In the past four years, first-tier airframe component supplier Moyola Precision Engineering, based in Castledawson, Northern Ireland, has invested £6.5 million in its aerospace division. More than two-thirds has been spent on three high-speed, six-axis machining centers from Dörries Scharmann Technologie (DST), the latest of which was installed in November.
Having an extra CNC axis in addition to the more usual five axes results in significant productivity and cost benefits when machining aircraft structural parts, according to Moyola Managing Director Mark Semple.
A major advantage is that deep recesses and other awkward areas on components can be accessed and machined at high speed by short cutters. If the same parts were machined on conventional five-axis machines, significantly longer tools would be needed for clearance. There would be a consequent risk of chatter, adversely affecting surface finish. The likelihood, therefore, is that cutting speeds and feeds would have to be reduced, compromising productivity, Semple said.
The kinematically driven Sprint Z3 head on the two DST EcoSpeed F2035 machining centers tilts through 40± degrees in both the vertical A axis and horizontal B axis. This is suitable for a majority of machining tasks.
The ability to automatically replace the in-line spindle with a right-angle milling head in under three minutes allows steep angles up to 130° to be achieved. By interpolating the 360° C-axis rotation of the head with the X, Y, Z, A, and B axes, even difficult-to-reach areas on aircraft parts can be machined easily with short, rigid tooling. The angle head is used to machine 50% of the parts that go through the EcoSpeed F2035s at Moyola.
Irrespective of whether the in-line or right-angle head is in use, full advantage can be taken of the 120-kW 30,000-rpm spindle on the latest F2035 and of the 80-kW 30,000-rpm spindle on an otherwise almost identical machine installed in 2005. It is noteworthy that, unlike on many high-speed machining centers, it is not necessary to operate at maximum rpm to achieve full power, which is available at speeds as low as 13,800 rpm—less than half of full speed.
This added flexibility enables cutting speeds, feeds, and depths of cut to be optimized to achieve maximum performance for each cutting tool assembly.
“In early trials carried out by various machine suppliers, DST produced in 2.05 h an Airbus A320 wing rib that used to take us 9.5 h on one of our five-axis machining centers,” said Semple. “The next quickest machine from another potential supplier took over 4 h.”
The use of oil mist lubrication rather than coolant through the predominantly solid carbide tools allows the area where metal is being cut to be seen clearly. Good visibility facilitates editing to shave further seconds off cycle times more effectively than if the milling operations were obscured by coolant. It is also more environmentally friendly.
Design features of the F2035 such as vertical pallet orientation and an absence of swarf traps allow the machines to remain free from swarf in the working area despite not having flood coolant. Minimum lubrication mist also saves a significant amount of money annually in coolant costs and improves the working environment.
The EcoSpeed 2035s have a 2.5-m Y-axis, larger than on any other machining center on the shop floor at Castledawson. More components can therefore be nested into each billet, which can be up to 2 x 3.5 m. The additional width is particularly useful when machining batches of curved fuselage ribs, with smaller parts placed in unused areas close to the billet edges. Reduced frequency of setup is a further benefit of using larger billets, as it maximizes spindle uptime and productivity.