Skip to main content

SuCoHS Newsletter No 3: Interview

Find out how the people involved in SuCoHS have been working to achieve the objectives of the project!

After almost two years of fruitful collaboration, the project partners know the software and hardware developed in SuCoHS like the back of their hand. Some of them showcased the benefits of their solutions to the entire consortium during a demonstration workshop that took place on the 11th of March 2020 at the NLR facilities in Marknesse, Netherlands, at the occasion of the mid-term review meeting of the project. The partners involved in the demonstration are happy to explain the ins and outs of the workshop:

Alexander Leutner, Managing Director, Apodius GmbH part of Hexagon Manufacturing Intelligence

Wilco Gerrits, Program Manager, NLR

Nikos Pantelelis, Director, Synthesites

Rolf Evenblij, Program Manager, Technobis Fibre Technologies

Alexander Leutner, Wilco Gerrits, Rolf Evenblij and Nikos Pantelelis
Interviewees Alexander Leutner, Wilco Gerrits, Nikos Pantelelis and Rolf Evenblij.

Question: The Apodius Vision System Technology is a solution for quality assurance and process automation in composite part production. Can you describe the components of this technology?

Answer by Alexander Leutner: The Apodius Automatic Fibre Placement (AFP) Inspection System consist of two subsystems:

  • Apodius AFP Inspection Sensor is a vision-based sensor system, tailor-made to measure material-specific characteristics, process parameters, to detect defects and other production faults. Its sleek hardware design has been engineered to be seamlessly integrated in fibre placement processes. The sensor fits picture-perfect in the lay-up machine’s end-effector. It has been designed in close cooperation with machine user and the with support from Coriolis, the machine manufacturer.
  • Apodius AFP Explorer software performs image processing and combines local measurement results with positioning and process information provided by the machine’s Programmable Logic Controller (PLC) to simultaneously provide process status and production quality feedback in part coordinates.

The combination of both subsystems makes a powerful tool, enabling full automation of manual visual inspection that consumes a lot of time and so far, is still required after manufacturing of every ply.            

What are the unique selling points of this technology compared the other solutions available on the market?

The main advantage of the Apodius AFP Inspection System is that its core technology is machine vision, measuring independently from differences in the height profile of the lay-up material. It allows the system to pick up every feature on the part’s surface, even though it is only micrometer thick, such as backing paper. The Apodius AFP Inspection System is also fully integrated in the whole production process: it fully digitalizes the process and measures in-situ right during lay-up. It provides quality feedback from the first millimeter laid up.

It also comes in very handy that the Apodius AFP Inspection System can be easily integrated in existing lay-up production cells – taking only four screws, an ethernet and a power cable, whereas the Inspection Computer is very straightforward. Partners can quickly mount and detach the system at different locations for different occasions.  

What is the specific application of this technology in SuCoHS?

Newly developed, very thin tape material featuring specific heat resistance is used for the demonstrator parts. It takes some time to set up material characteristics, process and lay-up machine to this new material, here the system can help to provide quality feedback such as gaps that occur in the lay-up. Of course, in the project, we have accordingly adjusted and further developed the system to work with this newly designed material. Now, we have a robustly running AFP Inspection System that provides in-situ quality feedback and process status in real-time.

With the database including all related data such as design, material, manufacturing (lay-up and curing) process, quality, feedback to simulation for every part produced, the actual lay-up quality assessment can be lopped back to simulation to offer a more accurate prediction of quality and general structural integrability.

We are very happy to work with these competent and enthusiastic partners on this relevant and cutting-edge technology topic and, together, have made such a great achievement!

The Apodius AFP Inspection System at NLR facilities in Marknesse.
The Apodius AFP Inspection System at NLR facilities in Marknesse.

 

Question: The development of new composites and their manufacturing technologies are part of NLR’s reputation based on comprehensive relevant research. The AFP facility at NLR allows for an automated manufacturing of complex composite structures.

NLR is the leader of the SuCoHS work package 5 “Integration, Testing and Validation”. Can you briefly describe your involvement in SuCoHS? 

Answer by Wilco GerritsRoyal NLR has been an ambitious knowledge organization for more than 100 years , with the deep-rooted desire to continue to innovate. With that in mind, we make the world of transport safer, more sustainable, more efficient and more effective. Together with our partners we may help to shape the exciting world of tomorrow. We are on the threshold of pioneering innovations.

Within SuCoHS, NLR develops innovative manufacturing concepts for stiffened structures for high temperature applications in close collaboration with industrial and other partners, by using automated technologies like AFP and hot-forming. Process monitoring techniques, developed by Apodius, are integrated on NLR’s AFP facility. Cure monitoring systems, developed by Synthesites, are integrated into NLR’s autoclave and ovens. Optical fibres with FBG sensors from Technobis are positioned by AFP and used as embedded system for process monitoring.   

What are the materials used for manufacturing activities within SuCoHS?

The AFP technology is one of the available options at NLR to automate the manufacturing of (complex) shaped composite components. Fibre reinforced thermoset and thermoplastic materials can be processed with this technology as well as dry fibre materials. Each material combination (fiber, resin, binder) asks for a special process window represented as a set of process parameters optimised for maximum material quality, accuracy and process speed. Within SuCoHS, the focus is created on new but also existing high temperature (multi) materials. 

What are the challenges of using the AFP technology in the project? What are the SuCoHS demonstrators that will be manufactured with the AFP?

Grid stiffened concepts to be manufactured by AFP were developed together with Collins Aerospace as carrying structure for interior parts. Preforms including grid stiffeners are manufactured in one process step. Flexible tooling for these complex shaped double curved structures is developed. Other manufacturing concepts for integrated blade stiffeners on single curved parts by a combination of AFP and automatic hot-forming, was developed together with Aernnova Engineering, manufactured and machined at NLR.

New was the use of thin ply toughened cyanate ester material for high temperature use, developed by FHNW and North Thin Ply Technology. NLR assisted to make this material ready for AFP and developed a feasible process window for this material in terms of AFP and hot forming. Another challenge for this risk mitigation structure was the development of a method to position optical fibres with FBG sensors by the AFP technology. Special guides were engineered to feed the optical fibre through the robot head of the fibre placement machine. Innovative methods were developed to prevent damage to the optical fibre and FBG sensors when positioned by AFP. In addition, special connection methods were developed together with Technobis to gain data from the FBG sensors (strain and temperature) after AFP, during autoclave curing at NLR and during structural compression tests at elevated temperatures at DLR. The whole deposition of material was monitored by an evolved 3D vision camera system, fully integrated on the AFP machine together with Apodius. Detected results are written to the central database, besides the cure data as gained from the Optimold system, by using special flanges from Synthesites on NLR’s autoclave wall for wire feed-through. This system was tested at 200°C and 8 bars of pressure at NLR.

Additional challenges were found in the manufacturing of slit tape material including development of a reliable AFP process window for application of fibre reinforced PolyFurfurylAlcohol (PFA), which is a 100% bio-based resin system produced by TransFurans Chemicals. Thin ply and conventional thickness UD materials were produced slit and further prepared for AFP. First trials were performed which are showing promising results. Small improvements to the material were made. A new batch is produced and will be tested on AFP in the coming months.

What are the SuCoHS demonstrators that will be manufactured with the AFP?

Within this project, as part of the whole development done by all partners within the consortium, NLR will develop strategies for automated manufacturing of the following demonstrators in this program:

  • High temperature resistance nacelle component together with Bombardier
  • Composite Aircraft Interior Shell together with Collins Aerospace
  • High temperature tail cone panel substructure with Aernnova Engineering
  • Several Risk Mitigation Structures as structural details for the demonstrators

 

It is a privilege to cooperate in this interesting consortium within this challenging program: the development of automation and integration of sensors on high temperature composite materials.

Demonstration of the NLR AFP machine.
Demonstration of the AFP technology at the NLR facilities in Marknesse.

 

Question: Sensors developed by Synthesites are used in SuCoHs for process monitoring of high temperature curing. What kind of sensors does Synthesites provide within the project?

Answer by Nikos Pantelelis: Synthesites developed within SuCoHS and provides to the trials and demonstrators high-temperature disposable sensors as well as the new durable sensor that can be used in direct contact with carbon fibres. Also, new self-sensing technologies have been developed in order to use the carbon fibres of the composites for sensing their process and structural properties.

The new CF sensor.
The new CF sensor.
The new high temp disposable cure sensor with special holes to improve the quality of the measurements when working with low resin content prepregs of the North Thin Ply Technologies.
The new high temp disposable cure sensor with special holes to improve the quality of the measurements when working with low resin content prepregs of the North Thin Ply Technologies.

 

Are there differences in performance between these sensors?

The durable and disposable sensors have basically the same performance while sometimes one type may be selected over the others due to specific requirements such as cost, tooling modifications, extreme temperature and performance.

What are the results of the tests of cure monitoring system for the different types of resins investigated in SuCoHS?

After the installation of the appropriate wiring in the autoclave and in the oven at NLR’s facilities (figure below) several trials have been already executed successfully while many others have been scheduled.

Installed feedthrough gland at the door with sensors cables and sensor adaptors at the NLR autoclave in Marknesse.
Installed feedthrough gland at the door with sensors cables and sensor adaptors at the NLR autoclave in Marknesse.

 

A typical example of cure monitoring of the newly developed Cyanate-Ester toughened prepreg can be seen in the graph below with comparison between a trial in the autoclave and in the oven.

Synchronized measurements from the trials in the oven and the autoclave.
Synchronized measurements from the trials in the oven and the autoclave.

 

Question: Technobis Fibre Technologies provides optical sensors for process monitoring in SuCoHS. What kind of sensors were selected for monitoring of composites cure process?

Answer by Rolf Evenblij: The selection of an optical fiber for monitoring a composites cure process required several investigations. From a wide availability of optical sensor types and configurations, key parameters were identified:

  • temperature stability up to 350°C
  • sufficient adhesion to the resin matrix
  • embedded optical fiber should not distort the composite structure
  • in addition, the optical fiber and integrated Fibre Bragg Grating (FBG) sensor should stay reasonably well within their specifications to ensure measurement performance.

Polyimide coated optical fiber was selected based on the process relevant criteria. These fibers can sustain temperatures of 300°C and even 400°C for a limited period. Also, the method of writing FBG sensors into the fiber core is being evaluated; traditional FBG manufacturing includes stripping and recoating of the optical fiber, which may affect mechanical and thermal properties of the fiber. To overcome the limitations of the traditional FBG manufacturing technique, directly writing the FBG sensor in the optical fiber core is done without the need for stripping and recoating the optical fiber. However, this method increases polarization sensitivity. In addition to evaluating the performance trade-offs of the optical fiber, the economic impact of the fiber selection is briefly evaluated. Polyimide coated fibers are commonly available and considered a standard. For some cases, the performance dependence and associated costs on the FBG writing method could be a trade-off. In this case, the most standard approach is selected and tested successfully.

What were the challenges of AFP integration of the FBG sensors?

For seamless integration of optical fiber sensors in composites for manufacturing process monitoring, the AFP machine from NLR was used for placement of optical fibers. The AFP machine utilizes a placement head that allows for 8 feeds of carbon strips to be laid out in pattern configurations to manufacture the composite panels. One of those feeders is used for the optical sensing fiber. The challenging principle is to guide this optical fiber feed in such a way that the fiber is laid-in properly without any significant (mechanical) distortions, which allows the optical fiber to retain its optimal optical signal transmission properties. Consequently, this ensures that the strain transfer into the FBG sensors during the cure process can be captured well by the interrogator. Another challenge was to ensure the optical fibers are protected at the ingress/egress location. At the ingress/egress location the optical fibers can be subjected to micro-bending due to the applied vacuum and pressure inside the autoclave, which can lead to attenuation of the optical signal, or, in the worst case scenario, optical fiber breakage due to transverse forces. Therefore, PolyEtherEtherKetone (PEEK) tubes were used to protect the optical fiber at the ingress/egress. Once the optical fibers were laid-in, the pigtails were connectorized for monitoring the cure process using the Technobis SwitchedGator interrogation system. A first attempt demonstrated attenuations of less than 50%. Although already considered a reasonable result, an improvement can be achieved by using for instance bend-insensitive optical fiber instead, allowing for tighter curves and less signal attenuation due to for instance micro-bending.  

Can we consider that the demonstration in March was successful? Were the results in line with your expectations?

Yes, the demonstration can be considered successful. The results demonstrated a high degree of feasibility of process monitoring. The embedded optical fibers survived the high temperature and pressure conditions in the autoclave. Now, the embedded optical sensors can be further tested for structural health monitoring of the composite panels, i.e. thermo-mechanical load monitoring, and damage and impact detection. At the same time, significant improvement possibilities were made visible, for instance aligned placement of optical fiber with the direction of the composite fiber direction will improve strain measurement accuracy. In subsequent tests, mitigation of FBG bi-refringence and non-uniform strain effects using pre-coated fiber, instead of the used bare-fiber, integrated with the AFP are expected to provide better results. No transmission losses were identified at high temperature and pressure due to the fiber feedthrough, therefore, allowing the optical fiber to enter the autoclave from the outside while the FBG interrogator could be placed outside the autoclave. This mitigates  the challenge to integrate the FBG interrogator inside the autoclave. During the curing process significant shift in the FBGs Bragg wavelength was observed. This means that to properly monitor the strain induced in the composite during the curing process, the material properties (Coefficient of Thermal Expansion i.e. CTE value) needs to be investigated to obtain the temperature-compensated strain.

Do you plan to bring improvements to the process by the end of the project?

Yes. The considered success of the tests performed are two-fold: they demonstrated a high degree of feasibility to implement optical fiber integration throughout the process of composites layup using the AFP, curing in the autoclave and finally using the surviving fibers for structural health monitoring. At the same time, they exposed several aspects that can be improved to increase measurement performance and optical fiber integrity, and thus systematic reliability. Further in-depth investigation and correlation with reference methods will allow for these improvements to emerge.

Rolf Evenblij during the demonstration at NLR facilities.
Rolf Evenblij during the demonstration at NLR facilities in Marknesse.