# Emerging Trends in Hybrid Additive and Subtractive Manufacturing
## 3 Results and Discussion
### Articles Analysis
#### 3.2.1 Processes and Materials  
Although some of the reviewed articles [1; 2; 3; 4; 5] justify the emergence and usefulness of hybrid additive and subtractive manufacturing, literally, with the need to reduce the limitations of additive manufacturing, such as the lack of surface quality, and subtractive, including the waste of high-cost material, and the desire to take advantage of its strengths, the ability to generate complex geometries in the case of additive manufacturing and the great geometric, dimensional, and surface quality in the case of subtractive manufacturing, this idea underlies practically all of the selected works, assuming it in a natural and unquestionable way. [PERSON] et al. [1] developed an experimental investigation to relate LPBF (Laser Powder Bed Fusion) parameters with cutting forces and milling anisotropy of Incelel 718 parts, in the context of a hybrid additive-subtractive manufacturing flow. After highlighting the capacity of hybrid manufacturing to achieve complex geometries, they emphasize the need for the participation of subtractive manufacturing to provide the parts with the required surface, dimensional, and geometric quality. The rapid heating and cooling cycles of the parts manufactured by LPBF give rise to columnar grain structures, which consequently produce crystalline textures and anisotropy. This makes both the mechanical properties and the cutting forces depend on the spatial directions. Through a study based on a Taylor oblique cutting model, the microstructures of the parts manufactured by LPBF, the layer thickness and the cutting parameters are related. The authors make a relevant contribution by limiting machining parameters to a finishing context, given that the objective of additive manufacturing is to obtain near-net-shape parts. \begin{table}
\begin{tabular}{c c c c} \hline Additive–subtractive manufacturing & Dry milling & Laser melting deposition & Structural design \\ Anisotropy & Electron microscopy & LMD clad sensorization & Superalloys \\ Application Programming & Energy demand & LPBF & Support structures \\ Interface (API) & Fatigue life extension & Manufacturing processes & Surface characterization \\ Ball end milling & Fatigue repair & Maraging steel & Surface integrity \\ CAD/CAM & FDM & Mean stress effects & Surface roughness \\ CF/PEEK & Feedback control & Metal 3D-printing & Surface treatment \\ CNC machining & Grain boundary density & Microcontroller & Sustainable manufacturing \\ Computer-Aided & Heat treatment & Milling & Taguchi method \\ Manufacturing & Heterogeneous precursors & Modelling & Taylor factor \\ Configuration cooling & High-speed machining & Monitoring System & Tensile properties \\ Channels & High-speed milling & Paw & Thin-walled parts \\ Construction rules & Hybrid & & \\ Control systems & additive–subtractive & Peek & Titanium alloy \\  & Hurwitz & & \\ Cost & additive/subtractive & Polymer-derived ceramics & Toolpath planning \\  & manufacturing & & \\ Crack arrest & Hybrid directed energy & Porosity & WAAM \\  & deposition & & \\ Cryogenic machining & Hybrid manufacturing & Post-processing processes & Wire and laser additive \\  & system & & manufacturing (WLAM) \\ Crystallographic effect & Hybrid process chain & Process chain & Wire arc additive \\ \hline \end{tabular}
\end{table} 
Table 6: _Cont._Research shows that although the influence of the crystalline structure on cutting forces is reduced when working with low VED (Volumetric Energy Density), this increases the impact of grain shape. Under these conditions, the increase in the density of the boundary grain requires lower cutting forces for a tool axis parallel to the main grain axis. On the contrary, they are higher for planes of the shear bands transverse to the columnar grains [1]. [PERSON] et al. [2] conducted a review of the scientific literature published on the manufacturing of molds with conformal cooling (CC), integrating L-PBF and CNC milling in a hybrid flow.