4 Unit 2- Solid State Welding (SSW)

7/27/2019 4 Unit 2- Solid State Welding (SSW)

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MANUFACTURINGTECHNOLOGY ISUBCODE: MEC230

Unit 2Welding (Metal Joining) Processes

Metal Forming Processes


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Unit 2 : Solid State Welding (SSW)


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Solid State Welding (SSW): Solid State Welding two pieces are joined under pressure& at a

temperatureessentially below the melting point Bonding of the materials is a result of diffusionof their interface

atoms

Joining of parts is achieved by Pressure, or Heat & pressure

If both heat and pressure are used, Heat is not enough to meltwork surfaces

For SSW processes, time is also a factor No filler metal is added

Each SSW process has its own way of creating a bond at the

surfaces


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Solid State Welding (SSW): Essential factors for a successful solid state weld are

Very clean surfaces

In very close physical contact with each other to permit

atomic bonding


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Advantages of Solid State Welding: No Melting, then no heat affected zone, so metal around joint

retains original properties

Weld is free from microstructure defects (pores, non-metallic

inclusions, segregation of alloying elements)

No consumable materials (filler material, fluxes, shielding gases)are required

Dissimilar metals may be joined (steel - aluminum alloy steel -

copper alloy).

Disadvantages of Solid State Welding: Thorough surface preparation is required (degreasing, oxides

removal, brushing/sanding)

Expensive equipment.


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The following are Solid State welding processes : Forge Welding (FOW)

Cold Welding (CW)

Roll Welding (RW)

Diffusion Welding (DFW)

Explosive Welding (EXW)

Friction Welding (FRW)

Ultrasonic Welding (USW)

Hot Pressure Welding (HPW)


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Forge Welding (FOW): Welding process in which components to be joined are heated to

hot working temperature range and then forged together byhammeringor 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

Prior to Forge Welding, the parts are joined by bevelling or

notching them so that they fit over or into each other in order to

prevent entrapment of oxides in the joint.

Forge Welding is used in general blacksmith shops and for

manufacturing metal art pieces and welded tubes.


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Advantages of Forge Welding: Good quality weld may be obtained Parts of intricate shape may be welded

No filler material is required.

Disadvantages of Forge Welding: Only low carbon steel may be welded

High level of the operators skill is required

Slow welding process

Weld may be contaminated by the coke used in heating furnace


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Forge Welding (FOW):


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Cold Welding (CW):

SSW process done by applying high pressure between cleancontacting surfaces at room temperature by deformation Intimate contact between these pure surfaces provide a strong

and defectless bonding.

Cleaning usually done by degreasing and wire brushingimmediately before joining

No heat is applied, but deformation raises work temperature

At least one of the metals, preferably both, must be very ductile

Soft aluminium and copper suited to CW

Applications: making electrical connections


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Cold Welding (CW):

Aluminum alloys, Copper alloys, low carbon steels, Nickel alloys,and other ductile metals may be welded by Cold Welding.

Cold Welding is widely used for manufacturing Bi-metal steel

Aluminum alloy strips, for covering of aluminum alloy strips by

other aluminum alloys or pure aluminum (Corrosion protectioncoatings).

Bi-metal strips are produced by Rolling technology

Presses are also used for Cold Welding

Cold Welding may be easily automated


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Roll Welding (ROW):

SSW process in which pressure sufficient to cause joining bymeans 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


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Roll Welding (ROW) Applications:

Covering stainless steel to mild or low alloy steel for corrosionresistance

Bimetallic strips for measuring temperature

"Sandwich" coins


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Diffusion Welding (DFW):

SSW process uses heat and pressure, usually in a controlledatmosphere, with sufficient time for diffusionand joining to occur Temperatures 0.4 Tm

Plastic deformation at surfaces is minimal

Primary joining mechanism is solid state diffusion

In order to keep the bonded surfaces clean from oxides and

other air contaminations, the process is often conducted in

vacuum. Limitation: time required for diffusion can range from seconds to

hours


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Advantages of Diffusion Welding:

Dissimilar materials may be welded (Metals, Ceramics, Graphite,glass)

Welds of high quality are obtained (no pores, inclusions,

chemical segregation, distortions)

No limitation in the work pieces thickness

Disadvantages of Diffusion Welding: Time consuming process with low productivity

Very thorough surface preparation is required prior to weldingprocess

The mating surfaces must be precisely fitted to each other

Relatively high initial investments in equipment


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Diffusion Welding Applications:

Joining of high-strength and refractory metals in aerospace andnuclear industries

Diffusion Welding is able to bond dissimilar metals, which are

difficult to weld by other welding processes:

Steel to tungsten Steel to niobium

Stainless steel to titanium

Gold to copper alloys

For joining dissimilar metals, a filler layer of different metal is

often sandwiched between base metals to promote diffusion

Diffusion Welding is used in rocket industries, electronics

applications, manufacturing composite materials


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Explosion Welding (EXW):

SSW process in which rapid joining of two metallic surfaces iscaused 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 interlockingthat results from a rippled or wavy interface between the metals

Commonly used to bond two dissimilar metals


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Explosion Welding (EXW):(1) Setup in parallel configuration, and(2) during detonation of the explosive charge


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Explosion Welding (EXW): One of the welded parts (base plate) is rested on an anvil, the

second part (flyer plate) is located above the base plate with an

angled or constant interface clearance.

Explosive charge is placed on the flyer plate.

Detonation starts at an edge of the plate and propagates at high

velocity along the plate.

The slags (oxides, nitrides and other contaminants) are expelled

by the jet created just ahead of the bonding front.

Most of the metals and alloys may be bonded (welded) by

Explosive Welding.


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Advantages of Explosive Welding

Large surfaces may be welded High quality bonding: high strength, no distortions, no porosity,

no change of the metal microstructure

Low cost and simple process

Surface preparation is not required

Disadvantages of Explosive Welding: Brittle materials (low ductility and low impact toughness)

cannot be processed

Only simple shape parts may be bonded: plates, cylinders

Thickness of flyer plate is limited - less than 2.5(63 mm)

Safety and security aspects of storage and using explosives


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Explosion Welding (EXW) Applications:Dissimilar metals may be joined by Explosive Welding:

Copper to steel

Nickel to steel

Aluminum to steel

Tungsten to steel

Titanium to steel

Copper to aluminum

Explosive Welding is used for manufacturing tubes and pipes,pressure vessels, aerospace structures, heat exchangers, bi-

metal sliding bearings, ship structures, corrosion resistant

chemical process tanks.


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Friction Welding (FRW):

SSW process in which joining is achieved by frictional heatcombined with pressure

When properly carried out, no melting occurs at faying surfaces

No filler metal, flux, or shielding gases normally used

Process yields a narrow HAZ

Can be used to join dissimilar metals

Widely used commercial process, agreeable to automation and

mass production


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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


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Friction Welding (FRW) Limitations:

At least one of the parts must be rotational Flash must usually be removed (extra operation)

Upsetting reduces the part lengths (which must be taken into

consideration in product design)

Friction Welding (FRW)Applications: Shafts and tubular parts

Industries: automotive, aircraft, farm equipment, petroleum andnatural gas

Carbon steels, Alloy steels, Tool and die steels, Stainless steels,

Aluminum alloys, Copper alloys, Magnesium alloys, Nickel alloys,

Titanium alloys may be joined by Friction Welding.


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Friction Stir Welding (FSW):

SSW process in which a rotating tool is fed along a joint linebetween two work-pieces, generating friction heat and

mechanically stirring the metal to form the weld seam

Distinguished from FRW because heat is generated by a separate

wear-resistant tool rather than the parts Applications: butt joints in large aluminum parts in aerospace,

automotive, and shipbuilding


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Friction Stir Welding (FSW):(1) Rotating tool just before entering work, and(2) partially completed weld seam


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Advantages and Disadvantages of Friction Stir Welding:Advantages Good mechanical properties of weld joint

Avoids toxic fumes, warping, and shielding issues

Little distortion or shrinkage

Good weld appearance

Disadvantages

An exit hole is produce when tool is withdrawn Heavy duty clamping of parts is required


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Ultrasonic Welding (USW) Two work pieces are bonded as a result of a pressure exerted to

the welded parts combined with application of high frequency

acoustic vibration.

Oscillatory shear stresses of ultrasonic

frequency are applied to interface to

cause joining

Oscillatory motion breaks down any

surface films to allow intimate contact

and strong metallurgical bonding

between surfaces


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Ultrasonic Welding (USW)

Ultrasonic cycle takes about 1 sec. The frequency of acoustic vibrations is in the range 20 to 70 KHz.

Thickness of the welded parts is limited by the power of the

ultrasonic generator.

Temperatures are well below Tm No filler metals, fluxes, or shielding gases

Generally limited to lap joints on soft materials


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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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Ultrasonic Welding (USW) Applications:

Wire terminations and splicing in electrical and electronicsindustry

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

Bonding of work pieces in electronics

For manufacturing communication devices

Medical tools, watches, automotive industry


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Advantages of Ultrasonic Welding:

Dissimilar metals may be joined Very low deformation of the work pieces surfaces

High quality weld is obtained

The process may be integrated into automated production lines

Moderate operator skill level is enough

Disadvantages of Ultrasonic Welding: Only small and thin parts may be welded

Work pieces and equipment components may fatigue at the

reciprocating loads provided by ultrasonic vibration

Work pieces may bond to the anvil

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4 Unit 2- Solid State Welding (SSW)