machining
Ian and Howard
Sheldon believe that
with the right plant, UK
manufacturers can
compete on a world stage
Candidates for a multi -
parts that need a
combination of
operations
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 camtype
machine and transferring it to a CNC multi that is still
being paid for, irrespective of any cycle time savings.
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 microns total).
CNC flexibility means smaller economic batch sizes
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. Moreover, 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 multis 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 down 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.
For manufacturers evaluating the purchase of an Index
multi, Ian Sheldon gives 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
68 MWP march 2008
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 says never leaks; and filtration
to extract all particles of metal larger than 20microns,
which he has noticed significantly improves tool life.
Coolant temperature is constantly controlled to promote
high machining accuracy, 24 hours a day.’
As a postscript, he mentions 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.
Concludes Ian Sheldon: ‘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. As in
our company, a subcontractor anywhere in the world
would need two or three people to run four Index multis.
So the overhead differential between the UK and lowwage
economies is much smaller with high-end machine
tools, added to which the UK has very experienced
engineers to extract maximum advantage from them.’
www.gkholdings.com
To view a Ceros magazine you need to have JavaScript enabled in your browser and have the flash player 8 or higher installed. To install the latest flash player, click the icon above, install the flash plugin and then click here to refresh this page.