Product category:
Abrasive machining - manual and CNC machines
News Release from: NCMT | Subject: VIPER grinding - horizontal machining centre
Edited by the Manufacturingtalk Editorial
Team on 21 June 2006
VIPER quadruples Inconel grinding rate
Continuous dress , high-speed VIPER grinding of a 700mm long, industrial turbine blade made from Inconel 718 was demonstrated to quadruple stock removal rate to 200cm3/min.
Continuous dress (CD), high-speed machining of a 700mm long, industrial turbine blade made from Inconel 718 was simulated on a Makino A99 horizontal machining centre at Makino UK agent NCMT's technical centre recently An air-cut cycle showed the strategy for roughing, semi-finishing and finish-grinding the root block using three separate wheels
This article was originally published on Manufacturingtalk on 21 Jun 2006 at 8.00am (UK)
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Abrasive machining ousts milling and broaching
'Very impressive performance extreme removal' - or VIPER - grinding is 10 times faster at removing metal than milling when machining aerospace and industrial turbine blades.
HMC VIPER-grinds and mills turbine blade
On a horizontal machining centre, using the VIPER grinding technique, 5-axis machining of a nickel alloy compressor blade involved grinding a radial dovetail root form, including a milling operation.
A single dresser was used continuously to maintain the profiles on all three wheels, quadrupling stock removal rate to 200cm3/min compared with non-CD VIPER grinding.
Crucial when machining a turbine blade root form is to maintain close tolerance on the seating faces that oppose the centrifugal force when the engine starts.
Allied to this, symmetry of form also needs to be very accurate, as otherwise the blade tries to twist out of alignment.
Further reading
Root slots VIPER ground on turbine disc
Believed to be a 'world first', a horizontal machining centre was demonstrated the complete VIPER grinding of root slots on a turbine disc at rates up to four times faster than milling.
VIPER grinding replaces turn/mill on big parts
How the VIPER grinding process can machine features on big nickel alloy components - like a 1.1m diameter jet engine casing - demonstrated the replacement of milling and lathe-turning.
It is difficult to maintain the required accuracy if the machining centre's rotary axes are interpolated during grinding.
Consequently, a narrow (30mm), 300mm diameter roughing wheel was used to grind most of the material from each fir tree serration in turn while simultaneously interpolating the rotary axes, as accuracy was not an issue during this operation.
The component was then swivelled through 180 deg and the same wheel was similarly used to rough the serrations on the other side.
For the finishing passes, however, both rotary axes were clamped and only the linear X-axis of the table was employed, while an 80mm wide wheel carrying the entire root form profile plunged vertically in Y.
To minimise 'stagger' between the two sides of the root form, the component was maintained in the same orientation and the wheel was swung below the component to finish grind the other side.
In a conventional production route, each side of the root form has to be machined on different grinders, compromising accuracy, unless the manufacturer invests in an extremely expensive, double-sided grinder.
Between 4 and 6 micron total tolerance for the stagger between the two sides of the root profile is maintained, even on large blades, which is three to four times better than traditional, multiple set-up manufacturing processes involving, say, eight operations on six different machine tools.
The application again highlighted the benefit of one-hit grinding, (plus milling, drilling, etc, as appropriate) using inexpensive, aluminium oxide wheels on a more or less standard machining centre with a large rotary axis.
On 5-axis grinders, the rotary axis tends to be much smaller.
In the demonstration, the turbine blade, which was originally fixtured off the aerofoil alone, was inverted and reclamped off the machined root block and the aerofoil for machining of the shroud end, Z notch and seal fins. Request a free brochure from NCMT ...
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