Ultrasonic-Impregnation for Fiber-Reinforced Thermoplastic Prepreg Production

Abstract

Fiber-reinforced thermoplastics have a high potential for big scale light weight process applications due to low processing times and recyclability. Further advantages are the low emissions during the manufacturing process and beneficial handling and storing properties of the semi finished materials. Thermoplastic composites are made of reinforcement fibers and a thermoplastic polymer matrix by applying two essential sub processes: (1) melting of the matrix-material and (2) impregnating the textile component with molten matrix-material. At present state of art both sub-processes are applied by using double-belt-presses, characterized by high processing temperatures and high processing forces. Therefore, a large amount of energy is needed to create the necessarily high compaction forces and temperatures with hydraulic cylinders and electric heating. Convection, infrared-radiation and the cooling (dynamic) of tempered machine parts leads to a significant dissipation of energy. Especially the process for generating the hydraulic pressure has a low level of efficiency. Therefore, in respect to economic and ecologic reasons, novel energy-efficient impregnation processes need to be investigated and developed. The represented novel impregnation process is based on ultrasonic technology. A stack of polymer film (outer layers) and a textile ply (inner layer) is formed and the energy is applied with an ultrasonic sonotrode. The efficient, fast and strongly concentrated energy application into the thermoplastic films allows the development of novel and highly flexible machine concepts. These can be used for development of small scale up to large scale production processes. The ultrasonic-technology allows a continuous impregnation of the textile component with molten matrix-material. A custom-designed prototype was developed. First material samples were produced and the technological parameters studied. A characterization of the experimental results, material samples, prototype machine and process is the focus of this paper.

Winding process of fibre-reinforced thermoplastic tubes with integrated tape production through in-situ roving impregnation and infrared consolidation

“…A process for impregnating continuous fibres for the production of fibre-reinforced semi-finished products using a sonotrode with ultrasonic vibration is also presented in Fischer [46]. Sockol et al [47] describe the use of ultrasound to melt thin thermoplastic films instead of a melting bath. Further investigation into powder impregnation could also serve as an alternative for the further improvement of impregnation technology.…”

Viscoelastic modelling of fibre-reinforced thermoplastics in hygrothermal circumstances

“…However, European legislation on increased recyclability requirements for newly produced vehicles from 2015 onwards led to the automotive industry investigating the use of thermoplastic matrix systems (European Parliament 2000). Additional merits of using a thermoplastic matrix include better damage tolerance, higher fatigue strength, and mass production capability (Gerstenberger et al 2016;Sockol et al 2017;Yao et al 2018). Furthermore, specific thermoplastic matrix materials are shown to pass through the automotive paint shop without deterioration of relevant mechanical properties (Grätzl et al 2019).…”

Energy Direction in Ultrasonic Impregnation of Continuous Fiber-Reinforced Thermoplastics

“…The approach has been successfully demonstrated for stacks of matrix films and dry fibers without pins by Gomer [18]. Other studies investigating the ultrasonic impregnation of CFRTs investigate continuous [19,20] and discontinuous processes [19]. Despite wide experimental and numerical investigations of different process parameters and material combinations, a deeper analysis of the underlying mechanisms has yet to be conducted, before it can be safely applied to more complex structures featuring pins for direct joining.…”