Tag Archives: RTM

-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

 

-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.

-Making a Preform – How Can I Count the Ways?

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Making a part by RTM or vacuum infusion has two basic steps – first a dry Preform is produced and then resin is infused into the Perform in a tool where the part is cured. Building a high quality Preform is essential to produce a high quality part, and the majority of part cost and time are associated with manufacturing the Preform. Dry fiber material is supplied on rolls, which are processed in three steps to make a Preform:

  • Material is cut from the roll (usually to specific ply shapes)
  • Plies are placed into a mold or forming tool with the part shape
  • Dry plies are consolidated (using heat and pressure) to assure they remain fixed in the proper position, hold their shape and to compact the Preform and reduce bulk before infusion.

Several different methods have been developed to create high quality Preforms suitable for structural parts:

Pick-and-Place (PNP) – Perhaps the most widely used approach, this consists of:

  • Ply patterns are cut on a CNC Table Cutter (same equipment used for prepreg pattern cutting)
  • Cut patterns are “picked up” from the Cutter table. Often plies from several material types used in a part are organized into a Kit, which is stored temporarily.
  • Plies are picked up from the Kit and transferred or “placed” into the forming tool. Placement of the plies (which are 2d flat objects) into a forming tool (usually a 3d contoured object) requires that the placement process also form the dry material without wrinkles, excessive skewing or other ply distortion.

Pick and place can be performed in one operation if the forming tool is able to accept the plies immediately after they are cut, and if the cutting equipment is adjacent on the shop floor. If Kits are used, plies are handled twice, and requires separate floor space for storage. “Picking” and “placing” can be performed manually but is increasingly being performed by machines.

Pick-and-place equipment

Pick-and-place equipment (see article and video)

Dry Automated Fiber Placement (DAFP) – This is an adaptation of prepreg AFP, using dry tapes instead of slit prepreg tapes:

  • Several suppliers now offer dry fiber tapes with suitable binders, designed to be used on current AFP machines to create dry Preforms. These dry tapes are analogous to slit prepreg tape, but with no resin. There is a small amount of binder powder on the tape surface to hold the dry tapes together with the application of heat and pressure.
  • Preforms are produced using many passes of narrow bands of dry tape that are consolidated as it is placed, just like AFP.
  • Resin is later infused into the preform using either vacuum pressure or higher pressure in a matched mold (RTM).
  • Conceptually DAFP is very similar to AFP, using the same basic equipment and design practices.
DAFP using AFP with dry fiber tapes (see NLR)

DAFP using AFP with dry fiber tapes (see link)

Automated Dry Material Placement (ADMP) – A newer approach is to cut and place ply patterns in one operation:

  • A moving machine head with a fabric supply roll dispenses the fabric and cuts the pattern shape as the material is dispensed. Cutting the ply edges is performed with multiple CNC controlled knives in the machine head.
  • The cut patterns that emerge from the machine head are placed directly on the forming tool as the head moves over the tool surface. This eliminates the “pick up” and “placement” handling in the PNP approach.
  • Conforming the fabric material to the 3d surface of the forming tool is also performed by the machine head using compliant mechanisms.

    Automated Dry Material Placement (ADMP) equipment (see link)

    Automated Dry Material Placement (ADMP) equipment (see link)

 

 

-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.

 

 

-Aerospace Looking to Dry Fiber/Infused Composites

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Most aerospace composite structures are produced today using prepreg and autoclave cure. Recently an increasing number and type of large and critical structures are being manufactured in a very different way – using Preforms assembled from dry fabrics and tapes and then infusing the epoxy resin into the Preform followed by cure. If the infusion is performed in a matched closed mold under high pressure, the process is called RTM. For many larger parts, infusion is performed using vacuum pressure only with single surface tools. This process has many different names reflecting slight differences in the infusion process including VARTM, CAPRI, VAP, RTI, RFI, BRI, SCRIMP and several others.

A wide range of aerospace parts are fully qualified and in production today made from dry fiber and vacuum infusion – a few examples are shown below. Some of these assemblies, such as flight control surfaces (flaps and ailerons) and fuselage frames are considered secondary or redundant components. Others such as the Aft Pressure Bulkheads of the A380 and 787 are primary structure – failure of these critical components would likely lead to loss of the aircraft. The A400 Cargo Door operates in an even more challenging environment – this flat and large door sees full cabin pressurization, and experiences significant bending  and tension loads during flight.

That these highly critical parts are made using these materials and processes speaks to the high degree of confidence that the aircraft OEM’s and regulatory authorities have in the reliability, performance and safety of the dry fiber/infusion approach.

787 Dry fiber/infused parts include (left to right) ailerons and flaps, fuselage frames and the aft pressure bulkhead (APB) of the fuselage

787 Dry fiber/infused parts include (left to right) ailerons and flaps, fuselage frames
and the aft pressure bulkhead (APB) of the fuselage

A380 Aft Pressure Bulkhead (APB) and A400 pressurized Cargo Door

A380 Aft Pressure Bulkhead (APB) and A400 pressurized Cargo Door

Arguably the most advanced use of dry fibers and infusion is in the wings of next generation airliners such as the Bombardier CSeries and Irkut MS21 aircraft shown below. These aircraft, serving 120 to 200 passengers, are the newest in commercial aviation and have leveraged the latest advances in composite materials, processes and production methods available today. The CSeries has passed ground structural tests and is expected to make its first flight mid 2013, with the MC21 to follow about a year later.

The Bombardier CSeries wing (left) and Irkut MS21 wing (right) both are made from dry fiber preforms and resin infusion

The Bombardier CSeries wing (left) and Irkut MS21 wing (right) both are made from dry fiber preforms and resin infusion

How about your company – is this technology being considered and for what applications? What are the benefits, tradeoffs, concerns and issues associated with the use of these processes? Let us know what you think.

-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!