## 3 Materials and Methods
### Camera Set-Up and Machine Integration  
One of the main objectives of this study was to implement a suitable and low-cost process monitoring system for PBF-LB/P that allows both a simple set-up and operability as well as a permanent monitoring of the process without the need for complex experimental set-ups. It was also clearly shown that the non-machine-learning approaches to process the monitoring of PBF-LB/P and PBF-LB/M described in Section 1 were able to achieve the targeted results, but a complex test set-up with particularly cost-intensive measurement equipment was always required. Based on the comparison of different camera systems, it was decided to use the Raspberry Pi Camera Module 2 for further investigation in this study. This HD camera module uses a Sony IMX219 sensor with 3280 \(\times\) 2464 pixels and a maximum frame rate of 30 fps [74]. However, this inexpensive and readily available model has an operating temperature range of \(-\)20 \({}^{\circ}\)C to only 60 \({}^{\circ}\)C, which in turn raises the first considerations for a cooling option within the machine, as the temperature during the ongoing production process is more than 170 \({}^{\circ}\)C throughout. When the maximum operating temperature is reached, these components lose the signal due to their characteristics [75]. To summarize the key requirements for the cooling system, the camera housing should be additively manufactured and able to withstand a continuous operating temperature of 180 degrees. In addition, the camera lens must be flushed with nitrogen (N\({}_{2}\)) to avoid coating defects during the process due to evaporation effects. A camera housing was designed that is cooled via the machine's internal N\({}_{2}\) supply. There is virtually no information in the literature on solutions for cooling cameras or other measuring equipment used in the PBF-LB/P build chamber during the process. Only the study by [PERSON] et al. [25], in which the powder bed is measured using laser profilometry, mentions that the sensor is cooled inside the build chamber; unfortunately, no further information is available on the implementation of the cooling concept. The components for the camera housing were produced on a stereolithography system using a high-temperature polymer. When cured, the resin can withstand sustained temperatures of just over 200 \({}^{\circ}\)C [76]. The camera window is a 20 \(\times\) 20 \(\times\) 0.13 mm piece of glass glued in place with high-temperature silicone. An additional line was installed on the N\({}_{2}\) generator and routed into the machine's build chamber. This leads into the body of the camera housing so that the camera is cooled throughout. The N\({}_{2}\) then exits the other side of the housing and is returned to the housing via an additional line to flush the glass with an air-knife. The design of the cooling system is shown in Figure 8.  
Tapered and airtight, 1/8\" stainless steel fittings were installed, as shown in Figure 8. The positioning on the heating system was such that the entire powder bed could be captured at the best possible camera angle, as can be seen in Figure 9.  
In summary, this approach provides a low-cost solution to capture the complete powder bed surface of the PBF-LB/P system with a standard RGB camera. The design of the housing allows the camera to be cooled, ensuring long-term use under the process conditions, even over multiple build jobs. By using the machine's internal N\({}_{2}\) generator, no external supply of coolant is required. This system enables permanent process monitoring without complex and cost-intensive test set-ups and the generation of high-quality data for evaluation using CNN. Figure 8: The CAD Design of the cooled camera housing. The N\({}_{2}\) inlet (a), the outlet (b), the return (c), and the flushing of the lens via the air knife (d) can be seen. The housing consists of two parts that are screwed together and sealed with heat-resistant material. The camera is positioned and fixed inside the housing with screws.