The aerospace world

Citation

(2002), "The aerospace world", Aircraft Engineering and Aerospace Technology, Vol. 74 No. 4. https://doi.org/10.1108/aeat.2002.12774dab.005

The aerospace world

Keywords: Aircraft, Engines, Machining

A flow-line manufacturing cell has been installed at the Isle of Man factory of Kenmac Ltd to produce mill-turned, ground and threaded components to world class standards for Rolls-Royce aero engines. First machine in the fine is an Index bar-fed CNC lathe from Germany, supplied through UK agent, Geo Kingsbury Machine Tools. There are also an external grinder and a thread rolling machine, both CNC, and a vacuum heat treatment furnace (Plates 5 and 6).

Plate 5 The Index G200 Compact mill-turn centre installed in a flow-line manufacturing cell at Kenmac's Isle of Man factory for producing Rolls-Royce aero engine components to world class standards

Plate 6 Close-up of the Index G200's machining area, illustrating front-end machining of bar at the left hand spindle using the top turret and simultaneous reverse-end working at the right hand spindle with the other turret

Justification for the £600,000 investment was the award by Rolls-Royce of a five year contract to Kenmac for the single-source supply a family of components. Each is produced in several variants, bringing the total number of component types to around 140.

"In return for this guaranteed business, Rolls-Royce demands stringent performance targets in terms of quality, cost and delivery," said Bob Hastings, managing director of Kenmac." Defective parts per million must be reduced by a factor of 10 every two years, unit production cost had to fall by 25 per cent to meet target price levels, and lead time compression from 44 to 21 days was stipulated."

In 2000, Kenmac adopted a factory-wide 'agile manufacturing' initiative to ensure continuous improvements in quality, delivery, accuracy, lead time and cost reduction. Many of the tools, techniques and working practices have been adopted within the cell, helping the company to meet the terms of the contract.

Many of the parts were already being produced at the Isle of Man facility, but on discrete machines; and the hardening operation was subcontracted to a company in the UK. To be able to take on the extra work and at the same time achieve Rolls-Royce's 'supplier charter' targets, it was essential to install a bespoke production cell capable of converting bar into finished products in one seamless, in-house operation. The cell became operational in March 2001, although the furnace was not on-line until the middle of the year.

Principal among the new machines is the Index CNC mill-turning centre, a twin- spindle, twin- turret model designated G200 Compact. It performs the same operations that previously required a succession of four different machine tools. A short bar magazine for feeding one metre stock was chosen to make material handling easier and reduce the floor space required for storage.

Considerable care is said to have been taken in selecting this machine, first because it establishes the fundamental accuracy of the parts and secondly, speed of throughput was essential as all subsequent operations have shorter cycle times. Five lathe suppliers from Europe and Japan were asked to produce a trial component that was about 50mm long, included a T-shaped head and required turning down to 12mm diameter from 26mm bar. Free issue material – a high nickel steel of Rolls-Royce specification – along with cutting tools and data were supplied by Kenmac.

The machines were not only to be assessed on cutting times but also on overall operating efficiency including the ease of changeover with respect to tooling, bar size and holding equipment. Various machine configurations were evaluated including the possibility of purchasing two single-turret twin-spindle turning centres. However, one twin-turret, twin-spindle turning centre was decided upon as it was shown to deliver superior productivity-to-capital cost performance.

Kenmac's production engineer, David Lowey, stated that cycle times on the twin- turret machines were, as expected, lower than the single turret machines. However the overall efficiency found in favour of the Index machine owing to a number of factors.

One was the rigidity of the Index which reportedly allowed relatively higher cutting feeds to be programmed despite the especially high cutting forces generated when machining high nickel steel. Another factor was the 14 tool capacity of each Index turret. Bearing in mind that nickel steel is highly abrasive, the ability to deploy additional sister tooling allows for longer continuous running times before having to stop the machine to change the carbide inserts.

According to Geo Kingsbury one-hit machining makes it possible to utilise the full drawing tolerances. It is no longer necessary to manufacture to accuracies higher than the drawing specifies in order to provide a location for reclamping or a means of checking during subsequent operations. In practice, it means that whereas a general machining tolerance of ± 0.05 mm would have been required, non-critical features can now be machined to their full drawing tolerance of ± 0.25mm.

The nature of the parts dictates front-end turning of a new component from bar whilst simultaneously machining the reverse end of a parted-off component in the right hand spindle. The latter takes about 75 per cent of front-end machining time, so additional deburring operations were included at the suggestion of Geo Kingsbury engineers to balance the cycles. A parts catcher accepts the completed component after ejection from where it is transferred to a conveyor for removal from the machine.

Concluded Bob, "Subject to the satisfaction of both parties we anticipate a renewal of the Rollls-Royce contract after five years, but recent events in the US are a stark reminder that business plans can change. Although our new manufacturing cell is currently dedicated, the constituent machines are sufficiently flexible to be reconfigured for different projects if required."

Details available from: Geo Kingsbury Machine Tools Ltd. Tel: +44 (0) 23 9258 0371; Fax: +44 (0) 23 9250 1741; E-mail: mtools@gkholdings.com; Website: www.testrigs.com