64826864 joining process

8/10/2019 64826864 Joining Process

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UNIT II

JOININGPROCESSES


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WELDING

The process of joining metals by the application of

heat is called welding

A good welded joint is as strong as the parent metal

Can be done with or without applying pressure and

with or with out filler materials

Used extensively in fabrication and erection works


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Classification of welding process

Major classification: Fusion Welding or Non- pressure welding

Filler material is required

Gas, Arc welding

Plastic welding or Pressure weldingFiller materials not required

Forge ,electrical resistance welding

Minor classification:

Autogeneous- no filler material

Homogeneous- same filler material

Heterogeneousdifferent filler material


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Types of welding

(i) Gas Welding Oxy-acetylene

Air-acetylene

Oxy-hydrogen

(ii) Arc welding

Carbon arc

Metal arc

Metal inert gas

Tungsten inert gas

Plasma arc

Submerged arc

Electro-slag


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iii) Resistance Welding

Butt Spot Seam

Projection

Percussion

(iv)Thermit Welding

(v)Solid State Welding

Friction

Ultrasonic

Diffusion

Explosive

(vi) Newer Welding

Electron-beam

Laser


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(vii)Related Process

Oxy-acetylene cutting

Arc cutting

Hard facing

Brazing

Soldering


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Gas welding

Oxy- acetylene welding

Oxy- hydrogen welding

Air- hyrogen welding


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Oxyacetylene Welding (OAW)

Fusion welding performed by a high temperatureflame from combustion of acetylene and

oxygen

Flame is directed by a welding torch

Filler metal is added

Composition must be similar to base metal

Filler rod often coated with fluxto clean

surfaces and prevent oxidation


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2 mm to 50 mm; 3200 degree c

Pressure in torch:

Oxygen:

High pressure system0.1 to 3.5 bar

Low pressure system - 0.5 to 3 bar

Acetylene:

High pressure system0.66 to 1bar

Low pressure system - up to 0.06 bar


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Gas welding Equipments

Gas cylinders oxygen- black

Acetylene- Maroon

Pressure regulators

Pressure gauges

Hoses

Welding torch

Goggles

Welding gloves

Spark lighter

Wire brush


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Flame characteristics

Neutral flame: inner cone & outer cone

Welding steel, cast iron , copper

Oxidizing flame- inner cone & outer cone

Brass & bronze

Carburizing flame-sharp inner cone, white

intermediate cone, bluish outer cone

Low carbon steel, alloy steels


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Gas welding technique

Leftward or forward welding


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Gas welding technique

Rightward or backward welding


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Filler rods

Additional material to weld the weld zone

Available as rod or wire

They can be used bare or coated with flux

Filler rod diameter d= t/2 +1

t- thickness of metal in mm


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Gas welding

Advantages

Flame temperature is easily controlled

Cost of equipment is less

Maintenance cost is less

requires very little specialized equipment.

Disadvantages

Not suitable for thick plates

Slow process Strength og joint is less than arc welding


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Arc Welding (AW)

A fusion welding process in which heat is developed by an

electric arc

The gap between electrode and work piece is 3mm

Temperature is about 5000oc to 6000oc

Transformer or generator supplies current

Depth to which metal is melted is depth of fusion

Flux prevents oxidation and rapid cooling

The depression in the metal is arc carter

Distance btw tip of electrode to bottom of carter is called arc

length


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Arc 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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Types of AW Electrodes

Non consumable Carbon, graphite, tungsten

Atomic hydrogen welding, TIG welding

Consumable electrode:

Bare electrodes

Do not have flux coating

Used to weld wrought iron, mild steel

Used in submerged arc, inert gas welding

Lightly coated electrodes

Flux coating of 1 to 5% of electrode weight Does not prevent oxidation

Heavily coated electrodes

Flux coating of 15 to 30% of electrode weight

Composed of deoxidizing, slag forming materials


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Carbon arc welding

D.C supply and carbon electrode is used Electrodenegative; work piecepositive

Steel sheets, copper alloys, aluminum are welded


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Metal Inert Gas (MIG) welding

Consumable electrode is used Power range from 100 to 400 A

Inert gases like argon or helium is sent through nozzle

Gas shield prevents oxidation

Aluminum, stainless steel are welded High speed, flux is not necessary


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Tungsten Inert Gas(TIG) welding

Non consumable tungsten electrode Inert gases like argon or helium is sent through nozzle

Filler rods may or may not be used

Aluminum, cast iron, steel are welded

High welding speed


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Plasma Arc Welding

Plasma or ionized gas is used to melt metal

Tungsten electrode is kept perpendicular in gas chamber

Nozzlepositive; electrodenegative

Through nozzle argon gas is sent into the arc and plasma is

formed which melts metal (1400oc)

Helium is sent outer side of the nozzle for gas shielding

Stainless steel, carbon steel, copper are welded

Filler rod not required


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Plasma Arc Welding


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Submerged Arc Welding (SAW)

Uses a continuous, consumable bare wire electrode, with arc

shielding provided by a cover of granular flux

Electrode wire is fed automatically from a coil

Electrode and metal are submerged under the flux and hence

welding cannot been seen

Flux will act as shield and form slag

Low carbon, alloy steel

High welding speed

Pressure vessel, boiler fabrication


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Electro slag welding

Welding happens while the temperature increases when currentpasses through molten slag

The work piece to be welded are placed in the bottom plate

Moving sliding plates are placed at both ends of the work piece

Flux is poured between work piece and sliding plate

When supply given flux melts and forms slag 2 to 3 mm

Arc stops and current passes from electrode to work piece through

the slag

Temperature increases due to high resistance and the ends of

electrode and metal melts and weld occurs Boiler plate, turbine shaft can be welded

Stronger welded joint

High speed


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Electro slag welding


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Resistance Welding (RW)

Parts are joined by heating to plastic state by theirresistance to electric current

Mechanical pressure is applied

Two copper electrodes are used

Heat generated, Q=I2RT

Bars, boxes, pipes are welded


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Types of Resistance welding

Spot welding Seam welding

Butt welding

Projection welding

Stud welding

Percussion butt welding

S t ldi


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Spot welding

Spot welding is a process in which contacting metal surfaces arejoined by the heat obtained from resistance to electric current.

Typically the sheets are in the 0.0255 to 1.25mm thickness range

Copper electrodes are used

Pressureup to 2 KN

S ldi


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Seam welding

Seam welding is a continuous process using electrode wheels ongenerally overlapping workpieces

Leak proof tanks, drums, radiators

B tt ldi


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Butt welding

1.Upset butt welding: the workpieces are clamped in copper jaws

which acts as electrodes

The edges of the workpieces are in contact

Pressurised by moving the jaws Bar, rod, pipe


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Butt welding

2.flash butt welding: Air gap between workpieces is maintained

Flash or arc is formed

Automobile body, frames


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Projection welding

welding process uses small projections on one or bothcomponents of the weld to localise the heat and pressure, the

projections collapse when the weld is made.

Sheet metals up to 3mm


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Stud welding

Stud welding is a form of spot welding where a bolt orspecially formed nut is welded onto another metal part

Gun, trigger, solenoid, timer are used

The stud end has flux coating

Time1 sec

Mass production


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Percussion welding

Percussion welding (PEW) is a type of resistance welding thatblends dissimilar metals together

Percussion welding creates a high temperature arc that is

formed from a short quick electrical discharge.

Discharge at 1.6 mm apart; Time - 0.1s

Percussion welding is similar to flash welding and upsetwelding but is generally considered to be more complex


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Special welding

Plasma arc welding Electron beam welding

Laser beam welding

Thermit welding

Friction welding Diffusion welding


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APPLICATIONS OF WELDING

It is used in almost all the branches of industryand construction. Especially fabrication and

erction steel structures.

Vessels of welded plate construction (Boilers,Pressure Vessel Tanks and Pipe Lines)

Fastening of Panels and members together into

automobile bodies and also in aviation industry.


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CLASSIFICATION OF WELDING

1. FUSION PROCESSES:

In these processes, the material at the

joint is heated to the molten state and allowed to

solidify to make the joint.

(Ex:Arc Welding, Gas Welding, Thermit Fusion

Welding)

2. PRESSURE PROCESSES:

In these processes, the parts to be joined

are heated to a plastic state ( fusion may occur to a

limited extent) and force together with external

pressure to make the joint.

(Ex: Forge Welding, Thermit Pressure Welding,

Pressure Gas Welding, Electric Resistance Welding


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TYPES OF WELD JOINTS

Butt Joint

Lap Joint

T-Joint

Corner Joint


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TYPES OF WELDS

Bead Weld

Fillet Weld

Groove Weld

Spot Weld


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EDGE PREPARATION

Edge preparation is necessary when

thickness increases so that heat would

be able to penetrate the entire depth


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WELDING POSITIONS

1.Horizontal Welding

2.Flat Welding

3.Vertical Welding

4.Over Head Welding


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Diversity of welding processes

welding

Solid state welding Soldering and brazingFusion welding

Electrical energy Chemical energy

Other processesNon consumable

electrode

Consumable electrode

Resistance welding

Cold welding

Friction welding

Diffusion welding

Flash welding

Ultrasonic welding

Explosion welding

Gas metal arc welding

Shielded metal arc welding

Submerged arc welding

Flux cored arc welding

Electrogas welding

Electroslag welding

Gas tungsten arc welding

Atomic hydrogen welding

Plasma arc welding

Oxyacetylene welding

Oxyfuel gas welding

Laser beam welding

Thermit welding

Electron beam welding

Soldering

Brazing


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Arc Welding (AW)

A fusion welding process in which coalescence ofthe metals is achieved by the heat from an

electric arc between an electrode and the work

Electric energy from the arc produces

temperatures ~ 10,000 F (5500 C), hot enoughto melt any metal

Most AW processes add filler metal to increase

volume and strength of weld joint


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What is an Electric Arc?

An electric arc is a discharge of electric currentacross a gap in a circuit

It is sustained by an ionized column of gas

through which the current flows

To initiate the arc in AW, electrode is broughtinto contact with work and then quickly

separated from it by a short distance.


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A pool of molten metal is formed nearelectrode tip, and as electrode is moved along

joint, molten weld pool solidifies in its wake

Basic configuration of an arc welding process.

Arc Welding


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Two Basic Types of AW Electrodes

Consumableconsumed during weldingprocess

Source of filler metal in arc welding

Nonconsumablenot consumed during

welding process Filler metal must be added separately


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Consumable Electrodes

Forms of consumable electrodes Welding rods are 9 to 18 inches and 3/8

inch or less in diameter and must be

changed frequently

Weld wire can be continuously fed fromspools with long lengths of wire, avoiding

frequent interruptions

In both rod and wire forms, electrode is

consumed by arc and added to weld joint asfiller metal


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Nonconsumable Electrodes

Made of tungsten which resists melting Gradually depleted during welding

(vaporization is principal mechanism)

Any filler metal must be supplied by a separate

wire fed into weld pool


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Arc Shielding

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

hydrogen in air

Mechanical properties of joint can be

seriously degraded by these reactions To protect operation, arc must be shielded

from surrounding 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 oxidesand 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 isconsumed


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Power Source in Arc Welding

Direct current (DC) vs. Alternating current (AC) AC machines less expensive to purchase

and operate, but generally restricted to

ferrous metals

DC equipment can be used on all metalsand is generally noted for better arc control

In DC Machines two types of Polarity is

there. One is DCSP another one is DCRP


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WELDING PROCESSES

1. Arc Welding (Consumable)

2. Arc Welding (Non Consumable Electrode)

3. Other/Special Fusion Welding Processes

4. Resistance Welding

5. Gas Welding

6. Solid State Welding


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Consumable Electrode AW Processes

Shielded Metal Arc Welding Gas Metal Arc Welding (MIG)

Flux-Cored Arc Welding

Submerged Arc Welding

Electrogas Welding

Electroslag Welding


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Shielded Metal Arc Welding (SMAW)

Uses a consumable electrode consisting of a

filler metal rod coated with chemicals that

provide flux and shielding

Sometimes called "stick welding"


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Shielded metal arc welding (SMAW).

Shielded Metal Arc Welding


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SMAW Applications

Used for steels, stainless steels, castirons, and certain nonferrous alloys

Not used or rarely used for aluminum

and its alloys, copper alloys, and

titanium


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Gas Metal Arc Welding (GMAW)

Uses a consumable bare metal wire aselectrode and shielding accomplished by

flooding arc with a gas

Wire is fed continuously and automatically

from a spool through the welding gun

Shielding gases include inert gases such as

argon and helium for aluminum welding, and

active gases such as CO2for steel welding

Bare electrode wire plus shielding gases

eliminate slag on weld bead - no need for

manual grinding and cleaning of slag


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Gas metal arc welding (GMAW).

Gas Metal Arc Welding


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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 than SMAW End of stick cannot be used in SMAW

Higher deposition rates

Eliminates problem of slag removal

Can be readily automated


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Flux-Cored Arc Welding (FCAW)

Adaptation of shielded metal arc welding, toovercome limitations of stick electrodes

Electrode is a continuous consumable tubing

(in coils) containing flux and other ingredients

(e.g., alloying elements) in its core Two versions:

Self-shielded FCAW - core includes

compounds that produce shielding gases

Gas-shielded FCAW - uses externallyapplied shielding gases


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Figure 31.6 Flux-cored arc welding. Presence or absence of externally

supplied shielding gas distinguishes the two types: (1) self-shielded,

in which core provides ingredients for shielding, and (2) gas-shielded,

which uses external shielding gases.

Flux-Cored Arc Welding


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

cover of granular flux

Electrode wire is fed automatically from a coil

Flux introduced into joint slightly ahead ofarc by gravity from a hopper

Completely submerges operation,

preventing sparks, spatter, and radiation


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Submerged arc welding.

Submerged Arc Welding


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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 hi C steel)

Not good for nonferrous metals


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Electrogas Welding (EGW)

Uses a continuous consumable electrode, eitherflux-cored wire or bare wire with externally

supplied shielding gases, and molding shoes to

contain molten metal

When flux-cored electrode wire is used and noexternal gases are supplied, then special case

of self-shielded FCAW

When a bare electrode wire used with shielding

gases from external source, then special case

of GMAW


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Electrogas welding using flux-cored electrode wire: (a) front view

with molding shoe removed for clarity, and (b) side view

showing molding shoes on both sides.

Electrogas Welding


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Non-consumable Electrode Processes

Gas Tungsten Arc Welding (TIG) Plasma Arc Welding (PAW)


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Gas Tungsten Arc Welding (GTAW)

Uses a non-consumable tungsten electrodeand an inert gas for arc shielding

Melting point of tungsten = 3410C (6170F)

A.k.a. Tungsten Inert Gas (TIG) welding

In Europe, called "WIG welding" Used with or without a filler metal

When filler metal used, it is added to

weld pool from separate rod or wire

Applications: aluminum and stainless steelmost common


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Gas tungsten arc welding.

Gas Tungsten Arc Welding


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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 noflux

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 constrictedplasma 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 28,000C

(50,000F), due to constriction of arc,

producing a plasma jet of small diameter and

very high energy density


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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

Other Fusion Welding Processes / Special


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g p

Welding Processes

FW processes that cannot be classified as arc,resistance, or oxyfuel welding

Use unique technologies to develop heat for

melting

Applications are typically unique Processes include:

Electron beam welding

Laser beam welding

Thermit welding


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Electron Beam Welding (EBW)

Fusion welding process in which heat for weldingis provided by a highly-focused, high-intensity

stream of electrons striking work surface

Electron beam gun operates at:

High voltage (e.g., 10 to 150 kV typical) toaccelerate electrons

Beam currents are low (measured in

milliamps)

Power in EBW not exceptional, but powerdensity is

ELECTRON BEAM WELDING


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EBW Advantages / Disadvantages


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EBW Advantages / Disadvantages

Advantages:

High-quality welds, deep and narrow profiles

Limited heat affected zone, low thermaldistortion

High welding speeds

No flux or shielding gases needed

Disadvantages:

High equipment cost

Precise joint preparation & alignment required

Vacuum chamber required

Safety concern: EBW generates x-rays


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LASER BEAM WELDING


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C i LBW EBW


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Comparison: LBW vs. EBW

No vacuum chamber required for LBW No x-rays emitted in LBW

Laser beams can be focused and directed by

optical lenses and mirrors

LBW not capable of the deep welds and highdepth-to-width ratios of EBW

Maximum LBW depth = ~ 19 mm (3/4 in),

whereas EBW depths = 50 mm (2 in)

Th it W ldi (TW)


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Thermit Welding (TW)

FW process in which heat for coalescence isproduced by superheated molten metal from

the chemical reaction of thermite

Thermite=mixture of Al and Fe3O4fine

powders that produce an exothermic reactionwhen ignited

Also used for incendiary bombs

Filler metal obtained from liquid metal

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

Th it W ldi


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

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

Thermit Welding

TW A li ti


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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

R i t W ldi (RW)


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Resistance Welding (RW)

A group of fusion welding processes that use acombination of heat 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)

Resistance Welding


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Resistance welding,

showing the

components in spot

welding, the main

process in the RWgroup.

Resistance Welding

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

C t i R i t S t/B tt W ldi


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Components in Resistance Spot/Butt 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 currentcan be applied for a specified time duration

Resistance Spot/Butt Welding (RSW)


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Resistance Spot/Butt Welding (RSW)

Resistance welding process in which fusion of

faying surfaces of a lap joint is achieved at one

location by opposing electrodes

Used to join sheet metal parts using a series of

spot welds

Widely used in mass production of

automobiles, 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/Butt Welding Cycle


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

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

Spot/Butt Welding Cycle

Resistance Seam Welding (RSEW)


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Resistance Seam Welding (RSEW)

Uses rotating wheel electrodes to produce aseries 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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Resistance seam welding (RSEW).

Resistance Seam Welding

Oxyfuel Gas Welding (OFW)


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Oxyfuel Gas Welding (OFW)

Group of fusion welding operations that burnvarious fuels mixed with oxygen

OFW employs several types of gases, which is

the primary distinction among the members of

this group

Oxyfuel gas is also used in flame cutting

torches to cut and separate metal plates and

other parts

Most important OFW process is oxyacetylene

welding



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Fusion welding performed by a high temperatureflame from combustion of acetylene and

oxygen

Flame is directed by a welding torch

Filler metal is sometimes added Composition must be similar to base metal

Filler rod often coated with fluxto clean

surfaces and prevent oxidation

Oxyacetylene Welding


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A typical oxyacetylene welding operation (OAW).

Oxyacetylene Welding

Acetylene (C H )


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Acetylene (C2H2)

Most popular fuel among OFW group becauseit is capable of higher temperatures than any

other - up to 3480C (6300F)

Two stage chemical reaction of acetylene and

oxygen:

First stage reaction (inner cone of flame):

C2H2+ O22CO + H2+ heat

Second stage reaction (outer envelope):

2CO + H2+ 1.5O22CO2+ H2O + heat

Oxyacetylene Torch


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Maximum temperature reached at tip of inner

cone, while outer envelope spreads out and

shields work surfaces from atmosphere

The neutral flame from an oxyacetylene torch indicating

temperatures achieved.

Oxyacetylene Torch

Alternative Gases for OFW


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Alternative Gases for OFW

Methylacetylene-Propadiene (MAPP)

Hydrogen

Propylene

Propane

Natural Gas

Solid State Welding (SSW)


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Solid State Welding (SSW)

Coalescence of part surfaces is achieved by: Pressure alone, or

Heat and pressure

If both heat and pressure are used, heat

is not enough to melt work surfaces For some SSW processes, time is also a

factor

No filler metal is added

Each SSW process has its own way of creatinga bond at the faying surfaces

Success Factors in SSW


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Success Factors in SSW

Essential factors for a successful solid stateweld are that the two faying surfaces must be:

Very clean

In very close physical contact with each

other to permit atomic bonding

SSW Advantages over FW Processes


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SSW Advantages over FW Processes

If no melting, then no heat affected zone, sometal around joint retains original properties

Many SSW processes produce welded joints

that bond the entire contact interface between

two parts rather than at distinct spots or seams

Some SSW processes can be used to bond

dissimilar metals, without concerns about

relative melting points, thermal expansions,

and other problems that arise in FW

Pressure / Solid State Welding Processes


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Pressure / 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 bejoined are heated to hot working temperature

range and then forged together by hammering

or similar means

Historic significance in development of

manufacturing technology

Process dates from about 1000 B.C., when

blacksmiths learned to weld two pieces of

metal

Of minor commercial importance today except

for its variants

Roll Welding (ROW)


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Roll Welding (ROW)

SSW process in which pressure sufficient tocause coalescence is applied by means of

rolls, either with or without external heat

Variation of either forge welding or cold

welding, depending on whether heating of

workparts is done prior to process

If no external heat, called cold roll welding

If heat is supplied, hot roll welding

Roll Welding


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Roll welding (ROW).

g

Roll Welding Applications


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Roll Welding Applications

Cladding stainless steel to mild or low alloysteel for corrosion resistance

Bimetallic strips for measuring temperature

"Sandwich" coins for U.S mint

Diffusion Welding (DFW)


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Diffusion Welding (DFW)

SSW process uses heat and pressure, usually ina controlled atmosphere, with sufficient time for

diffusion and coalescence to occur

Temperatures 0.5 Tm

Plastic deformation at surfaces is minimal

Primary coalescence mechanism is solid state

diffusion

Limitation: time required for diffusion can range

from seconds to hours

DFW Applications


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DFW Applications

Joining of high-strength and refractory metalsin aerospace and nuclear industries

Can be used to join either similar and dissimilar

metals

For joining dissimilar metals, a filler layer ofdifferent metal is often sandwiched between

base metals to promote diffusion

Explosion Welding (EXW)


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Explosion Welding (EXW)

SSW process in which rapid coalescence of twometallic surfaces is caused by the energy of a

detonated explosive

No filler metal used

No external heat applied

No diffusion occurs - time is too short

Bonding is metallurgical, combined with

mechanical interlocking that results from a

rippled or wavy interface between the metals

Explosive Welding


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Commonly used to bond two dissimilar metals,

in particular to clad one metal on top of a

base metal over large areas

Explosive welding (EXW): (1) setup in the parallel

configuration, and (2) during detonation of the explosive

charge.

g

Friction Welding (FRW)


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Friction Welding (FRW)

SSW process in which coalescence is achievedby frictional heat combined with pressure

When properly carried out, no melting occurs at

faying 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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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.

g

Applications / Limitations of FRW


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Applications: Shafts and tubular parts

Industries: automotive, aircraft, farm

equipment, petroleum and natural gas

Limitations: At least one of the parts must be rotational

Flash must usually be removed

Upsetting reduces the part lengths (which must

be taken into consideration in product design)

Ultrasonic Welding (USW)


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Two components are held together, oscillatoryshear stresses of ultrasonic frequency are

applied to interface to cause coalescence

Oscillatory motion breaks down any surface

films to allow intimate contact and strong

metallurgical bonding between surfaces

Although heating of surfaces occurs,

temperatures are well below Tm

No filler metals, fluxes, or shielding gases

Generally limited to lap joints on soft materials

such as aluminum and copper

Ultrasonic Welding


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Ultrasonic welding (USW): (a) general setup for a lap joint;

and (b) close-up of weld area.

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USW Applications


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Wire terminations and splicing in electricaland electronics industry

Eliminates need for soldering

Assembly of aluminum sheet metal panels

Welding of tubes to sheets in solar panels Assembly of small parts in automotive

industry

64826864 joining process

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