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HEPHAISTOS - A novel 2.45 GHz Microwave System for Aerospace Composite Fabrication
| Content Provider | Semantic Scholar |
|---|---|
| Author | Feher, Lambert Dr. Flach, Artur Nuss, Volker Pozzo, Paolo Seitz, Tanja |
| Copyright Year | 2003 |
| Abstract | A novel industrial microwave system for automated processing of carbon fibre reinforced plastics has been developed and tested for commercial use [1]. Composites for aerospace applications in prepreg and wet technology have been successfully fabricated and investigated for quality and certification issues. The use of microwaves shows new approaches on the process interaction for the fibre materials, precursors, resin systems, lay-up preparation etc. with direct consequences on the adjustable material properties to set new standards. The development has been assisted by extensive numerical simulations. Introduction Due to a strong decreasing price of carbon fibres in the next future, the potential use of carbon fibre reinforced plastics is significantly increasing. A specific bottleneck for wide spread application is the price/kg in comparison to aluminium, which is not yet competitive due to high fabrication costs (material costs just about 30% of the actual end price). The highest potential on cost reduction is carried by the manufacturing process which implies substantial long time and high energy consumption, as well as a low degree of automation. The HEPHAISTOS-System The developed microwave pilot system is named after Hephaistos, who is the builder and craftsman for the Greek gods, being also responsible since the past for oven and transportation technologies. The name HEPHAISTOS (High Electromagnetic Power Heating Autoclave InSeT Oven System) stands as well for the technological concept of this microwave approach. The current system integrates advantageously the basic processing steps as tooling, tempering of the resin and lay up, the impregnation of the fibres, pre-forming techniques as well as finally the process curing of the high performance laminate. Fig.l: Hephaistos (Greek God), painting ca. 525 BC. He is also known as Hephaestus and Vulcan (Roman). The most notable effect processing CFRP materials with microwaves is their volumetric heating, offering the opportunity of very high heating rates. In comparison to conventional heating where the heat transfer is diffusive and depends on the thermal conductivity of the material, the microwave field penetrates the material and acts as an instantaneous heat source at each point of the sample. The CFRP can be selectively heated, keeping the oven environment cool. Spatial temperature homogeneity is crucial for qualified material properties. The samples must be exposed therefore to excellent homogeneous field distributions. This is essential, as the carbon fibres imply a very high microwave reflectivity and the tendency for arcing and breakdowns at loose ends in areas of inhomogeneous microwave patterns. This problem is very severe and one of the major phenomena, that made microwaves not applicable yet for CFRP processing. A specific multimode applicator development aims to tackle these problems. Monomode applicators involve only controllable field properties in small specific applicator regions, whereas multimode ovens promise, especially for frequencies higher than 2.45 GHz, the possibility for low field fluctuations in larger regions. Simulations and experiments have shown, that achieving high quality homogeneous field distributions over most of an applicator volume is not trivial, even at frequencies in the millimetre-wave regime (30 GHz) [2]. An industrial microwave oven for production needs is successfully designed, if the available processing volume containing uniform field properties is about the size of the whole cavity and reflections are minimized. Conceptions of novel millimetre-wave technology have been transferred by DELFI simulations to 2.45 GHz technology to realize these demands by providing a large part capability for CFRP processing. The main hardware contribution of the system development is realized for a specific modular applicator containment providing an excellent homogeneous electromagnetic field distribution. The fabrication process can be performed pressurized up to 5 bar or at standard conditions. The processes are measured remotely by infrared sensors or shielded low-cost thermocouples. Fig. 2: Process setup: 1 bar vacuum bagged prepreg plate (left) and homogeneously cured sample after the process (HEPHAISTOS-BA System). CFRP can be distinguished generally in duroplastics and thermoplastics depending on the choice of matrix material, which is used in advanced composites to interconnect the fibrous reinforcements. They are as varied as the reinforcements. Today, epoxy resin is the primary thermoset composite matrix for airframe and aerospace applications. The HEPHAISTOS technology could successfully demonstrate that all commercial resin and fibre systems can be used. The most commonly used materials for industrial composite fabrication are prepreg materials, due to their easy handling and storing issues. The fibres here are impregnated with resin compositions. Of all the heating systems the autoclave is today the most popular system for this composite field, as prepregs usually need a high pressure environment along the curing process for forming. Concerns on this state of the art approach are [3] • Long process times • Inherently energy inefficient system • Major difficulties caused by large thermal gradients and slow heat up times |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://bibliothek.fzk.de/zb/veroeff/55640.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
