JEC COMPOSITES MAGAZINE - Issue #47 - March/April 2009 - 40

FEATURE “Automation” industrial requirements to exceed component quality. Therefore, the Fraunhofer IPT is currently focusing on even more complex tape-laying processes, with the aim to create geometricallycomplex structural components with thermoplastic prepregs meeting the highest standards and offering the excellent mechanical characteristics of the tape. g…/… Laser-assisted thermoplastic tape-laying systems can usually better absorb this type of load through their essentially higher energy absorption capacity, thereby contributing to sustainably higher safety characteristics. In addition, elongation crystallisation processes appear when moulding thermoplastics, e.g. through damage. These processes cause the material to solidify and locally increase component strength. At the end of their service life, thermoplastics can be reused and recycled, which is becoming a major advantage in environmental terms. In addition to short cycle times, thermoplastic matrix systems therefore promise good recyclability, low production costs and excellent material characteristics, a pre-requisite for industrial uses. Process Thermoplastics need to be heated to their fusion temperature in order to be processed. Various heating principles have been investigated in recent years, such as the use of hot gas, infrared radiation or microwaves. Fostered by the rapid development of high-performance lasers, these have excellent characteristics as heat sources for thermoplastic fibre placement. Very short heating times, combined with rapid controllability and even distribution of intensity over a defined heating area, produce hitherto unknown production quality and optimum material performance. With the laser-assisted tape-laying unit, thermoplastic fibre-reinforced plastics tapes are placed as layers on a mould to create a component. The tapes to be laid and those already laid are melted in situ on their under and upper side using a laser beam, placed next to one another with no gaps and pressed together with a roller to consolidate the component construction. Laser-assisted production of thermoplastic tapes The high potential of thermoplastics has resulted in intensified efforts to create new production processes. The Fraunhofer IPT, under various industrial and public projects such as the “3DThermoLay” joint project, has developed an automatic, flexible production process for the manufacture of fibre-reinforced thermoplastic structural components. The aim is to make this new production process capable of mass producing anything, from geometrically-simple components to highly complex, loadbearing components with load-optimised fibre orientation. To prepare the tapes, the Fraunhofer IPT uses a specially developed tape-laying unit which has the features required for production. The end-effector is a robot system that produces the movement tracks for the tape system, which deposits the tapes at the required speed and rolls them off the reels. Here, continuous fibre-reinforced thermoplastic tapes are deposited in the moulding tools. These tapes have a rectangular cross-section and consist of reinforcing fibres, such as carbon fibres, embedded in a thermoplastic plastic matrix system. The plastic fixes the individual fibres, which are uni-directionally embedded in the matrix and are rolled onto tape reels according to their breadth. Compared with the thermoset tape systems, thermoplastic tapes provide excellent production characteristics due to their fusion point and thereby offer a large reservoir for further, hitherto undeveloped, areas of use. The Fraunhofer IPT has undertaken the task of developing these production processes, up to and including suitability for mass production. Over the past few years, new developments in laser-assisted tape winding processes have allowed the Fig. 2: Process diagram for a laser-assisted tape-laying process. Following the laying process, the structure can be removed directly from the mould and further processed. To produce a component with a certain wall strength, a number of tape layers must be applied. Since the fibre angle of the individual tape layers can be individually set, the component can be tailored and optimised to the specific application and load. The component’s performance depends on the quality of the materials produced, how accurately the tape is applied and the consolidation temperature of the tapes. Following the local melting of the polymer and continuation of the tape laying process, the molten area solidifies when the outside temperature cools down. Additional energy is added in Fig. 1: Compact tape-winding unit for laser-assisted winding of tubular thermoplastic lightweight components. 40 jec composites magazine / No47 March-April 2009

JEC COMPOSITES MAGAZINE - Issue #47 - March/April 2009

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