machining
Idle/non-cutting time is sin as far as machine shop productivity is concerned, a fact that
is being recognised increasingly by machine tool designers. By Steed Webzell
The devil makes
work for idle hands
DMG DMC 75 linear
delivers short
positioning times by virtue
of linear drive systems on
the three main axes;
acceleration is 2G, up to
rapids of 90m/min.
IN simple terms non-cutting time occurs as soon as
the machine stops in order to do something else, and it
can be caused by a number of things, including in-cycle
operation, machine set-up and basic machine design.
‘Non-cutting time is any point where the tool is not in
contact with the component, so as a machine tool
company Mazak concentrates on reducing this by
achieving the fastest rapid travel rates in all axes to move
the tool around the component,’ says Lawrence McCann,
Yamazaki Mazak’s deputy applications manager. ‘But it is
not all about speed, we also look to get the fastest
acceleration. In other words, delivering the maximum
rate of change and rate of movement possible, so as to get
from A to B in the shortest possible time.’
In addition to the major machine elements Mazak also
puts a great deal of effort into developing its machine
spindles, with acceleration/deceleration rates being of
particular importance in order to get from a stationary
spindle at tool change to running speed as quickly as
possible. It is here that Mazak’s position of supplying both
the machine tool and control is a major advantage. With
40 MWP january 2008
the new Matrix control the speed at which data can be
transferred to the machine’s drives is much faster, reducing
the time required for a drive (spindle) to react. If you look
at other control-related issues Matrix now has the
capability to permanently engage the C-axis on a lathe so
eliminating the ‘spinning motion’ and associated
downtime when the C-axis is being engaged. Previously,
this typically accounted for a couple of seconds while the
C-axis ‘found itself’ prior to engaging. Now it is
instantaneous.
Mazak has also developed many ‘Intelligent Machine’
functions to help reduce non-cutting time, with many of
these functions such as these are available on the new
Integrex i-150 that was introduced at EMO last September.
‘Beyond the machine design users must look at improving
set-up time, much of which revolves around workholding,’
adds McCann. ‘In my opinion, unlike machine tools and
cutting tools, which have moved forward in leaps and
bounds, workholding has not advanced at the same rate. We
are now working with suppliers to make workholding
equipment more user-friendly so that they can, for
instance, use a chuck as it was designed, then add a mandrel
or fixturing to that same chuck to reduce setting time.’
According to Geoff Lloyd, the managing director of
Heller Machine Tools: ‘Efficient machining is
accomplished by more than just shrewd machine design’.
Although Heller horizontal machining centres deliver fast
cycle times, non-cutting time is most effectively minimised
by good process control and effective customer support
services. ‘Tool contact time is largely attributable to the
cutting tool itself,’ he says. ‘When machining a non-ferrous
material, for instance, idle time can be as much as 50% of
cycle time because it is easy to machine. It is therefore
critical that the machine tool manufacturer minimises the
time taken by activities around delivering the tool to the
workpiece to ensure non-cutting time is as low as possible.’
Prior to quoting any machine, Heller engineers
undertake a detailed machining analysis, which is
included in the quotation in the form of a ‘Cut View
Report’. In developing the study, Heller engineers assess
the use of individual tools, incorporating details such as
spindle acceleration times and evaluating the optimum
orientation of a part to give a reduced number of tool
changes and better utilisation of tool time. Created using
a specially-developed software package, the Cut View
Report gives the customer an exact breakdown of every
activity within the machining process, in seconds and
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