Aldershot-based company, FT Gearing, supplies the global defence and aerospace sectors with gears, miniature gearboxes and safety critical components for wing surface actuators, engine controls, instrumentation and fuel pumps. A few years ago, the manufacturer tried broaching the bore profiles in steel worm shafts to transmit the drive to thrust reversers, but the length-to-diameter ratios were too high and the tools broke frequently.
Therefore, the company put the work out to a wire-type EDM (Electric Discharge Machining) subcontractor in the Midlands. The service was expensive, partly because the firm needed to have Nadcap (National Aerospace and Defence Contractors Accreditation Programme) approval, which is a requirement of primes such as Boeing and Airbus as well as tier-one aerospace companies, all of which FT Gearing supplies.
The situation has been turned on its head following the arrival over an 18-month period of three Makino wire EDM machines at an FT Gearing satellite facility close to the company’s main factory. The machines were supplied by NCMT, UK agent for the Japanese machine builder. Within six months of the first arriving, the gear specialist had gained Nadcap approval, while the latest EDM machine installed mid-2017 provides capacity for internal development projects and offering a subcontract wire EDM service.
Managing Director Graham Fitzgerald, who started the business with his father Des in 1978, commented: “We chose U3 wire eroders from Makino after we employed a skilled EDM machinist that has a lot of experience operating machines of the same make and rates them highly.
“He says that ISO programming on the Fanuc-based control is far easier than on some other EDM machines that employ two languages, macros are simpler to create and operations like rotation and mirror imaging are straightforward.
“From my perspective, quicker programming leads to higher productivity. The machines are also reliable and their build quality means they sit well alongside top-end, 4- and 5-axis machining centres in our Unit 19, which we recently opened.”
The latest Makino wire EDM machines are fitted with the Hyper-i CNC system, which contains an extensive library of cutting conditions that automatically optimises the erosion process, even for sealed and poor flush applications. The control employs so-called HyperCut technology, a process developed to produce surface finishes as fine as three microns Rz in standard tool steels in a three-pass process. Chris Elwick, Manager of Unit 19, advised that the same result would take at least six passes on other makes of wire erosion machine.
This advanced technology is brought to bear on FT Gearing’s S106 and S82 aircraft steel worm shafts to produce bores of square, double-D, hexagonal and other shapes that provide the drive to the reverse thrust flap. Dimensional tolerance is to within ten microns and cycle times range from one to three hours.
There is spare capacity to wire-EDM other components as well, such as internal gears, splines and keyways. Elwick said: “Usually they require special gear cutters that can take up to 16 weeks to be delivered, but they can be put straight onto a Makino U3 without delay. Although machining takes a little longer, parts can be processed in their hardened state so distortion and potential rework are avoided.”
Makino’s U3 wire EDM machine and the larger U6 were launched in the UK on the NCMT stand at MACH 2016. They offer competitive cycle times as well as high accuracy and surface finish, even using uncoated brass wire, and also feature low wire consumption. The machine is of stationary table design and the entire bed casting serves as the dielectric reservoir, reducing the footprint and eliminating the need for additional external fluid tanks.
Makino’s optional High Energy Applied Technology (H.E.A.T.) is incorporated into the second machine installed in Unit 19, as it happened to be part of the specification of a model available at short notice from NCMT. A pair of high pressure, digitally controlled flush pumps and a large capacity, four-step filtration system provide even faster machining speeds and improved accuracy in cases that present difficult flushing conditions. It does not make much difference for FT Gearing’s mainstream work but its benefits may be harnessed for future applications.