Furnace Engineering

Carbon Fibre Composite Curing, Out Of Autoclave Project

The Challenge.

Our customer wanted to make carbon fibre composite aircraft wing components. These were to be heated and cured on a machined metal tool, in an oven rather than the traditional autoclave. While the autoclave operates under pressure which improves heat transfer, they are expensive, both to purchase and to operate.  

The temperature, fast heat up profile and close tolerances were defined by the client: how those were to be achieved was left to Furnace Engineering.

The Furnace Engineering Solution

Since this was new ground for all parties involved, the approach was a collaborative one between the customer, the machine tool provider and Furnace Engineering. The heat transfer requirements were quantified and expectations for the tool design and oven access were adjusted accordingly. CFD (computational fluid dynamics) modelling was a key tool in achieving this.

The key Technical Challenges

The key challenge was to determine the required heat transfer rates to achieve the temperature profile and then accomplish that heat transfer by means of airflow. The limits of practical airflow velocities and pressure then dictated that some changes were necessary to the shape and size of oven, as well as the tooling design, in order to achieve the desired heat transfer rates.  Quantifying the heat transfer from air to part was critical and required theoretical calculations and CFD modelling combined with experience and intuitive engineering. Finalisation of the design was a key milestone for the project, ensuring that equipment could be ordered with confidence.

Outcomes

The ovens’ performance was proven key through testing and importantly this validated the CFD models that had been produced. The first composite curing ovens are still in use and have been followed up by several subsequent orders of repeat ovens of the same fundamental design. This project showed that out-of-autoclave curing of composites is a viable and proven method including applications where materials require a high rate of temperature rise. It also showed that thorough design work prior to orders being placed was justified, and an important tool for mitigation of risk by Furnace Engineering and the tooling supplier