Aluminium machining in new dimensions

The aerospace industry is undergoing a transformation in terms of machine concepts. After decades of preferring to work on gantry machines or vertical machining centres, horizontal machines are now preferred for new investments, where the components are clamped upright and the spindle is moved horizontally. The main advantage of the horizontal design is the easier removal of the large quantity of chips, which practically fall into the chip conveyor by themselves.

At bavius, it’s clear that the aerospace industry has recovered from Covid. Passenger numbers have already returned to pre-pandemic levels and are continuing to rise. As a result, new planes are needed again, which keeps machine manufacturers busy. Demand in Germany, France, Spain and other countries reveals that there is a lot of investment in Europe again. Dynamic machines with high spindle power are particularly sought after.
 

Because milling cutters from the OptiMill-SPM series had previously been used at bavius and performed very well, MAPAL was asked again. It was perfect timing: the tool manufacturer had just finished developing a new solid carbide roughing cutter, the OptiMill-Alu-Wave, and also offered the new aluminium high-volume milling cutter NeoMill-Alu-QBig with indexable inserts for larger diameters.

The milling tests are kept simple in design but put the tools through their paces. bavius mills a series of flutes in a large aluminium plate for this. Stefan Diem takes a very pragmatic approach: “if the tool can do the flute, we can also use it to mill pockets and do any other machining.” This means that the determined cutting data can be directly applied to customer parts.
 

For the tests with the OptiMill-Alu-Wave, bavius chose the largest diameter of this three-fluted cutter at 25 mm. At a spindle speed of 25,465 rpm and a cutting speed of 2,000 m/min, the spindle power was gradually increased. Slot number 6 delivered the best material removal rate with a record-breaking 20 dm3/min. This test run was performed with a spindle power of 175 kW, with a torque of 66 Nm, and a material removal rate of 30 mm. The machine stopped during tests at higher powers. “The tool can be fully deployed, the limiting factor is the spindle”, Diem comments on the result. “With the 25 mm OptiMill-Alu-Wave, we have achieved a new dimension in aluminium machining. The milling cutter is definitely better than anything we had previously used.”

bavius used the Safe-LockTM system as pull-out protection. “In this speed range, symmetrical pull-out protection is very important in order not to create imbalance”, explains Tim Rohmer, Product Manager Solid Carbide Milling Tools at MAPAL. A Weldon flat, which is often attached to such tools as pull-out protection, is the wrong solution here. To guarantee the smooth running of the machine, there is no way around careful balancing, even with symmetrical tools.

The tests in Baienfurt were also met with a great deal of satisfaction in terms of surface quality. The cord geometry of the OptiMill-Alu-Wave ensures optimum chip formation. The polished groove profile ensures seamless chip removal, which is supported by the central cooling of the tool in cooperation with the external cooling in the machine.

In further tests, pockets were milled into the aluminium plate, with a material removal rate of 16 litres still being achieved with very good surfaces. For Application Engineer Thomas Jungbeck and Component Manager Alexander Follenweider, who monitored the tests for MAPAL, this is proof of the very good dynamics of the bavius machining centre: “Other machines often stop in the corners and cause high vibrations. This doesn’t occur at all with the AeroCell, which goes round corners almost unrestrained.”
 

Überaus positiv fielen auch die Versuche mit dem neuen Wendeplattenwerkzeug NeoMill-Alu-QBig von MAPAL bei bavius aus, wofür der Durchmesser 50 mm gewählt wurde. Der Aluminium-Hochvolumenfräser schaffte ein Zeitspanvolumen von 18,4 dm3/min. Auf der Maschine überzeugte der Fräser mit seiner hohen Stabilität und Laufruhe und geringen Schnittkräften. Für den Einsatz bei Drehzahlen bis zu 35.000 min-1 hat MAPAL den Grundkörper mit vier Gewindebohrungen zum Feinwuchten versehen. Die hochgenau umfanggeschliffenen Wendeschneidplatten erreichen Oberflächengüten von Ra 0,8 µm und Rz 4 µm bei der Vor- und Fertigbearbeitung. Sie sind mit polierter Spanleitstufe versehen, um den Reibwiderstand und die Hitzeentwicklung zu reduzieren. Auch wurde Gewicht eingespart, um Fliehkräfte zu reduzieren. „Bei größeren Durchmessern sind Fräser mit Wendeschneidplatten die wirtschaftlichere Lösung“, grenzt Heiko Rup, Produktmanager für Werkzeuge mit Wendeschneidplatten, sie gegenüber Vollhartmetallfräsern ab.

Beim Durchmesser 25 mm gehen die beiden Systeme ineinander über. „Manche unserer Kunden greifen nach Möglichkeit immer zu den kostengünstigeren Wendeschneidplatten, andere ersparen sich lieber einen zusätzlichen Arbeitsgang und machen mit dem Vollhartmetallfräser weiter“, berichtet Stefan Diem. Mit verschiedenen möglichen Radien seiner Werkzeuge gibt MAPAL den Anwendern Flexibilität. 

Mit dem Horizontalbearbeitungszentrum AeroCell 160 und den Aluminium-Hochvolumenwerkzeugen bieten bavius und MAPAL Anwendern eine Kombination, die die Bearbeitung von Strukturbauteilen auf ein neues Niveau hebt.