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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© inspire irpd – a joint project with the University of Applied Sciences St. Gallen

May 14th - 15th, 2013

Flowing Performance of SLS Powders at Elevated

Temperature

May 14th – 15th, 2013 Erfurt, Germany

Felipe Amado, M. Schmid & K. WegenerInspire AG - Institute for Rapid Product Development (irpd)

St. Gallen 9014, Switzerlandwww.inspire.ethz.ch


May 14th - 15th, 2013

Agenda

► Introduction of inspire IrpdOrganization & Core Competences

► SLS Polymer Powder CharacterizationState of the Art & Characterization Methods

► SummaryPrincipal Achievements & Future work

► Experimental Device & MethodologyOperational Principle & Experimental Set up

► Results & AnalysisFlowability - Fluidization at high Tº & SLS correlati on

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May 14th - 15th, 2013

Introduction


May 14th - 15th, 2013

Selective Laser Sintering (SLS), 3D-Printing (3DP)

LaserCUSING® (SLM)

Technologies

Rapid Prototyping (RP) Additive Manufacturing (AM)

Reverse Engineering

MedicalManufacturing

Process and Material Development

Introduction

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May 14th - 15th, 2013

SLS Polymer Powder Development

According to Dr. M. Schmid (inspire AG, Switzerland)

Absorption(10.6 µµµµm)


May 14th - 15th, 2013

Production Technology

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

spreading stepSource: Amado et al. 2011

SLS Polymer Powder Characterization

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May 14th - 15th, 2013

SLS Polymer Powder Characterization

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

Heap or pile angle of repose

Standard conditions (25ºC) DIN ISO 4324

Ring Shear Cell

Quasi-static powder stability on an annular

container under compression and shear

Failure locus of shear force versus normal

pressure

Standard conditions (25ºC) ASTM D6773

Bulk/Tap Density

Powder density ratio between a compacted and

loose state under mechanical tapping

Tap and bulk apparent powder density

Standard conditions (25ºC) ASTM D7481


May 14th - 15th, 2013

Experimental Device & Operational Principle

SLS powder spreading systems: Roller (3DSystems) & Blade (EOS) (adapted from Alscher 2000)

Schematic diagram of rotating and image acquisition system

Powder Stress State

Compacted

Loose

Measurement ConditionStatic Dynamic

SLS spreading

(φ 50 mm)

� Similar dynamic handling� Near stress state condition� Allows adjustments at different processing speeds� Temperature variation range: 30ºC-110ºC

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May 14th - 15th, 2013

Experimental Device & Indexes

- Drum speed +

Flowability Fluidization

Surface Fractal D :L : length estimate

ε : measurement scale

Test Index Definition

Flowability

AvalancheAngle

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


May 14th - 15th, 2013

Cumulative Avalanche Angle Distribution

Previous Results: Flowability (Room Temperature)

� Materials with a near spherical shape present the lowest avalanche angle and a narrow distribution (span).

� Powders with a broader particle morphological distribution increase their average value

� A second phase (mixture) has a mayor influence when different particle aspect ratios are present (HST v/s Alumide)

� Highly geometrical distorted particles depict a higher d50 and span

Increase of pile stability

Source: Amado et al. 2011

But what happens at higher

temperetaure?

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May 14th - 15th, 2013

� SLS Set Up:

� 2 semi-crystalline materials: icoPP (Inspire) & PA2200 (EOS)� Flowability and Fluidization analyses considered� 3 different temperatures for each material were selected:

- icoPP: 30ºC, 45ºC & 60ºC (powder sticks on surface)- PA2200: 30ºC, 70ºC & 110ºC (equipment limitation)

� Drum speed: - Flowability: 10 rpm- Fluidization: 50 rpm - 90 rpm

Experimental Set Up: RPA & SLS Tests

� RPA Heated Set Up:

� DTM Sinterstation 2000 machine� Solid cubes and hollow boxes (powder/sintered dens.)

Dimensions in mm

Solid cube

Hollow box

Upper Layer: Laser Power

variation

Lower Layer: Scan Spacing

variation

Previous work Actual

research

Low Speed

High SpeedLow Feed

Temperature LP variationSS variation

LP variationSS variation

MaterialRoller Speed

[mm/s]Feed

Temperature [ ºC]Part Bed

Temperature [ ºC]

icoPP 90, 180 45, 60 116

PA2200 90, 180 70, 110 171

Constant layer thickness (0.1 mm) & scan speed (5 m/s)

Target: To correlate RPA results with SLS Powder Packing Density


May 14th - 15th, 2013

20 30 40 50 60 70 800

100

200

300

400

500

Avalanche Angle icoPP [deg]

Cum

. A

vala

nche

Cou

nt [

N°]

30°C

45°C60°C

35

40

45

50

55

60

65

30ºC 45ºC 60ºCTemperature [°C]

Ava

lanc

he A

ngle

icoP

P [

deg]

20 30 40 50 60 70 800

100

200

300

400

500

Avalanche Angle PA2200 [deg]

Cum

. A

vala

nche

Cou

nt [

°N]

30°C

70°C110°C

40

50

60

70


Ava

lanc

he A

ngle

PA

2200

[de

g]

Results & Analysis: Flowability ( Heated Drum )

� 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

PA2200

Avalanche Angle Distribution

icoPP

D50

D50

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May 14th - 15th, 2013

1 2 3 4 5 60

100

200

300

400

500

Surface Fractal icoPP [/]

Cum

. A

vala

nche

Cou

nt [

N°]

30°C

45°C60°C

2

3

4

5


Sur

face

Fra

ctal

icoP

P [

/]

1 2 3 4 5 60

100

200

300

400

500

Surface Fractal PA2200 [/]

Cum

. A

vala

nche

Cou

nt [

°N]

30°C

70°C110°C

1

2

3

4

5

6


Sur

face

Fra

ctal

PA

2200

[/]

� 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)

Results & Analysis: Flowability ( Heated Drum )

icoPP

PA2200

Surface Fractal Distribution

Surface FractalRate

Temperature

∆=∆

Rate: 1.3e-2 [1/ºC]

Rate: 7.8e-3 [1/ºC]


May 14th - 15th, 2013

50 60 70 80 901.2

1.25

1.3

1.35

1.4

Tot

al V

ol E

xpan

sion

Rat

io [/

]

50 60 70 80 900

10

20

30

40

50

Flu

id V

ol F

ract

ion

[%]

50 60 70 80 901.2

1.25

1.3

1.35

1.4

Rotational Speed [RPM]

Tot

al V

ol E

xpan

sion

Rat

io [/

]

50 60 70 80 900

10

20

30

40

50

Rotational Speed [RPM]

Flu

id V

ol F

ract

ion

[%]

� 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

Results & Analysis: Fluidization ( Heated Drum )

30°C

45°C60°C

icoPP

PA2200

icoPP

PA2200

Total Vol. Expansion Fluidized Volume

Improved powder

rearrangement

∆T=40ºC

∆T=15ºC

High Fluidization Rate

Low Fluidization Rate

30°C

70°C110°C

30°C

45°C60°C

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May 14th - 15th, 2013

� Packing density values were normalized by 0.90 g/cm3 (icoPP) and 1.05 g/cm3 (PA2200) (datasheet values)

� icoPP achieves a higher normalized packing density in comparison to PA2200 for all parameter combinations

� As the powder deposition speed increases there is a slightly increase of the packing density

� For icoPP as the feed temperature increases, the packing density reduces its value

� Higher packing density is achieved for a:

- Lower Volume Expansion- Higher Fluidization Rate- Lower Surface Fractal-Tº Rate

Results & Analysis: SLS Packing DensityHollow

box

Lower Volume Expansion

Higher Volume Expansion

Higher Fluidization Rate

Lower Fluidization Rate

Higher Surface Fractal-Tº Rate

Lower Surface Fractal-Tº Rate


May 14th - 15th, 2013

0.05 0.1 0.15 0.2 0.250.6

0.7

0.8

0.9

1

0.05 0.1 0.15 0.2 0.250.6

0.7

0.8

0.9

1

Energy Density [J/mm3]

0.05 0.1 0.15 0.2 0.250.6

0.7

0.8

0.9

1

Nor

m. S

inte

red

Den

sity

[/]

0.05 0.1 0.15 0.2 0.250.6

0.7

0.8

0.9

1

Energy Density [J/mm3]

Nor

m. S

inte

red

Den

sity

[/]

� 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)

PA2200 LP

PA2200 SS

icoPP LP

icoPP SS

Low Feed Temperature High Feed Temperature

Low

Spe

edH

igh

Spe

ed

icoPP

PA2200

Solid cube

Scan Spacing variation (red)

Laser Power variation (blue)

Results & Analysis: SLS Sintered Density

2

3

4

1

1 23

4

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May 14th - 15th, 2013

Summary

� 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.


May 14th - 15th, 2013

Thanks for your attention!

Questions?

Documents

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 &