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    Plastic Turned Parts (PTP) was the first company in the UK to install a Citizen CNC sliding head turn-mill centre incorporating the patented Low Frequency Vibration (LFV) machining technology and as a result has been able to totally eliminate swarf control problems in producing thousands of plastics components.

    Said Managing Director Jonathan Newis: “For us, the development of LFV has transformed our turn-milling operations so we can now confidently progress the business and operate the Citizen bar machine from pressing the start button rather than having to continually interrupt the cycle to clear troublesome birds nesting of plastics swarf.”

    Mr Newis describes LFV as being especially effective on deep hole drilling and said: “We have totally eliminated any clogging of drill flutes. Previously we often had to set the machines with two or even three drills due to swarfing problems but we can now go straight to depth with a single tool and the flutes are completely clean.”

    Machine Setter Darren
    PTP based just outside Hertford employs five people all very proficient and skilled in machining plastics achieving consistent growth (20 per cent in the last two years) based largely on the use of nine Citizen supplied machines.

    A wide range of components are produced for customers in the marine, paint spraying, bearing, food, motorsport, telecommunications, automotive, valve and medical sectors. Indeed, a major long term medical contract won by Mr Newis is the production of 6,000 micro-machined ear grommets a month out of PTFE for babies that suffer from glue ear.

    In addition to PTFE, the plastics-based materials passing through the machine shop are wide ranging including Acetal, Delrin, Nylon, PVC, polypropylene, polyethylene, Nylatron, PEEK, graphite-filled PTFE as well as other high performance plastics including variants of glass reinforced plastics in batches between 500 and 10,000. Said Mr Newis: “As we provide a specialist service and have developed the skills we have to be able to respond to the demanding nature of some of these materials. Polypropylene, for instance, can react totally differently under cutting conditions and will even behave almost like machining chewing gum. Others can soften, melt and many just grow, deform or spring back under cutting conditions.”

    Also reflecting on machining polythylene, he describes this material as being a nightmare with swarf wrapping around the tools and often melting on drills. He said: “With LFV it readily chips so we can now even run unattended with the process carrying on for several of hours.” On the other hand, he then describes how reinforced materials kill any tooling. He said: “Previously, when these materials went through any machine the process had to be continuously monitored.”

    Birds Nesting

    The patented LFV process is now demonstrating significant improvements, not only on cutting plastics as PTP has found, but also on exotic materials, difficult to chip ferrous and non-ferrous materials such as copper.

    The LFV process can also enable depth-of-cut to be increased, it enables surface quality, to be enhanced, extends both tool life and spindle uptime and hence can transform machine utilisation. It can even be applied to very small diameter, as well as thin-walled components and be used for turning, facing, eccentric and interrupted cuts, drilling and even thread cutting.

    Plastic Birds Nesting

    The process is fully programmable activated through a G-code enabling on-demand application anywhere in the cutting cycle. The servo axes of the machine drive system are ‘oscillated’ in the direction of tool feed in phases involving tens of microns which are synchronised with rotation of the spindle. Toolpath includes ‘air-cutting’ which interrupts the cut that breaks the swarf into smaller lengths or pieces. It also importantly reduces the onset of built-up edge on the tool tip which is a bad influence on the geometry of the tool and is often a cause of premature failure.

    Said Darren Evans, responsible for setting the Citizen with LFV at PTP: “We are able to maintain a wiper action as the tool recuts the material which helps to create a superior surface finish. We can even program the LFV to tailor the ideal length of swarf through P1 and P2 codes that set the frequency of oscillation. To us this is very important benefit as ultra-small chips of plastic would just build up and clog the machine.”

    With plans for further LFV machine installations, Mr Newis is now able to move the business forward with even greater confidence. He said: “A major problem with plastics is variation in the material which can become a major headache on certain jobs. We now have the ability to easily influence the application to meet our needs.”

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