Browsing by Subject "polyamide 12"

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Aging Behavior of Polyamide 12: Interrelation Between Bulk Characteristics and Part Properties
(University of Texas at Austin, 2016) Wudy, K.; Drummer, D.
The high process temperatures in combination with long building times during the laser sintering process lead to chemical and physical aging mechanisms on the polymeric feed material. The unmolten partcake material, which acts as a supporting structure, can be removed after each building process and reused for further processes. However, material as well as bulk properties are changed due to thermal and mechanical load during the laser sintering process. Within this paper the interrelation between the aging state, bulk values and resulting part properties like porosity, surface roughness and mechanical behavior are derived. Therefore, polyamide 12 powder is used for at least five processing cycles without refreshing. Before and after each building process, bulk characteristics and changes of the particle surface were determined. Specimens were manufactured during the laser sintering process in order to study the part density, roughness and mechanical behavior.
A Control of Surface Quality in Selective Laser Sintering Additive Manufacturing with Reclaimed Polyamide Materials
(University of Texas at Austin, 2021) Yang, Feifei; Jiang, Tianyu; Chen, Xu; Lalier, Greg; Bartolone, John
In selective laser sintering (SLS) additive manufacturing (AM), a substantial amount of polyamide 12 materials remains un-sintered, recyclable, and reusable. However, using reclaimed polyamide 12 powder in SLS results in undesirable part surface finish. Very limited research has been done on the improvement of part surface quality and results barely exist on improving or modifying the surface quality of parts using extremely aged powders (powders held close to the heat-affected zones). Aiming to improve the surface quality, we propose a novel approach for SLS with (extremely) aged polyamide 12 powders. By combining material preparation, powder and part characterizations, and SLS with a customized method of post-heating, we obtain parts with improved surface quality (e.g., reduced roughness and porosities, and eliminated un-sintered particles). Particularly, parts 3D-printed using the 30%-30%-40% new-aged-extremely aged mixed powders exhibit the smoothest and flattest surface with no unmolten particles and nearly zero porosity.
The Influence of Grain Size Distribution of PA12 on Key Steps of the Polymer Laser Sintering Process
(University of Texas at Austin, 2021) Sesseg, Jens P.W.; Riedmann, Paul; Fischer, Sybille; Schmid, Hans-Joachim
As the industry pushes for higher resolution laser sintering, finer and finer powders are required. Yet, this also changes the way powders behave during the process. In this project, the influence of finer particles on the dosing and coating process during laser sintering is being investigated. PA12 laser sintering powder without flow additives was sieved to four fractions with grain sizes with a d50 of 42, 54, 61 and 66 µm. These fractions were characterized regarding powder flowability by FT4 powder rheometer. The dosing and coating behavior of these fractions was tested in separate experiments on an EOS P395, where the coating experiments were performed at both RT and 175°C. Furthermore, test jobs were built with the different powder fractions. The larger portion of fines in the finest fraction dominated the powder properties and led to significantly worse powder behavior during the dosing and coating steps, as predicted by analytical measurements.
Material Properties of Laser Sintered Polyamide 12 as Function of Build Cycles Using Low Refresh Rates
(University of Texas at Austin, 2015) Josupeit, Stefan; Lohn, Johannes; Hermann, Eduard; Gessler, Monika; Tenbrink, Stephan; Schmid, Hans-Joachim
Due to long process times at high temperatures, unmolten polyamide 12 material ages during the manufacturing process. Hence, it needs to be refreshed with new material for further build cycles. In application, refresh rates of about 50 % are commonly used. In this work, the recycling optimized material PA 2221 from EOS is analyzed along a series of 13 build and refresh cycles using a reduced refresh rate of 32 %. Before and after every build, the powder is analyzed regarding melt properties determined by MVR and DSC measurements. Thereby, in-process ageing effects are investigated and the steady-state conditions are determined accordingly. In addition, powder properties are directly linked to resulting mechanical and geometrical part properties. Key findings are a robust DSC measurement method for polyamide 12 powder, constant “circulated” material properties after three build/refresh cycles and robust tensile properties along the whole tested powder life cycle. As a result, process conditions of PA 2221 using reduced refresh rates can be derived from this work.
Measured Energy Densities for Polyamide 12 and Comparison of Values Calculated for Laser Sintering
(University of Texas at Austin, 2016) Chalancon, Antoine; Bourell, David
Energy density is a key factor in the Laser Sintering (LS) process, and impacts the properties of the built parts. Processing parameters have an important effect on Laser Sintering. This paper focuses on the evaluation of various energy density equations. Experiments were carried out by varying processing parameters, namely, laser power, scan speed, hatch distance/scan spacing and layer thickness to change actual and calculated energy density. Relative density was estimated using the Archimedes method and mensuration. As a result, a correlation between the laser energy density and the relative density has been established. Finally, the effect of parameters is discussed.
Mechanical and Thermal Properties of FDM Parts Manufactured with Polyamide 12
(University of Texas at Austin, 2015) Knoop, F.; Schoeppner, V.
Fused Deposition Modeling (FDM) is an Additive Manufacturing (AM) technology which is used for prototypes, single-part production and also small batch productions. For use as a final product, it is important that the parts have good mechanical properties, high dimensional accuracy and smooth surfaces. The knowledge of the mechanical properties is very important for the design engineer when it comes to the component design. End-use products out of the FDM process have to resist applied forces. In this paper, investigations were conducted with the polymer Polyamide 12 (FDM Nylon 12) from Stratasys Inc. This polymer can be processed with three different tip sizes resulting in different layer thicknesses from 178 μm to 330 μm. Thus, the mechanical properties were determined for these layer thicknesses and for different orientations on the build platform. In addition to the mechanical properties the thermal properties (e.g. with a DSC analysis) are also investigated.
Thermal Conductivity Measurements of Polyamide 12
(University of Texas at Austin, 2011-08-17) Yuan, Mengqi; Bourell, David; Diller, Tim
An important component in understanding the laser sintering process is knowledge of the thermal properties of the processed material. Thermal conductivity measurements of pure polyamide 12 were conducted based on transient plane source technology using a Hot Disk® TPS500 conductivity measurement device. Polyamide samples were packed to three different densities in nitrogen at steady state. Thermal diffusivity and conductivity were measured from 40°C to 170°C for both fresh powder and previously heated (“recycled”) powder. The fresh powder tests revealed that thermal conductivity increased linearly with temperature while for previously heated powder, more constant and higher thermal conductivity was observed as it formed a powder cake. Tests were also performed on fully dense polyamide 12 to establish a baseline. Polyamide 12 powder had a room-temperature thermal conductivity of approximately 0.1 W/mK which increased with temperature, whereas the bulk laser sintered polyamide 12 room-temperature value was 0.26 W/mK and generally decreased with increasing temperature.
Understanding Hatch-Dependent Part Properties in SLS
(University of Texas at Austin, 2018) Wörz, A.; Drummer, D.
Selective laser sintering of polymers (SLS) is on the verge from pure prototyping to producing individualized complex parts for series application. As the parts are generated layer-wise and the influence of process-parameters as well as part orientations are well-known, the aim of the paper is to point out the influence of the layer-wise manufacturing in dependence of the hatching strategy on the resulting part properties as these are constant process-steps. Therefore, tensile bars with different number of layers but constant layer-thickness were produced using different hatching strategies and investigated depending density, surface roughness and mechanical properties. The results showed a strong increase of the mechanical properties, ductile breaking behavior and part density as well as decreasing surface roughness with higher layer numbers as well as the hatching strategies. Therefore, the results point out significant interaction between constant process steps and resulting part properties.