What is Friction Stir Welding?
Friction stir welding (FSW) is a type of welding that uses frictional heat to join parts together in their solid state–that is, without reaching the materials’ melting point. This CNC technology can produce high-quality welds—fast—that would not be possible with traditional fusion welding.
As a result, friction stir welding has quickly become the first choice for many critical, high-precision applications in industries like aerospace, nuclear, automotive, marine, and rail.
Invented and patented by TWI in 1991, friction stir welding was developed to solve the problem of how to join high-strength alloys, like aluminum alloys, that were previously considered unweldable. The relatively low temperature generated by friction is both energy-efficient and dramatically reduces the workpiece from warping or shrinking during the welding process, reducing the risk of defects, distortion, or residual stress.
Now that we’ve answered the question, “what is friction stir welding,” let’s take a look at the process, step-by-step:
- 1. Plunging – The spinning tool is forced into the joint between the workpiece until the shoulder makes contact.
- 2. Dwelling – Heat is generated at the top of the tool and workpiece.
- 3. Welding – The welding action takes place along the desired joint line.
- 4. Retraction – At the end of the joint line, the tool is withdrawn, leaving an exit hole formation. There are multiple ways to address the exit hole such as plug welding.
As shown above, friction stir welding uses no filler material. This solid state process creates exceptionally strong, high-quality welds that can handle the stresses of the most demanding applications.
Friction Stir Additive Manufacturing
Friction stir additive manufacturing (FSAM) is a technique of additive manufacturing that utilizes solid state friction stir processing to apply a thick bead of material to act as a stiffener or to develop multilayer components by joining materials layer by layer.
Like FSW, FSAM is a solid state process that uses a spinning tool that traverses along the tool path, plasticizing and depositing material. Strength, ductility, and other properties achieved are similar to other friction stir processes.
Friction Stir Processing
Friction stir processing (FSP) is used when the improvement of a metal’s properties is needed, by processing the existing material and/or using other metals to support and improve upon the original. FSP is a solid state process that utilizes a rotating tool with a pin and shoulder on a single piece of material to make specific property enhancement—such as improving toughness or flexibility—via fine grain of a second material with properties that improve the original.
Friction Plug Welding
Friction plug welding is a solid-state process that can be used to repair existing welds or to fill the hole created from a restricted FSW pin. Using either a pull or push method– depending on the accessibility of the hole–a rotating tapered plug is forced into the hole until a preprogrammed distance has been achieved.
Self-Reacting Friction Stir Welding
Self-reacting friction stir welding is a process that uses two shoulders–one above and one below or behind the material being welded. The force of the top shoulder is reacted to by the shoulder underneath, eliminating the need for a stout tooling structure to react against the force generated by the weld.
Adjustable Pin Friction Stir Welding
Friction stir welding using an adjustable pin tool can reduce or eliminate the pin hole typically created as a result of conventional friction stir welding. An automated system uses a controller to sense the pressure on the shoulder and retract the tool slightly to keep pressure constant, and incrementally withdraws the tool as it reaches the end of the traverse, eliminating any keyhole that would be created.
Friction stir welding is ideal for producing superior, high-precision welds across a wide variety of applications and in industries like aerospace, nuclear, automotive, marine, and rail. There are many advantages to friction stir welding, including:
- Weld (Almost) Anything – In Single Pass. Friction stir welding can weld previously un-weldable alloys, dissimilar alloys, joints with complex curvatures, and materials less than 1 mm and greater than 75 mm thick in a single pass.
- Weld Stronger Joints. Friction stir welding creates stronger joints compared to traditional joining methods like mechanical fasteners or fusion welding. FSW also makes it easier to create high strength alloys, even with dissimilar alloys.
- Ensure Superior Precision and Consistency. Friction stir welding is a CNC controlled, solid state process that produces precise and consistent results by reducing the risk of defects, distortion, or residual stress.
- Real-time Quality Monitoring. Due to the solid state process, real time data can be collected while performing the weld that can be used in quality monitoring.
- Increase Cost-Efficiency. Friction stir welding requires less raw materials compared to traditional methods and is quick to set up, saving costs and increasing efficiency.
- Protect the Environment. Friction stir welding is a green, energy-efficient technology. FSW uses no filler metal or shielding gas, so no harmful emissions are created in the process.