## 4 PBF-LB/M Process
### Process Optimization
#### 4.2.3 Process Monitoring and Quality Control to Improve Component Life Service
This monitoring approach is crucial for managing residual stresses and maintaining dimensional accuracy, as it enables the early identification of anomalies, such as local contaminations or distortions resulting from thermal stresses or material inconsistencies. Beyond detecting defects and managing residual stresses, in situ melt pool monitoring is essential for gaining insights into the material properties of the final part. Numerous studies have shown that the microstructure, including grain size and phase composition, is largely determined by the solidification rate and thermal history of the melt pool [171; 172]. By observing melt pool characteristics, process parameters can be adjusted to optimize cooling rates, which in turn directly influence the microstructure and mechanical properties of the part. For instance, faster cooling rates can result in finer microstructures leading to improved strength and hardness. [PERSON] et al. [173], through the use of synchrotron radiation, investigated the effects of different laser powers and scanning speeds affected crystallographic texture and lattice defects. Their findings revealed that higher laser power and scan speed promoted a strong crystallographic orientation, while lower settings did not. Although the importance of real-time monitoring of melt pool characteristics is long-established, the importance of maintaining a feedback loop cannot be underestimated. Real-time feedback allows for adaptive process control, where laser parameters (such as power, speed, and focus) are dynamically adjusted based on the observed melt pool behavior. This dynamic adjustment ensures that melt pool conditions remain consistent, which is crucial for achieving uniform part quality and minimizing defects. A study explored the implementation of a feedback control system in layer-wise laser melting processes, utilizing optical sensors to enhance process precision [174]. The research specifically focused on monitoring the melt pool thermal profile through infrared thermography. This technique enables the real-time observation of thermal deviations from the target temperature profile. When such deviations are detected, the system dynamically adjusts the laser power to correct the temperature discrepancies. This feedback mechanism is crucial for maintaining a stable thermal environment within the melt pool, thereby promoting uniform part quality and mitigating common defects, such as porosity and cracking. The quality of the melt pool also affects the surface finish and dimensional accuracy of the printed parts. It was proved that a stable and well-controlled melt pool results in smoother surfaces and better adherence to the intended geometry. In a study [168], advanced in situ monitoring systems, including coaxial high-speed cameras and off-axis imaging, were employed to observe and record the behavior of the melt pool during the PBF-LB/M process. These systems captured essential data such as melt pool temperature and intensity. The gathered data were utilized to construct detailed melt pool signature maps, which were subsequently integrated into a neural network model to predict the surface topography of the printed layers accurately. By identifying melt pool temperature as a critical predictor of surface characteristics, the study facilitated real-time adjustments to process parameters, such as laser power and scanning speed. A comprehensive review of the published studies related to in situ monitoring techniques utilized in metal powder bed fusion was carried out by [PERSON] et al. [175]. The authors detailed how the continuous analysis of melt pool characteristics enhances the understanding of the interplay between process parameters and material properties. This insight is crucial for the refinement of process parameters, thereby contributing to improved repeatability and reliability in the production of high-quality components.