Aldershot-based FT Gearing supplies gears, miniature gearboxes and safety-critical components for wing-surface actuators, engine controls, instrumentation and fuel pumps to the defence and aerospace sectors (www.ftgearing.com).

Many years ago, the company tried broaching the bore profiles in steel worm shafts that transmit the drive to thrust reversers, but the length-to-diameter ratios were too high and the tools frequently broke.

It put the work out to a Midlands-based sub-contractor, which used wire-cut EDM to produce the bore profiles.

This was costly, partly because the firm needed to have Nadcap approval — a requirement of ‘primes’ such as Boeing and Airbus, as well as Tier One aerospace companies, all of which FT Gearing supplies.

The situation was turned on its head following the installation (over an 18-month period) of three Makino wire-cut EDM machines at an FT Gearing satellite facility close to the company’s main factory.

These machines were supplied by Thames Ditton-based NCMT Ltd (www.ncmt.co.uk), the Japanese machine builder’s UK agent.

Within six months of the first machine arriving, the gear specialist had gained Nadcap approval; the latest machine — installed in mid-2017 — provides the capacity for development projects and allows the company to offer a sub-contract wire-cut EDM service.

Valuable experience

Managing director Graham Fitzgerald, who started the business with his father Des in 1978, said: “We chose Makino’s U3 wire eroders after employing a skilled EDM machinist who had a lot of experience operating machines of the same make and rated them highly.

“He says that ISO programming on the Fanuc-based control is far easier than on some other EDM machines using two languages, that macros are simpler to create and that operations like rotation and mirror imaging are straightforward.

“From my perspective, quicker programming leads to higher productivity, while the machines’ build quality means that they sit well alongside the top-end four- and five-axis machining centres in our recently opened new facility — Unit 19.”

The latest Makino wire-cut EDM machines are fitted with the Hyper-i CNC system, which contains an extensive library of cutting conditions that automatically optimise the erosion process, even for sealed and poor-flush applications.

The control also uses HyperCut technology, a process developed to produce surface finishes as fine as 3µm Rz in standard tool steels using a three-pass process.

Chris Elwick, manager of Unit 19, says 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 steel worm shafts for aircraft to produce bores of square, double-D, hexagonal and other shapes that provide the drive to the reverse thrust flap.

The dimensional tolerance is to within 10µm, and cycle times are in the range 1-3hr.

Mr Elwick said: “There is spare capacity to also wire-EDM other components and features, such as internal gears, splines and keyways.

“They usually require special gear cutters that can take up to 16 weeks to be delivered, but these parts 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 re-work are avoided.”

Makino’s U3 wire-cut EDM machine and the larger U6 were launched in the UK on the NCMT stand at MACH 2016.

They have been designed to offer competitive cycle times as well as high accuracy and surface finish, even when using uncoated brass wire; they also offer low wire consumption.

The machines feature a stationary table, 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’ (HEAT) 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 and improved accuracy in cases where difficult flushing conditions are present.

This capability is not generally used for FT Gearing’s mainstream work, but it may be of benefit for future applications.