We are used to hearing about liquid moulding processes linking them with curing steps out of autoclave. However this is not always the case.
While the autoclave is one of the most expensive elements of the production process of big composite parts on the aeronautical sector, and therefore is highly interesting to develop processes that do not need it, this in not the only advantage of liquid moulding.
Among the main advantages, we find the use of dry materials with long shelf life that lowers costs. Furthermore it facilitates working with non crimp fabrics, reinforcements that are making great advances in properties that allow a simplification of the lay up. By liquid moulding it is also easier to manufacture monolitic parts, integral constructions as a single piece, i.e. skins and stringers, avoiding fastening step.
Composite wing
In this sense a very interesting interview was published in the latest edition of Aerospace Manufacturing .
They interviewed Mike Richardson, Bombardier Aerospace, Belfast´s vice president, engineering and business development .
He talks about the experience of Bombardier in the production of the all composite wings of the C-Series. For this purpose the use a patented proprietary process named RTI (Resin Transfer Infusion). The process was created as an alternative to RTM which results in high quality parts but would need two expensive big dimension moulds. The RTI consist in the infusion of very controlled amounts of resin into the dry fiber and an autoclave final curing step .
C-Series wing curing step
Collin Elliot explains that during the development of RTI they could state new advantages of the process that created very consistent parts reducing the gaps that should be filled with shim material, with the introduction of local “intensifiers” during cure, they were even able to completelly eliminate shim in certain areas.
They could also speed up the laying process, in his own words: “For the RTI process, we can use individual plies which are 2,5 to 3 times thicker than those used in traditional prepreg materials because the thickness of a pre-impregnated ply is limited in order to ensure the right resin saturation level. So we need many less individual plies of dry fabric to achieve the right strength and stiffness, thereby significantly reducing the labour content and cycle time”
The next step is to develop an automated lay up process which could also improve the costs associated to very sofisticated ATL/AFP systems.