PSI - Issue 18

Dan Ioan Stoia et al. / Procedia Structural Integrity 18 (2019) 163–169 Dan Ioan Stoia, Liviu, Marsavina/ Structural Integrity Procedia 00 (2019) 000–000

165 3

Fig. 1 Geometry of the specimen according to ASTM D 5045-99

The geometry was built without notch in order to prevent the undesirable deformations that might occur during manufacturing process. The samples were virtually arranged in the building environment at 0, 45 and 90 degrees in XY plane, respecting to the transversal axis (X) of the machine. In order to exclude the influence of process parameters on mechanical and geometrical characteristics, these were considered constants for all samples in all orientations. The numerical values can be found in the table 1.The energy density is a measure of laser power, velocity and scan spacing; T 1 and T 2 are the temperatures of the building and extraction environments; the scaling factor represents a uniform geometrical increase in all directions, introduced in order to compensate the shrinkage at cooling. Images showing the parts growing inside the building envelope are presented in Fig. 2.

Table 1. Process parameters used in manufacturing of samples

S S (mm)

ED (J/mm

2 )

T

1 (°C)

T 2 (°C)

t (mm)

f (%)

P (W)

v (mm/s)

25

2000

0.25

0.05

170

159

0.1

2.2

(a) (b) Fig. 2. Snapshot of the actual SLS process: a) Samples oriented at 0 deg.; b) Samples oriented at 45 deg.

The manufacturing process has ended by cooling the parts in machine’s environment for 6 hours. After complete cooling, the samples were removed from the building envelope and blasted for cleaning off all the excess powder. All samples were then measured and weighted using a digital caliper of 0.05 mm resolution and a digital balance of 0.01 g resolution. Because the geometry at this stage has no notch, the next step was to machine the notch geometry of the half of the samples using a horizontal head milling machine. 2.2 Mechanical tests The mechanical test was carried on 5 kN Zwick machine, using 3-point bending configuration. The opening between pin supports was 80 mm and the loading pin was placed in the middle section. A total number of 30 samples (15 without notch and 15 with notch) were tested to the breaking point using a constant 5 mm/min velocity and a recording sampling frequency of 600 Hz.