Milling cutters slash spar machining times
Keywords: Aircraft industry, Milling, Cutting, Matching
It is reported that by changing to Walter Novex milling cutters for roughing out two types of A320 Airbus wing spars for BAe Systems, the Welsh-based sub-contract machinist Prematec Corporation has reduced machining times on these very large parts by more than 25 per cent (Plate 2).
Plate 2 Walter milling cutters have helped reduce Airbus wing spar machining times by over 25 per cent at Prematec Corporation
As engineering manager Andy Green explains: "Basically, the cutters have out-performed anything we have used. Initial trials using a cutter which Walter GB borrowed for us from BAe at Filton showed an immediate improvement," he says."The tip life was phenomenal compared to the other makes of cutter we had tried."
The large savings in cycle time achieved from using the new cutters is also said to be bringing benefits to machine utilisation and return on the investment. The machines on which the spars are machined operate around the clock virtually all-year-round.
The new milling cutter is a 50 mm diameter F3040 three flute indexable router with two- edged indexable carbide tips. Prematec is said to have found that with its three effective teeth, the router can be run at speeds and feeds that are pushing to the limit at least one of the profiling machines on which the large components are produced.
At depths of cut ranging from 5 mm to 15 mm, the cutters are run at feed rates of between 1.8 m/min going into corners to 5.5 m/min on the straight."These are impressive speeds," added Andy Green, "with swarf flying everywhere."
He continues: "Previous makes of cutter failed before the machine reached its performance limits, but now it's the other way round. In addition, there are a lot of little features about the tip and the design of its holder which are producing marvellous benefits for us."
The changeover to Walter has reportedly been a major factor in helping the company bring down the overall time taken to rough and finish a spar typically from 30 to 20 hours. Also contributing have been improvements which Prematec has been able to make to the machining programs originally supplied by Bae Filton along with the tooling as part of the contract for producing the spar.
"Having three tips instead of the normal two gives a 50 per cent improvement straight away. We can't use all of that because it is down to available spindle power. We have 30 kW spindles, but would need 50 kW to take full advantage of the cutters."
There has also been a significant increase in tool life as a result of the change. "We used to change the tips twice during a 24-hour machining cycle,"comments Andy Green." Now the tables are turned and we are getting two or three roughing operations for one set of tips. And even then they are not showing any real signs of wear – we just change them when the power meter starts to go up."
According to Walter, while cycle times are coming down and tool life increasing three-fold, the cutters themselves are not costing any more than the company was previously paying for cutters which frequently failed. That, Walter aserts, means the overall spend on these inexpensive consumable items has also reduced.
Two types of wing spar are currently being machined on a continuous production basis at Prematec. One is the A320 mid-rear spar which is 8m long and is machined two at a time on either of two five-axis high speed vertical profilers which have work capacities of 2,286 mm by 10,263 mm and spindle speeds of 15,000 revs/min.
The other is the 16 m long A320 front spar which is machined on a three-spindle, 6,000 revs/min five-axis gantry profiler with a capacity of 3,050 mm by 18,000 mm.
Prematec has been based at the Llantrisant Business Park close to the M4 in South Wales for the past four years. It employs just over 100 people in the business of contract machining to the aerospace and automotive industries. In addition to the dedicated wing spar machining hall – which was set up two years ago at a total cost of £8.5 million – the main manufacturing site has several other CNC machine shops equipped with modern machining centres,turning machines and grinding machines.
Details available from: Walter GB Limited. Tel: +44 (0)1527 60281; Website: http://www.walter-ag.de
