Mill-turning aerospace connectors using Star Micronics' Star SV-32 sliding-head lathe followed by a single shaping operation is getting Doughty Precision Engineering closer to one-hit manufacture
Stainless steel plug shells for aerospace connectors are traditionally produced by Doughty precision engineering (DPE) in three operations, one on a fixed-head lathe and two on a gear shaper. Now the same component is machined 30 per cent faster on a twin-spindle Star SV-32 sliding-head lathe followed by a single shaping operation. The time saving will not end there.

In the same way that DPE and Star initially developed a special hobbing attachment that transferred machining of the shell's ratchet teeth to the SV-32, the Nottingham-based subcontractor and the machine supplier are now working together on another attachment that will allow the slider to complete the remainder of the shaping, ie machining of the alignment teeth.

In other words, a part that used to require transfer from one of three fixed-head, three-axis bar lathes to one of five gear shapers for two additional operations, will in future come off the Star complete.

This will allow one operator to be deployed on different work, reducing still further the already substantially lowered cost of producing plug shells.

Said Peter Doughty, 'Early sliders were able to reduce the original fixed-head, mill-turn cycle by only 20 seconds, so we could not justify the investment'.

In contrast, the 9-axis SV-32 has cut approximately one minute out of the mill-turning, which includes threading, boring, reaming, slotting and broaching.

This is because we get a lot of machining for free by working on a part in the counter spindle while simultaneously machining the next component at the main spindle.

'We have also got rid of one handling operation by incorporating on the lathe the cycle to shape the ratchet teeth'.

'When we transfer alignment key shaping onto the Star later this year, we will eliminate inter-operation handling altogether.' DPE will eventually use the Star, which is fed by an FMB Turbo bar magazine, to produce 10 sizes and varieties of 303, 304 and 316 stainless steel plug shell up to 32 mm diameter.

They account for 40 per cent of the total, as shells go up to 50 mm diameter.

Batch size is typically 5,000-off.

Mr Doughty intends to maximise his company's use of sliding-head technology, pointing out a number of benefits over fixed-head mill-turn centres.

One often-overlooked advantage is that a slider typically draws less than half the power of an equivalently sized fixed-headstock lathe, so are less costly to run, particularly with energy prices rising so fast.

The other main plus-point is the ability to reduce cycle times, as the ganged turning tools and powered tools are very close to the component, so have a shorter distance to travel.

For the same reason, accuracy is often better too.

As to his selection of Star for his first sliding-headstock lathe, Mr Doughty points to the machine's heavy, rigid structure, which lends itself to better accuracy and longevity over many years of 24-hour operation.

He has also been impressed with Star GB's back-up, in particular its assistance with programming while DPE was learning the technology, and the supplier's willingness to help develop the in-cycle shaping operations.

Founded in 1925 by Alan Doughty, Peter's grandfather, DPE is now part of the Nasmyth Group.

The company originally specialised in manufacturing diesel fuel injector parts for locomotive engines.

Aerospace connector contracts gradually took over and now account for all of the business.

Around 40 per cent of output goes to UK customers, with most of the remainder delivered to the USA.

Concluded Doughty, 'During the mid 1990s, we were finding that repeated 'cost-down' requirements from aerospace customers were eroding margins to the point where jobs were becoming financially unviable'.

'It became impossible to manufacture aerospace components economically without minimising the number of separate machining operations, so in 1997 we started down the fixed-head, twin-opposed-spindle, mill-turning route'.

'Purchase of the Star sliding-head mill-turn centre, which has even more CNC axes, has been a logical extension of that policy and is getting us even closer to one-hit manufacture.'