Polymer Powders for Laser Sintering: Powder Production and Performance Qualification

Transcription

1 Polymer Powders for Laser Sintering: Powder Production and Performance Qualification Manfred Schmid 1, Marc Vetterli 1, Konrad Wegener 2 1 Inspire, Innovation Center for Additive Manufacturing Switzerland (icams) St. Gallen, Switzerland, manfred.schmid@inspire.ethz.ch 2 ETH Zürich, Institute for Production Technology and Tooling (IWF), Zürich, Switzerland 1

2 Additive manufacturing - overview

3 Laser Sintering process steps Re-coating process (blade, roller) Fluidization/Flowability Recoating device Fresh powder feeder Galvano mirror Compaction Building platform/piston Preparation of next layer (Build platform lowers of one layer thickness ~ mm ) Layer illumination (CO 2 laser scans layers of sliced CAD objects )

4 Laser Sintering material properties influences on SLS materials extrinsic proper0es Polymer intrinsic proper0es cryogenic milling liquid-liquid phase separa0on (precipita0on) Par0cle (shape, surface) melt blending Powder (PSD) transfer of a polymer into a powder for Laser Sintering trans- mission Op0cal reflexion absorp0on (10.6 μm) surface tension spray drying melt - viscosity (η 0 ) Rheology Powder density heatcapacity thermal conduc0vity Thermal flowability Powder rheology fluidisa0on cristallisa0on enthalpy mel0ng point crystallisa0on point LS-powder sinter window extrinsic proper,es: > Par,cle (produc,on) - shape - surface > Powder - rheology (flowability, fluidisa?on) - PSD (20-80 µm) intrinsic proper,es: > Thermal behavior - sintering window > Rheology - low zero viscosity > Op,cal proper,es - absorp?on 10.6 µm

5 Laser Sintering production variances Powder produc,on by precipita,on Duraform/PA2200 (PA12) Powder produc,on by milling/grinding Duraform Flex powder Rilsan PA11 powder PEEK Many others (non-commercialized) Technology summary 1. Dissolve polymer (PA12) in solvent (ethanol) at high temperature and pressure 2. Reduce pressure to let polymer precipitate from solu?on 3. Remove solvent by evapora?on 4. Collect powder Technology summary 1. Cool polymer to far below TM and/or Tg with LN2 2. Grind in specialized mill 3. Collect and op?onally sieve powder Powder produc,on by solu,on polymeriza,on Orgasol Invent Smooth PA12 Powder produc,on by melt blending icopp Technology summary 1. Start with an incompa?ble mixture of monomer and solvent 2. Add surfactant and s?r 3. Start polymeriza?on 4. Evaporate solvent and extract powder Technology summary 1. Mix polymer with a sufficiently large quan?ty (water-)soluble resin 2. Melt blending 3. Remove soluble phase with solvent 4. Remove solvent and extract par?cles

6 Laser Sintering Powder Bed Formation Influence of powder shape on flowability and fluidisation and powder bed formation Duraform PA12 Precipitation icopp Melt Blending Diapow PP 5220 Milling/grinding PA12 Black R&D Milling/grinding

7 Particles Shape Factors high Major Axis Minor Axis medium low Circularity (C cir ) Aspect ra?o (A R ) Solidity (S Sol ) Perimeter and Area are measured along with shape factors Most of the par?cles encountered in AM are rather based on ellipses than on perfect circles for polymers and metals Fi#ed ellipse by Image J Convex Hull 5*(780%(*23=49!(4%/[:4(*;424(]² How similar to a circle Information about form and surface!"= $%&'(!)*+/$*-'(!)*+ How elongated Information about form /'0*1*23=!(4%/5'-64)!(4% How dense Information about surface

8 Particles new shape factors

9 Particle Shape combined shape factors icopp E S = 1.04 ± 0.02 [-] PEBAX Black R&D E S = 1.19 ± 0.16 [-] Duraform PA12 E S = 1.06 ± 0.05 [-] DiaPow PP 5220 E S = 1.23 ± 0.19 [-] Orgasol E S = 1.11 ± 0.05 [-] PA12 Black R&D E S = 1.23 ± [-] Duraform FLEX E S = 1.16 ± 0.16 [-] Part. Diameter [µm] Aspect Ratio [-] Solidity [-] Part. Diameter [µm] Aspect Ratio [-] Solidity [-]

10 Elliptic smoothness - impact on LS processability icopp DF PA12 Orgasol DF Flex PEBAX Black R&D DiaPow PP 5220 PA12 Black R&D LS - PROCESSABILITY The shape distribu?on described by ellip?c smoothness (E s ) of the powder impacts greatly on part bed forma?on and LS processability.

11 Summary Many parameters need to be fulfilled for successful LS processing The shape of par?cles has a great impact à iden?fica?on of a suitable shape factor The ellip?c smoothness (E S ) helps differen?a?ng between LS powders LOW E S and narrow distribu,on of E S is of advantage for good processing Qualita?ve and quan?ta?ve comparison of powders possible with E s Confirma?on of shape effect on powder packing: tapped or bulk and hence on compressibility flowing behavior: avalanche angle and surface fractal Which have a decisive impact on the SLS processing

12 AM-team at Inspire icams Prof. K. Wegener Scien?fic Supervisor Chair of IWF ETH Zürich M. Schmid head R&D-SLS A. Spierings head R&D-SLM Marc VeNerli influence of powder on SLS-parts / surfaces Rob Kleijnen new powders and produc?on processes Fabrizio Verga Process development for ceramic materials Francesco Sillani process understanding and simula?on Thomas Bauer process engineering/ materials characterisa?on Philipp Stoll new applica?ons and func?onal structures Lukas Haferkamp powder understanding/ Simula?on and analysis Alexandre Staub advanced and new SLMconcepts

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