Visco-elastic sintering kinetics in virgin and aged polymer powders

J.E Alvarez,H Snijder,T Vaneker,H Cheng,A.R Thornton,S Luding,T Weinhart

doi:10.1016/j.powtec.2021.11.044

J.E Alvarez, H Snijder + Show 5 more

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https://doi.org/10.1016/j.powtec.2021.11.044

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Journal: Powder Technology	Publication Date: Nov 24, 2021
Citations: 7	License type: cc-by

Affiliation: University of Twente

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This work provides a novel discrete element method (DEM) framework for modelling the visco-elastic sintering kinetics in virgin and aged polymer powders. The coalescence of particle pairs, over long times, is described by a combined three-stage model of the sintering process, where each stage is dominated by a different driving force: adhesive contact force, adhesive inter-surface force and surface tension. The proposed framework is implemented in MercuryDPM, an open-source package for discrete particle simulations. To quantitatively calibrate the particle-scale parameters, Bayesian filtering is used. Experimental data on Polystyrene (PS), Polyamide 12 (PA12), and PEEK powders, both virgin and aged, are analysed and confirm over a wide range of times the existence of the three distinct sintering mechanisms. In good agreement with the experimental observations, the estimation of sintering time is achieved with a significant accuracy compared to Frenkel's model. This study provides an efficient and reliable approach for future studies of strength evolution in powder-bed fusion processes.

Highlights

Selective laser sintering is a modern technique to build 3D objects from visco-elastic powders
Our main result is that the sintering of visco-elastic powders is accurately and quantitatively predictable, at both short and long time scales
This is successfully achieved in our discrete element method (DEM) framework by modelling the non-linear behaviour and including three different sintering mechanisms

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Introduction

Selective laser sintering is a modern technique to build 3D objects from visco-elastic powders. A laser beam heats selected particles resulting in solid sinter-necks at the contact points. It leads to a solidified surface layer, which is augmented with new powder deposition and their respective sintering. If the cohesion between particles is weak, texture defects arise on the sintered object such as delamination, distortion and dimensional inaccuracies [1,2]. An appropriate sintering time needs to be set to ensure sufficient cohesion among the particles. This sintering time depends on the powder properties and the specifications of the laser beam

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