Tag Archives: composite

Liquid moulding manufacturing- not necessarily OoA

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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.

ALAComposite 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 .

 AUTOCLAVEC-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.

Raw material suppliers outlook a good future for dry composite materials

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Key structural composite components are being manufactured with dry preforms and resin infusion, replacing in many cases the use of prepreg materials for parts manufacturing. In this sense, raw material suppliers play a key role when developing the newest materials to meet the aerospace sector strict quality requirements. What are their thoughts regarding the use of infusion process for the aerospace industry?
We have had a short interview with some experts in the area. Henri Girardy, from Hexcel and Sven Blank, from Saertex have shared their overview about this subject with us.
Thank you Henry and Sven!

Saertex HExcel

1. What are the primary benefits that Infusion offers in aerospace applications, compared with long established prepreg and autoclave curing processes commonly used today? What applications appear to be most promising?

Sven Blank (SB): Multiple layers/orientations in a single fabric can facilitate higher deposition rates resulting in savings of both time and money. Moreover, the use of NCF can eliminate some, if not all debulking processes. In addition, most infusion materials can be stored at ambient temperatures and have extended shelf life (1-2 years) when compared to prepregs. This way, the material handling is simpler and there is no need to chart out time or storage temperature and it is not required to wait until materials come to ambient temperature.
There is no risk of foreign materials to be present in laminates due to use of release paper, etc.

Henry Girardy (HG): Key benefits are cost and production rates. Cost savings have been demonstrated in part design, function integration, less assembly time, and potentially fewer finishing operations.

2. Automation such as AFP has played an important role increasing quality, increasing rate and reducing cost of parts made with prepreg. Are there opportunities to do the same with Infusion processes?

SB: Parts with complicated geometries, thick parts or parts with large surface areas are requiring higher deposition rates. Therefore automated dry fabric deposition technology could be a good option to enhance increasing rate and quality. On the other hand, narrow dry tapes could be used as localized reinforcement of NCF lay ups.

GH: We strongly think that automation of the dry preform is a key success of factor for aerospace structures made by OOA technologies. OEMs and Tier 1s are looking forward for eliminating the costly autoclave curing process.Moreover, as we see it, one of the main reasons why dry materials do not fully meet the mechanical performance requirements for primary structure, is the lack of automation in lay-up process. Therefore, there is a need to automate the process.

3. It is a commonly held perception that infused materials do not provide as good mechanical properties as prepreg/autoclave materials.
a. If true, this means that an Infused part will have a weight penalty?.
b. If false, what can be done to improve the understanding of these materials?

SB: Infused materials could also provide good mechanical properties, but there is some work to be done to improve the understanding of the materials. Such as…
-Educating customers regarding the advantages of NCF and infusion.
-Expand marketing of  infusion materials into aerospace applications
-Publish/present data from controlled experiments comparing infused and prepreg laminates.

GH: The new materials, such as our HiTape® fabric, enables really good properties in vacuum infused parts. Parts up to 30mm thick with a 58 to 60% fibre volume content can be achieved. Infused materials will play a key an important role for next generation aircraft, due to the fact that apart from weight, costs will also drive the material and technology choice.