28.04.2022

Automotive technology for aeroplanes

Titanium machining on a gantry machine of F. Zimmermann GmbH

The machine manufacturing company Zimmermann brought MAPAL aboard as a tool and technology partner to design a turnkey machine for producing titanium parts for the aerospace industry. MAPAL’s line boring technology combined with a new generation of tools to machine titanium made this particularly challenging project a resounding success.

The OptiMill-Titan-HPC in use for machining titanium.
  • The OptiMill-Titan-HPC in use for machining titanium.
  • A NeoMill-Titan from MAPAL is used for face milling on the six-axis gantry machine FZ42 from Zimmermann.
  • The team of Zimmermann and MAPAL responsibles: Bernd Scheurenbrand and Steffen Nüssle, as well as Jens Ilg, Andreas Rotenberger, Julian Kraus and Lukas Weiß.
  • The aeronautical component, a 1.50 metre long suspension made of titanium.
  • The OptiMill-Tro-Titan from MAPAL in use for titanium machining.
  • A right-angle drill head in use for titanium machining.
  • A FixReam reamer from MAPAL in use for titanium machining.
  • A MEGA-Speed-Drill-Titan from MAPAL is piloting the main bore of the first lug of the titanium part.
  • A MEGA-Speed-Drill-Titan in special design is pre-machining the main bores of the titanium part.
  • The line boring bar from MAPAL with a diameter of 17 mm and total length of 685 mm finishes the machining of the main bore.

The F. Zimmermann GmbH from the town Neuhausen auf den Fildern is known above all for its big portal milling machines. The export-oriented machine manufacturer has already delivered more than 550 systems in 37 countries worldwide. They can often be found in the R&D departments of large corporations where they support the entire product development process from drafting designs to the various stages of prototyping. “Everything which one day takes form was on one of our machines as a model”, says Steffen Nüssle, Head of Sales and Application Technology at Zimmermann.

Typical material for model making are wood, polystyrene and Ureol. Zimmermann began metalworking more than 20 years ago with aluminium. This was their door opener for the aerospace industry. Gradually, they tried their hand at machining composite material, steel and highly heat-resistant workpiece material like titanium, Waspaloy, Inconel and invar. Models and prototypes are not the focus anymore with these materials. The aerospace industry uses the portal milling machines to produce parts.
 

Bespoke turnkey manufacturing – focus on simultaneous engineering

„Im Grunde haben wir Manufakturcharakter und sind kein Massenhersteller“, beschreibt Steffen Nüssle die Produktion bei Zimmermann. Ihr modularer Aufbau macht es jedoch vergleichsweise einfach, die Maschinen an die Anforderungen der Kunden anzupassen. Bei einem asiatischen Flugzeugteilezulieferer sind bereits mehrere von ihnen im Einsatz, doch der neue Auftrag geht weit über das bisher Gelieferte hinaus. Dieses Mal verlangte der Kunde eine mit sehr vielen Funktionen und Zusatznutzen hoch individualisierte Portalfräsmaschine. Gewünscht war zudem eine Vorrichtung zur Bearbeitung eines bestimmten Bauteils. Daneben sollten die Verantwortlichen bei Zimmermann auch den Werkzeugsatz für die spezielle Bearbeitung auswählen und einfahren. Und auch die Programmierung des Bauteils war Teil des Auftrags. „Unter dem Strich ist das eine Turnkey-Maschine, bei der der Kunde nur noch auf den Knopf drücken muss, und das Teil läuft von allein durch“, so Nüssle.
Das Luftfahrtbauteil, eine 1,50 Meter lange Aufhängung aus Titan.
Die rund 1,50 m lange Aufhängung für einen asiatischen Flugzeugteilezulieferer  © F. Zimmermann GmbH

The part in question is an approximately 1.5-metre-long mount. A particular machining challenge was posed by the row of twelve bores in the lugs, which are located over a space of 990 mm on the workpiece. The customer required high precision here. A tolerance of H7 was stipulated at a bore diameter of 17 mm. Over the entire length of the part, the concentricity of the bore had to be less than 0.05 mm. The same accuracy is necessary for the perpendicularity of the bore lugs towards the part surface.

Zimmermann picked MAPAL as its tool partner for good reason. “Our application engineers don’t make any compromises for a turnkey project like this one. Only a very good system partner comes into question”, says Nüssle, who goes on to report that he had only the best experience with the tool manufacturer.

Past Zimmermann turnkey projects involved wing spars for the Airbus A350 or countersinks and deep bores on wind turbine blades made of fibreglass. While employed for another machine manufacturer, Nüssle also worked with MAPAL. This involved machining bearing seats for crankshafts and camshafts for large diesel motors using the line boring technology. MAPAL has acquired extensive knowledge about such line boring bars from the automotive industry. Now this knowledge is required for aerospace parts whose lugs are very similar to the journal bearings in the crankshaft bearing aisle of a combustion engine.
 

The team of Zimmermann and MAPAL responsibles: Bernd Scheurenbrand and Steffen Nüssle, as well as Jens Ilg, Andreas Rotenberger, Julian Kraus and Lukas Weiß.
Close technology partnership in a turnkey project from left: Application Engineer Bernd Scheurenbrand and Steffen Nüssle, Export Sales Manager and Head of Application Technology, from F. Zimmermann GmbH with Jens Ilg (Component Manager Titanium & Stainless Steel), Andreas Rotenberger (Test Engineer / CAM Team) as well as Julian Kraus and Lukas Weiß, both programmers in the CAM Team at MAPAL  © F. Zimmermann GmbH
“This project challenged our technological knowledge in all realms”, asserts Sven Frank, Global Head of OEM Management at MAPAL. “We didn’t even have a sketch of the part to start with, on which we could have based our concurrent engineering with Zimmermann.” That fact is all the more challenging as a CAD/CAM-based NC simulation is of upmost importance and forms the basis for a milling strategy, the individual process sequences and the definition of the fixture concept. Both partners highlight that detailed simulations and finetuning of individual steps were very important for the cooperation. The total cycle time was also calculated through simulations.

Powder-metallurgical titanium

The project partners brooded over the material for the part. The customer announced forged blanks made of the titanium alloy TA15m. “All of us have experience with aerospace titanium, so we knew what we were getting into, but even our full-fledged aerospace experts had never heard of this special alloy”, Steffen Nüssle admits. Jens Ilg, who works in the Aerospace & Composites segment at MAPAL, agrees: “The material was exotic for us, too.” They discovered that TA15m is a workpiece material that is manufactured powder-metallurgically. The sintered material is redensified in a special process, whereby the workpiece acquires the characteristics of a forged part.

The customer did not provide any blanks to design the machine with. Thus, the project partners had no other choice but to take a titanium bar and mill the form of the blank with its measurements from the solid block. In this way, a blank was imitated, which represented the starting point of manufacturing for the customer. This preparatory work alone took 30 hours of machining time.
 

A NeoMill-Titan from MAPAL is used for face milling on the six-axis gantry machine FZ42 from Zimmermann.
The outer contour is preroughed on the six-axis FZ42 with a VH60 milling head with a NeoMill-Titan  © F. Zimmermann GmbH

At the same time as the machine was being constructed by Zimmermann in Neuhausen, MAPAL began with tool tests in Aalen. The tool manufacturer could rely on a new generation of titanium tools for this purpose. In order to achieve high removal rates, the NeoMill-Titan shell end face milling cutter was chosen. MAPAL developed the new topography of the indexable insert in such a way that the chips are optimally formed and removed. An equally new cutting material concept minimises wear and tear and the formation of built-up edges.

Even experienced application engineers were surprised how smoothly and almost silently the tool works. The tool life is also impressive. The 60 minutes that Bernd Scheurenbrand expected were exceeded considerably. “Some of the tools were at work for almost seven hours – that’s a sensational tool life”, the experienced application engineer from Zimmermann praises. This result was made possible, among other reasons, due to the modern protective coating with a good adhesion to the tool, an effective temperature barrier and a very smooth surface that reduced heat on the cutting area.
 

Convincing new tool generation

To clear out pockets and cavities on the part, MAPAL selected the solid carbide milling cutter OptiMill-Titan-HPC in a special length. When machining the gaps between the lugs, the trochoidal milling cutter OptiMill-Tro-Titan was able to show off its strengths with short contact times and optimal heat removal. Over the entire milling area, it created absolutely straight walls with reflective surfaces. “In tests, we were able to mill the lug down to a wall thickness of 3 mm without it pushing away or vibrating”, Ilg reports. This was a relief for Nüssle: “If the end milling cutter hadn’t worked, we would have needed a special machine to work the journal bearings at the same time on both sides with disc milling cutters to balance the forces out.”
The OptiMill-Tro-Titan from MAPAL in use for titanium machining.
Snapshot from titanium machining: The OptiMill-Tro-Titan finishes the pocket wall. The complete depth is machined in one cut  ©MAPAL

Excellent cooling is essential when machining titanium to remove the heat that develops. MAPAL MillChucks with integrated coolant supply were used to bring the coolant pressure to the milling cutter. Zimmermann chose the company Blaser Swisslube as a further project partner to provide the cooling lubricant as their coolants are ideally suitable for high pressures.

For the bores on the sides of the lug, MAPAL developed a custom tool with angular drill head based on the MEGA-Speed-Drill-Titan. The drill bores, then deburs back in the countersink step and finally produces a chamfer in reverse.
 

Line boring from two sides

A MEGA-Speed-Drill-Titan from MAPAL is piloting the main bore of the first lug of the titanium part.
Snapshot from titanium machining: The main bore of the first lug pack is piloted by the MEGA-Speed-Drill-Titan  ©MAPAL
Line boring is an ideal way to create the main bore of the mount. The twelve lugs are arranged in four groups with three journal bearings. The first lug pack is initially piloted. The drill for machining the second lug pack is guided through these pre-machined bores. Due to the length of the part, the lug packs 3 and 4 had to be machined mirror-inverted from the other side.
A MEGA-Speed-Drill-Titan in special design is pre-machining the main bores of the titanium part.
A special design of the MEGA-Speed-Drill-Titan carries out the pre-machining of the main bore of the second lug pack. The tool is led through the first lug pack  ©MAPAL

Die 685 mm lange Reihenbohrstange mit Durchmesser 17 mm, die im Anschluss die Fertigbearbeitung übernimmt, ist mit zwei einstellbaren Schneiden bestückt und wird zwischen den Laschen in Führungsbuchsen geführt. Die erste Schneide bohrt die Hauptbohrung auf und egalisiert so einen eventuell durch die Vorbearbeitung entstandenen Versatz. Schneide 2 erzeugt unmittelbar danach den Fertigdurchmesser in H7-Qualität. Die lange Bohrstange erinnert Jens Ilg dabei an ein Laserschwert: „Dieses Schwenkmanöver, um das Werkzeug vor dem Bauteil zu positionieren, hat schon etwas von Star Wars.“ Die Portalfräsmaschine, eine sechsachsige FZ42 mit Fräskopf VH60, bietet mehr als genug Platz für das spektakuläre Herumwirbeln. Der Arbeitsraum hat eine Größe von 8,50 x 3,90 x 1,50 m und ist aufgeteilt in einen Bereich mit festem Maschinentisch und einen Bereich mit Rundtisch für weitere Bearbeitungen.

Das Übertragen der Ergebnisse aus dem Testzentrum von MAPAL auf die Maschine in Neuhausen war ein kritischer Schritt des Projekts, wie Nüssle schildert: „Nach den erfolgreichen Testläufen in Aalen wussten wir, wo die Reise hingehen musste. Unser Portalfräszentrum ist viel größer als das Bearbeitungszentrum in Aalen, hat größere bewegte Massen und größere Hebellängen. Und ist damit nicht ganz so steif.“

Die Befürchtungen erwiesen sich als unnötig: Hier wie dort wurden die gewünschten Genauigkeiten mit hoher Prozesssicherheit erreicht. Das gilt insbesondere auch für die Mitte des Werkstücks, wo die Bohrungen von beiden Seiten aufeinanderstoßen und ein kleiner Versatz möglich ist. Die Messergebnisse belegen, dass die Bearbeitung auf Umschlag geklappt hat: Gerade mal 8 µm Differenz wurden an dieser Stelle gemessen. Das Line Boring Verfahren sorgt dafür, dass eine einmal erreichte Präzision auch nach einigen Jahren noch reproduziert werden kann, denn die Maschine stellt nur Vorschub und Drehzahl bereit, während die eigentliche geometrische Führung aus der Vorrichtung kommt.
 

Eine Reihenbohrstange mit Durchmesser 17 mm und einer Gesamtlänge von 685 mm bearbeitet die Hauptbohrung fertig.
Eine Reihenbohrstange mit Durchmesser 17 mm und einer Gesamtlänge von 685 mm bearbeitet die Hauptbohrung fertig  ©MAPAL

Zimmermann hat bei der Konstruktion seiner Vorrichtung viel für die Schwingungsdämpfung getan. Durch die zahlreichen Spangen und Klammern kamen allerdings auch etliche Störkonturen ins Spiel. Hier hat der Maschinenhersteller seine Kompetenz aus dem Modellbau genutzt und zunächst einen Rohling aus Kunststoff angefertigt. „Wenn beim ersten Versuch etwas schiefgelaufen wäre, hätten wir weder das teure Titan, noch das Werkzeug oder gar die Maschine beschädigt“, erläutert Nüssle. Doch es lief auf Anhieb glatt durch und für das erste Titanteil waren nur noch die Schnittparameter anzupassen.

Von der guten Zusammenarbeit zwischen Zimmermann und MAPAL ist Steffen Nüssle sehr angetan: „Ich war schon bei vielen Turnkey-Entwicklungen dabei, habe aber noch nie ein Projekt erlebt, das so satt durchgeflutscht ist wie dieses. Das hat richtig Spaß gemacht.“ Die geografische Nähe zwischen Neuhausen und Aalen war dabei ein großer Vorteil: Nach einer Stunde Autofahrt konnte man direkt an der Maschine die jeweils nächsten Schritte gemeinsam besprechen.
 


Kathrin Rehor, PR Project Manager bei MAPAL

Kontakt

Kathrin Rehor Public Relations Kathrin.Rehor@mapal.com Tel.: +49 7361 585 3342


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