How is the background technology?

 

In the surface transport sector, advanced composite materials are now commonplace owing to their enhanced specific-strength (high strength/low weight) compared to traditional materials. Modern aircraft such as the Airbus A380 are comprised of thousands of advanced composite parts and can demonstrate much improved fuel efficiency when compared to earlier crafts. However, such composite components are expensive to produce owing to the cost of raw materials and the processing methods used in the sector. This is not a particular limitation in aerospace where higher costs can be accepted in return for enhanced performance. Some automotive components have been produced in composites, as seen in Figure 1. However, the relatively high cost of processing is a substantial limitation on the wider introduction of composite parts in sectors such as automotive, where manufacturing costs are a key issue.In sectors such as transport, increased specific-strength is highly desirable to improve payload or fuel efficiency. With the advent of low-carbon road transport such as BEV (battery-electric vehicles) or HEV (hybrid-electric vehicles), reduced weight is critical to increase the vehicle’s range between battery charging periods. For fossil fuelled cars, reduced vehicle weight will reduce the overall emissions of the vehicle per km of travel. Also in other surface transport sectors, weight-saving is always a desirable end-goal. The cost of conventional processed composites has been the major factor which has restricted the rapid uptake of composites. By their very nature composites can be complicated requiring more complex and time-consuming fabrication methods, adding cost to the final product, and in sectors such as automotive, often this cannot be justified.

Processing methods for producing polymer composite parts involve the application of heat to the material by a number of means, depending on the manufacturing process. Common methods are electrical heating of the polymer; heating of the tool and composite in an oven (pressurised/non-pressurised); electrical heating of mould/platens, and induction heating of mould.

The majority of these processes introduce the heat to the component gradually by heat conduction/convection through a mould, making the process time long and hence inefficient and costly. The proposed Mu-Tool microwave processing approach is fundamentally different in that it involves the direct heating of the component rapidly and uniformly, and in this concept specifically, only at the mould surface.

The Mu-Tool process is unique and a step change in current heating processes, in that the mould is developed to heat selectively when exposed to microwave radiation. A thin and low mass ‘microwave absorbing layer’, forming the mould surface, supported by a microwave transparent ceramic backing will heat rapidly and conduct that heat to the composite component, resulting in a more rapid heating and efficient processing. Consequently, upon removal of the microwave power, the low thermal mass of the absorbing layer allows the mould surface to cool rapidly, increasing the productivity of the moulding process. Upon completion of the process, the ceramic tooling and the microwave chamber will remain relatively cool, such that the work-piece can be extracted from the chamber rapidly, and the process can be repeated. The time and energy consumed for heating will be reduced. It is estimated that:

A typical component presently requiring 90 minutes processing time, could be cured in 45 minutes by this method – by purely removing the time required for the chamber and tool to heat/cool and some level of process optimisation.

The amount of process energy required could be reduced (the estimate is a 90% reduction).

Based on the Specific Energy Consumption for RTM2 of 12.1MJ/kg, a 90% energy saving in mould heating is predicted, resulting in an overall process energy saving of 33%).