# Emerging Trends in Hybrid Additive and Subtractive Manufacturing
## 3 Results and Discussion
### Articles Analysis
#### 3.2.1 Processes and Materials
The objective of CC is to achieve faster and more homogeneous cooling than that obtained with conventional channels. Throughout their systematic review, they focus on the additive manufacturing of multimaterial molds, such as 316L stainless steel/H13 hot work steel or steel/Cu combinations, after which they conclude that monomaterial additive manufacturing presents higher quality. They also conclude that the great capacity of hybrid additive and subtractive manufacturing to achieve higher standards in the production of parts with complex geometry, with high surface, geometric, and dimensional quality, becomes especially relevant and applicable in the mold manufacturing industry with conformal cooling (CC), since with traditional processes it would be impossible to provide the channels with the characteristics and qualities obtained through the integration and alternation of additive and subtractive subprocesses within the same manufacturing flow [2]. [PERSON] et al. [40] conduct a practical investigation to study the quality of hybrid additive and subtractive manufacturing (PAW-WAAM and milling) of Ti6 Al-4V titanium parts. The study is focused on PAW (Plasma Arc Welding), a type of WAAM (wire arc additive manufacturing) technology, and its feasibility is validated in combination with CNC milling. In fact, it is concluded from the study that the wall manufactured in their experiments meets aeronautical standards and does not present significant variations due to the position and orientation of the samples analyzed. Neither does the torque change significantly when performing up-milling or down-milling, although up-milling does improve surface quality. Torque is not affected by cutting depth, but it is affected by speed. Surface quality also improves when the tool approaches the clamping system. The work of [PERSON] et al. [41] presents comparative models of costs and accumulated energy demand of subtractive and hybrid additive-subtractive processes. These models consider the complete life cycle, including the operations that follow the hybrid manufacturing phase, such as final surface machining or the removal of support structures. The research proposes models based on hybrid additive and subtractive manufacturing of Ti-6 Al-4V parts through Electron Beam Melting and turning. The use phase is also considered. In the model, variables include the shape, the possibilities for part lightening, and the usage time. To compare the subtractive and hybrid processes, the premise is that both can meet the geometric requirements, which indicates the eminently economic focus of the study. Different approaches are alternated in the study: identical part; weight reduction thanks to additive manufacturing; focus on improving usage conditions. Although the study concludes that the hybrid process is the most advantageous from the point of view of energy demand, it does not go so far as to affirm the same from an environmental or economic perspective, as these are highly conditioned by the geometry or recyclability of the materials. [PERSON] et al. [3] conduct a technical review of hybrid manufacturing processes of metallic parts present in the scientific literature. Within this study, hybrid additive and subtractive manufacturing is addressed, identifying pairs of materials and processes such as 6511 Steel through SLM-milling (selective laser melting-milling), 316L Steel through DED-milling, ER2319 aluminum alloy through Laser Cold Metal Transfer, or 316 Stainless Steels through directed energy deposition--Process Laser Remelting Process. [PERSON] et al. [42] conduct an experimental study to analyze the mechanical properties and microstructure of 316L stainless steel parts manufactured through hybrid additive and subtractive manufacturing (DED and milling). For the fabrication of the designed hexagonal parts, a five-axis hybrid machine, Mazak VC500A/5x AM, was used. Both porosity and part distortion during the process were studied.