Friction Stir Welding (FSW) is a solid-state joining process that’s especially popular in the aerospace, transportation, and electronics industries.
Our detailed guide to FSW provides a deeper understanding of its unique capabilities and diverse applications. Below, we’ll explore some commonly asked questions about Friction Stir Welding.
1. What is Friction Stir Welding (FSW)?
The Friction Stir Welding process uses a non-consumable pin tool to create frictional heat between two materials. As the pin tool spins, it “stirs” the two materials together, creating plastic deformation between 70-90 percent of the solidus temperature. Solidus is the highest temperature at which an alloy is completely solid. Plastic deformation changes the shape of the solid body without weakening the material.
Because Friction Stir Welding is a solid-state joining process, the two materials being friction welded never melt, and joining occurs below the solidus of the equilibrium phase for the materials. As a result, the metals retain their original mechanical properties better.
Here’s a closer look at the FSW process:
- Tool and Material Preparation: A pin tool is mounted in a drive spindle. Before the two parts can be joined, they are clamped together to keep them stationary.
- Tool Rotation Begins: The pin tool begins to rotate and plunges into the two pieces of metal, maintaining a downward (Z-axis) force. This is referred to as the plunge or entry hole at the start of the weld path.
- Plasticization Occurs: The rotating pin tool shoulder creates mechanical friction. The resulting friction then preheats the materials, creating a plasticized state at a temperature range below the melting point, as described above.
- A Friction Weld is Formed: The pin forms a bond as it travels along the joint, consolidating the material along the weld profile/path while maintaining a downward force and Z-axis position.
- Tool is Withdrawn: At the end of the weld path, the tool is withdrawn in the Z axis. This extraction point is sometimes called the “exit hole” because the pin probe will leave an impression in the material at the point of extraction.
2. What is Friction Stir Welding used for?
Because Friction Stir Welding creates extremely high-quality, high-strength joints with low distortion, the solid-state joining process is the preferred technology for welding aluminum sheets, extrusions, panels, and other products.
At MTI, Friction Stir Welding is also commonly used to join dissimilar lightweight metals and hybrid electric vehicle applications.
3. What is a pin tool in Friction Stir Welding?
The pin tool is key to Friction Stir Welding. In rotary and linear friction welding, one part is rotated or oscillated while the other part is held stationary.
However, in Friction Stir Welding, both parts are held stationary, and a non-consumable spinning pin tool creates the frictional heat. This also makes Friction Stir Welding ideal for joining very large, long, or thin parts, such as sheet metal or an extrusion.
The key features of pin tools are the shoulder and the cone-shaped pin. This FSW head rotates and penetrates the material along the seam of the two parts while the shoulder rides along the surface of the parts and typically inputs most of the heat and force.
It’s important to remember that the pin tool’s features and geometry will differ depending on your application, joint, and the materials you’re joining.
When designing the shoulder, MTI considers several factors, including the profile geometry and the diameter of the shoulder:
- Shoulder Profile: The profile geometry of the shoulder can be flat, convex, or concave. Some shoulder designs also incorporate a pattern of grooves that generate and channel the desired amount of heat to the joint.
- Shoulder Diameter: The diameter of the shoulder depends on your part material, type of joint, and depth of weld penetration required for the weld joint and part application scope/heat requirement.
When designing the pin, MTI’s engineers consider material flow and material displacement.
- Pin Profile: For proper material flow, the tapered probe pin can contain a series of flutes, faces, or a combination of the two.
- Pin Depth: The pin depth, or thickness and taper angle design contribute to properly displacing and consolidating the plasticized material(s) being joined.
To determine the right FSW tool design for you, see our “Friction Stir Welding Tools: Types, Applications & Selection Guide.”
4. What are the advantages of using Friction Stir Welding?
There are several advantages to using friction stir welding, especially over fusion welding processes. Here are just a few:
Virtually Defect-Free Bonding
Because Friction Stir Welding is a solid-state joining process, many of the limitations associated with conventional fusion welding techniques do not apply to the Friction Stir Welding process—including shrinkage, solidification, cracking, and porosity.
Superior Mechanical Characteristics
Friction Stir Welding produces a weld with high strength, toughness, and a fine-grain structure that resists fatigue stress. Due to the low heat and small heat-affected zone, the joined parts are minimally distorted, reducing the costs associated with preparing them for subsequent use. FSW is commonly used for aluminum welding, where a strong yet lightweight material is required.
Machine-Controlled Process
Friction Stir Welding occurs via a machine-controlled process. It’s programmed with fine-tuned technical positions and values that can be saved and repeated with the exact same results each time. Part programs and their associated welded part data can be viewed live, recorded, and stored for future use.
The weld path profile and pin tool position can utilize proprietary closed-loop system software—such as MTI’s IntelliStir temperature control—which can monitor, adjust, and maintain critical weld features to ensure consistent mechanical properties and a solid, repeatable, successful weld.
These critical parameters include Z-axis force, position, and tool temperature. By controlling them in real time, Friction Stir Welding delivers highly consistent part quality, stable production, and weld results that are largely independent of operator influence.
Environmentally Friendly Process
Friction Stir Welding is a cleaner, greener process with low energy input and cost that requires no consumables, flux, filler material, or shielding gases to run.
Additionally, it doesn’t emit smoke, fumes, or gases that need to be exhausted from the process.
Join Dissimilar Alloys
Friction Stir Welding may be used to weld dissimilar alloys – including combinations that aren’t compatible with conventional welding methods. That’s because fusion methods rely on melting to join the two materials, and differences in melting temperatures could make it impossible to join certain combinations with fusion welding.
Fusion processes also alter the material properties of one or both materials through melting. On the other hand, the Friction Stir Welding process happens below the melting temperature and works only on the parent material(s). This means that in Friction Stir Welding, no additional filler materials, metals, or flux are used, which can alter the parent material properties. The result is a stronger weld.
To fully realize the benefits of Friction Stir Welding, selecting the right FSW machine for your application is essential. As a global leader in friction welding technology, we design and manufacture industry-leading Friction Stir Welding systems for demanding production environments.
Visit our Friction Stir Welders page to explore machines available in a range of sizes, configurations, and capabilities.
5. What are the Applications of FSW?
Friction stir welding is especially beneficial for industries where efficient high-strength welding is key. Here are some of the examples:
- Aerospace Industry: FSW is used to create stiffened skins and panels for high-speed engineering solutions.
- Electronics and Machines: This procedure plays a significant role in the fabrication of small parts. It seals cold boxes, hard drive cases, and welds panels in heat exchangers and electronic enclosures.
- Automotive Industry: FSW’s high-strength welding of lightweight aluminum and aluminum alloys is vital for producing safer, lighter, and more affordable vehicles.
- Nuclear Storage: FSW contributed to the development of long-term storage units for nuclear waste management.
- Electrical Vehicle (EV): EVs benefit from FSW’s ability to create a watertight seal to protect battery enclosures and electrical components from moisture and environmental contaminants.
- Rail Industry: Rail cars are made from welding aluminum extrusions with FSW for superior joint strength and structural durability.
Do you have a part concept you wish to prototype and manufacture? Whichever industry it serves, MTI has the FSW machines and other pre- and post-welding services to achieve it from concept to completion. See our FSW Contract Welding page to learn more.
6. What are the Mechanical Properties and Microstructure of Friction-Stir-Welded Materials?
When friction stir welding is used to bond materials, it produces a nugget zone, a thermo-mechanically affected zone (TMAZ), and a heat-affected zone (HAZ). While the nugget zone is the welded area where the two metals joined, the TMAZ does not experience dynamic recrystallization. However, the extent of the microstructural composition of these zones will depend on the material and processing.
7. When Was FSW Invented?
The Welding Institute invested in friction stir welding in 1991. Over the years, FSW technology has been used to weld light metal components with a high strength-to-weight ratio in products, construction, and vehicles.
8. What Does Friction Stir Welding Look Like?
To answer this question, view our video on friction stir welding to learn how friction stir welding bonds materials together.
For more Friction Stir Welding videos, check out MTI’s video center.
About MTI
MTI is an expert in Friction Stir Welding for mass production and industrial applications. As the only company in the world specializing in all three friction welding technologies—linear, rotary, and friction stir—our on-staff metallurgists, design engineers, and applications engineers can find the right technology to solve your joining challenges.
At MTI, we are committed to providing robust support to our customers throughout the entire process. While we hope our FAQs have enlightened you. You may have more questions. To learn if Friction Stir Welding is right for your project, contact us today.