In a joint project, MAPAL and the machine manufacturer bavius developed and manufactured a sample component for the aircraft industry. The aluminum component, measuring approximately three meters in size, is based on a real rear spar from aircraft construction, but has also been enhanced with a variety of other demanding applications. In addition to its complexity, the short processing time of ten hours, based on the productivity of the bavius AeroCell and the special tools for aluminum machining from MAPAL, is impressive.
bavius technologie gmbh in Baienfurt specializes in high-speed volumetric machining of structural components made of aluminum, as typically required in the aviation sector for wings and fuselages. bavius (formerly Handtmann A-Punkt Automation) has been operating as an independent, family-run company since 2017 and focuses on two product lines: Profile Machining Centers (PBZ) and Horizontal Machining Centers (HBZ) with the AeroCell series. With around 120 employees, bavius generates more than 80 percent of its revenue in the aerospace industry. As an OEM or supplier, their customers produce components for commercial and military applications. Components for satellites or rockets, such as the Ariane 6, are also manufactured on their machines.
Everything Made in Germany
Most of bavius's machines are located in Europe, with other strong markets being North America and Asia. In the USA, the machine manufacturer has its own branch, but production for the global market is exclusively carried out in Baienfurt in two climate-controlled halls covering an area of around 10,000 square meters.
A particular strength of bavius's five-axis machining centers is their extraordinary dynamics, which provide high productivity in high-speed machining. To extract the last performance from the machines, bavius manufactures its milling heads in-house. The flagship of the product line is the bavius AeroCell 160 I 400 with a spindle power of 140 kW and a maximum of 30,000 revolutions per minute. The 140 kW is already reached at 18,000 revolutions, so the maximum power is available over a wide range of speeds. 'When 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.
Over 90 percent chips
The rear spar was chosen as a sample component because it fits very well on the machine with its 1.6 meters table height and 4 meters width. This rear spar is a typical structural component in the wings. Ribs run perpendicular to the spars between the rear spar and front spar. The structural components define the geometry of the wing, to which the outer skin is riveted. The finished component made of aircraft aluminum 7075 measures exactly 2977 x 748 mm. Typical for aircraft parts is the flat shape with a height of 138 mm. From an initial weight of over one ton, only 70.61 kg remain after machining – this ratio is also not uncommon 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 also gave the responsible parties the freedom to adapt the design for a variety of other applications. Thus, the demonstration object is far more complex than any real rear spar and also contains applications that may not necessarily be associated with this component but could be required for other components.
'A customer who is familiar with structural components and sees our part recognizes themselves in it and finds features that are also present in their own components,' explains Dominik Merz regarding this approach.
The machining took place in Baienfurt in two setups. Setup 1 was performed in downward clamping, while vacuum technology ensured secure hold in Setup 2. The front side looks simpler at first glance than it actually is. The surface is not flat but curves slightly convex over a radius of 9.5 m. Therefore, the component cannot simply be planed but must utilize five-axis machining. For roughing and finishing, MAPAL used the NeoMill-Alu-QBig with a diameter of 50 mm and the OptiMill-Alu-Wave with a diameter of 25 mm. The surface finish was carried out by a PKD special cutter.
Pockets in all shapes
The machining of the backside proved particularly challenging, as it is divided into nine different sections, each with special applications. Like every rear spar, the sample component features many pockets, but here they are designed in every conceivable shape: rectangular, triangular, round, open, closed, some with slanted or vaulted bottoms. The webs are very thin, and the walls are predominantly slanted. The pockets have a depth of up to 137 mm.
After the pre-machining with the NeoMill-Alu-QBig, an OptiMill-Alu-Wave of various lengths was used to clear the pockets. Semi-finishing was taken over by a corner cutter specially modified for aerospace applications. Thanks to its special geometry, the tool is particularly suitable for machining residual material in the corners as well as for subsequent finishing of the bottoms and walls. The special core rise ensures optimal stability in the machining process. To efficiently machine all areas, MAPAL specialists used the modified corner cutter in various diameters and lengths.
As efficiency was also considered in programming at MAPAL, component manager Alexander Follenweider describes: "We work with a zigzag strategy in synchronous and counter-synchronous operation to save paths. During processing, the strategy is constantly changed." Despite high processing speeds, the aluminum must not be damaged, as overheating alters its properties.
The OptiMill-Alu-Wave was operated at 29,000 revolutions, with a cutting depth of 48 mm and a feed rate of 12 m/min at its peak. The larger NeoMill-Alu-QBig achieved a feed rate of over 25 m/min at a cutting depth of 10 mm. In the first 55 minutes of processing the second clamping, 425 kg of aluminum was machined, reaching a chip volume of more than 14 l/min at its peak.
"These are excellent values that we were able to achieve here – and we also produced very good surfaces," appreciates Stefan Diem, application technician at bavius, the results.
Nothing is standard
The various pockets are not the only challenges of the component: The holes on four tabs are only accessible with an angle head. At other points, undercuts are required.
A typical T-stiffener for structural components is also present on the sample part and is machined with a PKD special tool. Drilling and reaming operations are also required in certain areas. "Nothing is normal on our component," comments Dominik Merz on the fact that practically nowhere is there a right angle. Such angled constructions are typical for the aerospace sector.
For customer presentations at the involved partners and as an eye-catcher at trade fairs, five of these rear spars were produced in Baienfurt. The machining of a part takes exactly 10 hours, which the project participants are very satisfied with. "On other machines, such a component often takes 20 to 30 hours," estimates Merz. Typically, structural components are machined on vertical gantry machines with large tools, with cutter heads having diameters of 125 mm. Feed and speed remain low. A disadvantage of this method is that chips can remain and cause scratches. Additionally, there is a heat input into the component. Horizontal machining eliminates this. 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 collaboration for many years, from which both sides benefit. When MAPAL developed the NeoMill-Alu-QBig and the OptiMill-Alu-Wave, prototypes of the new tools could already be tested and further optimized in Baienfurt. The tool manufacturer does not have similarly powerful machines in Aalen itself. On the other hand, bavius also relies 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. Universal tools do not work for this; we gain no insights with them."
In collaboration, the partners demonstrated what the AeroCell 160 can do two years ago. In test operation with overload, the solid carbide cutter OptiMill-Alu-Wave achieved a chip volume of up to 20 l/min when full slot milling in normal aluminum. The now achieved peak value of 12 l/min with a component made from the stronger AL 7075 is not inferior.
"I greatly appreciate the collaboration with MAPAL because we communicate openly and fairly, and we always receive a solution," emphasizes Stefan Diem. For Jens Ilg, Business Development Aerospace & Composites at MAPAL, the joint success also has a personal aspect: "I also get an optimal feeling for our own products when I have used them under the real, required conditions. And then I can offer them to a customer with the corresponding recommendations."
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