The exponential growth in the use of composite materials in aviation is leading to problems with regard to the repair of these materials. Where composite manufacturing techniques are being automated and perfected, repair methods are lacking behind and still require manual processes only to be performed by (scarce) specialised technicians at dedicated repair locations. Automated repair and inspection methods requiring less skilled operators that can be performed “on the gate” will be the solution to improve the repair of damaged composite structures.
Innovation Track 5: Developing automated repair techniques for repair of composite structures
This project led by NLR focuses on the automation of composite repairs, long-term quality assurance, shortening the repair time and making repairs possible on site. A big advantage of performing this innovation track within the framework of the DCMC is that the parties involved in the DCMC together have all of the knowledge regarding certification, material properties and gluing methods to successfully perform this project.
In this project automation of the whole repair chain will be investigated and algorithms will be developed to combine NDI inspection data and geometry scans of the damaged area in order to create a milling file for automated manufacturing of the repair patch or as input for the Additive Manufacturing (AM) of the (metal) patch. Part of the project will be dedicated to the investigation of adhesives, preparation methods and determination of milling parameters for composite and AM materials. This will result in faster repair on location, cost reduction and higher deployability of the aircraft.
Small sized 2mm thick epoxy/carbon tensile samples were manufactured and adhesive bonded to define the optimal milling strategy. A 4 mm thick epoxy/carbon panel was then manufactured and assembled to a support frame. Impact damages at different energy levels were applied to the centre of the panel followed by Non Destructive Inspections (NDI), using visual, thermal and ultrasound inspection techniques, and geometry measurements. The data of the NDI measurements were merged into one milling file for the panel.
Two different milling robots were evaluated in the project (in combination with DCMC innovation track 6) for the automation trials:
- The MobileBlock (MB) developed and manufactured by DMGMORI
- The REPLY.5 Water Jet cutting robot developed and manufactured by BAYAB
The MB milling robot that was demonstrated can only be used for large airframe surfaces. Application on smaller and complex shaped surfaces (like the NH90 tail) is not possible. Also the large weight and size makes it difficult for positioning on aircraft structures. The MB was coupled to the NLR robot and positioned on a NH90 tail section and a 787 elevator. A promising abrasion method that was demonstrated in this project is the REPLY.5 Water Jet cutting robot. This machine can easily be positioned over the damaged area by the operator. Also for this machine it is not possible to use it on smaller and complex shaped surfaces.
Based on the experiences in this project an alternative approach will be investigated in follow up projects. This approach is concentrating on small and light weighted co-bot systems that assist the operator and can be used to automate the inspection and repairs on smaller and complex shaped locations.
In December 2019, a demonstration repair has been made on a representative fuselage panel within this project. The MB was used to prepare the fuselage panel. The patch was milled from a second composite panel with the same lay-up as the demonstrator panel and successfully bonded to the panel using a film adhesive.
The work continues with research to investigate the potential for applying Additive Manufacturing (AM) technologies to Titanium printed patch repairs for composite structures. The reason for printing these perfectly fitting 3D parts is, that they can be applied to the composite fuselage by adhesive bonding. However, environmentally friendly durable adhesive bonding to (printed) Titanium is not an off the shelf technology, and that is why this research is needed.
Runtime: 1st of November 2014 – May 2021
- Milestone 4: Demonstration (December 2019)
- Milestone 5: Development of AM methods (May 2021) – Application of Additive Manufacturing (AM) technology to the repair of composite aircraft structures.
Within this milestone the repair method was selected that will be used in the project. It is important to select a method that can be automated.
There will be more methods selected in the project. Ultrasound and Thermography will be part of the investigation.
The geometry of the repair panel will be measured and combined with the damage inspection data. The resulting data file will be used for the milling process.
A representative repair will be done using the generated data file and a milling robot.
Application of Additive Manufacturing (AM) technology to the repair of composite aircraft structures.