Numerical and experimental study on double coaxial gas assisted water jet guided laser machining of superalloy

Abstract

To achieve more uniform gas film and higher working temperature, the design of film holes on combustion section parts of aero engine is developing towards three trends: smaller diameter, higher aspect ratio and more quantity. To realize the high quality manufacture of small film holes with high aspect ratio, a new water jet guided laser (WJGL) machining method based on double coaxial assistant gas was proposed in this article. An outer coaxial gas jet with high density was added to the existing coaxial jet of water and helium. That outer coaxial gas jet can weaken the interference effect of reverse water and sweep out the low speed water in deep blind hole. The sweep effect of outer coaxial assistant gas was confirmed by simulation and experimental results. The penetration time of Ф0.7 mm holes with depth of 4 mm decreased from 410 s to 173 s with the help of outer coaxial assistant gas. A series of Ф0.7 mm holes with the aspect ratio of 14.6:1 were machined using double coaxial assistant gas WJGL method on superalloy specimens with thermal barrier coatings (TBCs). The roughness of side wall was better than 0.6 μm, and no breakage or stratification was found at the interface of TBCs and matrix. This method can also be used in the manufacture of SiC/SiC ceramic matrix composites (CMCs) parts with deep small holes.