Citizen Machinery UK has recently installed a further 15 of its CNC sliding head turn-mill centres as part of a single order for Renishaw’s UK manufacturing sites. The installations were made at Renishaw’s new 461,000 ft2 facility on a 193 acre site at Miskin, South Wales, and the Stonehouse production facility in Gloucestershire.
As a result of Citizen being its preferred supplier of CNC sliding head machines following its first installation of an F12 in 1982, Renishaw now has the largest installation of Citizen machines in a UK company. Altogether, 47 are in production producing over 3,000 different components for the group’s ever-growing product range.
Indeed, the likes of contact pins and styli components are produced in cycle times of under 20 secs from small diameter bar on 10 of the quick cycling Citizen B12 machines, right through to highly complex housings taking up to 15 minutes each on 11 of the top-of-the-range, 72 tool carrying, 32 mm bar capacity Citizen M32s.
Said Jonathan Davis, Engineering Group Leader of Renishaw’s Manufacturing Services Division: “The group strategy on plant installations is to maintain a standardised family of machine tools. This enables us to focus on being process led while maintaining high levels of machine familiarity in component design, production planning machine setting, serviceability and cost of ownership. As a result of our long term business with Citizen as the range of machines has been continuously developed, so too, over the years, has our production capability.”
He qualifies his statement with the inclusion of two Citizen A32A-VllPLs in the latest installation programme. “Because these machines are so quick on the type of work we are producing with their fast acceleration, 45 m/min rapid traverses and ultra-quick processing at the Cincom control, we have been able to transfer certain parts from existing Citizen machines to free-up capacity and in the meantime, are saving between 40 and 50 per cent on cycle times.”
Part of Renishaw’s installation programme involved three B12E-Vls, two A32A-VIIPLs and five K16E-VIIs, bringing the installed Citizen sliding head count at its Miskin and Stonehouse plants to 40 machines.
The recent burst of CNC sliding head installations during December 2014 and January 2015 was this highly successful company’s reaction to a massive surge in export business, which already accounts for 93 per cent of sales. Growth has mainly come from Asia, where customers tend to demand almost immediate supply from order.
This philosophy is helped through Renishaw’s progressive development over the years of a product design and engineering manual in the form of its ‘Design for Production Guidebook’. This outlines the gearing of the business to standardise upon materials selection. So for instance, for sliding head production, a restricted range of materials are nominated; aluminium, and 300 and 400 grade stainless steels in a limited number of sizes in order to optimise setting times and material logistics.
This restrictive strategy also applies to standardised component features, so tolerances of 0.05 mm are designated for turned diameters (0.02 mm for authorised special requirements), 0.1 mm on lengths (some are 0.05 mm), 0.05 mm on true position (TP) and 0.8 Ra for surface finish. The same discipline is applied to geometry and the use of threads and features such as slots, undercuts, radii and recesses.
As a result of this policy, overall machine utilisation on the Citizens is high at around 80 per cent. They are all run around-the-clock, five days a week on a three shift pattern with overtime at weekends as required.
Batches vary between 200 and 10,000 with most production runs averaging between 500 and 1,000 parts. Setting times, too, are well-proven and hence minimised because for each type of machine, changes are minimal and more buy cheap cymbalta than two-thirds of tools are common reducing changes during set ups.
Indeed, the CAM system used for programming also works on a priority tool selection, largely based on common items, to maximise efficiency. This means resetting a B12 is normally undertaken within an hour and other machines, depending on bar feed, take between two and four hours. However, more complex multi-featured parts produced on a Citizen M32, which carries up to 72 tools, can at times run a whole shift.
The ratio of machines to operators is well controlled with one person dedicated to three machines. Here the setter/operator is totally responsible for his machine setup, operational efficiency and quality produced. A data collection system is wired into each machine with terminals on a very practical design of working bench that also encloses the swarf conveyor and swarf bin making it a clean area at the end of the machine.
The Miskin site, close to Cardiff, was acquired from Robert Bosch in September 2011 and has been transformed into a prestige manufacturing unit absorbing some £30 million so far in its purchase, refurbishment and re-equipment to enable Renishaw to continue to improve on its made-in-house operational strategy. The site employs some 200 people out of 2,500 employed by the group in the UK and it produces metal components and electronic PCBs and assemblies for Renishaw’s measurement and healthcare products. It is also the base for assembly of Renishaw’s recent introduction to markets of laser melting, additive manufacturing machines (metal 3-D printers).
Such has been the success of the Renishaw business that sales increased by a record 36 per cent to £223.8 million in the first six months of trading up to December 2014. Forecasts for full year revenue continues to improve to around £500 million aided by the continued investment in facilities, development and manufacturing. In particular its machine tool product lines rocketed in the Far East due to the consumer electronics sector, supported by good growth in measurement automation, additive manufacturing and encoders.
The recent Citizen installations across the group tie in with capacity requirements and were selected largely against component features to again maximise a common production strategy and through the machine capability around main and sub-spindle arrangements, enable more cost-effective, optimised, largely single cycle with considerable levels of overlapped tool activities in machining operations.
The 15 machines installed included Citizen’s B12E-VI which is the fourth generation of this highly successful 4-axis short-cycling machine. The main spindle is 3.7 kW, 12,000 revs/min and the sub-spindle 1 kW, 6,000 revs/min. It has a 16 tool capacity with three driven, five for turning and eight for front and back machining.
The 7-axis Citizen A32A-VIIPL has a 7.5 kW main spindle and 3.7 kW sub-spindle both delivering 8,000 revs/min. It holds 23 tools, six for turning, four are driven for cross machining, nine for back and five for front end operations. Rapid traverse rates are the fastest available in a current sliding head machine at 45 m/min.
As with the A32, the Citizen K16E-VII has 7-axes with an 18 tool capacity. Six are available for turning, eight for front and back machining with its main spindle of 3.7 kW, 15,000 revs/min and sub-spindle 0.75 kW, 10,000 revs/min.
Meanwhile, the M32-III has a 72 tool capacity making it a universal turn-mill bar machining centre with the flexibility of a 10 station Y-axis turret able to half index to create 20 positions. A vertical gang toolpost with four driven tools and five turning tools plus a back toolpost with three driven tools forms the tooling arrangement. The main spindle is a 5.5 kW, 8,000 revs/min unit and the sub-spindle 2.2 kW, 7,000 revs/min.