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FAQs – Friction Stir Welding

Friction Stir Welding (FSW) is a solid-state joining process that’s especially popular in the aerospace, transportation, and electronics industries.

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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 better retain their original mechanical properties.  

Here’s a closer look at how it’s done:

1. A pin tool is mounted in a drive spindle. Before the two parts can be joined, they are clamped together to keep them stationary.
2. 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.
3. The rotating pin tool shoulder creates friction. The resulting friction then preheats the materials, creating a plasticized state at a temperature range below the melting point, as described above.
4. The pin forms a bond as it travels along the joint and consolidates the material along the weld profile/path while maintaining a downward force and Z-axis position.
5. At the end of the weld path, the tool is withdrawn in the Z axis. This extraction point is sometimes referred to as 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:

• The profile geometry of the shoulder can either be flat, convex, or concave. Some shoulder designs also incorporate a pattern of groves that are used to generate and channel the desired amount of heat to the joint.
• 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.

• For proper material flow, the tapered probe pin can contain a series of flutes, faces, or a combination of the two.
• The pin depth or thickness and taper angle design contribute to properly displacing and consolidating the plasticized material(s) being joined.

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’s 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 frequently used for aluminum welding where strong but lightweight material is needed.
• Machine-Controlled Process: Friction Stir Welding occurs via a machine-controlled process and program 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. Examples of critical weld features include Z Axis force, position, or tool temperature.  The resulting part, production, and weld quality are, therefore, very operator-independent.
• 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. Friction Stir Welding also does not emit smoke, fumes, or gases that need to be exhausted from the process or require the operator to use a traditional bulky welding helmet and spark resistant clothing.
• 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 change the material properties of one or both materials due to melting.  On the other hand, the Friction Stir Welding process happens below the melting temperature and works only the parent material(s).  This means that in Friction Stir Welding, no additional filler materials, metals, or flux are used that can cause additional changes to the parent material properties.  The result is a stronger weld.

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 small parts fabrication. 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 durability.

6. What are the Mechanical Properties and Microstructure of Friction Stir Welded Materials?

When friction stir welding is used to bond materials, it will have 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 . Through years of development, FSW technology has been used to prepare light metal materials into components with a high strength-to-weight ratio in products, construction, and vehicles.

With competitive price and timely delivery, World Wide Welding sincerely hope to be your supplier and partner.

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 Welding, 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.

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Friction Stir Welding is another friction welding technique that has beneficially impacted the aerospace, transportation and electronics industries. Like other friction welding processes, friction stir welding uses frictional heat and force to forge materials together creating extremely high-quality, solid-state joints.

In other friction welding processes, one of the two parts is typically moving — creating the friction and heat needed to form the bond. However, in friction stir welding both parts are stationary and the relative motion is created by a rotating pin tool.

The Process
The two parts being joined are clamped together to keep them stationary throughout the process. The friction stir welding process uses a non-consumable pin tool — for a visual, picture a dry erase marker with the cap on. The pin (the tip of the marker cap) rotates and penetrates the material along the seam of the two parts. The shoulder of the tool (the wider surface of the cap) rides along the surface of the parts and input most of the heat and force as the pin rotates. The rotating pin embedded between the two parts plasticizes and is mixes the two parts together; this is the stirring action. The tool moves along the length of the seam while the rotating pin literally stirs the two materials together leaving a distinctive flow pattern of forged material in its path. The grain structure in the weld zone is finer than that of the parent material and has similar strength, bending, and fatigue characteristics.

Applications
Friction stir welding can be used to weld very thin materials — as thin as 1mm or less. The materials can also be very wide or very long, such as panels or plates. One great friction stir welding application is welding extrusions. Extrusions are materials that are specifically shaped and can vary in many different geometries. The FSW process can be very cost effective because smaller extrusions are much less expensive to produce than really wide extrusions. And with friction stir welding, it is easy to weld together many small extrusions until the part is as large as needed.

Benefits
So why use friction stir welding instead of fusion welding? When using fusion welding one of the side-effects is melting. Melting means re-solidification, which can weaken the parent material. So to get the same joint strength of a solid-state bond, a fusion weld would require more material at the welding section which adds mass. The longer or wider the part, the more material is needed at the welding section and the more mass increases. Instead, friction stir welding results in the same solid-state joint using less material. This provides cost savings for the same high performance. Small weight savings in high volume automotive applications or significant weight savings in larger extrusions can add up to significant savings for the OEM.

MTI Can Solve Your Problems
MTI is the leading expert on welding processes and applications. Whenever manufacturing issues arise, contact MTI so we can work with you to identify the issues and develop solutions specifically gear to your needs. We’ll build a machine that makes your part, we’ll make the part for you, or we’ll help you make the part even better.

If you are looking for more details, kindly visit custom friction stir welding machine.