## 5 Post-Processing
### Strategies to Reduce Surface Post-Processing Operations
The material is melted along paths parallel to the component contour, either before or after the infill. The scan parameters can be optimized to reduce surface roughness. In general, it was stated that higher energy input ensures more uniform melt tracks, smoothing out peaks and valleys through re-melting [199]. [PERSON] et al. [205] investigated the impact of contour parameters on surface roughness and their effect on the fatigue performance of PBFed Scalmalloy(r). They stated that the application of optimized contour parameters yielded a 10-20% improvement in fatigue properties compared to the condition without contour scans. Most research has focused on the roughness of the top face of components, while some studies have also examined the roughness of other faces and overhanging surfaces. [PERSON] et al. [206] conducted a study to assess the impact of process parameters on the overhanging surface roughness of AlSi10 Mg specimens fabricated without support structures, at various build angles (30, 45, and 60\({}^{\circ}\)). The parameters analyzed included infill laser power, infill scanning speed, infill scanning angle, contour laser power, and contour scanning speed. The findings revealed that contour process parameters exerted a significantly greater influence on surface roughness compared to infill parameters. Moreover, the effect of these parameters on surface roughness decreased as the build angle increased, with contour scanning speed identified as the most critical factor. In order to reduce as much as possible experimental studies with consequent waste of dust, energy, and cost, a lot of attention is currently being paid to the development of models based on machine learning techniques to predict how various parameter combinations impact surface roughness and dimensional accuracy in the final PBFed components [207]. Although process parameter optimization has proven to be a successful ally in optimizing the component surface roughness by maximizing its dynamic mechanical properties and limiting post-processing operations, the average roughness in PBF-LB/M production is always above the 3.2 \(\upmu\)m required in aerospace applications [208]. In addition, post-processing machining becomes necessary when contact surfaces are present or when the dynamic properties of the component are particularly stressed during service [209]. Such a need is rendered particularly pronounced when Al-based alloys are involved. In fact, Al-based alloys processed for PBF-LB/M have been shown to have much higher surface roughness than Ni-, Ti-, or steel-based alloys, making them inapplicable in specific industrial applications [131]. In order to undergo post-processing operations, the component must be detached from the additive platform, brought onto a workbench, and subjected to one or more machining operations with possible repositioning. This results in laborious manual operations, downtime, and additional costs, making the process unsustainable. Hybrid manufacturing, which encompasses various combinations of processes and mechanisms, plays a pivotal role in enhancing sustainability by optimizing material usage, reducing energy consumption, and streamlining production stages. This approach effectively addresses the productivity challenges associated with traditional AM, such as extended production times and high per-unit costs, by leveraging the strengths of multiple manufacturing techniques. By consolidating production steps and minimizing the number of machines required, hybrid manufacturing not only improves operational efficiency but also strongly aligns with sustainability goals, promoting resource conservation and waste reduction [210,211]. In hybrid AM, additive processes are combined with subtractive techniques, such as CNC machining, to optimize material properties, precision, and dimensional tolerances [212].