Future single-aisle commercial aircrafts are considered to be produced of advanced thermoplastic composites. To this end flexible yet fully-automated production technologies are required in order to assure quick ramp-up, high production rates but also customization of high quality parts. At the Center for Lightweight Production Technology (ZLP) fully-automated patch-preforming has been established for individualized lay-up of variable ply books, such as of a fuselage skin. Ultrasonic spot welding is used to weld each cutpiece to the subjacent stack. In this study, we shall describe the routine for weld parameter determination and monitoring. In-line quality assurance to minimize production variabilities along the process chain is a self-evident requirement that is pursued in a consequent manner.