Two laser welding cases and suitable documentation methods

Sammanfattning: The thesis is about laser welding, in particular about geometrical defects, but it also addresses how to improve the documentation of the findings. Laser welding is an important and highly advanced manufacturing technique in industry. An emerging option is laser hybrid arc welding. In welding, control over the quality is essential, particularly to suppress defects and unfavourable surface geometries. The mechanical behaviour of a product in service can even suffer from small, hardly visible welding defects like undercuts. The process causing the quality involves complex multi-physics and is nonlinear. The documentation of parameters, process conditions and of the resulting quality is difficult and unsatisfactory so far. Therefore Paper 1 addresses the mechanisms and challenges for the documentation of laser welding knowledge. According to the knowledge lifecycle theory, these difficulties not only address how welding knowledge is generated, identified, captured and stored, but also how it is accessed, shared and eventually used. In Paper 2 the geometry resulting from fibre laser welding of a corner joint, including defects like undercuts, is studied for varying parameters. The results are categorized and mapped. Then they are documented by a new method, the Matrix Flow Chart, MFC, as an attempt to improve knowledge formalizing, storing and access, which is also discussed in Paper 1. In Paper 3 and 4 two different kinds of undercuts, caused by different metal surface conditions during the laser hybrid arc welding process, are investigated by visual analysis, SEM, chemical analysis and high speed imaging. In Paper 3 the observed findings are documented in common letter journal format as an extremely brief type of documentation. In Paper 4 the physical mechanisms of the welding process causing the two types of undercuts are explained in regular manuscript format. Here a sequential flow chart turned out to be suitable for documentation of the findings.