Joint development by bavius and MAPAL Strategic Aircraft Component With Every Conceivable Feature

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In a joint project, MAPAL and machine manufacturer bavius have developed and produced a sample component for the aviation industry. 

The aluminium component, measuring approximately three by one metres (approx. 9.8 by 3.3 ft), is based on a real rear spar from aircraft construction, but has been enhanced with a wide range of additional demanding applications. In addition to its complexity, the short machining time of ten hours is impressive, based on the productivity of the bavius AeroCell and MAPAL’s specialised tools for aluminium machining.

bavius technologie gmbh, based in Baienfurt (Germany), specialises in high speed volumetric machining of structural aluminium components, as typically required in the aerospace sector for wings and fuselages. bavius, formerly Handtmann A-Punkt Automation, has operated as an independent, family owned company since 2017 and focuses on two product lines: profile machining centres and horizontal machining centres with the AeroCell series. With around 120 employees, bavius generates more than 80 percent of its revenue in the aerospace industry. As OEMs or suppliers, its customers produce components for commercial and military applications. Components for satellites or rockets such as Ariane 6 are also manufactured on these machines.

Made entirely in Germany

Most of bavius machines are located in Europe, with other strong markets in North America and Asia. The machine manufacturer operates its own subsidiary in the United States, but production for the global market takes place exclusively in Baienfurt in two climate controlled halls with a production area of around 10,000 square metres (approx. 107,600 sq ft).

A particular strength of bavius five axis machining centres is their exceptional dynamics, delivering high productivity in high speed machining. To extract maximum performance from the machines, bavius manufactures its own milling heads. The flagship of the product line is the bavius AeroCell 160 I 400 with a spindle power of 140 kW and a maximum speed of 30,000 revolutions per minute. The 140 kW is already achieved at 18,000 revolutions, meaning maximum power is available across a wide speed range. “If we do something, we want to do it excellently, and with our AeroCell 160 I 400 we are technologically leading worldwide,” assures Dominik Merz, Director Global Sales at bavius.

More than 90 percent chips

The rear spar was selected as a sample component because it fits very well on the machine with its table height of 1.6 metres (approx. 5.25 ft) and width of 4 metres (approx. 13.1 ft). This rear spar is a typical structural component in aircraft wings. Between the rear spar and the front spar run ribs arranged at right angles to the spars. These structural components define the geometry of the wing, with the outer skin riveted onto them. The finished component made of aircraft grade aluminium 7075 measures exactly 2977 x 748 mm (approx. 117.2 x 29.4 in). Typical of aircraft parts is the flat shape with a height of 138 mm (approx. 5.4 in). From an initial weight of over one tonne, only 70.61 kg (approx. 155.7 lb) remains after machining, a ratio that is not unusual in the aerospace sector.

For legal reasons alone, bavius and MAPAL could not use a real component from an aircraft manufacturer for machining. However, this gave those responsible the freedom to adapt the design to include a wide range of additional applications. As a result, the demonstration object is far more complex than any real rear spar and includes applications not necessarily associated with this component but potentially required in others. “A customer familiar with structural components who sees our part recognises themselves in it and finds features also present in their own components,” explains Dominik Merz.

Machining in Baienfurt was carried out in two setups. Setup one used low clamp tension, while setup two ensured secure holding using vacuum technology. At first glance, the front side appears simpler than it actually is. The surface is not flat but slightly convex over a radius of 9.5 metres (approx. 31.2 ft). This means the component cannot simply be face milled but requires five axis machining. For roughing and finishing, MAPAL used the NeoMill-Alu-QBig with a diameter of 50 mm (approx. 2.0 in) and the OptiMill-Alu-Wave with a diameter of 25 mm (approx. 1.0 in). A PCD special milling cutter was used for the surface finish.

Pockets in every shape

Machining the rear side proved particularly demanding, as it is divided into nine different sections, each with specific applications. Like any rear spar, the sample component features many pockets, here designed in every conceivable shape: rectangular, triangular, round, open, closed, some with inclined or curved bases. The ribs are very thin, and most walls are inclined. The pockets have depths of up to 137 mm (approx. 5.4 in).

After pre machining with the NeoMill-Alu-QBig, an OptiMill-Alu-Wave in various lengths was used to clear the pockets. Semi finishing was carried out by a corner milling cutter specially modified for aerospace applications. Thanks to its geometry, the tool is particularly suitable for machining residual material in corners and for subsequent finishing of bases and walls. Its special core design ensures optimal stability in the machining process. To machine all areas efficiently, MAPAL specialists used the modified corner milling cutter in various diameters and lengths.

Efficiency was also a key factor in programming, as explained by component manager Alexander Follenweider: “We work with a zigzag strategy in climb and conventional milling to reduce travel paths. During machining, the strategy is continuously changed.” Despite high machining speeds, the aluminium must not be damaged, as overheating alters its properties.

The OptiMill-Alu-Wave was operated at 29,000 revolutions, a cutting depth of 48 mm (approx. 1.9 in) and a feed rate of 12 m/min (approx. 39.4 ft/min) at peak. The larger NeoMill-Alu-QBig achieved a feed rate of over 25 m/min (approx. 82.0 ft/min) at a cutting depth of 10 mm (approx. 0.4 in). In the first 55 minutes of machining the second setup alone, 425 kg (approx. 937 lb) of aluminium were removed, with peak chip volumes exceeding 14 litres per minute (approx. 3.7 gal/min). “These are outstanding values we achieved here, and we also produced very good surface finishes,” says Stefan Diem, application engineer at bavius.

Nothing is standard

The various pockets are not the only challenges of the component. The holes on four lugs are only accessible with an angle head. Undercuts are required in other areas. A so called T stiffener, typical for structural components and used for reinforcement, is also present and machined with a PCD special tool. Drilling and reaming operations are also required in certain areas. “Nothing about our component is standard,” comments Dominik Merz, noting that there is practically no right angle anywhere. Such inclined designs, however, are typical in the aerospace sector.

Five of these rear spars were produced in Baienfurt for customer presentations and as eye catchers at trade fairs. Machining a single part takes almost exactly 10 hours, a result with which those involved in the project are highly satisfied. “On other machines, such a component often runs for 20 to 30 hours,” estimates Merz. Traditionally, structural components are machined on vertical gantry machines using large tools, typically cutter heads with diameters of 125 mm (approx. 4.9 in). Feed rates and speeds remain low. One disadvantage of this method is that chips remain on the surface and can cause scratches. In addition, heat is introduced into the component. Horizontal machining eliminates these issues. Combined with powerful tools that allow high cutting values, the dynamic AeroCell 160 I 400 with its extreme acceleration opens up entirely new possibilities.

Close collaboration

MAPAL and bavius have maintained a very intensive partnership for many years, from which both sides benefit. When MAPAL developed the NeoMill-Alu-QBig and OptiMill-Alu-Wave, prototypes of the new tools could already be tested and further optimised in Baienfurt. The tool manufacturer itself does not have similarly powerful machines in Aalen. Conversely, bavius also depends on innovative tools, as Stefan Diem explains: “For our premium machine, we need top tools from a supplier like MAPAL with its high volume cutters that push our machine to the limit. This cannot be achieved with universal tools, as we gain no insights.”

Together, the partners had already demonstrated what the AeroCell 160 can achieve two years ago. In test operation under overload, the solid carbide cutter OptiMill-Alu-Wave achieved chip volumes of up to 20 litres per minute (approx. 5.3 gal/min) in full slot milling in standard aluminium. The current peak value of 12 litres per minute (approx. 3.2 gal/min) on a component made of the higher strength AL 7075 is equally impressive.

“I greatly value the collaboration with MAPAL because communication is open and fair, and we always receive a solution,” emphasises Stefan Diem. For Jens Ilg, Business Development Aerospace and Composites at MAPAL, the joint success also has a personal dimension: “I get an optimal feel for our own products when I have used them under real conditions. I can then offer them to customers with the appropriate recommendations.”