Evaluation of surface integrity after high energy machining with EDM, laser beam machining and abrasive water jet machining of alloy 718
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Development of future aero engine components based on new design strategies utilising topological optimisation and additive manufacturing has in the past years become a reality. This allows for designs that involve geometries of “free form” surfaces and material combinations that could be difficult to machine using conventional milling. Hence, alternative manufacturing routes using non-conventional high energy methods are interesting to explore. In this investigation, the three high energy machining methods abrasive water jet machining (AWJM), electrical discharge machining (EDM) and laser beam machining (LBM) have been compared in terms of surface integrity to the reference, a ball nosed end milled surface. The results showed great influence on the surface integrity from the different machining methods. It was concluded that AWJM resulted in the highest quality regarding surface integrity properties with compressive residual stresses in the surface region and a low surface roughness with texture from the abrasive erosion. Further, it was shown that EDM resulted in shallow tensile residual stresses in the surface and an isotropic surface texture with higher surface roughness. However, even though both methods could be considered as possible alternatives to conventional milling they require post processing. The reason is that the surfaces need to be cleaned from either abrasive medium from AWJM or recast layer from EDM. It was further concluded that LBM should not be considered as an alternative in this case due to the deep detrimental impact from the machining process.
KeywordsNon-conventional machining EDM Laser beam machining Abrasive water jet machining Surface integrity Residual stress EBSD Topography
Special thanks to GKN Aerospace Sweden AB for supplying test materials, information and expertise in the involved processes. The author would also like to acknowledge Swerea IVF, the KK-foundation and the SiCoMap research school for all support.
The majority of the results in this thesis work have been part of the research projects G5Demo-2 (Ref. no. 2013-04666) and SweDemo (Ref. no. 2015-06047) funded by VINNOVA, the Swedish Government agency within the Ministry of Enterprise.
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