2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Materials: Polymers Powder Bed Fusion
Program Organizers: Joseph Beaman, University of Texas at Austin
Tuesday 1:40 PM
August 15, 2023
Room: 416 AB
Location: Hilton Austin
Session Chair: Camden Chatham, Savannah River National Lab
1:40 PM
Analysis of Flow Additives in Laser-based Powder Bed Fusion of Polymers: Implications for Flow Behavior, Processing, Temperature Profile, and Part Characteristics: Simon Cholewa1; Andreas Jaksch1; Dietmar Drummer1; 1Collaborative Research Center 814: Additive Manufacturing
Powder bed fusion of polymers requires the use of flow additives to ensure adequate flowability of the feedstock material. However, information regarding flow additives and their load is limited, as is understanding of their impact on processing conditions. This study investigates the flow behavior using static and dynamic measurements under process conditions, with a particular focus on the influence of flow additives. Subsequently, processing studies are conducted using thermography to analyze the laser material interaction. The characteristics of parts produced from Polypropylene and Polyamide 12 systems are also examined. The findings of this research enhance the understanding of the impact of flow additives on the processing conditions of laser-based powder bed fusion of polymers, potentially leading to optimized process parameters and improved part quality and mechanical properties.
2:00 PM
Determination of Input Laser Energy for Melting Powder Layers of Various Thicknesses in High-speed PBF-LB/P using Near-infrared Laser and Absorbent: Yuki Yamauchi1; Takashi Kigure1; Toshiki Niino2; 1Tokyo Metro Ind Tech Research Inst; 2Institute of Industrial Science, the University of Tokyo
The rate of production of PBF-LB/P can be increased by increasing the layer thickness. However, this reduces the part resolution in the stacking direction. To obtain both, a high rate of production and high part resolution, layer thickness adjustment in accordance with part geometry can be effective. Optimizing the input laser energy with respect to the layer thickness ensures sufficient melting and part strength. According to previous studies, the use of a near-infrared laser and absorbent can increase penetration depth or depth of fusion. However, the optical properties of the powder bed can vary significantly depending on the layer thickness, and, therefore, the input energy that actually contributes to melting also changes with layer thickness. This study proposes a method for determining the input laser energy for various layer thickness without trial and error by estimating the amount of energy required to melt the powder layer while accounting for the optical properties of the bed.
2:20 PM
Effect of Temperature on the Cohesiveness of Polymeric Powders: Implications on Spreadability: Aurelien Neveu1; Marco Lupo1; Filip Francqui1; 1GranuTools
The powder spreadability is an important factor in powder bed based additive manufacturing such as Selective Laser Sintering (SLS). Previous studies have already demonstrated the close relation between the powder cohesiveness and the spatial homogeneity of the produced layers during the recoated process. However, in SLS applications polymeric powders are warmed up at a temperature close to the sintering. This temperature elevation will induce changes in the strength of the cohesive interactions leading to a modification of the spreadability. Therefore, an investigation of the effect of temperature is essential to better predict the spreadability of the material inside the machine. In this study, the influence of temperature on polymeric powders (polyamide 6, polyurethane and polypropylene) on cohesion has been evaluated with a rotating drum method (GranuDrum, Granutools, Belgium). The results clearly highlight the importance of performing the characterization at a temperature close to the one seen in the printer.
2:40 PM
Enhancing the Thermal Stability of Polyamide 6 in Powder Bed Fusion via Primary and Secondary Antioxidant Incorporation: Andreas Jaksch1; Simon Cholewa1; Dietmar Drummer1; 1University of Erlangen–Nuremberg
Polyamide 6 (PA6) is a widely used thermoplastic material in manufacturing due to its outstanding mechanical properties, such as high strength, stiffness, and toughness. However, PA6's vulnerability to thermo-oxidative aging makes it less suitable for powder bed fusion (PBF), as it results in material degradation and mechanical property deterioration over time. To address this issue, this study investigates the efficacy of antioxidants in improving PA6's aging resistance in PBF.To elucidate the physical and chemical changes in the material, process-adapted analyses are conducted using a coupled rheometer FTIR instrument. Furthermore, the study evaluates the viscosity number of the virgin and processed powder, the yellow index, and the part performance to characterize the aging occurring in the PBF process. The results indicate that addition of primary and secondary antioxidants significantly improves PA6's aging resistance in PBF, thus enhancing its potential as a suitable material for additive manufacturing applications.
3:00 PM
Fundamentals of Polymer Crystallization in Laser Powder Bed Fusion for New Material Screening: Camden Chatham1; Samantha Talley2; 1Savannah River National Lab; 2Kansas City National Security Campus
Although laser powder bed fusion (PBF/LB) was one of the first industrially viable additive manufacturing methods, polyamides remain dominant at both commercial- and research-scales. Researchers continue to develop screening methods for evaluating new polymers for PBF/LB. The so-called “SLS Process Window,” which is the difference between melting and crystallization temperature measured at 10 K min-1 as originally outlined in patent literature, is perhaps the most often reported method. The method’s simplistic guidelines are not sufficiently scientifically rigorous to understand how crystallization kinetics affects successful 3D printing. Common understanding of the Process Window omits details from published theories of polymer crystallization, as evidenced by assumptions in PBF/LB process modeling papers. The authors review polymer crystallization in the PBF/LB context and propose replacing the Process Window with crystallization halftime and physical gelation measurements. These measurements better indicate a lengthy coexistence of solid powder and molten polymer affecting warp-free parts.
3:20 PM
Halogen-free Flame-retardant Powder Materials for Laser Sintering: Evaluation and Process Stability Analysis: Fabian Neitzel1; Ivo Kletetzka1; Hans-Joachim Schmid1; 1Paderborn University (DMRC)
The high flammability of components manufactured by laser sintering (LS) using standard polyamide 12 (PA12) powder still severely restricts their use in industries such as electronics, aviation, and transportation. A key factor for the further establishment of laser sintering is the expansion of the material portfolio with, for example, refreshable and halogen free flame-retardant powder materials. Accordingly, various halogen-free flame-retardants are investigated in this work and evaluated with respect to their use in LS. First, their decomposition behavior and mode of action are examined. Subsequently, the additives are dry blended with PA12 to investigate properties relevant for LS, such as particle morphology, thermal behavior and melt viscosity. In the next step, test specimens for UL94 vertical flame-retardancy tests in the LS process are produced from the blends. Finally, the process stability of the process-aged powder blends is investigated by again examining the thermal behavior and melt viscosity.