welding ds8

8/4/2019 Welding DS8

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SOLDERING, BRAZING & WELDING

INTRODUCTION

Some products cannot be manufactured as a single piece.

The desired shape and size of such products can be

obtained by joining two parts of same or different

materials. These parts are manufactured individually andare joined together to obtain the desired product.

For example, aircraft and ship bodies, welded machine

frames, furniture, computers, bridges and the transmission

or electric towers etc., are all fabricated by joining several

different parts.

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Classification of joining processes:

Temporary Joint

Permanent Joint

A temporary joint can be easily dismantled

separating the original parts without any damage to

them

In case it is a permanent joint, an attempt to separate

the parts already joined will result in the damage of theparts. In a permanent joint, the joint is made such that

it has properties similar to the base metal of the two

parts. These parts cannot be separated into their

original shape, size and surface finish 3


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Based on the process used for making the joint, the

joining processes can be further classified as:

Soldering.

Brazing.

Welding.

Mechanical Fasteners - bolts, nuts, rivets, screws

Adhesive bonding.

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Welding is one of the most extensively used

fabrication method. The joint strength obtained in

welding is being equal to or some times more thanthat of the parent metal.

Welding is not only used for making structures,

but also for repair work such as the joining of

broken castings.

The choice of a particular joining processdepends on several factors such as application,

nature of loads or stresses, joint design, materials

involved and size and shape of the components 5


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WELDING

Welding is a process of metallurgical joining of

two pieces of metals by the application of heat with

or without the application of pressure and addition

of filler metal. The joint formed is a permanent

joint.

It is extensively used in the fabrication work in

which metal plates, steel sections, castings offerrous metals are joined together. It is also used for

repairing broken, worn-out or defective metal parts.

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Modern methods of welding may be classified

under two broad headings.

Plastic or pressure welding process Fusion or non-pressure welding process

In plastic or pressure welding process the pieces

of metal to be joined are heated to a plastic state

and then forced together by external pressure. This

procedure is used in forge welding, resistance

welding, spot welding in which pressure is required.

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In the fusion or non-pressure welding, the material

at the joint is heated to a molten state and allowed to

solidify. This includes gas welding, arc welding

The surfaces of the metal which are to be joined by

any of the welding processes must be sufficiently clean

to permit clean metallic surfaces to come in to contact.

Fluxes are applied to the parts being welded to

dissolve the oxides or to prevent the formation ofoxides.

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GENERAL WELDING PROCEDURE

1. Surface Cleaning:

Surfaces of the parts to be welded need to bethoroughly cleaned to remove dust, dirt, oil, grease etc.

2. Edge Preparation:

Preparing a contour at the edges of the pieces to be

joined. It may involve beveling or grooving. This is

done in order to get the fusion or penetration through

the entire thickness of the member.

3. Clamping:

Pieces to be welded are clamped suitably so that there

are no undesirable movements during welding. 9


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4. Safety Devices:

Goggles & shields to protect the eyes, Apron to prevent

the sparks and flying globules of molten metal, shoes,

hand gloves etc.

5. Initial Weld:

Initial tack welds are done at the opposite corners of the

joint to secure the pieces together. Any cracks at this

stage must be removed as they cause residual stresses.

6. Intermediate and Final Welding:The weld joint is formed through various weaving

movements (weld beads). During this process, filler

metal and a suitable flux are used. After the

intermediate run of welding, final run is taken. 10


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7. Removal of Excess Material:

Extra material on the weld surface can be removed

using tongs and chipping hammer. The weld is allowedto cool and then cleaned.

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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

DiffusionExplosive(vi)Newer Welding

Electron-beam

Laser

(vii)Related Process

Oxy-acetylene cuttingArc cutting

Hard facing

Brazing

Soldering


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Another criterion used for a classification of the welding

process is based on the composition of the joint

(i) autogeneous (ii) homogeneous, and (iii) heterogeneous

In autogeneous processes no filler material is added during

the joining. All types of solid phase welding and resistance

welding are examples of this category.

In homogeneous welding processes, the filler material used

to provide the joint is the same as the parent material. Arc,

gas, and thermit welding belong to this category

In third category of welding, a filler material different fromthe parent material is used. Soldering and brazing are two

such joining processes


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GAS WELDING

Gas welding is a fusion welding process

Flame produced by the combustion of gases is

employed to melt the metal

The molten metal is allowed to flow together thusforming a solid continuous joint upon cooling.

By burning pure oxygen in combination with other

gases, in special torches, a flame up to 33000C can be

attained.

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Principle

In oxy-fuel gas welding (OFW) the heat is obtained from the

combustion of a fuel gas such as acetylene in combination

with oxygen

The process is a fusion welding process wherein the joint is

completely melted to obtain the fusion.

The heat produced by the combustion of gas is sufficient to

melt any metal and as such is universally applicable

The fuel gas generally used is acetylene because of the high

temperature generated in the flame. This process is called

oxy-acetylene welding


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Principal Cont.


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Oxy-acetylene Gas Welding Equipment

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Oxy-acetylene Gas Welding Equipment

1. Welding torch & tip

2. An acetylene cylinder

15.5 bar, red or maroon3. An oxygen cylinder 125 bar. Blue or black

4. Pressure regulator Cylinder pressure to delivery

pressure

5. Pressure gauge- One shows cylinder pressure & the

other shows the working or delivery pressure

6. Rubber hoses - black/green hose for oxygen &

red/orange hose for acetylene7. Safety devices Goggle with coloured glasses, hand

gloves, helmet, apron, sleeves, shoes etc.

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The oxy-acetylene flame is used to pre heat the parts to

be welded around the joint and also to melt the filler

metal.

A jet of oxy acetylene flame issuing from the nozzle of a

burner is played on the junction of the two pieces to be

welded.

At the same time a filler rod is held in the zone of jet

and its melt is deposited on the fused junction.

A weld is obtained after the molten metal solidifies. The

coating on the filler rod acts as a flux to keep the joint

clean.23


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GAS WELDING FLAMES (OXY-ACETYLENE FLAMES)

(Based on Gas Ratio)

1. Neutral Flame: (Gas ratio is 1)

.A certain amount of oxygen is required for complete combustion of

fuel gases

When the oxygen supply varies, the flame appearance obtained

would also vary.

In neutral flame all the acetylene present is completely burned andthus all the available heat in the fuel gas is released.

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So this is the most desirable flame to be used in oxy-acetylene

welding.

Due to neutral flame no chemical change and no oxidation in

molten metal

This neutral flame is desired for most welding operations. Used

for welding steel, stainless steel, cast iron, Cu etc.


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2. Carburizing or Reducing Flame: ( Gas ratio 0.95 to 1)

Excess of acetylene is present, Low temp flame

The excess unburnt carbon is absorbed in ferrous metals,

making the weld hard and brittle.

An intermediate flame feather exists - reddish in colour.

The length of the flame feather is an indication of the excess

acetylene present.

Carbonizing flame is used for welding high carbon steels

and cast iron, alloy steel.

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Since this flame provides a strong reducing atmosphere in the

welding zone, it is useful for those materials which are readilyoxidize like oxygen free copper alloys.

It is also used for high carbon steels, cast iron and hard

surfacing with high speed steel and cement carbides.


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2. Oxidizing Flame: (Gas ratio 1.15 to 1.5)

Excess of oxygen is present, similar to the neutral flame

Inner white cone is some what small, giving rise to higher

tip temperatures. Excess of oxygen causes the metal to burn/oxidize quickly.

Used for brass, bronze

Widely used for oxyacetylene cutting and not suitable for

welding since the weld metal will be oxidised.

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Advantages of Oxy-acetylene Gas Welding

1.The equipment is inexpensive, simple and is easily portable and

versatile

2.The same equipment with a range of torches can be used for

oxygen cutting as well as for brazing

3. Source of heat is separate from the filler rod, filler metal and heat

can be properly controlling, giving rise to satisfactory result.

4. Gas flame temperature is lower and easy controllable which is

necessary for the delicate work. Therefore it is extensively used for

sheet metal fabrication

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Disadvantages of Oxy-acetylene Gas Welding

1. Equipment must always be handled carefully as in certain

circumstances acetylene is explosive as oxygen when used inan oily atmosphere (such as an old dirty garage floor pit).

2. A high temperature flame from a hand held torch is

dangerous when handled carelessly.

3. It is much slower than electric arc welding and does notconcentrate the heat close to the weld. Thus, the heat treated

area is larger, which causes more distortion.

4. Highly skilled operators are required to produce a good

weld.5. If electric arc welding is available gas welding is seldom

used for work over 3.2mm thick.

6. The process is not satisfactory for heavy sections

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Applications:

For joining of thin materials.

For joining materials in whose case excessively high

temperature or rapid heating and cooling of the job

would produce unwanted changes in the metal. For welding both ferrous and non-ferrous metals.

In automotive &aircraft industries, project site works,

workshops etc.


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IT 208 Chapter 14 33

GAS WELDING

Oxygen-Hydrogen Welding

The oxygen-hydrogen torch can reach temperatures much higher than the

oxy-acetylene torch.

More expensive than oxy-acetylene welding and involves the flammability

risk with hydrogen.

Plasma Welding

Hydrogen plasma burns even hotter than hydrogen gas, permitting the

welding of extremely high-melting-point metals.

Very clean procedure that results in very little slag or foreign matter in theweld.


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Gas Cutting

It is possible to rapidly oxidise (burn) iron and steel when it is

heated to a temperature between 800 to 10000 C

When a high pressure oxygen jet with a pressure of the order

of 300 KPa is directed against a heated steel plate, the oxygen

jet burns the metal and blows it away causing the cut

This process is used for cutting steel plates of various

thicknesses (can go up to 2 m) mainly because the equipment

required is simple and can be carried anywhere without

handling the heavy steel plates.


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Here the torch tip has a provision for preheating the plate as

well as providing the oxygen jet. Thus the tip has a central

hole for oxygen jet with surrounding holes for preheating

flames


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GAS CUTTING

Manual Gas Cutting
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Arc Welding Equipments


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Arc Welding Setup

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ARC WELDING


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ARC WELDING

Joining of metals with heat produced by an electric

arc.

Heat necessary to melt the edges of the metal to be

joined is obtained from an electric are struck betweenthe electrode (filler rod) and the work, producing a

temperature of 50000C, in the welding zone.

The heat of the arc melts the base metal or edges ofthe parts fusing them together.

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Filler metal, usually added melts and mixes with

molten base metal to form the weld metal.

The weld metal cools and solidifies to form the

weld.


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What is an Electric Arc?

An arc is an electric current flowing between twoelectrodes through an ionized column of gas.

It is sustained by an ionized column of gas(plasma) through which the current flows

To initiate the arc in AW, electrode is brought intocontact with work and then quickly separatedfrom it by a short distance


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ARC WELDING MACHINE: AC or DC

AC Arc Welding Machine:

A step down transformer - receives the AC supply

between 200 to 440volts and transforms it to the

required low welding voltage in the range of 80 to100volts.

A high current of 100 to 400A will be suitable for

general arc welding work.

In AC arc welding, there is no choice of polarity

since they change in every cycle. 42


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DC Arc Welding Machine:

In DC welding, the workpiece is connected to the

positive pole of a DC generator and the electrode to

the negative pole in order to melt greater mass of the

metal in the base material. This is called straight

polarity.

When the less heat is required at the base material, the

polarity is reversed. This is called reversed polarity.

We can select the polarity depending upon the type of

the job. Hence, in DC arc welding, it is possible to melt

many metals which require more heat to melt. 43


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DC arc welding

it is generally preferred because of the control of the heat

input offered by it. If more heat is required at the workpiece

side, such as for thicker sheets or for the work materials

which have higher thermal conductivity such as aluminium

and copper, the workpiece can be made as anode, liberatinglarge heat near it

For thinner materials where less heat input is required in the

weld zone, the polarity could be reversed by making theworkpiece as negative

Sl N A t AC W ldi DC W ldi


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Sl No. Aspect AC Welding DC Welding

1. Arc Stability Lower/ Unstable Higher/Stable

2. Cost Low High

3. Electrodes Only Coated Both Bare & Coated

4 Electrical

energy

Consumption

Less energy consumption per

kg of the metal deposited (3

to 4 kWh)

More energy consumption

per kg of the metal deposited

(6 to 10 kWh)

5. Efficiency High Low

6. Polarity No choice of polarity Straight or reversed polarity

can be used depending on thetype of job and heat required

at the base metal

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ARC WELDING ELECTRODES

1. Consumable Electrodes: Melt along with the

workpieces & fills the joint.

They are either Bare or Coated.

When the bare electrodes are used, the globules of

the molten metal while passing from the electrodes

absorb oxygen and nitrogen from the atmospheric

air to form non-metallic constituents which gets

trapped in the solidifying weld metal and thereby

decreasing the strength of the joint.

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Coated Electrodes facilitate:

1. Protection of molten metal from oxygen and

nitrogen of the air by providing a gaseous shield

around the arc and the molten metal pool.

2. To establish & maintain the arc throughout welding

3. The formation of slag over the joint, thus protects

from rapid cooling.

4. Addition of alloying elements

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2. Non-consumable Electrodes:

When non-consumable electrodes are used, an

additional filler material is also required. The

advantage of using this type of electrode is that the

amount of the metal deposited by the filler rod can be

controlled.

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Advantages of Arc Welding


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Advantages of Arc Welding

1.Applicable to an infinite variety of work & can be

executed in any position.

2.It produces strong sound and ductile welds.

3.Satisfactory welds can be produced in heavy & light

sections.

4.Low cost process & Low accuracy in setting up required.

5.Excellent joint properties can be obtained in mild, low

alloy and stainless steels, nickel and copper-base alloys.

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Di d t f A W ldi


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Disadvantages of Arc Welding

1.Basically a manual process requiring adequate operator

skill for good results.

2.Electrodes require frequent changing.

3.Multi run welds necessary on thick plate-slag chipping

necessary after each run.

4.The principal disadvantage has been the high heat of themetal arc which makes it unsuitable for use on materials

less than 1.55 mm thick.

5.High initial cost of welding equipment. 50

Th b hi ld d b i h d h


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The arc must be shielded because - as it hardens the

molten metal combines with oxygen and nitrogen to

form impurities that weaken the weld.

The electrodes are usually coated with a flux. This

coating forms a gaseous cloud that shields the molten

metal from the atmosphere.

The coating also forms a protective slag. The slag

floats on the molten pool and hardens as the weld

cools. This keeps impurities out of the weld.

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Arc Shielding

At high temperatures in AW, metals arechemically reactive to oxygen, nitrogen, andhydrogen in air

Mechanical properties of joint can be seriously degradedby these reactions

To protect operation, arc must be shielded fromsurrounding air in AW processes

Arc shielding is accomplished by: Shielding gases, e.g., argon, helium, CO2 Flux


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Flux

A substance that prevents formation of oxides

and other contaminants in welding, or

dissolves them and facilitates removal

Provides protective atmosphere for welding

Stabilizes arc

Reduces spattering


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Various Flux Application Methods

Pouring granular flux onto welding operation

Stick electrode coated with flux material that

melts during welding to cover operation

Tubular electrodes in which flux is contained

in the core and released as electrode is

consumed


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Shielded Metal Arc Welding


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(SMAW)

An arc welding process that produces a

coalescence of metals by heating with an arc

between a covered metal electrode and the

work pieces

Stick Welding

Shielding is obtained from decomposition of

the electrode covering.

Filler metal is obtained from the electrode.


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Figure 31.3 Shielded metal arc welding (SMAW).


Gas Metal Arc Welding


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Gas Metal Arc Welding

(GMAW)

An arc welding process that produces

coalescence of metals by heating them with

an arc between a continuous filler metal

(consumable) electrode and the work

MIG welding

Shielding is obtained entirely from an

externally supplied gas or gas mixture.


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GMAW Weld Diagram


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Gas Metal Arc Welding (GMAW)

Uses a consumable bare metal wire aselectrode and shielding accomplished byflooding arc with a gas

Wire is fed continuously and automaticallyfrom a spool through the welding gun

Shielding gases include inert gases such asargon and helium for aluminum welding,and gases such as CO2 for steel welding

Bare electrode wire plus shielding gaseseliminate slag on weld bead - no need formanual grinding and cleaning of slag


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GMAW Advantages over SMAW

Better arc time because of continuous wireelectrode Sticks must be periodically changed in SMAW

Better use of electrode filler metal thanSMAW End of stick cannot be used in SMAW

Higher deposition rates

Eliminates problem of slag removal

Can be readily automated


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Submerged Arc Welding (SAW)

Uses a continuous, consumable bare wireelectrode, with arc shielding provided

by a cover of granular flux

Electrode wire is fed automaticallyfrom a coil

Flux introduced into joint slightly ahead

of arc by gravity from a hopper

Completely submerges operation, preventing

sparks, spatter, and radiation

Submerged Arc Welding


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Submerged Arc Welding

(SAW)

An arc welding process that uses an arcbetween a bare metal electrode and the weldpool. The arc and molten metal are shielded

by a blanket of granular flux. a process in which welding is done by an

automatic electrode feeding machine whereinthe tip of the electrode is submerged into a

granular flux which shields the arc and themolten metal.


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SAW operations


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SAW Applications and Products

Steel fabrication of structural shapes (e.g.,

I-beams)

Seams for large diameter pipes, tanks, and

pressure vessels

Welded components for heavy machinery

Most steels (except high C steel)

Not good for nonferrous metals

Non-consumable Electrode


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Processes

Gas Tungsten Arc Welding

Plasma Arc Welding

Carbon Arc Welding

Stud Welding



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(GTAW)

An arc welding process that produces

coalescence of metals by heating them with

an arc between a tungsten (non-consumable)

electrode and the work piece. TIG welding

Shielding is obtained from an externally

supplied gas or gas mixture.


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GTAW or TIG process


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Gas Tungsten Arc Welding (GTAW)

Uses a non-consumable tungstenelectrode and an inert gas for arcshielding

Melting point of tungsten = 3410 C

(6170 F) Used with or without a filler metal

When filler metal used, it is added to weld poolfrom separate rod or wire

Applications: aluminum and stainlesssteel most common


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Advantages / Disadvantages of GTAW

Advantages:

High quality welds for suitable applications

No spatter because no filler metal through arc

Little or no post-weld cleaning because no flux

Disadvantages:

Generally slower and more costly than consumable

electrode AW processes


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Plasma Arc Welding (PAW)

Special form of GTAW in which a constricted

plasma arc is directed at weld area

Tungsten electrode is contained in a nozzle that

focuses a high velocity stream of inert gas (argon)into arc region to form a high velocity, intensely

hot plasma arc stream

Temperatures in PAW reach 28,000 C (50,000 F),due to constriction of arc, producing a plasma jet

of small diameter and very high energy density


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Figure 31.10 Plasma arc welding (PAW).

Plasma Arc Welding


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Advantages / Disadvantages of PAW

Advantages: Good arc stability

Better penetration control than other AW

High travel speeds

Excellent weld quality Can be used to weld almost any metals

Disadvantages: High equipment cost

Larger torch size than other AW

Tends to restrict access in some joints


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Other Fusion Welding Processes

FW processes that cannot be classified as arc, oroxyfuel welding

Use unique technologies to develop heat formelting

Applications are typically unique

Processes include: Electron beam welding

Laser beam welding Electroslag welding

Thermit welding


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Thermit Welding (TW)

FW process in which heat for coalescence isproduced by superheated molten metal from thechemical reaction of thermite

Thermite = mixture of Al and Fe3O4 fine powders

that produce an exothermic reaction whenignited

Also used for incendiary bombs

Filler metal obtained from liquid metal

Process used for joining, but has more incommon with casting than welding


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Figure 31.25 Thermit welding: (1) Thermit ignited; (2) crucible tapped,

superheated metal flows into mold; (3) metal solidifies to produce weld

joint.

Thermit Welding

l


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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

Electroslag Welding (ESW)


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Electroslag Welding (ESW)

Electroslag Welding is a welding process, in which the heat isgenerated by an electric current passing between theconsumable electrode (filler metal) and the work piecethrough a molten slag covering the weld surface.

Prior to welding the gap between the two work pieces is filledwith a welding flux

Electroslag Welding is initiated by an arc between theelectrode and the work piece (or starting plate)

Heat, generated by the arc, melts the fluxing powder and

forms molten slag. The slag, having low electric conductivity,is maintained in liquid state due to heat produced by theelectric current.


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The slag reaches a temperature of about 3500F (1930C).This temperature is sufficient for melting the consumable

electrode and work piece edges. Metal droplets fall to the

weld pool and join the work pieces.

Electroslag Welding is used mainly for steels.


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Ad t f El t l W ldi


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: Advantages of Electroslag Welding

High deposition rate - up to 45 lbs/h (20 kg/h); Unlimited thickness of work piece.

Disadvantages of Electroslag welding:

Coarse grain structure of the weld;

Low toughness of the weld;

Only vertical position is possible.

R i W ldi (RW)


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Resistance Welding (RW)

A welding processes that use a combination ofheat 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)

P i i l


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Principal

In resistance welding(RW), a low voltage(typically 1 V) andvery high current(15000 A) is passed through the joint for a

very short time (typically 0.25 sec)). This high amperage heats

the joint, due to contact resistance at the joint and melts it.

The pressure on the joint is continuously maintained and themetal fuses together under this pressure. The heat generated

in resistance welding can be expressed as

H=k* I2*R*t


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Where H= the total heat generated in the work,J

I=electric current,A

t = time for which the electric current is passing through the joint,s

R= resistance of the joint

K=a constant to account for the heat losses from the welded joint

The resistance of the joint, R is a complex factor to know because it

is composed of

a) the resistance of the electrode

b)the contact resistance between the electrode and work piecec) the contact resistance between the two work piece plates

d) the resistance of the work piece plates

Resistance Welding


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Figure 31.12 Resistance

welding, showing the

components in spot

welding, the main

process in the RW group.

Resistance Welding

Components in Resistance Spot


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p p

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

Ad t / D b k f RW


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Advantages / Drawbacks of RW

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

R i t S t W ldi (RSW)


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Resistance Spot Welding (RSW)

Resistance welding process in which fusionof faying surfaces of a lap joint isachieved at one location by opposingelectrodes

Used to join sheet metal parts using aseries of spot welds

Widely used in mass production ofautomobiles, appliances, metal furniture,and other products made of sheet metal Typical car body has ~ 10,000 spot welds Annual production of automobiles in the world is

measured in tens of millions of units

Spot Welding Cycle


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Figure 31.13 (a) Spot welding cycle, (b) plot of squeezing force & current incycle (1) parts inserted between electrodes, (2) electrodes close, force

applied, (3) current on, (4) current off, (5) electrodes opened.

Spot Welding Cycle

Resistance Seam Welding (RSEW)


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Resistance Seam Welding (RSEW)

Uses rotating wheel electrodes toproduce a series of overlapping

spot welds along lap joint

Can produce air-tight joints Applications:

Gasoline tanks

Automobile mufflers

Various other sheet metal containers

Resistance Seam Welding


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Figure 31.15 Resistance seam welding (RSEW).

Resistance Seam Welding

Resistance Projection Welding (RPW)


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Resistance Projection Welding (RPW)

A resistance welding process in whichcoalescence occurs at one or more small

contact points on parts

Contact points determined by design of partsto be joined

May consist of projections, embossments, or localized

intersections of parts

Resistance Projection Welding


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Figure 31.17 Resistance projection welding (RPW): (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

Solid State Welding Processes


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Solid State Welding Processes

Forge welding Cold welding

Roll welding

Hot pressure welding Diffusion welding

Explosion welding

Friction welding Ultrasonic welding

Forge Welding


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Forge Welding

Welding process in which components to be joinedare heated to hot working temperature range andthen forged together by hammering or similarmeans

Historic significance in development ofmanufacturing technology Process dates from about 1000 B.C., when blacksmiths learned

to weld two pieces of metal

Of minor commercial importance today exceptfor its variants

Friction Welding (FRW)


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Friction Welding (FRW)

SSW process in which coalescence is achieved byfrictional heat combined with pressure

When properly carried out, no melting occurs atcontact surfaces

No filler metal, flux, or shielding gases normallyused

Process yields a narrow HAZ

Can be used to join dissimilar metals

Widely used commercial process, amenable toautomation and mass production

Friction Welding


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Figure 31.28 Friction welding (FRW): (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 / Limitations of FRW


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Applications / Limitations of FRW

Applications: Shafts and tubular parts

Industries: automotive, aircraft, farm equipment,

petroleum and natural gasLimitations:

At least one of the parts must be rotational

Flash must usually be removed

Upsetting reduces the part lengths (which mustbe taken into consideration in product design)

Soldering


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Soldering

Soldering is a method of joining two metal work pieces bymeans of a third metal (solder) at a relatively low

temperature, which is above the melting point of the solder

but below the melting point of either of the materials being

joined. Flow of the molten solder into the gap between the work

pieces is driven by the capillary force

The solder cools down and solidifies forming a joint.

The parent materials are not fused in the process.


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Soldering is similar to Brazing. The difference is in the melting pointof the filler alloy: solders melt at temperatures below 840F

(450C); brazing filler materials melt at temperatures above this

point.

in the welding processes edges of the work pieces are either fused

(with or without a filler metal) or pressed to each other without any

filler material; soldering joins two parts without melting them but

through a soft low melting point solder.

Traditional lead containing solders consist of tin (Sn) and lead (Pb).

Brazing


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Brazing is a method of joining two metal work pieces bymeans of a filler material at a temperature above its melting

point but below the melting point of either of the materials

being joined.

Flow of the molten filler material into the gap between thework pieces is driven by the capillary force.

The filler material cools down and solidifies forming a strong

metallurgical joint, which is usually stronger than the parent

(work piece) materials. The parent materials are not fused in the process.

Brazing filler materials


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Copper filler alloys: Used for brazing Copper alloys, steels,Nickel alloys.

Aluminum filler alloys: Used for brazing Aluminum alloys.

Silver filler alloys: BAg-4 (40Ag-30Cu-28Zn-2Ni)

Used for most of metals and alloys except aluminum and

magnesium alloys.

Weldability


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Weldability

Capacity of a metal or combination of metalsto be welded into a suitably designedstructure, and for the resulting weld joint(s) topossess the required metallurgical propertiesto perform satisfactorily in intended service

Good weldability characterized by: Ease with which welding process is accomplished

Absence of weld defects Acceptable strength, ductility, and toughness in welded

joint

welding ds8

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