The increasing industrial demand for lighter, more complex and multi-material components supports the development of novel joining processes with increased automation and process control. Friction stir welding (FSW) is such a process and has seen a fast development in several industries. This welding technique gives the opportunity of automation and online feedback control, allowing automatic adaptation to environmental and geometrical variations of the component. Weld temperature is related to the weld quality and therefore proposed to be used for feedback control. For this purpose, accurate temperature measurements are required. This paper presents an overview of temperature measurement methods applied to the FSW process. Three methods were evaluated in this work: thermocouples embedded in the tool, thermocouples embedded in the workpiece and the tool-workpiece thermocouple (TWT) method. The results show that TWT is an accurate and fast method suitable for feedback control of FSW.

Friction stir welding is an emergent technique that still lacks optimization studies in the literature. Optimum parameters are of prime importance for future investigations, as it will allow for consistent and sound welds. This is of even greater relevance for industrial applications, as for friction stir welding to become a mainstream joining technology. This paper presents an optimization study of friction stir welded butt joints through the Taguchi method. The most influent welding parameters and their trends were identified. The process optimization for the selected aluminium alloy was achieved and the best parameters combination to accomplished quality welds was selected. The parameters combination that lead to higher mechanical stiffness were: 1000 min–1, 290 mm/min, 0.15 mm from the probe to the root surface and a shoulder/probe diameters ratio of 2 (shoulder diameter of 12 mm). Equations to estimate joint properties were derived by multiregression.