Advances in modeling the effects of selected parameters on the SLS process

Williams, John D.; Deckard, Carl

doi:10.1108/13552549810210257

Cited by 204 publications

(104 citation statements)

References 9 publications

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“…Ryder et al [7] extended the previous model to 2 dimensions, incorporating also the effect of a spatially dependent conductivity and porosity. Other research groups have further studied other related phenomena such as Z growth [8], thermal degradation [9], polymer densification [10] and temperature evolution during laser scanning [11]. One of the main limitations for SLS polymer processability is related to the so-called warpage or curling effect that develops when the polymer starts crystallizing.…”

Section: Introductionmentioning

confidence: 99%

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Amado

Schmid

Wegener

2015

AIP Conference Proceedings

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Abstract. Polymer processing using Additive Manufacturing Technologies (AM) has experienced a remarkable growth during the last years. The application range has been expanding rapidly, particularly driven by the so-called consumer 3D printing sector. However, for applications demanding higher requirements in terms of thermo-mechanical properties and dimensional accuracy the long established AM technologies such as Selective Laser Sintering (SLS) do not depict a comparable development. The higher process complexity hinders the number of materials that can be currently processed and the interactions between the different physics involved have not been fully investigated. In case of thermoplastic materials the crystallization kinetics coupled to the shrinkage strain development strongly influences the stability of the process. Thus, the current investigation presents a transient Finite Element simulation of the warpage effect during the SLS process of a new developed polyolefin (co-polypropylene) coupling the thermal, mechanical and phase change equations that control the process. A thermal characterization of the material was performed by means of DSC, integrating the Nakamura model with the classical Hoffmann-Lauritzen theory. The viscoelastic behavior was measured using a plate-plate rheometer at different degrees of undercooling and a phase change-temperature superposition principle was implemented. Additionally, for validation porpoises the warpage development of the first sintered layers was captured employing an optical device. The simulation results depict a good agreement with experimental measurements of deformation, describing the high sensitivity of the geometrical accuracy of the sintered parts related to the processing conditions.

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Section: Introductionmentioning

confidence: 99%

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Amado

Schmid

Wegener

2015

AIP Conference Proceedings

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“…Different layer thicknesses are influencing the data preparation. Reducing the layer thickness means a reduction of the energy density, which is determined by Williams and Deckard [1], which induces to a smaller laser beam spot. The number of hatch lines is influenced as well.…”

Section: Data Preparationmentioning

confidence: 99%

“…Process parameters were developed to get information about their influence on mechanical properties on laser sintered parts [4]. Regarding different energy densities as a function influencing factors like laser power, hatch distance and scanning velocity, determined by Williams and Deckard [1] the influence of diverse scanning strategies is shown. Kaddar and Sauer [3] have investigated diverse layer thicknesses as well as the powder quality and the powder temperature.…”

Section: Introductionmentioning

confidence: 99%

Advanced characterization method of nylon 12 materials for application in laser sinter processing

Ruesenberg

Schmid

2014

AIP Conference Proceedings

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Laser Sintering is a powder based additive manufacturing technology. The amount of used powder, which is not sintered, can be refreshed and used for further building jobs. Due to cost reduction, better mechanical properties and a simpler processing it is reasonable to combine virgin and used powder for part manufacturing. During the building time the powder is thermally loaded and its structure is changed. State of the art in laser sintering is a defined powder ratio. Since the powder ageing depends on the individual history of sintering, this procedure cannot ensure a defined powder quality. However, for a serial production it is necessary to characterize the raw material, as well as all other steps along the process chain, in order to ensure a high reproducibility and reliability. Rheological, physical and particle properties are considered to correlate powder and chosen material properties. Different powder qualities adjusted by the Melt Volume Rate (MVR) are tested using promising rheological properties like viscosity or molecular weight. Investigations about powder bed density, bulk properties as well as thermal characterization complement the experimental setup. These parameters are correlated with mechanical, electrical, thermal and physical material properties of laser sintered parts. The most important influencing factors along the process chain are kept constant. At the end a procedure is shown to obtain a defined powder quality. This procedure will be transferred to other materials and will be tested using other laser sintering machines of the same type as well as other types.

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“…The process parameters include: laser power (P), laser spot diameter (d), scanning speed (v), distance between scanning lines (h), layer thickness (w) and scanning geometry. The mentioned parameters can be expressed as an energy density function [20,[24][25][26][27]. Thermal power of laser (E) can be obtained by Eq.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of laser-assisted powder bed fusion of Fe-Cu powder mixture

Fatemi

Ashani

2017

Prog Addit Manuf

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Powder bed fusion is an additive manufacturing method which allows production of complex parts, in a shorter time compared to the conventional fabrication methods. During the last 60 years, Fe-Cu powders were widely used because of their anti-friction behavior and superior mechanical properties. Therefore, Fe-Cu powder has been selected as the basic material for the powder bed fusion process. In the present study, laser-assisted powder bed fusion of Fe-Cu powder mixture has been studied experimentally. Nd:YAG laser with a maximum power of 75 W has been used to melt the powder. The effects of volume fraction of the Cu powder in the mixture and applied energy density on thickness, surface concavity and geometrical accuracy of manufactured parts have been investigated. Results show that higher values of energy density lead to lower geometrical accuracy, higher thickness and surface concavity.

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Advances in modeling the effects of selected parameters on the SLS process

Cited by 204 publications

References 9 publications

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Simulation of warpage induced by non-isothermal crystallization of co-polypropylene during the SLS process

Advanced characterization method of nylon 12 materials for application in laser sinter processing

Experimental investigation of laser-assisted powder bed fusion of Fe-Cu powder mixture

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