Machining mechanics of additively manufactured metallic parts: Material characterization and constitutive modeling

Abstract

Additive manufacturing (AM) enables the production of complex, customized parts through its layer-by-layer process. However, high surface roughness and geometrical distortions often necessitate post-processing, with machining being the most widely used method. Therefore, understanding the machinability of AM parts is essential for selecting appropriate tooling and machining parameters. This requires insight into the material’s microstructure and mechanical behavior, which are significantly influenced by AM process conditions. Rapid solidification and steep thermal gradients inherent to AM processes result in distinct crystallographic textures and columnar grain growth, which affect the material’s response during machining. Due to inconsistent experimental findings in the literature, there is a need for microstructure-informed constitutive modeling. This study presents a comprehensive constitutive model to predict flow stress and cutting forces during orthogonal cutting, incorporating key strengthening mechanisms: thermal activation, solid solution, lattice resistance, grain boundary influence, and forest dislocation interactions. AM Inconel 718 which is widely used in critical industrial applications was fabricated using laser powder bed fusion (LPBF). Microstructural features and solute atom concentrations were characterized using electron backscatter diffraction (EBSD) and energy-dispersive X-ray spectroscopy (EDS), providing input for the constitutive model. Model validation was performed through orthogonal cutting experiments under various cutting conditions. Cutting forces were measured using a dynamometer, and chips were examined via scanning electron microscopy (SEM). The model predicts flow stress and cutting forces within 10 % of experimental values. Moreover, it enables a quantitative evaluation of each strengthening mechanism’s contribution, providing insight into their individual effects on the machining behavior of AM-fabricated parts.