In Wire and Arc Additive Manufacturing (WAAM) and fusion welding, various defects such as porosity, cracks, deformation and lack of fusion can occur during the fabrication process. These have a strong impact on the mechanical properties and can also lead to failure of the manufactured parts during service. These defects can be recognized using non-destructive testing (NDT) methods so that the examined workpiece is not harmed. This paper provides a comprehensive overview of various NDT techniques for WAAM and fusion welding, including laser-ultrasonic, acoustic emission with an airborne optical microphone, optical emission spectroscopy, laser-induced breakdown spectroscopy, laser opto-ultrasonic dual detection, thermography and also in-process defect detection via weld current monitoring with an oscilloscope. In addition, the novel research conducted, its operating principle and the equipment required to perform these techniques are presented. The minimum defect size that can be identified via NDT methods has been obtained from previous academic research or from tests carried out by companies. The use of these techniques in WAAM and fusion welding applications makes it possible to detect defects and to take a step towards the production of high-quality final components.

The challenge of planning and controlling the production of one-off manufacturing companies, especially small and medium-sized enterprises (SMEs), is high and requires a high level of experience to be able to plan the individual work steps accurately. If the planning is wrong or a machine breaks down, a delayed reaction can lead to delivery problems in time and thus cause additional costs. For this reason, a systematic literature review examines how individual manufacturers and producing SMEs can track work steps and what technologies exist to implement intelligent progress tracking in a company with variable and partly volatile work content and quantities. For this purpose, general problems are summarized and new machine vision technologies from the assembly and construction industries are compiled so that a broad overview can be created here. Finally, based on the literature, implementation opportunities are presented, and further research gaps are identified.