Automated surface inspection of friction stir welds by means of structured light projection

Friction stir welding is an innovative joining technology that is particularly suitable for aluminium alloys. Various studies have shown a significant dependence of the weld seam quality on the welding speed and the rotational speed of the tool. Frequently, an unsuitable setting of these parameters can be detected by visual examination of resulting surface defects, such as increased flash formation, surface galling, or irregular formation of the surface arc texture. The visual inspection for these defects is often conducted manually and is therefore associated with increased costs and personnel effort. In this work, a method to automatically detect irregularities and features on the weld surface is introduced. It is based on a threedimensional shape detection of the surface features using structured light projection. For this purpose, the topography of EN AW-5754-H111 sheets, welded in a butt joint configuration, was measured. The data were evaluated and characteristic key structures of the weld seam surface were derived. It was shown that welding irregularities can be detected automatically by an evaluation of the weld seam topography. The results are the basis for the future development of an inline quality monitoring and parameter control method for friction stir welding. (paper)