Friction Stir Welding is a not so new, but innovative welding process that is gaining traction in a number of industries. It was developed in 1991, at The Welding Institute of Cambridge, and was originally designed to seal copper canisters of nuclear waste. The NRC requires that nuclear waste containment vessels provide a corrosion-resistant barrier for at least 100,000 years. Though this sounds like a great way to get rid of my wife’s tuna casserole, it sounds a little extreme for, say, pipe welding. However, if you take a closer look, the reasons for its growing popularity become obvious. Friction Stir Welding does exactly what its name implies; the material to be welded is heated through friction and stirred. In the case of the copper vessels, FSW creates more than just a fused joint: after welding, the vessel is in effect a single piece.To understand the benefits of this unique process, let’s look at how it works. Unlike standard welding, FSW does not require an electrical current to bring the metal into a molten state; FSW relies on the heat of friction to bond metals. This method of stirring also makes it ideal for welding dissimilar metals such as steel to aluminum, and a wide range of dissimilar alloys. Parts are welded through a solid-state thermo-mechanical joining process which is a combination of extruding and forging. The tool which is cylindrical in shape with a shoulder features a profiled probe that is rotated and plunged into the material. Frictional heat is generated between the tool shoulder and the material, causing the material to soften; this allows the tool to traverse the joint line. The rotational speed of the probe, in combination with the liner speed across the surface, is determined by material type. As you can imagine, the tooling has to be composed of a super hard material. Modern tooling used in FSW applications is composed of PCBN (polycrystalline cubic boron nitride) for the probe, and tungsten carbide for the shoulder. This extremely hard, thermally stable material provides long tool life, which further enhances the benefits of FSW.
The number of OEMs providing these systems is growing at a rapid pace. With the integration of automation, FSW is reaching beyond the exotic and is becoming a mainstay in industries such as aerospace, automotive, oil & gas, and many more. The list of advantages that make FSW attractive is long. Weld consistency is provided by the fact that welding temperature is measured using a thermocouple inside the tool probe. In addition, there are no consumables such as welding wire, welding rods, or shielding gas; a certified welder is unnecessary, and finished joints require no grinding, brushing, or pickling. For mass production, this is a win-win scenario that is hard to ignore.
I’m not getting rid of my old Lincoln 225 yet, but it is safe to assume that Friction Stir Welding will be making an impact on the welding industry for a long time to come.
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