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Friction Stir Welding (FSW)


In 1991 a novel welding method was conceived.  The process was named Friction Stir Welding (FSW) by the inventors at The Welding Institute (TWI.)  TWI is one of the worlds leading independent research and technology organization and is based in Cambridge, England.

A US patent for FSW, # 5,460,317, was filed in November 1992  with W. H. Thomas et al as inventors, assigned to TWI.  A number of companies around the world are using the process in production, primarily for joining aluminum.

The Process

FSW employs a rotating cylindrical "tool" rubbing against a butted joint between to pieces to be joined.  Friction between the "tool" and the material heats the joint to a temperature where it becomes soft and plastic but well below the melting point.   The "tool" is then pushed along the joint line.  The parts have to be securely clamped in a manner that prevents the abutting joint faces from being forced apart. The softened material in front of the "tool" is pulled or dragged to the trailing edge.  It leaves a solid phase bond between the two pieces.   For many aluminum alloys the fact that the material is not melted may allow very high weld strength compared to low joint efficiency with arc welding.  The above picture is a schematic of the process sequence.

There is not much heat involved outside the actual joining area .  An interesting anecdote involves my first observation of the process in operation.  It was at an ESSEN Welding Fair in Germany.  Five or six foot long pieces of ~3/8 inch thick aluminum were being butt welded. Typical of my observation of allowed unsafe practices in Europe (compared to the US,) there were no guards or ropes around the FSW machine!  Show visitors were standing very close, shoulder to shoulder along the length of the weldment.  As the rotating welding "tool" passed in front of them, one person touched the welded plates about 18 inches after the "tool" had passed.  Then one by one, others next to him touched the plate, getting closer and closer to the rotating  "tool."  Finally one touched about 6 inches behind the slow moving "tool" and quickly pulled back like a child contacting a hot stove!
TWI holds a number of patents related to FSW.  Anyone using the process needs permission (a license) from TWI.  It is TWI's policy to grant non-exclusive licenses to any potential users on reasonable commercial terms.  (Note:  A former colleague and good friend Dr. Robert John retired as the CEO of TWI in July 2010.  Bob was CEO for 6 years and was previously the Institutes business manger.  He developed the license arrangements which allowed TWI to generate and expend the monies needed to advance the science of the process-which they did and continue to do.)
Friction Stir Welding Applications

Although FSW is being developed and has been used to some extent for a variety of base materials; it's success to-date has been  joining aluminum.

Marine Construction

The shipbuilding industry was one of the first to adopt the process.  FSW is useful for decks, sides bulkheads and floor panels; for aluminum extrusions; helicopter landing platforms; masts and booms.

   ESAB FSW  in Sweden

ESAB’s trade name for FSW is SuperStir.™ This machine is installed at Sapa in Sweden.  It is used to make large panels in welded lengths of up to 45 feet for ships etc. The machine has three welding heads, which allows welding from two sides of the panel at the same time. The heads can be positioned on the same side of the panel and starting at the center of the workpiece weld in opposite directions from each other.

     ESAB FSW in Norway

This ESAB SuperStir™ is installed at Marine Aluminum Aanenseen & Co.  It is used mainly for manufacturing panels for ships and railcars.  Maximum panel size 50 x 20 feet.  Aluminum alloys ranging in thickness from 1/16 to 5/8 inches are weldable in one pass.  The plant incorporates automatic material handling systems to keep high operating rates. The welding operation is fully automatic and all parameters are computerized with an easy to use Man Machine Interface.  Production started in the autumn of 1996 and has produced over 500,000 feet of weld.

Aerospace Industry

NASA partnered with Lockheed Martin and MT Aerospace to manufacture the first full-scale FSW spun-formed tank dome for liquid propellant tanks.  The 18 foot diameter tank dome is made from high strength 2195 aluminum-lithium alloy.  FSW allows the use of thinner, high strength alloy reducing weight by 25% compared to current designs.  To achieve the size needed a blank was constructed by FSW two commercial off-the-shelf plates reducing cost of raw material. 

Longitudinal and circumferential FSW are used for rocket booster tanks.  FSW  is used to make the Space Shuttle external tank  that contains the liquid hydrogen fuel and liquid oxygen oxidizer.  Prior to using FSW the 7000 series aluminum alloy achieved only 50% joint efficiency with arc welding.  The material had to be made twice as thick and the bulk machined away leaving a tapered section twice the thickness in the weld joint area.  This created a lot of  material waste, excessive time and cost.

Note: FSW can appear deceptively simple - it is NOT!  My group was involved in the support of the system sold to make the Space Shuttle tanks; one of the first large systems installed in the USA. The actual welding process and simple “tools” (at the time) were not that complicated; the massive and powerful holding fixture was!  The parts must be prevented from moving as welding progresses.  This requires very high forces and that large system cost over 5 million dollars!  In addition, since the mid 1990’s when that particular system was installed, the “tools” have become more complex. The newest designs can make quality appearance top and bottom deposits.  Some have a shape which assists moving the softened material from in front of the "tool" to the rear.  (The sketch right is of a "tool" from a recent patent.  The working part called the nib is screw shaped enhancing movement of the softened material around tool and the upper area helps form the top surface of the deposit.)
Transportation Industry

Fontain Trailer introduced FSW for flatbed trailer manufacture.  Market demand for lighter, stronger trailers to haul more payload was a key reason for a new design.  In addition, lighter weight was needed to compensate for tractors that are getting heavier due to the additional emission control technology. Fontain reports the typical 48-foot flatbed weighs about 10,000 pounds and requires 1,400 screws, 44 steel I-beams, eight wing braces, plus wood and aluminum strips for the flooring – a total of 3,700 parts.   By employing FSW techniques they reduced the weight of this all aluminum trailer to 8,000 pounds.

FSW is also used for welding light weight high speed trains, tank cars etc

More information on the History of:

  1.  Submerged Arc Welding (SAW)

  2.  MIG Welding (GMAW)

  3.  Electroslag Welding (ESW)

  4. TIG Welding (GTAW)

  can be found at these links on our site (just click on the process).

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Welding: Go Green

New innovations are still occurring in the welding industry.  Our recent inventions optimize MIG shielding gas flow at the weld start (2003 Patent Number 6,610,957; figure left and 2006 Patent Numbers 7,015,412 and 7,019,248)  These devices reduce  excess stored gas by over 80% when welding stops. This significantly reduces gas waste that published data shows typically exceeds over 60% of what is used!   Reducing shielding gas waste can save a MIG user over 50% of gas use while improving weld start quality.  Our Patent 7,462,709  issued in 2008 and defines a device that allows most flowmeters to be locked at the desired settings avoiding excess wasted gas.  Reducing waste is very important in a competitive world environment.

In 2012 we were granted two patents related to helping a welders environment.  These welding helmet designs not only filter the air entering the helmet they also cool the air using a Thermoelectric Cooling Module.  Cooling the head helps cool the whole body.  Excessive heat is a common complaint of welders.  This helmet helps solve the excess heat problem by providing cooled filtered, breathable air.

We are searching for a company to license these designs, including  fabricators that employ a number of welders who would benefit from the reduced heat and better environment. Contact Jerry_Uttrachi@NetWelding.com if interested.

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A home shop fabricator in Georgia with a Miller TM 175 amp welder purchased a 50 foot Gas Saver System ( GSS TM ) so he could use a larger cylinder and mount it on the wall of his shop.  He wrote:

"The system works great.  Thanks for the professional service and a great product."   Click To See His Home Shop


A Professional Street Rod Builder Had This to Say:

With their standard MIG welder gas delivery hose the peak shielding flow at weld start was measured at 150 CFH. That caused air to be sucked into the gas stream causing poor weld starts.  With the  replacing their existing hose, the peak flow surge at the weld start was about 50 CFH.  Total gas use was cut in half.

Kyle Bond, President, quickly saw the improvement achieved in weld start quality as a significant advantage!   Kyle, an excellent automotive painter, was well aware of the effects of gas surge caused by pressure buildup in the delivery hose when stopped.  He has to deal with the visible effects in the air hose lines on the spray gun in his paint booth!  The paint surge is visible and creates defects unless the gun is triggered off the part being painted!  We can’t do that with our MIG gun!