The search for laser sinterable polymers: identification of key material parameters Leander Verbelen

Transcription

1 STREAM SBO POLYFORCE The search for laser sinterable polymers: identification of key material parameters Leander Verbelen

2 Introduction Polyforce consortium machine development Jean-Pierre Kruth KU Leuven Mechanical Engineering Ludwig Cardon UGent CPMT polymer processing material behaviour Peter Van Puyvelde/Paula Moldenaers KU Leuven Chemical Engineering Bart Goderis KU Leuven Chemistry October 2013 SIM/SBO Polyforce 2

3 Introduction Laser sintering process wide possibilities for part design fast, no tooling required rapid prototyping increasing demand for end-use parts additive manufacturing Limited range of sinterable polymers PA12, PA11, TPU October 2013 SIM/SBO Polyforce 3

4 Polyforce workpackages WP1: definition of laser sinterable polymer materials benchmark PA12 screening methodology strategies to find new materials WP2: production of polymeric powders for SLS different ways of powder production investigate powder flow WP3: improvement of sinterability blends and reinforcements WP4: SLS testing and SLS process development optimize SLS process for new materials WP5: validation and application October 2013 SIM/SBO Polyforce 4

5 Polyforce workpackages WP1: definition of laser sinterable polymer materials benchmark PA12 screening methodology strategies to find new materials WP2: production of polymeric powders for SLS different ways of powder production investigate powder flow WP3: improvement of sinterability blends and reinforcements WP4: SLS testing and SLS process development optimize SLS process for new materials WP5: validation and application October 2013 SIM/SBO Polyforce 5

6 WP1: Definition of laser sinterable polymers Principal problem when trying new polymers for SLS: warpage due to differential shrinkage! bad part quality Strategies to overcome this: 1. Maximize processing window high T m low T c 2. Minimize shrinkage crystallization shrinkage amorphous polymers October 2013 SIM/SBO Polyforce 6

7 Strategy 1: maximize processing window Benchmark: PA12 T c T bed T m October 2013 SIM/SBO Polyforce 7

8 Strategy 1: maximize processing window Benchmark: PA12 1) Flexible melting point effect of annealing large crystal unit cell perfect crystal structure resulting from powder production process October 2013 SIM/SBO Polyforce 8

9 Strategy 1: maximize processing window Benchmark: PA12 2) Flexible crystallization point effect of postcondensation good for sintering, bad for recyclability October 2013 SIM/SBO Polyforce 9

10 Strategy 1: maximize processing window Benchmark: PA12 2) Flexible crystallization point Postcondensation confirmed by rheology and GPC PA12 virgin PA12 recycled PA12 printed PA12 virgin PA12 recycled October 2013 SIM/SBO Polyforce 10

11 Strategy 2: minimize shrinkage Semi-crystalline polymers vs. amorphous polymers Not easy to measure shrinkage, very few commercial setups P-V-T: high pressures V-T: non-contact (optical) dilatometers with confining fluid October 2013 SIM/SBO Polyforce 11

12 Strategy 2: minimize shrinkage 1. Semi-crystalline polymers polymers with intrinsically low shrinkage addition of fillers 2. Amorphous polymers high viscosity in the melt problem of sintering coalescence look for ways to increase coalescence October 2013 SIM/SBO Polyforce 12

13 Strategy 2: minimize shrinkage Sintering coalescence Function of viscosity and surface tension October 2013 SIM/SBO Polyforce 13

14 Polyforce workpackages WP1: definition of laser sinterable polymer materials benchmark PA12 screening methodology strategies to find new materials WP2: production of polymeric powders for SLS different ways of powder production investigate powder flow WP3: improvement of sinterability blends and reinforcements WP4: SLS testing and SLS process development optimize SLS process for new materials WP5: validation and application October 2013 SIM/SBO Polyforce 14

15 WP2: production of polymeric powders Different ways of powder production resulting in different particle morphologies straight from the reactor solution precipitation cryogenic milling impact on powder behavior, powder flow! M 15

16 Powder flow Importance of powder flow smooth spreading, no stripes high packing density part density and accuracy How to measure powder flowability? few techniques exist: angle of repose, powder rheometer mostly no direct link to powder flow in laser sintering October 2013 SIM/SBO Polyforce 16

17 Powder flow Angle of Repose powder angle in rotating jar quick and easy consistent results link with SLS? October 2013 SIM/SBO Polyforce 17

18 Powder flow Angle of Repose e.g. powder with increasing amounts of flow enhancing additives October 2013 SIM/SBO Polyforce 18

19 Conclusions WP1: definition of laser sinterable polymer materials benchmark PA12: large processing window, at the cost of limited recyclability screening methodology: DSC, rheology/coalescence, VT-data WP2: production of polymeric powders for SLS investigate powder flow: angle of repose, future SLS-like setup investigate influencing parameters: particle morphology, temperature, moisture Other workpackages underway! October 2013 SIM/SBO Polyforce 19