grinding
A new machining centre developed specifically for
Viper grinding boosts the productivity of this
specialised grinding process by 10%
Enhanced
efficiency
Probably the most
critical improvement is in
the design of the
programmable coolant
nozzles. They are more
versatile on the i-Grinder
G5, as they may be
positioned by two rotary
NC axes anywhere through
360˚ around the periphery
of the grinding wheel,
rather than through just
180˚, as was the case with
the A55. To achieve this
greater degree of freedom,
power and coolant supplies
are built-in, rather than
being delivered through an
umbilical cord. Nozzle
positioning speed is faster
and therefore more
responsive when changing
position to direct coolant
accurately towards the
point of cutting.
THE process patented by Rolls-Royce that employs a
machining centre for creep feed grinding of nickel alloy
components for the ‘hot’ end of gas turbine engines, has
been an international success since its introduction in 2001.
VIPER proved to be faster than all the machining
techniques it was introduced to replace - CBN grinding,
broaching, milling and turning. As a result, Makino, one
of the partners in the project has introduced a machine,
called i-Grinder G5, designed specifically to exploit the
technology to the full. Until now, the platform used was a
standard horizontal machining centre, albeit extensively
modified with very high-pressure coolant delivery to the
vitrified aluminium oxide wheel via programmable
nozzles and through the high-speed spindle.
The new, purpose-built, 7-axis machine made its
European debut at EMO. It was demonstrated by Makino-
NCMT Grinding Division, a UK operation which has
acquired a reputation as world leader in the research and
development of the superabrasive process. Consequently,
the company has been made responsible for VIPER
machining centre sales for not only in the UK, but also
across Europe and Scandinavia.
Even before the show, i-Grinder G5s had been sold by
Makino to a major aero engine manufacturer in Japan and
by Makino-NCMT Grinding Division to one of the largest
manufacturers in Europe of compressor and turbine blades,
and blisks. In addition to the machining of aerospace and
land turbine components, VIPER grinding is also suitable
for cost-effective manufacture of medical implants,
especially as their increasing complexity is making
manufacture more difficult on conventional or modified
tool and cutter grinders.
Overall, the i-Grinder G5 is 10% quicker at machining
nickel alloy components than the modified Makino A55
machining centre that it supersedes. Metal removal rate is
of the order of 80cc/min. The machine accepts parts
58 MWP november 2007
nominally up to 300mm in diameter and was demonstrated
at EMO grinding the fir tree root form of a power
generator blade close to the maximum capacity.
The enhancement in grinding efficiency comes from a
number of factors, including an increase in linear rapid
traverse rate from 40 to 48m/min. Faster rotary workhead
speed, which has more than doubled to 100revs/min, is
especially beneficial when grinding smaller components.
Manual access to the working area from the front of the
machine has been improved to allow the operator to
exchange components and dressing rolls more easily.
Automated loading and unloading is optional.
A big advantage of using a horizontal machining centre
platform is that in addition to abrasive wheels, other live
and static tools such as milling cutters, drills, broaches or
turning tools may be exchanged automatically between the
tool magazine and the spindle, allowing additional
machining operations to be carried out in the same
cycle.The i-Grinder G5 has a 60-tool magazine capable of
holding 20 grinding wheels up to 220mm diameter. Any
number of wheels can be sacrificed to allow conventional
milling or drilling tools to be deployed, allowing full
advantage to be taken of the machine’s multi-functionality.
As with all VIPER-specification machining centres, i-
Grinder G5 has three linear axes and two rotary axes as well
as the two axes for positioning the coolant nozzles.
Reinforced guarding, specially designed covers, pressurised
rather than grease lubrication of the slideways, a double
coolant filtration system, and positively pressurised
electrical cabinets are all standard features to prevent
ingress of dirt and contaminants. Related technologies that
have been developed by Makino-NCMT to enhance process
capability and throughput include EasyGrind and
EasyGear programming software, flexible fixturing, and
manual or in-cycle part measurement, verification and
truing. www.ncmt.co.uk
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