Microwave curing of composite structures at HEPHAISTOS Experimental Centre (HEC)

The use of microwave heating and processing in the composite field shows new approaches on the process interaction, e.g. for the fibre materials, precursors, resin systems, lay-up preparation with direct consequences on the adjustable material properties. Carbon fibre reinforced plastics (CFRP) materials can be heated volumetrically with microwaves, offering the opportunity of very high heating rates and improved mechanical performance. 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 volumetric point of the structure. The HEPHAISTOS microwave systems have been the first overmoded resonators to be designed on a modular hexagonal applicator concept originally at 30 GHz. This concept for obtaining highly homogeneous fields was refined by simulations and industrialized in 2002 from mm-wave technology to a highly energy efficient industrial microwave technology at 2.45 GHz to meet low component costs. The technology has been patented world-wide and licensed by Forschungszentrum Karlsruhe to the company of Votsch, Reiskirchen in Germany. Several HEPHAISTOS systems have been built since 2005 and successfully tested in-house Forschungszentrum Karlsruhe or at the applicant site. The technology offers a maximum effort using autoclave-less fabricating methods which are currently under development in the aviation and supplier industry. In December 2007 the HEPHAISTOS Experimental Centre (HEC) has been opened up to demonstrate and test the technology for interested companies. As well the development for continuous HEPHAISTOS systems will be worked out as the HEPHAISTOS-CA3 system, being currently the largest microwave chamber system in the world (70001 volume) is equipped first time with a throughput capability. Process developments for CFRP structures and other application are continuously proceeding.