scholarly journals A new approach for getting more homogeneous temperature fields in selective laser sintering of polymers

2019 ◽  
Author(s):  
Sandra Greiner ◽  
Lydia Lanzl ◽  
Katrin Wudy ◽  
Dietmar Drummer
Keyword(s):  
Selective Laser Sintering ◽  
Laser Sintering ◽  
Temperature Fields ◽  
New Approach ◽  
Homogeneous Temperature

scholarly journals Hybrid Approaches for Selective Laser Sintering by Building on Dissimilar Materials

Materials ◽  
2020 ◽  
Vol 13 (22) ◽  
pp. 5285
Author(s):  
Babette Goetzendorfer ◽  
Thomas Mohr ◽  
Ralf Hellmann
Keyword(s):  
Substrate Surface ◽  
Selective Laser Sintering ◽  
Dissimilar Materials ◽  
Polyamide 6 ◽  
Laser Sintering ◽  
New Approach ◽  
Metallic Substrates ◽  
Polyamide 12 ◽  
Melting Temperatures ◽  
Hybrid Approaches

We introduced a new approach in selective laser sintering for hybrid multicomponent systems by fabricating the sintered polyamide 12 (PA12) part directly onto a similar (PA12) or dissimilar (polyamide 6 (PA6) and tool steel 1.2709) joining partner. Thus, the need for adhesive substances or joining pressure was completely circumvented, leading to the possibility of pure hybrid lightweight bi-polymer or metal–polymer systems. By taking advantage of the heating capabilities of the sinter laser regarding the substrate surface, different exposure strategies circumvented the lack of overlapping melting temperatures of dissimilar polymers. Therefore, even sintering on non-PA12 polymers was made possible. Finally, the transfer on metallic substrates—made up by selective laser melting (SLM)—was successfully performed, closing the gap between two powder-based additive processes, selective laser sintering (SLS) and SLM.

On thermodynamics and the nature of the second law

1977 ◽  
Vol 357 (1690) ◽  
pp. 253-270 ◽  
Keyword(s):  
Mechanical Response ◽  
The Body ◽  
Temperature Fields ◽  
Second Law ◽  
Fading Memory ◽  
New Approach ◽  
Spatially Homogeneous ◽  
Dissipative Material ◽  
Point Of Departure ◽  
Homogeneous Temperature

The contents of this paper represent a new approach to continuum thermo­dynamics and are chiefly concerned with ( a ) a procedure for obtaining restrictions on constitutive equations, ( b ) an appropriate mathematical statement of the second law and ( c ) the nature of restrictions placed by the latter on thermo-mechanical behaviour of single phase continua. Our point of departure is the introduction of a balance of entropy and the use of the energy equation as an identity for all motions and all temperature distributions after the elimination of the external fields. This is in contrast to the approach adopted in most of the current literature on continuum ther­modynamics based on the use of the Clausius-Duhem inequality. In order to gain some insight into the nature of our procedure we first study the case of an elastic material, which includes that of an ideal fluid as a special case, before the consideration of the second law. We then go on to postu­late an inequality which reflects the fact that for every process associated with a dissipative material, a part of the mechanical work is always con­verted into heat and this cannot be withdrawn from the medium as mech­anical work. The restriction on the heat conduction vector is considered separately and is confined to equilibrium cases in which heat flow is steady. A restriction is also obtained for the internal energy when the body is in mechanical equilibrium subjected to spatially homogeneous temperature fields. Using the above approach, next we study the nature of thermodynamic restrictions on the thermo-mechanical response of a viscous fluid and simple materials with fading memory. A drawback to the Clausius-Duhem inequality is discussed by means of an example. For a class of rigid heat conductors in thermal equilibrium, the Clausius-Duhem inequality requires that if heat is added to the medium, the resulting spatially homogeneous temperature of the conductor decreases . Moreover, the in­-equality denies the possibility of propagation of heat in the conductor as a thermal wave with finite speed. The inequalities proposed in this paper do not suffer from these shortcomings.

scholarly journals Improvement on Selective Laser Sintering and Post-Processing of Polystyrene

Polymers ◽  
2019 ◽  
Vol 11 (6) ◽  
pp. 956 ◽  
Author(s):  
Zhi Zeng ◽  
Xiaohu Deng ◽  
Jiangmei Cui ◽  
Hai Jiang ◽  
Shuo Yan ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Orthogonal Experiment ◽  
Selective Laser Sintering ◽  
Single Layer ◽  
Dimensional Accuracy ◽  
Amorphous Polymers ◽  
Laser Sintering ◽  
Temperature Fields ◽  
Post Processing ◽  
Forming Process

Amorphous polymers are heavily utilized materials in selective laser sintering (SLS) due to their good dimensional accuracy. However, sintered parts of amorphous polymers cannot be used as functional parts owing to their poor forming performance, including their low relative densities and tensile strength. Therefore, post-processing methods are employed to enhance the mechanical properties of amorphous polymers SLS parts without damaging their relatively high dimensional accuracy. In this study, the forming process of selective laser sintering (SLS) and post-processing on polystyrene (PS) was investigated. The orthogonal experiment was designed to obtain the optimal combination of process parameters. The effect of a single process parameter and the laser volumetric energy density (LVED) on dimension accuracy and warpage of the sintered parts were also discussed. In addition, a three-dimensional (3D) thermal model was developed to analyze the temperature fields of single-layer SLS parts and PS powder sintering mechanism. Then, infiltrating with epoxy resin was employed to enhance the mechanical properties of the PS parts. Good resin-infiltrated formulation was obtained based on the mechanical property tests and fractured surface analysis. This research provides guidance for SLS process and post-processing technology in polymers.

scholarly journals A new approach to coat PA12 powders with laser-generated nanoparticles for selective laser sintering

Procedia CIRP ◽  
2018 ◽  
Vol 74 ◽  
pp. 244-248 ◽  
Author(s):  
T. Hupfeld ◽  
T. Laumer ◽  
T. Stichel ◽  
T. Schuffenhauer ◽  
J. Heberle ◽  
...  
Keyword(s):  
Selective Laser Sintering ◽  
Laser Sintering ◽  
New Approach

Selective Laser Sintering of Resin-Coated Sands—Part I: The Laser-Material Interaction

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Fabrizio Quadrini ◽  
Loredana Santo
Keyword(s):  
Focal Spot ◽  
Selective Laser Sintering ◽  
Laser Sintering ◽  
Laser Source ◽  
Layer By Layer ◽  
Sintering Process ◽  
New Approach ◽  
Laser Material ◽  
Definition Of ◽  
Material Interaction

Selective laser sintering of precoated sands is a process utilized to produce molds and cores for rapid casting by adding sand layer by layer and heating it using a laser beam. During the process, the resin flows and binds the grains; subsequently, an oven is used for the postcuring treatment to complete the curing of the resin. The aim of this paper was to study the laser-material interaction using a diode laser to directly obtain the material consolidation. It was the first step in the definition of a new approach for process investigation and innovation. Two main aspects were investigated with the laser source in a standstill position: first, the influence of the laser power, the location of the focal spot, and the exposure time on sand consolidation; second, the shape and dimension of cured samples depending on the process parameters. The experimental data, in terms of weight and size of the hardened sands, were analyzed, and a master curve was found. In Part II of this paper the selective laser sintering process will be implemented to produce shells.

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