STREAM SBO POLYFORCE - SIM-Flanders€¦ · SBO POLYFORCE The search for laser sinterable polymers:...

STREAM

SBO POLYFORCE

The search for laser sinterable polymers:

identification of key material parameters

Leander Verbelen

Introduction

October 2013 – SIM/SBO Polyforce 2

• Polyforce consortium

Peter Van Puyvelde/Paula Moldenaers

KU Leuven

Chemical Engineering

Bart Goderis

KU Leuven

Chemistry

Jean-Pierre Kruth

KU Leuven

Mechanical Engineering

Ludwig Cardon

UGent

CPMT

machine

development

polymer

processing

material

behaviour

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

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




benchmark PA12











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 Tm

• low Tc

2. Minimize shrinkage

• crystallization shrinkage

• amorphous polymers

Strategy 1: maximize processing window


Benchmark: PA12

Tm

Tc

Tbed



Benchmark: PA12

1) Flexible melting point

• effect of annealing

• large crystal unit cell

• perfect crystal structure

resulting from powder

production process



Benchmark: PA12

2) Flexible crystallization point

• effect of postcondensation

• good for sintering, bad

for recyclability



Benchmark: PA12

2) Flexible crystallization point

• Postcondensation confirmed by rheology and GPC

PA12 virgin

PA12 recycled

PA12 virgin

PA12 recycled

PA12 printed

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



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



• Sintering coalescence

• Function of viscosity and surface tension




benchmark PA12











WP2: production of polymeric powders

M 15

Different ways of powder production

resulting in different particle morphologies

• straight from the reactor

• solution precipitation

• cryogenic milling

impact on powder behavior, powder flow!

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

Powder flow


Angle of Repose

• powder angle in rotating

jar

• quick and easy

• consistent results

• link with SLS?

Powder flow


Angle of Repose

• e.g. powder with increasing amounts of flow enhancing

additives

Conclusions



benchmark PA12:

large processing window, at the cost of limited recyclability

screening methodology:

DSC, rheology/coalescence, VT-data


investigate powder flow:

angle of repose, future SLS-like setup

investigate influencing parameters:

particle morphology, temperature, moisture

• Other workpackages underway!

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