Browsing by Subject "Laser sintering"

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Additive manufacturing of laser sintered polyamide optically translucent parts
(2013-12) Yuan, Mengqi, 1989-; Bourell, David Lee
Lithophane is a translucent image created by varying the plate thickness; the image is observed using a back lit light source. Software Bmp2CnC linearly converts the black and white image grayscale into the thickness, thus generates CAD file and lithophane is fabricated by additive manufacturing machines. Additive manufacturing makes highly complex lithophane fabrication possible. It is a convenient, rapid, green, design-driven, and high precision way to make lithophanes, and no post processing is needed. Optical properties of laser sintered polyamide 12 translucent additive manufactured parts were analyzed in this dissertation. First, selected optical properties of laser sintered polyamide 12 blank plates under different monochromatic light and white light were investigated and applied in production of laser sintered lithophanes to achieve better performance. A spectrophotometer was used to measure the transmittance of visible light through laser sintered polyamide 12 plates as a function of plate thickness. The transmittance decreased with increasing plate thickness according to a modified Beer-Lambert Law, and it varied significantly depending on the monochromatic wavelength. Monochromatic LEDs were used to assess the wavelength dependence on the transmission and contrast. Highest transmission was observed with green light (540 nm), and poorest transmission was measured for yellow light (560 nm). Second, several parameters affecting lithophane manufacturing performance were analyzed including lithophane orientation with respect to light source, brightness and contrast versus plate thickness and grayscale level, quantized plate thickness correction, surface finish quality, and manufacturing orientation. It was found that brightness was relative to the plate thickness. The contrast was defined by the lithophane grayscale level, which was influenced by sintering layer thickness, plate thickness, and sintering orientation. Thinner sintering layers resulted in more grayscale levels of the image and smaller difference between the theoretical thickness and actual thickness. Relatively larger plate thickness defined greater contrast; however, the plate thickness was limited due to the light transmission. Lithophane quality was largely improved by changing the manufacturing orientation from the XY plane orientation to the ZX/ZY plane orientation. The grayscale level changed continuously when parts were constructed in the z orientation. Third, other thermoplastic semi-crystalline materials were analyzed for LS optically translucent part production. Last, plates and lithophanes were built using a different AM platform: stereolithography (SL) with Somos® ProtoGen[Trademark] O- XT 18420 white resin. Different optical properties and lithophane performance were found and compared with PA 12 parts. In conclusion, laser sintered polyamide 12 optical properties varied with light wavelength and reached the maximum under green light. When building in the XY plane, thinner layer thickness (0.07 mm) and relative thicker maximum plate thickness (3.81 mm) leaded to higher contrast and greyscale level. Lithophane quality was largely improved when fabricated in the ZX/ZY plane orientation. Lithophanes made from stereolithography were analyzed but showed lower contrast due to the optical property difference of the white resin. Laser sintered lithophanes serve as an interesting and complex LS industrial application. Optical properties, manufacturing aspects, and other related issues were analyzed and discussed in this dissertation. Future work may include the use of nanocomposites for optimal lithophane performance, and more precise manufacturing processing to improve the lithophane resolution.
Design and verification of a finite element analysis model for predicting deflection of actively actuated prosthetic sockets
(2011-12) Rodriguez, Rafael, 1985-; Crawford, Richard H.; Bourell, David L.
A lower limb prosthesis provides assistance to its user in both ambulation and stationary support. The lower limb prosthesis consists of a socket, which interfaces with the residual limb, a pylon, attachment hardware to secure the pylon to the socket, and a prosthetic foot. For the prosthesis to be effective, the socket must be comfortable, functional and aesthetically appealing, usually in that order. Lack of comfort and fit can cause movement problems and health issues. The residual limb of the amputee changes its volume throughout the day and in order to maintain comfort a socket must be able to adapt to these volume changes. Previous research has resulted in the development of concepts for inflatable prosthetic sockets capable of addressing this need. The concepts rely on laser sintering (LS) to manufacture the parts. This research focuses on the development of a finite element analysis (FEA) method to assist in the design of adaptive sockets. The FEA can be used to predict the pressure-deflection curve of a given socket design. The FEA method was verified by experiments using LS manufactured test specimens. Results from FEA simulations indicate that the LS-manufactured sockets will achieve the desired deflection (~0.1 in) for relatively low pressures (< 10 psi), providing evidence for the feasibility of this approach.
Effect of in-plane voiding on the fracture behavior of laser sintered polyamide
(2011-12) Leigh, David Keith; Bourell, David Lee; Beaman, Joseph J.
Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture.
Electrochemical deposition of metal ions in porous laser sintered inter-metallic and ceramic preforms
(2010-12) Goel, Abhishek, 1986-; Bourell, David Lee; Beaman Jr., Joseph J.
Selective laser sintering (SLS) is a commercial, powder-based manufacturing process that produces parts with complicated shape and geometry based on a computer solid model. One of the major drawbacks of SLSed inter-metallic and ceramic parts is their high porosity because of the use of binder system. High porosity results in poor mechanical, electrical and thermal properties of the preform and hence renders it unsuitable for various applications. This thesis attempts to infiltrate SLSed preforms by carrying out electrochemical deposition of metal ions inside the interconnected pore network. One of the major benefits of carrying out this novel process is low processing temperature as opposed to existing methods such as melt infiltration. Low temperature reduces both energy consumption and associated carbon-footprint and also minimizes undesirable structural changes. Both conductive and non-conductive preforms may be electrochemically infiltrated, and MMCs produced by this method have potential for use in structural applications.
Electrochemical infiltration into laser sintered porous graphite and silicon carbide
(2015-05) Bhat, Abhimanyu; Bourell, David Lee; Kovar, Desiderio; Wheat, Harovel; Beaman, Joseph; Juenger, Maria
Indirect laser sintering is a technique used for direct manufacturing of high melting materials such as graphite and silicon carbide. This technique produces parts with high pore volume fraction and poor structural stability. Such parts are post processed using melt infiltration techniques with metals or alloys such as copper and brass. These processes require high temperature and are not environmentally sustainable and may also encounter restrictions because of infiltration atmosphere. Electrodeposition of a metal into the porous parts produced via laser sintering is an alternate route for filling these parts. Such a route required infiltration of the porous parts with a suitable electrolyte and subsequent electrodeposition of the metal ions into the pore network. Electrodeposition provides a versatile and convenient route to the realization of bulk structures and coatings of metal matrix composites. In the present study, electrodeposition of copper into the pore network of laser sintered graphite and silicon carbide was studied. A theoretical model based on Butler-Volmer equation was made to predict electrodeposition rates across the porous preforms by simulating the current density distribution across the porous part in an electrodeposition cell. The theoretical model was used to determine most favorable conditions required to complete electrolytic infiltration. Electrolytic infiltration of copper was carried out into laser sintered graphite and silicon carbide parts and commercially available porous preforms such as Nomex felt, graphite felt and a stainless steel mesh, using flow electrolysis methods. This study shows that electrochemical deposition of metals in the pore network of a highly porous material is possible under certain conditions. It was realized that the most favorable conditions for electrolytic infiltration exist when the porous preform being infiltrated is thin, and is a poor conductor of electricity. Hence, it is possible to fabricate highly dense metal matrix composite coatings via electrochemical infiltration. In this study Nomex fibers, Stainless Steel 316 mesh, graphite and silicon carbide were used to reinforce electrodeposited copper coatings on copper-110 alloy, and their thermal and tribological properties were measured.
Improving process stability and ductility in laser sintered polyamide
(2019-01-25) Leigh, David Keith; Bourell, David Lee; Beaman, Joseph J; Kovar, Desiderio; Mangolini, Filippo; Juenger, Maria
The desire to manufacture production parts using additive manufacturing has created an increased demand on the laser sintering technology to supply this need. A significant issue in laser sintered polymers is the variability of mechanical properties from build-to-build and the inability to determine the success or failure of the production process until the production builds are complete. Interlayer ductility of parts produced in the laser sintering process has been shown to be uncontrolled and unpredictable. This research focuses on improving interlayer ductility and establishing a baseline for modeling the time-temperature-transformation of production-grade, laser-sintered polymers. The background shows that there has been a significant amount of research to map processing parameters to mechanical properties and that industry has been focused on recording processing parameters and mechanical properties as part of the quality record. The research shows trends in mechanical performance that are not adequately explained with current analytical techniques. The experimental research characterized the thermal attributes of the laser sintering process using onboard sensors, production build data, external thermal cameras, and in-situ thermocouples to map the thermal profile of a complete laser sintering build. This information, used in conjunction with an array of over 80,000 production build tensile data points, provides the basis for a thermal model for laser sintered polymers. Current laser energy models in laser sintering are incomplete and do not consider many processing parameters available in the laser sintering process, focusing primarily on the build surface temperature and the laser energy applied to the part region. A more complete thermal model must also account for the energy exposure during the build. The thermal process model is developed to integrate the thermal history during the build and cooldown cycle as a metric of success. It will be shown that improved and more predictable ductility performance is achievable, and that a thermal process model can be used to characterize the energy input required over time to achieve optimal results. Ultimately, increased reliability in laser sintered polymer parts will increase their usage in commercial applications.
Integration of Numerical Modeling and Laser Sintering with Investment Casting
(1994) Pintant, T; Sindel, M.; Greul, M.; Burblies, A.; Wiklening, C.
Industry has a great demand for metallic prototypes to speed up product development. At present there are several RP-technologies for direct fabrication of metal components in development. Today secondary processing of polymer or wax models, like investment casting or sand casting, is a very common way for the production of metallic prototypes. There are, however, several problems in investment casting resulting from laser sintered models made of wax or polycarbonate. Recently a polymer mixture consisting of nylon material and a second polymer has been tested with the laser sinter process in a newly developed sinter machine (EOSINT 350 - 60). Shells for investment casting could be prepared easily with the models in a conventional assembly-line. Several castings of laser sintered models in Al were successfully realized. In future, integration of modeling based on FEM calculations with RP for castings will become more important. Calculations will support the designer to optimize the structure of components and their processing. A viable method will be presented where a new FEM based calculation method to optimize the structure design of a model is integrated with RP. Optimizing castings with FEM will be supported by integration with RP.
Laser sintering for high electrical conduction applications
(2012-05) Murugesan Chakravarthy, Kumaran; Bourell, David Lee; Manthiram, Arumugam; Meyers, Jeremy P.; Beaman, Joseph J.; Juenger, Maria G.
Applications involving high electrical conduction require complex components that are difficult to be manufactured by conventional processes. Laser sintering (LS) is an additive manufacturing technique that overcomes these drawbacks by offering design flexibility. This study focuses upon optimizing the process of laser sintering to manufacture functional prototypes of components used in high electrical conduction applications. Specifically, components for two systems – high current sliding electrical contacts and fuel cells – were designed, manufactured and tested. C-asperity rails were made by LS and tested in a high current sliding electrical setup. Corrugated flow field plates were created by LS and their performance in a direct methanol fuel cell (DMFC) was tested. This is the first experimental attempt at using laser sintering for manufacturing such complex components for use in high electrical conduction applications. The second part of this study involves optimization the laser sintering process. Towards this, efforts were made to improve the green strength of parts made by LS. Particle size of graphite/ phenolic resin and addition of nylon/11 and wax were tested for their effect upon green strength. Of these, significant improvement of green strength was observed by altering the particle size of the graphite/ phenolic resin system. New methods of improving green strength by employing fast cure phenolic resins with carbon fiber additions were successfully demonstrated. This study also identified a binder system and process parameters for indirect LS of stainless steel –for bipolar plate compression/ injection mold tooling. All the experimental results of this study lead us to believe that laser sintering can be developed as a robust and efficient process for the manufacture of specialized components used in advanced electrical conduction systems.
Laser-based solid freeform fabrication techniques for the direct production of ceramic and metal/ceramic shapes
(1995-08) Birmingham, Britton Ray; Not available
Methodology for mechanical property optimization of selective laser sintered parts using design of experiments
(2017-05) Milisits, Lauren Violet; Djurdjanovic, Dragan; Bourell, David Lee
Selective laser sintering (SLS) is a form of additive manufacturing progressively used to manufacture end-use parts for industries including aerospace, automobile and biomedical. Machine settings, laser settings, and powder properties are all input parameters that affect the dimensional quality and mechanical properties of the produced SLS parts. A key challenge to successfully manufacturing SLS parts is learning how to control these parameters and finding the optimal settings such that desired mechanical properties are robustly achieved. This thesis proposes a design of experiments (DOE) based methodology to optimize mechanical properties of SLS parts. The study performs a DOE on three design variables (fill laser power, outline laser power, scan spacing) with three levels and measures six response variables (tensile strength, tensile modulus, tensile elongation-at-break, density, hardness, surface roughness). Experiments are performed using a work material of ALM PA 650 unfilled nylon 12 performance polyamide blend. The effects of the selected parameters on different part quality metrics are analyzed and discussed. A confirmatory test to prove the optimized model is performed and evaluated.