PSI - Issue 42

Saveria Spiller et al. / Procedia Structural Integrity 42 (2022) 1239–1248 Saveria Spiller/ Structural Integrity Procedia 00 (2019) 000 – 000

1243

5

the material more viscous than a regular polymer it was fundamental to keep the nozzle temperature high to avoid a non-homogeneous deposition.

wedges, delamination

a1)

a2)

a)

inhomogeneous deposition

poor shape retention

warping

b1)

b)

b2)

Fig. 3. a) STL file of a hollow 1x1x1cm 3 cube; the printing parameters used are listed in Table 1 under Trial 1 (a1) and Trial 2 (a2); b) STL file of the solid cube; the printing parameters used are listed in Table 1 under Trial 3 (b1) and Trial 4 (b2) Some parameters sets used are reported in Table 1. The most promising are listed as trials 5, 6, and 7. Those were also used to print larger boxes (1.5×1.5×1cm 3 ), shown in Fig. 4. This was done to facilitate the polishing and the study of the surface. On these larger specimens, several studies were performed. First, the surface roughness was assessed using a digital microscope (Infinite Focus Alicona, Austria). The density of the specimen was measured using the Archimedes method. To qualitatively assess the porosity of the green parts, the commercial software Image J was used on pictures of polished cross-sections of the solids. The results of these analyses are listed in the table below. Finally, with the three best configurations, tensile specimens were printed and tested. The specimens were modeled following the design used by Kurose et al. (2020) in a study about MEAM where tensile specimens were printed out of a filament composed of binder and 316L metal powder. For each of the three configurations, three specimens were printed to assess the repeatability of test results. All the specimens were printed flat and in the center of the building platform (see Fig. 2c). The tests were carried on using a universal testing machine with a load cell of 5kN (MTS Criterion Model 42), with a displacement rate of 2 mm/min. The values of the average ultimate tensile strength obtained from the tensile tests of the green parts are also reported in Table 1 for each configuration.

Table 1: some of the printing parameters used to print preliminary specimens with corresponding green parts characteristics

Porosity

UTS* [MPa]

TRIAL

Nozzle temp [°C]

Layer thickness [mm]

Cooling fan speed

Printing speed [mm/s]

Flow rate multiplier

Ra [µm]

Density [g/cm 3 ]

1 2 3 4 5 6 7

270 280 280 280 295 280 295

0.2 0.2 0.1 0.2 0.1 0.1

100% 100%

60 70 30 45 15 15 30

100% 100% 100% 100% 100% 100% 100%

/ / / /

/ / / /

/ / / /

75% 75%

100% 100% 100%

2.94 3.42 2.66

4.87 5.16

6.23% 8.08% 3.71%

10.53±1.03 10.03±0.17 10.01±0.34

0.05

4.9