A new spin on welding inspection
FSW is a solid-state technique. The frictional heat of an FSW tool rotating between the two pieces to be joined softens the materials. Precisely controlled forging pressure is also applied by the tool as it passes to produce high-integrity welded joints at temperatures below the melting point. Despite its economic, environmental and technical advantages, FSW’s full potential has not been realised as no reliable quality inspection system exists. Faulty welds, although rare, affect the performance and safety of welded parts. An unprecedented real-time FSW laser-ultrasound inspection system with a user-friendly interface promises to enhance penetration in existing markets and open new ones. EU-funding of the project 'Development of an in-process quality assurance system for friction stir welding' (SIGNASTIR) brought the concept out of the lab and into the production environment. The SIGNASTIR system is mounted on the trailing side of the welding tool to have optical access to the newly formed weld as the tool moves along its path. Using a holistic weld signature created from a database of weld parameters, the non-contact technology assesses the quality of the weld. It is designed to detect and report the presence and location of defects. A modified lab prototype was also able to detect the size of voids of interest to industrial FSW users. Scientists are currently optimising the SIGNASTIR system based on outcomes of trials in a real production environment. The technology promises to boost the competitive position of the numerous small- and medium-sized enterprises active in the FSW sector. Commercial implementation will not only enhance the quality of welds and boost confidence in the technique but also decrease expensive off-line inspection, scrap and re-work rates.
Keywords
Friction stir welding, in-line, quality, inspection, laser ultrasound, weld signature, prototype