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A diamond-like solution overcomes lithium aluminium drilling problems

It was the use of the recently introduced Aurora DLC 1500 (diamond-like-carbon) insert coating in combination with the SumiDrill WDX series of drills from Sumitomo Electric Hardmetal that has transformed troublesome drilling operations on a range of lithium aluminium aerostructure components at Magellan Aerospace UK.

With the £70 million turnover company based in Wrexham succeeding to standardise processes as part of its continuous improvement policy machining wing ribs, butt straps, thrust fittings, access panels and wing spars up to 20 m long, a recurring drilling problem on its rib production was consistently high on the management meeting agenda. Despite significant process changes and trials of different tools with suppliers, none could better 10 holes before either insert changes had to be initiated or total tool failure and breakage occurred. Even the use of solid carbide tools, which made heavy inroads to the tooling budget, never came close to providing an acceptable solution.

The focal point was to solve the tooling problem against growing concern as production schedules were increasing. However, with some parts having machining cycles over 14 hours on the recently installed high specification 120 kW, 30,000 revs/min spindle, 6 m by 2 m pallet Dorries Scharmann DST Ecospeed F2060 fixed column horizontal machining centre, maximum utilisation was important.

The Sumitomo WDX drill design combined with its DLC coated inserts immediately overcome other drilling tool initiated experiences of built-up-edge created by the material that caused immediate overheating, the welding of swarf in the drill flute and repeated seizure of tools in the hole being processed. Previous supplier trials involving different tool types and process changes including solid carbide, pilot drilling, slot drilling and revised speeds and feeds had always failed to overcome the problem. And even with the use of MQL (minimum quantity lubrication) an air-oil stream coolant supply on the high performance machine, swarf control was proving very difficult but, according to Sumitomo engineers, this system works very efficiently as part of the new drilling set up. 

There are multiple variations of wing ribs that are milled from solid in 100 mm thick plate. These can have up to 150 bolt-down holes, some with counterbores of 14 mm, 20 mm and 26 mm diameter by up to 70 mm deep produced on the machine. Such is the requirement that the Wrexham site is currently having to produce up to 1,500 holes a month.

The major cause of the problem was the change to lithium aluminium alloy on some of the aerostructure parts. This advanced aluminium alloy contains between 2 and 3 per cent lithium copper magnesium alloying elements creating a high strength to weight ratio with a lower density and an improved elastic modulus. While giving greater resistance to elements such as fatigue cracking for the designer, this specification of material is far from tolerant to the process of drilling, and especially on deeper holes.

The Aurora DLC 1500 coated insert was originally developed for non-ferrous materials in order to present a high hardness with a lubricated cutting surface that creates a co-efficient of friction of between 0.05 and 0.2. As Magellan engineers have found, this high efficiency coating provides the ability to precisely control chips and supress the formation of any built-up-edge. As a result a consistent penetration rate can be maintained. It also greatly extends the in-cut life and reliability of the tool.

When used in the SumiDrill WDX high feed rate drill body, its adjacent insert design with inner and outer cutting edges provides a balanced cut with the ability to drill from solid on a plain surface. It is so rigid and stable that the drill body can even be used to, in effect, mill an outside diameter, drill with half the wall of a hole exposed and be started on an inclined slant surface, for instance, or in a pre-drilled hole. Diameter-to-depth ratios can be up to 5xD due to the insert positioning and the design of the tool enables the creation of an almost flat bottom blind hole, ideal for counterboring applications. 

Said John McGrail Project Engineering Manager: “The initial trial using a 26 mm diameter WDX drill produced 200 holes with no apparent wear showing on the insert. Chip formation was excellent without having to result to a pecking action and we were then able to increase speeds and feeds to run the tools 25 per cent faster. On certain holes that have deep 20 mm diameter counterbores, we are now running 60 per cent faster than before.” 

Now proven in production the company is currently achieving insert cutting life of 50 mins per edge on the Ecospeed machine. As result with the drills having the added economy of four cutting edges, inserts are now programmed to be changed after 200 mins. Now as part of the company's drive towards standardisation of processes and improved tool inventory control, Sumitomo's SumiDrill WDX and insert solution is planned to be progressively introduced more widely across normal aluminium aerostructure components. 

On the lithium alloy components, the WDX drill body with DLC 1500 coated inserts are being run at 13,500 revs/min with a feed of 0.075 mm/rev, for the 14 mm drills to produce holes 50 mm deep and for 20 mm diameter holes by 70 mm deep, these tools are run at 10,000 revs/min with 0.15 mm/rev feed. Meanwhile, for the 26 mm hole sizes the speed is 7,700 revs/min with a feed rate of 0.2 mm rev.

In addition to Wrexham, Magellan Aerospace has UK sites in Blackpool, where hard metal components up to 1 m cube are produced; Bournemouth for machining aluminium parts between 500 mm to 2,000 mm cube, Chalfont for aluminium components up to 500 mm cube; and Greyabbey for larger wing ribs up to 4 m.

Explained Adrian Young, Operations Manager, Wrexham: “The ability to produce large complex aerospace components for Airbus has enabled our operation to grow from £20 million in 2004 to £70 million this year.” The site employs 400 people and is investing some £4 million a year in new equipment which should take the business to a turnover of some £85 million within the next five years. “This means that machine utilisation is critical to help control capital expenditure and solutions such as the Sumitomo drilling application are important in achieving our objective,” he said. 

Press release issued by Sumitomo Electric Carbide, Inc. on July 10, 2014


 Contact details from our directory:
Magellan Aerospace (UK) Ltd Wing Spars, Precision Machined Parts, Aircraft Structural Components
Sumitomo Electric Carbide, Inc. Turning, Boring Equipment, Milling, Drilling Equipment


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