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.

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.

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.

Rotary Friction Welding is a solid-state process in which one part is rotated at a high speed and is pressed against another part that is held stationary. The resulting friction heats the parts, causing them to forge together. MTI is the only company that offers all three types of RFW technologies - Direct Drive, Inertia, and Hybrid.

There are dozens of applications suitable for Rotary Friction Welding, but here is a list some of the most common examples by industry:

• Aerospace components such as engine rotor components, rotor assemblies, jet engine fan shafts, landing gear
• Automotive applications including drive shafts, bi-metallic valves, turbocharger shafts, pistons
• Construction and Agriculture parts such as hydraulic cylinder rods, piston rods, water pumps, track rollers
• Oil & Gas components including rock drill pipe, drill pipe and directional drill pipe

Rotary Friction Welding is a quicker, stronger and more environmentally friendly alternative to fusion welding processes such as electric arc or gas welding or high-energy processes like electron beam or laser welding. Other key benefits of Rotary Friction Welding include the ability to join bi-metallics or dissimilar metals, faster weld cycles, and minimal joint preparation.

The Low Force process uses an external energy source to raise the interface temperature of the two parts being joined, thereby reducing the process forces required to make a solid-state weld compared to traditional friction welding. The process applies to Rotary Friction Welding.