Gemma Barsby stated that Rolls Royce had been investigating DMLS since 2004/2005 with the cooperation of the University of Birmingham where a DMLS facility had been set up on the campus. The initial focus was on developing optimised shapes for aero engine components, she said, whilst at the same time seeking to achieve weight savings without compromising performance, and to improve the ‘fly-to-buy’ ratio for aero engine components.
Barsby stated that more than 500 DMLS components have been produced in the development phase of the DMLS process at Rolls Royce for test rig validation, and the results have led to advances in engine technology especially for the advanced T1000 and the Trent XWB engines produced by the company.
The lead time in producing prototypes using DMLS for test rig validation has been cut by up to 95% compared with cast materials resulting in significant cost reductions, said Barsby.
Further advantages of the DMLS process were the ability to cut expensive waste through eliminating many machining steps normally required, improved shape accuracy, and to achieve better material integrity compared with castings. This has been especially the case since nickel-base superalloy prototypes started to be produced by DMLS in the Rolls Royce R&D programme in 2008, stated Barsby.
The introduction of new fine powder-based superalloys such as IN 718 and IN 625 required for the DMLS process, and the need to transform the traditional supply chain for cast and wrought products to cater for the new DMLS process, has required a complete culture shift at Rolls Royce, said Barsby.
Each new powder and component supplier has to be validated for sensitive aero engine parts, and validation can cost over £1 million each time a new material is introduced. Nevertheless Ben Penny, Leader of the Rapid Prototyping Facility at Rolls Royce, stated during the joint presentation that the results of physical testing on engine test rigs had already brought many positive results. He showed an aero engine gearbox which had been redesigned to achieve weight savings of 70% by using DMLS, and a single piece, highly complex aero engine casing with integral blade and cooling channels also produced by the DMLS process.
Although no DMLS superalloy parts are actually flying, Penny did not rule out the possibility of their future use in aero engines with research already underway on post-DMLS processing such as heat treatment, EDM and hot isostatic pressing to evaluate part properties and performance.
DMLS technology is ideal for low volume part production, he said. The company is already using DMLS to produce complex moulds for the lost wax investment casting process.