Novel testing device and routine to characterise the spreadability of powders for powder bed fusion processes – a problem-oriented approach

Figures & data

Figure 1. Spreading tester [32].

Figure 2. Internal setup of the feeder/builder [32].

Figure 3. Mounted blade [32].

Figure 4. Attachment for polymer blades [32].

Figure 5. Mountable blades (1 and 2: polymer blades with different shapes; 3: HSS blade with rhombic shape) [32].

Figure 6. Simplified spreading routine inspired by an EOS machine [12].

Figure 7. Simplified spreading routine inspired by a Concept Laser machine [12].

Figure 8. Position of the examined spots [15].

Figure 9. Sufficiently large (left) and too small (right) range to fit at least the smallest particle [32].

Figure 10. Special feature of the surface of a spread powder layer [30].

Figure 11. Different surfaces with the respective lowest and highest marked particle and the resulting deviation of height (ΔH_par).

Figure 12. Cumulative distribution of the height of all found particles referring to the exemplary surfaces illustrated in Figure 11 with the respective marked first (Q₁) and third quartiles (Q₃).

Figure 13. Detailed triangulation of four pixels (left) and different ways of triangulation (right) [32].

Figure 14. Schematically description of the equalising volume (V_equ).

Figure 15. Cross-section of the builder.

Figure 16. Enlarged cross-section of the builder with the marked spots for measuring the height differences in red (h_cylinder, h_platform and h_cover) and the marked additional volumes (V_p, and V_c).

Figure 17. Dummy for measuring the surface coverage of a single spread powder layer.

Figure 18. Technical drawing of the upper part of the dummy.

Figure 19. Cube-shaped RGB colour space (left) and cone-shaped HSV colour space (right).

Figure 20. Crisp two-dimensional image (left) and masked B/W image (right).

Figure 21. Crisp two-dimensional image of a magnified area from Figure 20 (left) and the corresponding masked B/W image (right).

Figure 22. SEM image of the plasma spheroidised IN718 powder used.

Table 1. Volume-related characteristic d-values (d_{10, 3}, d_{50, 3}, d_{90, 3}) and volume-related sphericity (SPHT3).

d10, 3 [µm]	d50, 3 [µm]	d90, 3 [µm]	SPHT3 [/]
22.9	33.3	44.6	0.967

Table 2. Basic powder characteristics (FR = flow rate; ADH = apparent density measured using a Hall funnel; ADA = apparent density measured using an Arnold Meter; TD = tap density) of the plasma spheroidised IN718 powder used.

FT [s/50 g]	ADH [g cm^−³]	ADA[g cm^−³]	TD [g cm^−³]
10.1 ± 0.1	4.67 ± 0.02	4.83 ± 0.01	4.96 ± 0.01

Table 3. Surface roughness-related (ΔH_par, ΔQ_par, V_equ, A, n_par) arithmetic mean values (x_i) including their standard deviation (s_i) of the five single measurements and the weighted mean value $\left(\overline{x}\right)$, its standard deviation $\left(\overline{s}\right)$ and relative standard deviation (RSD) calculated from this.

	ΔHpar [µm]	ΔQpar [µm]	Vequ [mm³]	A [mm²]	npar [/]
x1 ± s1	74.5 ± 5.1	19.9 ± 0.5	(1.74 ± 0.03) E-02	4.76 ± 0.04	937 ± 13
x2 ± s2	77.9 ± 2.8	21.0 ± 1.1	(1.82 ± 0.03) E-02	4.87 ± 0.05	934 ± 26
x3 ± s3	75.1 ± 4.0	20.1 ± 1.3	(1.75 ± 0.02) E-02	4.75 ± 0.05	966 ± 29
x4 ± s4	77.3 ± 6.7	20.1 ± 1.2	(1.77 ± 0.03) E-02	4.78 ± 0.06	946 ± 15
x5 ± s5	66.7 ± 2.5	18.0 ± 0.9	(1.58 ± 0.04) E-02	4.55 ± 0.04	983 ± 29
$\overline{\mathrm{x}}$	72.8	19.7	1.74E-02	4.72	945
$\overline{\mathrm{s}}$	3.5	0.8	2.98E-04	0.04	19
RSD [%]	4.81	3.97	1.71	0.91	1.99

Table 4. Arithmetic mean values (x_i) including their standard deviation (s_i) of the surface coverage (ψ) of the five single measurements and the weighted mean value $\left(\overline{x}\right)$, its standard deviation $\left(\overline{s}\right)$ and relative standard deviation (RSD) calculated from this.

	Ψ [%]
x1 ± s1	35.4 ± 0.9
x2 ± s2	34.6 ± 1.6
x3 ± s3	35.8 ± 1.7
x4 ± s4	33.8 ± 2.3
x5 ± s5	33.9 ± 1.8
$\overline{\mathrm{x}}$	35.0
$\overline{\mathrm{s}}$	1.4
RSD [%]	3.98

Table 5. Powder bed density (ρ_pb) of the five single measurements (x_i), arithmetic mean value (x_ave), its standard deviation (s_i) and relative standard deviation (RSD).

	ρpb [g cm^−³]
x1	4.81
x2	4.80
x3	4.80
x4	4.82
x5	4.83
xave	4.81
si	0.01
si – %	0.24

Table 6. Measured filling characteristics of the plasma spheroidised IN718 powder used listed in increasing order: ADH = apparent density measured using a Hall funnel; ρ_{pb, EOS} = powder bed density measured using an EOS-inspired spreading strategy; ADA = apparent density measured using an Arnold Meter; ρ_{pb, CL} = powder bed density measured using a Concept Laser-inspired spreading strategy; TD = tap density.

ADH [g cm^−³]	ρpb, EOS [g cm^−³]	ADA [g cm^−³]	ρpb, CL [g cm^−³]	TD [g cm^−³]
4.67 ± 0.02	4.81 ± 0.01	4.83 ± 0.01	4.87 ± 0.00	4.96 ± 0.01

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