Final Report Summary - ADVANCED (Advanced heating system and control mode for homogeneous high temperature curing of large composite repairs)
Executive Summary:
GMI AERO, based in Paris, is a worldwide recognized expert in technology for advanced composite structural repairs. Right from its creation, back in 1980, GMI has initially developed its capabilities towards composite structure fabrication processes. Specific sensors and control equipment have greatly helped in investigation of critical quality parameters and improved productivity. When composite repairs became a first preoccupation, GMI started early in 1984 to innovate with the equipment and toolings for repair and conduct processes in all steps from NDT to bonding. These works have been the result of regular cooperation both with aircraft manufacturers and end-users (i.e. airlines and MROs). Today, the business activity of the company is worldwide, cooperating with major aeronautical stakeholders in Europe, USA, Canada and China. The innovation of equipment has been the result of both internal development and extensive cooperation with researchers coming the National Technical University of Athens, with which a “strategic cooperation” is in place, participating together in several EU funded R&D projects. Recently, CleanSky GRA, ECO and SFWA R&D projects have offered to the company the opportunity to focus its research activities in order to further mature innovations towards a higher TRL.
Within ECO Design ITD a project titled “Advanced heating system and control mode for homogeneous high temperature curing tf large composite repairs – ADVANCED” has been recently finished by GMI and the NTUA, Topic Manager being Aircelle (Group SAFRAN). ADNANCED concerned the development of innovative solutions for the application of very large composite repairs, to be performed outside autoclaves. Even though achieving the very strict temperature tolerances (usually in the area of (+/-5 at 180 or 225oC) for repairs of several m2 is rather challenging, the expected benefits are very significant, as reduction of autoclave utilization induces direct reductions both to the overall repair cost and to the CO2 footprint of the repair, as the energy requirements for out-of-autoclave curing is minimal, compared to autoclave curing. Detailed 3D FE thermal transfer simulation of the full repair case was performed, in order to retrieve “thermal signature” of the repair, thus achieving customization of heating blankets design, while reduction of number of heating zones was achieved by using non-uniform heating generation elements. A 48 KW Power Supply and Control Unit has been developed, capable of heating up to 18 heating zones, together with the associated software for simultaneous data acquisition from eighty (80) control & monitoring thermocouples, using innovative control algorithms with increased flexibility in defining control mode. User friendly HMI was applied (similar to those of standard GMI ANITA EZ heating consoles), for immediate transition of operating personnel. The developed equipment has been successfully tested and approved at industrial environment, on an extremely demanding application (A380 reverser).
Project Context and Objectives:
The main concept driving the ADVANCED project is to optimise the existing and well known heating methodology using flexible heating blankets, to perform high quality, efficient and cost effective out-of-autoclave repair curing of large aircraft parts (nacelles, reversers etc.), by tailoring the localised heat generation to the exact thermal signature of the part to be repaired. This will lead to an environmentally friendly, low-energy, low-cost and easily interfaced out-of-autoclave solution, that will achieve better repair quality, mainly through minimization of temperature inhomogeneity problems. Moreover, the proposed solution addresses the challenge of increased temperature requirements specified in this CfP (i.e. 250oC) compared to standard requirements of maximum 180oC, through the application of appropriate solutions, not only in terms of heat generation, but in terms of involved materials, as well. The application field of the new heating equipment could range from typical small or large composite to composite repairs with high temperature homogeneity requirements (performed today using the GMI Aero resistance hot bonders), up to composite to metal repairs.
Consequently the main objectives of this proposal, through the optimisation of the resistance heating blankets design and construction methodology, would be:
a. Achievement of more homogeneous temperature distribution in large repair areas, by applying a multi zone closed loop control and customized variable heating elements, adapted to the “thermal signature” of the repaired part.
b. Increase of overall repair process reliability, by guarantying the adequate performance of the heating elements, through deletion of parameters that need to be defined by the operators (e.g. compensation for dissimilar heat losses, selection of thermocouples positioning etc.).
c. Reduction of overall power requirements, compared to autoclave curing, as the area to be heated and the overall thermal losses will be significantly lower, compared to traditional autoclave operations.
d. Increase of repair speed, through minimization of disassembling / re-assembling requirements of the parts to be repaired.
e. Reduction of overall repair costs, due to :
- Less energy consumption, compared to autoclave curing.
Less fasteners / material consumption, as minimized disassembly / re-assembly of parts will be required.
- Reduction of overall repair time requirements, due to minimization of preparatory works required for repair bonding (assembly / disassembly etc.).
f. Increase of range of applicability of bonded composite repairs, by ensuring the reliable achievement of specified temperature homogeneity requirements for more complex repair cases, thus reducing rejected parts.
g. Development of an environmentally friendly methodology for the curing of extensive bonded composite repairs, through:
- Reduction of the CO2 released to the atmosphere, given the largely reduced electrical power requirements, compared to autoclave curing.
- Minimization of wastes produced, through reduction of assembly / disassembly requirements.
- Reduction of disposal requirements for rejected composite parts, through increase of number of parts within economical repair limits
Project Results:
Within WP1 of the ADVANCED project the definition of the main design parameters and repair process constraints that need to be taken into consideration for the preparation of the specifications and the overall design of the new heating system have been performed. According to this definition, an initial design of the heating device was performed, including the heating system architecture, while the testing plan to be followed at the end of the development phase was frozen, in order to prove the compliance to the specification requirements. As a next step, in WP2, a detailed thermal mapping of the part designated by the Topic Manager has been performed, using numerical simulation (FEA), in order to tailor the heating elements performance to the part’s geometry and specificities, thus calculating the thermal signature of the part. This procedure included definition of zone numbers (i.e. number of closed loop control zones by the control unit) and their corresponding shapes and thermal capacities, in order to tailor the system capabilities to the actual application requirements and achieve maximum temperature homogeneity. According to the analysis results and respecting the overall specifications and architecture defined in WP1, a first prototype of the overall heating device was manufactured. In WP3, the field testing of the developed curing tool took place, in cooperation with the Topic Manager, according to the test plan defined in WP1. According to the test results a design feedback and upgrade of the developed heating system was performed, in close cooperation with the Topic Manager. The WP was concluded by a final testing phase of the developed heating device and the optimization of the performance of the heating equipment, which has proven the compliance of the developed system to the set specifications. Finally, WP4 concerned practically the industrialization of the developed system, in order to achieve maximum robustness, as well as practicability and simplicity for its application in repair cases. At this stage the final heating device prototype was developed and delivered to the Topic Manager. Moreover, a detailed heating device user’s guide was prepared, including all device operational aspects, in order to enable the enlargement of the equipment application range to future composite parts repair requirements.
Potential Impact:
Economic growth around the world has led to a continuous increase of air-traffic numbers during the past decades. This increase is expected to continue at an even stronger pace for the next two decades. As the operating fleet grows, the costs and hazard exposure will also increase. Despite the recent difficulties faced by the industry, the market forecast over the next twenty years for commercial aircraft is expected to be of the order of €1.6 Trillion. The Aerospace Market remains a highly competitive one and any aspect of commercial advantage must be sought. ADVANCED will address a key element of competitive advantage for the industry, those of aircraft reliability during operation and maintenance costs. Replying directly to JTI CfP, the primary drivers for ADVANCED relate to safety, economic and societal issues. The application of the proposed advantages to the composite repair process will improve reliability during operation, improve performance and minimise the time the aircraft needs to spend on the ground for repair, which are among the main targets of the CleanSky JTI. This will permit increased aircraft availability and lower maintenance costs to be incurred by the operating companies. The increase in reliability will lead to a reduction in accidents, loss of life and associated compensation costs resulting from failure of critical aircraft structural components. It is expected that this project will lead to a major change in the development of bonded composite repair procedures, thereby strengthening the EU position within the global Aerospace Market, whilst maintaining the competitive advantage of the EU companies over its US and Japanese rivals, in the field of maintenance equipment development. It is planned that full industrialization of the results of the project, in terms of application of the new processes to various cases where bonded composite repair will be engaged, could take place VERY SHORTLY after the end of the project, according to the requirements of the “Topic Manager” and CSJU. Due to the increased number of “large” composite parts manufactured for modern aircraft (both for fuselage and engine nacelle applications) it is expected that the proposed methodology benefits will have a very wide range of application and, consequently, assist companies using it in achieving very important benefits. This way, EU based manufacturers and repair centers using this technology could enjoy a very important advantage compared to international competition.
GMI AERO, based in Paris, is a worldwide recognized expert in technology for advanced composite structural repairs. Right from its creation, back in 1980, GMI has initially developed its capabilities towards composite structure fabrication processes. Specific sensors and control equipment have greatly helped in investigation of critical quality parameters and improved productivity. When composite repairs became a first preoccupation, GMI started early in 1984 to innovate with the equipment and toolings for repair and conduct processes in all steps from NDT to bonding. These works have been the result of regular cooperation both with aircraft manufacturers and end-users (i.e. airlines and MROs). Today, the business activity of the company is worldwide, cooperating with major aeronautical stakeholders in Europe, USA, Canada and China. The innovation of equipment has been the result of both internal development and extensive cooperation with researchers coming the National Technical University of Athens, with which a “strategic cooperation” is in place, participating together in several EU funded R&D projects. Recently, CleanSky GRA, ECO and SFWA R&D projects have offered to the company the opportunity to focus its research activities in order to further mature innovations towards a higher TRL.
Within ECO Design ITD a project titled “Advanced heating system and control mode for homogeneous high temperature curing tf large composite repairs – ADVANCED” has been recently finished by GMI and the NTUA, Topic Manager being Aircelle (Group SAFRAN). ADNANCED concerned the development of innovative solutions for the application of very large composite repairs, to be performed outside autoclaves. Even though achieving the very strict temperature tolerances (usually in the area of (+/-5 at 180 or 225oC) for repairs of several m2 is rather challenging, the expected benefits are very significant, as reduction of autoclave utilization induces direct reductions both to the overall repair cost and to the CO2 footprint of the repair, as the energy requirements for out-of-autoclave curing is minimal, compared to autoclave curing. Detailed 3D FE thermal transfer simulation of the full repair case was performed, in order to retrieve “thermal signature” of the repair, thus achieving customization of heating blankets design, while reduction of number of heating zones was achieved by using non-uniform heating generation elements. A 48 KW Power Supply and Control Unit has been developed, capable of heating up to 18 heating zones, together with the associated software for simultaneous data acquisition from eighty (80) control & monitoring thermocouples, using innovative control algorithms with increased flexibility in defining control mode. User friendly HMI was applied (similar to those of standard GMI ANITA EZ heating consoles), for immediate transition of operating personnel. The developed equipment has been successfully tested and approved at industrial environment, on an extremely demanding application (A380 reverser).
Project Context and Objectives:
The main concept driving the ADVANCED project is to optimise the existing and well known heating methodology using flexible heating blankets, to perform high quality, efficient and cost effective out-of-autoclave repair curing of large aircraft parts (nacelles, reversers etc.), by tailoring the localised heat generation to the exact thermal signature of the part to be repaired. This will lead to an environmentally friendly, low-energy, low-cost and easily interfaced out-of-autoclave solution, that will achieve better repair quality, mainly through minimization of temperature inhomogeneity problems. Moreover, the proposed solution addresses the challenge of increased temperature requirements specified in this CfP (i.e. 250oC) compared to standard requirements of maximum 180oC, through the application of appropriate solutions, not only in terms of heat generation, but in terms of involved materials, as well. The application field of the new heating equipment could range from typical small or large composite to composite repairs with high temperature homogeneity requirements (performed today using the GMI Aero resistance hot bonders), up to composite to metal repairs.
Consequently the main objectives of this proposal, through the optimisation of the resistance heating blankets design and construction methodology, would be:
a. Achievement of more homogeneous temperature distribution in large repair areas, by applying a multi zone closed loop control and customized variable heating elements, adapted to the “thermal signature” of the repaired part.
b. Increase of overall repair process reliability, by guarantying the adequate performance of the heating elements, through deletion of parameters that need to be defined by the operators (e.g. compensation for dissimilar heat losses, selection of thermocouples positioning etc.).
c. Reduction of overall power requirements, compared to autoclave curing, as the area to be heated and the overall thermal losses will be significantly lower, compared to traditional autoclave operations.
d. Increase of repair speed, through minimization of disassembling / re-assembling requirements of the parts to be repaired.
e. Reduction of overall repair costs, due to :
- Less energy consumption, compared to autoclave curing.
Less fasteners / material consumption, as minimized disassembly / re-assembly of parts will be required.
- Reduction of overall repair time requirements, due to minimization of preparatory works required for repair bonding (assembly / disassembly etc.).
f. Increase of range of applicability of bonded composite repairs, by ensuring the reliable achievement of specified temperature homogeneity requirements for more complex repair cases, thus reducing rejected parts.
g. Development of an environmentally friendly methodology for the curing of extensive bonded composite repairs, through:
- Reduction of the CO2 released to the atmosphere, given the largely reduced electrical power requirements, compared to autoclave curing.
- Minimization of wastes produced, through reduction of assembly / disassembly requirements.
- Reduction of disposal requirements for rejected composite parts, through increase of number of parts within economical repair limits
Project Results:
Within WP1 of the ADVANCED project the definition of the main design parameters and repair process constraints that need to be taken into consideration for the preparation of the specifications and the overall design of the new heating system have been performed. According to this definition, an initial design of the heating device was performed, including the heating system architecture, while the testing plan to be followed at the end of the development phase was frozen, in order to prove the compliance to the specification requirements. As a next step, in WP2, a detailed thermal mapping of the part designated by the Topic Manager has been performed, using numerical simulation (FEA), in order to tailor the heating elements performance to the part’s geometry and specificities, thus calculating the thermal signature of the part. This procedure included definition of zone numbers (i.e. number of closed loop control zones by the control unit) and their corresponding shapes and thermal capacities, in order to tailor the system capabilities to the actual application requirements and achieve maximum temperature homogeneity. According to the analysis results and respecting the overall specifications and architecture defined in WP1, a first prototype of the overall heating device was manufactured. In WP3, the field testing of the developed curing tool took place, in cooperation with the Topic Manager, according to the test plan defined in WP1. According to the test results a design feedback and upgrade of the developed heating system was performed, in close cooperation with the Topic Manager. The WP was concluded by a final testing phase of the developed heating device and the optimization of the performance of the heating equipment, which has proven the compliance of the developed system to the set specifications. Finally, WP4 concerned practically the industrialization of the developed system, in order to achieve maximum robustness, as well as practicability and simplicity for its application in repair cases. At this stage the final heating device prototype was developed and delivered to the Topic Manager. Moreover, a detailed heating device user’s guide was prepared, including all device operational aspects, in order to enable the enlargement of the equipment application range to future composite parts repair requirements.
Potential Impact:
Economic growth around the world has led to a continuous increase of air-traffic numbers during the past decades. This increase is expected to continue at an even stronger pace for the next two decades. As the operating fleet grows, the costs and hazard exposure will also increase. Despite the recent difficulties faced by the industry, the market forecast over the next twenty years for commercial aircraft is expected to be of the order of €1.6 Trillion. The Aerospace Market remains a highly competitive one and any aspect of commercial advantage must be sought. ADVANCED will address a key element of competitive advantage for the industry, those of aircraft reliability during operation and maintenance costs. Replying directly to JTI CfP, the primary drivers for ADVANCED relate to safety, economic and societal issues. The application of the proposed advantages to the composite repair process will improve reliability during operation, improve performance and minimise the time the aircraft needs to spend on the ground for repair, which are among the main targets of the CleanSky JTI. This will permit increased aircraft availability and lower maintenance costs to be incurred by the operating companies. The increase in reliability will lead to a reduction in accidents, loss of life and associated compensation costs resulting from failure of critical aircraft structural components. It is expected that this project will lead to a major change in the development of bonded composite repair procedures, thereby strengthening the EU position within the global Aerospace Market, whilst maintaining the competitive advantage of the EU companies over its US and Japanese rivals, in the field of maintenance equipment development. It is planned that full industrialization of the results of the project, in terms of application of the new processes to various cases where bonded composite repair will be engaged, could take place VERY SHORTLY after the end of the project, according to the requirements of the “Topic Manager” and CSJU. Due to the increased number of “large” composite parts manufactured for modern aircraft (both for fuselage and engine nacelle applications) it is expected that the proposed methodology benefits will have a very wide range of application and, consequently, assist companies using it in achieving very important benefits. This way, EU based manufacturers and repair centers using this technology could enjoy a very important advantage compared to international competition.
