Flowing Performance of SLS Powders at Elevated …...Flowing Performance of SLS Powders at Elevated Temperature May 14 th – 15 th, 2013 Erfurt, Germany Felipe Amado, M. Schmid &
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Intrinsic characterization test Non-intrinsic characterization test Author/ Research
Group DSC TG MFI/ Rheo. *Others PSD Particle
Shape Tap/Bulk Density **Others
Powder mixing (polymer, fiber,
beads)
� � � � � � � � [7][10][12]
� � � � � � � � [13][14][15][16]
� � � � � � � � [17]
Melt mixing & cryogenic
grinding/spray drying
� � � � � � � � [18]
� � � � � � � � [19]
� � � � � � � � [11][20]
Dissolution-precipitation
� � � � � � � � [21]
� � � � � � � � [22]
� � � � � � � � [23]
Mechano-chemical alloying/
Solid state
� � � � � � � � [6][8]
� � � � � � � � [9]
� � � � � � � � [24]
Other characterization methods: *FTIR, EDX, XRD, etc.; **Angle Of Repose, Carr Index, etc.
� In general, extrinsic properties are barely reported or just not considered� Trial & error tests dominate over any preliminary characterization� Several authors achieve adequate intrinsic properties for processing, but fail during the
Which system suites the best powder characterization towards SLS?
� Not a general theory for powder behaviour is available � Results provided by each method are strongly dependent upon the
powder stress condition and packing (HR=Bulk/Tap widely used)� In principle all systems present complementary information� More accurate results for systems that emulate the final handling
condition� Temperature effect/variations are not taken into account with standard
methods
Powder Stress State
Compacted
Loose
Measurement ConditionStatic Dynamic
SLS spreading
Test Method Name
Measurement Concept
Characterization Parameters
Measurement Temperature
Measurement Procedure
Fluidimeter Dynamic powder
expansion under vertical fluid flow drag effect
Powder bed expansion height versus
upstream fluid flow
Standard conditions (25ºC) Not specified
Angle of Repose Vertical powder deposition through a funnel / orifice under the gravity effect
Angle obtained from a linear regression of the free surface at the maximum potential energy prior to the start of the powder avalanche occurrence
Surface Fractal
Fractal dimension D obtained from the free surface of the powder. D corresponds to a dimensionless parameter based on the self-similarity concept and constitutes a powder rearrangement indicator
Fluidization
Total Volume Expansion
Ratio
Ratio between the total volume measured inside the drum (expanded volume) and the volume occupied by the powder in the preparation sample container (tap density volume: 25 cc)
Fluidized Volume
Fraction of the total volume that develops a fluidized state defined by quasi-horizontal powder surface inside the drum
� 2 semi-crystalline materials: icoPP (Inspire) & PA2200 (EOS)� Flowability and Fluidization analyses considered� 3 different temperatures for each material were selected:
� At 30ºC (or close to room temperature) the avalanche angle distribution of icoPP presents a lower median and narrower distribution in comparison to PA2000
� In case of icoPP the avalanche angle distribution remains almost constant with an increase of the drum temperature (no statistically difference between medians at a significance level of 5%)
� In case of PA2200 at the highest temperature the avalanche angle distribution presents a slight increase above its median. However the differences are not statistically significant
� At 30ºC (or close to room temperature) the surface fractal distribution of icoPP presents a considerable lower median and narrower dispersion in comparison to PA2000
� In case of icoPP the surface fractal distribution continuously increases with an increment of the drum temperature (statistically differences between medians at a significance level of 5%)
� In case of PA2200 at the lowest temperature the surface fractal distribution presents a high median and broad dispersion of values.
� At 70ºC a significant reduction is observed, even below icoPP results. The authors relate this effect with the transition above the glass point (~50ºC)
� As the rotational speed increases both materials experience a higher total volume expansion ratio and fluidized volume
� In case of icoPP the total volume expansion curve presents a non-linear expansion rate in contrast to the linear behavior of PA2200
� As the temperature increases icoPP presents a vertical shift of the volume expansion curves. In case of PA2200 the total volume expansion experiments a first reduction from 30ºC to 70ºC. This reduction corresponds to a better rearrangement of the particles in concordance with the surface fractal behavior
� The fluidization rate is higher for icoPP in comparison to PA2200
� The normalized density achieved for icoPP is higher in comparison to PA2200 and correlates with the comparative higher initial packing deposition
� icoPP curves present less sintered density variations in comparison to PA2200 due to the higher part bed temperature (closer to the onset point than PA2200)
� Scan space variation curves present equal or lower values than laser power variation curves (particularly at lower energy density values)
� A new powder characterization system has been introduced that emulates a near SLSspreading stress state when the powder is mechanically agitated inside a turning drum atelevated temperatures.
� The commercial powders PA2200 (EOS) and icoPP (Inspire) were studied in detail andthe correlation with the SLS powder packing density was presented.
� New aspects regarding the dynamic powder behavior characterization were analyzedand correlated to SLS process conditions: Avalanche Angle constitutes a first roughinvariant estimator about powder flowability, but Surface Fractal, Volume ExpansionRatio and Fluidized Volume parameters enhance the detailed analysis.
� This research was limited to semi-crystalline materials. Analyses of other thermoplasticmaterials are going to be addressed in the future.
� These results can be used to complement the existing methods to achieve a moreaccurate and detailed understanding about SLS powder suitability and thus reduce thepowder development cycle time.