Process optimization: Semi-finished products for large-area fiber reinforced composite components

The availability of different fiber-based reinforcing structures and a large selection of polymer matrices in combination results in a variety of materials that is attracting more and more industries to their potential.  The high specific strength and stiffness is used to replace existing components with corresponding FRPC structures in order to obtain weight-optimized components with at least equal mechanical characteristics. One of the central topics in the establishment of FRPC structures is the development of efficient manufacturing processes.

While FRPCs based on thermosetting polymers are already established, there have been increasing efforts in recent years to promote the use of thermoplastic FRPC. The reason for this lies in the advantages of thermoplastic polymers: due to their polymer structure, they can be melted and solidified repeatedly, which in turn establishes the possibility of changing the geometric shape in both: primary forming and semi-finished product based thermoforming processes. In addition, thermoplastic components can be joined together by means of different welding processes, but also in the course of hybridization with other materials such as metals.

Fully impregnated, consolidated and continuously fiber-reinforced semi-finished products in the form of organic sheets provide an ideal basis for the manufacture of mechanically efficient lightweight components from FRCP. In the thermoforming process, flat semi-finished products can be shaped into complex geometries within short cycle times. In combination with established processing methods for thermoplastics, such as injection molding or extrusion, the spectrum of components is further expanded. The dimensions of the producible components however, depend on the available size of corresponding semi-finished products. With regard to the mechanical properties, it is important to maintain the continuous fiber structure in the component (the fiber length corresponds to the geometric dimensions of the component). For this reason, several small semi-finished products cannot be combined for large components. The required organic sheet dimension must at least correspond to the components total surface area. Thus, the maximum component size that can be produced is directly dependent on the dimensions of semi-finished products available on the market.

An economically and technically efficient process for the production of organic sheets is the continuous compression molding technology (CCM) [1]. While the current state of the art allows a sheet width of approx. 1 m, the market is experiencing an increasing demand for even larger semi-finished products due to the demand for larger FRCP components. The challenge in the production of wide laminates is the impregnation of fiber strands lying transversely to the process direction with the viscous polymer melt. The impregnation of fibers - oriented in process direction (0° direction) - is sufficiently achieved by current CCM technology. In order to produce a completely impregnated and high-quality semi-finished product, the rapid displacement of enclosed air from the layer structure to the open tool edges must be ensured. To achieve this, a combination of an inhomogeneous process temperature over the tool width at constant process pressure was selected. This procedure is intended to achieve a rapid impregnation of the reinforcement structure in the laminate center, which simultaneously leads to a corresponding displacement of enclosed air. For this purpose, IVW, together with its partners Teubert Maschinenbau GmbH and Neue Materialien Fürth GmbH, is developing an innovative CCM tool technology for the production of 50" organic sheets as part of the ZIM project „IMAPRESS“.

For this project, IVW will first examine the prevailing process conditions of current CCM technology using appropriate measurement technology. Based on process modeling, geometric specifications for pressing tools are derived, which enable an optimized impregnation process. At the same time, a concept for process monitoring and control is developed, which later provides the basis for integration into the current system technology and ensures the necessary process control. The combination of optimized tool geometry and smart control should finally result in the possibility to influence the impregnation process, which leads to a significantly higher impregnation performance as well as high efficiency and semi-finished product quality.

Further information:

Andreas Krämer, M.Sc.
Manufacturing Science
Institut für Verbundwerkstoffe GmbH
Erwin-Schrödinger-Str. 58
67663 Kaiserslautern
Phone: +49 631 2017 441
E-Mail: andreas.kraemer@ivw.uni-kl.de

_{[1] Christmann, M.: Optimierung der Organoblechherstellung durch 2D-Imprägnierung. IVW Schriftenreihe Band 114, Kaiserslautern: IVW GmbH, 2014.}