Why autoclave carbon fiber

The difference with OOA curing is that it achieves the elimination of voids and desired fiber content by placing the layup within a closed mold and applying vacuum, pressure, and heat by means other than an autoclave. Prepreg carbon fiber reinforcement is one of the most advanced techniques for making composite material. With high-quality surface finish and low resin content, OOA prepreg carbon fiber composites have excellent structural performance. OOA prepregs cure lower pressures and temperatures than traditional autoclave methods.

Uncured prepreg carbon fiber is also easy to handle and can be hand-cut and laid precisely into detailed and intricate molds. This makes it an ideal process for smaller, more complex parts. So, is the production of large composite materials viable without the huge upfront costs of building and housing a large enough autoclave? Using new OOA methods combined with traditional autoclave curing methods, SMI is able to deliver to its customers highly customizable and quality composite components.

Although not necessarily an exhaustive list, the following tools and materials, supplied by Easy Composites, were used in this project. The quantity shown below is the approximate amount used in the project rounded up to the nearest available kit size or quantity. In this video tutorial we aim to provide a complete introduction to out-of-autoclave prepregs. We explain what they are, how they are stored, shipped and handled and what moulds, equipment and materials are required to work with them.

The tutorial includes detailed practical information on templating-out and then cutting the prepreg, laminating the surface ply, debulking the surface ply, laminating the backing ply and then vacuum bagging and curing the component. In this video we use the prepreg carbon fibre mould made in the preceding video in this tutorial series.

There are two main methods of curing prepreg composite materials; in a curing oven and in an autoclave. The difference between these two pieces of equipment is pressure; an autoclave is a pressure chamber like the air receiver on an air compressor whereas a curing oven only has normal atmospheric pressure inside.

Because an autoclave is a large pressure vessel, and particularly because it is a pressure vessel that needs to have a large door on it for access, they are - necessarily - large and expensive pieces of equipment. They are also very large, heavy pieces of equipment that an be expensive to run and requiring regular inspection and servicing to ensure their safety. As the resin matrix in a prepreg has already been activated i.

Fortunately, the very low reactivity of the resins typically used in prepregs mean they cure incredibly slowly at ambient temperature, allowing the prepreg to be stored and handled at room temperature for a limited amount of time, known as the prepreg's outlife. In the case of the XC system, the freezer-life is at least 12 months.

One major advantage to working with prepregs is that the material can be cut extremely accurately into different sections needed to laminate the part. When a part is laminated for the first time, it is typical to begin by making temporary paper or masking tape 'templates' of the different shaped pieces. These temporary templates can be transferred to the prepreg, marked out and cut. Once the pieces of reinforcement are test fitted into the mould, the temporary templates are often adjusted and refined until they produce perfect fitting pieces of reinforcement.

At this point, the temporary templates can be transferred to more durable materials such as plastic sheet to be retained and re-used again and again. Once you've created your cutting templates the outline is typically transferred to the prepreg by tracing round the outside of the cutting template using a marker pen. In its uncured state, prepreg reinforcement is extremely easy to handle and cutting is usually best done using a sharp knife.

Prepregs can be cut using scissors but the tacky resin on the material tends to build up on the scissors, clogging them and requiring cleaning. Before you start laminating your first prepreg component, it's important to consider what type of moulds are suitable for use with prepreg processing. In this tutorial we're using a mould that is itself made from prepreg carbon fibre using our XT tooling prepreg which is highly suitable for making prepreg components. Before you start to place the pre-preg into the mould, you must first apply your release agent in accordance with its instructions.

In this case EasyLease was used. The actual handling of the pre-preg is relatively simple, however, great care must be taken to ensure the material is properly down in the mould. Generally work from the centre lowest point and work out systematically so that you do not end up bridging over any corners or detail.

Vacuum-bagged, oven-cured material systems for secondary structures flaps, fairings and the like are well established. What is new is the ability for such materials to deliver the less than 1 percent void content and autoclave-quality mechanical properties required for aerospace primary structures, such as wings, fuselages and empennage components with integrated stiffeners.

Although these processes are gaining acceptance among those who fabricate highly loaded structures, VBO prepregs, which encompass traditional hand layup as well as automated material placement methods, are of particular interest due to a combination of unique advantages. The U. Air Force has identified OOA prepregs as vital to achieving the fast and affordable manufacturing that the U. Department of Defense DoD will require for future military platforms, and the Air Force sees additional cost savings when one OOA prepreg system can be used for prototyping, production and spares.

Yet many issues remain. OOA cycle times might actually be longer, due to the time-dependent process of edge-breathing required for low void content. Other issues include compatibility of adhesives, surface quality of sandwich structures, and using automation in lay-up. Also, because these materials are new, a complete database of B-basis design allowables will have to be established, requiring time and money. Louis, Mo. Not necessarily. OOA prepregs ensure even resin distribution, avoiding the dry spots and resin-rich pockets common with infusion processes.

Also, OOA prepregs can be cured at lower pressures and temperatures vacuum pressure vs. Therefore, tooling for large composite structures with integrated stiffeners that can be cocured in a single cycle, which is typically very complex and expensive, now might be fabricated much more simply and cost-effectively. Further, mismatches between tool and part coefficients of thermal expansion CTEs are smaller at lower temperatures and, therefore, more easily managed, positioning OOA prepregs as a potential solution for part cracking caused by cure-temperature differentials.

One of the most widely cited OOA benefits is the potential to reduce high capital and operating costs. DoD advisories indicate that future military aircraft programs will be produced in small volumes with very small budgets. Future NASA programs will be cost-constrained to an even greater degree. Tier 1 suppliers to commercial aircraft OEMs agree, seeing OOA prepregs as a way to attain faster, more agile manufacturing. LTM series, enabled cheaper, low-temperature vacuum-cure prototypes of large, unitized parts.

These early prepregs were cheaper because they cure at lower temperatures under vacuum pressure, but they had neither the mechanical properties nor the sufficiently short cycle times necessary for production parts. CYCOM — were approaching the properties of autoclave-cured prepregs. The to day tack life and maximum day open mold life were deemed insufficient by both AFRL and NASA because layup and bagging of large, complex structures require, at minimum, three to four weeks.

A range of demonstrator parts were built and subjected to limited nondestructive and dissection evaluations. Gardena, Calif. Boeing Irvine, Calif. Lee found that when the materials were heated and softened, the capillary effect of the nanotubes would draw the materials tightly together. Testing the approach, the researchers wrapped the layers in a second film of carbon nanotubes, to which they applied an electric current to heat it up.

The resulting composite showed no voids and the production quality was equal to high-performance composites that are produced in a usual autoclave, according to the MIT researchers. So, we are excited that we can cover the breadth of existing and forward-looking advanced carbon fiber composites, and therefore can also cover wind and automotive applications as well. In their experiments, the team worked with small samples.

They were large enough to show that the nanotube films are able to heat and pressurize materials to fuse the layers without voids. To make this process viable for manufacturing wings and other components, the researchers will have to find ways to manufacture carbon nanotubes at a much larger scale.

Research article found at: B. Wardle, et al.