Browsing by Author "Drummer, D."

Now showing 1 - 9 of 9

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.
Analysis of Flow Additives in Laser-Based Powder Bed Fusion of Polymers: Implications for Flow Behavior, Processing, Temperature Profile, and Part Characteristics
(University of Texas at Austin, 2023) Cholewa, S.; Jacksch, A.; Drummer, D.
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 an understanding of their impact on processing conditions. This study investigates the flow behavior using static and dynamic measurements under process conditions, focusing 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.
Coalescence Behavior of Polyamide 12 as Function of Zero-Shear Viscosity and Influence on Mechanical Performance
(2022) Cholewa, S.; Jaksch, A.; Drummer, D.
The favored material for powder bed fusion of polymers (PBF-LB/P) is polyamide-12. Its molecular weight increases from post-condensation at elevated temperatures in the building chamber, consequently having different properties when reused. An important aspect of PBF directly affected hereby is the coalescence behavior, as it significantly determines the surface quality, porosity, and thus the component’s mechanical properties. However, detailed studies on coalescence are limited to virgin powders with low viscosity; therefore, coalescence behavior of polyamide-12 with different molecular weights is investigated using hot stage microscopy. Additionally, the zero-shear viscosity is determined using the Carreau model, allowing comparison of experimental results to sintering models. Furthermore, the mechanical properties and surface qualities are analyzed, and components with adequate values are made with two-cycle reprocessed powder. Since surface flaws do not exist uniformly across all components, the orange peel effect is not attributed solely to the increased viscosity of the reused powder.
Curing Behavior of Thermosets for the Use in a Combined Selective Laser Sintering Process of Polymers
(University of Texas at Austin, 2018) Wudy, K.; Drummer, D.
Selective laser sintering (SLS) of polymers is an additive manufacturing process, which enables the production of functional technical components. Unfortunately, the SLS process is restricted regarding the materials that can be processed and thus resulting component properties are limited. The investigations in this study illustrates a totally new additive manufacturing process which combines reactive liquids like thermoset resins and thermoplastics to generates multi material SLS parts. To introduce thermoset resins into the regular SLS process, the time-temperature-dependent curing behavior of the thermoset and the infiltration behavior has to be understood in order to assess the process behavior. The curing behavior was analyzed by rotational viscosimeter. Furthermore, the fundamental infiltration behavior was analyzed with micro dosing infiltration experiments. Finally, a thermoset resin in combination with a dosing system was chosen for integration in a laser sintering system.
Enhancing the Thermal Stability of Polyamide 6 in Powder Bed Fusion via Primary and Secondary Antioxidant Incorporation
(University of Texas at Austin, 2023) Jacksch, A.; Cholewa, C.; Drummer, D.
Polyamide 6 (PA6) is a thermoplastic material widely used in manufacturing for its excellent mechanical properties, such as high strength, stiffness, and toughness. However, its suitability for powder bed fusion (PBF) is limited due to its susceptibility to thermo-oxidative aging, resulting in material degradation and mechanical property deterioration over time. To address this issue, the efficacy of antioxidants in increasing the aging resistance of PA6 in PBF was investigated. Process-adapted analysis was employed using a coupled rheometer FTIR instrument to elucidate physical and chemical changes in the material. In addition, the viscosity number of the virgin and processed powder, the yellow index, and the part performance were evaluated. Results revealed that the addition of primary and secondary antioxidants significantly enhanced the aging resistance of PA6 in PBF, thereby increasing its potential as a suitable material for additive manufacturing applications.
Influence of Temperature Fields on the Processing of Polymer Powders by Means of Laser and Mask Sintering Technology
(University of Texas at Austin, 2011-08-17) Rietzel, D.; Drexler, M.; Kühnlein, F.; Drummer, D.
Besides their high potential for individual series-production, powder and beam based additive manufacturing technologies, like laser and mask sintering, are in general still restricted to prototyping applications. This is a result of multiple limitations concerning part properties (e.g. mechanical and geometrical), their insufficient reproducibility due to transient thermal conditions and the limited range of available materials. The main focal point of this paper is to show the influencing parameters (e.g. temperature fields in the building chamber) of powder-based thermoplastic processing technologies on part properties, like porosity and surface quality, and on the processability of further new polymers (e.g. polypropylene and polyoxymethylene).
Thin-Walled Part Properties in PBF-LB/P — Experimental Understanding and Nonlocal Material Model
(2022) Jaksch, A.; Spinola, M.; Cholewa, C.; Pflug, L.; Stingl, M.; Drummer, D.
to fully realizing the potential of lightweight design in powder bed fusion of polymers (PBF-LB/P). In this work, parts built with rectangular cross sections of different sizes and orientations are described by their geometry, surface roughness, mechanical characteristics, and specific component geometry dependent on energy input. Experimental findings are supported by a nonlocal material model developed to adequately describe weakened material behavior at the surface of PBF-LB/P parts. This approach allows the simulation of the elastic modulus and density for complex part geometries while simultaneously considering boundary effects. Furthermore, the volume-surface ratio for thin-walled components were linearly correlated to the rectangular cross sections in different building orientations. This uniformity indicates that this ratio is a suitable quantity to consider. Therefore, the process knowledge is improved, especially in new design standards for thin-walled structures in PBF-LB/P.
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.
Understanding the Influence of Energy-Density of the Layer Dependent Part Properties in Laser-Sintering of PA12
(University of Texas at Austin, 2019) Wörz, A.; Wudy, K.; Drummer, D.
As the demand for individualization and complex parts is continuously growing, laser-sintering of polymers is on the edge from a pure prototyping technology to manufacturing parts for applications in series production. The influences on resulting parts and layer depending part properties are well known in the literature but the understanding of the interaction between process parameters and layer dependent properties is missing and limiting the dimensioning. Within this study, tensile bars with different amounts of layers and energy densities were produced and investigated for the resulting mechanical properties, roughness, density and the degree of particle melt. The results showed a strong interaction between the energy density and amount of layers, which results in differences in the fracture behavior as well as the mechanical properties. Therefore, the presented results enable the prediction of necessary part thickness for dimensioning thin parts with laser-sintering.