Recently, a new methodology for 5-axis flank computer numerically controlled (CNC) machining, called double-flank machining, has been introduced (see “5-axis double-flank CNC machining of spiral bevel gears via custom-shaped milling tools—Part I: Modeling and simulation”). Certain geometries, such as curved teeth of spiral bevel gear, admit this approach where the machining tool has tangential contact with the material block on two sides, yielding a more efficient variant of flank machining. To achieve high machining accuracy, the path-planning algorithm, however, does not look only for the path of the tool, but also for the shape of the tool itself. The proposed approach is validated by series of physical experiments using an abrasive custom-shaped tool specifically designed for a particular type of a spiral bevel gear. The potential of this new methodology is shown in the semifinishing stage of gear manufacturing, where it outperforms traditional ball end milling by an order of magnitude in terms of machining time, while keeping, or even improving, the machining error.

Productivity in the manufacture of aircrafts components, especially engine components, must increase along with more sustainable conditions. Regarding machining, a solution is proposed to increase the cutting speed, but engines are made with very difficult-to-cut alloys. In this work, a comparison between two cutting tool materials, namely (a) cemented carbide and (b) SiAlON ceramics, for milling rough operations in Inconel^® 718 in aged condition was carried out. Furthermore, both the influence of coatings in cemented carbide milling tools and the cutting speed in the ceramic tools were analysed. All tools were tested until the end of their useful life. The cost performance ratio was used to compare the productivity of the tested tools. Despite the results showing higher durability of the coated carbide tool, the ceramic tools presented a better behavior in terms of productivity at higher speed. Therefore, ceramic tools should be used for higher productivity demands, while coated carbide tools for low speed-high volume material removal.

Fracture toughness anisotropy is a key concern in IN718 components produced by Laser Powder Bed Fusion (LPBF), due to their strong crystallographic texture and characteristic lamellar microstructure. In this study, the effect of grain orientation on fracture toughness was evaluated by testing two LPBF IN718 builds with the same laser scanning strategy (R0), but with two different orientations: vertical (R0-0) and 45° inclined (R0-45) relative to the build direction. The mechanical response was assessed through compact tension (CT) tests following ASTM E399 and ASTM E1820 standards. Results show that the R0-45 specimens exhibited a fracture toughness nearly 2.5 times higher than R0-0 specimens. Detailed microstructural analysis, supported by EBSD and SEM, reveals that the higher toughness in the R0-45 orientation is linked to a combination of smaller effective grain size along the crack path, higher levels of geometrically necessary dislocations (GND), and increased kernel average misorientation (KAM), which collectively enhance plastic accommodation and crack-tip shielding. These findings support and reinforce the established understanding of the relationship between microstructure and anisotropic fracture behavior in LPBF IN718, facilitating its practical application in the design and orientation of additively manufactured components.

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 $$^{\circ }$$ ∘ 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.