Traub TNM series CNC lathes have progressively replaced existng machines on a 2:1 ratio at subcontractor H McGrail and increased productivity by 300%.
With years of experience using automated bar capstan lathes, subcontractor H McGrail and Sons based in Central Birmingham had based many of its machining methods for brass and some steel components on the use of form tools in order to plunge diameters and combine different features, length, dimensions and forms. Some four years ago the decision was made to upgrade to CNC and an evaluation of the machines on the market combined with the type of tooling, methods and expertise available in-house, it was decided that the Traub TNM series of multi-slide CNC automatic lathes fitted the bill. Explains managing director Paul McGrail: 'We have purchased four Traub TNM multi-slide lathes from Traub Heckert UK in Brackley, two TNM 28s, a TNM 42 and most recently, a 65mm bar capacity TNM 65.

They have progressively replaced our existing machines at a ratio of 2:1 increasing our productivity by some 300 per cent.

We are now able to run unmanned at night, cycle times are halved and, we can easily change over two machines every day to new components.' The original company was founded at the end of the First World War in 1918, and was purchased in 1965 by Paul McGrail's grandfather, primarily to supply his Armac furniture fittings company with turned and pressed parts.

It is still part of the Armac Group and operates from a purpose-built factory adjacent to the parent company.

While it continues to supply components to Armac, the subcontract business has flourished so that today, 60 per cent of its sales of quality turned parts and small pressings comes from outside the Group.

Components include a variety of furniture knobs, handles and some door and window fittings.

Produced in batches between 500 and 5,000, most are machined from brass mixed with some steel components using bar stock up to 65mm diameter.

'Plunge forming is the most efficient way to remove brass quickly', argues Paul McGrail, 'and, our operators are highly skilled at free hand grinding the respective form tools.

In changing our machine tools to increase productivity, we still wanted to retain this expertise and to continue exploiting the same efficiency of metal removal.

But, we also wanted to modernise our plant and work with smaller batch sizes that customers were demanding.' The first Traub TNM 28 CNC multi-slide auto was installed in 1997.

Commenting on the reasons for choosing the Traub machine, Paul McGrail says: 'It was the only CNC lathe available at the time that suited our style of form tool based production.' The TNMs have four independently CNC controlled plunge slides, which are radically mounted around the spindle.

They can be easily fitted with form tools as well as the parting-off tool.

On the eight-station turret, one station can be utilised to hold a pick-up spindle, which allows the part-off face and any end features to be machined by the rear tooling attachment.

In addition to the efficient metal removal that can be achieved by the plunge form tools in a modern rigid machine tool structure, McGrail has the benefit of respective spindle powers of 11 kW on the TNM 65 and 42 and 4.6 kW on the TNM 28.

The machines have also given other productivity benefits such as the availability of centrally driven tools for all the eight turret stations, C-axis spindle, the turret-mounted component pick-up spindle and rear tool machining attachment for back-end working.

This means 'single hit' cycles for many of the parts can be utilised and combined with overlap machining.

'The result has been a significant reduction of up to 50 per cent in overall cycle times,' says Paul McGrail.

He follows on: 'Now that we can run the TNMs unmanned, we can exploit 'after shift working'.' To which Works manager, Graham Jones confirms: 'We run at least two of the TNMs every night for two to six hours depending on the component and numbers required.

We can set-up a job in the afternoon, prove it out and easily run a batch of 500 overnight.' One major benefit has been that because the machines are so easy to set-up by the two setters, they readily changeover two machines each day.

'Batches today are rarely more than 10,000 and will take no more than one or two days to complete,' explains Graham Jones.

'Even if all four machines should finish a batch during the day, at least two will be back and running in a matter of hours and, should a different size of bar be needed, channels in the bar loader, can be switched well inside 20 minutes,' he maintains.

A further effect of investing in modern technology has been an important improvement in quality and consistency of production.

This stems from the rigid machine structure, the superiority of the CNC control and the elimination of re-clamping for second operations.

'A combination of plunge tools to remove the bulk of the material with single point tools in the turret for finish sizing, also results in better quality and no loss in productivity,' adds Graham Jones.

In addition he says: 'The feed rate of the plunge slide is programmable so it can be automatically reduced as the final diameter is reached in order to accurately size the part.

If required, a G9 code can be selected that allows the finish diameter to be sized,' he says.

As Paul McGrail comments: 'The overall effect of the Traub TNMs is increased productivity across the board while maintaining the workforce skills.

In fact, these have now been improved following the first-class training and applications engineering provided by Traub Heckert.' To which Graham Jones adds: 'Before, no one had any experience of CNC, but the Traub machines are so user-friendly that everyone on the shop floor found the transition easy, both for setting and programming.

Traub Heckert produced the first few programs but now we do it all.

It's easy really and very quick as we can repeat machined features by just 'cannibalising' blocks from already proven programs.

Its all done at the TX 8H control using the Flex IPS dialogue software while the machine continues in production,' he insists.