ISO/ASTM TR 52952:2023
(Main)Additive manufacturing of metals — Feedstock materials — Correlating of rotating drum measurement with powder spreadability in PBF-LB machines
Additive manufacturing of metals — Feedstock materials — Correlating of rotating drum measurement with powder spreadability in PBF-LB machines
This document provides an example of the relation between the characterization of certain macroscopic properties of metallic powders and their spreadability in an PBF-LB/M AM machines. This relation is based on a new technique combining measurements inside a PBF-LB/M machine and image processing developed to quantify the homogeneity of the powder bed layers during spreading. In this document, the flowability of five metal powders are investigated with an automated rotating drum method, whose dynamic cohesive index measurement is shown to establish a correlation with the spreadability of the powder during the layer deposition operation. Furthemore, the particule size distribution (PSD) and morphology of each powder is characterized before testing by static image analysis method (according to ISO 13322-1). The general principle of the method is described in Figure 1.
Fabrication additive de métaux — Matières premières — Corrélation de la mesure du tambour rotatif avec la capacité d'étalement de la poudre dans les machines PBF-LB
Le présent document fournit un exemple de la relation entre la caractérisation de certaines propriétés macroscopiques des poudres métalliques et leur étalabilité dans les machines PBF-LB/M de FA. Cette relation repose sur une nouvelle technique combinant les mesurages à l’intérieur de la machine PBF-LB/M et le traitement d’image, développée pour quantifier l’homogénéité des couches du lit de poudre pendant l’étalement. Dans le présent document, la coulabilité de cinq poudres métalliques est étudiée en utilisant une méthode automatisée avec un tambour rotatif, dont le mesurage de l’indice de cohésion dynamique est représenté pour établir une corrélation avec l’étalabilité de la poudre pendant l’opération de dépôt des couches. De plus, la distribution granulométrique (PSD) et la morphologie de chaque poudre sont caractérisées avant l’essai par une méthode d’analyse d’image statique (conformément à l’ISO 13322-1). Le principe général de la méthode est décrit à la Figure 1.
General Information
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Standards Content (Sample)
TECHNICAL ISO/ASTM TR
REPORT 52952
First edition
2023-06
Additive manufacturing of metals —
Feedstock materials — Correlating
of rotating drum measurement with
powder spreadability in PBF-LB
machines
Fabrication additive de métaux — Matières premières — Corrélation
de la mesure du tambour rotatif avec la capacité d'étalement de la
poudre dans les machines PBF-LB
Reference number
© ISO/ASTM International 2023
© ISO/ASTM International 2023
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ii
© ISO/ASTM International 2023 – All rights reserved
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Designation . 2
5 Methodology .2
5.1 General principle . 2
5.2 Powder selection . 3
5.3 Layer homogeneity evaluation . 3
5.4 Rotating drum . 4
6 Results and discussion .5
6.1 Spreadability . 5
6.2 Rotating drum analysis . 7
6.2.1 Experimental protocol . 7
6.2.2 Experimental results . 7
6.3 Discussion . 9
7 Conclusions .10
8 Additional data .11
9 Perspectives .12
Bibliography .13
iii
© ISO/ASTM International 2023 – All rights reserved
Foreword
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www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 261, Additive manufacturing, in
cooperation with ASTM Committee F42, Additive Manufacturing Technologies, on the basis of a
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ISO/ASTM standards on additive manufacturing, and in collaboration with the European Committee for
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iv
© ISO/ASTM International 2023 – All rights reserved
Introduction
Granular materials and fine powders are widely used in industrial applications. To support control and
optimize processing methods, these materials have to be precisely characterized. Characterization
methods are related either to the properties of the grains (granulometry, morphology, chemical
composition, etc.) or to the behaviour of the bulk powder (flowability, density, blend stability,
electrostatic properties, etc.). The complex behaviours of granular and powder materials have motivated
the development of numerous techniques to obtain reproducible and interpretable results. Many
industries are concerned in different fields: additive manufacturing, food processing, pharmaceuticals,
bulk material handling. This document is focused on Additive Manufacturing (AM).
Metallic powders are widely used in AM processes involving powder bed fusion (PBF-LB/M PBF-EB/M
etc.) or binder jetting. During such operations, successive thin layers of powder are deposited with a
blade or with a rotating cylinder. Each layer is then fused (most commonly melted) by an energy beam
or joined by an adhesive binder to build the parts. The layer thickness defines the vertical resolution
of the process; a thin layer leads to a better resolution. In order to obtain a thin layer, the powder is as
fine as possible. However, if it is assumed that among the cohesive forces, the Van der Waal forces are
[25]
predominant, it can be stated that as the grain size decreases, cohesiveness typically increases . This
increase in cohesiveness could have an impact on the spreadability of a powder.
The quality of the parts built with AM is thus directly influenced by powder flow properties.
According to ISO/ASTM 52900, spreadability is the ability of a feedstock material to be spread out in
layers that fulfil the requirements for the AM process; this includes the ability to form a flat powder-
atmosphere interface without waves and irregularities.
Visual observation of layer homogeneity is usually the only way for operators to assess the spreadability
of powders during the spreading of new layers. However, linking the powder characteristics to its
spreadability during the layer deposition beforehand can provide a more cost-effective way to classify
and select the optimal powder and layer deposition speed combinations.
v
© ISO/ASTM International 2023 – All rights reserved
TECHNICAL REPORT ISO/ASTM TR 52952:2023(E)
Additive manufacturing of metals — Feedstock materials
— Correlating of rotating drum measurement with powder
spreadability in PBF-LB machines
1 Scope
This document provides an example of the relation between the characterization of certain macroscopic
properties of metallic powders and their spreadability in an PBF-LB/M AM machines.
This relation is based on a new technique combining measurements inside a PBF-LB/M machine and
image processing developed to quantify the homogeneity of the powder bed layers during spreading.
In this document, the flowability of five metal powders are investigated with an automated rotating
drum method, whose dynamic cohesive index measurement is shown to establish a correlation with
the spreadability of the powder during the layer deposition operation. Furthemore, the particule size
distribution (PSD) and morphology of each powder is characterized before testing by static image
analysis method (according to ISO 13322-1).
The general principle of the method is described in Figure 1.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO/ASTM 52900, Additive manufacturing — General principles — Fundamentals and vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO/ASTM 52900 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
cohesiveness
physical powder behaviour relating to the degree to which the attractive forces between particles
exceed the average particle mass
Note 1 to entry: Cohesive powders are qualified as powders where the attractive force between particles exceed
the average particle mass
3.2
powder flowability
ability of a solid bulk material to flow
Note 1 to entry: Powder flowability is a function of multiple factors, and particularly powder size and distribution,
see also ISO/ASTM 52907.
© ISO/ASTM International 2023 – All rights reserved
4 Designation
In this document, five powders described in Table 1 are used:
Table 1 — Designation of powders
Denomination used in this
Common designation European spefication
document
1)
Scalmalloy® AlMgSc AlMgSc_Std
2)
Inconel® NiCr Mo Nb NiCr Mo Nb_Std
22 9 22 9
AlSi Mg AlSi Mg AlSi Mg_Std
7 7 7
Titanium Fine Ti Al V Ti Al V_Fine
6 4 6 4
Inconel® Fine NiCr Mo Nb NiCr Mo Nb_Fine
22 9 22 9
5 Methodology
5.1 General principle
The general principle for comparing rotating drum measurements with powder spreading in a
PBF-LB AM machine is described in Figure 1.
Key
1 AlSi Mg
2 NiCr Mo Nb (inconel® fine)
22 9
a
Good.
b
Bad.
c
Rotating drum.
d
PBF-LM machine.
e
Regular layer.
f
Irregular layer.
Figure 1 — General principle of comparing rotating drum measurements with powder
spreading in a PBF-LB AM machine
1) Scalmalloy is an example of a suitable product available commercially. This information is given for the
convenience of users of this document and does not constitute an endorsement by ISO of this product.
2) Inconel is an example of a suitable product available commercially. This information is given for the convenience
of users of this document and does not constitute an endorsement by ISO of this product.
© ISO/ASTM International 2023 – All rights reserved
5.2 Powder selection
The recoating performance of the powders inside a PBF-LB AM machine is evaluated experimentally
with in situ observation of layer homogeneity. Five metallic powders are selected for this study: two
Nickel alloys (NiCr Mo Nb_Std and NiCr Mo Nb_Fine), two Aluminium alloys (AlSi Mg_Std and
22 9 22 9 7
AlMgSc_Std) and one Titanium alloy (Ti Al V_Fine). Particle size distribution (PSD) is summarized in
6 4
Table 2 and shape and morphology in Table 3.
Table 2 — Summary of the PSD (D10 and D90) of the five powders (volume)
D10 D90
Powder
µm µm
AlMgSc_Std 26 66
AlSi Mg_Std 27 69
NiCr Mo Nb_Std 17 45
22 9
NiCr Mo Nb_Fine 6 27
22 9
Ti Al V_Fine 7 28
6 4
Table 3 — Shape and morphology comparison
Aspect ratio comparison
Mean P10 P50 P90
Aspect ratio (number)
µm µm µm µm
AlMgSc_Std 79,7 62,5 81,6 93,8
AlSi Mg 76,6 58,4 78,7 91,8
NiCr Mo Nb_Std 81,9 63,5 85,3 94,6
22 9
NiCr Mo Nb_Fine 81,8 63,5 85,8 93,3
22 9
Ti Al V_Fine 79,7 60,9 82,9 92,8
6 4
Bluntness comparison
Mean P10 P50 P90
Bluntness (number)
µm µm µm µm
AlMgSc_Std 74,6 54,0 74,6 95,1
AlSi Mg 75,5 57,1 75,5 93,8
NiCr Mo Nb_Std 84,3 67,9 86,7 97,2
22 9
NiCr Mo Nb_Fine 88,0 76,5 89,9 97,1
22 9
Ti Al V_Fine 85,0 70,2 87,4 96,5
6 4
Successive powder layers are deposited in the PBF-LB AM machine with no laser melting. Between
each layer deposition, a picture of the powder layer is taken by a staring camera placed inside the AM
machine. The pictures are then processed numerically to evaluate the layer homogeneity. Three powder
spreading speeds are investigated: 30 mm/s, 80 mm/s and 160 mm/s to highlight their influence on the
layer quality.
5.3 Layer homogeneity evaluation
The powder layer surface homogeneity is experimentally evaluated using a staring camera placed
orthogonal to the powder bed. After each powder spreading operation, a picture is taken. For this
experiment, the focus is made on metallic coater and 30 µm layer thickness only. For the same recoater
speed, 15 layers are created and therefore, 15 pictures are taken as well. This methodology provides a
quantitative and operator independent way to quantify the layer topography homogeneity.
© ISO/ASTM International 2023 – All rights reserved
The gathered pictures are then processed numerically to obtain "Interface Fluctuation”, a measure of
the inhomogeneity of the produced layers. The image processing analysis principle is as follow:
a) each picture is analysed separately. The picture size is 1 200 pixels × 1 200 pixels;
b) horizontal and vertical pixel intensity profiles are extracted at discrete positions of the picture [see
Figure 2 a)];
c) an average “smooth” profile is computed for each position [see Figure 2 b)];
d) interface fluctuation is then computed based on the deviation around the averaged profile, and
then averaged over all positions;
e) the process is repeated for all images, and the interface fluctuation is averaged over the whole set
of pictures.
b) Pixel intensity profile (plain) and average
a) Horizontal and vertical lines from which
profile (dashed) used to compute the interface
pixel intensity profiles are extracted
fluctuation
Key
X position along the line
Y pixel intensity (before normalisation)
AlSi Mg (top)
NiCr Mo Nb_Fine (bottom)
22 9
Figure 2 — In situ layer quality assessment
5.4 Rotating drum
Powder flowability is evaluated with a rotating drum method which allows an automated measurement.
A horizontal cylinder with transparent sidewalls called drum is filled with the sample of powder. The
filling ratio of the drum can influence the flow of the powder and thus is kept constant to allow relevant
comparison of the results.
The volume of the drum used in this study is 100 ml and the filling ratio is fixed as 50 %. Therefore, a
50 mL powder sample is used for the measurements.
The drum rotates around its axis at an angular velocity ranging from 2 r/min to 60 r/min. A CCD
(charge-coupled device) camera takes snapshots at a framerate of 1 image per second for each angular
velocity.
© ISO/ASTM International 2023 – All rights reserved
The air/powder interface is detected on each snapshot with an edge detection algorithm.
Afterwards, the average interface position and the fluctuations around this average position are
computed. The number of snapshots taken influences the statistical relevance of the averaged interface.
[18]
In this experiment and, based on previous studies , a value of 40 is chosen for each rotating speeds.
[27]
This value is considered sufficient to guarantee accurate and reproducible measurements .
The number of revolutions performed during the measurement is dependant on the rotating speed.
However, the rotating drum allows a continuous flow of material regardless of the angular position of
the drum and number of revolutions, justifying the use of a fixed number of snapshots taken whatever
...
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