At Renishaw plc, Wotton-under-Edge, an ambitious project is in progress to apply a 'nesting' technique to turned components produced from bar. Four of the latest Citizen M20 computer controlled sliding headstock mill/turning centres, supplied by NC Engineering of Watford, have been programmed and tooled for a current range of 70 part numbers, all are machineable from aluminium alloy or stainless steel round bar. Each M20 machine is capable of machining all 70 parts in a single operation using a resident suite of 48 tools.
When compared with previous machining practice, the Citizen M20s have already achieved 'significant' reductions in machining cycle time.
Meanwhile, as the project is progressing towards its stated goal of minimal changeover time, further savings are 'on the cards'.
The ultimate goal of any modern manufacturing operational thinking is the elusive ability to achieve batch-of-one flexibility while maintaining the economies associated with volume production.
In most cases, the objective is to achieve it all in a single set-up.
Here, Renishaw has a long history of pushing the boundaries of manufacturing.
The company was one of the first to exploit 'one-hit' machining cycles to reduce manufacturing lead times and enhance accuracy.
With the Citizen M20 project, the aim has been to apply this principle to multiple components so that a single machine becomes a flexible manufacturing system in its own right.
Chris Milcoy, Director and General Manager of Renishaw's Manufacturing Services Division comments: 'The machines were sourced to address additional production requirements resulting from introducing products such as the TP 20 and TP 200 inspection probes for co-ordinate measuring machines (CMM).
This offered an additional opportunity to optimise efficiencies on components produced elsewhere in the machine shop, with the added capability for 'lights-out' production.' Renishaw's initial success was due to the development of the touch-trigger probe, invented by David McMurty, Chairman and Chief Executive, in the early 1970's.
Today, Renishaw stands at the forefront of automated metrology.
The Group's products - CMM probe systems, CNC machine tool probe systems, digitising systems, calibration systems, encoder systems, and laser scale systems provide manufacturers with the ability to perform measurement traceable to International Standards.
Wherever precision manufacturing is required, the use of Renishaw's products ensures that exacting specifications are met, with cost-effective methods.
The Group also has expertise in spectroscopy products for spectral analysis.
Renishaw, which celebrated its Silver Jubilee in 1998, has won numerous awards worldwide.
Nine of its products were commended as Millennium products.
The company, which ploughs some 14 per cent of annual revenues into R and D and engineering - is a strong proponent of in-house manufacturing for a number of reasons.
Firstly, its manufacturing tends to be relatively low volume with high value added which would be costly to subcontract; secondly, in-house manufacture permits Renishaw to maintain ownership of its quality.
Equally important is that, by manufacturing in-house, Renishaw is able to enhance its credibility by confronting and solving manufacturing challenges that are familiar to its customer base.
'In a sense the machine shop forms an extension of our research and development facilities,' Chris Milcoy remarked, 'Our own manufacturing needs have spawned development of new products and the shop is often used as a test site for them.
This is continuing with the Citizen M20 machines as we intend to equip them with tool setting and monitoring systems.' The Citizen M20 was selected following an appraisal of similarly specified sliding head lathes against the broad machining requirement.
Confidence in NC Engineering was born from a long history of Citizen success at Renishaw, and backward compatibility with existing tooling assisted the final choice.
Individual components range from being little more complicated than a washer, to being highly demanding in terms of machining internal and external features.
If all current and future 'half inch probe' components are to be produced with a minimum need for tool change, then a turret-type sliding head cnc machine is the only option capable of providing the acceptable level of tooling flexibility.
As installed, the four Citizen M20s have six linear axes - X1, Y1 on the eight-station gang tool plate, X2, Z2 on the turret, Z1 on the main spindle, Z2 on the sub-spindle - and two full rotary 'C' axes on the main and sub-spindles together with an A2 intermediate positioning axis on the turret.
This A2 capability permits multiple, bi-directional tool positions to be hosted on the ten position turret.
In the company's application, use of multiple tool holders, including duplex-driven devices designed by Renishaw engineers, has boosted turret capacity to 40 tools.
All four machines are equipped with IEMCA magazine-type bar feed systems and parts catchers with integral conveyorised off-load.
The target for the project is SMED-style changeover between different components.
Experience to date has shown that the diversity of parts, coupled with the non-free cutting properties of the specified materials, is such that 'customised' tool off-set adjustments between components are critical to achieving the required levels of precision and finish.
By installing its own-developed automated tool setting arm, Renishaw will be able to measure tool wear and adjust off-sets automatically.
Probing also allows detection of tool breakage which is especially beneficial on some of the very small diameter tools that are in use.
By gathering data using the probing system it is intended that a reproducible 'tooling profile' be developed to enable each component-specific set-up to be replicated without time consuming manual adjustment.
Production at Renishaw is scheduled according to a mix of methods in what best suits the component requirement.
Production is 'finished assembly' driven, according to demand and batches can range from just one to 5,000.
On the Citizen M20s, batches of 500 to 800 are the norm.
Renishaw's Senior production engineer Graham Newling comments: 'We're in the process of determining optimum batch quantities, taking account of setting time.
To assist us we've embarked on a computer based modelling exercise that will help us to develop a sequence of production routines which minimise the variables between successive set-ups.' Components up to 35 mm long are currently produced on the machines.
Cycle time averages three minutes but ranges between one and six minutes.
Renishaw's established 'single-hit' machining philosophy is rigorously applied, to the extent that deburring is incorporated into the machining cycles.
As a result, components coming from the machines are ready for the next stage of manufacture.
Programming and process parameters have been developed to guarantee a very high degree of repeatability between set-ups and between machines.
Typically, the process is tuned to achieve half the permitted tolerance so for a 0.8 micron Ra finish, the target is 0.4 microns, while a dimensional tolerance of 30 microns is closed down to 15 microns.
'The Citizen M20s have proved fully capable of meeting these requirements with production from all four machines being identical,' Graham Newling confirmed.
'Components made on the machines were previously produced on a twin spindle, twin turret conventional CNC mill-turning lathe or on earlier generations of Citizen F-Series sliding head machines.
In both cases we have made considerable gains in productivity through a combination of eliminating non-cutting time, superimposition of machining operations and optimising speeds and feeds.
Once the machines have been set, they run consistently and the tighter process parameters and automated deburring have had a positive affect on quality,' he maintains.
This consistency of performance has facilitated unmanned night-time production while day-shift operation is manned at a ratio of one man to four machines.
Renishaw has adopted the 48-tool suite on the machine as the design standard for some of its components so that future production can be flexible.
As production demand increases, adding further identical machines will provide a straightforward facilities expansion.
This is directly in line with a manufacturing policy shift that will reduce the number of discrete machine types as production is moved onto a 'unitary flexible manufacturing system' footing, based on either turning or prismatic machining.
As Chris Milcoy concluded: 'The application is certainly progressing towards our goal.
From a machining standpoint, the Citizen M20s have performed well and we are gaining significant advantages.
Manufacturing using the Citizen M20 complements Renishaw's RAMTIC operation where milling, turning and inspection of components is undertaken using the company's patented 'Methodology' to produce parts.