from the flame is

concentrated on the joint edges until the metal

melts and starts to flow. When the molten metal

from both sides melts it starts to fuse, when the

metal cools down the two parts become

PermanentlyjoinedAdditional Filler

Metalis fed in by

hand into the weld

pool, at regular

intervals where it

becomes molten

and joins with the

parent metal.

Th O t l ldi Fl


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Carburising

This kind of flame

is used for welding

High carbon steel

& cast iron.

Amount of

acetylene gas is

high in carburising.

Neutral

A flame resulting

from the burning ofgases supplied in the

proper proportions

for perfect

combustion as

approximately equal

volumes of acetyleneand oxygen

Oxidising

Widely used for

cutting and notsuitable for welding.

When the amount of

oxygen increases, the

flame shortens but

temperature goes toohigh.

The Oxy-acetylene welding Flame

G d


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Gases usedOxygen extracted from air and compressed into

cylinders at high pressure. Cylinder is black.These

cylinder have no welding joint these are complete tube

like cylinders. Pressure contains 1800 psi

Acetylene (C2H2) is a fuel gas. Cannot be compressed

directly as explodes at high pressures. Cylinder colour

coded maroon. We made these cylinders by welding

three parts. Pressur contains 250 psi


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Gas Pressure Regulators

One gauge indicates the pressure of the cylinder and the

other indicates the pressure in the supply pipe to the torch.


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Welding torch

Oxygen and acetylene are delivered to the torch by separatehoses. Each gas is controlled by a valve on the torch. The

two gases mix in the torch and after they are ignited burn at

the nozzle.


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Flashback Arrestors

These are positioned on both the fuel gas and oxygen

supply between the hose and the regulator. Their purpose

is to prevent the return of a flame through the hose into

the regulator.

BackFire

Back fire is a process in which a

Tiny fire particle goes into the cylinder

Through torch and pipe. As a result

It cause big blast.


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Filler Rods and fluxes

Filler rods are used for welding the parts to eachother. they come in different diameters.

Fluxesprotect the weld pool from contamination by

oxygen and nitrogen, they are normally in paste

form placed on a heated filler rod before weldingbegins.11


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Advantages of gaswelding

The equipment is inexpensive, simple and is easily

portable.

Useful for welding light

metals such as automobilebodies and repair works.

Alarge variety ofmaterial can be welded.

Welds can be producedat reasonable cost.

Disadvantages of gaswelding

Equipment must always behandled carefully as incertain circumstancesacetylene is explosive.

A high temperature flamefrom a hand held torch isdangerous when handledcarelessly.

It causes more distortion. The process is not

satisfactory for heavysections.


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Resistance welding

Resistance welding uses the application of electric

current and mechanical pressure to create a weld

between two pieces of metal. Weld electrodes conduct

the electric current to the two pieces of metal as they are

forged together.The welding cycle must first develop

sufficient heat to raise a small volume of metal to the

molten state. This metal then cools while under pressureuntil it has adequate strength to hold the parts together.


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Spot welding

Seam Welding


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Spot welding

Ideal for joining light sheet metal. Theelectrodes are made from copper.

Pressure is applied to the electrodes and

an electric current is passed through the

circuit. The high resistance between the

joint faces causes rapid heating andfusing of a small globule of metal from

both faces.


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Seam welding

The rollers allow the workpiece to

move through the welder

continously. A stream of electrical

pulses pass through the rollers andwelds the joint


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Resistance Welding Benefits

High speed welding

Easily automated

Suitable for high rate production

Economical

Resistance Welding Limitations

Initial equipment costs

Lower tensile and fatigue strengths

Lap joints add weight and material


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Friction welding is a solidstate joining process thatproduces coalescence bythe heat developed

between two surfaces bymechanically inducedsurface motion.


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Friction welding

One part is held stationary while

the other part is rotated

When the parts are hot enough the

rotation is stopped and the parts

forged together

Workpieces

Non-rotating viseMotor

Chuck

SpindleHydraulic cylinder

Brake


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Advantage of frictionalwelding

Easily joins dissimilarmetals.

Friction welds are higherstrength.

Friction welds often costless.

Friction welds minimizethe Heat Affected Zone.

No need of furnace .

A machine of sufficientpower is needed.

T oo high power needed. Tight concentricity

requirements.

Disadvantages offrictional welding


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Robotic welding

A computer sends instructions in electrical

signals or pulses. An interface converts these

digital pulses into analogue electricity for the

motors. The robot is fitted with sensors whichcan send feedback on the position of the robot.

Robots are driven using actuators which

control the robotic arm from an input signal.They can use hydraulic (large robots),

pneumatic(small actuators with simple

control movements) or electrical principles of

operation.


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Advantages of Robotic welding

Faster production rates

Efficent continous operation

Safe working practice

Reliable and consistent welds

Full automation

Cost effective

ExamplesAutomated welding of motor vehicles

skeletel frames and bodies.


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welding an its types

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