2023 Annual International Solid Freeform Fabrication Symposium (SFF Symp 2023): Materials: Polymer AM Processes
Program Organizers: Joseph Beaman, University of Texas at Austin
Monday 1:30 PM
August 14, 2023
Room: 417 AB
Location: Hilton Austin
Session Chair: Jackson Bryant, Virginia Tech
1:30 PM
Investigation of Crack Formation Process during Low Temperature Laser Sintering of PEEK by Observing Melt and Solidification Behavior: Takashi Kigure1; Yuki Yamauchi1; Toshiki Niino2; 1Tokyo Metropolitan Industrial Tech Rsch Inst; 2Institute of Industrial Science, the University of Tokyo
In a previous study, PEEK was successfully laser sintered at a mild powder bed preheating temperature below the recrystallization point with in-process part warpage suppressed by fixing the parts to a rigid base plate instead of using "process window," but serious surface finish degradation and large crack formation were observed. In this study, a video camera observation of the melting and solidification processes is performed to investigates formation process of such rough surfaces and cracks, with the aim of improving the part quality out of "low-temperature process," which does not preheat the powder bed above recrystallization temperature. The results reveals that volume changes during melting and solidification play an important role in the generation of rough surfaces and the cracks.
1:50 PM
Investigation of the Processability of Polyether Block Amide in High Speed Sintering: Marco Wimmer1; Jan Kemnitzer2; Johann Schorzmann1; Frank Döpper1; David Förster1; 1Universität Bayreuth; 2Fraunhofer IPA
The High Speed Sintering (HSS) process ranks among the Powder Bed Fusion processes of polymers (PBF-P) of Additive Manufacturing (AM). Its scalability, constant layer time and high quality of complex parts compared to other AM processes are some of the characteristics of the HSS showing its potential for series production for small to medium series. Most of the conducted investigations for the PBF-P processes were conducted using commercially available materials Polyamide 12 (PA12), Polyamide 6 (PA6), Thermoplastic polyurethane (TPU), Polypropylene (PP) and Polybutylene terephthalate (PBT). This work reports from the processing of Polyether block amide (PEBA) in HSS. As a block-copolymer on amide basis, PEBA shows higher performance compared to other block-copolymers like TPU: The high elastic properties, low density and high service temperature make PEBA an ideal material for the use in the athletic footwear and outdoor industry. Until now, no research was conducted using PEBA powder in HSS.
2:10 PM
Photothermal Bleaching of Nickel Dithiolene for Bright Multi-colored 3D Printed Parts
: Paul Olubummo1; Aja Hartman1; 1HP Labs
HP’s Multi Jet Fusion is a powder bed fusion 3D printing technology that utilizes a carbon-based radiation absorber in combination with a near infrared (NIR) light source to facilitate the fusion of polymer powder in a layer-by-layer fashion to generate 3D parts. Most available carbon-based and NIR radiation absorbers have an intrinsic dark color, which as a result will only produce black/gray and dark colored parts. However, there are many applications that require variable color, including prosthetics, medical models, and indicators, among others. To create white, bright colored, and translucent parts with MJF, a visibly transparent and colorless radiation absorber is required. In this paper, we designed an activating fusing agent (AFA) that contains a red, strong NIR absorbing dye that turns colorless after harvesting irradiation energy during the MJF 3D printing process and provide a bright colored part when working with other color agents.
2:30 PM
Powder Bed Fusion of Polypropylene-ethylene Co-polymers: Jackson Bryant1; Michelle Pomatto1; Robert Moore1; Michael Bortner1; Christopher Williams1; 1Virginia Tech
Polypropylene has proven challenging to process in powder bed fusion (PBF) technologies. This work uses flash DSC to demonstrate how the crystallization kinetics in polypropylene-ethylene copolymers slow down with increasing ethylene content. Slower crystallization kinetics enable more time for the coalescence of polymer particles such that the mechanical properties frequently expected from polypropylenes – impact resistance, flexibility – improve. However, the addition of the ethylene copolymer results in a much smaller processing window due to widening of the melting endotherm. A series of PP-PE copolymers with 1 – 5 wt% ethylene content were compared to a PP homopolymer samples. It was possible to process all samples and the higher ethylene content samples resulted in higher extensions at break. However, the broader melt endotherm narrowed the usable bed temperature for copolymer samples, which frequently resulted in problems during powder recoating at higher z-heights and much longer layer times.
2:50 PM
Powder Bed Fusion of Ultra-high Molecular Weight Polyethylene via Novel Scan Strategy and Post-process: Jackson Bryant1; Michael Bortner1; Christopher Williams1; 1Virginia Tech
Ultra-high molecular weight polyethylene (UHMWPE) is a polymer known for its especially high wear properties. Currently, there is no successful method for printing UHMWPE components with mechanical properties sufficient for end-use applications. When irradiated by the laser during powder bed fusion (PBF), UHMWPE undergoes melt explosion, which makes the powder expand and causes recoating failure. Furthermore, the melt viscosity of UHMWPE prevents the powder particles from coalescing and densifying. In this work we employ a novel scan strategy with large hatch spacing to minimize layer growth in the z-direction and enables multilayer UHMWPE prints. Printed parts are then post-processed under pressure above melting temp to further coalesce the powder. Due to UHMWPE’s high melt viscosity, part shape is retained durig postprocessing without distortion. This approach is validated on a 3000 kDA UHWMPE powder, and resulted in complex printed parts with ultimate tensile strength 2 > MPa.
3:10 PM Break
3:40 PM
Structural Stability During Thermal Post-curing of Direct Ink Write Thermoset Composites: Stian Romberg1; Anthony Kotula1; 1National Institute of Standards and Technology
Thermoset composites are excellent candidates for direct ink writing because they shear thin during extrusion but retain their shape once deposited via a yield stress. However, thermal post-curing is often required to solidify these materials, which can destabilize printed parts. To understand instability during post-curing, we utilize rheo-Raman spectroscopy to simultaneously measure rheological properties and extent of reaction (i.e., conversion) at different temperatures. Although elevated temperatures accelerate the curing process, they decrease the yield stress before crosslinking solidifies the material, explaining why collapse occurs during thermal post-curing. On the other hand, curing at lower temperatures reduces instability at the cost of processing speed. The simultaneous Raman-based conversion measurements are used to determine when temperature can be increased without risking structural collapse. The results enable the design of a curing schedule that avoids instability, but still quickly drives the reaction towards full conversion.
4:00 PM
Ultrasonic Non-destructive Characterization of Anisotropic Additively Manufactured Polymers: Akash Nivarthi1; Michael Haberman1; Christina Naify1; 1Applied Research Laboratories, The University of Texas at Austin
Ultrasonic nondestructive testing can be used to infer the print settings of additively manufactured (AM) polymers to macroscopic elastic properties. We present a comparison of measurements of angle- and frequency-dependent ultrasonic transmission through AM plates in water tank to model predictions that consider infill properties. The experiment employs a point source ultrasonic source and a synthetic linear array to measure the transmission coefficient of fused deposition-modeled polylactic (PLA) acid plates over various frequencies and incident angles. Measurements are compared to predictions from a finite element (FE) model of the effective stiffness based on assumed infill geometry and PLA material properties paired with a reflection-transmission model for anisotropic elastic plates submerged in a fluid. Minimizing the difference between measured and modeled transmission coefficients by varying FE model inputs provides an improved understanding of the effects of the print settings on the as-built mechanical properties for 3D-printed materials.
4:20 PM
Magnetic Characterization of 3D Printed High-performance Polyamide Magnetic Composite: Oluwasola Arigbabowo1; Yash Tate2; Wilhelmus Geerts1; 1Texas State University; 2James Bowie High School
Polyamide 4.6 is classified as a high-temperature thermoplastic because of its service temperatures of up to 175°C, bringing them close to high-temperature plastics like PPS or PEEK. Due to its high-temperature capability and price/performance ratio, Polyamide 4.6 is considered viable in developing high-performance bonded magnets by serving as a binder/matrix to magnetic powders/fillers to form multifunctional magneto polymeric composites that offer superior properties to conventional materials. The thermal integrity of the polyamide 4.6 matrix would lock the orientation of the magnetic particles in place by limiting the sporadic motion that could arise due to heat which causes misalignment of the magnetic domains and a decrease in magnetism. Strontium ferrite magnetic powders were compounded with polyamide 4.6 using a co-rotating twin screw extruder. Thermal, mechanical, and magnetic characterization was performed on 3D printed samples using Simultaneous Differential Thermogravimetry, MTS Servo hydraulic test system, and Vibrating Sample Magnetometer, respectively.This work was supported in part by NSF through DMR- MRI Grant under awards 2216440 and in part by DOD instrumentation grant (78810-W911NF-21-1-0253).