Tag Archives: NCF

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.

Why the use of NCF is growing in complex structural components

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NCFs are a type of “engineered fabrics” to reinforce polimeric composites that are made up of multiple layers or fibers stitched together. The most used NCF’s are biaxial, triaxial and cuadriaxial fabrics, where the fiber tows are straight and with different orientations (0, 45, 90 degrees) to provide multidirectional properties.

Non  Crimp FabricImage: Non Crimp Fabric

The combination of multiple layers of fibers, stacked in just one fabric, leads to faster and cheaper preforms production processes than unilayer based processes. It also has advantages for LCM (Liquid Composite Moulding) methods as NCF present better drappability due to the good deformability of unidirectional plies versus vowen fabrics that are undulated (crimp). An additional advantage of the NCF reinforced composites is that they generally feature better mechanical properties as the tows are not crimped or woven. Furthermore the delamination resistance and impact strenght of the NCF reinforced composites is better.

One key advantage of the NCF’s is the ability to drap into relatively complex shapes without giving rise to wrinkles that normally appear with standard woven textiles and preimpregnated tapes. The excelent conformability of biaxial fabrics under “dome type” deformation conditions is caused by a slipage of the fiber tows as there is no joints that restrict this movement.
This is why the use of NCF is rapidly growing in aircraft, automotive, yatching , wind energy and complex structural components.

A lot of work is being done in NCF to push the boundaries of this materials:

Research is beeing developed to increase the limits of the deformability of NCFs through the determination of the best stitching conditions. These studies show that the deformation of the biaxial y triaxial NCF under load (bias extensión test), happens through rotation, sliding and compaction of the tows. The resistance of the NCF to biaxial deformation is dependant on the density, the tension and the position of the stitches. Higher tension on the stitches gives bigger resistance to deformation due to better sliding resistance.

The veils and binders used by the different suppliers play also an important role. A veil is a thin layer of polimeric material formed by fibers with random orientation. Binders are thermoplastic particles that act like an adhesive. Nowadays they are used to minimice fragility of the epoxi matrix on the composite.They also avoid fraying or wrong orientation and specially optimize the permeability, improving process times. Permeability of the material is a key feature. On one hand high permeability accelerates infusion processes, on the other hand too much space between the fibers can lead to a worse impregnation of the fibers worsening the fatigue behaviour. Many innovations are beeing lauched in these topics.

The manufacturing requires handling and depositing the NCF on the mouls with big precision, repeatability and productivity. Drappability modeling is also an important research area , predicting and improving the deformation of the fabrics depending on the tension applied is the basis for the good part design and process optimization.

In this line developments like Drapetest http://bit.ly/1wu2Sm4 allows to automatically characterize drapability and the formation of defects during draping and forming The tester combines the measurement of the force required for forming with an optical analysis of small-scale defects .

Video: Bombardier CSeries uses NCF

-Sampe Europe 2014: from aerospace OoA to automotive thermoplastics

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The title of the 35th International Technical Conference & Forum organized by SAMPE was “Low cost Composite Processing, from Aerospace OOA to Automotive Thermoplastic”. As the title indicates the main issues were the way to decrease the manufacturing cost in aerospace composites and the relation between thermoplastics and composites in automotive.

As it is known, it is very important to avoid the autoclave in order to reduce the composites manufacturing

  • reducing tooling cost for component development and low-rate production runs
  • adding capability for manufacturing of very large highly integrated composite components
  • reducing capital costs for autoclave and associated facilities
  • and removing autoclave bottleneck for production

Different methods for avoiding the autoclave were discussed along the conference, the experts presented different projects related to this subject, focused on the use of NCFs and resin infusion methods (summarized below).

Taking into account the unique challenge of increasing the presence of composites in new single aisle aircraft, current works are targeting at developing robust, fully automated processes for the realization of large scale structures. New functionalities are being added to existing materials, like e.g. enhancing conductivity for the improvement of lightning strike behavior.

On the other hand, thermoplastic materials are being optimized and, last but not least, new multi-functional composite materials are under development to broaden the range of composite applications. In addition, huge efforts are being undertaken to enable structural bonding for composite repair.

With respect to the automotive application, the use of carbon fiber reinforced thermoplastic was considered the next challenge. The laser assisted and induction processes in welding and heating with thermoplastics were the most important topics of discussion.

Related to the main subject of the DRY COMPOSITES blog, some projects have been outlined from the conference:

  • In terms of OoA manufacturing technologies by means of NCF and RTM, Airbus Military presented its BAHIA project, focused on alternative fan cowl doors configuration and manufacturing.  Within the project framework a new fan cowl door is designed and a RTM technology is used in order to manufacture the structure, by eliminating 2 autoclave curing cycles and joining grid and skin through a unique bonding line. This way, Airbus Military intends to obtain a more competitive and reliable product.

       Co-authors: Javier Gomez Vega, Maria Antonia River Orellana, Luis Rubio García

Airbus 340-642 fan colw door

Airbus 340-642 fan cowl door

  • Researches from Irish Centre for Composite Research, MSSI and University of Limerick presented a design of experiments study assisted in optimising the LRI manufacturing process (liquid resin infusion). According to them, LRI processes is challenging due to the difficulty in achieving full fibre wet-out, target fibre volume fraction and acceptable void content etc. In this study, flat composite panels were manufactured using aerospace grade Benzoxazine resins systems (one of which is targeted at high temperature applications) and aerospace grade carbon fibre NCF (non-crimp fabric with and without powder binder).

      Co-authors: Anthony Comer, Dipa Ray, Winifred Obange, Gearoid Lancy, Inga Rosca, Walter    Stanley

Double-omega stiffened skin manufactured by VIM using Benzoxazine B.

Double-omega stiffened skin manufactured by VIM using Benzoxazine B.

  • Other EADS, Eurocopter and University of Stuttgart researchers did also present a study, aimed at the fundamental material behavior of such unidirectional-braided structures, which are converted from carbon-fibers and thin thermoplastic auxiliary-yarns directly to the part geometry as UD-plies. The promising results emphasize the feasibility of using UD-braiding for structures with high stiffness as well improved damage resistance.

Co-authors: C. Metzner a, A. Gessler a, C. Weimer a, U. Beier b, P. Middendorf

UD-braiding – the machine, process and textile

UD-braiding – the machine, process and textile

 

-BMW i3: first mass produced composite car in production

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BMW has started production of its revolutionary i3 city car, which is the first mass-produced automobile using a composite frame. The company invested $533 MM (€ 400 MM) in its composite and assembly facilities in Germany and expects first deliveries to European customers in November. Production facilities have been sized to support a rate of 40,000 vehicles per year.

BMW i3: first mass produced composite car

BMW i3: first mass produced composite car

The heart of the structure is the 330 pound (150 kg) passenger compartment, called the Life Module. It is made from dry, carbon non-crimp fabric (NCF) preforms that are resin transfer molded (RTM). This permits substantial parts integration of the Life Module comprising 150 parts total, with two thirds fewer parts and 50% less production floor space than with a steel design, according to BMW. Parts consolidation of this magnitude cannot be achieved using steel or aluminum according to BMW’s Project Director Dr. Carsten Breitfeld. The Gr/Ep Life Module weighs half of a steel design, and contributes to total vehicle weight savings of 770 pounds (350 kg).

Production cost and rate of the i3 composite structure are critically important. Compared with existing production of composite parts for the BMW M3 and M6, 50% cost savings are realized with the i3 process and cycle time is reduced by 30%. “We have optimized the process, achieved a shorter manufacturing time, and succeeded in taking a lot of the cost out” says Breitfeld. He attributes these achievements to “a fresh approach to manufacturing and materials use and a very clear business plan…… The production process is a very significant time saver and means that industrialization of large CFRP components is now realistic.”

BMW’s experience has been so favorable that its larger i8 electric sports car to be offered next year will be built the same way.

More details are provided in SAE Automotive Engineering and CompositesWorld articles.