Physical characteristics of selective laser sintering of metal—polymer powder composites

Powder flowability is key to achieving high process stability and part quality by application of smooth and dense layers in selective laser sintering (SLS). This study sheds light on the rarely investigated effect of tribo-electric charge build-up during powder delivery in the SLS process. This is achieved by a novel approach to quantify electrostatic potentials during doctor blading. The presented model setup is used in combination with charge spectrometry and impedance spectroscopy to investigate the alterations in tribo-electric charging behavior for the most commonly used laser sintering material polyamide 12 in its virgin and aged, c.f. reused, states. We show that the electrostatic charge build-up is significantly enhanced for aged polymer powder material, likely contributing to altered performance in SLS processing.

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3D Modeling of Additive Manufacturing Process: The Case of Polymer Laser Sintering

Volume 10: Fluids Engineering ◽

10.1115/imece2020-23550 ◽

2020 ◽

Author(s):

Lan Zhang ◽

M'hamed Boutaous ◽

Shihe Xin ◽

Dennis A. Siginer

Keyword(s):

Selective Laser Sintering ◽

Laser Sintering ◽

Heat Diffusion ◽

Laser Scattering ◽

Transient Phenomena ◽

Powder Bed ◽

Process Characteristics ◽

Polymer Powder ◽

Volume Method ◽

Air Diffusion

Abstract This work focusses on studying multiphysical transient phenomena in polymer powders occurring during selective laser sintering in polymers powders. Multiple phenomena stemming from the interaction of the laser with the polymer powder bed and the transfer of the laser power to the powder bed including laser scattering and absorption, polymer heating, melting, coalescence, densification, and the variation of the material parameters with the temperature are simulated via the modified Monte Carlo-ray tracing method coupled with the Mie theory. A finite volume method is adopted for the heat transfer. The model couples heat diffusion, melting, coalescence and densification of the polymer grains, and the crystallization kinetics during the cooling steps. Laser intensity is concentrated on the surface of the material contrary to the predictions of the Beer-Lambert law. Laser acting on thermoplastic material cause the polymer powder melt, coalescence between melted grains, air diffusion versus densification, crystallization and volume shrinkage. All these processes are simulated by a series of multiphysical models. The reliability of the modeling is tested by comparison with experiments in the literature, and a parametric analysis is performed, based on the process characteristics such as laser sweep speed, its intensity and shape, polymeric grain size among others. Several recommendations to optimize the process are proposed.

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A Test Part for Evaluating the Accuracy and Resolution of a Polymer Powder Bed Fusion Process

Journal of Mechanical Design ◽

10.1115/1.4037303 ◽

2017 ◽

Vol 139 (10) ◽

Cited By ~ 9

Author(s):

Jared Allison ◽

Conner Sharpe ◽

Carolyn Conner Seepersad

Keyword(s):

Selective Laser Sintering ◽

Statistical Design ◽

Laser Sintering ◽

Industrial Applications ◽

Design Guidelines ◽

Powder Bed Fusion ◽

Sintering Process ◽

Powder Bed ◽

Test Part ◽

Polymer Powder

Additive manufacturing (AM) has many potential industrial applications because highly complex parts can be fabricated with little or no tooling cost. One barrier to widespread use of AM, however, is that many designers lack detailed information about the capabilities and limitations of each process. To compile statistical design guidelines, comprehensive, statistically meaningful metrology studies need to be performed on AM technologies. In this paper, a test part is designed to evaluate the accuracy and resolution of the polymer powder bed fusion (PBF) or selective laser sintering process for a wide variety of features. The unique construction of this test part allows it to maximize feature density while maintaining a small build volume. As a result, it can easily fit into most existing selective laser sintering builds, without requiring dedicated builds, thereby facilitating the repetitive fabrication necessary for building statistical databases of design allowables. By inserting the part into existing builds, it is also possible to monitor geometric accuracy and resolution on a build- and machine-specific basis in much the same way that tensile bars are inserted to monitor structural properties. This paper describes the test part and its features along with a brief description of the measurements performed on it and a representative sample of the types of geometric data derived from it.

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Optical analysis of polymer powder materials for Selective Laser Sintering

Polymer Testing ◽

10.1016/j.polymertesting.2016.10.010 ◽

2016 ◽

Vol 56 ◽

pp. 207-213 ◽

Cited By ~ 20

Author(s):

T. Laumer ◽

T. Stichel ◽

K. Nagulin ◽

M. Schmidt

Keyword(s):

Selective Laser Sintering ◽

Laser Sintering ◽

Powder Materials ◽

Optical Analysis ◽

Polymer Powder

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Investigating the Potential Plasticizing Effect of Di-Carboxylic Acids for the Manufacturing of Solid Oral Forms with Copovidone and Ibuprofen by Selective Laser Sintering

Polymers ◽

10.3390/polym13193282 ◽

2021 ◽

Vol 13 (19) ◽

pp. 3282

Author(s):

Yanis Abdelhamid Gueche ◽

Noelia M. Sanchez-Ballester ◽

Bernard Bataille ◽

Adrien Aubert ◽

Jean-Christophe Rossi ◽

...

Keyword(s):

Carboxylic Acids ◽

Heating Temperature ◽

Selective Laser Sintering ◽

Laser Sintering ◽

Scanning Calorimetry ◽

Disintegration Time ◽

Polymer Powder ◽

Tartaric Acids ◽

The Stability ◽

Optimal Heating

In selective laser sintering (SLS), the heating temperature is a critical parameter for printability but can also be deleterious for the stability of active ingredients. This work aims to explore the plasticizing effect of di-carboxylic acids on reducing the optimal heating temperature (OHT) of polymer powder during SLS. First, mixtures of copovidone and di-carboxylic acids (succinic, fumaric, maleic, malic and tartaric acids) as well as formulations with two forms of ibuprofen (acid and sodium salt) were prepared to sinter solid oral forms (SOFs), and their respective OHT was determined. Plasticization was further studied by differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). Following this, the printed SOFs were characterized (solid state, weight, hardness, disintegration time, drug content and release). It was found that all acids (except tartaric acid) reduced the OHT, with succinic acid being the most efficient. In the case of ibuprofen, only the acid form demonstrated a plasticizing effect. DSC and FTIR corroborated these observations showing a decrease in the glass transition temperature and the presence of interactions, respectively. Furthermore, the properties of the sintered SOFs were not affected by plasticization and the API was not degraded in all formulations. In conclusion, this study is a proof-of-concept that processability in SLS can improve with the use of di-carboxylic acids.

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