3361. Developments of Composite Manufacturing Technologies at NLR

Paper

Abstract

Over the last two decades the use of fiber reinforced composites in secondary and primary aircraft structures has increased tremendously. The weight savings that were realized by applying composites in stead of metals used to be one of the main drivers to apply these materials. However, nowadays a reduction in fabrication and maintenance costs is becoming more and more important.
The objective therefore is to combine cost effective fabrication methods with lightweight structural concepts in order bring the exploitation of composite materials to a higher level. The autoclave process used to be the standard fabrication technique to produce composite components for the aerospace industry. Recent developments show the evolution of new cost efficient fabrication techniques and of composite materials for these new techniques. One of these (for the aerospace) relatively new fabrication methods is pressurized Resin Transfer Moulding (RTM). The RTM fabrication concept is based on the injection of resin into a mould cavity containing dry fibers (preform). During the injection process, air in the mould is being replaced by resin and the fibers are impregnated. For pressurized RTM normally matched die concepts are being used. Although these matched die tools can be complex and expensive, RTM has several major advantages compared to autoclave processing:
? Components can be made within very tight dimensional tolerances. This means that during assembly of the components no or a very limited amount of shimming is required.
? Components can be made (nearly) net shaped. This means that the amount of trimming and milling activities after curing of the component can be reduced.
? Components can be made with a high level of part integration. This means the cost savings can be realized during assembly.
? Thick complex shaped components can be made. This means that components can be designed in composite that would be impossible or very cumbersome to make by autoclave processing (e.g. landing gear components).
Over the last decade the National Aerospace Laboratory NLR in the Netherlands has contributed to the development of pressurized RTM technology by participating to a wide variety of application driven research projects. These programs were carried out in close collaboration with the industry in order to make sure that innovations made, keep lined-up with the requirement specifications of the structural components te be developed.
The present paper presents an overview of a number of composite RTM prototypes that were developed by NLR over the last ten years. These are:
? Bracket for the Ariane V launcher
In this project, techniques for preform manufacturing like stitching and bindering were evaluated. Also, design rules for concentrated load introduction were developed
? Composite cargo door for an Airbus A320 type of aircraft
In this project combining the pre-preg technology with resin injection principles developed a novel manufacturing technique. A manufacturing process was developed in which a cargo door including doorstops, pin locks and hinges was manufactured in one single production cycle
? Integrated beam concepts
In this project, the integration of brackets as well as net shaped fabrication issues were Addressed
? NH-90 composite trailing arm
In this project injection strategies were developed, braiding was evaluated, exothermal peaks were dealt with and new RTM tooling concepts were generated.
? Composite fuselage frames for an A320 sized aircraft
In this project, in which a large series of fuselage frames were manufactured, the issue of high production rates was addressed.