Fundamentals of Welding

1MAJU,ISLAMABAD 11/26/2013

211/26/2013MAJU,ISLAMABAD

MANUFACTURING PROCESSES- I

P R O J E C T N A M E : W E L D I N G P R O C E S S E S

G R O U P M E M E B E R S :

1. A B U B A K R AY U B

2. W A Q A S A S H R A F

3. H A F E E Z - U R - R E H M A N

4. B I L A L J A V E D

5. S A L M A N A Z I Z

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CLASSIFICATION OF ASSEMBLY PROCESSES

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What is Welding?

Welding is a materials joining process in which two or

more parts are coalesced at their contacting surfaces by a

suitable application of heat and/or pressure

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T E R M S

1) Filler Material: Facilitate coalescence, Increase bulk and strength.

2) Weldment: The assemblage of parts that are joined by welding is called a

weldment.

3) Faying Surfaces: Surfaces in contact or in close proximity that are to be

joined.

4) Welding Fixture: Holds and clamps the components in fixed position for

welding.

5) Welding positioner: Hold the parts, can also moves the assemblage to the

desired position for welding.11/26/2013

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TY

PE

S O

F W

EL

DIN

G

PR

OC

ES

SE

S

FUSION WELDING

ARC (AW)

RESISTANCE (RW)

OXYFUEL (OFW)

OTHER

ELECTRON BEAM

LASER BEAM

SOLID STATE WELDING

DIFFUSION (DFW)

FRICTION (FRW)

ULTRASONIC (USW)

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The principal applications of welding are:

1. Construction, such as buildings and bridges

2. Piping, pressure vessels, boilers, and storage

tanks

3. Shipbuilding

4. Aircraft and Aerospace

5. Automotive and Railroad

6. They can be performed at construction sites, in

shipyards, at customers’ plants, and in

automotive repair shops

VERSATILITY OF WELDING

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The Weld Joint: It is the junction of the edges or surfaces of

parts that have been joined by welding.

Types of Joints

• Butt Joint

• Corner

Joint

• Lap Joint

• Tee Joint

• Edge Joint

Types of Welds

• Fillet Weld

• Groove Weld

• Plug Weld

• Slot Weld

• Spot Weld

• Seam Weld

• Flange Weld

• Surfacing Weld11/26/2013

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(a) butt, (b) corner, (c) lap, (d) tee, and (e) edge

Variousforms of fillet welds

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Some typical groove welds

Plug and Slot Welds

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a) SPOT WELD and

b) SEAM WELD

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PHYSICS OF WELDING

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Physical relationships

Power Density

“ Power transferred to the work per unit surface

area ”

PD = P/A (Watt/mm^2)

Heat Balance

Equations

Hw (net heat used by the welding

operation)=Um*V (Joules)

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PHYSICAL RELATIONSHIPS

There are two physical relationships that allow fusion welding to

be performed.

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• Inverse Relation (PD is inversely proportion to time of

melting)

• If power density is too low, the heat is conducted into the

work as rapidly as it is added at the surface, and melting

never occurs.

• The minimum power density required to melt most metals

in welding is about 10 W/mm^2.

• Differences in the range of PD among different welding

processes.(See Table on next slide)

EFFECT OF TIME


• For metallurgical reasons, it is desirable to melt the metalwith minimum energy, and high power densities are generally preferable.


Heat required to melt depends upon:

• Metal’s volumetric specific heat

• The melting point of metal

• Metals heat of fusion


The unit Energy for melting is given by,

Not a l l the energy Generated by Heat source is used to melt the weld meta l

Eq # A


HEAT BALANCE EQUATION and Heat Transfer Mechanism


• Heat Energy available for welding is given by:

Hw= f 1*f 2*H

• f1 and f2 are proportions

• H = total Heat generated by the welding process

• Heat balance will be (from Eq # A)

Hw= Um*V

• Rate form

RHw=f 1*f 2*RH= Um*Aw*v


FUSION WELDED JOINT, ZONES AND GRAIN STRUCTURE

Figure (a)


Figure(b)


• Fusion Zone (Completely Melted)

• Epitaxial Grain Growth (Atoms from the molten pool solidify

on preexisting lattice sites)

• Weld Interface (Narrow boundary)

• Heat Effected Zone (Welding failures occur)

• Unaffected Base Metal (residual stresses)

Cont.

Fundamentals of Welding

Automotive

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