Monthly Archives: June 2014

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.

-Automated inspection coming to composites

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Automation of composite manufacturing processes has improved productivity (pounds produced per hour) by roughly a factor of ten or more compared with older manual methods. However, in process inspection of these parts at the layup stage is still performed 100% by eye. The irony of this situation is that some parts produced today by “automated” methods actually take longer to inspect than to produce.

Consider the 787 Fuselage Barrel sections 47 and 48 produced by Boeing using Automated Fiber Placement (AFP). A recent paper co-authored by Boeing (see reference of the article below) describes the challenges and improvements made over several years of AFP production experience.

Cycle time of different elements to produce

Cycle time of different elements to produce the assembly

This figure from the paper breaks down the cycle time elements to produce the assembly. “Program” represents the time spent executing the NC program to lay up the part and comprises 24% of the total cycle time. “Inspect and Rework” consumes 63% of the total cycle time, by far the largest element. In other words, Inspection/Rework takes more than 2.5 times as long to perform as does the layup itself. This even more significant because this time distribution is after several years of process improvements, including Inspection improvements, had been implemented and overall cycle time had been reduced considerably.

The AFRL (US Air Force Research Laboratory), NCDMM and Ingersoll Machine Tools, Inc. are working together to develop and demonstrate an automated system capable of detecting and categorizing defects such as missing tows, fiber twists and gaps commonly found during Automated Fiber Placement (AFP). They are developing Automated Composite Structure Inspection System (ACSIS) designed for AFP layups. The system consists of a camera, lamps and a line scanner mounted on a Gantry that scans the layup to identify and flag flaws. Inspection is performed offline on an AFP layup after it has been produced. For some geometries such as spars made on a dual sided mandrel, one side of the mandrel can be inspected while the opposite side is undergoing layup. In other cases layup and inspection must be performed in series. A prototype system is now operating and beta trials are planned during 2014. ATK has been selected to collaborate with them for a three-month beta site.

Ref.: Harper, R., Halbritter, A., “Big Parts Demand Big Changes to the FP Status Quo”, SME Composites in Manufacturing, Charleston, SC, October 2012)