Sliding-Head Turning…With A Difference

Sliders also operate without the guide bush for fixed-head turning

Business is booming at Vire Engineering, Totnes, which produces high-quality hose and pipe fittings for plumbing race cars, from Clubman up to Formula One, to ensure that brake fluid, fuel, oil and coolant all flow reliably. Subcontract work is also carried out, notably for the defence and security industries. Order intake in the first four months of 2013 was up 10 per cent over the same period last year.

To help cope with the increased demand, and also to improve margins on what are highly price-sensitive stainless steel, mild steel, titanium and aluminium parts, in January this year the company installed its second sliding-head mill-turn centre. Built by Traub in Germany and supplied through sole UK agent, Kingsbury Machine Tools, the versatile, 36 mm bar auto has the ability to be changed over quickly to fixed-head operation, should that configuration better suit the type of component to be produced.

Designated TNL32, the twin-spindle, twin-turret machine joins a similar but smaller (20 mm) capacity Traub TNL18P sliding / fixed-head, which has been in use at Totnes since the beginning of 2012.

Vire’s managing director, Janet Vincent, said, “Back then, we needed a new, twin-spindle, multi-axis lathe to meet our delivery schedules and were keen to install a model with a lot of driven tooling to avoid second operations.

“The TNL18P fitted our specification and filled a gap in our lathe size range, which goes from 12 through to 65 mm bar capacity.

“However, rather than opt for another fixed-headstock machine, we chose the versatility of the Traub sliding-head lathe on which the bar can be clamped in a collet in the spindle for fixed-head mill-turning.”

There are two main advantages to this approach. First, subcontracted sliding-head turning was brought in-house, saving money and shortening lead-times. One example was a 148 mm long by 3 mm diameter EN9 hinge pin that was needed in batches of 1,000-off.

The other benefit to buying a lathe configured for sliding-head turning is that productivity is improved, even during fixed-head turning, as the cutting tools are positioned closer to the workpiece, so slideway movements are short and quick during machining. Superior provision of live tooling in the latest Traub lathes, with all stations in the turrets being driven, also plays a big part in ensuring efficient cycles and getting parts off in one hit.

The TNL18P at Vire is currently used for about 15 per cent of the time in sliding-head mode, but that proportion is increasing as turning supervisor Tim Woodward transfers more parts to the machine.

For example, a range of three small rivets, even though not of high length-to-diameter ratio, are nevertheless produced efficiently on the slider to 30 microns dimensional tolerance. Compared with fixed-head turning, surface finish is better due to the proximity of the tools to the guide bush during cutting, according to Mr Woodward, as it is in almost every instance that sliding-head turning is employed.

He continued, “Switching the machine between fixed- and sliding-head modes is quick to carry out, so has minimal impact on productivity.

“The guide bush is of so-called ‘breathable’ design that supports the bar by air pressure, which is forgiving of bar diameter variation.

“It means we can use drawn bar, hexagonal as well as round, instead of the more expensive ground variety and the stock is held more rigidly, which improves accuracy.”

When the time came for Vire to replace a 36 mm capacity Traub TNK36 fixed-head lathe that had worked 24/7 for nearly ten years, Janet Vincent again chose to install a machine that could be either a sliding- or fixed-head turning centre. The TNL32, despite its designation, also handles 36 mm bar and features a full Y-axis on both the top and bottom turret, with the top tool carrier also capable of moving in Z.

In this size range, there is little requirement for shaft-type, sliding-head work at the Totnes facility, so the machine has been used as a fixed-head lathe for all but two jobs since it was installed at the beginning of 2013. Vire benefits from shorter bar remnants compared with when sliding-head turning is employed, saving on material costs.

Many of the 1,200 programs written for the TNK36 are being moved across to the TNL32, a process that was underway before the latter arrived on the shop floor thanks to the Traub WinFlex IPS-Plus off-line programming facility at Totnes. A similar advantage was taken a year ago before the TNL18P was installed.

Mrs Vincent concluded, “We installed our first Traubs a decade ago and have been consistently impressed with the quality of build and high power of the spindles and live tooling as well as their reliability and productivity.

“While there is some evidence of reshoring of manufacturing from low-wage countries, due to quality issues, rising wage costs overseas and long lead-times, the UK is still under threat from the likes of India and China.

“The best way to counter it is to install automated, highly capable machine tools such as the Traub lathes and to keep updating them to take advantage of the latest innovations for reducing one-hit cycle times.”