Laser-based Automated Fiber Placement (AFP) enables the in-situ production of fiber composite structures when using thermoplastic matrix materials, eliminating the need for an energy-intensive autoclave process. In addition, there are further advantages due to improved recyclability and material bonding techniques. The challenge, however, is to achieve mechanical properties equivalent to the autoclave process. The joining strength is set by thermal-mechanical process control, which ideally is based on knowledge of the thermal-mechanical conditions in the joining zone. The interlaminar strengths can then be predicted using known models so that time-consuming and cost-intensive test methods can be minimized and, if necessary, quality can be improved during the process. One problem here is the in-process recording of the temperature history in the joining zone. While the temperature before and after the joining zone can be recorded using IR thermography, for example, the joining zone is concealed by the consolidation roller. Thermocouples or fiber optic sensors inserted into the laminate measure the temperature only selectively and are used exclusively for model validation, although they also act as interference points and therefore overestimate or underestimate the temperature. Accordingly, there is currently no method of obtaining empirical knowledge about the temperature history within the joining zone in the continuous AFP process. For this reason, a new measuring method was designed at the Institute of Production Engineering and Machine Tools (IFW) in which the consolidation roller is equipped with fiber optic Rayleigh sensors. This creates a strain-sensitive lateral surface that is in continuous contact with the joining zone and thus enables the recording of thermal-mechanical conditions.
The aim of this project is therefore to investigate the thermal-mechanical sensitivity of the Rayleigh sensors, which are embedded in a form-adaptive consolidation roll typical of AFP, and thus to enable the measurement method for temperature detection in laser-based AFP. For this purpose, experimental studies on fiber embedding and the resulting thermal and mechanical sensitivities will be carried out. The findings are used to compensate for mechanical and thermal disturbances so that the remaining strains are available as process-induced thermal strains. In further investigations, a model-based method for calibrating the sensitive consolidation roller will be developed by correlating the thermal strains with the temperature curves. The combination of disturbance compensation with model-based calibration should enable temperature detection in a continuous, roller-based manufacturing process, such as laser-based AFP.
Contact information:
For further information, please contact Dr.-Ing. Carsten Schmidt, Institute of Production Engineering and Machine Tools at Leibniz Universität Hannover, on +49 4141 77638 11 or by e-mail (schmidt_c@ifw.uni-hannover.de).
