“We work with complete machining”
If you are producing around 1.7 million aircraft parts with 23,000 different drawing numbers every year, high flexibility is essential. aerotec magazine spoke to Matthias Lange, Head of Technology and Stefan Mangels, Head of Investment and Plant Planning at the aircraft structure manufacturer Premium AEROTEC (PAG) in Varel.
Mr Lange, here in Varel, you use machinery considered to be the most advanced of its kind in Europe to produce highly complex cut, turned and milled parts of aluminium, steel and titanium – parts that are destined for all models of the Airbus family, the A400M military transport aircraft and the Eurofighter. How many parts are made here each year?
In Varel, we produce around 1.7 million components annually, with 23,000 different drawing numbers. This large range of parts manufactured in small batches requires a very high degree 
of flexibility. Therefore, our plant is organised in quite different cycles than, say, an automobile plant.
How do you manage to produce such small batches flexibly and cost-effectively at the same time?
We work with complete machining. Varel cuts many parts in a single machine clamping. Also, we use around 30 five-axis machining centres for small components and nine-axis turn-milling centres for rotary parts. Since the parts have large surfaces and mostly require machining on both sides, we need to turn them over at least once. This is where the 17 large machining centres with a total of 44 spindles come in handy.
In the matter of special machining procedures, your industry is somewhat of an exception. Why is it that, in principle, only aircraft manufacturers use tool machines with parallel geometry – in your case, tripod technology?
I consider it an advantage that we can employ the Ecospeed tripod machine from DST for highly dynamic simultaneous 5-axis milling. It comes to the fore in very complex large aluminium components, where, for instance, the ribs are shaped in five axes. This means that parallel geometry only pays off for large components, which require a lot of 5-axis machining.
Mr Mangels, what makes aircraft construction so special in terms of manufacturing technology?
So far, I have hardly ever seen requirements comparable to the ones we work to outside the aircraft construction sector. For example, we have to be able to machine large spherical surfaces on a component as large as five metres long in five axes.
Lange: For instance, we routinely perform simultaneous roughing cutting in five axes with feeding speeds of 20 to 25 metres per minute. We have to modify the angular position for corners with only slightly adjusted ribs. Conventional clevises can only do this with extreme pivoting movements; with parallel geometry, however, it can be done much faster and in a more elegant manner.
What are the current material trends?
Lange: Thanks to, among others, the Airbus A350, carbon fibre laminates are on the rise. And since aluminium cannot be used with carbon fibre laminates due to corrosion, titanium is a must.
Nevertheless, aluminium is still the most important material. How much do you use?
Lange: Around 14,000 tonnes of aluminium per year. The chip removal rate is around 50 per cent on average and 96 per cent in the case of large components.
How does the series production of small parts work?
Mangels: We use interlinked Makino machining centres. Each line comprises separate setup stations, pallet buffers, measuring stations and a handling system. The unmachined parts, normally pre-cut aluminium sheet material, but sometimes cast or forged parts with defined starting points, are fixated on machine pallets with hydraulic clamping systems in the setup stations and then brought to the pallet buffer. The handling system provides the six machining stations of the centre with pallets carrying parts, which are then cut completely from six sides in one clamping.
The centres have a main spindle with an input capacity of 55 kilowatts and a maximum speed of 24,000 rpm. We normally work at maximum capacity. Besides a rinsing station, the centre also includes a coordinate measuring machine, which allows us to carry out quality assurance during serial production.
Do you only process untreated raw aluminium?
Lange: No, for larger quantities we also use drop-forged parts. As part of our process for technological improvements, we regularly carry out benchmark testing to establish for which parts drop forging is economically viable.
Are your largest tool machines used to manufacture the largest components?
Mangels: That’s right. It is true, for example, of the two interlinked DST high-speed machining centres of the Ecospeed type from Dörries Scharmann Technologie GmbH (DST) from Mönchengladbach, which we use to cut integral aircraft parts on 7.8 metre long pallets with the parallel geometry processing head Sprint Z3. At a chip removal rate of over 90 per cent, we cut the parts completely from contour pre-cut parts that have been face milled and drilled on both sides.
What are the typical machining characteristics in this case?
Lange: The machine works with a 75 kilowatt spindle at a maximum speed of 24,000 rpm. The mostly three-edged tools produce 1,000 chips per second. The material removal rate amounts to around five litres per minute. The operating life of the tools used for aluminium is around ten hours.
Is this your largest machining centre?
Mangels: No. There is another machine from DST; the special so-called ACM-1, which is equipped with a conventional processing head instead of a tripod. Behind each of the two collapsible pallet tables, there is one 40-tonne moving column with two spindles set up horizontally, one above the other. Here, rack and pinion drives are used instead of linear technology. The dual-spindle machine performs high performance cutting (HPC) of large integral aluminium components. By the way, an HPC machine with two spindles is very rare anywhere in the world. In order to manage the production of small batches cost-effectively, we also rely on parallel setups during primary processing time. In theory, we can even cut components that are as long as 22 metres and 4.5 metres wide.
You are also participating in the Agilita project (Agile Produktionslogistik und Transportanlagen) of the Institute of Production Engineering and Machine Tools (IFW) at Leibniz University in Hanover, where your production of large components is visualised as a digital factory. How does the virtual factory influence the day-to-day production?
Mangels: Agilita consists of four distinctive modules. Information is immediately transmitted via Radio Frequency Identification (RFID), so that we always know at the control station where an order is currently being handled. Since aluminium and titanium block the data transfer, we specifically developed concepts for attaching RFID labels or chips. The first parts with RFID chips are already being used. The second stage of this process is to develop a system for client-based production control according to the lean management principle. It is organised around an online simulation of our production processes.
Why is the EMO 2011 trade fair in Hanover important for you?
Mangels: We like to visit the EMO in order to find out what is going on outside our own industry. Also, we participate in the Machining Innovations Network’s special showcase during the fair. As a member of this machining network, we will present our products at EMO 2011, from 19 until 24 September in hall 26.
Interview conducted by Nikolaus Fecht
German Summary
Jährlich etwa 1,7 Millionen Flugzeugbauteile mit 23 000 unterschiedlichen Zeichnungsnummern zu fertigen, erfordert eine sehr hohe Flexibilität. aerotec-Autor Nikolaus Fecht sprach mit Matthias Lange, Leiter Technologie und Stefan Mangels, Leiter Investitions- und Werkplanung Werkzeugwesen, beim Flugzeugstrukturen-Hersteller Premium AEROTEC in Varel darüber, wie sich diese Herausforderungen meistern lassen. Der deutschsprachige Beitrag ist nachzulesen auf: www.aerotec-online.com/aero0111varel
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