Abstract: In resistance spot welding, weld quality is influenced by many factors, which are coupled to each other and at the same time, behave different features. With a test system developed in this project, the features of these influencing factors can be drawn and analyzed based on the data acquired during welding. An online aluminum spot weld quality monitoring system is created based on fuzzy logic. This system is useful in evaluating nugget sizes and proposing possible causes for the variation in nugget sizes. In case of expulsion, the system can also detect the strength of expulsion, the time at which the expulsion occurs, and the possible causes for it.