By Martin Brennan
When friction stir welding (FSW) was invented in 1991, it was consid- ered to be more of a laboratory curiosity than a fabrication process with broad application. Advances in the technology have changed
this thinking and made FSW a versatile and innovative welding method that
continues to mature.
FSW is a solid-state process, which means the base materials to be joined do
not melt during welding but are plasticized, similar to joining clay together (see
Figure 1). Fast, high-quality welds of 2xxx and 7xxx series alloys, traditionally
considered unweldable, are possible using FSW. It can also successfully weld numerous alloys and materials, including high-strength steels, stainless steel, titanium, and simple carbon steel. It can even be used to join dissimilar materials.
FSW has changed the way components for aerospace, defense, shipbuilding,
transportation, medical, and electronics are fabricated, and its scope is expanding to more industries and applications.
What does it take to bring this welding process to the production floor?
Making the Business Case for Friction Stir Welding
A friction stir welding system can cost the same as a very basic press brake or a
modern laser cutting machine with advanced material handling automation. It
depends on the application.
To justify the investment, it’s important to go beyond the capital cost and focus on the big picture. The low heat input that occurs during the joining process and the resulting high-strength welds have the potential to change the way
many common structures are built. The process produces welds with increased
tensile strength, outstanding fatigue properties, and improved corrosion resistance, all while creating minimal distortion and shrinkage. FSW allows manufacturers to redesign components for lighter weight, lower cost, and higher performance.
When considering an automated FSW system, which costs more than conventional welding equipment, a fabricator needs to take into account all aspects of
the operation to determine return on investment. For example, FSW requires no
welding consumables such as shielding gas, wire, liners, or tips.
FSW stands out in other ways:
• Preweld setup is simple. Degreasing and surface cleaning of the material’s
weld path is all that’s needed.
• FSW welds three to four times faster than gas metal arc welding (GMAW)
in most aluminum materials. With automated FS W equipment, the typical production speed to join 0.20-inch AA6082 extruded profiles is 10 feet per minute ( 3
meters per minute).
• Material thicknesses from 0.02 to 2. 56 in. (0.5 to 65 mm) can be welded
from one side at full penetration, without porosity or internal voids (often a
challenge when arc welding aluminum).
• Joint quality is superior to conventional fusion-welded joints. The solid-state process produces virtually zero defects. Tensile strength is high, and the
appearance of the weld is improved over conventional welding.
• The high quality of the weld, consistently straight and dimensionally accurate, requires no secondary processing or postweld heat treatment in most
cases (see Figure 2).
• Because the process doesn’t require shielding gas, a fabricator doesn’t require an investment in pressure tanks, pipe fittings, and gas regulators. This also
eliminates the need for storage and transport of consumables in the production
• Generally, FSW demands less energy input to the weld than GMAW or
gas tungsten arc welding (GTAW). FSW is always a single-pass process, offering
greater energy savings as wall thickness increases.
• FSW generates no noise, sparks, or fumes. This eliminates the need for
fume extraction equipment or added measures to protect workers from UV or
Fr ict ion
THE ADVANCED JOINING TECHNOLOGY
USED FOR MORE THAN JUST ADVANCED
This friction stir welding head and tool are not common sights in metal fabricating
facilities, but that may be changing.