welding and Casting Process

7/24/2019 welding and Casting Process

1/84


2/84

Defnition Method o

abricationintended togive physicalcontinuity

betweenpieces to be

joined

Piece 1Piece 2Filler

metal


3/84

Characteristics rapid/local heating in a mold

appearance o molten metal (in amold-parent metal as a mold)

ormation o single molten pool

rapid cooling development o internal stress


4/84

Metallography o weld distinct area

!eld ment (meltedarea)

"eat a#ected $one("%&)

'arent metal(una#ected byheat)

'late !eld

metal

"eata#ected $one

'arent

metal

'arent

metal


5/84

*ype o welding joints

BUTT BUTT-UNEQUALTHICKNESS-FILLET

WELDED

T-JOINT-FILLET

WELDED

T-JOINT-BUTT

WELDED CONE JOINT-BUTT

WELDED

LAP JOINT-FILLET WELDED

CONE JOINT-FILLET

WELDED


6/84

!elding application in

vessel manuacturing

A

A

A

A

A

A

A A

A

B

B

B

B

B

B

C

C

C

C

C

C

D

D

D

D


7/84

*ype o !elding 'ressure

+usion


8/84

'ressure welding no melting o metal high pressure applied to metals to obtain atomic bond pressure must achieve plastic deormation or atomic

bond to happen and to brea, oide layer bond obtain by di#usion and crystal growth across the

surace need low heat applicable to dissimilar metal less used


9/84

+usion !elding molten metal more easily orm atomic bond when melt lattice destroy and atom mi new lattice orm during cooling-may di#erent rom

original why.. 0C%120

rate o heating and cooling additional o other elements properties di#erent rom original

heat re3uired to melt metal e4g4 steel 55-655C * in pool 655-555C %rc *emp about 7555C %dditional thing come unintentionally e4g4 gas rom air


10/84


11/84

8y %cetylene

!elding %cetylene 9 oygen

gives :ame about55deg C

high temperature :ameis used to bring smallarea o parent metal upto melting point4 %separate fller wire is

then dipped into themolten pool and aportion melted o#;mied with the basemetal to provide weld


12/84

8y%cetylene!elding


13/84

8y %cetylene !elding %pplicable to most metal including carbon

steel; stainless steel; cast iron; bron$e

copper Main application is or metal less than

6mm but thic,er also can

*ypical application< light abrication suchas ventilation duct; small bore pipewor,;motor vehicle repair

ecoming less popular now because o

new development o new and e=cient


14/84

8y %cetylene !elding

%dvantage Manual >ow e3uipment

cost

'ortable and

versatile

Disadvantage 2low speed

(produce larger"%&)

>ow rate o metaldeposition

>ow productivity

"igh heat causedistortion

?enerally poorer3uality


15/84

Manual Metal %rc (MM%) !elder establish arc between the piece

and the electrode

%rc melt pieces and electrode to orm poolprotected by :u

Most versatile

%pplicable to all thic,ness and most

materials Can be carried out in all positon

0conomy


16/84

Manual Metal%rc (MM%)


17/84

Manual Metal %rc (MM%) 0lectric arc ormed between :u cored

electrode and metal

%rc temperature @ 7555C %rc causes metal deposition to

wor,piece and arc shielded the $onewhy.

*ypical application< +abrication opressure vessel; ship; structuralsteelwor,; joint in pipewor, andpipeline; construction and repair o

machine plant


18/84

Manual Metal %rc (MM%)

%dvantage< >ow cost

0conomical orsmall volumeproduction

%pplicable in all

positions Aersatile and

trouble ree

Disadvantages< 2low-"ave to

change electrodeand remove slag

Be3uired manuals,ill

>ow depositioncapacity


19/84

Metal nert ?as (M?) 1se bare wire (typically 54-47mm)

consumable to provide arc 0lectrode continuously ed rom a coil through

specially design welding gun ecause o bare wire gas shielding is re3uired

to eliminate reaction with atmosphere %rgon; helium and Co is common why..

E0B* %pplication< medium abrication such as earth

moving e3uipment; plate ; car bodies


20/84

Metal nert

?as (M?)


21/84

Metal nert ?as (M?) %dvantageess re3uentchanging o electrode

Eo interpass cleaning-no slag

'roduce heavier bead

ast

Disadvantages< Bis, o porosity

More maintenancere3uires "igh ris, lac, o

usion >ess suitable or

feld application "igh cost o

shielding gas


22/84

*ungsten nert ?as (*?) %rc provided by nonconsumable

tungsten electrode

0lectrode itsel is not melting +iller is ed separetely rom a fller rod

% shielding gas; e4g4 argon is ed

through torch Eo :u


23/84

*ungsten

nert ?as(*?)


24/84

*ungsten nert ?as (*?) 0pensive and generally use or carbon

steel or high metallurgical and

mechanical properties Can be manual; semi manual or

mechanised %pplication< high 3uality welds such as

aluminum; stainless steel; nimonicallooy and copper in chemical plant;sheet wor, in aircrat and structure4


25/84

*ungsten nert ?as (*?) %dvantages8+; '; ;

1C

MM%< 2lag ; ';>8+; >8'; Crac,;spattering; 1C; over deposition

M?< >8'; >8+; '; !ormhole;

spattering*?< *ungsten ; crac,; >8'; >8+

2M%!< >8'; ' Crac,


31/84


32/84

Crac,s a linear discontinuity due to

tearing o metal when in plastic

condition (hot crac,) or racturewhen cold (cold crac,)

weld metal crac, caused byac, o +usion +ailure to raise the temperature o base

metal (or previously deposited bead tomelting point)

Conse3uently two adjacent layer o weldmetal or adjacent weld metal and parentmetal ail to use

types o >8+< between bead; between parent metal and weld metal and lac, o root usion


44/84

>ac, o +usion

Lac$ %. "i(e/all .'"i%!

Lac$ %. r%%t

.'"i%!

Lac$ %.

I!ter-r'! .'"i%!


45/84

>ac, o +usion Causes

same as lac, o penetration

contaminated weld preparationpreventing the melting o materialunderneath

the presence o slag; oides or other

materials on suraces that should use too high welding current tend to

persuade welder to use higher speed also considered as a dangerous deect


46/84

'orosity reer to a group or individual gas poc,ets or void cause by entrapment o gas during solidifcation how.. n steel oygen reacts with carbon to orm carbon

monoide gas ?as have not enough time to rise on the surace-metal

already solidiy mostly spherical but sometimes tubular-called !8BM"8>0

or ''E?

large void reerred as >8!"8>02 hollow bead-elongated porosity in the root bead herringbone porosity-wormhole side by side porosity can be clustered; linear or isolated


47/84

'orosity

Pi0i!&/%rm%leHerri!&)%!e

0%r%"it

Cl'"tere(

0%r%"it

POROIT'

blowholes


48/84

'orosity Causesap

'erectalignment

Misalignmentcausing lap

olding o metal in a thin plate on thesurace o the orging

cause < mating surace o dies is not

match-as the metal s3uee$e down;metal will be sheared and olded upinto lap

-as the orging stoc, s3uee$e downbetween two dies some o the metalwill be orced out between the matingsurace

- as the metal urther s3uee$e downthe metal will be sheared and olded

up into lap


79/84


80/84

nservice Discontinuities

Corrosion< Destruction or deterioration o amaterial because o reaction with itsenvironment

+atigue< Discontinuities developed due torepeated application o load

2tress corrosion crac,ing< Crac,s developeddue to the presence o stress in corrosiveenvironment

0mbrittlement< loss o ductility due to thepresence o element such as hydrogen in thegrain boundary


81/84

0amples o in-service

discontinuities

+atigue crac, in turbine casing o a powerplant


82/84

0amples o inservice

discontinuities

ntergranular

stress corrosioncrac,ing (?2CC)in inconel heatechanger tube


83/84

0amples o in-service

discontinuities

2tress corrosion

crac,ing due tothe presence ochloride instainless steel

7 in achemicalprocessingacilities


84/84

0#ects o deect

2harp edge deects act as a stressriser; hence a#ect mechanical

properties Deect may reduce the e#ective

thic,ness o material; thus reduce

strength 2everity depends on types; 3uantity;

location; orientation and si$e4

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welding and Casting Process