Flexible manufacturing system cuts lead times for missile launcher parts

Citation

(2002), "Flexible manufacturing system cuts lead times for missile launcher parts", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 1. https://doi.org/10.1108/aeat.2002.12774aab.014

Flexible manufacturing system cuts lead times for missile launcher parts

Keywords: Aircraft, Military, Missiles

A flexible manufacturing system (FMS) based on a pair of Makino A77 machining centres supplied by NCMT to Flight Refuelling, Wimborne, is providing high levels of flexibility and productivity in support of the Eurofighter Typhoon military aircraft programme. The system is said to be capable of all operations needed to machine a family of critical components used in the aircraft's missile launch system (Plates 8, 9, 10 and 11).

Plate 8 Viper grinding of a slot in the flange of an Inconel test piece on a Makino machining centre during the NCMT open house in Coventry. The continuous dressing wheel may be seen above the grinding wheel and the NC coolant nozzle is shown in the foreground

NCMT asserts that the combination of accuracy and rigidity available from the Makino's allows single micron tolerance requirements to be met when machining maraging steel and titanium. The capabilities are such that some components which would formerly have been produced from castings are now machined from solid material. This saves lead time in production, reduces the number of manufacturing steps as no patterns are required, and allows straightforward modification of components under development.

Plate 9 The Tokio Polygon Face table, which is indexed by the machine. spindle, is used by Flight Refuelling to orientate components precisely without the need for multiple dedicated fixtures

Flight Refuelling is a major operating division of Cobham Plc., specialising in civil and military aircraft systems including its own in-flight refuelling equipment. The Makino FMS is part of a major investment in resources to produce the weapons carriage and release system for Eurofighter. The system also incorporates a pair of advanced millturning centres for producing a variety of other parts for these mechanisms, which are integrated into the aircraft wing as part of its weapons system rather than being attached as required.

Plate 10 Missile release system components for the Eurofighter Typhoon agile combat aircraft machined from solid maraging steel on the Makino FMS at Flight Refuelling

Principal application of the FMS is to machine six "core" components. Each is required in right-and left-hand variants to form an aircraft set. Four are machined from solid material while two are produced from high quality investment castings. Batch quantities of around 20-off are anticipated when the aircraft is in full production.

Plate 11 High integrity titanium casting and finished missile release system component produced by Flight Refuelling on the Makino FMS for incorporation into the Eurofighter Typhoon

Tolerances are extremely tight. One of the difficulties inherent in machining maraging steel is that the material shrinks during heat treatment at the rate of five microns per 10mm. As the material is virtually impossible to machine once heat treated, it is necessary at the machining stage to allow for shrinkage, including that of any threads.

Dave Broadhurst, Flight Refuelling production engineer, commented, "NCMT 1 Makino was one of very few vendors capable of meeting the accuracy requirements on production of these components. In addition they have strong experience of configuring turnkey flexible manufacturing projects for machining complex components. Our requirement was for a system capable of machining any of six components at random, taking into account availability of materials; castings for instance are on rather long lead times so the system has to be flexible in every sense."

The FMS comprises two Makino A77 machining centres connected by a materials handling system under overall control of a Makino Model C cell controller. The system has two load 1 unload stations for its 16 pallets which are handled by a rail mounted vehicle. Each machining centre is set up for three of the core components. With 244-tools in each magazine there is sufficient tooling for all six parts to be machined without need for tool exchange. The tool inventory, whose. make-up draws on Flight Refulling's experience of machining "difficult" materials, includes a variety of special tooling.

Due to the nature of the materials being machined, through-tool coolant is available for all drilling and boring operations. In addition, Demis power and torque monitoring is used on both machines in conjunction with tool probing. To ensure optimum component accuracy and correct alignment in the fixtures, spindle-mounted probing is used prior to commencement of machining.

"Dedicated fixtures were needed for three of the components, including the breech block," said Mr Broadhurst. "However, for the other three we use. modular fixtures mounted on Wixroyd cubes. This offers more flexibility of configuration and will enable us to put additional new components onto the system as the application develops."

The breech block is the largest of the core components machined on the Makino system. Its operational duty is to assist ejection of the missile from the launcher to a safe distance from the aircraft before the rocket motor fires. The part is machined from a solid block of maraging steel in four sequential operations. One of these requires a number of holes to be drilled inside the bores of the component at a precise angle to the bore surface. This would be a difficult operation even on a flat exposed surface in a free-cutting material and would normally demand use of a purpose-made fixture to hold the component at the required angle.

NCMT provided a novel solution to the positioning problem in the form of the Tokio Polygon Face table. This is a mechanical rotary positioning system which is operated by a spindle-mounted "key" which resides in the toolchanger when not in use. It is reportedly capable of rotating in increments of one degree of arc and thus provides an automated means of positioning a component very accurately. However the device does not need electric or hydraulic connection, or supplementary CNC software. Although a little slower than a dedicated CNC device, it is thought to be ideal for use on multi-pallet systems such as that at Flight Refuelling.

The machining sequence for the breech block is as follows:

Op 1. Rough mill, drill, bore and machine location points for Op 2.

Op 2. Mount the billet on a slave plate for location on Tokio table. Position and drill angled cross holes using long drill with through-tool coolant.

OP 3. Locate in fixture for external profiling, drilling and finish boring.

Op 4. Locate using mandrels on finished bores to complete external feature machining.

Mr Broadhurst remarked, "Using the Tokio table makes everything straightforward. In the past we would have needed to use multiple dedicated fixtures to achieve the same result. Moreover the fact that most of the core components need four operations means that we have been able to more-or-less standardise on cubic fixtures – although the Tokio table is an exception in this respect."

The Makino A77s are said to have proved capable of maintaining machining speeds of 80 surface metres per minute on maraging steel. In addition, the machines' ability to rapid traverse at 50 m/min combined with sub 2 second tool exchange minimises non- machining time. Positioning to a reported ±0.0025mm with repeatability of ±0.00015mm help to maintain accuracy. However, the very high added value content and ultimate application of the components produced on the FMS means that virtually all components produced on the system remain subject to 100 per cent inspection.

"We are aiming to develop a capable process for all of the components," Mr Broadhurst said. "However the nature of the materials and the very tight tolerances applied to certain features mean that we are working at or near the leading edge of machining and tooling capabilities. Also, the machining cycles are long; the breech block, for instance, needs around seven hours of machining time to complete all operations while components produced from castings demand around four hours. Given the ultimate application of the parts it is unlikely that we would ever be content simply to push the button and walk away, whatever our level of confidence in the manufacturing route."

He concluded, "Nevertheless the FMS system has brought some important advantages to production of these components. Not least is the ability to manufacture from billet, which provides us with shorter lead times and much more scope for modifying the components in the light of experience on the test range. It would also have been very difficult to maintain some of the component tolerances without availability of machines of the calibre of the Makino A77s."

Details available from: NCMT Limited, Tel: +44 (0) 20 8398 4277; Fax: +44 (0) 20 8398 3631; E-mail: richardtrimbee@ncmt.co.uk