Browsing by Subject "laser sintering"

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A NOVEL COATING METHOD USED TO ENABLE MULTILAYER STRUCTURES WITH MICROSCALE SELECTIVE LASER SINTERING
(University of Texas at Austin, 2023) Liao, A.; Behera, D.; Cullinan, M.A.
The microscale selective laser sintering process (µSLS) is an additive manufacturing technique that enables the creation of metal features with sub-5 µm in-plane resolution. In this process, a layer of metal nanoparticle ink is deposited onto a substrate and positioned beneath an optical subsystem with a nanopositioning stage. Using a digital micromirror device, a laser is spatially modulated to selectively heat up particles in desired regions to cause sintering. The substrate is then moved to a coating station where a new layer of nanoparticle ink is applied atop the sintered features. Initially, the slot-die coating process was adopted as the recoating method for this technique. However, due to challenges with depositing consistent ink thickness across the recoated part and limitations with the minimum layer thickness achievable, a new approach inspired by blade coating has been developed to achieve layer thicknesses of less than 1 µm.
Approach to Defining the Maximum Filler Packing Volume Fraction in Laser Sintering on the Example of Aluminum-Filled Polyamide 12
(University of Texas at Austin, 2019) Tarasova, A.; Wegner, A.; Witt, G.
Laser sintering is one of the most popular additive manufacturing techniques that uses thermoplastic polymer powders to generate layer-by-layer complex structures. Despite its broad application, some limitations exist restricting its further development. One such restriction is a narrow assortment of commercially available materials that would allow the production of the parts with the desired mechanical characteristics, which is the case with the widely used Polyamide 12 (PA12). Reinforcement of a matrix polymer with metal particles is routinely performed to achieve better mechanical properties. In this work, a PA12 system enhanced with a 35% volume ratio of aluminum was investigated. Mechanical characteristics, e.g. elastic and flexural moduli, were examined with respect to variation of manufacturing process parameters. In addition, a new methodology was tested, which should help determine the maximum filler packing volume fraction corresponding to the highest mechanical characteristics of a polymer-filler mixture.
Areal Surface Characterization of Laser Sintered Parts for Various Process Parameters
(University of Texas at Austin, 2017) Delfs, P.; Schmid, H.-J.
Laser sintered polymer parts consist of rough surfaces due to the layered manufacturing and adherence of incomplete molten particles. The absolute roughness depend on various process parameters like build angle, spatial position, build temperature, exposure order and layer time. Analyses with the help of several areal roughness values of DIN EN ISO 25178-2 considering these parameters are introduced in this paper. Multiple build jobs with 120 µm layer thickness and PA2200 powder were built on an EOS P396 machine using the same build job design with varying process parameters. An individual sample part was designed to receive lots of surface topography information with optical 3D measurements. The results show roughness dependencies for 0° to 180° build angles in 15° steps and eleven distributed in-plane and three axial direction positions depending on different build temperatures, reversed exposure order and layer times. Limitations of the varied parameters are finally derived for the manufacturing of improved surface qualities.
Assessing the Impact of the Powder Production Method on Ceramic-filled Polyamide Composites made by Laser Sintering
(University of Texas at Austin, 2023) Kletetzka, I.; Neitzel, F.; Schmid, H.-J.
Polymer composites represent the industry standard in injection molding for the production of plastic components with increased requirements in terms of heat resistance and stiffness. In the field of laser sintering (LS), these materials are less common so far. In order to extend the available material variety for the LS process, new ceramic-filled Polyamide 613 powders are investigated within the scope of this work. Here, the resulting properties from two different powder production methods are compared. One filled powder is produced by dry blending and the other powder with the same filler and filling ratio is produced by encapsulating the filler particles inside the polymer particles within the dissolution-precipitation process. It was found that encapsulating the filler particles can provide certain benefits for the processability, for example an improved powder flowability or better filler dispersion. However, encapsulating the filler also alters the thermal properties of the precipitated powder.
Carbon Nanotube Reinforced Polyamide 12 Nanocomposites for Laser Sintering
(University of Texas at Austin, 2012-08-22) Bai, Jiaming; Goodridge, Ruth D.; Hague, Richard J.M.; Song, Mo
In this work, Polyamide12 (PA12) and Carbon nanotube (CNT) added PA12-CNT nanocomposites were laser sintered and investigated. The powder morphology and CNT dispersion of the PA12-CNT were examined. Laser sintering process parameters: powder bed temperature and laser power were studied and optimised. The effect of the addition of CNT on the thermal properties of PA12 was identified. Compared to the laser sintered parts produced from commercially available laser sintering PA12 powder, the laser sintered PA12-CNT parts showed increased tensile modulus and tensile strength.
Characterizing the Bulk & Flow Behaviour of LS Polymer Powders
(University of Texas at Austin, 2013-08-16) Ziegelmeier, Stefan; Wöllecke, Frank; Tuck, Christopher; Goodridge, Ruth
The properties of laser sintering (LS) powders affect processability and the quality of parts manufactured. This study compared three different methods used to quantify both the static and dynamic powder properties – a Revolution Powder Analyzer, FT-4 Powder Rheometer and Hausner Ratio. The aim of the work was to identify the most reliable method to characterize powder properties in correlation to the dynamic conditions that occur during LS. The experiments focused on different particle size distributions of a cryogenically ground polyurethane powder compared to a standard polyamide 12 LS material, PA2200. The results have led to a deeper understanding regarding powder interactions and therefore serve as input for material design and quality assurance.
A Comparison of Polyamide 11 Mechanical Properties Between Laser Sintering and Traditional Molding
(University of Texas at Austin, 2012) Leigh, David K.
Tensile properties of laser sintering grade Polyamide-11 are processed using laser sintering, compression molding, and injection molding and the resultant mechanical properties are reported. The primary contributor to the enhanced mechanical properties of injection molded specimens is a fully healed polymer melt with preferred polymer chain orientation. It can be shown that laser sintering and compression molding specimens have comparable to compression molding specimens Ultimate Tensile Strength (UTS) and Elongation at Break (EOB).
Considerations of internal void generation process by observation of melting and solidification behavior in low temperature laser sintering of PEEK
(University of Texas at Austin, 2023) Kigure, T.; Yamauchi, Y.; Ninno, T.
Laser sintering of PEEK performed below the crystallization temperature has been achieved in previous study by low temperature process that anchors the part to a rigid base plate to suppress warpage during processing. However, significant surface roughness and large internal voids are sometimes generated in the parts built by low temperature process, and there are problems in stability of parts quality. The purpose of this study is to contribute to quality improvement of laser sintering of PEEK by low temperature process. It was attempted that clarify the process of surface roughness and void generation by observing the melting and solidification behavior of the material during process with a video camera. From these observation results, it was assumed that the amount of volume change from powder to liquid due to melting and the amount of shrinkage due to solidification affect part quality such as surface roughness and internal voids.
Controlled Multi-Scale Turbulence through the Use of Laser Sintered Sierpinski Pyramids
(University of Texas at Austin, 2013) Liu, Y.; Beck, S.; Nicolleau, F.; Majewski, C.E.
The research presented here is the result of a new collaboration between the Centre for Advanced Additive Manufacturing (AdAM) and the Thermofluids group at The University of Sheffield, regarding the use of fractal geometries for the control and influence of fluid flow. It is believed that the use of multiscale objects can be used to introduce many different orders of turbulence into a flow. However, whilst substantial simulations have been carried out in this area, the complexity of the physical geometries means that to date these have not been validated via physical testing. In this work, varying orders of Sierpinski pyramids were produced using Laser Sintered PA2200 and analysed in a wind tunnel with regards to their effects on air flow through the structures. As predicted by theoretical analyses, the coarsest pyramids induced large vortices into the air-stream, whereas the more complex orders induced vortices at a number of different scales, rapidly developing into a standard turbulent flow. Further investigations are planned to isolate the effects of the smaller-scale turbulence in this situation.
Controlling the Quality of Laser Sintered Parts Along the Process Chain
(University of Texas at Austin, 2012-08-22) Rüsenberg, S.; Weiffen, R.; Knoop, F.; Schmid, H.-J.
The quality of laser sintered parts, in this work, manufactured by polymer laser sintering by using an EOSINT P395 Laser Sintering system, depends on several steps along the process chain. The first step is the characterization of the powder quality, whereas the rheological and physical investigations of nylon 12 powder are shown. By changing some important influencing factors, for example the powder ratio, the powder ageing and the moisture content, the influence on mechanical and physical properties, density and porosity, are investigated. The composition of the used powder is known. The previous process (storage conditions, etc.) as well as the laser sintering process (regarding energy density, temperature, etc.) is kept constant for the duration of this work. Regarding the post process in this work the cooling down phase is investigated as well. With an automatically blasting system it is possible to keep the post process parameters blasting distance and blasting time, constant. All of the tests will be performed using dry and conditioned test specimens. This work is showing the dependence on mechanical, rheological and physical parameters by varying important influencing factors along the laser sintering process quality chain.
Cost Impact of the Risk of Build Failure in Laser Sintering
(University of Texas at Austin, 2016) Baumers, M.; Holweg, M.
While the feasibility of adopting Additive Manufacturing (AM) has been demonstrated in a range of industrial sectors, the total costs associated with the operation of the technology are not fully understood. This study reports the results of a series of build experiments in a controlled environment for the analysis of the total cost of the AM technology variant Laser Sintering (LS). Incorporating a structured representation of the process flow of LS, the developed cost model shows for a LS system of the type EOSINT P100 that the expected cost impact of build failure has a substantial effect, responsible for a share of up to 38% of total costs. The analysis further demonstrates that, due to the adverse effects of such ill-structured costs, the cost efficient level of build volume utilization is sub-maximal. This result is discussed in the context of the operational reality of using LS technology and the availability of economies of scale.
Creating Complex Hollow Metal Geometries using Additive Manufacturing and Electroforming
(University of Texas at Austin, 2012-08-22) McCarthy, D.L.; Williams, C.B.
Additive manufacturing introduces a new design paradigm that allows the fabrication of geometrically complex parts that cannot be produced by traditional manufacturing and assembly methods. In this paper, the authors investigate the combination of laser sintering with an electroforming process using electroless nickel plating to produce complex, thin-walled, hollow, metal geometries. The resulting geometries cannot be produced directly with other additive manufacturing systems. The resulting process is used to produce a cellular nickel structure featuring 800µm walls that is 65 vol% air from a polyamide substrate with 3mm pores.
Curing and Infiltration Behavior of UV-Curing Thermosets for the Use in a Combined Laser Sintering Process of Polymers
(University of Texas at Austin, 2019) Wudy, K.
The investigation in this study addresses a new additive manufacturing process, which enables the production of multi-material parts consisting of thermosets and thermoplastics. A liquid thermoset resin will be applied with a micro value syringe in the laser sintering (LS) system. The liquid thermoset reacts parallel to the laser exposure of the thermoplastic powder. Therefore, in this study the UV curing and the infiltration behavior of the thermoset will be investigated under process relevant conditions. The investigations show a strong temperature dependent absorption of the liquid in the powder bed, whereas, the surface tension of the liquid plays a minor role. Furthermore, the UV curing of the thermosets takes place at low interaction times and at lamp powers between 100 and 300 mW/cm².
Development of an Experimental Laser Sintering Machine to Process New Materials Like Nylon 6
(University of Texas at Austin, 2017) Lohn, Johannes; Kummert, Christina; Schmid, Hans-Joachim
Selective Laser Sintering (SLS) is an Additive Manufacturing technology which allows the production of functional polymer parts. Conventionally, Nylon 12 (PA 12), Polyamide 11 (PA 11), glass- or aluminum filled materials are used. Those materials do not always meet the requirements for direct production of serial parts by laser sintering. For the so called “Direct Manufacturing” of high quality, functional parts, the laser sintering process needs to be further developed and the choice of materials and needs to be expanded. During this research, a laser sintering machine for material qualification has been built up. The advantages are an optimized software solution, an innovative optical system with an adjustable laserspot, an alternative powder coating system and an improved temperature control. The functionality of the test equipment is proved with the standard material PA2200 and the new laser-sintering-material, Polyamide 6X (PA6X) is investigated. The required process parameters for processing PA6X are derived and the mechanical properties are determined by tensile tests.
Effect of Segregated First and Second Melt Point on Laser Sintered Part Quality and Processing
(University of Texas at Austin, 2012) Fulcher, Ben; Leigh, David K.
Efforts to tailor laser sintering polymers to enhance part quality, performance, and processing have relied on the characterization of the polymers using Melt Flow Index (MFI) and Differential Scanning Calorimetry (DSC). Two grades of laser sintering nylon polyamide are compared and the resultant processing window, part quality, and mechanical behavior are discussed. A better understanding of characterization techniques and the processing of laser sintered polymers is leading to engineering thermoplastics for exclusive use in additive manufacturing.
Effects of Laser Window Degredation on Laser Power and Distribution in Laser Sintering
(University of Texas at Austin, 2013) Fulcher, Ben; Leigh, David K.
Laser power is a key parameter in the laser sintering (LS) process, and tight control on laser power is necessary to produce quality parts with desirable mechanical properties. Unfortunately, temperature limitations hinder real-time monitoring and feedback of laser power within the process chamber. Therefore, in order to maintain consistent laser power during an LS build, the laser window, which provides a barrier between the processing chamber and the laser housing, must remain clean throughout the build. However, material outgassing leads to the buildup of condensation on the window, thereby reducing the amount of energy imparted to the powder bed. The buildup of condensation also necessitates frequent cleaning of the laser window and significantly reduces its life. Thus, laser window replacement is a large source of cost in a production environment. To compensate for the loss of laser power through the window, current practice is to steadily increase the laser power at the laser source during the build. This practice can be largely inaccurate, as it is difficult to predict the loss of laser power through the window at various stages in a given LS build. Thus, to achieve consistent mechanical properties in this manner, a trial and error-based approach is used. The study presented in this paper aims to characterize laser power and distribution for various levels of laser window degradation. In addition, methods to reduce or eliminate the buildup of condensation on the laser window are explored in an effort to improve the consistency of part quality, as well as to reduce maintenance requirements and costs.
Effects of Spherical Fillers on the Processability and Mechanical Properties of PA613 and PP-Based Laser Sintering Dry Blends
(2022) Kletetzka, I.; Gawlikowicz, R.; Schmid, H.-J.
Polymer materials filled with particles may show substantially altered mechanical properties. Therefore, it is an important aim to be able to tailor the mechanical properties of LS components by adding fillers and thus to create new application areas for additively manufactured components. In this work, the influences of spherical fillers on the processing properties and the resulting mechanical properties of laser-sintered components are investigated. For this purpose, micro glass spheres, hollow glass bubbles and mineral spheres are dry blended to the matrix polymers polyamide 613 and polypropylene with filling ratios of 20 and 40 vol%. First, relevant properties of the blends, such as powder flowability, thermal behavior and melt viscosity, are investigated. Based on the results, processing parameters are then developed for the laser sintering (LS) process and the mechanical properties of the components are investigated.
Efforts to Reduce Part Bed Thermal Gradients During Laser Sintering Processing
(University of Texas at Austin, 2012-08-15) Yuan, Mengqi; Bourell, David
Part bed surface thermal gradients (x-y plane) are usually present in laser sintering (LS) fabricators. The purpose of this study was to investigate various means to reduce these thermal gradients. Several experiments were conducted using a FLIR™ infrared camera to examine the thermal profile of the part bed during the LS operation. Experiments included thermal profile characterization of the part bed with different nitrogen shielding gas flow rates, assessment of the proper experimental settings, and a temperature profile record of the part bed from the warm-up to the cool-down stage. A series of experiments were conducted using the laser as a heat source to preheat part bed surface cold spots to decrease the thermal gradients, which effect was limited by the natural low thermal conductivity of nylon 12 powder and large heat convection. Moreover, manifolds were mounted below the piston to provide warm nitrogen down draft flow during the LS operation.
An Experimental Study of the Relationship between Microstructure and Mechanical Properties of a Ceramic Composite Fabricated by Selective Laser Sintering
(1992) Lakshminarayan, Uday; Marcus, H.L.
Alumina-ammonium phosphate powder blends were processed with Selective Laser Sintering. Ammoniumphosphate with a melting point of 190°C, acts as a binder when processed with a laser and holds the alumina (m.p. 2300°C) particles together to form a "green" body. When the green body is heat treated at 850°C for 6 hours, ammonium phosphate decomposes evolving ammonia and water vapor. Residual P205 reacts with alumina to form aluminum phosphate. This results in a composite of unreacted alumina with a coating of aluminum phosphate around the alumina particles. The variation of compressive strength of these low density ceramic composites was investigated in terms of the particle size distribution the amount of binder in the initial blend. It was observed that the strength depends on the relative density and initial blend composition and the critical flaw size. A constitutive equation was formulated to characterize the influence of the relative density, binder composition and the critical flaw size on the strength of the composite.
Fabrication of Custom Dynamic Pedorthoses for Clubfoot Correction via Additive-Based Technologies
(University of Texas at Austin, 2009-10-07) Gervasi, Vito; Cook, Douglas; Rizza, Robert; Kamara, Sheku
Additive technologies have created many opportunities to improve the quality of life for patients in a range of medical applications. This paper provides an overview of how several of these technologies were leveraged to transform custom pedorthosis designs into physical, end-use, custom pedorthoses for clubfoot patients. The pedorthoses that were produced are currently being tested on the respective patients for their improvement in mobility and degree of clubfoot correction, and will continue through early 2010. The advantage of this approach is the reduction in labor and the increase in degrees of design freedom available, compared to conventional methods of fabricating orthotic devices. Several new approaches for fabricating custom orthotic devices that were explored, and the related results, are discussed.