Machining aluminum at 16.8 m/min
Machine manufacturer bavius technologie conducted a test cut under real conditions to convince a customer that even long overhanging tools run smoothly on the machine with the smaller HSK tool holder. An important part of the test was to get the right tools. With a tool set for roughing and finishing from ISCAR, the test exceeded all expectations.
“An American company in the aerospace industry was looking for a machine that offers high removal rates, dynamics, and availability while also delivering high machining quality for the production of large aluminum structural components,” explains Dominik Merz, Director of Global Sales | Applications at bavius. “A perfect task for our HBZ AeroCell 160 I 400.” The machine has a high-performance spindle that runs up to 30,000 rpm and delivers 140 kilowatts of power in continuous operation (S1 mode). In operating mode S6, power outputs of up to 175 kilowatts are available for short periods. “Since the 140 kilowatts are already available at 19,000 rpm, high power outputs can be achieved even in the medium speed range, which offers a number of advantages,” explains Dominik Merz.
Only the HSK-A63/80 tool holder that bavius uses as standard caused concern for the US customer. Based on experience and for stability reasons, he preferred a larger one. However, this would have significantly limited the available machining capacity of the machining center. “In order to be able to run at 30,000 rpm, the AeroCell 160 is equipped with an HSK 63/80 tool holder, which, thanks to its larger contact surfaces, provides the necessary stability to the tool even with long overhangs,” explains Stefan Diem, application engineer at bavius. “With a HSK100 holder, on the other hand, only 20,000 rpm would have been achievable. That was not an option for bavius at first and would have limited the advantages of the machine.” Dominik Merz adds: “Above all, 70 to 80 percent of the machining of such parts, which often takes several hours, is carried out with short tools. During production, it quickly becomes apparent whether the user can utilize the full speed and full power.”
To demonstrate to the customer that the smaller holder also offers the necessary stability for long tools, the bavius team arranged a live test run under real conditions at bavius in Baienfurt. The plan was the following: To machine a 170 × 626 millimeter and 260 millimeter deep V-shaped pocket, as typically found in structural components for aviation, into a 600 × 780 × 500 millimeter block of EN-AW 7012 (AlZn6Mg2Cu) aluminum- wrought alloy.
Even with tool lengths of up to 357 mm, the processes ran smoothly and without vibration.
Using ISCAR’s HeliAlu monoblock tool, up to 148 kW could be achieved at the spindle in the S6 range.
“We contacted our longtime partner ISCAR to put together the optimal tool package for roughing and finishing,” explains Stefan Diem. Michele Piccolantonio, Equipment Projects Consulting and Sales, Calogero La Quatra, Product Specialist Multi Master, Solid Carbide and PCD Tools, and Anton Kress, Product Specialist Milling, were briefed on the task and, together with the bavius team, assembled a set precisely tailored to the task and the material.“Aluminum can generally be machined quickly and easily, but it still has its peculiarities,” says Anton Kress. In this instance highly positive systems with very sharp polished cutting edges are required to prevent chips from sticking to the cutting edge and surface, ensuring reliable operation. This also results in lower cutting forces during machining. This offers enormous advantages when using long tools and significantly reduces deflection and vibrations.“Important selection criteria therefore included the use of soft-cutting standard tools that support the machine’s high dynamics, allow high speeds, and run reliably in order to maintain high machine availability,” says Michele Piccolantonio. “In addition, very high removal rates should be possible during roughing — keyword: high-volume machining — and top surface qualities during finishing,” adds Anton Kress. The result was a tool set with milling cutters from the HELIALU, MegaAlu, and MULTIMASTER families.
HELIALU milling cutters with targeted JHP cooling and a diameter of 50 millimeters were used to remove large quantities of material in a short time. For roughing the surface contour and the first part of the pocket, the milling cutter was designed as a 110-millimeter-long monoblock tool equipped with four indexable inserts with two helical cutting edges. The circumferentially ground, 22-millimeter-long, sharp cutting edges with a highly positive rake angle and polished rake faces cut smoothly and ensure excellent chip flow. “This allowed us to rough at a spindle speed of 25,400 rpm, drawing up to 148 kilowatts at the spindle,” says Stefan Diem happily. “At a feed rate of 25,400 millimeters per minute and a cutting depth of 16.5 millimeters, we were able to remove up to 14.5 liters of material per minute.” bavius used HELIALU face mills in lengths of 157, 207, and 257 millimeters equipped with 14mm long inserts – with speeds of up to 28,000 rpm, a power output of up to 65 kilowatts, and feed rates of up to 16,500 millimeters per minute. “It was really impressive to see how the machine whizzed through the material,” says Dominik Merz.
The AeroCell 160 | 400 from bavius features a high-performance spindle that runs at up to 30,000 rpm and delivers 140 kW of power in continuous operation.
Proper Aluminum Milling: The horizontal machining center equipped with the bavius bmh 3 fork-type milling head is designed for high-volume aluminum machining and—with the right tools—reliably milled the large pocket in just 3 hours.
Using four three-edged MegaAlu solid carbide endmills with a diameter of 25 millimeters and lengths ranging from 5xD to 8xD, bavius reduced the corner radii from R50 and R25 to R12.5 and premachined the pocket to its final depth of 260 millimeters. “For this, we also use the only exceptions to the standard. The two endmills in 7xD and 8xD are special tools,” says Calogero La Quatra. “A particular advantage of these three-edged aluminum specialists is that they have an unequal pitch and, thanks to their special cutting geometry, the process is virtually chatter-free even with such high overhangs.”
Using MegaAlu solid carbide end mills in lengths ranging from 5xD to 8xD, bavius reduced the corner radii and rough-machined the pocket to its final depth of 360 mm.
For finishing operations, screw-on solid carbide ball-end and barrel cutters from ISCAR’s Multimaster family, with tool lengths ranging from 155 to 293 mm, ensured a high surface finish.
However, manufacturing aerospace components is not just about removing large amounts of material quickly. High-quality surfaces are equally important. This makes finishing a crucial process. For the test, screw-on solid carbide ball nose and barrel heads from ISCAR’s MULTIMASTER family, with tool lengths between 155 and 293 millimeters, were used. With spindle speeds between 21,000 and 27,000 rpm, fine, burr-free surfaces with rough depths of 6.5 micrometers were created on the bottom and walls of the pocket within a few minutes.
A three-edged EBA ball-nose cutter with a diameter of 16 millimeters and an 8-millimeter radius was used to finish the bottom of the pocket. Mounted on a 200-millimeter shank, the tool measures 280 millimeters. To finish the larger sides of the pocket, bavius used the barrel-shaped EOBA cutter with a diameter of 16 millimeters, four cutting edges, and a 75 millimeter profile radius on the 200-millimeter shank. “This barrel cutter finishes up to nine times faster than a comparable ball-nose cutter. This is because the radius serves as a mathematical factor and, allowing the steps to be increased axially by a multiple,” explains Calogero La Quatra. “And this is achieved at low speeds and regardless of cutting parameters.”
“The test run exceeded all expectations. The customer was completely convinced and so enthusiastic that he would have liked to take the machine with him immediately,” says Dominik Merz. “Thanks to the combination of our dynamic AeroCell and ISCAR’s innovative tools, we were able to offer him an efficient solution.”
In just three hours, around 70 kilograms of material were removed and the pocket was machined into the block reliably, meeting the required quality standards. “The combination of a dynamic, powerful machining center and the right tool ensures shorter processing times and significantly increases productivity,” says Stefan Diem, summarizing the result. “as predicted, even the long overhanging tools operated completely stably and without vibrations with the HSK63/80 holder.” Using a 357-millimeter-long HELIALU face mill with a diameter of 50 millimeters, the machine manufacturer pushed this stability test to the extreme: In addition to the V-pocket, they milled another cavity into the aluminum block with a feed rate of 8,100 millimeters per minute and a spindle speed of 18,000 rpm in a process-reliable manner.
