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Engineering Science in
Additive Manufacturing Impact of machine factors on PBF part surface quality

The argon gas was blown from the inert gas outlet on 3.4. Effect of build position
the right of the build chamber. Spattering and soot were The average Ra of each part is defined as the average
formed during the rapid laser melting process. Although value of its front, back, left, and right surfaces’ Ra values
most spattering and soot were expected to be blown away (Equation I):
from the powder bed working area, a portion of this
spattering and soot would still fall onto the powder bed, R (sample) = average (R [front] + R [back] + R [left] + R
a
a
a
a
a
affecting the surface quality if it fell onto the edges of the [right]) (I)
fabricated parts. This issue became more significant for In this study, a twin laser PBF system was used. The
those parts placed on the left part of the building areas laser positions are marked as “X” in Figure 6. Detailed data
because more spattering and soot were generated from the of all 20 parts and their positions are shown in Figure 6.
right areas. Parts placed near the center of the laser, such as parts 2, 3,
In addition, Figure 5 shows that the standard deviation 6, 7, 14, 15, 18, and 19, had a better surface quality in the
of the Ra increases gradually when the distance to the gas range of 15 – 20 μm. Parts placed further away from the
flow outlet increases from 20.0 mm to 120.0, 160.0, and center of the laser, such as parts 1, 4, 8, and 13, had poorer
260.0 mm, with the same number of measurements and surface quality in the range of 25 – 35 μm.
parts at each location. When parts were placed further The effect of building positions was analyzed.
from the gas outlet, unpredictable spattering and soot Figure 7 and Table 5 show the average Ra compared to the
would have a more significant impact on the parts’ Ra. distance of the fabricated parts from the center of the laser
Moreover, while the argon gas flow speed was maintained spot positions. Ra values of PBF fabricated parts increased
inside the build chamber, its effectiveness in removing gradually when the parts were placed further away from
the spattering and soot decreased when the parts were the center of the laser spot location.
further away from the gas outlet position. A sintered wall
was used at the argon gas outlet to ensure a laminar flow When the parts were placed further away from the
was blown into the build chamber. Turbulence would still center of the laser spot, the laser spot became more
be formed in the chamber, especially in spaces further A B
away from the gas flow outlet. Such turbulence would
also bring some spattering and soot back to the powder
bed in the left area, affecting the as-built parts’ surface
quality.

Table 4. Surface roughness for all surfaces against their
distance to the gas flow outlet
Distance to gas Part number Average surface Figure 6. The position of parts in the build chamber and their overall
flow outlet (mm) roughness (µm) surface quality. (A) Overall surface quality of the parts. (B) Positions of
20.0 4, 5, 16, 17 20.7±2.5 parts with labeling.
Note: The “X” marks in (B) indicate the laser position in the powder
70.0 10, 11 21.4±2.1
bed fusion system. Red circles indicate regions close to the center of the
120.0 3, 6, 15, 18 20.4±3.1 laser, whereas green circles indicate further regions. The parts included
160.0 2, 7, 14, 19 22.3±3.5 in rectangles in (A) correspond to the parts included in the circles of the
same color in (B).
210.0 9, 12 25.1±1.1
260.0 1, 8, 13, 20 26.4±5.7

Figure 5. Standard deviation of the parts’ surface roughness against their Figure 7. Surface roughness for all surfaces against their distance to the
distance to the gas flow outlet center of the laser spot

Volume 1 Issue 2 (2025) 5 doi: 10.36922/ESAM025240014