03 The first automatic scarfing system in MRO (Part 1/4)

Text:

In the aviation industry, composite materials such as carbon fibre reinforced plastics – in short CFRP - have recently been showcased as the go-to material for most modern long-range aircraft types like the Boeing 787 and Airbus A350. This however is just one side of the story. When it comes to so-called Airframe Related Components (ARC), such as thrust reversers, engine cowlings or nose radomes, they have been the predominant material for decades and repair procedures have evolved with them. That said, one thing has remained the same when repairing composite aircraft structures: they are all done manually with the corresponding labor intensiveness, lengthy time factors and costs. Adding to this are the limitations in accuracy and repeatability that manual repair brings with it. As a result, bonded repairs of primary aircraft structures (e.g. fuselage) are limited in size. Moreover, manual processes limit repair strategies leading to technically unnecessary high material use.

In the aviation industry, composite materials such as carbon fibre reinforced plastics – in short CFRP - have recently been showcased as the go-to material for most modern long-range aircraft types like the Boeing 787 and Airbus A350. This however is just one side of the story. When it comes to so-called Airframe Related Components (ARC), such as thrust reversers, engine cowlings or nose radomes, they have been the predominant material for decades and repair procedures have evolved with them. That said, one thing has remained the same when repairing composite aircraft structures: To tackle these challenges, we at Lufthansa Technik, together with iSAM AG, have developed the first automated adaptive robot system that can be applied to a multitude of ARC® repair processes in aviation maintenance, repair and overhaul (MRO).

In the aviation industry, composite materials such as carbon fibre reinforced plastics – in short CFRP - have recently been showcased as the go-to material for most modern long-range aircraft types like the Boeing 787 and Airbus A350. This however is just one side of the story. When it comes to so-called Airframe Related Components (ARC), such as thrust reversers, engine cowlings or nose radomes, they have been the predominant material for decades and repair procedures have evolved with them. That said, one thing has remained the same when repairing composite aircraft structures: I will now briefly introduce you to this unique system and all its specific features.

In the aviation industry, composite materials such as carbon fibre reinforced plastics – in short CFRP - have recently been showcased as the go-to material for most modern long-range aircraft types like the Boeing 787 and Airbus A350. This however is just one side of the story. When it comes to so-called Airframe Related Components (ARC), such as thrust reversers, engine cowlings or nose radomes, they have been the predominant material for decades and repair procedures have evolved with them. That said, one thing has remained the same when repairing composite aircraft structures: A multitude of ARC repair processes – fully automized

When developing our adaptive robot system, our goal was to optimize a multitude of processes in aviation MRO. It covers:

When developing our adaptive robot system, our goal was to optimize a multitude of processes in aviation MRO. It covers: 1.      scarfing

When developing our adaptive robot system, our goal was to optimize a multitude of processes in aviation MRO. It covers: 2.      removal of one skin and honeycomb core material from sandwich structures

When developing our adaptive robot system, our goal was to optimize a multitude of processes in aviation MRO. It covers: 3.      transfer of drill holes and edges to oversized and undrilled replacement parts

When developing our adaptive robot system, our goal was to optimize a multitude of processes in aviation MRO. It covers: All of these processes take into account the part-specific geometry caused by an adaptive algorithm that plans the robot’s path based on 3D scan data. Thanks to the geometric and operational versatility of our system design, these processes can be easily transferred to further aircraft parts and key functions have already been developed. The stationary system can be employed at any larger MRO facility, which deals with composite parts. The system is capable of changing milling tools and drills in an 18-piece tool changer. Heightened operating efficiency, reduced material use, faster turn-around-time and less required spare parts are among its many benefits. Work safety is also greatly enhanced, making the system ideal for a wide array of deployment situations.

During the project, my colleagues and I at Lufthansa Technik detailed all part-specific repair processes. This included single process steps, as well as the parameters and tolerances regarding repair process alternations from the manual that were automated. Based on the information provided by us, iSAM AG designed, developed and installed the robot cell, including the control systems, 3D scan data processing, CAD and material information. The part handling systems were manufactured by iSAM AG, while we again developed all support structures and jigs for the individual parts. The resulting system carries out repairs for three major part groups: Nose Radomes (4 different types), Fan Cowl Doors (2 types) and Inlet Cowls (5 types). We will dive a little deeper into the following aspects a bit later.

During the project, my colleagues and I at Lufthansa Technik detailed all part-specific repair processes. This included single process steps, as well as the parameters and tolerances regarding repair process alternations from the manual that were automated. Based on the information provided by us, iSAM AG designed, developed and installed the robot cell, including the control systems, 3D scan data processing, CAD and material information. The part handling systems were manufactured by iSAM AG, while we again developed all support structures and jigs for the individual parts. The resulting system carries out repairs for three major part groups: Nose Radome repairs

Nose radome repairs are conducted by removing the damaged section of the GFRP-honeycomb sandwich. To aid load transfer during laminate reparation, the remaining radome skins with a thickness of 0.66 mm are scarfed with a scarfing ratio of ~1: 70. These repairs can take up a large area of the entire radome. Our system scans the actual surface of the radome, including the marked damaged area from the inspection. Via a graphical user interface, the operator can plan the repair area on the scanned surface, which leads to a scarf milling path calculation on the curved structure. In an iterative milling and scanning process, we have already achieved proven accuracies in the range of ±0.06 mm.

Nose radome repairs are conducted by removing the damaged section of the GFRP-honeycomb sandwich. To aid load transfer during laminate reparation, the remaining radome skins with a thickness of 0.66 mm are scarfed with a scarfing ratio of ~1: Learn more about nose radome repairs in the upcoming part 2 of this series.

Nose radome repairs are conducted by removing the damaged section of the GFRP-honeycomb sandwich. To aid load transfer during laminate reparation, the remaining radome skins with a thickness of 0.66 mm are scarfed with a scarfing ratio of ~1: Fan cowl door repairs

Nose radome repairs are conducted by removing the damaged section of the GFRP-honeycomb sandwich. To aid load transfer during laminate reparation, the remaining radome skins with a thickness of 0.66 mm are scarfed with a scarfing ratio of ~1: In addition to scarfing, our automated system is capable of removing one skin and the honeycomb material down to the adhesive layer of the second skin for various repairs. Here, we apply an adaptive scanning/milling process with an accuracy in the range of 0.1 mm. The process can also be applied to complex curved structures such as radomes and CFRP engine housings like fan cowl doors.

Accuracy is not the only challenge: compensated thermal stresses also require an adaptive process and milling strategy. Throughout the milling process, plies and honeycomb material are removed, which compensated thermal deformation during manufacture. This leads to in-process deformations of the part, which are significantly larger than the required accuracies, which we had to take into account during the process.

Accuracy is not the only challenge: Learn more about fan cowl door repairs in the upcoming part 3 of this series.

Accuracy is not the only challenge: Inlet Cowl repairs

Accuracy is not the only challenge: In terms of Inlet Cowlings and engine air intakes, we frequently had to remove and replace structural components, e.g. Lip Skins and Outer Barrels. Lip Skins are aluminum parts at the front of the inlet cowl, while Outer Barrels are usually CFRP structures on the side of the inlet cowling. In order to achieve this, the system employs a process that transfers all final dimension drill holes and edges to oversized and undrilled replacement structures. Before that, the system automatically removes hundreds of bolts and rivets from the part.

Accuracy is not the only challenge: Learn more about inlet cowl repairs repairs in the upcoming part 4 of this series.

Accuracy is not the only challenge: Increased process efficiency, less spare parts required

Accuracy is not the only challenge: By automating the milling and drilling processes, we managed to significantly increase process efficiency and reduce the turn-around-time in repair shops. The high degree of accuracy ensured fast processing with little to no manual re-work. As a result, fewer spare parts were needed. Furthermore, we could reduce the amount of repair materials such as prepregs with the automated process. Thanks to the automatically programmed milling path, the repair of plies is accelerated by cutting the plies while milling is still ongoing. The plies can be cut on an automatic ply cutter allowing ply nesting to further improve material efficiency.

Accuracy is not the only challenge: For us at Lufthansa Technik, this technology is a key factor in improving repair quality and repeatability, thus laying the groundwork for larger structural repairs. The versatility of our robot, combined with the adaptive software allows easy and cost-effective upgrades to further composite structures. 

Accuracy is not the only challenge: Improved working conditions for coworkers

Accuracy is not the only challenge: A big plus of the automated system is that it significantly helps us to improve the working conditions for our maintenance staff. Until now, scarfing as well as composite skin and honeycomb removal had to be conducted manually and required the necessary protection. Moreover, the position of the parts often lead to less ergonomic working positions, where maintenance crews had to work overhead or in kneeling positions for a long period of time. The removal of hundreds of rivets and bolts was also exhausting, especially for shoulder and arm joints. Now, our maintenance personnel can conveniently conduct all these operations from a control desk without the risk of being exposed to hazards such as noise, dangerous substances and difficult working conditions.

Accuracy is not the only challenge: When it comes to the nose radome repair process, our system even allows crews to perform operations that were not economically feasible during manual processes. In many cases, the outer skin of the radome sandwich material is not damaged and does not have to be removed. The robot makes it possible to only remove the inner skin and honeycomb material, without damaging the outer skin in areas up to 2-3 m². This not only saves time regarding the repair area but also significantly reduces the needed prepreg material for the repair by up to 50%. Thus, we can conduct various ARC repairs with heightened efficiency and sustainability. The integrated vacuum extraction of milling dust and chips provides better waste flow control and removes the need of personal protective equipment and complex waste disposal.

Accuracy is not the only challenge: As an approved design organization - Part 21J - we have obtained the full aviation certification for the entire bandwidth of new automated repair processes in November 2020, which paved the way for their introduction into our daily business.

Accuracy is not the only challenge: Let me finish today by pointing out that he second part of this series will go more into detail on automation of radome repairs. The third part will focus on fan cowl door repairs. The final episode will conclude with inlet cowls.