Producing composites by microwave heating
Heat, ultraviolet light or chemical catalysts are most commonly used for resin polymerisation, also known as curing. However, these methods are either impracticable or require long curing times, thus raising cost and energy consumption. Scientists on the EU-funded 'Microwave assisted curing for carbon fibre reinforced epoxy composites' (WAVECOM) project worked on developing microwave heating techniques to decrease processing time and cost. Focus was laid on selecting suitable susceptor materials to enhance absorption of microwave radiation and therefore reduce resin heating time. Polymer additives, such as dipole organic molecules or nano-structured magnetic materials, were added to the resin. With proper transition temperature values, the modified carbon pre-impregnated with epoxy resin was cured by microwave heating. An important part of the work revolved around investigating the impact of microwave heating on sample properties, including shrinkage and deformation of manufactured parts. To characterise residual stresses and distortion, project partners used fibre Bragg grating sensors. To allow curing complex sample shapes, several microwave antennas were tested, and the microwave curing system was integrated into a six-axis robot. Finally, the project team selected the proper mould materials exhibiting minimum deformation and abrasion wear. The mould was developed through a vacuum-assisted infusion process. Compared to conventional curing treatments, microwave heating reduces processing time by approximately 30 %, and microwave equipment is twice as cheap. Advances in this area are expected to increase EU aerospace industry competitiveness.
Keywords
Carbon fibre-reinforced, epoxy composite, microwave heating, resin, processing time
