A new cell based on a robotically fed Makino machining centre configured for VIPER (Very Impressive Performance Extreme Removal) grinding has been installed at one of the Crewe production facilities of Trac Group. It follows the award of a long term contract to produce four types of nickel alloy turbine vane for a leading European power generation company.

NCMT, Makino’s agent in Britain and Ireland, undertook turnkey responsibility for the supply of a Makino A99e machining centre and the process for producing the vanes. Included in the package were programs, grinding wheels, workpiece fixtures and a Fanuc M-900/A 6-axis robot for exchanging fixtured components automatically.

The remainder of the production cell comprises two Tek4 deep hole EDM drilling machines, two die sink EDM machines from AgieCharmilles and a Hexagon/DEA coordinate measuring machine.

The background to the £2 million investment was Trac’s installation in 2004 of a smaller Makino A55 VIPER grinding machine to supplement conventional 5-axis CNC creep feed grinding on Blohm and Mägerle grinders.

The A55 was deployed mainly on machining blades and vanes for power generation to cope with increased demand, but also on machining varieties used in aero engines. A year later, a similarly sized Makino iGrinder G5, purpose built from the ground up for VIPER grinding, was installed to meet a further increase in demand.

It was the award in 2008 of a contract lasting well into the next decade to machine four varieties of larger vane for power generation that prompted investment in the new VIPER production cell. It was installed at the end of 2008 in a new satellite factory opposite Trac’s main production facility in Crewe. Now in full production, it will grind a total of 186 engine sets of vanes during the life of the contract.

Craig Barnes, the engineer in charge of the A99e cell, says: “I had experience of VIPER grinding at a previous company that produced aero engine blades for Rolls-Royce. The company steered us towards Makino/NCMT, which helped to develop the patented technology.

“We were very happy with the performance of our first two Makino cells, which proved to be reliable, more productive than creep feed grinders, and resulted in fewer scrapped parts. We decided to continue with the same technology when the new power gen vane work was secured.”

He explains that conventional grinders are slow to set-up for a new job and tend to suffer from coolant leaks, valve problems and sundry other niggles such as frequent alarm messages. None of these shortcomings apply to the VIPER process on Makino platforms, which are reliable production centres right from the outset.

More features can be ground in a single set-up on a VIPER grinder, which saves refixturing time and promotes higher accuracy as well, leading to less scrap and non-conformance. A single operation on a Makino A55 takes typically four set-ups during non VIPER production.

For example, conventional grinding of a fir tree and root wedge face plus all shroud features on a nickel alloy casting requires four separate operations on CNC grinders, plus there is a significant amount of handling time. The same blade is completed much faster on a Makino A55 or G5 in two operations, owing to the increased metal removal rate. There is also less set-up time and work in progress.

Average batch size on these machines is 300 off, requiring monthly changeover, although one aero engine blade job ran continuously on the A55 for nine months at a rate of 220 parts per week.

All of the benefits of the VIPER approach are being achieved when producing the larger vanes on the A99e, with the added benefit of less downtime during changeover due to offline component fixturing and robotic exchange of fixtured vanes.

In the case of two of the vane varieties, a small amount of milling and drilling on one vane per engine set is required to allow subsequent internal boroscopic inspection. It highlights another useful benefit of VIPER grinding on a machining centre, in that other metalcutting tools can be brought into use from the same tool magazine that houses the small diameter, profiled grinding wheels.

Such has been the success of VIPER grinding at Crewe that Trac is constantly migrating its existing blade and vane work across from conventional grinders to the Makino machines. They are also the automatic choice for new work as it is won.

NCMT
www.ncmt.co.uk