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Increased Strength Improved leakproofness Improved repeatability Reduced heat distortion Friction Stir Welding

Sapa Friction Stir Welding

Apr 09, 2018



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Reducedheat distortion

FrictionS tirWelding

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FSW: the joining method which exploits the lawsof nature . All we add is mechanical effort.

The Friction Stir Welding method of joining is based on thefact that the metal is subjected to heavy plastic deformation athigh temperatures, but lower than the melting point.

When the rotating tool is plunged into the metal, frictionheat is generated. The tool produces severe plastic deformationunder high pressure, during which the weld interfaces arestirred together and a homogenous structure is formed.

Compared with fusion welding, Friction Stir Welding provides: – increased strength

– improved sealing. Completely void-free, leakproof joints

with greater strength than fusion-welded joints – the weld is in principle ush with the parent material – reduced heat distortion – improved repeatability. The FSW operation comprises a small

number of variables which it is easy to monitor: tools, feedingrate, rpm, and position of tool. This also permits closetolerances.

A rotating tool is plunged into the joint line and moved along the joint.Neither ux nor ller material are used.

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The Sapa production line

Precipitation structure in a FSW weld

Topview of MIG weld Topview of FSW weld

The MIG weld builds up. The ller material hasa different chemical composition compared to theparent material.

The FSW weld: The weld is in principle ushwith the material which is being welded. No llematerial is used.

Precipitation structure in a MIG weld

The FSW weld is homogenous and void-free without any oxide inclusions

To provide a picture of FSW, we havedecided to compare it with the mostcommonly used method of welding – fusionwelding.

As we show in this brochure, FSWprovides advantages which can be exploitedin a variety of designs.

At the same time we must stress thatwe often use fusion welding (MIG) in thefurther re nement of aluminum pro les. Thisprocedure does have its place in production.

Fusion welding , MIG for example, usesller material and shielding gas.

The ller material and the parent metalare melted and produce a weld with adifferent solidi cation structure.

With MIG and TIG welding it is necessaryto protect the metal from reaction with theatmosphere since the rapidly formed oxidecan cause failure in the weld. The oxide isheavier than the molten metal, and may forminclusions.

There is also a risk of porosity.

FSW is created without uxes, and noshielding gas is used.

The joint is made subject to thein uence of friction heat, and severe plastideformation. The material which will be

joined never reaches the melting point,but the pro les are welded together in thesame way as in the case of the extrusionhollow pro les.

The result is a homogenous and void-free weld without inclusions. The FSW process is marked by itslimited number of variables, which are easyto monitor. This gives the same results fromone weld to the next.

Fusion welding is a more complicatedprocess, which means that results oftenvary.

In this folder we have decided to carryout a comparison with high-quality fusion-welded joints.

FSW is an established techniqueFSW was invented by The Welding

Institute (TWI) in Cambridge, England.Sapa has played an active part in

the process of converting theory andlaboratory experiments into full-scaleproduction.

Sapa started series production in1996, and can supply panels up to 3min width and 14.5 m in length, joinedtogether using FSW.

After extensive tests, severalleading Classi cation Associations haveapproved deliveries from the processfor demanding tasks within railway andmarine applications.


The structureof the joint

Panels up to 14.5 m inlength



7.4 mm

50 µm

4.7 m

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The deviation in levelness of the heat sink panel isless than the tolerance demands for the combined

pro les it contains.

Since the FSW process takes place at atemperature which is lower than the metal’smelting point, the result is:

– minimal heat distortion

– low residual stress levels and thereforeeasier deformation control.The product in the illustration below is a

heat sink panel which is used during theprocessing of instant coffee (freeze-drying).

The aluminum pro les have been joineusing FSW to a tray measuring 530 x 129mm.

Any deviation in levelness in a FSW panelis less than the combined tolerances for thepro les it contains.

Heat sink panel : Here the heat conductibility ofaluminum is used.

A leakproof heat sinkThe parent material is a solid pro le which hasbeen CNC processed by Sapa.

The machined cooling channels are closed witha cover. The joining method is FSW.

The joint will be absolutely leakproof.The material is welded together to form ahomogenous unit.

When we test the leakproofness we

are therefore testing the reliability of themanufacturing process.Some 25,000 units of the heat sink

( gures below) have been supplied tothe customer ABB Semiconductors AG.

Method of leak testing: helium leakdetection. Result: no leaks due to weldingdefect. FSW joints have also been testedusing the water-pressure test.

The results are clear: the processensures a joint which can be used incomponents with the greatest requirementfor leakproofness.

25,000 produced units. All equally leakproof.Roof of train : A number of leading Classi cationAssociations have approved deliveries from theprocess for demanding tasks within railway andmarine applications.

Deck panels : Pro les joined together to panels upto 3 m in width and 14.5 m in length.

1. e.g. MIG or TIG. 2. standard value only.

The tensile strength (R m (w)) of the welded specimenshall satisfy the following requirements:Rm (w) = R m (pm) x T,

where R m (pm) is the speci ed minimum tensilestrength of the parent material and T is the jointsef ciency factor.

Experience and extensive testing showthat a FSW joint is usually stronger than afusion weld.

The table below shows the standardized

joint ef ciency factor T for arc-welded buttjoints as speci ed in SS-EN 288-4.The values given for FSW joints are

based on a large number of measurements,and should be regarded as standard values.

Since standards do not yet exist forFSW joints, the values for fusion-weldedjoints will be used to calculate strength instandardized designs.

Strength Leakproofness Levelness

Weld factor for the ultimate tensile strengthof butt welds , Al-Mg-Si alloys

Condition ofparent metalmaterialbefore welding


T = Rm (w)Rm (pm)





Arcwelding 1







≥ 0.9

≥ 0.7

≥ 0.8

Sapa joins pro les measuring up to400 mm across for panels with a high levelof mechanical strength.





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Designs based on aluminum pro lesare used in virtually all industries.

Sapa pro les replace othermaterials and construction methods.

Aluminum instead of steel, copper,plastic and wood. Extrusion instead ofmore expensive techniques, such ascasting or injection moulding.

The joint effort of aluminum,profles and Sapa

Aluminum offers properties such aslow weight combined with high tensilestrength and corrosion resistance.

The metal can be re-used for thesame applications, time and time again,without losing its unique qualities.

In remelting, only 5% of the originalenergy input is required. Aluminum isthe perfect ecocycle metal.

Pro les: The die cost is veryreasonable. Technical limitationsare few. The possibilities are nearlyendless. Several functions can beintegrated in the pro le, making it easierto process and simpler to assemble.High-quality surface nish is anotheroption.

Sapa offers extensive fabricationof pro les. Cutting, bending, CNC

processing, hydroforming, melt welding,anodizing and, of course, FrictionStir Welding, are examples of suchprocesses.

What will the pro le be used for?Can the customer’s production line besimpli ed? Can the end product bemade even more competitive? Can thecost be reduced?

At Sapa we ask questions, and theanswers we give are based on experiencethat is unique.

Sapa Pro les is the world’s leadingproducer of extruded aluminum pro leswith production plants throughout theUnited States, China and Europe.

Our assets are our unique wealthof knowledge and experience,our technical resources and ourknowledgeable, highly motivatedemployees.

We strive to create long-termbusiness relationships in which mutualpro tability is the overriding aim.

FSW requires a stable workxture, and it is therefore at present

dif cult, for example, to produce

a joint at an intersection betweenpro les.

This means, among other things,that deposit welding on nisheddesigns is seldom possible with FSW.Repairs can, of course, be carried outeffectively using traditional methods.

Potential: FSW gives increased strength, improved leakproofness,improved repeatability and reduced heat distortion.

How can you take advantage ofthis?

The chemical composition of thematerial in the joint is identical tothat in the original material. Nothinghas been added. Nothing has been

removed. Resistance to corrosionthus remains unchanged in principle.Tests of SS-EN-AW 6082 have

shown, for example, that the yield andultimate strength are not affected after1,000 hours of SWAAT testing.

Panels for multi-plate freezer designed forfsh industry: After joining the joint is milled.This gives a completely smooth surface easyto keep clean. The repeatability applies to allvariables: the structure of the joint, its strength,

leakproofness and panel levelness.

Heat sink for power electronics: High anduniform quality with extreme requirementfor leakproofness.

FSW in the automotive industry: Thecomponent produced in a fully automated line.

The FSW operation has a smallnumber of variables which are easy tomonitor: tools, feeding rate, rpm, andposition of tool. This also permits close

tolerances.In addition: with the experienceof series production which we haveacquired since 1996 we can con dentlystate that:

– very small differences will beapparent between one joint andanother during the production cycleand in the case of recurrent orders.This applies to all variables:

the structure of the joint, its strength,leakproofness and levelness.


Repeatability Resistance tocorrosion

Sapa: so muchmore than FSW

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Torsten Höglund, Dr. Techn., Professor at Royal Institute ofTechnology (KTH), Stockholm, on Friction Stir Welding:

“The heat affected zone is considerably smaller in the caseof FSW joints than with fusion welding. This means an increasein strength and a reduction in distortion.

It can also be stated that the quality of, for example, MIGwelds varies considerably from one weld to another. FSWensures a constant and high quality of joint.

The Sapa production process is tried and tested, and thequalities of aluminum which make the FSW method possibleare well known.”

Comment from the worldof scientifc research

Shaping the future

Sapa Profles, Inc.7933 NE 21st Avenue. Portland Oregon les