Peel Ply and Grinding for CFRP Adhesive Bonding - a never ending Story in Aerospace?

摘要

After more than 30 years in aerospace manual grinding of CFRP laminate surfaces after peel ply removal is still state-of-the-art for adhesive bonding. Manual grinding is very difficult to control, particularly in case of shaped and curved parts, is very time consuming and creates a lot of grinding dust in the bond shop. With the upcoming introduction of automated adhesive bonding processes alternative surface treatment processes are needed to keep a high, reproducible quality standard. Treatments like automated grit blasting have been developed [2] and promising alternatives like pre-impregnated peel plies [4,8,9], laser treatments [6] ultrasonic agitation [7], corona and atmospheric plasma methods are under investigation. The focus of this paper concentrates on the characterization of different peel ply fabrics and ply fabric treatments (release agents) as well as on the investigation of corona and atmospheric plasma treatment as alternatives for CFRP grinding. The quantity of peel plies for aerospace applications is increasing. Nevertheless peel plies are only a minor market for filament producers and for the industrial weavers. Currently it is not state-of-the-art in aerospace to qualify and purchase peel plies in the same manner as it is done for structural materials like pregregs and adhesives. Physical / chemical methods (e.g. IR, DSC, TGA, XPS) have been applied to characterize peel plies and release coatings. These methods can be adopted in material qualification of peel plies. The efficiency of corona and atmospheric plasma treatment was tested on a CFRP surface after removal of two different PA peel plies. Corona is restricted to flat parts and exhibited good bonding results only for one peel ply, which was coated with a hydrocarbon based release agent. Atmospheric plasma performed excellent for the examined peel plies, even when a siloxane release coating was on the peel ply. Further, the application on CFRP showed a very time stable activity of the plasma treatment on the CFRP surface before bonding and reproducible mechanical bonding performance after bonding.