PSI - Issue 77

Y. Bakir et al. / Procedia Structural Integrity 77 (2026) 639–648 Y.Bakir et al./ Structural Integrity Procedia 00 (2026) 000–000

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Figure 1 Off-axiss observation scheme[4].

The machine has additional monitoring system equipment. As it can be seen in the Figure 1 , the view axis of the camera does not align with the axis of the laser beam. This method is called off-axis observation. Therefore, instead of observing each melt pool created by the laser, the camera is constantly observing the entire building platform of a machine.

Figure 2 Location of the thermal camera and mirror with respect to the building platform of the machine that is used for the experiment.

Figure 2 is a photograph of the machine that is used for the experiments. Thermal camera is mounted to the building chamber with an off-axis configuration. View of the camera is adjusted with a mirror to focus on the building platform. According to Planck’s law metals emit their peak radiation at melting roughly around 1500 K by near infrared light spectrum. In this work a camera equipped with a Complementary Metal Oxide Semiconductor(CMOS) sensor is used. Such sensors are more sensitive to record infrared radiation wavelengths(0.78-1 µm)[3], [5]. Therefore, with this set up camera only captures radiation emitted by the melting of the material and it does not take real time photographs. The heat applied to the material by the laser mainly converts raw material in loose powder form to the solid metal. And a significant amount of heat is transferred to the ambient through radiation and convection and another substantial amount of heat is conducted to the previously melted material and also to the raw material around melt pool. Conduction and radiation of the heat are important aspects of process monitoring that took place for this work.

Figure 3 Schematics of laser and powder interaction and heat transfer modes such as conduction, radiation and convection[6].

Material choice of use for this work is EOS Maraging Steel MS1. This material has the chemical composition of %18Ni Maraging 300 according to US classification and 1.2709 according to European system.