Glass fiber curved sandwich panel

This part is a process mock-up demonstrator showcasing the capabilities of Fiber Patch Placement technology on curved sandwich structures. In this case study, a non-graphite fiber reinforced composite sandwich structure was considered. The curved panel consists of sandwich and monolithic areas. The material used in this application was a satin weave glass fiber fabric prepreg and a Nomex paper honeycomb pre-shaped in the required curvature; no adhesive layer is included. 

Process: How was this part produced?

This simplified mock-up demonstrator was manufactured using our SAMBA Pro lab system with 10 robotic axis, following the Fiber Patch Placement (FPP) process. The material was slit glass fiber prepreg tape that was fed automatically through the system. The tape was then cut into 200mm long patches, in this case with a laser (ultrasonic cutting options also exist). Each patch was inspected twice by vision cameras for quality control (shape, size, alignment) and then placed directly into the metallic mold using the form-flexible Cevotec patch gripper. 

During manufacturing, the external skin was laid-up directly on the metallic tool according to the ply book, followed by the monolithic flange area. In the next step, the manual placement of the Nomex honeycomb core was performed and finally the internal skin was placed directly on the honeycomb core. Finally, the part was bagged and both skins co-cured in the autoclave according to material specification. There was no intermediate compaction or debulking step performed as it would be typical for a manual lay-up process for such component. 

Results: What is special about it?

This demonstrator showcases the unique strengths of Fiber Patch Placement technology:  

• Layup of external skin and multi-layer monolithic area in one integrated production program without interruption 
• Direct placement of very tacky, difficult-to-handle composite material on the honeycomb core 
• Achieving good compaction pressure during the entire lay-up cycle on the entire part, therefore eliminating time-consuming intermediate debulking steps 
• Composite material placement directly on a metallic mold (already pre-treated with release agent) without experiencing first-ply adhesion issues  

The cured part was then tested for porosity in the multi-layer monolithic flange area and skin adhesion pull-out tests on both skins. The porosity results came out with a very low, aerospace-compatible value and all pull-out tests were successful resulting in honeycomb core failure and not interface debonding. 

Relevance: Which components are featuring similar challenges?

This mock-up demonstrator is a representative geometry of various fairings, generally non-structural or secondary composite sandwich structures. Aircraft components of medium to high geometrical complexity featuring a combination of sandwich and monolithic areas can be processed fully automated with Fiber Patch Placement technology. Components with similar features are various types of aerodynamic fairings (antenna domes, nosecone covers, belly fairings, etc.), components of the empennage, winglets, nacelle fairings or landing gear access doors.