View source for Friction stir welding

{{Short description|Spinning a tool to mix metal workpieces together at the joint, without melting them}}
[[File:Friction Stir Weld.jpg|thumb|Close-up view of a friction stir weld tack tool.]]
[[File:Bulkhead & Nosecone Of Orion Spacecraft Joined By Friction Stir Welding.jpg|thumb|The bulkhead and nosecone of the [[Orion spacecraft]] are joined using friction stir welding.]]
[[File:Shapes and joints.png|thumb|Joint designs]]'''Friction stir welding''' ('''FSW''') is a solid-state joining process that uses a non-consumable tool to join two facing workpieces without melting the workpiece material.<ref>{{Cite journal|last1=Li|first1=Kun|last2=Jarrar|first2=Firas|last3=Sheikh-Ahmad|first3=Jamal|last4=Ozturk|first4=Fahrettin|date=2017|title=Using coupled Eulerian Lagrangian formulation for accurate modeling of the friction stir welding process|journal=Procedia Engineering|volume=207|pages=574–579|doi=10.1016/j.proeng.2017.10.1023|doi-access=free}}</ref><ref name=":0">{{Cite web |title=Welding process and its parameters - Friction Stir Welding |url=http://www.fswelding.com/application-of-friction-stir-welding-in-aircraft-structures/welding-process-and-its-parameters |archive-url=https://web.archive.org/web/20200722150809/http://www.fswelding.com:80/application-of-friction-stir-welding-in-aircraft-structures/welding-process-and-its-parameters |archive-date=2020-07-22 |access-date=2017-04-22 |website=www.fswelding.com}}</ref> Heat is generated by friction between the rotating tool and the workpiece material, which leads to a softened region near the FSW tool. While the tool is traversed along the joint line, it mechanically intermixes the two pieces of metal, and forges the hot and softened metal by the mechanical pressure, which is applied by the tool, much like joining clay, or dough.<ref name=":0" /> It is primarily used on wrought or extruded [[aluminium]] and particularly for structures which need very high weld strength. FSW is capable of joining aluminium alloys, copper alloys, titanium alloys, mild steel, stainless steel and magnesium alloys. More recently, it was successfully used in welding of polymers.<ref>{{Cite journal|last1=Sheikh-Ahmad|first1=J.Y.|last2=Ali|first2=Dima S.|last3=Deveci|first3=Suleyman|last4=Almaskari|first4=Fahad|last5=Jarrar|first5=Firas|date=February 2019|title=Friction stir welding of high density polyethylene—Carbon black composite|journal=Journal of Materials Processing Technology|volume=264|pages=402–413|doi=10.1016/j.jmatprotec.2018.09.033|s2cid=139970404 }}</ref> In addition, joining of dissimilar metals, such as [[Aluminium joining|aluminium]] to magnesium alloys, has been recently achieved by FSW.<ref>{{Cite journal|last1=Hou|first1=Z.|last2=Sheikh-Ahmad|first2=J.|last3=Jarrar|first3=F.|last4=Ozturk|first4=F.|date=2018-05-01|title=Residual Stresses in Dissimilar Friction Stir Welding of AA2024 and AZ31: Experimental and Numerical Study|journal=Journal of Manufacturing Science and Engineering|volume=140|issue=5|doi=10.1115/1.4039074|issn=1087-1357}}</ref> Application of FSW can be found in modern shipbuilding, trains, and aerospace applications.<ref>{{Cite web|url=http://www.fswelding.com/application-of-friction-stir-welding-in-aircraft-structures/practical-use-of-fsw|title=Practical use of FSW - Friction Stir Welding|website=www.fswelding.com|access-date=2017-04-22}}</ref><ref name="LCS" /><ref name="C-17 & 747" /><ref name=":1" /><ref name="DSB" /><ref name=":2" />

The concept was patented in the Soviet Union by Yu. Klimenko in 1967,<ref>{{cite web | url=https://patents.google.com/patent/SU195846A1/en | title=METHOD OF WELDING METAL BY Friction }}</ref> but it wasn't developed into a commercial technology at that time. It was experimentally proven and commercialized at [[The Welding Institute]] (TWI) in the [[United Kingdom|UK]] in 1991. TWI held patents on the process, the first being the most descriptive.<ref>Thomas, WM; Nicholas, ED; Needham, JC; Murch, MG;Temple-Smith, P;Dawes, CJ.''Friction-stir butt welding'', GB Patent No. 9125978.8, International patent application No. PCT/GB92/02203, (1991)</ref>

==Principle of operation==
[[File:Anand-FSW-Figure1-A.jpg|thumb|Two discrete metal workpieces butted together, along with the tool (with a probe)]]
[[File:Anand-FSW-Figure1-B.jpg|thumb|The progress of the tool through the joint, also showing the weld zone and the region affected by the tool shoulder]]
[[File:Friction stir weld on helium-filled hard drive close-up 2.jpg|thumb|Aluminium friction stir weld with imprint of the tool where it entered/left the joint]]

Friction stir welding is performed with a rotating cylindrical tool which has a profiled pin (also known as a probe) having a diameter smaller than the diameter of its shoulder. During welding the tool is fed into a [[butt joint]] between two clamped workpieces, until the probe pierces into the workpiece and its shoulder touches the surface of the workpieces.<ref name="Book">{{cite book |url=https://www.taylorfrancis.com/books/mono/10.1201/9781315116815/friction-stir-welding-noor-zaman-khan-arshad-noor-siddiquee-zahid-khan |title=Friction Stir Welding |author1= Noor Zaman Khan|author2= Arshad Noor Siddiquee |author3= Zahid A Khan|date=2017-11-01 |publisher=Taylor & Francis |doi=10.1201/9781315116815 |isbn=978-1-315-11681-5 |access-date=2021-05-29}}</ref> The probe is slightly shorter than the weld depth required, with the tool shoulder riding atop the work surface.<ref name="TWIintro">{{cite web |url=http://www.twi.co.uk/content/fswintro.html |title=Friction Stir Welding at TWI |last=Kallee |first=S. W. |date=2006-09-06 |publisher=The Welding Institute (TWI) |access-date=2009-04-14 |archive-date=2011-10-11 |archive-url=https://web.archive.org/web/20111011203856/http://www.twi.co.uk/content/fswintro.html }}</ref> After a short dwell time, the tool is moved forward along the joint line at the pre-set welding speed.<ref name="Friction Stir Welding process - Stirweld">{{Cite news |url=https://stirweld.com/en/friction-stir-welding-process/ |title=Friction Stir Welding Process |work=StirWeld |access-date=2018-01-22 |language=fr-FR}}</ref>

[[Friction]]al heat is generated between the wear-resistant tool and the work pieces. This heat, along with that generated by the mechanical mixing process and the [[adiabatic]] heat within the material, cause the stirred materials to soften without [[melting point|melting]]. As the tool is moved forward, a special profile on the probe forces plasticised material from the leading face to the rear, where the high forces assist in a forged consolidation of the weld.

This process of the tool traversing along the weld line in a plasticised tubular shaft of metal results in severe solid-state [[Deformation (engineering)|deformation]] involving dynamic recrystallization of the base material.<ref name="Ding2008">{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080009619_2008009118.pdf |title=A Decade of Friction Stir Welding R&D At NASA's Marshall Space Flight Center and a Glance into the Future |last=Ding |first=Jeff |author2=Bob Carter |author3=Kirby Lawless |author4=Dr. Arthur Nunes |author5=Carolyn Russell |author6=Michael Suites |author7=Dr. Judy Schneider |date=2008-02-14 |publisher=NASA |access-date=2009-04-14}}</ref>

==Micro-structural features==
The solid-state nature of the FSW process, combined with its unusual tool shape and asymmetric speed profile, results in a highly characteristic [[micro-structure]]. The micro-structure can be broken up into the following zones:

* The ''stir zone'' (also known as the dynamically recrystallised zone) is a region of heavily deformed material that roughly corresponds to the location of the pin during welding. The [[Crystallite|grains]] within the stir zone are roughly equiaxed and often an order of magnitude smaller than the grains in the parent material.<ref>{{cite journal |author1=Murr, L. E. |author2=Liu, G. |author3=McClure, J. C. | title=Dynamic re-crystallisation in the friction-stir welding of aluminium alloy 1100 | journal=Journal of Materials Science Letters | year= 1997| volume=16 | issue=22 | pages= 1801–1803 | doi=10.1023/A:1018556332357|s2cid=135215434 }}</ref> A unique feature of the stir zone is the common occurrence of several concentric rings, which has been referred to as an "onion-ring" structure.<ref>{{cite journal | last1 = Krishnan | first1 = K. N. | year = 2002 | title = On the Formation of Onion Rings in Friction Stir Welds | journal = Materials Science and Engineering A | volume = 327 | issue = 2| pages = 246–251 | doi = 10.1016/S0921-5093(01)01474-5 }}</ref> The precise origin of these rings has not been firmly established, although variations in particle number density, grain size and texture have all been suggested.
* The ''flow arm zone'' is on the upper surface of the weld and consists of material that is dragged by the shoulder from the retreating side of the weld, around the rear of the tool, and deposited on the advancing side.{{Citation needed|date=December 2008}}
* The ''thermo-mechanically affected zone'' (TMAZ) occurs on either side of the stir zone. In this region the strain and temperature are lower and the effect of welding on the micro-structure is correspondingly smaller. Unlike the stir zone, the micro-structure is recognizably that of the parent material, albeit significantly deformed and rotated. Although the term TMAZ technically refers to the entire deformed region, it is often used to describe any region not already covered by the terms stir zone and flow arm.{{Citation needed|date=December 2008}}
* The ''[[heat-affected zone]]'' (HAZ) is common to all welding processes. As indicated by the name, this region is subjected to a thermal cycle but is not deformed during welding. The temperatures are lower than those in the TMAZ but may still have a significant effect if the micro-structure is thermally unstable. In fact, in [[Precipitation hardening|age-hardened]] aluminum alloys this region commonly exhibits the poorest mechanical properties.<ref>{{cite journal | last1 = Mahoney | first1 = M. W. | last2 = Rhodes | first2 = C. G. | last3 = Flintoff | first3 = J. G. | last4 = Bingel | first4 = W. H. | last5 = Spurling | first5 = R. A. | year = 1998 | title = Properties of Friction-stir-welded 7075 T651 Aluminum | journal = Metallurgical and Materials Transactions A | volume = 29 | issue = 7| pages = 1955–1964 | doi = 10.1007/s11661-998-0021-5 | bibcode = 1998MMTA...29.1955M | s2cid = 137071435 }}</ref>

==Advantages and limitations==
The solid-state nature of FSW leads to several advantages over fusion welding methods, as problems associated with cooling from the liquid phase are avoided. Issues such as [[porosity]], [[solute]] redistribution, solidification cracking and liquation cracking do not arise during FSW. In general, FSW has been found to produce a low concentration of defects and is very tolerant to variations in parameters and materials.

Nevertheless, FSW is associated with a number of unique defects if it isn't done properly. Insufficient weld temperatures, due to low rotational speeds or high traverse speeds, for example, mean that the weld material is unable to accommodate the extensive deformation during welding. This may result in long, tunnel-like defects running along the weld, which may occur on the surface or subsurface. Low temperatures may also limit the forging action of the tool and so reduce the continuity of the bond between the material from each side of the weld. The light contact between the material has given rise to the name "kissing bond". This defect is particularly worrying, since it is very difficult to detect using nondestructive methods such as [[X-ray]] or [[ultrasonic testing]]. If the pin is not long enough or the tool rises out of the plate, then the interface at the bottom of the weld may not be disrupted and forged by the tool, resulting in a lack-of-penetration defect. This is essentially a notch in the material, which can be a potential source of [[fatigue crack]]s.

== Advantages ==
A number of potential advantages of FSW over conventional fusion-welding processes have been identified:<ref>{{cite conference | author=Nicholas, E. D. | title=Developments in the friction-stir welding of metals | book-title=ICAA-6: 6th International Conference on Aluminium Alloys | year=1998| location=Toyohashi, Japan}}</ref><ref name="Technologie – StirWeld">{{Cite news |url=http://stirweld.com/index.php/fsw/ |title=Technologie – StirWeld |work=StirWeld |access-date=2018-01-22 |language=fr-FR}}</ref>
* Good mechanical properties in the as-welded condition.
* Improved safety due to the absence of toxic fumes or the spatter of molten material.
* No consumables&nbsp;— A threaded pin made of conventional [[tool steel]], e.g., hardened H13, can weld over {{convert|1|km|mi|1|abbr=on}} of aluminium, and no filler or gas shield is required for aluminium.
* Easily automated on simple milling machines&nbsp;— 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 thickness under/over-matching, thus reducing the need for expensive machining after welding.
* Can use thinner materials with same joint strength.
* Low environmental impact.
* General performance and cost benefits from switching from fusion to friction.

== Disadvantages ==
However, some disadvantages of the process have been identified:
* 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.

==Important welding parameters==

===Tool design===
The design of the tool<ref name="Mishra">By Rajiv S. Mishra, Murray W. Mahoney: [https://books.google.com/books?id=JW2l2L-UYS4C&dq=friction+stir+processing+propeller&pg=PA7 Friction stir welding and processing], ASM International {{ISBN|978-0-87170-848-9}}.</ref> is a critical factor, as a good tool can improve both the quality of the weld and the maximal possible welding speed.

It is desirable that the tool material be sufficiently strong, tough, and hard wearing at the welding temperature. Further, it should have a good oxidation resistance and a low [[thermal conductivity]] to minimise heat loss and thermal damage to the machinery further up the drive train. Hot-worked [[tool steel]] such as AISI H13 has proven perfectly acceptable for welding aluminium alloys within thickness ranges of 0.5–50&nbsp;mm <ref>{{cite journal |author1=Prado, R. A. |author2=Murr, L. E. |author3=Shindo, D. J. |author4=Soto, H. F. |title=Tool wear in the friction stir welding of aluminium alloy 6061+20% Al2O3: A preliminary study |journal=Scripta Materialia |year= 2001 |volume=45 |pages=75–80 |doi=10.1016/S1359-6462(01)00994-0}}</ref> but more advanced tool materials are necessary for more demanding applications such as highly abrasive [[metal matrix composites]]<ref>{{cite conference |author1=Nelson, T. |author2=Zhang, H. |author3=Haynes, T. | title=friction stir welding of Al MMC 6061-B4C | book-title=2nd International Symposium on FSW (CD ROM) | year=2000| location=Gothenburg, Sweden}}</ref> or higher-melting-point materials such as steel or titanium.

Improvements in tool design have been shown to cause substantial improvements in productivity and quality. TWI has developed tools specifically designed to increase the penetration depth and thus increasing the plate thicknesses that can be successfully welded. An example is the "whorl" design that uses a tapered pin with re-entrant features or a variable-pitch thread to improve the downwards flow of material. Additional designs include the Triflute and Trivex series. The Triflute design has a complex system of three tapering, threaded re-entrant flutes that appear to increase material movement around the tool. The Trivex tools use a simpler, non-cylindrical, pin and have been found to reduce the forces acting on the tool during welding.

The majority of tools have a concave shoulder profile, which acts as an escape volume for the material displaced by the pin, prevents material from extruding out of the sides of the shoulder and maintains downwards pressure and hence good forging of the material behind the tool. The Triflute tool uses an alternative system with a series of concentric grooves machined into the surface, which are intended to produce additional movement of material in the upper layers of the weld.

Widespread commercial applications of friction stir welding process for steels and other hard alloys such as [[titanium alloy]]s will require the development of cost-effective and durable tools.<ref>{{cite journal |author1=Bhadeshia H. K. D. H. |author2=DebRoy T. | title=Critical assessment: friction stir welding of steels| journal=Science and Technology of Welding and Joining| year= 2009| volume=14| issue=3| pages=193–196| doi=10.1179/136217109X421300|s2cid=137947326 }}</ref> Material selection, design and cost are important considerations in the search for commercially useful tools for the welding of hard materials. Work is continuing to better understand the effects of tool material's composition, structure, properties and geometry on their performance, durability and cost.<ref>{{cite journal |author1=Rai R. |author2=De A. |author3=Bhadeshia H. K. D. H. |author4=DebRoy T. |title=Review: friction stir welding tools |journal=Science and Technology of Welding and Joining |year= 2011 |volume=16 |pages=325–342 |doi=10.1179/1362171811Y.0000000023 |issue=4|s2cid=16838735 }}</ref>

=== Tool rotation and traverse speeds ===
There are two tool speeds to be considered in friction-stir welding;<ref>{{cite journal | author1= V Buchibabu. |author2= G M Reddy. | author3= D V Kulkarni. | author4= A De. | doi=10.1007/s11665-016-1924-8 | volume=25 | issue=3 |title=Friction Stir Welding of a Thick Al-Zn-Mg Alloy Plate | journal=Journal of Materials Engineering and Performance | pages=1163–1171|year= 2016 |bibcode= 2016JMEP...25.1163B |s2cid= 138343148 }}</ref> how fast the tool rotates and how quickly it traverses along the interface. These two parameters have considerable importance and must be chosen with care to ensure a successful and efficient welding cycle. The relationship between the rotation speed, the welding speed and the heat input during welding is complex, but in general, it can be said that increasing the rotation speed or decreasing the traverse speed will result in a hotter weld. In order to produce a successful weld, it is necessary that the material surrounding the tool is hot enough to enable the extensive plastic flow required and minimize the forces acting on the tool. If the material is too cold, then voids or other flaws may be present in the stir zone and in extreme cases the tool may break.

Excessively high heat input, on the other hand, may be detrimental to the final properties of the weld. Theoretically, this could even result in defects due to the liquation of low-melting-point phases (similar to liquation cracking in fusion welds). These competing demands lead onto the concept of a "processing window": the range of processing parameters viz. tool rotation and traverse speed, that will produce a good quality weld.<ref>{{cite journal | doi=10.1016/j.scriptamat.2007.10.031 | volume=58 | issue=5 | title=A flow-partitioned deformation zone model for defect formation during friction stir welding | journal=Scripta Materialia | pages=372–376| date=March 2008 | last1=Arbegast | first1=William J. | url=https://zenodo.org/record/1259355 }}</ref> Within this window the resulting weld will have a sufficiently high heat input to ensure adequate material plasticity but not so high that the weld properties are excessively deteriorated.

===Tool tilt and plunge depth===
[[File:Friction_Stir_Weld_Schematic_Canted.png|thumb|A drawing showing the plunge depth and tilt of the tool. The tool is moving to the left.]]
The plunge depth is defined as the depth of the lowest point of the shoulder below the surface of the welded plate and has been found to be a critical parameter for ensuring weld quality.<ref>{{cite conference | author=Leonard, A. J. | title=Microstructure and aging behaviour of FSW in Al alloys 2014A-T651 and 7075-T651 | book-title=2nd International Symposium on FSW (CD ROM) | year=2000 | location=Gothenburg, Sweden}}</ref> Plunging the shoulder below the plate surface increases the pressure below the tool and helps ensure adequate forging of the material at the rear of the tool. Tilting the tool by 2–4 degrees, such that the rear of the tool is lower than the front, has been found to assist this forging process. The plunge depth needs to be correctly set, both to ensure the necessary downward pressure is achieved and to ensure that the tool fully penetrates the weld. Given the high loads required, the welding machine may deflect and so reduce the plunge depth compared to the nominal setting, which may result in flaws in the weld. On the other hand, an excessive plunge depth may result in the pin rubbing on the backing plate surface or a significant undermatch of the weld thickness compared to the base material. Variable-load welders have been developed to automatically compensate for changes in the tool displacement, while TWI have demonstrated a roller system that maintains the tool position above the weld plate.

==Welding forces==
During welding, a number of forces will act on the tool:<ref>{{cite journal | author1= V Buchibabu. |author2= G M Reddy. | author3= A De. | doi= 10.1016/j.jmatprotec.2016.11.008 | volume=241 | issue=1 |title= Probing torque, traverse force and tool durability in friction stir welding of aluminum alloys | journal= Journal of Materials Processing Technology | pages=86–92|date= March 2017 }}</ref>
* A downwards force is necessary to maintain the position of the tool at or below the material surface. Some friction-stir welding machines operate under load control, but in many cases the vertical position of the tool is preset, and so the load will vary during welding.
* The traverse force acts parallel to the tool motion and is positive in the traverse direction. Since this force arises as a result of the resistance of the material to the motion of the tool, it might be expected that this force will decrease as the temperature of the material around the tool is increased.
* The lateral force may act perpendicular to the tool traverse direction and is defined here as positive towards the advancing side of the weld.
* Torque is required to rotate the tool, the amount of which will depend on the down force and [[friction coefficient]] (sliding friction) and/or the flow strength of the material in the surrounding region ([[stiction]]).

In order to prevent tool fracture and to minimize excessive wear and tear on the tool and associated machinery, the welding cycle is modified so that the forces acting on the tool are as low as possible, and abrupt changes are avoided. In order to find the best combination of welding parameters, it is likely that a compromise must be reached, since the conditions that favour low forces (e.g. high heat input, low travel speeds) may be undesirable from the point of view of productivity and weld properties.

==Flow of material==
Early work on the mode of material flow around the tool used inserts of a different alloy, which had a different contrast to the normal material when viewed through a microscope, in an effort to determine where material was moved as the tool passed.<ref>{{cite journal |author=Reynolds, A. P. |title=Visualisation of material flow in autogenous friction stir welds |journal=Science and Technology of Welding and Joining |year= 2000 |volume=5 |issue=2 |pages=120–124 |doi=10.1179/136217100101538119|s2cid=137563036 }}</ref><ref>{{cite journal |author1=Seidel, T. U. |author2=Reynolds, A. P. |title=Visualization of the Material Flow in AA2195 Friction-Stir Welds Using a Marker Insert Technique |journal=  Metallurgical and Materials Transactions A|year= 2001 |volume= 32|issue=11 |pages=2879–2884|doi=10.1007/s11661-001-1038-1 |s2cid=135836036 }}</ref>
The data was interpreted as representing a form of in-situ [[extrusion]], where the tool, backing plate and cold base material form the "extrusion chamber", through which the hot, plasticised material is forced. In this model the rotation of the tool draws little or no material around the front of the probe; instead, the material parts in front of the pin and passes down either side. After the material has passed the probe, the side pressure exerted by the "die" forces the material back together, and consolidation of the joint occurs, as the rear of the tool shoulder passes overhead and the large down force forges the material.

More recently, an alternative theory has been advanced that advocates considerable material movement in certain locations.<ref>{{cite journal |author1=Guerra, M. |author2=Schmidt, C. |author3=McClure, J. C. |author4=Murr, L. E. |author5=Nunes, A. C. |title=Flow patterns during friction stir welding |journal=Materials Characterization |year= 2003 |volume=49 |issue=2 |pages=95–101 |doi=10.1016/S1044-5803(02)00362-5|hdl=2060/20020092188 |s2cid=135584450 |hdl-access=free }}</ref> This theory holds that some material does rotate around the probe, for at least one rotation, and it is this material movement that produces the "onion-ring" structure in the stir zone. The researchers used a combination of thin copper strip inserts and a "frozen pin" technique, where the tool is rapidly stopped in place. They suggested that material motion occurs by two processes:
# Material on the advancing side of a weld enters into a zone that rotates and advances with the profiled probe. This material was very highly deformed and sloughs off behind the pin to form arc-shaped features when viewed from above (i.e. down the tool axis). It was noted that the copper entered the rotational zone around the pin, where it was broken up into fragments. These fragments were only found in the arc-shaped features of material behind the tool.
# The lighter material came from the retreating side in front of the pin and was dragged around to the rear of the tool and filled in the gaps between the arcs of advancing side material. This material did not rotate around the pin, and the lower level of deformation resulted in a larger grain size.

The primary advantage of this explanation is that it provides a plausible explanation for the production of the onion-ring structure.

The marker technique for friction stir welding provides data on the initial and final positions of the marker in the welded material. The flow of material is then reconstructed from these positions. Detailed material flow field during friction stir welding can also be calculated from theoretical considerations based on fundamental scientific principles. Material flow calculations are routinely used in numerous engineering applications. Calculation of material flow fields in friction stir welding can be undertaken both using comprehensive numerical simulations<ref>{{cite journal |author1=Nandan R. |author2=DebRoy T. |author3=Bhadeshia H. K. D. H. |title=Recent advances in friction-stir welding – Process, weldment structure and properties |journal=Progress in Materials Science |year= 2008 |volume=53 |issue=6 |pages=980–1023 |doi=10.1016/j.pmatsci.2008.05.001|citeseerx=10.1.1.160.7596 }}</ref><ref>{{cite journal |author=Nandan R. |author2=Roy G. G. |author3=Lienert T. J. |author4=DebRoy T. |title=Three-dimensional heat and material flow during friction stir welding of mild steel |journal=Acta Materialia |year= 2007 |volume=55 |issue=3 |pages=883–895 |doi=10.1016/j.actamat.2006.09.009|bibcode=2007AcMat..55..883N }}</ref><ref name=seidle_stwj>{{cite journal |author=Seidel T. U. |author2=Reynolds A. P. |title=Two-dimensional friction stir welding process model based on fluid mechanics |journal=Science and Technology of Welding and Joining |year= 2003 |volume=8 |issue=3 |pages=175–183 |doi=10.1179/136217103225010952}}</ref> or simple but insightful analytical equations.<ref>{{cite journal |author1=Arora A. |author2=DebRoy T. |author3=Bhadeshia H. K. D. H. |title=Back-of-the-envelope calculations in friction stir welding – Velocities, peak temperature, torque, and hardness |journal=Acta Materialia| year= 2011 |volume=59 |issue=5 |pages=2020–2028 |doi=10.1016/j.actamat.2010.12.001|bibcode=2011AcMat..59.2020A }}</ref> The comprehensive models for the calculation of material flow fields also provide important information such as geometry of the stir zone and the torque on the tool.<ref name=arora_torque>{{cite journal |author=Arora A. |author2=Nandan R. |author3=Reynolds A. P. |author4=DebRoy T. |title=Torque, power requirement and stir zone geometry in friction stir welding through modeling and experiments |journal=Scripta Materialia |year=2009 |volume=60 |issue=1 |pages=13–16 |doi=10.1016/j.scriptamat.2008.08.015 }}</ref><ref name=mehta_torque>{{cite journal |author=Mehta M. |author2=Arora A. |author3=De A. |author4=DebRoy T. |title=Tool Geometry for Friction Stir Welding—Optimum Shoulder Diameter |journal=Metallurgical and Materials Transactions A |year= 2011 |doi=10.1007/s11661-011-0672-5 |volume= 42 |issue= 9 |pages= 2716–2722|bibcode=2011MMTA...42.2716M |s2cid=39468694 }}</ref> The numerical simulations have shown the ability to correctly predict the results from marker experiments<ref name=seidle_stwj /> and the stir zone geometry observed in friction stir welding experiments.<ref name=arora_torque /><ref>{{cite journal |author=Nandan R. |author2=Roy G. G. |author3=DebRoy T. |title=Numerical simulation of three-dimensional heat transfer and plastic flow during friction stir welding |journal=Metallurgical and Materials Transactions A |year=2011 |volume=37 |issue=4 |pages=1247–1259 |doi=10.1007/s11661-006-1076-9|s2cid=85507345 }}</ref>

==Generation and flow of heat==
For any welding process, it is, in general, desirable to increase the travel speed and minimise the heat input, as this will increase productivity and possibly reduce the impact of welding on the mechanical properties of the weld. At the same time, it is necessary to ensure that the temperature around the tool is sufficiently high to permit adequate material flow and prevent flaws or tool damage.

When the traverse speed is increased, for a given heat input, there is less time for heat to conduct ahead of the tool, and the thermal gradients are larger. At some point the speed will be so high that the material ahead of the tool will be too cold, and the flow stress too high, to permit adequate material movement, resulting in flaws or tool fracture. If the "hot zone" is too large, then there is scope to increase the traverse speed and hence productivity.

The welding cycle can be split into several stages, during which the heat flow and thermal profile will be different:<ref name="frigaard2001">{{cite journal |author1=Frigaard, O. |author2=Grong, O. |author3=Midling, O. T. |title=A process model for friction-stir welding of age hardening aluminium alloys |journal=Metallurgical and Materials Transactions A |year= 2001 |volume=32 |issue=5 |pages=1189–1200 |doi=10.1007/s11661-001-0128-4|bibcode=2001MMTA...32.1189F |s2cid=137271711 }}</ref> 
* ''Dwell''. The material is preheated by a stationary, rotating tool to achieve a sufficient temperature ahead of the tool to allow the traverse. This period may also include the plunge of the tool into the workpiece.
* ''Transient heating''. When the tool begins to move, there will be a transient period where the heat production and temperature around the tool will alter in a complex manner until an essentially steady state is reached.
* ''Pseudo steady state''. Although fluctuations in heat generation will occur, the thermal field around the tool remains effectively constant, at least on the macroscopic scale.
* ''Post steady state''. Near the end of the weld, heat may "reflect" from the end of the plate, leading to additional heating around the tool.

Heat generation during friction-stir welding arises from two main sources: friction at the surface of the tool and the deformation of the material around the tool.<ref>{{cite conference |author=Chao, Y. J. |author2=Qi, X. |year=1999 |title=Heat transfer and Thermo-Mechanical analysis of FSW joining of 6061-T6 plates |book-title=1st International Symposium on FSW (CD ROM) |publisher=TWI| location=Thousand Oaks, USA}}</ref> The heat generation is often assumed to occur predominantly under the shoulder, due to its greater surface area, and to be equal to the power required to overcome the contact forces between the tool and the workpiece. The contact condition under the shoulder can be described by sliding friction, using a friction coefficient μ and interfacial pressure ''P'', or sticking friction, based on the interfacial shear strength at an appropriate temperature and strain rate. Mathematical approximations for the total heat generated by the tool shoulder ''Q''<sub>total</sub> have been developed using both sliding and sticking friction models:<ref name="frigaard2001"/>

:<math>Q_\text{total} = \frac{2}{3} \pi P \mu \omega \left(R_\text{shoulder}^3 - R_\text{pin}^3\right)</math>   (sliding)

:<math>Q_\text{total} = \frac{2}{3} \pi \tau \omega \left(R_\text{shoulder}^3 - R_\text{pin}^3\right)</math>   (sticking)

where ω is the angular velocity of the tool, ''R''<sub>shoulder</sub> is the radius of the tool shoulder, and ''R''<sub>pin</sub> is that of the pin. Several other equations have been proposed to account for factors such as the pin, but the general approach remains the same.

A major difficulty in applying these equations is determining suitable values for the friction coefficient or the interfacial shear stress. The conditions under the tool are both extreme and very difficult to measure. To date, these parameters have been used as "fitting parameters", where the model works back from measured thermal data to obtain a reasonable simulated thermal field. While this approach is useful for creating process models to predict, for example, residual stresses, it is less useful for providing insights into the process itself.

==Applications==
The FSW process has initially been patented by TWI in most industrialised countries and licensed for over 183 users. Friction stir welding and its variants{{snd}} friction stir spot welding and [[friction stir processing]]{{snd}} are used for the following industrial applications:<ref name="Lohwasser">[http://www.woodheadpublishing.com/en/book.aspx?bookID=1503 D. Lohwasser and Z. Chen: "Friction stir welding&nbsp;— From basics to applications" Woodhead Publishing 2010] {{Webarchive|url=https://web.archive.org/web/20110718082537/http://www.woodheadpublishing.com/en/book.aspx?bookID=1503 |date=2011-07-18 }}, Chapter 5, Pages 118–163, {{ISBN|978-1-84569-450-0}}.</ref> shipbuilding and offshore,<ref name="Ships">[http://www.twi.co.uk/content/spswkjune07.html Fred Delany, Stephan W Kallee, Mike J Russell: "Friction stir welding of aluminium ships"] {{Webarchive|url=https://web.archive.org/web/20101111014106/http://www.twi.co.uk/content/spswkjune07.html |date=2010-11-11 }}, Paper presented at 2007 International Forum on Welding Technologies in the Shipping Industry (IFWT). Held in conjunction with the Beijing Essen Welding and Cutting Fair in Shanghai, 16–19 June 2007.</ref>
aerospace,<ref>[http://www.twi.co.uk/jsp/flashlist.jsp?flash=Friction%20stir%20welding%20at%20British%20Aerospace.flv Video: "FSW at British Aerospace"] {{Webarchive|url=https://web.archive.org/web/20110927181639/http://www.twi.co.uk/jsp/flashlist.jsp?flash=Friction%20stir%20welding%20at%20British%20Aerospace.flv |date=2011-09-27 }}. Twi.co.uk. Retrieved on 2012-01-03.</ref><ref>[http://www.twi.co.uk/jsp/flashlist.jsp?flash=Friction%20stir%20welding%20of%20aircraft%20fuselages.flv Video: FSW of aerospace fuselages] {{Webarchive|url=https://web.archive.org/web/20110927181645/http://www.twi.co.uk/jsp/flashlist.jsp?flash=Friction%20stir%20welding%20of%20aircraft%20fuselages.flv |date=2011-09-27 }}. Twi.co.uk. Retrieved on 2012-01-03.</ref> automotive,<ref name="Auto">S. W. Kallee, J. M. Kell, W. M. Thomas und C. S. Wiesner: [http://www.twi.co.uk/content/spswksept2005.html "Development and implementation of innovative joining processes in the automotive industry"] {{Webarchive|url=https://web.archive.org/web/20110927181508/http://www.twi.co.uk/content/spswksept2005.html |date=2011-09-27 }}, Paper presented at DVS Annual Welding Conference "Große Schweißtechnische Tagung", Essen, Germany, 12–14 September 2005.</ref> rolling stock for railways,<ref name="Trains">S. W. Kallee and J. Davenport: [http://www.twi.co.uk/technical-knowledge/published-papers/trends-in-the-design-and-fabrication-of-rolling-stock-january-2007/ "Trends in the design and fabrication of rolling stock"], Paper published in European Railway Review, Volume 13, Issue 1, 2007.</ref><ref>{{Cite news|url=https://stirweld.com/en/home-2/|title=Applications - StirWeld|work=StirWeld|access-date=2018-01-22|language=fr-FR}}</ref> general fabrication,<ref name="EuroStir">[http://www.manufacturingtalk.com/news/mij/mij107.html Mike Page: "Friction stir welding broadens applications base"] {{Webarchive|url=https://web.archive.org/web/20081122042522/http://www.manufacturingtalk.com/news/mij/mij107.html |date=2008-11-22 }}, Report of a EuroStir meeting, 3 Sept 2003.</ref> robotics, and computers.

===Shipbuilding and offshore===
[[File:Super Liner Ogasawara.jpg|thumb|Friction stir welding was used to prefabricate the aluminium panels of the ''Super Liner Ogasawara'' at Mitsui Engineering and Shipbuilding]]

Two Scandinavian aluminium extrusion companies were the first to apply FSW commercially to the manufacture of fish freezer panels at [[Sapa Group|Sapa]] in 1996, as well as deck panels and helicopter landing platforms at Marine Aluminium Aanensen. Marine Aluminium Aanensen subsequently merged with Hydro Aluminium Maritime to become [[Norsk Hydro|Hydro Marine Aluminium]]. Some of these freezer panels are now produced by Riftec and Bayards. In 1997 two-dimensional friction stir welds in the hydrodynamically flared bow section of the hull of the ocean viewer vessel ''The Boss'' were produced at Research Foundation Institute with the first portable FSW machine. The ''Super Liner Ogasawara'' at [[Mitsui|Mitsui Engineering and Shipbuilding]] is the largest friction stir welded ship so far. {{Citation needed|date=September 2020}} The ''[[Sea Fighter]]'' of Nichols Bros and the [[Freedom class littoral combat ship|''Freedom''-class]] [[Littoral Combat Ship]]s contain prefabricated panels by the FSW fabricators Advanced Technology and Friction Stir Link, Inc. respectively.<ref name="LCS">[[William Arbegast|Bill Arbegast]], Tony Reynolds, Rajiv S. Mishra, Tracy Nelson, Dwight Burford: [http://faculty.washington.edu/scottcs/NSF/2009/CFSP.pdf Littoral Combat System with Improved Welding Technologies] {{Webarchive|url=https://web.archive.org/web/20121008053257/http://faculty.washington.edu/scottcs/NSF/2009/CFSP.pdf |date=2012-10-08 }}, Center for Friction STIR Processing (CFSP).</ref> The [[Houbei class missile boat|''Houbei''-class missile boat]] has friction stir welded rocket launch containers of China Friction Stir Centre. [[HMNZS Rotoiti (P3569)|HMNZS ''Rotoiti'']] in New Zealand has FSW panels made by Donovans in a converted milling machine.<ref name="Blizz">[http://www.camtec.org.nz/downloads/IPENZ-FSWArticle.pdf Richard Worrall: "Welded Bliss"] {{Webarchive|url=https://web.archive.org/web/20100602181016/http://www.camtec.org.nz/downloads/IPENZ-FSWArticle.pdf |date=2010-06-02 }}, e.nz magazine March/April 2008.</ref><ref name="NZ">[http://www.twi.co.uk/content/spswkaug2006.html Stephan Kallee: "NZ Fabricators begin to use Friction Stir Welding to produce aluminium components and panels"] {{Webarchive|url=https://web.archive.org/web/20100316134257/http://www.twi.co.uk/content/spswkaug2006.html |date=2010-03-16 }}, New Zealand Engineering News, August 2006.</ref> Various companies apply FSW to [[armor plating]] for [[amphibious assault ship]]s.<ref name="AAAV1">[http://www.aws.org/w/a/wj/2003/03/feature3/index.html Friction Stir Welding Demonstrated for Combat Vehicle Construction ... for 2519 aluminium armor for the U.S. Marine Corps' Advanced Amphibious Assault Vehicle], Welding Journal 03 2003.</ref><ref name="Stotler">G. Campbell, T. Stotler: [http://www.aws.org/wj/dec99/campbell.html Friction Stir Welding of Armor Grade Aluminum Plate] {{Webarchive|url=https://web.archive.org/web/20110716220124/http://www.aws.org/wj/dec99/campbell.html |date=2011-07-16 }}, Welding Journal, Dec 1999.</ref>

===Aerospace===
[[File:SpaceX factory Falcon 9 booster tank.jpg|thumb|Longitudinal and circumferential friction stir welds are used for the [[Falcon 9]] rocket booster tank at the SpaceX factory]]

[[United Launch Alliance]] applies FSW to the [[Delta II]], [[Delta IV]], [[Atlas V]], and the new [[Vulcan (rocket)|Vulcan]] expendable launch vehicles along with their [[Cryogenic rocket engine|Cryogenic Upper Stages]], and the first of these with a friction stir welded interstage module was launched in 1999. The process was also used for the [[Space Shuttle external tank]], for [[Ares I]] until the project was canceled in 2012, [[Space Launch System#Core stage|the SLS Core]] which replaced the Ares, and for the [[Orion (Constellation program)|Orion Crew Vehicle]] test article and the current model of the [[Orion (spacecraft)|Orion]] at [[NASA]], as well as [[Falcon 1]] and [[Falcon 9]] rockets at [[SpaceX]].<ref>{{Cite web |title=friction stir welding – Rocketology: NASA's Space Launch System |url=https://blogs.nasa.gov/Rocketology/tag/friction-stir-welding/#:~:text=SLS%20uses%20%E2%80%9Cfriction%20stir%20welding,,%20domes,%20and%20barrel%20segments. |access-date=2022-08-27 |website=blogs.nasa.gov |language=en-US}}</ref> The toe nails for ramp of [[Boeing C-17 Globemaster III]] cargo aircraft by Advanced Joining Technologies<ref name="C-17 & 747">Walter Polt [http://www.boeing.com/news/frontiers/archive/2004/september/i_tt.html "A little friction at Boeing"], Boeing Frontiers Online, September 2004, Vol. 3, Issue 5.</ref> and the cargo barrier beams for the [[Boeing 747 Large Cargo Freighter]]<ref name="C-17 & 747" /> were the first commercially produced aircraft parts. FAA-approved wings and fuselage panels of the [[Eclipse 500]] aircraft were made at [[Eclipse Aviation]], and this company delivered 259 friction stir welded business jets, before they were forced into Chapter 7 liquidation. Floor panels for [[Airbus A400M]] military aircraft are now made by [[Pfalz Flugzeugwerke]] and Embraer used FSW for the Legacy 450 and 500 Jets<ref name=":1">[http://www.bartintl.com/content/embraer-performs-first-metal-cut-legacy-500-jet Embraer Performs First Metal Cut for Legacy 500 Jet] {{Webarchive|url=https://web.archive.org/web/20110707213302/http://www.bartintl.com/content/embraer-performs-first-metal-cut-legacy-500-jet |date=2011-07-07 }}, BART International.</ref> Friction stir welding also is employed for fuselage panels on the [[Airbus A380]].<ref>{{cite web |title=How Airbus uses friction stir welding |url=http://www.reliableplant.com/View/10740/how-airbus-uses-friction-stir-welding |publisher=Reliable Plant |access-date=7 August 2013}}</ref> BRÖTJE-Automation uses friction stir welding for gantry production machines developed for the aerospace sector, as well as other industrial applications.<ref>{{cite web |title=JEC Composites Show – Day 3: EADS licenses its patented DeltaN friction-stir welding technology to BRÖTJE-Automation |url=http://www.technology-licensing.com/etl/int/en/News/Latest-News/JEC-Composites-show-Day-3-EADS-licenses-its-patented-DeltaN-friction-stir-welding-technology-to-BR-TJE-Automation.html |publisher=EADS |access-date=30 July 2013}}</ref>

===Automotive===
[[File:Ford GT interior.jpg|thumb|The centre tunnel of the [[Ford GT]] is made from two aluminium extrusions friction stir welded to a bent aluminium sheet and houses the fuel tank]]

Aluminium engine cradles and suspension struts for stretched [[Lincoln Town Car]]s were the first automotive parts that were friction stir welded at [[Tower Automotive]], who use 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. for the flatbed trailer "Revolution" of Fontaine Trailers.<ref>[http://www.fontainetrailer.com/pdfs/Revolution%20Aluminum.pdf A Revolution makes a lot of difference]. fontainetrailer.com.</ref> In Japan FSW is applied to suspension struts at [[Showa Denko]] and for joining of aluminium sheets to galvanized steel brackets for the boot (trunk) lid of the [[Mazda MX-5]]. Friction stir spot welding is successfully used for the bonnet (hood) and rear doors of the [[Mazda RX-8]] and the boot lid of the [[Toyota Prius]]. Wheels are friction stir welded at Simmons Wheels, UT Alloy Works and Fundo.<ref name="Fundo">[http://www.twi.co.uk/content/autonews.html#wheel Fundo's FSW Wheels provide improved performance and reduced running costs] {{Webarchive|url=https://web.archive.org/web/20100815024249/http://www.twi.co.uk/content/autonews.html#wheel |date=2010-08-15 }}. twi.co.uk.</ref> Rear seats for the [[Volvo V70]] are friction stir welded at Sapa, [[HVAC]] pistons at Halla Climate Control and [[exhaust gas recirculation]] coolers at Pierburg. Tailor welded blanks<ref>[http://www.twi.co.uk/jsp/flashlist.jsp?flash=FSW%20used%20in%20auto%20blanks.flv FSW used in automotive tailor welded blanks] {{Webarchive|url=https://web.archive.org/web/20110927181617/http://www.twi.co.uk/jsp/flashlist.jsp?flash=FSW%20used%20in%20auto%20blanks.flv |date=2011-09-27 }}. Twi.co.uk. Retrieved on 2012-01-03.</ref> are friction stir welded for the [[Audi R8 (road car)|Audi R8]] at Riftec.<ref name="Riftec">[http://www.riftec.de/joining-processes/friction-stir-welding/applications/?L=2 FSW applications at Riftec] {{Webarchive|url=https://web.archive.org/web/20110719074938/http://www.riftec.de/joining-processes/friction-stir-welding/applications/?L=2 |date=2011-07-19 }}, riftec.de.</ref> The B-column of the Audi R8 Spider is friction stir welded from two extrusions at Hammerer Aluminium Industries in Austria.{{cn|date=January 2023}} The front subframe of the 2013 Honda Accord was friction stir welded to join aluminum and steel halves.<ref>{{citation|title=Two Metals Enter, One Leaves: The Miracle of Friction Stir Welding|author=K.C. Colwell|date=May 15, 2013|work=Car and Driver|url=https://www.caranddriver.com/features/a15115566/two-metals-enter-one-metal-leaves-the-miracle-of-friction-stir-welding-tech-dept/}}</ref>

===Railways===
[[File:Class395Javelin.JPG|thumb|The high-strength low-distortion body of [[Hitachi A-train]] [[British Rail Class 395]] is friction stir welded from longitudinal aluminium extrusions]]

Since 1997 roof panels were made from aluminium extrusions at Hydro Marine Aluminium with a 25&nbsp;m long FSW machine, e.g. for [[S-train|DSB class SA-SD]] trains of [[Alstom|Alstom LHB]].<ref name="DSB">[http://www.aws.org/wj/oct02/feature.html S.W. Kallee, J. Davenport and E.D. Nicholas: "Railway Manufacturers Implement Friction Stir Welding"] {{Webarchive|url=https://web.archive.org/web/20091018162522/http://www.aws.org/wj/oct02/feature.html |date=2009-10-18 }}, Welding Journal, October 2002.</ref> Curved side and roof panels for the [[Victoria line]] trains of [[London Underground]], side panels for [[Bombardier Electrostar]] trains<ref name=":2">[https://web.archive.org/web/20110927181625/http://www.twi.co.uk/jsp/flashlist.jsp?flash=Trainmakers%20adopt%20friction%20stir.flv Video: "Friction stir welding of Bombardier trains"], archived from [http://www.twi.co.uk/jsp/flashlist.jsp?flash=Trainmakers%20adopt%20friction%20stir.flv the original] on 27 September 2011. Twi.co.uk.</ref> at Sapa Group and side panels for Alstom's [[British Rail Class 390]] [[Pendolino]] trains are made at Sapa Group.{{Failed verification|date=January 2012}}<ref name="Capabilities">[http://www.sapagroup.com/en/Company-sites/Sapa-Mass-Transportation/FSW/Long-length-FSW Sapa's Capabilities] {{Webarchive|url=https://web.archive.org/web/20090624024936/http://www.sapagroup.com/en/Company-sites/Sapa-Mass-Transportation/FSW/Long-length-FSW/ |date=2009-06-24 }}, Long length FSW&nbsp;— Max. length 26 m&nbsp;— Max. width 3,5 m&nbsp;— Double sided welding, Sapa company brochure.</ref> Japanese commuter and express [[Hitachi A-train|A-trains]],<ref name="FSW">[http://www.hitachi-rail.com/products/rv/a_train/features/index_2.html History, Principles and Advantages of FSW on Hitachi Transportation Systems Website] {{webarchive|url=https://web.archive.org/web/20110719001923/http://www.hitachi-rail.com/products/rv/a_train/features/index_2.html |date=2011-07-19 }}. Hitachi-rail.com. Retrieved on 2012-01-03.</ref> and [[British Rail Class 395]] trains are friction stir welded by [[Hitachi]],<ref>[http://www.railalliance.co.uk/docs/rsl10hitachi.pdf Hitachi Class 395 Railway Strategies Live 2010] {{webarchive|url=https://web.archive.org/web/20120328090347/http://www.railalliance.co.uk/docs/rsl10hitachi.pdf |date=2012-03-28 }}. 23 June 2010, pp. 12–13. (PDF). Retrieved on 2012-01-03.</ref> while [[Kawasaki Heavy Industries|Kawasaki]] applies friction stir spot welding to roof panels and [[Sumitomo Group|Sumitomo Light Metal]] produces [[Shinkansen]] floor panels. Innovative FSW floor panels are made by Hammerer Aluminium Industries in Austria for the [[Stadler Kiss]] double decker rail cars, to obtain an internal height of 2 m on both floors and for the new car bodies of the [[Wuppertal Suspension Railway]].<ref>F. Ellermann, S. Pommer, G. Barth: [https://www.dvs-ev.de/call4papers/images/70/20140915_Programm-DVSCongress2014.pdf Einsatz des Rührreibschweißens bei der Fertigung der Wagenkästen für die Schwebebahn Wuppertal.] DVS Congress: ''Große Schweißtechnische Tagung'', 15./16. September, Hotel Pullman Berlin Schweizerhof, Berlin.</ref>

Heat sinks for cooling high-power electronics of locomotives are made at Sykatek, EBG, Austerlitz Electronics, EuroComposite, Sapa <ref name="Sapa">[http://www.sapagroup.com/Companies/Sapa%20Thermal%20Management/files/FSW_folder_Eng.pdf FSW: Increased strength, Improved leakproofness, Improved repeatability. Reduced heat distortion] {{Webarchive|url=https://web.archive.org/web/20110716005314/http://www.sapagroup.com/Companies/Sapa%20Thermal%20Management/files/FSW_folder_Eng.pdf |date=2011-07-16 }}, Sapa company brochure.</ref> and [[:de:Rapid_Holding|Rapid Technic AG]], and are the most common application of FSW due to the excellent heat transfer.

===Fabrication===
[[File:Top of a canister for waste nuclear fuel.JPG|right|thumb|The lids of 50-mm-thick copper canisters for nuclear waste are attached to the cylinder by friction stir welding at SKB]]Façade panels and cathode sheets are friction stir welded at [[Austria Metall AG|AMAG]] and Hammerer Aluminium Industries, including friction stir lap welds of copper to aluminium. [[Bizerba]] meat slicers, Ökolüfter HVAC units and Siemens X-ray vacuum vessels are friction stir welded at Riftec. Vacuum valves and vessels are made by FSW at Japanese and Swiss companies. FSW is also used for the encapsulation of nuclear waste at [[Svensk Kärnbränslehantering AB|SKB]] in 50-mm-thick copper canisters.<ref>[http://www.twi.co.uk/news-events/videos/canister-sealing-for-nuclear-waste-eb-or-fsw/ Video: "Electron Beam Welding and Friction Stir Welding of Copper Canisters"] {{Webarchive|url=https://web.archive.org/web/20120510144154/http://www.twi.co.uk/news-events/videos/canister-sealing-for-nuclear-waste-eb-or-fsw/ |date=2012-05-10 }}. Twi.co.uk. Retrieved on 2012-01-03.</ref><ref>{{cite thesis |degree=M.Sc. |first=Isak |last=Nielsen |title=Modeling and Control of Friction Stir Welding in {{convert|5|cm|0|abbr=on}} thick Copper Canisters |publisher=Linköping University |year=2012 |url=http://liu.diva-portal.org/smash/record.jsf?pid=diva2:535544&rvn=4}}</ref> Pressure vessels from ø1&nbsp;m semispherical forgings of 38.1&nbsp;mm thick aluminium alloy 2219 at Advanced Joining Technologies and Lawrence Livermore Nat Lab.<ref name="AJT">E. Dalder, J. W. Pasternak, J. Engel, R. S. Forrest, E. Kokko, K. McTernan, D, Waldron. [http://research.vuse.vanderbilt.edu/vuwal/Research/SphDocs/LwrncLvrmrFSWpressVessels.pdf Friction stir welding of thick walled alumnium pressure vessels], Welding Journal, April 2008, pp. 40–44.</ref> [[Friction stir processing]] is applied to ship propellers at Friction Stir Link, Inc. and to hunting knives by DiamondBlade. Bosch uses it in Worcester for the production of heat exchangers.<ref>{{YouTube|eyV3rKNd3x8|CDi innovative friction stir welding}}.</ref>

===Robotics===

[[KUKA]] Robot Group has adapted its KR500-3MT heavy-duty robot for friction stir welding via the DeltaN FS tool. The system made its first public appearance at the EuroBLECH show in November 2012.<ref>{{cite web|title=Partnership success with EADS' DeltaN FS friction-stir welding technology for industrial robots|url=http://www.technology-licensing.com/etl/int/en/News/Latest-News/Partnership-success-with-EADS--DeltaN-FS--friction-stir-welding-technology-for-industrial-robots.html|publisher=EADS|access-date=30 July 2013}}</ref>

===Personal computers===

Apple applied friction stir welding on the 2012 iMac to effectively join the bottom to the back of the device.<ref>{{cite web |url=https://techcrunch.com/2012/10/23/apple-unveils-totally-redesigned-27-and-21-5-imac-thinner-ssdhd-fusion-drive/ |publisher=TechCrunch |title=Apple unveils totally redesigned 27 and 21.5 imac|date=23 October 2012 }}</ref>

==See also==
*[[Dissimilar friction stir welding]]
*[[Friction hydro pillar processing]]<ref>{{cite journal | author1= B Vicharapu. |author2= L F Kanan. | author3= T Clarke. | author4= A De. | doi= 10.1080/13621718.2016.1274849 | volume=22 | issue=7 |title= An investigation on friction hydro-pillar processing  | journal= Science and Technology of Welding and Joining | pages=555–561|year= 2017 |s2cid= 136318372 }}</ref><ref>{{cite journal | author1= L F Kanan. |author2= B Vicharapu. | author3= A F B Bueno. | author4 = T Clarke. | author5= A De. | doi= 10.1007/s11663-018-1171-5 | volume=49 | issue=2 |title= Friction Hydro-Pillar Processing of a High Carbon Steel: Joint Structure and Properties| journal= Metallurgical and Materials Transactions B | pages=699–708|year= 2018 |bibcode= 2018MMTB...49..699K |s2cid= 139420827 }}</ref>
*[[Friction stir processing]]
*[[Friction welding]]
*[[:Category:Friction stir welding experts]]
{{clear}}

==References==
{{Reflist|30em}}

==External links==
*{{commonscatinline}}
*[https://web.archive.org/web/20131205065416/http://www.twi.co.uk/technologies/welding-coating-and-material-processing/friction-stir-welding/ Friction stir welding at TWI]
*[http://www.msm.cam.ac.uk/phase-trans/2003/FSW/aaa.html Friction-stir welding research at University of Cambridge]
*[http://files.aws.org/wj/supplement/10-2004-KIMAPONG-s.pdf Friction-stir welding of aluminum alloy to steel; academic article from the 2004 Welding Journal]
*[http://research.vuse.vanderbilt.edu/vuwal/index.shtml Friction stir welding research at Vanderbilt University Welding Automation Laboratory] {{Webarchive|url=https://web.archive.org/web/20121216073021/http://research.vuse.vanderbilt.edu/vuwal/index.shtml |date=2012-12-16 }}
*[https://web.archive.org/web/20120327192200/http://www2.matse.psu.edu/modeling/boe_manual.pdf Back of the envelope calculations in friction stir welding]
*[https://web.archive.org/web/20120111150117/http://www2.matse.psu.edu/modeling/ Theory of materials processing/welding research group at Penn State University]
*[http://www.holroyd.com/heavy-industries/new-machines/friction-stir-welding.php Friction Stir Welding Machines: Applications & Key Features]
*[https://amit.people.iitgn.ac.in/ Friction stir welding research at IIT Gandhinagar, India]

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