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Jonathan Newis’ subcontract machining operation, PTP, which is focused on the production of plastic components, relies on Citizen CNC sliding-head turn-mill centres.

A recent installation of a Citizen L20-IX to meet much needed additional capacity has demonstrated reductions in machining times to the order of 5sec on a typical 30sec cycle time.

This is largely explained through Citizen’s development of Streamline Machining Technology on the new machine, which has also helped in achieving quicker and easier setting through the Windows-based CNC program editing, especially on the more complex work.

As the result of the latest installation, Newis has been able to take on new business and has relieved the work loading on his existing Citizen L16, K16 and B20 machines.

PTP produces a range of components out of a diverse array of different plastic materials, such as PTFE, Delrin, Nylon, PVC and Nylatron, plus special plastics such as PEEK, graphite-filled PTFE and other filled high-performance plastics including variants of glass-reinforced plastics.

Customers cover most manufacturing sectors,including medical, fastener, product finishing, paint-spraying seals and nozzles largely destined for the automotive sector, various marine, food, bearing, motorsport and specialist cars, communications, sensor and a range of tips produced on a regular basis for the pole-fishing fraternity.

One of PTP’s most repetitive contracts is the micro machining of ear grommets for glue ear cases in babies.

These are turned and drilled on the Citizen K16 out of 5mm-diameter PTFE material turned down to below 1mm diameter and supplied at a rate of 3,000 per month.

Other micro-sized single-operation machined parts include a range of minute plastic screws for the spectacle industry.

On the latest Citizen L20-IX, PTP has included turning, drilling and milling including slots and keyways, threadcutting, which is preferred to tapping, knurling, which requires special care in setting to achieve finish size, extensive grooving, slitting and slotting of screwheads, for instance.

Quite a few components are formed on the Citizen rather than being single-point turned as the swarf created from certain plastics is easier to control.

Inspection equipment includes shadowgraph and a Vision Kestrel 200 two-axis non-contact optical measuring microscope.

Newis describes how cycle times vary between 5sec for simple parts such as spacers and washers to 50sec or so for very complex multi-featured parts.

Within PTP’s machine portfolio are three fixed-head lathes giving a bar capacity of 65mm and a billet capacity of 250mm.

A vertical machining centre provides an additional milling capability.

Tooling has to be very sharp – PTP tends to use tools destined for cutting aluminium, which have high top rake, but his two setters also make many of their own tools from high-speed steel to specifically suit the material and job.

The latest Citizen, despite its 10,000rev/min spindle capability and depending on the material, is mainly run at a maximum speed of 3,000rev/min to avoid creating heat in the material.

However, PTP’s setters have also made use of the high-pressure coolant manifolds that would normally feed pressurised coolant, to blow compressed air to help cool the material and clear the clingly plastic swarf from the tooling and working area.

Whenever possible, PTP’s setters try to remove all burrs during the single-hit machining cycle, but Newis maintains that with the closeness of Citizen Machinery in Watford, the application engineers have been particularly supportive in helping to develop cutting cycles when his people run into problems.

Contamination of the plastics is always a concern and here he maintains that the Citizen machine is very easy to keep clean.

Due to the small sizes on components, PTP uses a conveyor to outfeed the parts following ejection from the subspindle, which makes monitoring of the quality of components very simple.

The Citizen L20-IX can hold up to 32 tools, giving plenty of positions to continuously house common tooling, and has a maximum turning diameter of 20 by 200mm in a single clamping.

The main spindle is powered by a 3.6kW motor, giving 200-10,000rev/min, and the subspindle 1.5kW with 200-8,000rev/min.

Up to seven turning tools and six driven tools with speeds of 5,000rev/min can be applied to the main spindle operations, while up to eight tools can be applied for front- and back-end machining and seven tools in the vertical tool holder for transverse operations.

A recent job that was run on the Citizen L20-IX was a yellow PTFE sleeve made from 16mm bar, which was turned to an absolute polished finish, drilled and bored to 6.3mm diameter with an 8deg taper machined over a distance of 22.7mm within the front of the bore.

The part was then parted off and faced to 64mm overall length in the subspindle in a cycle time of 36sec.

The machine spindles were run at 4,000rev/min with applied feed rates between 0.5 and 0.1mm/rev.

Using the same program when the part was previously machined on the Citizen L16, the new Streamline Technology-controlled L20 machine was producing parts 5sec quicker.

Citizen Machinery

Citizen is the world leader in CNC sliding head ‘one-hit’ turn-milling technology. It has a range of machines having a maximum bar capacity between 4 mm on the compact micro-machining capable Citizen R04 to 32 mm on the top of the range Citizen M32-VII which has the added capability of two Y-axis cross-feeds.   

The M32 can carry up to 80 tools, of which 20 can be driven, and can cut with three tools simultaneously giving low cycle times and high levels of productivity.  Also, fully automated unmanned cycles can be utilised through an integrated gantry option and conveyor system that helps ensure damage free parts during uninterrupted batch production.  A high pressure 2,000 psi CoolBlaster coolant system is a further option to optimise swarf control, tool life and machining difficult materials.

Following the acquisition in Japan in 2008 of 65 per cent shares in Miyano, the fixed head turning centre specialist, the two companies are maintaining their separate high profile brand names utilising a single sales operation.  However, turn-milling solutions from bar up to 64 mm diameter can now be provided.  In addition, with the Miyano range of turning and turn-milling machines for chucking operations, cell-type applications can now be accommodated with a wide range of automation options.   

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