Tag Archives: VARTM

-Resin Infusion techniques in the aerospace industry

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Many methods have been developed to perform the resin infusion in the aerospace industry, once the dry preforms are created manually or automatically. These processes are identified by different names and acronyms, which can lead to some confusion. Here is a description of some of the more widely known infusion methods.

SCRIMP (Seemann Composites Resin Infusion Molding Process) is one of the earliest patented infusion methods. It is used for many marine and Wind blade applications, but was also licensed by some aerospace firms. It relies upon the use of a flow or “distribution media” with high permeability between the layup and vacuum bag to rapidly and evenly distribute resin laterally across the part.

SCRIMP Schematic

SCRIMP Schematic (link)

VARTM (Vacuum Assisted Resin Transfer Molding) is the name of the process used by Lockheed Martin that is similar to SCRIMP, but does not use a flow media. The entire fuselage of the AGM 159 JASSM missile is made using VARTM.

JASSM made with VARTM

JASSM made with VARTM (link)

CAPRI (Controlled Atmospheric Pressure Resin Infusion) was patented by Boeing and is said to reduce thickness variation and result in fiber volumes and mechanical properties equivalent to prepreg/autoclave materials. First it uses vacuum debulking cycles on the dry preform to reduce compressed thickness prior to infusion. During infusion, the resin supply is held at partial vacuum, which assists in degassing the bulk resin but also reduces the pressure differential driving resin into the preform.

CAPRI Schematic

CAPRI Schematic (link)

VAP (Vacuum Assisted Process) was patented by EADS and used in parts like the A380 Aft Pressure Bulkhead and the massive A400 Cargo Door. VAP features a gas permeable membrane placed over the infused layup, which helps to evacuate trapped air and volatiles in the infused layup prior to cure. By letting gases through the membrane (but not the resin) VAP is said to achieve lower voids and higher, more controlled fiber volume for better laminate quality.

VAP membrane

VAP membrane (link)

RTI (Resin Transfer Infusion) is a Bombardier patented process used to produce the wing skins of its CSeries aircraft. Infusion of resin into the preform is performed with vacuum pressure only. However, the mold is located in an unpressurized  autoclave during the infusion step. After the preform is fully infused, the autoclave is pressurized and heated to perform cure. This makes it easier to achieve high laminate quality because positive cure pressure (>14 psi) helps prevent void formation from entrapped air and volatiles. It has the drawback that a suitable size autoclave is still requited. All other methods cited above are true Out of Autoclave processes.

C-Series wing made with RTI

C-Series wing made with RTI (link)

There are also other acronyms for similar processes, which can create a kind of “alphabet soup” confusion about infusion.

The important thing to remember is that many different users have had success making a wide range of parts (some very large and critical) using infusion processes.

-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!