main welding

8/6/2019 Main Welding

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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.

WELDING


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Classification of welding processesClassification of welding processes

welding

Forge or Pressure

Welding

( Under pressure

without additional filler

metal )

Fusion or non

pressure welding

( With additional filler

metal )

Forge or Pressure welding :- The work piece are heated to plastic state & then work

pieces are joined together by applying pressure on them. In this case no filler material

is used.

Fusion or non- pressure welding :- Here edge of work piece to be joined & filler material

both are heated to a temp. above the melting point of the metal & then allow to solidify


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Forge or

pressure welding

Welding heat created by

Furnace Electric current friction

Forge or furnace welding Resistance welding friction

welding

Spot seam projection flash butt


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Fusion or non

pressure welding

Welding heat created

by

gas Electric Arc chemical reaction

Oxy-acetylene welding Thermit welding

Carbon arc metal arc atomic hydrogen submerged arc plasma arc electro slagTIG MIG


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Other processes of welding are :

Solid State welding : The solid state welding depends upon the theory

that if two perfectly clean metallic surfaces are placed in an intimate contact ,

the cohesive force between atoms of the two surfaces is sufficient to hold them

together.

The various solid state welding process are:

Friction Welding

Ultrasonic Welding

Diffusion Welding

Explosive Welding

Modern Welding Processes: Electron Beam Welding

Laser Beam Welding


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Classification of welding processes:(i). Arc welding

Carbon arc

Metal arc

Gas Metal arc

Gas Tungsten arc

Plasma arc

Submerged arc

Electro-slag

Atomic hydrogen arc

Flux core arc

(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)NewerWelding

Electron-beam

Laser

(vii)Related Process

Oxy-acetylene cutting

Arc cutting

Hard facing

Brazing

Soldering


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Resistance Welding

ResistanceWelding is a pressure welding technique using high

current and low voltage

The current passing through the two overlapping work pieces causes

local heating and temperature of the metallic pieces raises to the

fusion point due to resistance offered by the work pieces to flow of

current

Subsequent application of pressure results in permanent joining of the

work pieces by the formation of weld without the use of filler material

Work pieces are placed between two rods or wheels(rolls), which

serve as conductor for producing welds

AC electric current is supplied through copper electrodes or rolls

connected to the secondary coil of a welding transformer.

It is used for welding thin sheets of similar metallic materials


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The following metals may be welded by Resistance Welding:

Low carbon steels - the widest application of Resistance Welding

Aluminum alloys

Medium carbon steels, high carbon steels andAlloy steels (may be welded, but theweld is brittle)

Advantages of Resistance Welding:

High welding rates;Low fumes;

Cost effectiveness;

Easy automation;

No filler materials are required;

Low distortions.

Disadvantages of Resistance Welding:High equipment cost;

Low strength in case of discontinuous welds;

Thickness of welded sheets is limited - up to 6 mm


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Resistance Welding (RW) is used for joining vehicle body parts, fuel tanks, domesticradiators, pipes of gas oil and water pipelines, wire ends, turbine blades, railway tracks.

The most popular methods of Resistance Welding are:

Resistance spot welding

Resistance seam weldingResistance butt welding

Resistance flash welding

Resistance projection welding


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Spot Welding (RSW)

Spot Welding is a Resistance Welding (RW) process, in

which two or more overlapped metal sheets are joined by

spot welds.

.

Spot welding is widely used in automotive industry for

joining vehicle body parts.


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Spot Welding is a Resistance

Welding (RW) process, in which

two or more overlapped metal

sheets are joined by spots,accompanied by heating

relatively small sections of the

parts or pieces between suitable

electrodes under pressure.

The method uses pointed copper

electrodes providing passage of

electric current. The electrodes

also transmitt pressure required

for formation of strong weld

Diameter of the weld spot is in

the range (3 - 12 mm).


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(a) Spot welding cycle,

(b) plot of squeezing force &

current in cycle

(1) parts inserted between

electrodes

(2) electrodes close, forceapplied

(3) current on

(4) current off

(5) electrodes opened.

Spot Welding Cycle


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.

Seam Welding is a Resistance

Welding (RW) process of

continuous joining of overlapping

sheets by passing them betweentwo rotating electrode wheels.

Heat generated by the electric

current flowing through the

contact area and pressure

provided by the wheels are

sufficient to produce a leak-tight

weld.

Seam Welding is high

speed and clean process,

which is used when

continuous tight weld isrequired (fuel tanks, drums,

domestic radiators).


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Resistance Seam Welding

Side view


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Spot

1. The electrodes are a

pair of copper rods

between which the

sheets to be welded are

positioned2. The welding takes place

at discrete intervals

3. It is used for

components such as flat

sheets , panels as in car

bodies.

Seam

1. Electrodes are apair of rotating

copper rolls

between which

sheets to be

welded are passed2. The seam weld

joints are

continuous

3. It is used to weld

components such

as a fuel tankshells & other

application which

require the joint to

be leak proof

ResistanceWelding


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Flash Welding (FW) or Flash butt

welding is a Resistance Welding

(RW) process, in which ends of rods

(tubes, sheets) are heated and fusedby an arc struck between them and

then brought into a contact under a

pressure) producing a weld.

The welded parts are held in electrode

clamps, one of which is stationary and

the second is movable.


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Flash Welding (FW)

Flash Welding method permits fast (about 1 min.) joining of large and complex parts.

Steels,Aluminum alloys, Copper alloys, Magnesium alloys, Copper alloys and Nickel

alloys may be welded by Flash Welding.

Thick pipes, ends of band saws, frames, aircraft landing gears are produced by Flash

Welding.


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Resistance Butt Welding (UW)

The process is similar to Flash Welding, however in Butt Welding pressure and

electric current are applied simultaneously in contrast to Flash Welding where

electric current is followed by forging pressure application.

Butt welding is used for welding small parts. The process is highly productive andclean. In contrast to Flash Welding, Butt Welding provides joining with no loss of

the welded materials.


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Resistance ProjectionWelding (RPW)

A resistance welding process inwhich coalescence occurs at

one or more small contact

points on parts

Contact points determined by

design of parts to be joined

May consist of projections,

embossments, or localized

intersections of parts

Resistance projection welding (RPW): (1)

start of operation, contact between parts isat projections; (2) when current is applied,

weld nuggets similar to spot welding are

formed at the projections.


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Percussion welding


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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


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Arc Welding Equipments


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Metal arc welding


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Arc Welding

Uses an electric arc to coalesce

metals

Arc welding is the most commonmethod of welding metals

Electricity travels from electrode

to base metal to ground


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Carbon Arc Welding


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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.


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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


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Comparison of A.C. and D.C. arc weldingDirect 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


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GASWELDING

Sound weld is obtained by selecting proper size of flame, fillermaterial and method of moving torch

The temperature generated during the process is 33000c

When the metal is fused, oxygen from the atmosphere and the torchcombines 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 andborax.

Flux can be applied as paste, powder,liquid.solid coating or gas.


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GASWELDINGEQUIPMENT...

1. Gas CylindersPressure

Oxygen 125 kg/cm2

Acetylene 16 kg/cm2

2. RegulatorsWorking pressure of oxygen 1 kg/cm2Working pressure of acetylene 0.15 kg/cm2

Working pressure varies depends upon the thickness of thework pieces welded.

3. Pressure Gauges

4. Hoses5. Welding torch

6. Check valve

7. Non return valve


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Oxy-Acetylene welding


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TYPESOF 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 abalance of fuel gas and oxygen) (32000c)

Used for welding steels, aluminium, copper and cast iron

If more oxygen is added, the cone becomes darker and more

pointed, while the envelope becomes shorter and more fierce iscalled Oxidizing flame

Has the highest temperature about 34000c

Used for welding brass and brazing operation


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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.


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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.


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Ferrous metal is heated in to red hot condition and a jet of pureoxygen is projected onto the surface, which rapidly oxidizes

Oxides having lower melting point than the metal, melt and areblown away by the force of the jet, to make a cut

Fast and efficient method of cutting steel to a high degree ofaccuracy

Torch is different from welding

Cutting torch has preheat orifice and one central orifice foroxygen jet

PIERCINGand GOUGINGare two important operations

Piercing, used to cut a hole at the centre of the plate or awayfrom the edge of the plate

Gouging, to cut a groove into the steel surface

GAS

CUTTING


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GAS CUTTING

Manual Gas Cutting


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Weld joints


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Brazing and Soldering Brazing

It is a low temperature joining process. It is performed at

temperatures above 840F 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 asTorch brazing

Dip brazingFurnace brazing

Induction brazing


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Brazing


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Advantages

& DisadvantagesAdvantages

Dissimilar metals which canot 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


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Soldering

It is a low temperature joining

process. It is performed at

temperatures below 840F for

joining.

Soldering is used for,

Sealing, as in automotive

radiators or tin cans

Electrical Connections

Joining thermally sensitive

components

Joining dissimilar metals

main welding

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