PSI - Issue 34

Zoé Jardon et al. / Procedia Structural Integrity 34 (2021) 32–38 Zoé Jardon/ Structural Integrity Procedia 00 (2019) 000 – 000

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With this process parameter combination, the first sequence of operations is performed (printing, milling, drilling) for the different printing strategies. Note that the difference in print strategy as well as the laser power adjustment can implicate different material properties around the capillary w.r.t. the infill. This is an advantage of the first strategy, where no control of the material properties is required (since they remain uniform). The milling operation is firstly required to precisely locate the sample edge to start the new sequence. Secondly, undesired fatigue crack initiation is known to be triggered by poor surface quality, near surface defects (pores, lack-of-fusion) and higher roughness values. It is therefore also required to perform the milling operation on the contours and the top sample surface to avoid any crack initiation at the outer surface of the sample for future fatigue tests. The associated geometrical tolerance equals common milling tolerances around ~0.1 . After repetition of the sequence of operations, the samples are sawed off from the build-plates and subjected standard heat treatments for stress relief (2h, 450°C). The result is shown in the 3D view of Fig. 6. The 2 left samples are realized according to the print strategy 1 with optimal settings described above for the first sequence. For the second sequence powers = 500 W, = 450 W and = 550 W, = 400 W are used. For the third sample the first sequence is realized with strategy 1 and the second with strategy 2 and = 650 W, = 450 W (without drilling through the second -layers). The transition between the 2 sequences is indicated for all the samples with red dashed lines and is also associated with a color change due to the cooling rates induced by the re-print. The resulting capillary diameters are measured between 3.229 − 3.235 mm and the final sample dimensions of the samples correspond to (24-25)x(14-15)x(35-36)mm. The achieved printing tolerance is considered around ~0.5 .

2.3. Channel finish and surface roughness

Figure 6 : Micrograph analyses of hybrid samples considering different printing strategies (left). Roughness profiles (right).