Right ingredients for plastic parts

06 Jan 2020

Engineering capacity news posted by Andy Sandford

Reliable barfeeders and low frequency chip management have helped Plastic Turned Parts (PTP) doubled turnover in the past four years.

In that time it has invested over £750,000 in six new CNC turning centres. Of the six new machines, five were supplied by Citizen Machinery – four Cincom sliding-head lathes and most recently a Miyano fixed-head model.

These are complemented six further turning machines, allowing PTP to machine bar up to 65 mm and billets up to 150 mm in diameter. A Haas CNC mill is used for occasional second-operation work and for destructive testing.

All except two of the Citizen lathes are fitted with Iemca bar magazines.

PTP's managing director and owner Jonathan Newis said, "To enable us to achieve sustained business growth, we only use the best production equipment on the market. That applies to everything in use on the shop floor including the barfeeds, which is why there are seven Iemcas in use here.

He says turning flexible plastic bar is an specialised business – one of the problems being that, unlike metal bars, thinner stock sags under its own weight both within the magazine and in the space between it and the lathe. Through UK supplier 1st MTA, the Italian barfeed manufacturer modified the equipment to include solid panels rather than standard cross struts for supporting the plastic bars along the length of the magazine along with bespoke clamping blocks to ensure that small diameter bar remains horizontal in between the barfeed and the turning centre.

Mr Newis added, "We have been using Iemca bar magazines since we took over a turned parts subcontractor on this site and inherited two Cincom sliding-head lathes and three cam-type autos.

"We bought our first new Citizen slider in 2007, a 16 mm capacity machine, to replace the cam machines. In all that time the barfeeds have proved to be reliable and well built, which translates into absence of vibration and hence high dimensional accuracy of machined components as well as good surface finish."

Citizen’s LFV two-axis oscillating chipbreaking software also helps ensure quality when turning plastics, many of which tend to produce bird nests of long, stringy swarf. The main culprits are polyethylenes and thermoplastics, while fluoropolymers also have a tendency to string.

Mr Newis explained, "With either of the two LFV software modes switched on when turning these materials, swarf is broken into short lengths that do not wrap around the component or spindle. We can even program the ideal length of swarf through P1 and P2 codes that set the frequency of oscillation so that, at the other end of the scale, unnecessarily small plastic chips do not build up and clog the machine.

"It results in higher productivity and lower labour costs, as we no longer have to include regular breaks in programs, typically hourly, to stop the lathes for swarf to be cleared from the working area. Lights-out running also becomes possible, leading to higher profitability and allowing us to quote more competitive prices and win extra business.”