Manufacturing Technology- JOINING

8/9/2019 Manufacturing Technology- JOINING

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Joining Processes

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)oining * The B+" icture

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usion %elding

/efinition: melting together and coalescing of

materials using chemical or electrical

means.

Types of fusion welding processes:

0 (onsumable electrode arc welding

0 on!consumable electrode arc welding

0 igh!energy!beam welding



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(haracteristics of usion %elding

rocessesTABLE 27.1

Joining process Operation Advantage

Skill level

required

Welding

position

Current

type Distortion*

Cost of

equipment

Shielded metal-arc Manual Portable and

flexible

High All ac, dc 1 to 2 Low

Submerged arc Automatic High

deposition

Low to

medium

Flat and

horizontal

ac, dc 1 to 2 Medium

Gas metal-arc Semiautomatic

or automatic

Most metals Low to

high

All dc 2 to 3 Medium to

high

Gas tungsten-arc Manual or

automatic

Most metals Low to

high

All ac, dc 2 to 3 Medium

Flux-cored arc Semiautomatic

or automatic

High

deposition

Low to

high

All dc 1 to 3 Medium

Oxyfuel Manual Portable and

flexible

High All — 2 to 4 Low

Electron-beam,

Laser-beam

Semiautomatic

or automatic

Most metals Medium

to high

All — 3 to 5 High

* 1, highest; 5, lowest.



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Oxyfuel!"as %elding

0 (an be used for most ferrous and non ferrousmetals up to a thic5ness of 4 mm.

0 2 types of combustion occur:rimary combustion:

(22 6 O2 2(O 6 2 6 heat

&econdary combustion:

2(O 6 2 6 1.2O2 2(O2 62O 6 heat

7ses fuel gas 8normally acetylene9 combined with oxygen to produce

flame. lame proides heat 8up to '';;o(9 to melt metals at the


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Oxyacetylene lames 7sed

in %elding

Three basic types of oxyacetylene flames used in oxyfuel!gas welding and cutting operations: 8a9neutral flame> 8b9 oxidi?ing flame> 8c9 carburi?ing, or reducing, flame. The gas mixture in 8a9 is

basically eual olumes of oxygen and acetylene.



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iller metals in oxyfuel!gas welding

0 iller metals 8filler rods9 are used to supply additional metal tothe weld ?one

0 iller rods are normally coated with flux to: * suppress oxidation on the welded parts by producing a gaseous shieldaround the weld ?one

* /issole and remoe oxides

* elp deelop slag that protects the molten metal against oxidation



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Torch 7sed in

Oxyacetylene %elding

8a9 "eneral iew of and 8b9 cross!section of a torch used inoxyacetylene welding. The acetyleneale is opened first> the gas is lit

with a spar5 lighter or a pilot light>then the oxygen ale is opened andthe flame ad


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$rc %elding rocesses

There are 2 types of arc welding processes:

1. on!consumable electrode * xamples: "as tungsten arc welding, lasma arc welding,

$tomic hydrogen welding

* &hielding gas is supplied to preent oxidation at weld ?one

* ormally use direct current. olarity depends on type ofelectrode, type of wor5piece.

2. (onsumable electrode * xamples: &hielded metal!arc welding, &ubmerged!arc welding,

"as metal!arc welding,

Heat is generated from the electric arc produced between the tip of

an electrode and the workpiece. Temp generated is about 30,000oC



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"as Tungsten!$rc %elding

8"T$%CT+"9eatures:

0&hielding gas is normally argonChelium

0"ood for thin metals

0(an be used on a wide ariety of metalsincluding aluminum, magnesium, titanium,refractory metals.

0ortable euipment0"ood uality surface finish

07ses $( current at 3;; $ or /( current at

2;; $> @!1; 5%



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"as Tungsten!$rc %elding

8"T$%CT+"9

The gas tungsten!arc welding process, formerly5nown as T+" 8for tungsten inert gas9 welding.

uipment for gas tungsten!arc weldingoperations. Source: $merican %elding&ociety.



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&hielded #etal!$rc

%elding 8$%9Features

0 Dery common industrial 8construction, shipbuilding, pipeline, etc.9welding process

0 $rc is generated by touching the tip of electrode and withdrawing ituic5ly to maintain the arc

0 eat generated by the arc melts the electrode tip, its coating and thewor5piece metal

0 The weld consists of the wor5piece metal, electrode metal and coatingmaterial.

0 The coating material deoxidi?es the weld area and proides a shielding

gas to inhibit oxidation0 &lag must be cleaned as it can cause corrosion

0 7ses $( or /( current, 3;!';; $> up to 1;5%

0 &uitable for wor5piece thic5ness of '!1A mm

0 &imple process.



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&hielded #etal!$rc

%elding 8$%9

&chematic illustration of the shielded metal!arcwelding process. $bout 3;E of all large!scaleindustrial welding operations use this process.

&chematic illustration of the shielded metal!arcwelding operations 8also 5nown as stic5 welding, because the electrode is in the shape of a stic59.



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"as #etal!$rc %elding

8"#$%C#+"9

eatures:0 The consumable electrode is fed automatically through a no??le

into the weld arc using a wire!feed drie motor.

0 lectrode contains deoxidi?ers to preent oxidation of molten!weld puddle.

0 $rgonCheliumCcarbon dioxide shielding gas is used to protectweld area against oxidation.

0 Felatiely low temperature generated. Therefore suitable forthin sheets of less than 4mm.

0 &uitable for ferrousCnon!ferrous metals. (ommonly used onmetal fabrication industry.

0 &imple operation, low s5ill reuired, ersatile process,economical, easily automated, 2 x productiity of $%.



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"as #etal!$rc %elding

8"#$%C#+"9

&chematic illustration of thegas metal!arc welding process,formerly 5nown as #+" 8formetal inert gas9 welding.



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uipment 7sed in "as

#etal!$rc %elding

8"#$%C#+"9

Basic euipment used in gasmetal!arc welding operations.

Source: $merican %elding&ociety.



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lectrodes for $rc %elding

0 lectrodes for consumable arc!welding processesare classified according to: * &trength of the deposited weld metal

* (urrent 8$( or /(9 * Type of coating

0 lectrodes are classified by numbers and letters or by colour code.

0 &pecifications for electrodes and filler metals are published by the $merican %elding &ociety 8$%&9and the $merican ational &tandards +nstitute8$&+9.



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/esignations for #ild &teel

(oated lectrodesTABLE 27.2

The prefix “E” designates arc welding electrode.

The first two digits of four-digit numbers and the first three digits of five-digit numbersindicate minimum tensile strength:

E60XX 60,000 psi minimum tensile strength



The next-to-last digit indicates position:

EXX1X All positions

EXX2X Flat position and horizontal fillets

The last two digits together indicate the type of covering and the current to be used.

The suffix (Example: EXXXX-A1) indicates the approximate alloy in the weld deposit:

—A1 0.5% Mo

—B1 0.5% Cr, 0.5% Mo

—B2 1.25% Cr, 0.5% Mo

—B3 2.25% Cr, 1% Mo

—B4 2% Cr, 0.5% Mo—B5 0.5% Cr, 1% Mo

—C1 2.5% Ni

—C2 3.25% Ni

—C3 1% Ni, 0.35% Mo, 0.15% Cr

—D1 and D2 0.25–0.45% Mo, 1.75% Mn

—G 0.5% min. Ni, 0.3% min. Cr, 0.2% min. Mo, 0.1%min. V,

1% min. Mn (only one element required)



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lectrode coatings

0 lectrode coatings consist of silicate binders,oxidesCcarbonatesCfluoridesCmetal alloysCcellulose.

0 lectrode seres to: * &tabili?e the arc

* "enerate gasses to protect weld area against oxidation

* (ontrol rate of melting of electrode

* $ct as a flux to preent formation of oxides, nitrides atthe molten!weld pool

* $dd alloying elements to the weld ?one to improe theintegrity of the weld



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The !eld Joint, "ualit# and Testing

0 Three distinct ?ones can be identified in a typical weld


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Solidifications of the weld metal

0 $fter the application of heat and the introduction of the filler metal8if any9 into the weld ?one, the weld


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&howing the "rain structure in a 8a9 deep weld and 8b9 shallow weld.

ote that the grains in the solidified weld metal are perpendicular to

their interface with the base metal. 8c9 %eld bead on a coldrolled

nic5el strip produced by a laser beam. 8d9 #icrohardness 8D9

profile across a weld bead.



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Heat-affected zone0 The heat-affected zone 8$G9 is within the base metal

itself.

0 +t has a microstructure different from that of the base

metal prior to welding, because it has been sub


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%eld Huality

%eld uality is affected by the presence of discontinuities. Types of

discontinuities:1. orosity

* /ue to: gasses released, chemical reactions during welding, contaminants

* reention by: select electrodesCfiller metals carefully, preheat weld area, cleancontaminants, reduce welding speed

2. &lag inclusions * /ue to: trapped oxidesCfluxesCcoatings, contaminants from enironment

* reention by: (lean weld!bead before next layer is deposited, roidesufficient shielding gas, roper design of


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%eld Huality

-. %eld profile

3. (rac5s

* /ue to: temperature gradient causing thermal stress, etc.

* reention by: improe


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%eldability of #etals

errous metals:

0 lain carbon steel: excellent 8low (!steel9, medium

8medium (!steel9, poor 8high (!steel9

0 Low!alloy steel: medium

0igh alloy steel: good under well!controlled conditions

0 &tainless: arying 8differ by process9

0 (ast iron: arying 8differ by process9

on ferrous metals:

0 $luminum alloys: good at high rate of heat input> reuireshielding gas, absence of moisture



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Testing of welds

/estructie testing0 Tension test

0 Tension!shear test

0 Bend test

0 acture toughness test

ondestructie testing

0 Disual inspection

0Fadiography

0 #agnetic particle

0 Liuid penetrant

0 7ltrasonic



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)oint design

&



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&ummary1. usion welding is melting together and coalescing of

materials using chemical or electrical means.

2. usion welding may be achieed ia chemical or

electrical means

'. Oxyfuel!gas welding inoles generating heat by

combustion of a fuel gas with oxygen

-. $rc welding inoles generating heat from an electrical

arc

3. /ifferent types of welding processes proide different

weld ualities, incur different costs, and reuire arious

leels of s5ills.

4. /ifferent metals hae arying weldabilities with low

carbon steels proiding the best weldability

=. /estructie and non!destructie tests can be used to

i t th i t it f ld

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Manufacturing Technology- JOINING