Friction-stir-welding:how FSW could help you.SOLUTIONS with Effective, Practical Advice
Friction-stir-welding is a young process that has enjoyed a hefty development from the time it was first conceived at the Welding Institute, UK, less than two decades ago. Some of its most demanding and successful applications were performed on items of aerospace travel hardware, demonstrating its highest reliability. We published a short note on this process in Issue 47 of our Practical Welding Letter for July 2007. Click on PWL#047 to see it. Although it is considered a variant of well known Friction Welding Processes it seems to share only part of its name with the older versions, being effectively a new and different process.
At the heart of Friction-stir-welding is a special rotating tool, not exactly non-consumable (except when used to weld soft materials) but built to last for a few welds at least, depending on the base metal. The weld tool has the task of penetrating the joint and of generating heat by its rotary motion, thus transforming a mass of material into plastic state. The displaced hot worked material gathers in the space behind the tool that moves along the joint leaving in its wake a continuous weld. Two elements are critical in the welding tool: the pin or probe whose shape is optimized to stir the material, and a shoulder or disk that contains the worked material within the joint. In the most common configuration two plates, presenting a butt joint without gap (or up to 10% the thickness at most), are firmly clamped on a machine base, similar to certain milling machines. As the base material is not melted, Friction-stir-welding is a solid state machine process producing high quality welds with minimum operator's influence. Aluminum alloys, even those not weldable by fusion processes, are readily Friction-stir welded, resulting in high mechanical properties in the joints. Because of its limited heat input, Friction-stir-welding produces minimum distortions and leaves much lower residual stresses. Its elevate welding speed contributes to the economics of production, even if the initial investment in equipment and tooling is considerable. Although a number of possible weld discontinuities have been described, well developed processes are usually free from defects, notably from those being caused during solidification in fusion processes. Energy efficiency is high and environmental impact is minimal. Different materials have been successfully welded like Aluminum, Magnesium, Copper, Titanium, Nickel, Steel and Stainless Steel. The Friction-stir weldability or ease of welding these materials closely parallels their suitability to being extruded. Therefore Aluminum and Magnesium are most easily welded, Copper is more difficult to process as its hot working temperature is higher, while the rest of the above mentioned material are definitely more difficult to FS (Friction-stir) weld. Several variants of basic Friction-stir-welding have been proposed and tested for specific applications as documented in investigation reports. The following TWI publications are proposed for further reading. FSW Process Variants and Mechanical Properties FSW Process Variants and Developments in the Automotive Industry Application of Friction Stir Welding in the Shipbuilding Industry
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