New Machining Center Specifically For Viper Grinding
Twickenham, UK - VIPER grinding, a production process patented by Rolls-Royce that employs a machining center 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. It has proved to be much faster than all of the machining techniques it was introduced to replace, namely CBN grinding, broaching, milling and turning.
As a result, one of the partners in the development project – Makino – 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 center, 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 on the Makino stand at EMO 2007, Hannover. It was demonstrated by Makino-NCMT Grinding Division, a UK operation run by the Japanese manufacturer's sales agent, 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 center 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 per cent quicker at machining nickel alloy components than the modified Makino A55 machining center that it supersedes. Metal removal rate is of the order of 80 cc/min. The machine accepts parts nominally up to 300 mm 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 48 m/min. Faster rotary workhead speed, which has more than doubled to 100 rpm, 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.
Probably the most critical improvement, however, 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 degrees around the periphery of the grinding wheel, rather than through just 180 degrees, 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.
A big advantage of VIPER grinding on a horizontal machining center 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 220 mm 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 centers, 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 achieve world class process capability and throughput include EasyGrind and EasyGear programming software, flexible fixturing, and manual or in-cycle part measurement, verification and truing.
SOURCE: Makino