friction stir welding/ processing - -the technology & future potential

1

16 April 2015

FRICTION STIR WELDING/

PROCESSING

-the technology & future potential

By

M. Puviyarasan Research Scholar

Department of Mechanical Engineering

College of Engineering Guindy campus

Anna University, Chennai -25

1. Joining Processes – Intro.

2. Importance of FSW : A Case study

3. Friction Stir Welding – Intro.

4. What happens inside?

5. The Process

6. Pros and Cons

7. Why it is better?

8. Related Processes

9. Real time applications

16 April 2015 M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg..

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Sl. No. CONTENTS Assembly vs Joining

Almost all products are assemblies of a

large number of components.

Some of the components or subassemblies

can move with respect to each other -

kinematic joint.

16 April 2015 M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg.. Slide 4

The term assembly usually refers to

mechanical methods of fastening

parts together.

Some of these methods allow for

easy disassembly, while others do

not.

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Assembly vs Joining

Many components are physically fixed

together, with no relative motion

possible - Rigid joint (Structure).

Joining is generally used for welding,

brazing, soldering, and adhesive

bonding, which form a permanent joint

between the parts—a joint that cannot

easily be separated.


Section of Tsing Ma Bridge being lifted, before joining

To restrict some degrees of freedom of motion for components (i.e.

to make mechanisms).

A complex shaped component may be impossible/expensive to

manufacture, but it may be possible/cheaper to make it in several

parts and then join them.

Some products are better made as assemblies, since they can be

disassembled for maintenance.

Transporting a disassembled

product is sometimes

easier/feasible compared to

transporting the entire product.

Why do we need Welding (joining)?



History of Welding

The earliest examples come from the Bronze and Iron

Ages in Europe and the Middle East.

Welding was used in the construction of the Iron pillar of Delhi,

erected in Delhi, India about 310 AD and weighing 5.4 metric tons.

1885 - Welding with carbon electrode.

1886 - Resistance butt welding.

1902 - oxy – acetylene welding (due to Production of cheap oxygen )

1907 - Coated electrodes were developed.

1930 - Release of stud welding, became popular in shipbuilding and

construction.

1930 - Submerged arc welding ;continues to be popular today.


http://en.wikipedia.org/wiki/Iron_Age

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History of Welding cont.

1941- Gas tungsten arc welding, was finally perfected.

1950 - Shielded metal arc welding was developed.

1957 - flux-cored arc welding process ; Plasma Arc Welding.

1958 - Electron beam welding.

1960 - laser beam welding, high-speed, automated welding.

1967 - Magnetic pulse welding .

1991 - Friction stir welding (FSW) was invented by Wayne Thomas

at The Welding Institute (TWI, UK) and found high-quality

applications all over the world.

2000 – Friction Stir Processing (FSP) and related processes

16 April 2015 M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg.. Slide 9 16 April 2015

M. Puviyarasan, Research Scholar/Associate Professor, Mech. Engg.. Slide 10

Friction stir welding requires no blow torches

and no solder.

It literally "stirs" materials together at a

molecular level using friction.

Learn why this matters in OUR life!!


Importance of FSW

A Case study

Columbia Launch: 16 January 2003

Space Transportation System (STS) - 107

16 April 2015 M. Puviyarasan, Research Scholar/Associate Professor, Mech. Engg.. 12

Columbia Disaster February 1, 2003,

Columbia

disintegrated over Texas and Louisiana

as it reentered Earth's atmosphere

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Importance of FSW : A Case study cont. The tragedy of space shuttle Columbia happened on February 1,

2003 as it was reentering earth’s atmosphere.

The shuttle fell into pieces without any notice.

Subsequently, it was realized that the cause of failure was the loss of

a piece of foam insulation on an external tank at the time of

launching.

On reentering the atmosphere of earth at a speed of the 23 Mach,

wings of the shuttle experience temperature of 2800°F.

Investigation team of NASA smelt aluminum on thermal tiles plus the internal

edges of the left wing of the spacecraft, supporting the idea that the Columbia’s

destruction was because of hot gases that pierced through the damaged part of

the wing.

An unfortunate engineering disaster of modern times! 16 April 2015 M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg.. Slide 13

Importance of FSW : A Case study cont. The failure of the crew module resulted from the thermal degradation

of structural properties, which resulted in a rapid catastrophic

sequential structural breakdown rather than an instantaneous

"explosive" failure.

After the loss of space shuttle Columbia in February 2003, NASA

redesigned and improved many components of the structures of the

external tanks and the application processes of the all important foam,

also known as the Thermal Protection System or TPS.

Major improvements have been made to the tank’s forward bipod

fitting area, the liquid hydrogen tank Ice Frost Ramps, the intertank

flange area, and the liquid oxygen feedline brackets and bellows.

The tank’s protuberance air load ramps — known as PAL ramps —

were also removed.


Importance of FSW : A Case study cont. In 1993, NASA challenged Lockheed Martin Laboratories in Baltimore,

Md., to develop a high-strength, low-density, lighter-weight

replacement for aluminum alloy Al 2219–used on the original Space

Shuttle External Tank.

The External Tank Project Managers chose to use the Friction Stir

Welding process on its Super Light Weight Tank, which is made from

Al-Li 2195.

The Friction Stir Welding process produces a joint stronger than the

fusion arc welded joint, obtained in the earlier Light Weight Tank

program.

The increase in joint strength combined with the reduction in process

variability provides for an increased safety margin and high degree of

reliability for the External Tank.


Importance of FSW : A Case study cont. The newest tanks, including ET-134, have been welded using a

new welding technology called Friction Stir Welding, a

technique better than conventional fusion welding.

Friction stir welding is different in that the materials are not melted.

Weld joints are more efficient, yielding 80 percent of the base

strength.

Fusion welding averages 40 to 50 percent of the base material’s

strength.

ET-134 is the first external tank to have most of its liquid hydrogen

tank welding performed by friction stir welding.


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Series of images showing

various stages of the process

to assemble an external tank.

ET-134 is the first external tank

to have most of its liquid

hydrogen tank welding

performed by friction stir

welding.


The first space shuttle external tank to be partially built using the friction stir welding technique.

Several graphic images show the internal and external views of the Liquid Oxygen Tank, Intertank, Liquid Hydrogen Tank and

a completed external tank with thermal protection system.

Image credit: NASA/MSFC


Slide 19

Its journey from NASA’s Michoud Assembly Facility in New Orleans to the Kennedy Space Center, Florida, was loaded onto a barge to begin its six-day, 900-

mile journey to the Kennedy Center.

Friction Stir Welding – Intro.

FSW was invented at “The Welding

Institute “(TWI) of the United Kingdom in

1991.

It’s a Solid-state joining technique and

was initially applied to aluminum

alloys.

The basic concept of FSW is

remarkably simple.


A nonconsumable rotating tool with a specially

designed pin and shoulder is inserted into the

abutting edges of sheets or plates to be joined

and subsequently traversed along the joint line.

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Friction Stir Welding – Intro.


Two discrete metal workpieces butted together, along with

the tool (probe).


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Friction Stir Welding – The Process


Here, the advancing side is on the right, where the tool rotation

direction is the same as the tool travel direction (opposite the

direction of metal flow), Friction stir welding (FSW) is a relatively

new solid-state joining process.

Shoulder

Pin / Probe


The tool serves three

primary functions.

1. Heating of the workpiece

2. Movement of material to

produce the joint, and

3. Containment of the hot metal

beneath the tool shoulder.


•Heating is created within the workpiece both by friction between the rotating tool pin and

shoulder and by severe plastic deformation of the workpiece.

•The localized heating softens material around the pin and, combined with the tool rotation and

translation, leads to movement of material from the front to the back of the pin, thus filling the

hole in the tool wake as the tool moves forward.

•The tool shoulder restricts metal flow to a level equivalent to the shoulder position, that is,

approximately to the initial workpiece top surface.

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As a result of the tool action, when performed properly, a solid-state

joint is produced, that is, no melting.

Because of various geometrical features on the tool, material

movement around the pin can be complex, with gradients in strain,

temperature, and strain rate.

In spite of the local microstructural in-homogeneity, one of the

significant benefits of this solid-state welding technique is the fully

recrystallized, equiaxed, fine grain microstructure created in the

nugget by the intense plastic deformation.


FSW: Process Parameters

Tool rotational speed

Welding speed (Traverse feed)

Axial force

Shoulder diameter

Pin diameter and profile

Tilt angle

Work piece material

Shoulder and pin material

All these variables may affect the characteristics of the weld joint

significantly.


FSW: Process Parameters Cont.

Tool rotational speed is the rotation speed of friction stir

welding tool and can be directly related to the frictional

heat generation.

The term welding speed is preferred to transverse speed,

which is the rate of travel of tool along the joint line.

Tool rotational speed and welding speed decide whether

enough heat input is being supplied to weld so as to

favourably affect the weld characteristics.



Tool Tilt Angle

Forces are important

parameters parts of

friction stir welding

technology.


The force applied parallel to the axis of rotation of the

tool (Z-direction) is the downward force or Axial force.

Insufficient and excessive downward force produce

defects in the weld.

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The defect free weld is decided by the use of proper tool

design.

Tool consists of three parts, these are shoulder, pin and shank.

Pin having small diameter and plunged into the work piece materials

completely.

The pin is responsible for proper stirring of the material and

transportation of plasticized material from the leading edge of the tool

to trailing edge of the tool.

Shoulder is part of the tool which produces most of heat due to its

rubbing with work piece surface.

Shoulder generates the frictional heat and also prevents the escape of

the plasticized material from the upper surface of the work piece.


The different micro structural zones existing after FSW


The different micro structural zones existing after FSW Cont.


• Unaffected material or parent metal:

This is material remote from the weld that has not been deformed and that, although it may

have experienced a thermal cycle from the weld, is not affected by the heat in terms of

microstructure or mechanical properties.

• Heat-affected zone:

In this region, which lies closer to the weld-center, the material has experienced a thermal cycle

that has modified the microstructure and/or the mechanical properties. However, there is

no plastic deformation occurring in this area.

• Thermomechanically affected zone (TMAZ):

In this region, the FSW tool has plastically deformed the material, and the heat from the

process will also have exerted some influence on the material. There is generally a distinct

boundary between the recrystallized zone (weld nugget) and the deformed zones of the TMAZ.

• Weld nugget:

The fully recrystallized area, sometimes called the stir zone, refers to the zone previously

occupied by the tool pin. The term stir zone is commonly used in friction stir processing, where

large volumes of material are processed.

The different micro structural zones existing after FSW Cont.


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What happens inside?

The FSW process consist of three phases:

The plunge phase: where the weld is initiated;

The main phase: where the weld is made; and

The termination phase: where the welding tool is

withdrawn from the workpiece.


What happens inside?

The plunge phase consists of inserting the rotating welding

tool into the joint, at a specific rate.

Frictional heating and pressure, at the end of the pin, induce

work-piece material to displace, forming a ring of expelled,

plastically deformed material around the pin as the pin enters

the work-pieces.

As the tool is plunged into the joint, heat is generated into

the surrounding material.

Once the welding tool is plunged into the work-piece, it

rotates at several hundred rpm and heat is generated between

welding tool and work-piece to reach a higher temperature.



THE MACHINE


Slide 36

The world’s largest friction stir welding machine, designed to manufacture core stages for NASA’s heavy-lift SLS.

At 170 ft. tall, the friction stir welder that will assemble SLS core stages

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Slide 37

Custom-built machines for welding long extrusions


Slide 38


Slide 39

Articulated and Parallel-Kinematic arm robot

16 April 2015 M. Puviyarasan, Research Scholar/Associate Professor, Mech. Engg..

Slide 40

An indigenously

developed servo

controlled

friction stir

welding/processing

machine

@

Anna University,

Chennai - 25

Funding Agency: DST/SERB, Govt. of India.

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What happens inside

Material flow:

The material flow during FSW is complicated and the understanding

of deformation process is limited.

Many factors would influence the material flow during FSW.

These factors include tool geometry (pin and shoulder design,

relative dimensions of pin and shoulder), welding parameters (tool

rotation rate and direction, i.e., clockwise or counter clockwise,

traverse speed, plunge depth, spindle angle), material types,

workpiece temperature, etc.

It is very likely that the material flow within the nugget during FSW

consists of several independent deformation processes.


What happens inside


Metallurgical processing zones developed during friction stir welding

What happens inside


Metal flow patterns

What happens inside

Heat flow:

FSW results in intense plastic deformation around rotating tool and

friction between tool and workpieces.

Both these factors contribute to the temperature increase within

and around the stirred zone.

Since the temperature distribution within and around the stirred

zone directly influences the microstructure of the welds, such as

grain size, grain boundary character, coarsening and dissolution of

precipitates, and resultant mechanical properties of the welds, it is

important to obtain information about temperature distribution

during FSW.


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What happens inside

However, temperature measurements within the stirred

zone are very difficult due to the intense plastic

deformation produced by the rotation and translation of

tool.

The maximum temperatures within the stirred zone during

FSW have been either estimated from the microstructure of

the weld or recorded by embedding thermocouple in the

regions adjacent to the rotating pin.


Welding tools for FSW

Welding tool geometry development led to sound

welds.

Advancement in Tools led to: Higher weld production

speeds, higher workpiece thickness, improved joint

property.

Has enabled welding of high melting point materials,

such as titanium, steel, and copper

New welding tool features have been developed with,

for the goal of reducing process forces, increasing the

robustness of the process, or simplifying welding

control. 16 April 2015 M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg.. Slide 46

Welding tools for FSW Cont.

Different features are used by different practitioners

of FSW, depending on the materials being welded

and the process performance goals required.

FSW practitioners needing to weld at higher travel

speeds or with deeper weld penetration may adopt

variations to the original tool design.

Tool steel materials are generally acceptable for the

FSW of aluminium alloys.

Even for welding aluminium alloys there is no

accepted standard tool material.


Welding tools used for FSW Cont.


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Welding tools used for FSW Cont.


Bobbin Tool

Advantages

Environmental benefits:

No harmful emissions are created during welding, thereby

making the process environmentally friendly.

No shielding gas required.

No/Minimum surface cleaning required.

Eliminate grinding wastes.

Eliminate solvents required for degreasing.

Consumable materials saving, such wire or any other gases.


Advantages Cont.


Metallurgical benefits:

Solid phase process.

Low distortion of workpiece.

Good dimensional stability and repeatability.

No loss of alloying elements.

Excellent metallurgical properties in the joint area.

Fine microstructure.

Absence of cracking.

Replace multiple parts joined by fasteners.

Advantages Cont.

Energy benefits:

Improved materials use (e.g., joining different thickness)

allows reduction in weight.

Only 2.5% of the energy needed for a laser weld.

Decreased fuel consumption in light weight aircraft,

automotive and ship applications.

It’s a “green” technology due to its energy efficiency,

environmental friendliness, and versatility.


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Limitations

Exit hole left when tool is withdrawn.

Large down forces required with heavy-duty clamping

necessary to hold the plates together.

Less flexible than manual and arc processes (difficulties with

thickness variations and non-linear welds).

Often slower traverse rate than some fusion welding

techniques, although this may be offset if fewer welding

passes are required. (up to 750mm/min for welding 5mm

thick 6000 series aluminum alloy on commercially available

machines).

Backing bar is sometimes required.


Limitations


Underwater FSW

Many researchers have conducted underwater FSW, during

which the whole work piece was immersed in the water

environment.

The results indicated that the tensile strength of the

underwater joint was higher than that of the normal joint,

confirming the feasibility of underwater FSW to improve the

joint properties.

Underwater FSW creates a milder and lower thermal cycle

than traditional FSW which is helpful to reserve the excellent

performance of base metal furthest.


Underwater FSW Cont.

Water environment

has reduced the

residual stress of the

joint obviously and

even reserved

compression stress

in the weld.


The mechanical and microstructural properties

are higher than that of the normal FSW joint.

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FRICTION-STIR PROCESSING

FRICTION STIR PROCESSING (FSP) is an adaptation of friction

stir welding.

The unique features of friction stir welding can be used to develop new

processes based on the concept of friction stirring:

Low amount of heat generated

Extensive plastic flow of material

Very fine grain size in the stirred region

Healing of flaws and casting porosity

Random misorientation of grain boundaries in the stirred region

Mechanical mixing of the surface and subsurface layers



FSP can be used as a generic process to modify the

microstructure and change the composition, at selective

locations.

At this time, FSP is the only solid state processing

technique that has these unique capabilities.


16 April 2015 59

FSP

Rotating Tool Pin is plunged into workpiece

Tool traverses on the plate until a fully recrystallized

fine grain microstructure is obtained

Shoulder touches the surface

FRICTION-STIR PROCESSING Cont.

MICROSTRUCTURAL MODIFICATION

During FSP, the rotating pin with a threaded design produces

an intense breaking and mixing effect in the processed zone,

thereby creating a fine, uniform, and densified structure.

Therefore, FSP can be developed as a generic tool for

modifying the microstructure of heterogeneous metallic

materials such as cast alloys, metal matrix composites, and

nanophase aluminum alloys prepared through the PM

technique.


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FRICTION-STIR PROCESSING Cont.

MICROSTRUCTURAL MODIFICATION


Optical micrographs showing morphology and distribution

of Si particles in A356 samples:

(a) as-cast and (b) FSP at 900 rpm

16 April 2015 62

Composite Fabrication using FSP

Fabricating composites through FSP results in:

Good Interface bonding between particles and

reinforcements.

Reduces Hydrogen porosity, common in composites

fabricated through stir casting.

Reduced distortion and defects in materials.

FRICTION STIR PROCESSING though developed as a

grain refinement technique, can be applied

successfully in fabricating composites.

Composite Fabrication using FSP Contd.

SURFACE/BULK COMPOSITE

The use of the FSP technique results in the intense plastic

deformation and mixing of material in the processed zone;

incorporate the ceramic particles into the metallic

substrate plate, to form the surface/Bulk composites.

A groove can be cut on the plate, and the particles filled

into the groove.

With deeper grooves being cut, it is possible to fabricate

bulk composites via. FSP

The bulk composites fabricated via FSP showed enhanced

hardness and strengths.




Optical micrograph showing surface composite layers

fabricated by FSP in (a) A356 and (b) 5083Al substrates

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SEM micrographs showing the SiO2 particle dispersion in

the SiO2/AZ61 composite prepared by FSP



Applications


Engineers at NASA's Marshall Space Flight Center have

worked to perfect the FSW technique, which will be used

to help send astronauts to the moon

and further in space travel.

It might also make better products --

ships, cars, trains -- for use here on Earth.

Applications Cont.


Aerospace industry include:

Wings, fuselages, empennages,

Cryogenic fuel tanks for space vehicles,

Aviation fuel tanks, external throw away tanks for

military aircraft,

Military and scientific rockets,

Repair of faulty MIG welds.

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Applications Cont.


Four aluminum domes, each created using innovative friction stir welding processes, are seen in this overhead view of the

Marshall Space Flight Center.

Applications Cont.


Achieved high-strength,

defect free, uniformly

bonded aluminum structures

- a vital requirement for

next-generation

launch vehicles and

hardware designed for

long-term space

travel.

Applications Cont.


Successfully

manufactured tank

dome which ensures the

strength and reliability

of these novel tank

forming processes.

Applications Cont.


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Applications Cont.


NASA has invested in the Friction Stir Weld

Spun Form Dome Project since 2005

Applications Cont.


Applications Cont.


Shipbuilding and marine industries include:

Panels for decks, sides, bulkheads and floors,

Aluminum extrusions, hulls and superstructures,

Helicopter landing platforms,

Offshore accommodation, marine and transport

Structures, masts and booms,

e.g. for sailing boats, refrigeration plant.

Applications Cont.


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Applications Cont.


Land transportation includes:

Engine and chassis cradles, wheel rims, tailored

blanks, e.g. welding of different sheet thicknesses,.

Truck bodies, tail lifts for lorries, mobile cranes,

Armor plate vehicles, fuel tankers, caravans, buses

and airfield transportation vehicles.

Motorcycle and bicycle frames, articulated lifts and

personnel bridges, skips, repair of aluminum cars,

magnesium and magnesium/aluminum joints.

Applications Cont.


Applications Cont.


The process is also used to fabricate suspension rods,

steering columns, gear box forks and drive shafts.

As well as engine valves, in which the ability to join

dissimilar materials means that the valve stem and head

can be made of materials suited to their different duty

cycles in service.

Wheel assemblies using two aluminum alloys have

been made in which the butt or lap welds can be

fabricated in wrought and/or cast materials

Applications Cont.


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Applications Cont.


Construction industry includes:

Aluminum bridges, facade panels made from aluminum,

copper or titanium, window frames, aluminum pipelines,

aluminum reactors for power plants and the chemical

industry, heat exchangers and air conditioners and pipe

fabrication.

FSW has also been used to weld lightweight panels made of

plastic foam sandwiched between two sheets of aluminum,

for which any fusion welding technique would encounter

serious problems because of the much higher temperatures

involved.

Applications Cont.


Section of Tsing Ma Bridge being lifted, before joining

Applications Cont.


Construction industry includes:

Foamed aluminum

Applications under review include the bodies and floors of

coaches and buses, military bridge-laying vehicles (and

bridges/pontoons), and waste skips .

Applications Cont.


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Applications Cont.


Other industry sectors includes:

Refrigeration panels

Cooking equipment

Gas tanks and gas cylinders

Furniture

Connecting aluminum or copper coils in rolling mills

Applications Cont.


Applications


Image Credits


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Thank you

M. Puviyarasan,Research Scholar/Associate Professor, Mech. Engg.. 16 April 2015 Slide 90

friction stir welding/ processing - -the technology & future potential

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