Friction Stir Welding (FSW) is a revolutionary, environmentally friendly, solid-state welding technology invented in 1991 by Wayne Thomas of The Welding Institute in the United Kingdom.  In FSW, materials to be joined are clamped together; a non-consumable, rotating pin tool is plunged into the joint line and traversed along the joint.  Heat generated from the rotating pin and from the tool shoulder rubbing against the materials that are being joined softens the metal so that it flows plastically, creating a welded joint.  Since no discernable melting occurs, problems with hot cracking and shrinkage porosity are eliminated.  The process accomplishes solid-state welds in many metals, such as aluminum, copper, lead, magnesium, steel, and titanium alloys.

CTC Enables New FSW Applications

CTC has advanced the state-of-the-art in FSW, making once impossible welds now commonplace and leading to numerous advantages over conventional fusion welding.  In addition to superior strength and ductility, these advantages include significant reduction in residual stresses, elimination of filler wire, greatly simplified weld preparation procedures, and reduced environmental health and safety concerns.

One example of an alloy that has been shown to be friction stir weldable is Al-Cu 2519.  This finding is extremely beneficial to the design of the U.S. Marine Corps’ Advanced Amphibious Assault Vehicle (AAAV).  CTC and its partners proposed that FSW replace conventional fuse welding on the AAAV.  In 2003, the friction stir welds for the AAAV passed the mine-blast test—a milestone in the development of the combat vehicle and the final challenge that the 2519 welds had to pass.  Since the project’s inception, CTC scientists and engineers have produced welds that progressively achieved the following:

• Weldment tensile strength 47 percent higher than the minimum weld strength obtained by gas metal arc welding
• An increase in weldment ductility by more than a factor of three
• A passing score on the ballistic shock impact test.  The welds attained significantly higher velocities than the 1946 Mil Spec requirement.

New Welding System Fills Critical Need

CTC and the Navy Metalworking Center, under TARDEC sponsorship, have installed a three-story tall FSW system capable of fabricating a full-size combat vehicle.  The system is able to create welds in two-inch thick aluminum plates in a single pass.  The system is used to develop the process for Navy applications and to fabricate concept trailers and Future Combat Systems combat vehicle test articles for the U.S. Army.  In addition, the system gives prime manufacturers the opportunity to explore the benefits of FSW for their applications before installing their own systems.

Welding Tool Designs for Thick-Section Aluminum Armor Applications

Central to the success of the friction stir welding process is the design and construction of the welding tool.  In 2000, friction stir welding of ¾-inch thick aluminum was considered a challenge.  CTC has led the development of welding tools and equipment to make welding of over 1.5 inches relatively routine.  Careful testing of various tools for different materials has made it possible to propose this process for the welding of thick-section aluminum and alloys for ground vehicle applications in a production setting.

Patent-pending tool embeds powder into a substrate

Pinless Tool Design Earning Patent

In 2005 CTC demonstrated a new “pinless” friction stir processing tool that was successfully used to embed a uniform, thin layer of a powder into a substrate.  This method could have applications for wear components, corrosion protection, thermal protection, etc.  CTC has applied for a patent for this tool design.

Contact CTC for FSW Solutions

The creation of additional process variants, the development of new welding tool designs, and the identification of best practices are likely to make FSW even more versatile and effective in the future.  CTC and its clients will remain on the cutting edge of FSW and all its benefits.