In Stationary shoulder friction stir welding (SSFSW) the probe rotates and protrudes through a hole in a stationary shoulder/slide component. The stationary shoulder adds no heat to the surface so all of the heat is provided by the probe and the weld is made with an essentially linear heat input profile. The key welding mechanism consists of a rotating pin running through a non-rotating shoulder component, which slides over the surface of the material during welding. The weld surface is very smooth, almost polished, with no or minimal reduction in cross-section.
Using the SSFSW technique on a robot can reduce issues associated with controlling the depth of the tool during welding. The robot structure is prone to deflection as it holds the FSW tool on the material’s weld line, meaning changes in the material’s softness and subsequent resistance can alter the depth at which the tool operates, producing flaws and defects.