CNC sliding head automatics that have a large recess under the main spindle allow a sub-contractor to turn difficult-to-machine PTFE components under 'lights-out' conditions.
After 50 years of turning PTFE, Clacton, UK-based Dalau has every right to call itself a specialist in machining this plastics material. Typical PTFE components made by Dalau include insulators for the electronics industry, connectors for the telecommunications sector and various aerospace and medical parts. Dalau makes over 100 million PTFE and plastic components a year, to help maintain a lead in the market, the company has been a long-term user of turning machines from Tornos.

In the mid 1980s Dalau installed its first Tornos cam-driven automatic, the company now has 45.

In recent years the shift has been towards Tornos Deco CNC sliding head models and the company now owns four Deco 20 and seven Deco 10 machines.

The most recent addition is a pre-owned Deco 10, which was installed in January 2005.

'As a general rule of thumb, straightforward components that only require a single operation are loaded to the cam-driven autos, while anything more complex, perhaps involving PCD drilling, milling or second operations of any kind, will be put on the Deco CNCs so they come off complete,' explains Philip Alston, production and QA manager for machined components at Dalau.

Although Dalau sometimes undertakes batches up to 1 million, typical batch sizes are around 500 on the Deco CNC machines, which means a fair amount of changeovers and set-ups.

'All of our setter/operators are trained off-site at Tornos and we have found this provides more than enough grounding for them to be competent at creating the programs offline and setting the machines,' adds Alston.

PTFE has become enormously popular because of its insulating properties, chemical resistance, low co-efficient of friction and high temperature resistance (up to 260 deg C).

However, the excellent design characteristics of PTFE are countered by 'difficult' machining properties.

The machine shop at Dalau is a temperature-controlled environment as PTFE components are subject to expansion at elevated temperatures making it difficult to hold tolerances in the realm of +/-0.015mm.

'Many sub-contract machinists will not touch PTFE,' says Alston, 'But with the help of the Tornos machines we have gained the experience to make us a leader in our field'.

'The reliability of the Tornos machines is first class, which is exactly what we require for rapid throughput parts.' In the past five years, Dalau has diversified into machining other plastics materials, which has become a growing market.

Around 75% of Dalau's output is exported.

Another problem with machining PTFE is the continuous 'string' of swarf it produces when cut.

To overcome this difficulty Dalau uses bespoke tooling with an exceptionally sharp edge.

The company also says that one of the benefits of the Tornos machines is the large recess under the spindle that allows swarf to fall away.

Some machines produced by alternative suppliers do not have this, which allows swarf to accumulate and create problems.

In negating this difficulty the design of the Swiss-made Deco sliding head machines allows Dalau to run lights-out operations overnight, a capability that has become critical in its battle with competitors from low wage economies.

Quality is another key issue, Dalau has developed its own SPC system as part of its TQM system that is linked to the CNC control of the Deco machines.

The innovative system allows operators at the ISO 9001:2000 accredited company to monitor every dimension and characteristic on every drawing in real time.

If a problem occurs it can be rectified immediately and not after an entire batch has been produced.

It also ensures full component traceability.