Kevin Clynes, who heads up research and process technology engineering for the Airbus division, said the complex machining operation on the base cone for its new satellite was done “during a very difficult time with speed, efficiency and accuracy” by engineers from the Composite Centre at the University of Sheffield Advanced Manufacturing Research Centre (AMRC).
“Despite the restrictions and challenges of the Covid-19 lockdown, it was crucial to Airbus Defence and Space to continue with operations,” he says. “This was not only about keeping our business going but also about keeping our customers, partners and suppliers operating as well.
“When we contacted the AMRC, it was clear they wanted to assist us with this project to keep our business plan on schedule. This was very much appreciated and successfully demonstrated how we could work together, communicating remotely, to achieve this. The AMRC showed great effort and commitment to keep UK industry going during this challenging time.”
This work forms the latter stages of two years of research collaborations between Airbus Defence and Space and the AMRC that initiated the establishment of a method to machine aluminium honeycomb with composite skins, achieving with zero defects.
Dr Kevin Kerrigan, who heads up composite machining research at the AMRC, says: “It was an honour for the AMRC to be able to support the team at Airbus Defence and Space during these challenging times and to witness translational research deliver value back to UK manufacturing.”
The cone is a key component of the Eurostar Neo, a new high performance communication satellite developed by Airbus Defence and Space that combines increased payload capacity, more efficient power and thermal control systems with faster production time and reduced cost.
Due for launch in 2021, the cone forms the central structure and base of the service module of the satellite, which houses the propulsion tank. It is made from aluminium honeycomb, which is sandwiched between an inner and outer skin made of carbon fibre reinforced polymer (CFRP).
The AMRC team took on the challenge to machine 288 holes and three larger access panels, whilst achieving tolerances smaller than the diameter of a human hair (40 microns at its smallest) into the already high-value-added component. Further machining work included machining flats on upper and lower rings that had been bonded to the cone.
John Halfpenny, technical lead at the AMRC Composite Centre, worked with AMRC machine tool operator Lewis Nicholson to carry out the complex job; operating under strict lockdown conditions and stringent health and safety guidelines, and all while maintaining the necessary social distancing measures.
“This project was a little bit special, because we had to come in under lockdown,” explains John. “We knew it was important because Airbus had been given permission from the government to do the work during lockdown as it is industry specific and critical to their work packages.
“The cone itself is quite large, 1.3 m high, but a very lightweight structure; to give a sense of size, four people could stand inside it.It is a typical sandwich structure with three layers - carbon fibre on the outer and inner surfaces, with aluminium honeycomb layer in the middle - and quite difficult to machine without damaging the super lightweight, high-value structure.”
He explained that while carbon fibre is a strong and light composite material, it is very easy to damage the component when machining features. “The carbon fibre has a tendency to splinter and break away, if machined incorrectly,” he said. “Airbus had a zero-defect feature requirement, which meant no splintering on entry and exit of all features. This is critical to the component, so the AMRC developed techniques to eliminate all delamination.
“Also, another requirement was the honeycomb structure had to have a clean burr-free cut. If machined with conventional tools and drills, it would be very easy to damage the thin sandwich structure, so specialist tools were sourced that were capable of producing a really fine, neat edge on the honeycomb.”
After every 10 holes, a visual inspection was carried out for delamination and measurement of diameter. This was to ensure tool wear had no effect on the quality of holes.
Continues Halfpenny: “OSG, a tier one research partner, was the tool supplier on this project and they have worked with us to develop the process. We carried out some machining trials with their tools and found they were really good; they are solid carbide diamond coated tools, which are very hard wearing and the geometry of the tools is unique as well.”
The machining work was performed using the Starrag STC 1250, 5-axis machine tool that Clynes says was perfectly suited to the task.
“The holes have a very tight tolerance requirement on diameter size of ±0.015 mm, as well as positional accuracy requirement of ±0.05 mm. The AMRC’s Starrag machine gave us the required volume and accuracy to carry out these machining operations.”
Once complete, the cone was delivered to Airbus’ Stevenage site, where metal inserts were accurately bonded into the carbon holes machined by the AMRC to give precision fixing points for brackets and panel attachments.
The cone project is the culmination of two years of ‘small steps’ of incremental research and development carried out by the AMRC for Airbus Defence and Space in which various-scaled cones were machined using a newly established machining process developed for Airbus Defence and Space as part of its manufacturing development programme.
Concludes Halfpenny: “We got the order for the cone before Covid; it was a critical project for us to complete and to help the industry keep moving during lockdown. We knew that if this wasn’t machined on time it could have delayed the final assembly process. The satellite is due to launch in 2021 - slots for launches like this are booked years in advance, so we knew there were deadlines to meet. That’s why, as an organisation, we were determined to deliver and make sure we could complete the machining to keep Airbus on schedule.”
The Eurostar Neo product line has been developed in the frame of ESA's Advanced Research in Telecommunications Systems (ARTES) programme, in cooperation with space agencies from ESA Member States, particularly CNES and the UK Space Agency.
* Eurostar Neo - two of its platforms will host identical Eutelsat HOTBIRD payloads, and help them broadcast more than a thousand television channels into homes across Europe, Northern Africa and the Middle East. The state-of-the-art Airbus-built spacecraft will replace three older satellites currently in orbit.