Subcontract Milling and Turning
Ufone, a specialist in subcontract machining and Subcontract Milling and Turning of large, heavy components, has chosen the DMF500 Linear four-/five-axis vertical machining centre from DMG to cut drilling and milling cycle times.
The DMF machine has a 5m X-axis and extends the size of prismatic component that the Dudley-based precision machinist can produce, as the previous maximum was 3m in X.
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Capable of machining parts weighing up to seven tonnes within a 5000 x 1100 x 900mm working envelope, the DMF machining centre has a linear motor that accelerates the spindle head in the X-axis at 6m/s2 to a rapid traverse speed of 80m/min.
Non-cutting times are therefore minimised, resulting in high productivity.
Steve Davis, Operations Director at Ufone, said: ‘Apart from allowing us to produce larger components, the DMF500 Linear is much faster than our three-axis CNC travelling-table milling machines.
‘Drilling multiple holes around a ring or flange takes half the time or less, while thread milling is similarly rapid thanks to the HSK 100A spindle taper, whose rigidity also eliminates chatter, improving both surface finish and tool life,’ he added.
Davis went on to cite even greater improvements in machining efficiency.
He described the 23.5kW/10,000rev/min spindle with 40 bar delivery of coolant or air through the centre as being ‘a world apart’ from the 3,000rev/min spindle available on the CNC milling machines.
He said: ‘Using a solid carbide drill with through-coolant, hole production is three times faster than we were previously able to achieve.
‘We are getting similar time savings on some milling operations using the latest indexable-insert cutters.
‘Moreover, with standard ball-nose mills we consistently achieve a good surface finish, which is difficult on our other plant.
‘Having a 30-station magazine and automatic tool change is much faster than manually exchanging cutters and reduces machining cycle times further.
‘So too does the fourth axis indexer with tailstock, which can accommodate components spanning the full length of the table.
‘We use this facility about 40 per cent of the time to machine spirals or drill holes on a PCD, for example, but the proportion is growing,’ he added.
Auto-indexing to incline the spindle head on the DMF machine is positional in one-degree increments, but this fifth CNC axis cannot be interpolated with the other four.
A majority of the programming is carried out at the machine’s Heidenhain ITNC530 3D control, this option having been selected as Ufone’s other prismatic machining equipment is fitted with CNC systems from the same manufacturer.
Advantage can therefore be taken of existing setter/operator knowledge on the shop floor.
The speed with which a job is turned around at the Dudley factory and delivered to the customer is crucial.
Before the recession, 18 weeks was the norm, compared with 12 weeks now.
Additionally, margins are down 50 per cent owing to fierce competition from China and other low-wage countries.
Despite these challenges, unlike some of its competitors the subcontractor has managed to avoid short-time working by quoting competitive prices and deliveries, notably using the DMF machine.
There is a growing demand, especially in the offshore drilling sector, for larger, more complex components machined to higher levels of precision, which plays to the strengths of the DMF500 Linear.
Other sectors for which jobs are regularly carried out include industrial fans, power generation, nuclear, defence and shipping.
The railway industry is also served, with work currently going through for rebuilding steam and diesel rolling stock for the Gloucestershire Warwickshire Railway.
It was a large con-rod for actuating the valve gear on one of the heritage railway’s steam locomotives that Ufone used as the yardstick when evaluating which large machining centre it would buy.
The DMF500 Linear was selected partly due to DMG’s reputation as well as the machine’s 28 tonnes installed weight, which obviated the need for special foundations.
Another advantage was the availability of an HSK A100 spindle as an alternative to 50-taper, providing the rigidity and precision necessary for machining features down to 20 micron total, as demonstrated during cutting trials.
There was the additional merit of being able to partition the table into two zones, each 2.5m in X, and machining a pair of smaller components sequentially without interruption, as each set-up is carried out in-cycle.
This facility has not been used yet, but Ufone has quoted several jobs that, if secured, would benefit from such pendulum machining.
One big difference between tackling the machining of parts up to, say, 1m3 and the larger components often handled by Ufone is the approach to each job.
Machining is rarely completed in one hit.
Several separate operations are normally needed, one problem being that long, heavy components tend to bend by 0.5mm or more during each operation and the error has to be allowed for in the next cycle.
Meusz said that this is carried out manually on the CNC mills by clocking the component position and entering the offsets into the control.
The DMF500 Linear has been fitted with Renishaw part probing and automatically checks component position and dimensions after roughing and feeds the information back to the control, including the amount of stock that remains to be removed.
The control recognises if the cutters in the tool magazine are suitable for the next cutting cycle and flags up if that is not the case.
The advantage to Ufone, apart from saving time, is that the possibility of human error is eliminated from the process.
With material costing several thousands of pounds – even before any value-added machining, and errors of as little as 25 micron sufficient to result in components being scrapped – the potential for savings is enormous, according to DMG.
In-cycle tool length measurement has also been adopted for the same reason.
Matthew Wild, managing director at Ufone, said: ‘Our DMF machine has proved to be an ideal piece of production plant to position us for the upturn, which we are already seeing, particularly in the oil industry.
‘The machine’s high torque and rigidity means we can easily cut tough, high-nickel-content alloys quickly and accurately, while the higher spindle speed has raised productivity when dealing with aluminium alloys.
‘Every week we are picking up a new customer, or else a customer we have not dealt with for many years, largely due to having this additional capacity for Subcontract Milling and Turning .
‘It is strengthening our order book and giving us an increasingly competitive edge as we come out of recession.’
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