Having invested in CNC automatics, a manufacturer of machined complex plastics parts has found it can take smaller batches and diversify into other areas.
Plastic turned components as small as half the size of a matchhead with an intricate and accurate profile and a central drilled hole for use by children with ‘glue-ear’ and PTFE insulators for fly-catchers used in restaurants, are typical of the sort of work Tefloturn pass through their citizen cnc sliding head automatic lathes. The company, which is based near to Hertford, has two Citizens, an L16 bought second hand from NC Engineering of Watford which has been followed up with a new B20. It processes a wide range of plastic materials including PTFE, PEEK, nylon, acetal and other ‘engineering’ plastics in quantities from a single component to batches of 250,000.
Customers include electronics, medical, steam management and bearing manufacturers.
Managing Director Mick Finney describes how accuracy and repeatability of tolerances can be quite tight especially given the properties of the materials being machined.
‘Bore tolerances of +/-0.025mm often apply while the general machining tolerance is +/-0.050mm.
Likewise, surface finish is usually very important while the degree of complexity of some parts can be considerable,’ he says.
He describes how medical applications especially demand high finish and total freedom from burrs which demand good machine and setting techniques.
‘We also make a lot of plain rings and seals and there is a large demand for threads, knurling and some cross-drilling and slotting on plastic turned parts,’ he says.
Tefloturn was formed in the mid-1990s on the back of a pair of cam actuated sliding head machines.
By 1998, however, the company had reached the limits capable from these machines and started to look for a more flexible solution.
‘We couldn’t afford a new sliding head machine at that time,’ Mick Finney admits, ’so we approached a couple of suppliers to try and source a good secondhand machine.
‘NC Engineering came back to us quite swiftly with our L16, which was already five years old and since it was installed it has proved to be a very good buy.
Reliability has been very good and NC’s back-up in terms of both training and service/maintenance has also been above reproach.’ ‘One of the first components we ever machined on the L16 required multiple operations, and we could never produce more than 30 an hour.
When the L16 was set up, the part was turned complete in a single operation in under 28 seconds.
Now that was a massive increase in productivity for us,’ Mick Finney maintains.
The combined performance of the machine and support by NC Engineering paved the way for Tefloturn to select a larger capacity five-axis Citizen B20 which was justified against one particular contract.
However, the additional capabilities with 10,000 revs/min spindle, 12 tools and extended unmanned running with an improved accuracy has been the catalyst to draw in even more work.
‘Accuracy and consistency are much easier to maintain on the Citizen B20, and it’s also much faster than the L16,’ Mick Finney admits.
‘Availability of an additional powered tool station means that its second operation capabilities are extended.
Together with a conventional CNC lathe, which we bought in between, the citizen machines provide us with the ability to supply exactly what any customer wants up to 300mm diameter.’ Although virtually all of the plastic materials processed by Tefloturn are free machining, the company always uses coolant to help maintain stable temperatures and overcome the influence of thermal growth which is significantly greater than with metals.
And although most materials can be machined using high speed steel, some of the more abrasive ‘filled’ materials have to be cut using carbide.
‘Machining plastics is quite a specialised business,’ says Mick Finney, ‘but the Citizen machines have allowed us to apply our knowledge across a wider range of work.
With the B20 we have the option of lights-out running, something that we’ve never had before.
Although some plastics cause a problem due to swarf and have to be overseen, those jobs where we can use the unmanned capability, make a huge difference to our manufacturing efficiency.
We have also found on short batch work we can program, set the machines and produce the parts in less time than it would take us to perform a cam change on one of the old machines.’ Mick Finney describes how the Citizens have made a very big difference to the way Tefloturn works.
‘When we had the cam machines, if we hadn’t got a suitable cam set, then we couldn’t make a part unless the volume was either very small, or large enough to justify commissioning a new set of cams.
That meant that we had to turn away quite a lot of small to medium volume business.
We also had a substantial amount of work that required secondary operations and it was rare to be able to complete a job in one set-up.’ ‘Investing in the Citizen machines has certainly allowed us to move the company forward quickly.
Our minimum batch quantity is now much smaller while the level of component complexity that we can competitively handle is so much higher.
This has allowed us to diversify the business along lines that we would never have thought possible before,’ he says.
http://www.cncmachinesinfo.com/articles/category/cnc-stepper-moter/
November 21st, 2008 by 
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