05 Next level of composite repair: Radomes (Part 2/4)

Intro

Today, Dr. Hendrik Schmutzler will share with you how we at Lufthansa Technik are taking composite repairs to a new level. Materials technology and non-destructive testing has occupied Hendrik since 2003. In this second part he focuses on radome repairs.

Jingle

In the first episode of my four-part series, I provided a basic overview regarding the capabilities of our new scarfing robot for Airframe Related Components. In this, and the two following episodes, I will try to go a little further into the details of each individual process. Also, I will elaborate on the respective ARC parts repair capabilities that we have developed and introduced into daily MRO operations at the Lufthansa Technik base in Hamburg.

The first ARC parts that I would like to shed some more light on are the nose radomes of commercial aircraft.

When it comes to a short- and medium-haul “workhorse” like the Airbus A320 family, the spectrum of causes for radome damage is varied. In daily operations, it ranges from bird strikes and excessive hail and lightning, to water ingress. What all these causes have in common is that they usually affect rather large areas of the respective parts in which they cause delaminations and/or disbonds in the composite material structure.

Standard repair processes for damaged radomes are described in every Component Maintenance Manual, but they usually require a lot of manual labour and are very time-consuming. For maintenance crews the manual process also causes excessive stress, as the geometry of nose radomes often mandates some rather unergonomic working positions: Usually, the radome is placed on a trestle and the worker sits underneath, grinding above his head or within a constricted room.

With the introduction of the automated scarfing robot system for radome repairs, we tried to accomplish two goals at the same time:

With the introduction of the automated scarfing robot system for radome repairs, we tried to accomplish two goals at the same time: relieving maintenance crews from these stressful overhead grinding tasks

With the introduction of the automated scarfing robot system for radome repairs, we tried to accomplish two goals at the same time: AND

With the introduction of the automated scarfing robot system for radome repairs, we tried to accomplish two goals at the same time: heightening efficiency because the automated process allows for a much higher repair volume in the same amount of time

With the introduction of the automated scarfing robot system for radome repairs, we tried to accomplish two goals at the same time: Now, let’s take a look on how we achieve this

Once the radome is placed in the robot cell, our robot starts with a three-dimensional scan of its inner contours using structured light. Compared to parts made of Carbon Fiber Reinforced Plastic, this procedure is already ready for the first challenge: The reason is that the material used in radomes is partially transparent.

Once the radome is placed in the robot cell, our robot starts with a three-dimensional scan of its inner contours using structured light. Compared to parts made of Carbon Fiber Reinforced Plastic, this procedure is already ready for the first challenge: To save time, the scanning process can be limited to just those areas with marked findings from the incoming inspection. All maintenance crews have to do is pre-select those areas where repairs need to be carried out. In the respective graphical user interface, he or she can already choose from a number of predefined setups for standardized repairs. It is also possible to independently define the intended repair areas with a free form tool.

They then select one of the following repair scopes for each individual area:

They then select one of the following repair scopes for each individual area: Scarfing of the inner skin only

They then select one of the following repair scopes for each individual area: Scarfing of the inner skin and subsequent removal – so called milling – of the honeycomb core material within the scarfing area. With this robotic approach, the repair scope has reached commercial viability for the very first time. In all “traditional” repair scenarios, it would have required an uneconomical amount of manual work.

They then select one of the following repair scopes for each individual area: Scarfing of the inner and outer skin

They then select one of the following repair scopes for each individual area: Following this, the automated scarfing/milling process is started. From this point on, no further supervision is required. The maintenance crews can already concentrate on those tasks with much higher added-value, such as preparations for re-laminating the scarfed-out areas within the radome.

They then select one of the following repair scopes for each individual area: However, not all types of damage require scarfing through both sides of laminated skin. Let’s imagine that the composite part has “only” suffered a debond between the honeycomb core and outer skin, and the latter itself has not been damaged. In this case the automated system is capable of scarfing and removing only the inner skin and then the honeycomb material down to the adhesive layer of the outer skin, leaving the latter fully intact.

They then select one of the following repair scopes for each individual area: During a manual process for this type of damage, the entire damaged area of the radome, including the outer skin, would need to have been removed. The automated process thus saves both material and time and can be easily applied to a whole number of damage scenarios. As a result, repair costs are reduced even further.

They then select one of the following repair scopes for each individual area: What now sounds so fairly easy is much more difficult to achieve in real working conditions.

They then select one of the following repair scopes for each individual area: So let me tell you a bit more about our challenges and our lessons learned

They then select one of the following repair scopes for each individual area: The time span from development to deployment of our robot had many challenges for us. One important factor in our “lessons learned” was that the geometry of a part often varies during its service life. This is due to operational deformations or previous repairs. Therefore, an identical part number does not always guarantee the repeatability of the repair process. This had to be taken into account and makes a thorough scanning and an adaptive process inevitable.

They then select one of the following repair scopes for each individual area: Another important factor is the fixture of the radome during the entire process. We permanently have to balance the required geometric variance versus the required support for machining.

Moreover, each of the four-part numbers we can work on with our robot have varying material thicknesses, as well as other specifics. These are for example the mounting points for the lightning diverters, which consist of different materials:

Moreover, each of the four-part numbers we can work on with our robot have varying material thicknesses, as well as other specifics. These are for example the mounting points for the lightning diverters, which consist of different materials: some are metallic

Moreover, each of the four-part numbers we can work on with our robot have varying material thicknesses, as well as other specifics. These are for example the mounting points for the lightning diverters, which consist of different materials: some are plastic

Moreover, each of the four-part numbers we can work on with our robot have varying material thicknesses, as well as other specifics. These are for example the mounting points for the lightning diverters, which consist of different materials: some are made of glass-fibre reinforced plastics

Moreover, each of the four-part numbers we can work on with our robot have varying material thicknesses, as well as other specifics. These are for example the mounting points for the lightning diverters, which consist of different materials: To make our process feasible and repeatable for all conditions, we have to treat each material differently.

However, the greatest challenge in implementing our ARC robot for radome repairs was to still enable a load transfer from the remaining skin to the repair laminate. Radome skins are fairly thin (< 1 mm) as they are designed to be highly permeable to radar waves. Scarfing these glass-fibre reinforced plastics skins with a ratio of approximately 1: 70 leads to immensely high accuracy requirements.

However, the greatest challenge in implementing our ARC robot for radome repairs was to still enable a load transfer from the remaining skin to the repair laminate. Radome skins are fairly thin (< 1 mm) as they are designed to be highly permeable to radar waves. Scarfing these glass-fibre reinforced plastics skins with a ratio of approximately 1: With our adaptive scanning and milling process, we have already proven accuracies in the range of ±0.06 mm, which is incredibly close to the general maximum that can be achieved with an industrial robot of this size and accuracy class.

However, the greatest challenge in implementing our ARC robot for radome repairs was to still enable a load transfer from the remaining skin to the repair laminate. Radome skins are fairly thin (< 1 mm) as they are designed to be highly permeable to radar waves. Scarfing these glass-fibre reinforced plastics skins with a ratio of approximately 1: Overcoming these challenges and finally reaching the required accuracy for the wide-scale deployment of the scarfing robot called for a long and painstaking iterative process. However, the effort finally paid off and paved the way for us to commence daily operations of the world’s first automated scarfing robot in our Airframe Related Components

However, the greatest challenge in implementing our ARC robot for radome repairs was to still enable a load transfer from the remaining skin to the repair laminate. Radome skins are fairly thin (< 1 mm) as they are designed to be highly permeable to radar waves. Scarfing these glass-fibre reinforced plastics skins with a ratio of approximately 1: workshops here in Hamburg.

However, the greatest challenge in implementing our ARC robot for radome repairs was to still enable a load transfer from the remaining skin to the repair laminate. Radome skins are fairly thin (< 1 mm) as they are designed to be highly permeable to radar waves. Scarfing these glass-fibre reinforced plastics skins with a ratio of approximately 1: In episode 3  I will describe our robot’s repair capabilities for fan cowl doors. These parts do not require the extremely high precision described for the radome process, but they pose other tricky challenges finally leading us to develop our own fully individual repair process. So, please, stay tuned!