Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Anisotropy in ultra-precision machinability of additively manufactured Inconel 718 alloys

Yuchao Bai, Yunfa Guo, Hao Wanga

Department of Mechanical Engineering, College of Design and Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117575, Singapore


Laser powder bed fusion (LPBF) is highly effective at fabricating metal functional components with complex geometries. However, the poor surface quality of the as-built components necessitates post-machining to meet the high precision requirement. Ultra-precision machining can obtain nanoscale surface roughness through micro-scale material removal, which is a promising process for improving the surface quality of the LPBFed parts. The bottom-up manufacturing method and rapid solidification of the LPBF process result in anisotropy in microstructure and mechanical properties, which will highly affect the machinability of the LPBFed metal parts, especially in ultra-precision machining. At present, this effect is not thoroughly understood. In this study, microstructure and microhardness on the XY and XZ planes of Inconel 718 part fabricated using the LPBF process were characterized first. Then, orthogonal cutting experiments were conducted on the corresponding planes to study the anisotropy in machinability using ultra-precision machining, including cutting force, surface topography and chip morphology. In addition, the effect of cutting speed on the machining process was also investigated systematically. The results show that the LPBFed Inconel 718 alloy has an apparent building-direction-dependent anisotropy in machinability, which corresponds to the microstructure and microhardness. Two distinct microstructural features were observed on the XY and XZ planes, respectively. The side flow on the XZ plane is much severer than that on the XY plane during orthogonal cutting, thereby leading to poor microgroove quality. In addition, the cutting force on the XZ plane is much higher (more than 37.7%) and fluctuates more significantly than that on the XY plane. This study provides an in-depth understanding of the micro-machining of additively manufactured metal parts as well as a reference for improving the surface quality through post-processing.

Keywords: Hybrid manufacturing, Ultra-precision machining, Laser powder bed fusion, Microstructure, Cutting force, Machinability

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