Thermal conductivity of polyamide 12 powder for use in laser sintering

Yuan, Mengqi; Diller, Timothy T.; Bourell, David L.; Beaman, Joseph J.

doi:10.1108/rpj-11-2011-0123

Cited by 32 publications

(16 citation statements)

References 21 publications

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“…and a maximum of about 5%. The thermal conductivity of PA12 is in good agreement to what was reported by [11], although the transient hot wire method used in this work is very different from the methodology used by the other authors.…”

Section: Validation and Repeatabilitysupporting

confidence: 87%

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Influence of packing density and fillers on thermal conductivity of polymer powders for additive manufacturing

Sillani

Gasparo

Schmid

et al. 2021

Int J Adv Manuf Technol

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Additive manufacturing of polymer powders is nowadays an industrial production technology. Complex thermal phenomena occur during processing, mainly related to the interaction dynamics among laser, powder, and heating system, and also to the subsequent cool-down phase from the melt to the parts. Thermal conductivity of the powder is a key property for material processing, since an inhomogeneous temperature field in the powder cake leads to uneven part properties and can strongly limit productivity because only a smaller portion of the build chamber can be used. Nevertheless, little is known about the relationship between thermal conductivity, packing density, and presence of fillers, which are used to enhance specific properties such as high temperature resistance or stiffness. The development and consequent validation of a device capable of measuring thermal conductivity as a function of powder packing density are then extremely important, providing an additional tool to characterize powders during the development process of new materials for PBF of polymers. The results showed a positive correlation between packing density and thermal conductivity for some commercially available materials, with an increase of the latter of about 10 to 40% with an increase of the packing density from 0 to 100%. Problems arose in trying to replicate the compaction state of the powder, since the same amount of taps led to a different packing density, but this is a known problem of measuring free-flowing powders such as the ones used for additive manufacturing. Regarding fillers, an increase of about 40 to 70% of thermal conductivity when inorganic fillers such as carbon fibers are added to the neat polymer was observed, and the expected behavior following the rule of mixture was only partially observed.

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Section: Validation and Repeatabilitysupporting

confidence: 87%

“…At the same time, the entire powder cake cools down to room temperature. Thermal conductivity is reported to be dependent on the compaction state of the powder: [11] investigated this relationship in the bulk and tap density states for commercially available PA12, the most common polymer powder used for PBF-LB/P [1].…”

Section: Introductionmentioning

confidence: 99%

Influence of packing density and fillers on thermal conductivity of polymer powders for additive manufacturing

Sillani

Gasparo

Schmid

et al. 2021

Int J Adv Manuf Technol

View full text Add to dashboard Cite

show abstract

“…Mengqi Yuan et al [ 47 ] also investigated the range of thermal conductivity as 0.09 to 0.12 W/mK for polyamide 12 powder depending of the test temperature, whereas the counterpart in bulk laser sintered polyamide 12 had a thermal conductivity of 0.22 to 0.33 W/mK from 40 to 170 °C, which is approximately three times more than that of the loose powder. The thermal conductivity is a key parameter in the LS of polymer powders.…”

Section: Resultsmentioning

confidence: 99%

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering

et al. 2021

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We present a comparison of the influence of the conditioning temperature of microspheres made of medical grade poly(L-lactide) (PLLA) and polylactide with 4 wt % of D-lactide content (PLA) on the thermal and structural properties. The microspheres were fabricated using the solid-in-oil-in-water method for applications in additive manufacturing. The microspheres were annealed below the glass transition temperature (Tg), above Tg but below the onset of cold crystallization, and at two temperatures selected from the range of cold crystallization corresponding to the crystallization of the α’ and α form of poly(L-lactide), i.e., at 40, 70, 90, and 120 °C, in order to verify the influence of the conditioning temperature on the sinterability of the microspheres set as the sintering window (SW). Based on differential scanning calorimetry measurements, the SWs of the microspheres were evaluated with consideration of the existence of cold crystallization and reorganization of crystal polymorphs. The results indicated that the conditioning temperature influenced the availability and range of the SWs depending on the D-lactide presence. We postulate the need for an individual approach for polylactide powders in determining the SW as a temperature range free of any thermal events. We also characterized other core powder characteristics, such as the residual solvent content, morphology, particle size distribution, powder flowability, and thermal conductivity, as key properties for successful laser sintering. The microspheres were close to spheres, and the size of the microspheres was below 100 µm. The residual solvent content decreased with the increase of the annealing temperature. The thermal conductivities were 0.073 and 0.064 W/mK for PLA and PLLA microspheres, respectively, and this depended on the spherical shape of the microspheres. The wide angle X-ray diffraction (WAXD) studies proved that an increase in the conditioning temperature caused a slight increase in the crystallinity degree for PLLA microspheres and a clear increase in crystallization for the PLA microspheres.

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“…Powder samples of 25 g are evenly distributed in a large rectangular stainless steel tray to facilitate a highest possible contact area to the ambient atmosphere. Since the used bulk polyamide 12 powder has a very low thermal conductivity of about 0.1 W/m K, a high surface to volume ratio is important to enable highest possible heating/cooling rates within the powder. The trays are then stored in a vacuum oven.…”

Section: Methodsmentioning

confidence: 99%

Experimental analysis and modeling of local ageing effects during laser sintering of polyamide 12 in regard to individual thermal histories

Josupeit

Schmid

2017

J of Applied Polymer Sci

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Polymer laser sintering (LS) is an important additive manufacturing (AM) technology. Individual and complex parts are directly produced from CAD data without the need of specific tools. The raw material is a polymer powder, which is deposited layerwise and melted selectively with a laser. Built parts are embedded in residual unmolten powder, the so-called part cake, which undergoes thermal ageing effects due to the exposure to high temperatures for long times during the manufacturing process. Hence, the recyclability of the unmolten powder is limited. This article focuses on a fundamental analysis of the ageing kinetics dependent on time, temperature, and oxygen content in the gas atmosphere. A model is developed and applied to measured, position-dependent process temperature histories to successfully predict the ageing distribution within a part cake. The results can be used to optimize the thermal process management in LS and to develop new efficient powder recycling methods.

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Thermal conductivity of polyamide 12 powder for use in laser sintering

Cited by 32 publications

References 21 publications

Influence of packing density and fillers on thermal conductivity of polymer powders for additive manufacturing

Influence of packing density and fillers on thermal conductivity of polymer powders for additive manufacturing

Influence of Thermal Annealing on the Sinterability of Different Grades of Polylactide Microspheres Dedicated for Laser Sintering

Experimental analysis and modeling of local ageing effects during laser sintering of polyamide 12 in regard to individual thermal histories

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