Tag Archives: manufacturing composites

Bombardier Learjet 85- OoA prepreg and infusion process

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Bombardier Learjet 85- OoA prepreg and infusion process

At the end of the year we have thought it would be interesting to review one of the most interesting discussions we have had in our activity on linkedin. It was at the Composites Group. The news that Bombardier was using dry fiber and Resin Transfer infusion on the Learjet 85 wing box started an enriching discussion about the technical difficulties and possibilities of resin infusion processes and out of autoclave curing.

Learjet-85-mockupLearjet 85

Bombardier Learjet – composite

“Bombardier unveils OoA composites process for Learjet. Wingskins and spars for the plane are manufactured in Belfast using an in-autoclave resin transfer infusion (RTI) process. The fuselage and autoclave are manufactured in Querétaro, Mexico, via an out-of-autoclave (OOA) prepreg process.”

“ It makes use of composites not only to reduce airframe weight and increase fuel economy, but also to significantly reduce the part count because composites have enabled Learjet to produce large, integrated structures.”- Composites World

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Mitsubishi Regional Jet (MRJ), new aircraft program with dry composites for the empennage using A-VaRTM technology

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Recently we assisted to the roll out first flight of the test aircraft for the Mitsubishi Regional Jet (MRJ) programme. The empennage of the MRJ is produced by a RTM process using dry fabrics .

MRJ_1 MRJ_2MRJ first flight

We have found many informations published on the issue and we want to share with you some of the most interesting aspects we have read refering to the use of dry fabrics to manufacture the composite part in this project.

The company is developing a highly competitve aircraft. On the one hand, they are offering interesting operating costs with a good efficiency, in a big measure, thanks to light weight materials. On the other hand, they are working on a price competitive airplane, through improved production costs.

Cost reduction strategies:

  • Precision on parts production for easing assembly.
  • Lean manufacturing concepts like moving assembly lines: the product moves through the factory from one manufacturing process to the next.
  • Circular body cross section for simplified tool design.
  • Oven cured composite parts.

The composite empennage (horizontal and vertical stabilizers and fuselage interface) has been fabricated using an improved Liquid Moulding process called A-VaRTM. This process was developed jointly with Toray.

A-VaRTM molding technology is an advanced version of VaRTM. Vacuum Asisted Resin Transfer Moulding is a low cost composite manufacturing technique where, differing from prepreg laminated composites, the resin is infused into dry fabric, formed on a mold near product shape under vacuum pressure and cured in an oven.

A-VaRTM is a new version of it, suitable for aeronautic parts and with very good mechanical properties, by means of:

  • Adoption of a fiber-reinforced base material with high quality and strength (dry Non Crimp Woven). Carbor fiber bundles form the primary structural element. Very fine glass fibers are used as auxiliary warp fiber to facilitate flow during resin infusion and to tie warp and auxiliary and fibers toghether.
  • Application of thermoplastic particles designed to toughen the composite materials. They are used as a tackifier to consolidate the preform and also permit the use of a lower-viscosity and less expensive epoxy thermoset resin.
  • Optimization of the forming process to obtain a high volume fraction of fiber (Vf = volume of fiber/volume of object × 100, targeted value 55 to 60%). MHI uses a proprietary diffusion or flow media to control the resin infusion flow and rate, as well as to bleed off excess resin. This maximizes fiber volume in the finished composite part; for aircraft primary structure.
  • Oven cure occurs in two steps: first, cure under vacuum and then postcure in an oven at 350°F/180°C VaRTM

    Conventional process vs VaRTM

With the A-VaRTM process mechanichal properties similar to prepreg have been achieved.

Mechanical propertiesMechanical properties

The new process improves costs in all the aspects. Cost associated to materials are lower , the composite manufacturing using oven heating to cure is cheaper, we see cost improvements even in assembly and quality assurance. Although aluminium is still more cost competitive, A-VaRTM gets very close to it, as the component in composite has only 1.2 times the cost of the aluminium part.

CostCost comparison

The VaRTM uses dry fabric that is not impregnated with resin so the material is easier to fit around a three dimensional geometry.

WrinklesNo wrinkles using dry woven fabrics

The composite manufacturing cycle times have also been dramatically reduced on the stringers. They are cobonded with the precured skin panel, using a film adhesive, and the assembled component is subsequently postcured in an oven more than 19.7-ft/6m long.

Vertical stabilizer
Therefore Liquid Moulding with dry (engineered) fabrics proves succesful for the composite manufacturing of exigent aeronautic parts at lower overall costs.
You will find more information in the following articles : FightGlobal; CompositesWorld; MHI(1); MHI(2) ; ICCM

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

-We go dry

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Dry Composites is an initiative by Danobat Composites to share the latest advancements in automation using dry composite material. This online community aims to connect companies, research centers, academics and experts interested in the use of dry composite material to develop structural parts in aerospace.

What do we mean by Dry Composites? There are two distinct methods of making composite structures. The first involves impregnating the fibres in a dedicated off-line machine to make a pre-impregnated material, called pre-preg. This is then transported to a factory that makes structures where it is laid up by machines or manually.

The second, more direct route is to take dry fibres, usually in some textile format and after assembly into a pre-form, infuse them with liquid resin. The infusion process is known by a number of trade names and acronyms such as RTM, VARTM etc.

The pre-preg route involves an extra process and hence cost, but it does result in structures with good consistent properties. Recently, the performance of structures made by infusing Dry Preforms has improved and is now claimed by some, to match that of more conventional pre-preg materials. Working with dry fibers, fabrics and textiles enables thicker layers to be used, saving time and labour costs, plus aiding in the creation of more complex, one-piece structures.

However whereas the pre-preg manufacturing industry is well served by automation with dedicated machine tools, the lay-up of dry fabrics has not received the same attention. Danobat Composites has pioneered the development of Automatic Tape Laying using woven and NCF fabrics. This has improved laminate quality, repeatability and reduced the cost of composite structures by significantly cutting manufacturing labour and material costs. Moreover, it is worth mentioning that the use of dry materials can give rise to out of autoclave curing processes acquiring required properties in primary structural aerospace parts.

Today, manufacturers face the challenge of doing more with less, the aerospace industry needs to adapt quickly to new material and process developments to remain competitive. In doing so, the ultimate goal of a disruptive automation technology is to introduce new processes that may deliver better high efficiencies and control at less cost. This requires broad support from an ecosystem of R&D, manufacturing, engineering teams and material developers.

Dry Composites is an open space for those interested in learning more about how automation using dry composite material can be applied to the aerospace industry. From sharing industry news, information, data and technical solutions about dry composite solutions to interviews and perspectives from expert sources. Our target audience includes decision makers, R&D engineers, global suppliers of advanced materials, software and automation companies.

If you are interested in learning more about advancements in the use of dry material in the aerospace industry, follow us on Twitter @drycomposites and join the LinkedIn Group Dry Composites.

Stay tuned for more!