What Is Friction Stir Welding and How Have Spacex Embraced It?

Marta Danylenko
on April 18, 2018

Friction Stir Welding (FSW) is a process of solid-state joining of two metals with a rotating tool (without melting the workpiece material). Friction Stir Welding uses friction, just like you when rub your hands together on a cold day to warm them.

Here’s an example of how it works: two aluminium alloy plates clamped together tightly in a machine. A metal tool resembling a drill bit is inserted in between the plates. The tool spins as it travels along both edges.

The friction created by the spinning tool heats the atoms in the solid metal, making them move around (or diffuse). The metals become deformed and atoms from both plates are bonded together, without any melting. In a matter of minutes, the aluminium plates have been welded together and are cool enough to touch. The bond created by Friction Stir Welding is almost perfectly smooth and as strong as original aluminium plates.

Friction between the tool and the work piece creates the heat, which then allows the material to become softer and become more plastic. So, the plasticized material moves around.

Rajiv Mishra, University of North Texas

In recent years, the field of engineering has experienced a wide variety of innovations that have led to novel manufacturing methods that are much more efficient regarding energy consumption and performance than conventional means.

Friction Stir Welding 20mm Copper DHP using MegaStir designed pin tool (Densimet). 250 RPM traveling at 6 ipm.

Arguably, the professionals most affected by such developments are design engineers; the very people who are responsible for the design and fabrication of every complex device and structure we see and use in our daily lives.

With design engineers always deeply concerned about the optimal utilisation of material and financial resources, and the overall quality of their inventions, such engineering innovations are always just around the corner.

This means that professional engineers continuously need to update themselves regarding recent developments in their field, in order to achieve perfection in their projects and stay up to the mark.

This article explores a mechanical welding technique that has gained significant popularity in modern times and discusses how engineers at Elon Musk’s aerospace manufacturing company, SpaceX, have put it to use in their recently launched Falcon Heavy rocket.

friction stir welding SpaceX falcon Heavy

How does friction stir welding work?

Friction Stir Welding (FSW) is a welding technique developed by The Welding Institute Ltd. back in 1991. Although it was invented more than 25 years ago, it has seen a swift rise in demand in the last few years, particularly owing to the increased demand of higher strength and durability requirements in modern engineering applications.

It boasts a distinct method of fusing metals into each other which is significantly different from traditional techniques such as arc welding or gas welding. Its uniqueness lies in the fact that it is a solid-state welding method, which means that neither of the materials being joined together are melted.

FSW is a solid-state process which produces welds of high quality in difficult-to-weld materials such as aluminium, and is fast becoming the process of choice for manufacturing lightweight transport structures such as boats, trains and aeroplanes.

Instead, they are merely softened to the point where they can penetrate each other’s surface with a little assistance. This technique yields extraordinary mechanical properties like fatigue strength and stiffness, and minimal defects in the weld region.

Moreover, this welding method also involves less wastage of material and a better appearance, which means lower surface finishing requirements. Finally, one of the most praised advantages is that it has no adverse effects on the environment, as no toxic fumes are produced in the whole process.

How is friction stir welding performed?

FSW is performed with the help of:

  • a profiled welding tool
  • a clamp to hold the workpieces together
  • a mechanical setup to guide the tool along the joint line.

These components work in conjunction with each other to create the weld joint.

The tool is quite similar to a milling cutter in shape, which rotates throughout the machining process and is movable along the workpiece surface. The tool is practically pushed into the joint line surface initially and then traversed along the joint line periphery by the welding machine. The friction between this non-wear tool and the workpiece produces heat, raising the temperatures of the metals in the vicinity of the joint line.

A profiled probe placed at the very end of the tool is shaped in a way that it forces metals on both sides of the joint line into each other. Since they have been softened considerably due to the heat generated in the process at this point, they merge easily.

Friction Stir Welding and SpaceX’s Falcon Heavy

Owing to the superior qualities of this technique, it has particular relevance in applications requiring high strength properties and intense working conditions. The aerospace industry is one such example, with modern space vehicles being built to withstand unfathomable forces and temperatures.

SpaceX, the aerospace manufacturing company headed up by Elon Musk, has recently launched its Falcon Heavy rocket into space with a Tesla Roadster as the payload. This rocket is the fourth-highest of all rockets built up until now in terms of load-carrying capacity, and it featured the use of friction stir welding. This fact highlights FSW’s importance in the aerospace industry and its possible usage in future engineering applications.

Design engineers at SpaceX used FSW to join the break-off fuel tanks of their rocket, which play a crucial role in the propelling of the spacecraft once it is in space and settled in its orbit. The reason for this application was obviously the need of exceptional strength in break-off fuel tanks of a rocket this powerful, which cannot be met by conventional means such as liquid-state welding or non-permanent joints like rivets.

friction stir welding SpaceX Elon Musk Falcon Heavy

Final Thoughts

Summing up everything discussed above, it is safe to say that the future of welding lies in the use of novel techniques like FSW that are more efficient, less costly, and environmentally friendly. It is a prime choice for design engineers who are looking for permanent joining techniques with results better than the ones being used currently.


  • Paul Cheng
    Paul Cheng
    Apr 28th 2020 at 7:30 pm

    We can Weld in Space? Yes! A superior alternative to high energy and FWS. New science but rock solid. Flawless, no Heat Affected Zone. Fine Grained from base, transition to fusion area.
    I posted a sincere offer to Mr. Elon Musk on sme.org. I would like to offer one valid USPTO patent on advance manufacturing in Space towards his mission to Mars for his autograph.
    My quest to the scientific community is that we can perform Solid State Fusion weld on the Space Station safely. Experiment can be self contained, the size of a bread box requiring electricity. No gas, no fumes, no spark. And no BS.
    Once proven, we can plan on welded structures in Space, on Mars and beyond.

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