Helical milling hole finishing of Inconel 718 parts manufactured by laser powder bed fusion

Additive manufacturing through laser powder bed fusion (LPBF) has evolved into a key manufacturing process, but machining is still crucial to improve part quality. Holes in LPBF parts present poor accuracy, and helical milling with conventional endmills can be a suitable operation to finish holes in printed metal parts. Due to its superior properties, Inconel 718 is widely applied in aero-engine parts, requiring high reliability. However, Inconel 718 presents a tendency of machining hardening, being classified as a difficult-to-machine material. This work investigates the finishing through helical milling of holes in parts of Inconel 718 obtained through LPBF. LPBF parts of Inconel 718 were obtained with pre-holes and these were finished through helical milling. Holes of LPBF parts may present significant geometrical error. The results indicate that helical milling is suitable for improving the quality of LPBF holes. LPBF parts obtained with the laser scan angle of 67 \(^{\circ }\) $_{}^{\circ }$ with thermal treatment presented higher grain refinement and precipitates, resulting in the highest cutting forces and roughness. Cutting force patterns presented a significant correlation with geometrical error variation. Process modeling highlighted the most influential LPBF and helical milling parameters on cutting forces and roughness. The axial and tangential feeds presented directly and inversely proportional effects on cutting forces, respecting the kinematics and undeformed chip volumes. Finally, bi-objective optimization was performed to guide the choice of the best conditions to achieve improved roughness and lowest cutting forces.