For gas metal arc welding a vision system was developed, which was robust to monitor the position of the arc. The monitoring documents the welding quality indirectly and a closed loop fuzzy control was implemented to control an even excess penetration. For welding experiments on a butt-joint with a V-groove with varying root gapthe system demonstrated increased welding quality compared to the system with no control. The system was implemented with a low cost vision system, which makes the system interesting to apply in industrial welding automation systems. Index Terms-Gas metal arc welding, fuzzy control, closed loop control, welding documentation, vision, automation Morten Kristiansenis associate professor in the Department of Mechanical and Manufacturing Engineering, Aalborg University, Denmark, where he is teaching and researching in the area of manufacturing technology, robotics and process automation. Currently his research is in automation and modeling of the laser cutting and welding process. Previously Morten Kristiansen has worked at Aalborg University and received in 2007 his Ph.D. degree, in the field of modeling of the welding process using different knowledge sources and artificial intelligence.