Category Archives: Process

-“Dark-on-dark”: a machine vision approach for dry carbon fiber inspection

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As automation of dry carbon fiber manufacturing gains more and more momentum across the board, inspection systems become a crucial factor when it comes to assuring the quality of final products and the efficient use of available resources. Due to their ability to detect mistakes and faults at an early stage, it is straightforward to infer the great impact inspection systems can have when suitably integrated in a production line.

The systems presented in this entry are focused mainly in machine vision technology and cover inspection for both dry composite fabrics and post-infusion manufactured pieces. One of the main drawbacks they will need to overcome is the fact that carbon fabric absorbs a wide spectrum of light and presents a black color. Therefore, the design of an adequate lighting system will play a critical role at the task of detecting faults on the material (holes, fuzzballs, foreign-object-debris,etc.) and at providing good performance in the so called “dark-on-dark” scenario where vision systems tend to struggle.

APODIUS VISION SYSTEM

The Apodius Vision System (AVS) is designed to measure the fiber orientation of composite fabrics and, based on the irregularities of the obtained pattern, also detect gaps or impurities that dry composite plies may exhibit. Specifically, it can take orientation angle measurements of 0.1º precision for every 50×50 mm² of both woven and non-woven fabrics thanks to its diffuse lighting technology that minimizes reflections on the fabric’s surface. Also, it is attachable to a robotic arm and, combined with an intuitive software interface the AVS, enables an easy integration of fabric inspection inside a production system.

Apodius inspection head

Apodius´ inspection head

PROFACTOR FSCAN

Another product worth mentioning and highly related to quality control of composite parts is the FScan, designed by the Austrian applied research company Profactor. Instead of using the above mentioned diffuse lighting technique, their machine vision system exploits the reflection model of carbon fiber material and allows to produce high-contrast images. The sensor has a field of view of 60×60 mm² and its capable of scanning a surface with a speed of 1 m/s while detecting in real time all sorts of defects suchs as gaps, inclusions or missing rovings.

Profactor´s high constract carbon fiber images

Profactor´s high constrast carbon fiber images

EDIXIA

This French company with worldwide presence has a very strong background on automation of processes in several industries and is now expanding into the composite market. Their vast experience with different technologies allows them not only to look for defects in several kinds of fabrics, but also to inspect cracks, surface roughness and even fiber orientation of manufactured pieces, after the infusion process is completed. Contrary to 2D systems that infer the presence of defects from irregularities in the observed patterns, Edixia also makes use of 3D technologies which allows them to take direct measurements of the height of a wrinkle, depth irregularities or the 3D location of a cut edge.

Edixia features

Edixia´s features

SURAGUS

Finally, although they do not integrate cameras in their solution, a very original alternative is provided by Suragus. Taking advantage of the conductive properties of carbon fiber, Suragus takes an eddy current approach for this problem, allowing them to successfully leap over the challenging “dark-on-dark” scenario of vision systems. Furthermore, since eddy currents have some penetration in the material, the obtained measurements are not limited to the properties of the surface but also cover a few layers below it. This enables fast inspection for mulitple-layer fabrics (up to 5-7) that otherwise could not be inspected with standard vision systems. Their current  products are able to inspect a square surface of up to 600×600 mm² with a resolution up to 100-200 microns.

Suragus´ Eddy Current Inspection system

Suragus´ Eddy Current Inspection system

 

 

-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

 

-Advancements in dry reinforcements for aerospace infusion process

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While in some previous posts we focused on talking about different automated processes for dry material deposition (ADMP, Pick-and-place and DAFP), this post deals with information about dry reinforcements aimed at aerospace infusion process and automation.

  • Why dry reinforcements?

Dry reinforcements offer significant advantages versus prepreg materials that have been traditionally used in the aerospace sector. They present several benefits, thanks to their low prices, their long shelf life, reduction in inventory costs, potential to increase parts integration and  potential to avoid the costly autoclave curing process.

The growth of the resin infusion process in the aerospace industry (as  can bee seen in the image above and our -Aerospace Looking to Dry Fiber/Infused Composites post) is increasing the need to adapt dry materials to the aerospace and new technologies requirements.

Infused Aerospace parts

Infused Aerospace parts  in Boeing 787, A380, A400, Bombardier C-Series and IRKUT MS-21

  • What is driving innovation in dry reinforcements?

Although there is still much to do in the area, material suppliers offer more and more products oriented to automated dry material deposition processes. Focusing our attention on dry reinforcements, the main research and developments in the area are aimed at:

Binders which are compatible with the resin to be infused and ease the manageability of the fiber during the material deposition.

Thin layers of thermoplastic veils to facilitate the flow of resin infusion and provide the final part with a greater toughness.

Dry carbon fibers that provide the strength and stiffness in a unique or multiple directions (unidirectional or multiaxial reinforcements). Different forms of dry carbon fabrics can be used to this end. NCF (Non crimp fabrics) are the most used fabrics nowadays, whereas the woven fabrics have also improved their properties in order to ensure the achievement of the required qualities.

The combination of the dry reinforcements with the proper resin is essential in order to manufacture a good quality part. Great developments are being carried out in this area.

  • Unidirectional tapes or Non Crimp Fabrics: Different choices for automation.

Unidirectional tapes up to 1″ offer high flexibility in terms of the geometries they can achieve. Automated process, such as the Dry Automated Fiber Placement (DAFP), use these tapes to produce preforms that will be infused during further stages. The productivity they can reach is low so far.

Wider Non Crimp Fabrics (NCF) can be used with the automated process such as ADMP and Pick-and-Place. The improvements in these materials and related automated deposition technologies could revolutionize the composites sector because of the great production rates they can accomplish.

You can have an overview of these different automated process in our post Making a Preform – How Can I Count the Ways?

  • What are the most common dry material forms used by the latest aerospace programmes?

It is known that the Saertex group supplies high-performance multiaxial and unidirectional NCFs for the manufacturing of the Bombardier´s C-Series and Learjet 85´s major primary structures.

Meanwhile, AeroComposit has qualified Hexcel´s OoA Hi-Tape material to produce Irkut Ms-21´s wings and wingboxes, whereas Spirit AeroSystems has also used the same material to form a skin of an engine nacelle outer fan cowl. Aircraft structures made with HiTape are reported to demonstrate mechanical properties as high as those found in parts  made with the latest generation primary structure prepregs.

Hexcel´s OoA HiTape

Hexcel´s OoA dry HiTape

Finally, it is worth mentioning that Cytec offers a material with equivalent properties, being applied also in the Irkut  MS-21. Both tapes (Hexcel´s and Cytec´s) will be used to manufacture the aircraft structures automatically within a DAFP machine.

-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)

 

 

-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.