It used to take Watford-based Parker Hannifin 30 minutes to machine both ends of complex cylinder rods in two set-ups on different lathes, plus there was handling time in between. The same job is now completed automatically by simultaneous front-end machining and reverse end-working in seven minutes on one machine - a Nakamura Tome TW-20 twin-spindle, twin-turret lathe supplied by Mills Manufacturing Technology. The cycle time includes shaft in-feed and component unload.
The resulting improvements in productivity are part of Parker Hannifin's investment in its 'Fastrak' cylinder manufacturing service which provides a rapid response mechanism for customers.
Lead time from material issue to completion of a pneumatic or hydraulic cylinder, each of which can have a bespoke 'user' end, has been cut by 20 per cent.
This has resulted in faster delivery from receipt of order and hence improved customer satisfaction.
Furthermore, cost of production is reduced as the same output is achieved in a single shift rather than two-shift working as previously.
'Such cycle time savings, while impressive, are not unusual on modern mill-turning centres', says Derek Lilley, production engineering Supervisor at Parker Hannifin.
'What sets this application apart from most is the ability of the lathe's opposing spindle to pick up a running centre automatically from the right hand turret and travel across to support the end of rods being turned in the left hand spindle.
In this way we can machine our longer rods using the other spindle effectively as a tailstock support, in one uninterrupted cycle.' When the TW-20 lathe was installed, it was the only machine on the market capable of doing this.
The ability to control closely the pressure exerted by the second spindle is said to be key to the success of the operation.
Certainly it is of considerable importance to Parker Hannifin as five per cent of its cylinder rods are sufficiently long to warrant centre turning.
It would be an even larger proportion were it not for the rigidity of the machine, which allows components of 3:1 length-to-diameter ratio to be chucked without loss of accuracy.
The turnkey installation supplied by Mills included a standard Hydrafeed shaft loader and a specially built, automatic unloader to cope with all configurations of component.
The unloader has 13 interchangeable pullers to suit the different bar diameters used, in the range 12mm to 50mm.
Each puller is designed to screw itself over the thread that has been machined during the operation at the first spindle, and then extract the component through the bore of the right hand spindle.
Nylon runners prevent marking of the chrome plating.
Any length of shaft up to a maximum of 1.5m is placed on the inclined magazine of the loader.
All shafts in a production run are of the same diameter, changeover to a new size of shaft being carried out in just half an hour, three times a day on average.
This frequency of resetting is dictated by the low average batch size of two, with one-offs the norm and 20-off being unusually large.
It means that all the length variations of a particular diameter of stock are completed relatively quickly.
Such a short resetting time is achieved by having two operators simultaneously working at both ends of the machine; and by using 13 sets of Hainbuch dead-length collet chucks which can be exchanged in a matter of seconds.
Contributing further to rapid set-up is tool probing built into the front of the machine which utilises Nakamura 'NT Nurse' software to check automatically the tooling in both 12-station turrets when the inserts are changed.
Tools had to be preset off the machine before.
The components manufactured on the TW-20 are produced from an induction case hardened, hard chrome plated, precision ground, high tensile, carbon alloy steel.
The sequence is to feed the shaft through the left hand spindle to a stop in turret 1, then rough and finish turn the first end followed by thread rolling (M24 and below) or thread cutting.
Spindle 2 then comes in to grip the front end, leaving the appropriate length protruding for the second operation, and the collet in spindle 1 releases the part.
The same cycle is performed on the reverse end as on the front, plus face cutting and polygon turning of two, four or six flats on the user end of the rod.
A variation to the above sequence is when longer rods are being produced, in which case the running centre in spindle 2 is brought into play within the cycle.
There is also the occasional drilling and optional rigid tapping of female ends.
The previous production machinery which has been replaced was 15 years old and approaching the end of its useful life.
Breakdowns were becoming more frequent and spares were difficult to source.
More importantly, according to Derek Lilley, productivity was limited by the restricted spindle speeds.
Cycle times were consequently longer than they should have been; and the chip-breaking characteristics of modern cutting tools could not be harnessed effectively.
It resulted in the machines being stopped in the middle of every cycle for long strings of swarf to be removed from the working area in order to protect the critical chrome surface of the rod.
Cutting speeds have now been increased dramatically, producing short chips which clear effectively from the point of cutting, so it is no longer necessary to stop the machine in-cycle.
Another reason for frequent interruption of the machining cycle was loss of accuracy.
The tolerance on the turned diameter for subsequent thread rolling is tight at - 0.01mm, + nil, and on the previous machine tool this would sometimes drift, causing problems with thread rolling.
Oversize meant the risk of damage to the Fette head while undersize would produce unacceptable flats on the tops of the threads.
Accuracy problems no longer occur with the Nakamura Tome lathe.
The TW-20 is currently devoted to cylinder rod production for which the core manufacturing NC programs were written and supplied by Parker Hannifin production engineers and interfaced to the machine by Mills application engineers as part of a turnkey project.
Macro-based programs to produce the customised cylinders are prepared off-line and sent to the machine's Fanuc 18T control over a DNC link.
However, it is planned that the machine will be deployed on manufacturing other product lines in the future.
A major benefit when reconfiguring the TW-20 will be its two-lathes-in-one design complete with central partition which is currently slid back.
It is possible to operate either end of the machine as a separate lathe with its own door, allowing the production of dis-similar components with different cycle times, if required.