Continuous monitoring of tack during AFP production of fiber composites

One of the most important processes for manufacturing components made of fiber-reinforcedplastic (CFRP/GFRP etc.) is Automated Fiber Placement (AFP). In this process, the componentgeometry is created additively, by depositing pre-impregnated tapes in layers on a moldsurface. The control of all process parameters is crucial, since the quality of the laminate has amassive impact on the component‘s operational stability. In addition to the exact placement,the processing temperature, the deposition speed and the compaction of the layers all affectthe quality. An essential feature of process control has so far remained unconsidered: the tack.To date, no technology exists to monitor the tack of the tape online during the depositionprocess. This is necessary, however, because even small changes in temperature, humidity,resin quality and layer thickness dramatically alter the value, and laminar delamination(incomplete bonding) poses enormous risk of structural failure. Quality control is thereforecarried out retrospectively in elaborate tests or qualitatively in preliminary tests withoutreference to the actual conditions at the time of deposition.

At the Chair of Carbon Composites at the Technical University of Munich, a team of scientistsdeveloped an online measuring system that monitors the tack during tape deposition andenables immediate adjustments. It is located inside the depositing head or in the creel. Thetape is applied in a defined way to a rotating steel belt and peeled off for measurement,with the tack being determined by the amount of peeling force measured when the tape isdetached from the steel belt.

• Online detection of defective raw material (tape)

• Optimization of process parameters according to the current tack

• Improvement of the product quality

The proof of concept was successful: a stationary prototype system exists that reliably determines values for the tack. This serves as an excellent basis for transforming the process into a depositing unit.