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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.

-Pros and Cons of Automated Preform manufacturing methods

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In our last post we described three methods to automate dry fiber Preform manufacturing: Pick-and-Place, Dry Automated Fiber placement and Automated Dry Material Placement.

Pick-and-Place (PNP) – Ply patterns are cut on a Table Cutter, “picked up” and then transferred or “placed” into the mold.

Dry Automated Fiber Placement (DAFP) – Similar to prepreg AFP, where bands of narrow unidirectional tapes are placed into the mold, except that the tape is dry (not impregnated). A small amount of binder holds the tapes in place as they are placed under heat and pressure.

Automated Dry Material Placement (ADMP) – Fabric rolls are cut into Ply patterns and placed into the mold, all in one operation and one machine pass over the mold.

PNP, DAFP and ADMP preform manufacturing methods

PNP, DAFP and ADMP preform manufacturing methods

Each of these automation methods provides advantages and disadvantages, as presented below.

Preforming Methods – Pros and Cons

Preforming Methods – Pros and Cons

PNP has been used to produce preforms for some time, and directly mimics the way many prepreg, RTM and infused parts are made today. The industry is comfortable with designing, producing and inspecting CNC cut ply patterns, whether from prepreg or dry fabric forms. Flat pattern shapes of any complexity can be accommodated (internal windows, cutouts, etc.) Instead of manually placing plies in the mold, with PNP this operation is performed by a machine, therefore the complexity of the layup (mold contour, folded flanges, etc) is more limited. Both woven and noncrimp fabric (NCF) styles provide good mechanical properties as well as excellent permeability for complete resin wetout and infusion. A drawback to PNP is that more floor space is needed for both the Table Cutter and the PNP transfer mechanism. If cut plies are not laid directly in the mold (i.e. are stored in kits before layup), PNP requires more ply handling, which makes it more difficult to manage fabric distortion and placement accuracy.

The design practices, machinery and manufacturing approach with DAFP are very similar to prepreg AFP. This familiarity or aerospace “pedigree” makes DAFP attractive because it is a less disruptive process change where AFP equipment is already in use. Other benefits of DAFP include very good properties achieved with unidirectional fiber and the lowest material scrap rate, since each tow is dropped or added exactly as needed. This feature also means that complex patterns can be produced, though there remain limitations associated with minimum cut-and-add length and edge crenulation. The use of individual tapes allows DAFP to conform to complex shapes. The drawback of DAFP is similar to that of AFP – in practice, actual productivity (pounds deposited per hour, i.e. the floor-to-floor or C rate) is relatively low.  The time required to manually inspect every placed tape against the defined drawing often far exceeds the time the machine is actually placing material, and this is another factor in low throughput.

ADMP’s value proposition is that it can achieve very high productivity due to wider materials (than DAFP tow bands), multilayer materials (such as NCF) and pre-made layup schedules provided in the fabric form itself. For example, to produce a balanced, symmetric quasi-isotropic layup only requires 2 passes of an ADMP machine (using a four layer [0/45/-45/90] NCF fabric placed back-to-back) but requires 8 passes of an DAFP machine to produce a [0/45/-45/90]s layup from uni dry tape. Like PNP, the textile forms used in ADMP have very good through thickness infusion properties, but ADMP textile forms do not provide mechanical properties as high as unidirectional tape used in DAFP. The mold contours and ply pattern geometry suitable for ADMP is somewhat more limited than for other methods, and the method has yet to be proven for use in aerospace applications.

So there are many factors and tradeoffs to consider. Nor are PNP, DAFP and ADMP the only ways to automate the Preforming process. Other methods like stitching, 2D and 3D braiding, 3D weaving and others are also being used.  Ultimately the choice of Preforming method, when it comes to automation, depends on the specifics needs of the application and the customer.

-Advanced dry composite materials offer new opportunities in the aerospace industry

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The number of flights expected for the next 2 decades shows a an annual growth rate of 4.7%, but needs to satisfy very tight constrains on fuel consumption (with fuel consumption being about 30% of the operating cost). It is required to strongly reduce fuel consumption of the future aircrafts manufactured.


ScreenHunter_1350Growth perspective for annual flights from AIRBUS market forecast

One of the approaches required to do so is the introduction of advanced materials to reduce their weight, and composite materials in particular. Major manufacturers have increased the content of composite materials from 5% (A300) to 52% (A350XWB) for AIRBUS or to 46% for the CSeries (Bombardier), including wings, fuselage, and other structural parts etc.

Traditionally, structural components in aerospace have used carbon fiber pre-impregnated with epoxy resins (pre-pregs) that require to be cured in an Autoclave. Although the properties of the pre-pregs are outstanding, the cost associated to the maintenance, shelf life and autoclave processing of these pre-pregs represents a high percentage of the total cost of the part.

In order to reduce these costs, a strong effort has been performed to develop dry composite materials with suitable material properties, and reduced manufacturing costs due to higher deposition rates, no costs of refrigeration, and longer shelf life.  Due to this effort, the use of dry composite materials emerges as a new material feasible for the manufacture of structural components.

The CSeries Aircrafts, from Bombardier Aerospace represents a breakthrough in the use of composite materials, since some of their structural components, such us the wings are being manufactured using dry composite materials. Bombardier expects to reduce 20% the fuel consumption, and have 25% less maintenance costs. The CSeries aircraft is expected to make the first flight shortly. In particular, the manufacturing process is based on pick and place of dry composite material cut on a 2D table and positioned in the mould.

Bombardier

Bombardier is not the only one aircraft manufacturer that uses dry composites in the design of the new aircraft to reduce costs and increase productivities: A400M from AIRBUS cargo door (also a structural component) is also manufactured using dry composite materials. Furthermore, their manufacturing method uses alternatives to autoclave, by means of the VAP (vacuum-assisted process) demonstrating that dry composite materials can achieve mechanical properties required to be used in structural components. The manufacture of these components also takes benefit of the combined infusion of the different parts (skin and stringers), avoiding about 3000 metallic rivets.

0507HPC_IM_A400M_Step_3The investigation and development on dry composites, offers a critical opportunity to push forward the presence of composite materials in the aeronautic field by reducing costs, and maintaining the mechanical properties of pre-preg materials.

Airbus and Bombardier are setting up the first steps regarding the use of dry composites in the aeronautic sector. This sets the path to the industrial development of processing technologies of the fabrication of the materials and the components, and moving from manual manufacturing for short series to high production for larger series, as has happened with glass fiber or pre-preg carbon fiber materials.

There are still strong challenges remaining to take full advantage of this disruptive material that require a strong synergy between all the agents responsible of the introduction, design and development of components manufactured from dry composite materials: companies, Research Centers, academics and experts. 


-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!