Friction stir welding

Close-up view of a friction stir weld tack tool.

The bulkhead and nosecone of the Orion spacecraft are joinedusing friction stir welding.

Joint designs

Friction-stir welding (FSW) is a solid-state joining pro-cess (the metal is not melted) that uses a third body tool tojoin two facing surfaces. Heat is generated between thetool and material which leads to a very soft region near

the FSW tool. It then mechanically intermixes the twopieces of metal at the place of the joint, then the softenedmetal (due to the elevated temperature) can be joined us-ing mechanical pressure (which is applied by the tool),much like joining clay, or dough. It is primarily used onaluminium, and most often on extruded aluminum (non-heat treatable alloys), and on structures which need supe-rior weld strength without a post weld heat treatment.It was invented and experimentally proven at TheWeldingInstitute UK in December 1991. TWI holds patents onthe process, the first being the most descriptive.[1]

1 Principle of operation

Schematic diagram of the FSW process: (A) Two discrete metalworkpieces butted together, along with the tool (with a probe).

(B) The progress of the tool through the joint, also showing theweld zone and the region affected by the tool shoulder.

A constantly rotated non consumable cylindrical-shouldered tool with a profiled probe is transversely fedat a constant rate into a butt joint between two clamped

1

2 3 ADVANTAGES AND LIMITATIONS

pieces of butted material. The probe is slightly shorterthan the weld depth required, with the tool shoulderriding atop the work surface.[2]

Frictional heat is generated between the wear-resistantwelding components and the work pieces. This heat,along with that generated by the mechanical mixing pro-cess and the adiabatic heat within the material, cause thestirred materials to soften without melting. As the pin ismoved forward, a special profile on its leading face forcesplasticised material to the rear where clamping force as-sists in a forged consolidation of the weld.This process of the tool traversing along the weld line ina plasticised tubular shaft of metal results in severe solidstate deformation involving dynamic recrystallization ofthe base material.[3]

2 Microstructural features

The solid-state nature of the FSW process, combinedwith its unusual tool and asymmetric nature, results in ahighly characteristic microstructure. The microstructurecan be broken up into the following zones:

• The stir zone (also nugget, dynamically recrystallisedzone) is a region of heavily deformed material thatroughly corresponds to the location of the pin duringwelding. The grains within the stir zone are roughlyequiaxed and often an order of magnitude smallerthan the grains in the parent material.[4] A uniquefeature of the stir zone is the common occurrence ofseveral concentric rings which has been referred toas an “onion-ring” structure.[5] The precise origin ofthese rings has not been firmly established, althoughvariations in particle number density, grain size andtexture have all been suggested.

• The flow arm zone is on the upper surface of theweld and consists of material that is dragged by theshoulder from the retreating side of the weld, aroundthe rear of the tool, and deposited on the advancingside.

• The thermo-mechanically affected zone (TMAZ) oc-curs on either side of the stir zone. In this regionthe strain and temperature are lower and the effectof welding on the microstructure is correspondinglysmaller. Unlike the stir zone the microstructure isrecognizably that of the parent material, albeit sig-nificantly deformed and rotated. Although the termTMAZ technically refers to the entire deformed re-gion it is often used to describe any region not al-ready covered by the terms stir zone and flow arm.

• The heat-affected zone (HAZ) is common to allwelding processes. As indicated by the name, thisregion is subjected to a thermal cycle but is not de-formed during welding. The temperatures are lower

than those in the TMAZ but may still have a signif-icant effect if the microstructure is thermally unsta-ble. In fact, in age-hardened aluminium alloys thisregion commonly exhibits the poorest mechanicalproperties.[6]

3 Advantages and limitations

The solid-state nature of FSW leads to several advantagesover fusion welding methods as problems associated withcooling from the liquid phase are avoided. Issues such asporosity, solute redistribution, solidification cracking andliquation cracking do not arise during FSW. In general,FSW has been found to produce a low concentration ofdefects and is very tolerant of variations in parametersand materials.Nevertheless, FSW is associated with a number of uniquedefects. Insufficient weld temperatures, due to low rota-tional speeds or high traverse speeds, for example, meanthat the weld material is unable to accommodate the ex-tensive deformation during welding. This may result inlong, tunnel-like defects running along the weld whichmay occur on the surface or subsurface. Low tempera-tures may also limit the forging action of the tool and soreduce the continuity of the bond between the materialfrom each side of the weld. The light contact betweenthe material has given rise to the name “kissing-bond”.This defect is particularly worrying since it is very diffi-cult to detect using nondestructive methods such as X-rayor ultrasonic testing. If the pin is not long enough or thetool rises out of the plate then the interface at the bot-tom of the weld may not be disrupted and forged by thetool, resulting in a lack-of-penetration defect. This is es-sentially a notch in the material which can be a potentialsource of fatigue cracks.A number of potential advantages of FSW over conven-tional fusion-welding processes have been identified:[7]

• Good mechanical properties in the as-welded con-dition

• Improved safety due to the absence of toxic fumesor the spatter of molten material.

• No consumables—A threaded pin made of conven-tional tool steel, e.g., hardened H13, can weld over1 km (0.62 mi) of aluminium, and no filler or gasshield is required for aluminium.

• Easily automated on simple milling machines —lower setup costs and less training.

• Can operate in all positions (horizontal, vertical,etc.), as there is no weld pool.

• Generally good weld appearance and minimal thick-ness under/over-matching, thus reducing the needfor expensive machining after welding.

4.2 Tool rotation and traverse speeds 3

• Low environmental impact.

However, some disadvantages of the process have beenidentified:

• Exit hole left when tool is withdrawn.

• Large down forces required with heavy-duty clamp-ing necessary to hold the plates together.

• Less flexible than manual and arc processes (dif-ficulties with thickness variations and non-linearwelds).

• Often slower traverse rate than some fusion weld-ing techniques, although this may be offset if fewerwelding passes are required.

4 Important welding parameters

4.1 Tool design

Advanced friction stir welding and processing tools by MegaStirshown upside down

The design of the tool[8] is a critical factor as a good toolcan improve both the quality of the weld and the maxi-mum possible welding speed.It is desirable that the tool material is sufficiently strong,tough, and hard wearing at the welding temperature. Fur-ther it should have a good oxidation resistance and a lowthermal conductivity to minimise heat loss and thermaldamage to the machinery further up the drive train. Hot-worked tool steel such as AISI H13 has proven perfectlyacceptable for welding aluminium alloys within thicknessranges of 0.5 – 50 mm [9] but more advanced tool mate-rials are necessary for more demanding applications suchas highly abrasive metal matrix composites[10] or highermelting point materials such as steel or titanium.

FSW of two USIBOR 1500 high-strength steel sheets

Improvements in tool design have been shown to causesubstantial improvements in productivity and quality.TWI has developed tools specifically designed to increasethe penetration depth and thus increasing the plate thick-nesses that can be successfully welded. An example is the“whorl” design that uses a tapered pin with re-entrant fea-tures or a variable pitch thread to improve the downwardsflow of material. Additional designs include the Trifluteand Trivex series. The Triflute design has a complex sys-tem of three tapering, threaded re-entrant flutes that ap-pear to increase material movement around the tool. TheTrivex tools use a simpler, non-cylindrical, pin and havebeen found to reduce the forces acting on the tool duringwelding.The majority of tools have a concave shoulder profilewhich acts as an escape volume for the material displacedby the pin, prevents material from extruding out of thesides of the shoulder and maintains downwards pressureand hence good forging of the material behind the tool.The Triflute tool uses an alternative system with a seriesof concentric grooves machined into the surface whichare intended to produce additional movement of materialin the upper layers of the weld.Widespread commercial applications of friction stir weld-ing process for steels and other hard alloys such astitanium alloys will require the development of cost-effective and durable tools.[11] Material selection, designand cost are important considerations in the search forcommercially useful tools for the welding of hard mate-rials. Work is continuing to better understand the effectsof tool material’s composition, structure, properties andgeometry on their performance, durability and cost.[12]

4.2 Tool rotation and traverse speeds

There are two tool speeds to be considered in friction-stirwelding; how fast the tool rotates and how quickly it tra-verses the interface. These two parameters have consid-erable importance and must be chosen with care to en-sure a successful and efficient welding cycle. The rela-

4 6 FLOW OF MATERIAL

tionship between the welding speeds and the heat inputduring welding is complex but, in general, it can be saidthat increasing the rotation speed or decreasing the tra-verse speed will result in a hotter weld. In order to pro-duce a successful weld it is necessary that the materialsurrounding the tool is hot enough to enable the extensiveplastic flow required and minimize the forces acting onthe tool. If the material is too cold then voids or otherflaws may be present in the stir zone and in extreme casesthe tool may break.Excessively high heat input, on the other hand may bedetrimental to the final properties of the weld. Theoreti-cally, this could even result in defects due to the liquationof low-melting-point phases (similar to liquation crackingin fusion welds). These competing demands lead onto theconcept of a “processing window": the range of process-ing parameters viz. tool rotation and traverse speed, thatwill produce a good quality weld.[13] Within this windowthe resulting weld will have a sufficiently high heat inputto ensure adequate material plasticity but not so high thatthe weld properties are excessively deteriorated.

4.3 Tool tilt and plunge depth

A drawing showing the plunge depth and tilt of the tool. The toolis moving to the left.

The plunge depth is defined as the depth of the lowestpoint of the shoulder below the surface of the weldedplate and has been found to be a critical parameter for en-suring weld quality.[14] Plunging the shoulder below theplate surface increases the pressure below the tool andhelps ensure adequate forging of the material at the rearof the tool. Tilting the tool by 2–4 degrees, such that therear of the tool is lower than the front, has been foundto assist this forging process. The plunge depth needsto be correctly set, both to ensure the necessary down-ward pressure is achieved and to ensure that the tool fullypenetrates the weld. Given the high loads required, thewelding machine may deflect and so reduce the plungedepth compared to the nominal setting, which may re-sult in flaws in the weld. On the other hand, an excessiveplunge depth may result in the pin rubbing on the back-ing plate surface or a significant undermatch of the weld

thickness compared to the base material. Variable loadwelders have been developed to automatically compen-sate for changes in the tool displacement while TWI havedemonstrated a roller system that maintains the tool po-sition above the weld plate.

5 Welding forces

During welding a number of forces will act on the tool:

• A downwards force is necessary to maintain the po-sition of the tool at or below the material surface.Some friction-stir welding machines operate underload control but in many cases the vertical positionof the tool is preset and so the load will vary duringwelding.

• The traverse force acts parallel to the tool motionand is positive in the traverse direction. Since thisforce arises as a result of the resistance of the ma-terial to the motion of the tool it might be expectedthat this force will decrease as the temperature ofthe material around the tool is increased.

• The lateral force may act perpendicular to the tooltraverse direction and is defined here as positive to-wards the advancing side of the weld.

• Torque is required to rotate the tool, the amount ofwhich will depend on the down force and frictioncoefficient (sliding friction) and/or the flow strengthof the material in the surrounding region (stiction).

In order to prevent tool fracture and to minimize exces-sive wear and tear on the tool and associated machinery,the welding cycle is modified so that the forces acting onthe tool are as low as possible, and abrupt changes areavoided. In order to find the best combination of weld-ing parameters, it is likely that a compromise must bereached, since the conditions that favour low forces (e.g.high heat input, low travel speeds) may be undesirablefrom the point of view of productivity and weld proper-ties.

6 Flow of material

Early work on the mode of material flow around the toolused inserts of a different alloy, which had a differentcontrast to the normal material when viewed through amicroscope, in an effort to determine where material wasmoved as the tool passed.[15] [16] The data was interpretedas representing a form of in-situ extrusion where the tool,backing plate and cold base material form the “extrusionchamber” through which the hot, plasticised material isforced. In this model the rotation of the tool draws little

5

or no material around the front of the pin instead the ma-terial parts in front of the pin and passes down either side.After the material has passed the pin the side pressure ex-erted by the “die” forces the material back together andconsolidation of the join occurs as the rear of the toolshoulder passes overhead and the large down force forgesthe material.More recently, an alternative theory has been advancedthat advocates considerable material movement in certainlocations.[17] This theory holds that some material doesrotate around the pin, for at least one rotation, and it is thismaterial movement that produces the “onion-ring” struc-ture in the stir zone. The researchers used a combinationof thin copper strip inserts and a “frozen pin” technique,where the tool is rapidly stopped in place. They suggestedthat material motion occurs by two processes:

1. Material on the advancing front side of a weld en-ters into a zone that rotates and advances with thepin. This material was very highly deformed andsloughs off behind the pin to form arc-shaped fea-tures when viewed from above (i.e. down the toolaxis). It was noted that the copper entered the rota-tional zone around the pin, where it was broken upinto fragments. These fragments were only found inthe arc shaped features of material behind the tool.

2. The lighter material came from the retreating frontside of the pin and was dragged around to the rearof the tool and filled in the gaps between the arcs ofadvancing side material. This material did not rotatearound the pin and the lower level of deformationresulted in a larger grain size.

The primary advantage of this explanation is that it pro-vides a plausible explanation for the production of theonion-ring structure.The marker technique for friction stir welding providesdata on the initial and final positions of the marker inthe welded material. The flow of material is then re-constructed from these positions. Detailed material flowfield during friction stir welding can also be calculatedfrom theoretical considerations based on fundamentalscientific principles. Material flow calculations are rou-tinely used in numerous engineering applications. Cal-culation of material flow fields in friction stir weldingcan be undertaken both using comprehensive numericalsimulations[18][19][20] or simple but insightful analyticalequations.[21] The comprehensive models for the calcula-tion of material flow fields also provide important infor-mation such as geometry of the stir zone and the torqueon the tool.[22][23] The numerical simulations have shownthe ability to correctly predict the results from markerexperiments[20] and the stir zone geometry observed infriction stir welding experiments.[22][24]

7 Generation and flow of heat

For any welding process it is, in general, desirable to in-crease the travel speed and minimise the heat input as thiswill increase productivity and possibly reduce the impactof welding on the mechanical properties of the weld. Atthe same time it is necessary to ensure that the tempera-ture around the tool is sufficiently high to permit adequatematerial flow and prevent flaws or tool damage.When the traverse speed is increased, for a given heat in-put, there is less time for heat to conduct ahead of the tooland the thermal gradients are larger. At some point thespeed will be so high that the material ahead of the toolwill be too cold, and the flow stress too high, to permit ad-equate material movement, resulting in flaws or tool frac-ture. If the “hot zone” is too large then there is scope toincrease the traverse speed and hence productivity.The welding cycle can be split into several stages dur-ing which the heat flow and thermal profile will bedifferent:[25]

• Dwell. The material is preheated by a stationary, ro-tating tool to achieve a sufficient temperature aheadof the tool to allow the traverse. This period mayalso include the plunge of the tool into the work-piece.

• Transient heating. When the tool begins to movethere will be a transient period where the heat pro-duction and temperature around the tool will alter ina complex manner until an essentially steady-state isreached.

• Pseudo steady-state. Although fluctuations in heatgeneration will occur the thermal field around thetool remains effectively constant, at least on themacroscopic scale.

• Post steady-state. Near the end of the weld heat may“reflect” from the end of the plate leading to addi-tional heating around the tool.

Heat generation during friction-stir welding arises fromtwo main sources: friction at the surface of the tool andthe deformation of the material around the tool.[26] Theheat generation is often assumed to occur predominantlyunder the shoulder, due to its greater surface area, and tobe equal to the power required to overcome the contactforces between the tool and the workpiece. The contactcondition under the shoulder can be described by slid-ing friction, using a friction coefficient μ and interfacialpressure P, or sticking friction, based on the interfacialshear strength at an appropriate temperature and strainrate. Mathematical approximations for the total heat gen-erated by the tool shoulder Q ₒ ₐ have been developed us-ing both sliding and sticking friction models:[25]

Qtotal =23πPµω

(R3shoulder −R3

pin

)(Sliding)

6 8 APPLICATIONS

Qtotal =23πτω

(R3shoulder −R3

pin

)(Sticking)

where ω is the angular velocity of the tool, R ₒᵤ ₑᵣ is theradius of the tool shoulder and R ᵢ that of the pin. Sev-eral other equations have been proposed to account forfactors such as the pin but the general approach remainsthe same.A major difficulty in applying these equations is deter-mining suitable values for the friction coefficient or theinterfacial shear stress. The conditions under the tool areboth extreme and very difficult to measure. To date, theseparameters have been used as “fitting parameters” wherethe model works back frommeasured thermal data to ob-tain a reasonable simulated thermal field. While this ap-proach is useful for creating process models to predict,for example, residual stresses it is less useful for provid-ing insights into the process itself.

8 Applications

The FSW process is currently patented by TWI inmost industrialised countries and licensed for over 183users. Friction stir welding and its variants frictionstir spot welding and friction stir processing are usedfor the following industrial applications:[27] shipbuildingand offshore,[28] aerospace,[29][30] automotive,[31] rollingstock for railways,[32] general fabrication,[33] robotics,and computers.

8.1 Shipbuilding and Offshore

Friction stir welding was used to prefabricate the aluminium pan-els of the Super Liner Ogasawara atMitsui Engineering and Ship-building

Two Scandinavian aluminium extrusion companies werethe first to apply FSW commercially to the manufactureof fish freezer panels at Sapa in 1996, as well as deckpanels and helicopter landing platforms at Marine Alu-minium Aanensen. Marine Aluminium Aanensen subse-quently merged with Hydro Aluminium Maritime to be-come Hydro Marine Aluminium. Some of these freezer

panels are now produced by Riftec and Bayards. In 1997two-dimensional friction stir welds in the hydrodynami-cally flared bow section of the hull of the ocean viewervessel The Boss were produced at Research FoundationInstitute with the first portable FSW machine. The SuperLiner Ogasawara at Mitsui Engineering and Shipbuild-ing is the largest friction stir welded ship so far. The SeaFighter of Nichols Bros and the Freedom class LittoralCombat Ships contain prefabricated panels by the FSWfabricators Advanced Technology and Friction Stir Link,Inc. respectively.[34] The Houbei class missile boat hasfriction stir welded rocket launch containers of ChinaFriction Stir Centre. HMNZS Rotoiti in New Zealand hasFSW panels made by Donovans in a converted millingmachine.[35][36] Various companies apply FSW to armorplating for amphibious assault ships [37][38]

8.2 Aerospace

Longitudinal and circumferential friction stir welds are used forthe Falcon 9 rocket booster tank at the SpaceX factory

Boeing applies FSW to the Delta II and Delta IV ex-pendable launch vehicles, and the first of these with afriction stir welded Interstage module was launched in1999. The process is also used for the Space Shuttleexternal tank, for Ares I and for the Orion Crew Vehi-cle test article at NASA as well as Falcon 1 and Falcon9 rockets at SpaceX. The toe nails for ramp of BoeingC-17 Globemaster III cargo aircraft by Advanced Join-ing Technologies[39] and the cargo barrier beams for theBoeing 747 Large Cargo Freighter[39] were the first com-mercially produced aircraft parts. FAA approved wingsand fuselage panels of the Eclipse 500 aircraft were madeat Eclipse Aviation, and this company delivered 259 fric-tion stir welded business jets, before they were forced intoChapter 7 liquidation. Floor panels for Airbus A400Mmilitary aircraft are now made by Pfalz Flugzeugwerkeand Embraer used FSW for the Legacy 450 and 500 Jets[40] Friction stir welding also is employed for fuselagepanels on the Airbus A380.[41] BRÖTJE-AutomationGmbH uses friction stir welding – through the DeltaNFS® system – for gantry production machines devel-oped for the aerospace sector as well as other industrial

8.5 Fabrication 7

applications.[42]

8.3 Automotive

The centre tunnel of the FordGT is made from two aluminium ex-trusions friction stir welded to a bent aluminium sheet and housesthe fuel tank

Aluminium engine cradles and suspension struts forstretched Lincoln Town Car were the first automotiveparts that were friction stir at Tower Automotive, whouse the process also for the engine tunnel of the Ford GT.A spin-off of this company is called Friction Stir Link,Inc. and successfully exploits the FSW process, e.g. forthe flatbed trailer “Revolution” of Fontaine Trailers.[40]In Japan FSW is applied to suspension struts at ShowaDenko and for joining of aluminium sheets to galvanizedsteel brackets for the boot (trunk) lid of theMazdaMX-5.Friction stir spot welding is successfully used for the bon-net (hood) and rear doors of theMazdaRX-8 and the bootlid of the Toyota Prius. Wheels are friction stir welded atSimmons Wheels, UT Alloy Works and Fundo.[43] Rearseats for the Volvo V70 are friction stir welded at Sapa,HVAC pistons at Halla Climate Control and exhaust gasrecirculation coolers at Pierburg. Tailor welded blanks[44]are friction stir welded for the Audi R8 at Riftec.[45] TheB-column of the Audi R8 Spider is friction stir weldedfrom two extrusions at Hammerer Aluminium Industriesin Austria.

8.4 Railways

Since 1997 roof panels were made from aluminium ex-trusions at HydroMarine Aluminiumwith a bespoke 25mlong FSW machine, e.g. for DSB class SA-SD trainsof Alstom LHB [46] Curved side and roof panels for theVictoria line trains of London Underground, side panelsfor Bombardier’s Electrostar trains[47] at Sapa Group andside panels for Alstom’s British Rail Class 390 Pendolinotrains aremade at SapaGroup[48] Japanese commuter andexpress A-trains,[49] and British Rail Class 395 trains arefriction stir welded by Hitachi,[50] while Kawasaki appliesfriction stir spot welding to roof panels and Sumitomo

The high-strength low-distortion body of Hitachi’s A-trainBritishRail Class 395 is friction stir welded from longitudinal alu-minium extrusions

Light Metal produces Shinkansen floor panels. Innova-tive FSWfloor panels aremade byHammerer AluminiumIndustries in Austria for the Stadler KISS double deckerrail cars, to obtain an internal height of 2 m on both floorsand for the new car bodies of the Wuppertal SuspensionRailway.[51]

Heat sinks for cooling high-power electronics of locomo-tives are made at Sykatek, EBG, Austerlitz Electronics,EuroComposite, Sapa [52] and Rapid Technic, and are themost common application of FSW due to the excellentheat transfer.

8.5 Fabrication

Façade panels and athode sheets are friction stir welded atAMAG and Hammerer Aluminium Industries includingfriction stir lap welds of copper to aluminium. Bizerbameat slicers, Ökolüfter HVAC units and Siemens X-rayvacuum vessels are friction stir welded at Riftec. Vac-uum valves and vessels are made by FSW at Japaneseand Swiss companies. FSW is also used for the encap-sulation of nuclear waste at SKB in 50-mm-thick coppercanisters.[53][54] Pressure vessels from ø1m semisphericalforgings of 38.1mm thick aluminium alloy 2219 at Ad-vanced Joining Technologies and Lawrence LivermoreNat Lab.[55] Friction stir processing is applied to ship pro-pellers at Friction Stir Link, Inc. and to hunting knives byDiamondBlade. Bosch uses it in Worcester for the pro-duction of heat exchangers.[56]

8.6 Robotics

KUKARobot Group has adapted its KR500-3MT heavy-duty robot for friction stir welding via the DeltaN FS tool.The systemmade its first public appearance at the EuroB-LECH show in November 2012.[57]

8 11 REFERENCES

The lids of 50-mm-thick copper canisters for nuclear waste areattached to the cylinder by friction stir welding at SKB

Friction stir processed knives by MegaStir

8.7 Personal Computers

Apple applied friction stir welding on the 2012 iMac toeffectively join the bottom to the back of the device.[58]

9 Friction stir welding experts

• List of friction stir welding experts

10 See also• Friction Welding

• Friction stir processing

11 References[1] Thomas, WM; Nicholas, ED; Needham, JC; Murch,

MG;Temple-Smith, P;Dawes, CJ.Friction-stir butt weld-ing, GB Patent No. 9125978.8, International patent ap-plication No. PCT/GB92/02203, (1991)

[2] Kallee, S.W. (2006-09-06). “Friction Stir Welding atTWI”. The Welding Institute (TWI). Retrieved 2009-04-14.

[3] Ding, Jeff; Bob Carter; Kirby Lawless; Dr. Arthur Nunes;Carolyn Russell; Michael Suites; Dr. Judy Schneider(2008-02-14). “A Decade of Friction Stir Welding R&DAt NASA’s Marshall Space Flight Center And a Glanceinto the Future”. NASA. Retrieved 2009-04-14.

[4] Murr, LE; Liu, G; McClure, JC (1997). “Dynamic re-crystallisation in the friction-stir welding of aluminium al-loy 1100”. Journal of Materials Science Letters 16 (22):1801–1803. doi:10.1023/A:1018556332357.

[5] Krishnan, K. N. “On the Formation of Onion Rings inFriction Stir Welds.” Materials Science and EngineeringA 327, no. 2 (April 30, 2002): 246–251. doi:10.1016/S0921-5093(01)01474-5.

[6] Mahoney, M. W., C. G. Rhodes, J. G. Flintoff, W. H.Bingel, and R. A. Spurling. “Properties of Friction-stir-welded 7075 T651 Aluminum.” Metallurgical and Mate-rials Transactions A 29, no. 7 (July 1998): 1955–1964.doi:10.1007/s11661-998-0021-5.

[7] Nicholas, ED (1998). “Developments in the friction-stirwelding of metals”. ICAA-6: 6th International Conferenceon Aluminium Alloys. Toyohashi, Japan.

[8] By Rajiv S. Mishra, Murray W. Mahoney: Friction stirwelding and processing, ASM International ISBN 978-0-87170-848-9.

[9] Prado, RA; Murr, LE; Shindo, DJ; Soto, HF (2001).“Tool wear in the friction stir welding of aluminium alloy6061+20% Al2O3: A preliminary study”. Scripta Mate-rialia 45: 75–80. doi:10.1016/S1359-6462(01)00994-0.

[10] Nelson, T; Zhang, H; Haynes, T (2000). “friction stirwelding of Al MMC 6061-B4C”. 2nd International Sym-posium on FSW (CD ROM). Gothenburg, Sweden.

[11] Bhadeshia HKDH; DebRoy T (2009). “Critical as-sessment: friction stir welding of steels”. Science andTechnology of Welding and Joining 14 (3): 193–196.doi:10.1179/136217109X421300.

[12] Rai R; De A; Bhadeshia HKDH; DebRoy T (2011).“Review: friction stir welding tools”. Science andTechnology of Welding and Joining 16 (4): 325–342.doi:10.1179/1362171811Y.0000000023.

9

[13] http://www.sciencedirect.com/science/article/pii/S1359646207007701

[14] Leonard, AJ (2000). “Microstructure and aging behaviourof FSW in Al alloys 2014A-T651 and 7075-T651”. 2ndInternational Symposium on FSW (CDROM). Gothenburg,Sweden.

[15] Reynolds, AP (2000). “Visualisation of materialflow in autogenous friction stir welds”. Science andtechnology of welding and joining 5 (2): 120–124.doi:10.1179/136217100101538119.

[16] Seidel, TU; Reynolds, AP (2001). “Visualization of theMaterial Flow in AA2195 Friction-Stir Welds Using aMarker Insert Technique”. Metallurgical and MaterialTransactions 32A (11): 2879–2884.

[17] Guerra, M; Schmidt, C; McClure, JC; Murr, LE;Nunes, AC (2003). “Flow patterns during friction stirwelding”. Materials Characterisation 49 (2): 95–101.doi:10.1016/S1044-5803(02)00362-5.

[18] Nandan R; DebRoy T; Bhadeshia HKDH (2008). “Re-cent advances in friction-stir welding – Process, weldmentstructure and properties”. Progress in Materials Science 53(6): 980–1023. doi:10.1016/j.pmatsci.2008.05.001.

[19] Nandan R; Roy GG; Lienert TJ; DebRoy T (2007).“Three-dimensional heat and material flow during frictionstir welding of mild steel”. Acta Materialia 55 (3): 883–895. doi:10.1016/j.actamat.2006.09.009.

[20] Seidel TU; Reynolds AP (2003). “Two-dimensional fric-tion stir welding process model based on fluid mechan-ics”. Science and Technology of Welding and Joining 8(3): 175–183. doi:10.1179/136217103225010952.

[21] Arora A; DebRoy T; Bhadeshia HKDH (2011).“Back-of-the-envelope calculations in friction stirwelding – Velocities, peak temperature, torque, andhardness”. Acta Materialia 59 (5): 2020–2028.doi:10.1016/j.actamat.2010.12.001.

[22] Arora A; Nandan R; Reynolds AP; DebRoy T (2009).“Torque, power requirement and stir zone geome-try in friction stir welding through modeling andexperiments”. Scripta Materialia 60 (1): 13–16.doi:10.1016/j.scriptamat.2008.08.015.

[23] Mehta M; Arora A; De A; DebRoy T (2011). “ToolGeometry for Friction Stir Welding—Optimum ShoulderDiameter”. Metallurgical and Materials Transactions A42 (9): 2716. doi:10.1007/s11661-011-0672-5.

[24] Nandan R; Roy GG; DebRoy T (2011). “Numerical sim-ulation of three-dimensional heat transfer and plastic flowduring friction stir welding”. Metallurgical and MaterialsTransactions A 37 (4): 1247–1259. doi:10.1007/s11661-006-1076-9.

[25] Frigaard, O; Grong, O; Midling, O T (2001). “A pro-cess model for friction-stir welding of age hardening alu-minium alloys”. Metallurgical and Material Transactions32A (5): 1189–1200. doi:10.1007/s11661-001-0128-4.

[26] Qi, X, Chao, Y J (1999). “Heat transfer and Thermo-Mechanical analysis of FSW joining of 6061-T6 plates”.1st International Symposium on FSW (CD ROM). Thou-sand Oaks, USA: TWI.

[27] D. Lohwasser and Z. Chen: “Friction stir welding—Frombasics to applications”Woodhead Publishing 2010, Chap-ter 5, Pages 118–163, ISBN 978-1-84569-450-0.

[28] Fred Delany, Stephan W Kallee, Mike J Russell: “Fric-tion stir welding of aluminium ships”, Paper presented at2007 International Forum onWelding Technologies in theShipping Industry (IFWT). Held in conjunction with theBeijing Essen Welding and Cutting Fair in Shanghai, 16–19 June 2007.

[29] Video: ''FSW at British Aerospace''. Twi.co.uk. Re-trieved on 2012-01-03.

[30] Video: FSW of aerospace fuselages. Twi.co.uk. Re-trieved on 2012-01-03.

[31] S. W. Kallee, J. M. Kell, W. M. Thomas und C. S.Wiesner:“Development and implementation of innova-tive joining processes in the automotive industry”, Paperpresented at DVS Annual Welding Conference “GroßeSchweißtechnische Tagung”, Essen, Germany, 12–14September 2005.

[32] S. W. Kallee and J. Davenport: “Trends in the design andfabrication of rolling stock”, Paper published in EuropeanRailway Review, Volume 13, Issue 1, 2007.

[33] Mike Page: “Friction stir welding broadens applicationsbase”, Report of a EuroStir meeting, 3 Sept 2003.

[34] Bill Arbegast, Tony Reynolds, Rajiv S. Mishra, TracyNelson, Dwight Burford: Littoral Combat System withImproved Welding Technologies, Center for FrictionSTIR Processing (CFSP).

[35] Richard Worrall: “Welded Bliss”, e.nz magazineMarch/April 2008.

[36] Stephan Kallee: “NZ Fabricators begin to use Friction StirWelding to produce aluminium components and panels”,Paper published in New Zealand Engineering News, Au-gust 2006.

[37] Friction Stir Welding Demonstrated for Combat VehicleConstruction ... for 2519 aluminum armor for the U.S.Marine Corps’ Advanced Amphibious Assault Vehicle,Welding Journal 03 2003.

[38] GCampbell and T Stotler: Friction StirWelding of ArmorGrade Aluminum Plate , Welding Journal, Dec 1999.

[39] Walter Polt “A little friction at Boeing”, Boeing FrontiersOnline, September 2004, Vol. 3, Issue 5

[40] Embraer Performs First Metal Cut for Legacy 500 Jet,BART International.

[41] “How Airbus uses friction stir welding”. Reliable Plant.Retrieved 7 August 2013.

[42] “JEC Composites Show - Day 3: EADS licensesits patented DeltaN friction-stir welding technology toBRÖTJE-Automation”. EADS. Retrieved 30 July 2013.

10 12 EXTERNAL LINKS

[43] Fundo’s FSWWheels provide improved performance andreduced running costs.

[44] Video:;FSW used in automotive tailor welded blanks’'.Twi.co.uk. Retrieved on 2012-01-03.

[45] FSW applications at Riftec, Company web site.

[46] S.W. Kallee, J. Davenport and E.D. Nicholas: “RailwayManufacturers Implement Friction Stir Welding”, Weld-ing Journal, October 2002.

[47] Video: ''Friction stir welding of Bombardier trains’',archived from the original on 27 September 2011.Twi.co.uk.

[48] Sapa’s Capabilities, Long length FSW—Max. length 26m — Max. width 3,5 m — Double sided welding, Sapacompany brochure.

[49] History, Principles and Advantages of FSW on HitachiTransportation Systems Website. Hitachi-rail.com. Re-trieved on 2012-01-03.

[50] Hitachi Class 395 Railway Strategies Live 2010. 23 June2010, pp. 12–13. (PDF) . Retrieved on 2012-01-03.

[51] F. Ellermann, S. Pommer, G. Barth: Einsatz desRührreibschweißens bei der Fertigung der Wagenkästenfür die Schwebebahn Wuppertal. DVS Congress: GroßeSchweißtechnische Tagung, 15./16. September, HotelPullman Berlin Schweizerhof, Berlin.

[52] FSW: Increased strength, Improved leakproofness, Im-proved repeatability. Reduced heat distortion, Sapa com-pany brochure.

[53] Video: ''Electron Beam Welding and Friction Stir Weld-ing of Copper Canisters’'. Twi.co.uk. Retrieved on 2012-01-03.

[54] Nielsen, Isak (2012). Modeling and Control of FrictionStir Welding in 5 cm (2 in) thick Copper Canisters (M.Sc.thesis). Linköping University.

[55] E Dalder, J W Pasternak, J Engel, R S Forrest, E Kokko,KMcTernan and DWaldron Friction stir welding of thickwalled alumnium pressure vessels, Welding Journal, April2008, pp. 40–44.

[56] YouTube Video.

[57] “Partnership success with EADS’ DeltaN FS® friction-stir welding technology for industrial robots”. EADS. Re-trieved 30 July 2013.

[58] “Apple unveils totally redesigned 27 and 21.5 imac”.TechCrunch.

12 External links

• Friction stir welding at TWI

• Friction-stir welding research at University of Cam-bridge

• Friction-stir welding of aluminum alloy to steel; aca-demic article from the 2004 Welding Journal

• Friction stir welding research at Vanderbilt Univer-sity Welding Automation Laboratory

• Back of the envelope calculations in friction stirwelding

• Theory of materials processing/welding researchgroup at Penn State University

• Friction Stir Welding Machines: Applications &Key Features

11

13 Text and image sources, contributors, and licenses

13.1 Text• Friction stir welding Source: http://en.wikipedia.org/wiki/Friction%20stir%20welding?oldid=646313963 Contributors: Michael Hardy,

CesarB, Ahoerstemeier, Nv8200p, Wolfkeeper, Fudoreaper, BenFrantzDale, Ferkelparade, Edcolins, Chowbok, ConradPino, TreyHarris,Woolstar, Chris j wood, Brianhe, Rich Farmbrough, Sladen, MeltBanana, Antaeus Feldspar, Elipongo, Slinky Puppet, Hooperbloob, Grut-ness, Fritz Saalfeld, Spangineer, Simone, Danthemankhan, Bobrayner, Sympleko, DavidCane, Aalegado, StuffOfInterest, Hydrargyrum,Gaius Cornelius, NawlinWiki, Saberwyn, Lockesdonkey, Cstaffa, ArielGold, SmackBot, Bluebot, OrphanBot, John, PRRfan, Wizard191,Iepeulas, CmdrObot, CWY2190, Sanspeur, Christian75, Dtgriscom, Bedlamhotel, Modernist, Dougher, Mwarren us, Jasonbrotherton,JaGa, Rhowes, R'n'B, Cgregory42, VolkovBot, Rharding13, Sdsds, Dismayhem, Martarius, Sfan00 IMG, ClueBot, Nailedtooth, Auntof6,Sun Creator, SchreiberBike, Pleides, Johnuniq, XLinkBot, Addbot, Lancshero, DOI bot, Monkeyshateme, VSteiger, Lightbot, Yobot,Starbois, ShreadedWheat, Adam Zábranský, Materialscientist, Xqbot, Zad68, Shadowjams, V12, Originalwana, Volpix0, Citation bot1, Bryancpark, MastiBot, Surena, RjwilmsiBot, Koteshwor, EmausBot, WarEqualsPeace, Infowest, ZéroBot, NearEMPTiness, EdoBot,FeatherPluma, ClueBot NG, Mmarre, Savantas83, Helpful Pixie Bot, Bakerbrett, Amit fsw, Soni, Catherinecondie, Jimten, Rsander-son1100, Debouch, Advocatejake, Monkbot, Watermelon24 and Anonymous: 102

13.2 Images• File:Advanced_friction_stir_welding_and_processing_tools_by_MegaStir.JPG Source: http://upload.wikimedia.org/wikipedia/

commons/3/33/Advanced_friction_stir_welding_and_processing_tools_by_MegaStir.JPG License: CC BY-SA 4.0 Contributors: Ownwork Original artist: NearEMPTiness

• File:Anand-FSW-Figure1-A.jpg Source: http://upload.wikimedia.org/wikipedia/commons/3/35/Anand-FSW-Figure1-A.jpg License:CC BY-SA 3.0 Contributors: https://en.wikipedia.org/wiki/File:Anand-FSW-Figure1-B.jpg Original artist: Anandwiki

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• File:Class395Javelin.JPG Source: http://upload.wikimedia.org/wikipedia/commons/a/a5/Class395Javelin.JPGLicense: CCBY3.0Con-tributors: Own work Original artist: Rob500

• File:Ford_GT_interior.jpg Source: http://upload.wikimedia.org/wikipedia/commons/1/10/Ford_GT_interior.jpg License: CC BY-SA2.0 Contributors: flickr Original artist: stephenhanafin

• File:Friction_Stir_Weld.jpg Source: http://upload.wikimedia.org/wikipedia/commons/4/4e/Friction_Stir_Weld.jpg License: Public do-main Contributors: NASA Image of the Day Original artist: NASA

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• File:Shapes_and_joints.png Source: http://upload.wikimedia.org/wikipedia/commons/c/cb/Shapes_and_joints.png License: Public do-main Contributors: http://www.ntefsw.com/shapes_and_joints.htm Original artist: Nova-Tech Engineering

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