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

645

7

Another significant difference between GV curves generated by using different scanning strategies was the standard deviation. Scanning strategies differ for each layer by rotating and shifting the exposure patterns between subsequent layers. Therefore, even though cross-sections of the part do not change throughout the built, length of the hatching lines may change thus heat applied for each layer may show some changes. Idle time seem to have decreased the standard deviation of the curve of mean GV, thus suggesting it may provide more steady heat input during a built. Geometry of the parts dictate the GV graphs, by causing variations in the conduction rates as well as amount of heat applied. If the cross section of the part is getting smaller on building direction, it usually leads to drop in on the average GV. Which means, the amount of the heat applied on a layer is conducted to the previously built metal mass beneath the layer, therefore the amount of radiation emitted from the melting pool decrease. The decreasing trend of GV curve is firstly visible while the size of the cross section is reduced from grip section of tensile specimen of the gauge section. This can be seen between 8-11 mm of building heights in the Figure 9.

Figure 9 Mean GV curves along building height that are generated by data based on printing tensile specimens.

In contrast between the building heights of approximately 11 mm to 18 mm, there is a linear increase in the GV curve. This increase takes place even though, the cross section of the part does not change in between those building heights thus the amount of heat applied during exposure of each layer does not change. Therefore, such increase can be attributed to reduction in conduction rates. A possible cause of the dropping conduction rate might be due to the fact that the exposed layers are becoming further from the grip section of the tensile specimen as well as further from the building platform. From around 18 mm forward to 20 mm building height, parts cross section grows to reach grip section’s surface area. Which means the heat applied by the laser is increasing however there is a drop of approximately 3500 GV in average of the curve. This can be attributed to the pockets of solid mass in the prop supports which might have the capacity of storing heat.

Figure 10 Images that are generated by monitoring software for different scanning strategies and at different building heights.