PRODUCTION ENGINEERING

In order to better align the ecology and economy of passenger aircraft during operation, engine manufac-

turers especially have additional de-mands placed on them. Without losing per-formance, modern engines must operate more fuel efficiently, emit less exhaust gases and run quieter. In the ideal case they also score points with the operators with longer maintenance intervals. Whoever wants to take care of this list of requirements must place the question of material in focus from the beginning.

According to the location in the en-gine different materials are used: chrome nickel alloys, nickel base alloys and titanium alloys. The properties of these materials at high temperatures and the temporally predictable wear characteristics are important to the en-gine manufacturer. The poor thermal conductivity of these materials and an especially high wear of the tools make it difficult for the machine tool and tool manufacturers.

The trend is moving to BLISKsWith engine components it predomi-nantly regards rotationally symmetrical components, disks, rings and shafts, which are assembled to the complex ro-tors of the engines. Until now the blades and the rotor components were manufactured separately and assem-bled using a so-called christmas tree profile.

With the new energy efficient and resource-friendly engine types the trend is moving to integral components for the rotors, so-called BLISKs or BLINGS (Blade integrated disks /rings). In this case the discs including the blades are turned or milled from a bil-

Machine tool technology gives wings to engine construction The mechanical machining on engine components is an increasingly demanding task. In addition to the trend towards integral components, the challenge especially is with the materials that are difficult to machine. Here machines tools, which work with hydrostatic guides, are able to provide further benefits.

German SummaryDie mechanische Bearbeitung von Trieb-werkskomponenten wird eine immer anspruchsvollere Aufgabe. Neben dem Trend zu Integralbauteilen sind insbeson-dere die schwer zu bearbeitenden Werk-stoffe die besondere Herausforderung. Hier helfen Werkzeugmaschinen weiter, die mit dämpfender hydrostatischer Führung arbeiten. Der deutschsprachige Beitrag ist nachzulesen auf:www.aerotec-online.com/0112mon

36 aerotec · JUNE 2012

With the new energy efficient and resource-friendly engine types the trend is moving to integral compo-nents for the rotors, so-called BLISKs or BLINGs (Blade inte- grated disks/rings). In this case the discs including the blades are turned or milled from a billet.

Picture fotolia: Pixel 3000

37aerotec · JUNE 2012

38 aerotec · JUNE 2012

PRODUCTION ENGINEERING

let. This has the advantage that the mass at the foot of the blade can be re-duced because the christmas tree pro-files are omitted. As a result the compo-nents become lighter and allow a higher blade density and thereby, can reach a higher turbine efficiency.

In the manufacture of the rotary parts the trend towards integral compo-nents (BLISKs) means that the separa-tion in the past between the turned parts (discs and rings) as well as the milled parts (blades) does no longer ex-ist. The processing machines must now include both processes in one machine as economi-cally as possible, or a cost and quality effective transfer of the components between the various ma-chines must be realised. In addition to this the technological improvements have also made the geometry on the ro-tors on the new modern engines more complex. For the turning processes, that

Left: With this machine the B axis can be used for turning by interpolation. The turning tools are rigidly clamped in the milling spindle in a Hirth coupling.

Multi-task machines, which can link their capabilities in turning and milling are consid-ered as being future-oriented.

The milling of the difficult to manufacture blade geometry is achieved today by high-produc-tive HSC-Milling (High Speed Cutting).

means that the contour machining pushes the limits of the conventional turret lathes. Increasingly, more com-plex geometries such as undercuts must be manufactured. For this, a flexible adjustable tool adapter is required.

In practice in industry some of these tasks are taken care of already innova-tively with multi-task machines, which can play to their capabilities in turning and milling. Many OEM and suppliers in this industry pace their trust, for the manufacture of rotor components for engines, in the Turning/Milling Centres of the "UniCen 1000" type from ma-chine tool manufacturer A. Monforts. One of them was procured for research in the context of the Fraunhofer Inno-vation Cluster `TurPro´.

The manufacturer emphasises three characteristics, which predestine these machines for the application from their view:

■ a high rigidity, which enables a safe machining of difficult materials,

■ and exceptional damping, which prevents the vibrations from spreading and

■ guaranteeing the product quality in the long term, in short, long-term accu-racy.

In this regard the machine is con-vincing with its characteristic special feature - a hydrostatic guide in the Z-axis, i.e. in the "UniCen 1000" the slide with the tool carrier is guided on a mas-sive column that has a thin oil film. The circumferentially arranged hydro-static pocket constantly holds the col-umn, due to the pressurised oil, in the middle of the slide bore and prevents metal-to-metal contact. Thus this guide operates without any friction contact and is maintenance and wear free.

The oil film between the bore and the column provides the machine with

In the UniCen 1000 the slide with the tool carrier is guid-ed on a massive column that has a thin oil film. The cir-cumferentially arranged hydrostatic pocket constantly holds the column, due to the pressurised oil, in the mid-dle of the slide bore and prevents metal-to-metal contact. Thus this guide operates without any friction contact and is maintenance and wear free.

39aerotec · JUNE 2012

PRODUCTION ENGINEERING

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very good damping characteristics. Be-cause especially during heavy machin-ing it is an advantage if vibrations can-not spread; the tool life is then mas-sively extended.

An advantage of the low friction is that the Stick-Slip-Effect does not oc-cur. This is particularly favourable with small machine movements. As a result smallest travel increments of 1µm can be traversed stick-slip free.

The `UniCen 1000´ is equipped with a tilting motor milling spindle, which enables 5 axis milling in the interaction of the X, Y, Z, B and C axes. A typical machining task in milling is machining out the blades in the BLISK integral component. In addition, with this ma-chine the B axis can be used for turning by interpolation. The turning tools are rigidly clamped in the milling spindle in a Hirth coupling. The flexible employ-ment of the B axis for turning thereby permits the manufacturing of contours, for which conventional turret machines have reached their limits. The milling of the difficult to manu-facture blade

geometry is achieved today by high-productive HSC-Milling (High Speed Cutting). The machines for this ma-chining are designed for the highest dynamics. If they were used for rough machining, the difficult to ma-chine materials cause an immense machine load and premature wearing. One ap-proach from the work on the TurPro project is to also use the outstanding damping of the Monforts machine in the heavy rough machining.

HPC is used increasinglyIf the sturdy `UniCen 1000´ turning/milling centre, with its hydrostatic guide, takes over this heavy work, the HSC milling centres, which do the highly dynamic finish machining, will have a longer life and maintain accura-cy. The transfer of the components be-tween the `UniCen 1000´ turning/mill-ing centre and the HSC milling centre is achieved with a zero-point clamping system.

While machining hard to machine materials, such as nickel base alloys,

high pressure coolant (HPC) is used in-creasingly. In this cooling concept the coolant stream is sprayed directly be-tween the tool and the chip and thereby cools directly at the point of heat gen-eration. Through the clearly improved cooling, the chip breaks either due to thermal shock or is simply mechanically shot away.

As a result the cooling concept ena-bles higher cutting speeds and elimi-nates the problem of long chips com-monly experienced with these materi-als. During machining with the `UniCen 1000´ the coolant can be used with a pressure of 120 bar via an internal line or up to 350 bar via an external line.

The turning/milling centres on the market often have a substantially long-er turning length than that required for the manufacture of disc-shaped compo-nents for the rotors of turbines. Mon-forts provides the "UniCen 1000" mill-ing/turning centre starting with a turn-ing length of 800 mm and as a result saves the user valuable space in the machine shop. Dr Dominic Deutges