Product category:
CNC automatic lathes
News Release from: Geo Kingsbury Machine Tools | Subject: CNC multi-spindle at Witon Engineering
Edited by the Manufacturingtalk Editorial
Team on 27 March 2008
CNC multi-spindle automatics save on
costs
Regarded by many subcontractors as expensive, the CNC multi-spindle automatic lathe can do the work of four to six four, CNC single-spindle lathes for a lower labour cost.
egarded by many subcontractors as expensive, the CNC multi-spindle automatic lathe can do the work of four to six four, CNC single-spindle lathes for a lower labour cost UK distributor of Index CNC multi-spindle automatics, Geo Kingsbury Machine Tools said that if one suggested to a turned parts manufacturer that it should invest in a CNC multi-spindle automatic (multi), the most likely response would be: "Too expensive"
This article was originally published on Manufacturingtalk on 26 Aug 2003 at 8.00am (UK)
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The managing director of subcontractor Witon Engineering in Barnstaple,Devon, Ian Sheldon, would disagree.
Witon operates four German-built Index CNC multi's in addition to around 30 single-spindle, fixed- and sliding-head lathes.
Witon purchased its first Index MS32C six-spindle multi in 2002 and a second, identical model was installed less than a year later.
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The company added a further 32mm capacity multi in 2006 and in 2007, bought an MS52C for mill-turning parts up to 52mm diameter.
"The business case for these machines is straightforward, provided that you can feed them with enough work," explained Sheldon.
He added: "People calculate payback in different ways, but however you do it, I see no difference in the amortisation period of a multi and that of a single-spindle auto - or any other machine tool, for that matter".
* Output/m2 of factoy space - Sheldon said that there are several factors to take into account when considering buying a CNC multi.
The most significant benefit is the high production output for the footprint.
Factory space in the UK is expensive and in any case, many companies do not have room to fit in the four, five or six single-spindle lathes and their full-length bar magazines that would be needed to match the output of one multi.
* Machine price - machine proice is important and there is no doubting that a multi is an expensive item of plant, said Sheldon, albeit the price has been coming down in real terms over the years.
However, he that his Index MS machines are only between two and three times the price of a good quality, twin-spindle mill-turning centre of equivalent capacity.
Sheldon added: "When you consider that a turned and prismatically machined component coming off a single-spindle mill-turn lathe can be produced four times faster on a multi with driven tool capability, the latter, more expensive machine starts to look good value".
* Lower labour costs - in discussing labour costs, Sheldon said: "There is only one machine to operate, not several, so labour costs are lower.
One setter and two operators look after all four of our multi's during the days and at night we often have only one operator, unless we are running very close-tolerance work".
Sheldon said: "The efficiency of our MS machines is high too, as reliability is good and set-up times rapid.
All of our CNC multi's produce parts for over 90% of available hours".
One of Witon Engineering's specialisms is mill-turning of mainly ferrous components up to 60mm diameter, for which purpose the plant list includes four Index G200 twin-opposed, single-spindle turning machines.
Three are fitted with high-pressure coolant delivery to increase efficiency when machining stainless steel and when cutting cycles include deep hole drilling.
* Raising productivity - Witon bought the MS52C to introduce the productivity benefits of the multi to these larger parts.
One example is a 45mm diameter, stainless steel component for the automotive industry that Witon had been machining since 2005 in a 50s cycle on the G200s at the rate of 40,000/month.
The job, which does not use driven tooling, involves removing about 75% of the bar volume by boring and turning a stepped bush, so high power is important.
Now that the job has been moved to the MS52C, cycle time is 16s - over three times faster than on a single-spindle G200.
Second-generation director, Howard Sheldon, has been impressed at how quickly the machine converts bar into high precision components.
He said: "We operate 120h/week, during which time the MS52C can work its way through 12 tonnes of 41 mm diameter stock.
When the machine is running stainless steel, that material accounts for more than half of our throughput".
* Synchro sub-spindle mounted on a robot arm - feature of the MS52C is the synchro sub-spindle mounted on a robot arm, which picks up a parted-off component and presents it to static and live endworking tools.
This modern system is more flexible than the endworking on the older MS32Cs at Witon as it allows the component to visit extra tools for more comprehensive in-cycle reverse-end machining.
According to Howard Sheldon, there is a perception that it is cam-type multi users that are migrating their work onto the more capable CNC versions.
He said that this is not necessarily the case, even though a CNC multi can be between two and three times more productive than a cam multi.
The latter machines in firms all around the UK have probably been in operation for many years, so their purchase has already been amortised.
Financially, therefore, it is difficult to justify taking a component that can be produced free from capital plant costs on a cam-type machine and transferring it to a CNC multi that is still being paid for, irrespective of any cycle time savings.
* One-hit machining - what, then, are the criteria for producing a component on a CNC multi? One example is a part currently produced in two hits, one on a cam multi and another in a separate operation on another machine.
Even a relatively simple component requiring an internal thread at both ends cannot be machined in one hit on a cam auto, as tapping at the back end is not possible, whereas it is on an Index MS.
Removal of a second operation may justify transferring such a simple component to a CNC multi, but the more usual candidate is a fairly complex part that currently undergoes a combination of turning, milling, drilling and machining at both ends on a single-spindle lathe to tight tolerance (down to 10 micron total).
Type of material also has a bearing on whether a component is put onto a CNC multi.
The tougher it is to machine, the more appropriate it is to put it onto an Index MS, owing to the machine's high power and rigidity.
* Optimisining machining - the slides and spindle at every station on an Index MS can have independent feeds and speeds to optimise the machining characteristics at all six positions to suit the type of operation and the material being cut, be it aluminium, brass, steel or titanium.
In contrast, cam multi's have to use identical feeds and speeds at all six stations, resulting in compromised machining characteristics at most if not all stations, which in turn lowers productivity and often reduces quality.
The flexibility of CNC has also dramatically reduced economic batch size to 10,000-off on a multi, giving the machine much more scope than before.
Changeover is faster than on a cam machine and the expense of machining or purchasing cams is avoided.
If a family of similar parts is being produced from the same bar size, Witon is able to change the program and swap a few tools over on an MS machine and start producing again in a matter of minutes.
If a manufacturer is evaluating the purchase of an Index multi, Ian Sheldon gave some pointers to help in the decision-making process.
One has to keep in mind that the user gets six C-axis spindles, each served by two tool slides able to perform boring, or internal or external turning.
The user is not restricted to designating one type of tool in any position, helping to optimise flexibility and reduce machining times.
Powered tooling can also be specified at whichever stations the user wants and there is considerable flexibility here too.
For example, Witon has opted for live tools at two positions on its MS52C, plus a tool for polygon generation at another station.
The machine has one robotic sub-spindle for simultaneous back endworking rather than the possible two.
It must also be remembered that the equivalent of six automatic bar feeders are included in the price of an MS machine.
So too is high-pressure, through-tool coolant delivery that Ian Sheldon said never leaks; and filtration to extract all particles of metal larger than 20 micron, which he has noticed significantly improves tool life.
Coolant temperature is constantly controlled to promote high machining accuracy, 24h/day.
* Outsourcing overseas - as a postscript, he mentioned the current situation regarding overseas competition in low-wage economies, especially India and China but increasingly Eastern Europe.
There is no doubt that a lot of work has been lost to those areas and large volume machining of relatively simple components has tended to stay there.
However, some UK manufacturers have started using domestic subcontractors again due to long lead times and poor quality from overseas.
Contracts for small to medium volumes of high precision, complex work did not generally leave our shores in the first place.
The real danger is when OEMs in the UK relocate overseas, as that business is usually gone for good.
On the positive side, the burgeoning middle classes in China and India, with their expectations of a higher standard of living, are fuelling demand for goods manufactured worldwide, including in the West.
Certainly the UK turned parts industry had a busy 2007, following a strong 2006, which is reflected in Witon's turnover figures.
Ian Sheldon said: "With the right plant, UK manufacturers and subcontractors can compete on a world stage.
There is no place for outdated machinery though.
Good quality CNC machines are essential to produce top quality components for on-time delivery.
The CNC multi-spindle automatic is a prime example of how the manufacturing sector in the UK can fight back.
He concluded: "As in our company, a subcontractor anywhere in the world would need two or three people to run four Index multi's.
So the overhead differential between the UK and low-wage economies is much smaller with high-end machine tools, added to which the UK has very experienced engineers to extract maximum advantage from them.".
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