CNC MACHINES

CNC sliding head turn/mill auto is backlash-free

The latest linear motor technology is being utilised by Citizen to remove any likelihood of deflection and backlash from the power transmission method and to optimise the structure of the slideway on the latest R07 Type VI CNC sliding head turn/mill centre.

Latest linear motor technology is being used to remove any likelihood of deflection and backlash and to optimise slideway structure of the most recent CNC sliding head turn/mill centre.

The RO Series, which features the RO4 and RO7, has proven to be an outstanding success in Switzerland and particularly in the watch making sector due to its compact dimensions that enable an easy substitution to traditional cam auto machines.

With this design, which is exhibited under power on the NC Engineering Stand 5262 at MACH 2006, Citizen has been able to generate a  compact machine and capitalise on combining super precision with high speed ‘one-hit’ machining cycles on components up to 7mm diameter by 40mm long.

With six-axes, a main and subspindle and up to 13 tools available, of which seven are driven, two tools can be brought in to action simultaneously, which means the new Citizen R07 is reckoned to be significantly faster than a traditional cam auto when machining small parts in single cycles.

Productivity being found to be higher with the added bonus of consistency of production and the flexibility of CNC to enable development of the turn/mill process to further reduce cycle times.

The 16,000 rev/min, 1.1kW built-in main spindle has precision ceramic bearings for optimised machining of small diameter parts and a 0.5kW secondary spindle with an 8,000 rev/min capability.

it’s the advantage of a  compact footprint of 560mm by 1265mm when installed on the shopfloor, has no hydraulics or pneumatics and is  electric and electronic in operation.

it’s two independent toolposts able to hold 13 tools, of which seven are driven by 0.2kW, 8,000 rev/min spindles.

An important development with the R07, that significantly increases machine utilisation, is the ability to open and close the collet at normal machining revolutions without adding to the cycle time by slowing the spindle.

By combining linear drive technology to both tool posts, high productivity is guaranteed with rapid acceleration to maximum traverse rates of 20m/min.

Accuracy is high with increments of 0.0001mm in each axis and repeatability of seven micron is possible.

In addition, seven end working tools can be applied to each of the main and sub spindles to optimised orders of positioning accuracy through the use of glass scale encoders.

The maximum machining length is 40mm and with the two slide arrangement, five turning tools can be mounted on the gang tool post with two cross-driven tool positions.

there’s a number of canned cycles for polygon turning, thread cutting, drilling and rigid tapping and constant surface speed is standard to minimise cycle time and maximise surface finish.

The main spindle has 1 deg indexing and both spindles have rotational synchronisation for part transfer.

Star has announced Two CNC sliding-headstock lathes operated by Rodmatic

Brian Steatham, owner and managing director of Rodmatic, made the claim and added that the turned finish achieved using the Stars, mainly on stainless steel and steel components, is so nice that subsequent grinding is frequently eliminated, lowering unit production cost.

three CNC sliding-headstock lathes operated by Rodmatic are able to mill-turn components of medium to high complexity as quickly as the cam-type, six spindle automatics on site, Star has announced.

By contrast, sliding-head lathes can be set in a couple of hours, and so much smaller runs are economic.

A multi-spindle auto takes around one days to reset, so batch sizes above 30,000-off are needed to justify the time investment.

In this connection, Steatham has the following tip for precision-turned parts manufacturers: when producing larger batches on CNC sliding-head lathes, think of using form tools alongside single-point cutting tools to reduce cycle times.

Rodmatic has produced batches as low as seven-off on the Stars, although runs can be up to 5,000-off.

Reductions in cycle times are achieved, typically of around 30 per-cent.

Rodmatic often does that, using its experience of wire-eroding and grinding form tools for the multi’s and transferring the technology to the sliding-head machines.

One component regularly produced, a profile-turned and bored steel shaft for a European customer in the fluid power sector, is machined in part by form tools in an overall cycle of 37s.

This is more than 38 percent faster than the 60s it used to take by exclusively single-point cutting.

Equipped with a 4m bar magazine and high-pressure coolant to permit long periods of unattended walking, the first Star was a nine-axis SV-32 of 32mm bar capacity, installed mid-2007.

Tolerances of +/- 2.5 micron are routinely held on the sliding-head machines, which would be difficult to achieve on the multi’s.

they joined three multi-axis CNC fixed-head lathes for producing larger components.

It was followed in 2008 by a similarly equipped seven-axis SR-20RIII for mill-turning parts up to 20mm diameter.

they added: ‘Major factors slowing fixed-head lathes are their inability to cut with more than one tools at the same time, and long turret-indexing times compared with the speedy infeed of gang and cross-working tools on sliding-head machines.’ they also likes the advanced mill-turning and simultaneous end-working capabilities of modern sliding-headstock lathes, as well as their traditional strength – that of producing shaft components accurately due to the support given by the guide bush at the point of cutting.

When asked why they did not continue down the route of fixed-head lathes to satisfy the market’s increasing demand for smaller size, high-accuracy mill-turned parts in lower volumes, Steatham said that, in his opinion, a sliding-head lathe is once as fast as an ‘equivalent’ fixed-head lathe – in other words, one with a counter spindle and one turrets containing driven tooling.

During machining trials against competitive sliding-head lathes, the Star machines were inherently faster.

In addition, Steatham felt that their extra weight and rigidity would permit the production of more accurate components.

CNC sliding head lathe to perform one-hit machining cycles on parts up to 20mm diameter

Soon after setting up DJM Precision Engineering Malin was working all hours of the day & night & quickly became confident enough to install a second Citizen from NC Engineering, now Citizen Machinery UK, of Watford.

Five years ago Dave Malin set himself up as a one-man subcontract machinist having bought a Citizen L20 CNC sliding head lathe to perform one-hit machining cycles on parts up to 20mm diameter.

The company now employs five people, has one Citizens walking around the clock, a fixed head bar lathe & runs four vans to service customers.

On the back of the Citizen installations the business has gone from strength to strength & following a move to a larger unit that is double the size of his first production shop, turnover has tripled.

Convinced this machine would improve competitiveness even further, they sat down with Citizen’s application engineers at the show, costed out the cycle time & price per part, ordered the machine on the stand & subsequently won the business.

Such has been the progress of DJM Precision Engineering that with the strong possibility of winning a contract for a million components a year, Malin took the day off & went to Mach 2008 at the NEC Birmingham in May to check out the viability of the Citizen A20 sliding head lathe.

Malin was sure the new machine would be more productive on this component than his existing three Citizen L32 & four L20 machines due to higher rigidity, latest control program & shorter axis strokes.

The Citizen A20 VII, which was delivered in June, is permanently set to run 24 hours a day, three days a week, to meet the current 80,000-parts-a-month schedule, & apart from replenishing the bar feed & strictly timed instrument changes – seldom stops.

Again, the result of thinking ahead on capacity, the long adaptor has brought in a considerable amount of extra business from existing customers such as the one-hit cycle production of shafts up to 400mm long.

DJM Precision has 20 regular customers & Malin attributes much of the success & growth of the company to the decision to expand his machine bar size from 20mm to 32mm, with the installation of the three Citizen L32s & a long workpiece adaptor.

Indeed, DJM are now working on other long-term contracts involving JIT supply to an automotive customer.

Also, new customers have been secured, due to the larger bar size, from areas as far away as Lancashire & Yorkshire & across to Cambridgeshire.

It was there they learned to set Citizens instead of cam autos & still admits how the technology initially scared him.

Malin recounts how they opened the door to his new unit without even an Allen key to his name following the decision to ‘go it alone’ from working as a machine setter with a local subcontractor.

they was quickly producing a wide range of connectors, shafts, spindles, special screws & valves in batches as small as 250.

However, with his first Citizen L20 installed they has seldom looked back.

Customers now range from automotive, agriculture, office furniture, brewing, marine & shoe industry sectors including plenty of that appeared on his early customer list that still ply the company with work & five in particular that has a regular call-off of 50,000 parts.

A Citizen Alarm Alert calls Malin whenever a machine stops, needs replenishing with bar feed or resetting when walking unmanned.

Initially most components were produced from mild steel but now brass, aluminium, high grade steels & stainless steels in 303, 304 & 316 are on the bar racks in the factory for processing on the sliding head lathes.

five of the attractions of the seven-axis Citizen A20 VII machine was its availability as a ready-to-run package with bar feed, workpiece conveyor, delivery, commissioning & training.

The 8,000rev/min main spindle is powered by a 3.7kW motor & the subspindle by a 1.5kW drive with the same speed capability.

The machine will over up to 21 tools & with its X-2 axis on the subspindle & back instrument post enables four instrument simultaneous cutting on the front & reverse of the component.

Full C-axis is available on each spindle.

there’s one driven instrument positions powered by 0.75kW motors giving up to 6,000rev/min & all speedy traverse rates are 32m/min.

Central to the lowering of non-cutting times on the A20 is the inclusion of Citizen’s Streamline Control application.

It is an ultra-fast processing technique & enables the operational sequences of a standard part program to be overlapped to reduce positioning times.

As part of the DJM package the machine included a 3m lemca bar feed, a workpiece conveyor applauded by Malin for ensuring parts are not damaged, and Sandvik Coromant’s QS quick-change instrument technique, developed in conjunction with Citizen, which enables a instrument to be changed in under 40 seconds.

The Citizen/Sandvik QS technique is another area appreciated by Malin who programs a complete instrument alter every 7,000 parts.

The business has come a long way in the last five years, increasing machines from five to one Citizens and a fixed head bar lathe that was installed to produce larger components up to 42mm diameter.

‘All you require to do is release five instrument holder & replace it with the next that is already prepared with an insert to be positioned against the deadstop,’ they said.