Browsing by Subject "Additive manufacturing"
Now showing 1 - 13 of 13
Results Per Page
Sort Options
Item Additive manufacturing of laser sintered polyamide optically translucent parts(2013-12) Yuan, Mengqi, 1989-; Bourell, David LeeLithophane 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.Item Characterization of quartz lamp emitters for high temperature polymer selective laser sintering (SLS) applications(2013-12) Kubiak, Steven Thomas; Beaman, Joseph J.This thesis provides investigation into the interaction between quartz lamp emitters and polyether ether ketone (PEEK) powder. Calculations and experiments concerning the conductivity and emissivity of the powder at various temperatures are performed. The thermal profile of the emitter on a flat powder bed is captured using thermal imaging. The effect of exposing a pile of powder to the emitter and the subsequent thermal gradient through the pile is measured and analyzed. Based on these results, ramifications for the application of these emitters to selective laser sintering (SLS) machines for processing high temperature polymers such as PEEK are discussed.Item A compilation of design principles and guidelines for selective laser sintering(2016-05) Pradhan, Nivedita; Seepersad, Carolyn C.; Crawford, Richard HThe term Additive Manufacturing (AM) is used to describe several manufacturing technologies that share the same basic principle of producing parts directly from their CAD models without the need for special tooling, by adding material selectively one layer at a time. Current research focuses on one such technology called Selective Laser Sintering (SLS) where thin layers of powdered thermoplastic material are fused using a laser beam. With no part-specific tooling required, the product development cycle is drastically shortened. This lack of tooling, coupled with freedom of placement of material, opens the door to several design opportunities unique to AM such as increased geometrical design freedom and the ability to manufacture low production volumes economically. Gradual improvements in process accuracy and selection of materials over time have resulted in a shift in application of AM from rapid prototyping to direct manufacturing and even ‘democratization’ of the product development process in which even non-professional users can rapidly manufacture products as long as there is a CAD model for the part. However, the move to direct manufacturing of end-use parts also means that part quality in terms of conformance to product specification becomes important for the product to successfully perform its function. The research in this thesis is focused on documenting these manufacturability capabilities and limitations for Selective Laser Sintering. It focuses specifically on thermoplastics, especially Nylon 12 polyamide materials known by the trade names PA 2200 and Duraform PA. While several design resources have been created based on industry best practices developed through experience, they are scattered throughout the literature and are not readily available to designers. It is also difficult to compare and draw quantitative inferences from existing guidelines as they are developed independently under dissimilar process conditions. Therefore, a prime focus of this research is to synthesize and compile existing guidelines into a comprehensive document. The first objective of this research is to compile a user-friendly resource, in the form of design principles and guidelines, to help designers make early process selection decisions, optimize part quality and minimize manufacturing cost. A systematic literature review of available guidelines, exploratory studies and case studies is conducted to develop actionable design recommendations that are within the scope of the designer. The second objective of this research is to address the lack of adequate process tolerance information that can reliably predict the quality of parts produced by the selective laser sintering process. This information is important to accurately evaluate the process during early process selection. A test part is proposed to measure dimensional deviations for various features (such as holes, gaps, cylinders, walls, clearances, etc.) across a range of dimensions and along different orientations. Finally, a sampling plan that represents sources of variability in the process is put forward to collect statistical data in an economical manner.Item Design and evaluation of negative stiffness honeycombs for recoverable shock isolation(2015-05) Correa, Dixon Malcolm; Seepersad, Carolyn C.; Haberman, Michael RNegative stiffness elements are proven mechanisms for shock isolation. The work presented in this thesis investigates the behavior of negative stiffness beams when arranged in a honeycomb configuration. Regular honeycombs consisting of cells such as hexagonal, square, and triangular absorb energy by virtue of plastic deformation which is unrecoverable. The major goal of this research is to investigate the implementation of negative stiffness honeycombs as recoverable shock isolation so as to better the performance of regular honeycombs.To effectively model the honeycomb behavior, analytical expressions that define negative stiffness beam behavior are established and finite element analysis (FEA) is used to validate them. Further, the behavior of negative stiffness beams when arranged in rows and columns of a honeycomb is analyzed using FEA. Based on these findings, a procedure for the optimization of negative stiffness honeycombs for increased energy absorption at a desired force threshold is developed. The optimization procedure is used to predict trends in the behavior of negative stiffness beams when its design parameters are varied and these trends are compared to those observed in regular honeycombs. Additionally, experimental evaluations of negative stiffness honeycombs under quasi-static loading are carried out using prototypes built in nylon 11 material manufactured by selective laser sintering (SLS). Energy absorption calculations conclude that optimization of negative stiffness honeycombs can yield energy absorption levels comparable to regular honeycombs. A procedure for dynamic testing of negative stiffness honeycombs is discussed. Results from dynamic impact testing of negative stiffness honeycombs reveal excellent shock absorption characteristics. FE models are developed for static and dynamic loading and the results show strong correlation with experiments. Further, temperature dependency of nylon 11 is investigated using impact tests on honeycomb prototypes. Finally, example applications utilizing negative stiffness honeycombs are discussed and recommendations are made for their refinement.Item Design of desktop-scale metal wire-feed prototyping machine(2016-12) Chang, Yu-Chuen; Crawford, Richard H.The appearance of desktop 3D printers has inspired a trend toward increased personal fabrication. However, there are few desktop systems that can process metal for prototyping. This thesis reports on the design of a desktop scale prototyping machine that uses metal wire as a precursor material. The machine is intended for use by makers to produce wire-form prototypes, such as wire sculptures. The design of the system assumes a layer-based fabrication approach. As such, the joining capability of the machine is the most important subsystem. During the research, various conceptual configurations were developed and investigated to determine their thermal bonding efficiency using a metallurgical welding simulation model. The selected bonding method is TIG welding. Two experiments were conducted to test the bonding speed and strength of the bonding spot to validate the feasibility of the concept. A wire bending subsystem was also developed. The selected wire bender is oriented vertically and uses a servo motor and solenoid to perform wire bending and cutting.Item Development of novel tapered pin fin geometries for additive manufacturing of compact heat exchangers(2016-08) Cohen, Julien Harry; Bourell, David Lee; Beaman, Joseph JPin fin arrays are widely used to enhance forced convection heat transfer across various industries, finding application in turbine blade trailing edges, electronics cooling, and broadly for compact heat exchange. Fin shape greatly affects flow separation and turbulence generation, and optimizing performance relies on a balance between increased heat transfer and increased pressure loss along the array. Straight circular pin fins are well-characterized in the literature, and recent works have proven more complex elliptical and teardrop cross-sectional shapes to exhibit performance enhancements in both parameters. There exist few studies in the public record on tapered circular pin fins, but these have also proven to exhibit performance enhancements. To date, no example of research has been identified for tapered, complex pin fin geometries, and although these represent an avenue for overall performance gains, manufacturing the intricate components is difficult and time-consuming using conventional machining processes. The unique and nascent capabilities of additive manufacturing now allow their economical fabrication in an increasing number of fully-dense engineering materials. This thesis compares 21 fin arrays of varying fin cross-section, taper angle, taper profile, and array pattern, separated into eight geometry families. Experimental testing was carried out on a prototype open-loop wind tunnel and corroborated with computational fluid dynamics simulations. Non-dimensional metrics were defined and used to holistically compare heat transfer efficiency, pressure loss characteristics, and overall balanced performance between fin arrays. Topics for future work and potential methods of investigation are suggested.Item 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.Item Extreme energy absorption : the design, modeling, and testing of negative stiffness metamaterial inclusions(2013-08) Klatt, Timothy Daniel; Seepersad, Carolyn C.; Haberman, Michael R.A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes, et al., Nature, 410, pp. 565-567, (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The nonlinear multiscale model is then utilized in a set-based hierarchical design approach to explore the design space over a wide range of inclusion geometries. Finally, prototype NS inclusions are fabricated using an additive manufacturing technique and tested to determine quasi-static inclusion stiffness which is compared with analytical predictions.Item The innovation station : a 3D printing vending machine for UT Austin students(2015-05) Kuhn, Joshua Brian; Seepersad, Carolyn C.; Crawford, Richard HThe Innovation Station is designed to provide on-demand, web-enabled 3D printing securely in a public space. The overarching goal is to lower the barriers to 3D printing at a university, to facilitate innovation and creativity, and to inspire future engineers. Both hardware and software innovations were required to realize this capability. From the hardware side, the design team invented a process to automatically remove parts from the 3D printer and sweep them into a bin from which users can retrieve them without directly accessing the 3D printer. From the software side, in partnership with the Faculty Innovation Center (FIC) at UT Austin, the design team created a web portal that allows students to upload parts remotely and access detailed directions for creating parts. It also allows administrators to remotely manage the queue and initiate builds. Together, the hardware and the software innovations enable printing multiple jobs continuously without user intervention and remote cancellation of jobs. Plans for the entire station, both hardware and software, are intended to be open source, with a startup cost of less than $4,000, plus the cost of the printers, for recreating the station at a new location.Item Mobility in individuals with traumatic lower-limb injuries : implications for device design, surgical intervention and rehabilitation therapies(2016-05) Ranz, Ellyn Cymbre; Neptune, Richard R.; Barr, Ronald E; Crawford, Richard H; Sulzer, James S; Wilken, Jason MTraumatic injuries to the extremities are commonly observed in emergency room patients and military personnel in combat. Restoring high mobility and functionality is a primary goal post-injury, which may require the use of rehabilitative devices, surgical interventions, and rehabilitation therapies. The research detailed in this dissertation investigates specific elements of these approaches through the use of experimental study and modeling and simulation. In the first study, the influence of passive-dynamic ankle-foot orthosis bending axis on the gait performance of limb salvage subjects was investigated. Bending axis location was altered by fabricating customized orthosis components using additive manufacturing and was tested in a gait laboratory. Altering bending axis location did not result in large or consistent changes in gait measures, however subjects expressed strong preferences for bending axis condition and preference was strongly related to specific gait measures. This suggests that preference and comfort are important factors guiding the prescription of bending axis location. In the second study, musculoskeletal modeling was used to examine the influence of transfemoral amputation surgical techniques on muscle capacity to generate forces and moments about the hip. Muscle reattachment tension and stabilization were shown to be critical parameters for post-amputation capacity, which supports the use of myodesis stabilization (muscle is reattached directly to bone) in amputation procedures. In the third study, a forward dynamics simulation of transfemoral amputee gait was developed and used to examine individual muscle and prosthesis contributions to walking subtasks. The residual hip muscles, and intact ankle, knee, and hip muscles worked synergistically to provide body support, anteroposterior propulsion, mediolateral control, and leg swing. Increased contributions of contralateral muscles to ipsilateral subtasks as well as increased duration of specific muscle contributions were observed in comparison to non-amputee and transtibial amputee walking. These findings can be used to help develop targeted rehabilitation therapies and improve transfemoral amputee locomotion. Through elucidating the influence of PD-AFO bending axis on gait performance as well as the influence of transfemoral amputation surgical techniques on muscle capacity and function, this research provides a foundation for improved rehabilitation outcomes, and thus mobility for individuals who have experienced traumatic lower-limb injuries.Item Size effects in out-of-plane bending in elastic honeycombs fabricated using additive manufacturing : modeling and experimental results(2011-12) Mikulak, James Kevin; Kovar, Desiderio; Taleff, Eric M.; Rodin, Gregory J.; Bourell, David L.; Haberman, Michael R.Size effects in out-of-plane bending stiffness of honeycomb cellular materials were studied using analytical mechanics of solids modeling, fabrication of samples and mechanical testing. Analysis predicts a positive size-effect relative to continuum model predictions in the flexure stiffness of a honeycombed beam loaded in out-of-plane bending. A method of determining the magnitude of that effect for several different methods of constructing or assembling square-celled and hexagonal-celled materials, using both single-walled and doubled-walled construction methods is presented. Hexagonal and square-celled honeycombs, with varying volume fractions were fabricated in Nylon 12 using Selective Laser Sintering. The samples were mechanically tested in three-point and four point-bending to measure flexure stiffness. The results from standard three-point flexure tests, did not agree with predictions based on a mechanics of solids model for either square or hexagonal-celled samples. Results for four-point bending agreed with the mechanics of solids model for the square-celled geometries but not for the hexagonal-celled geometries. A closed form solution of an elasticity model for the response of the four-point bending configuration was developed, which allows interpretation of recorded displacement data at two points and allows separation the elastic bending from the localized, elastic/plastic deformation that occurs between the loading rollers and the specimen’s surface. This localized deformation was significant in the materials tested. With this analysis, the four-point bending data agreed well with the mechanics of solids predictions.Item Sustainability and thermal aspects of polymer based laser sintering(2010-12) Sreenivasan, Rameshwar; Bourell, David Lee; Beaman Jr., Joseph J.Additive Manufacturing (AM) processes which include Selective Laser Sintering (SLS) have experienced tremendous growth and development since their introduction over 20 years ago. It becomes highly important at this stage to evaluate the sustainability of the process and refine it to reduce energy and material consumption. In this study, a sustainability analysis was performed on the SLS process with Nylon-12 using the Environmental and Resource Management Data (ERMD) known as Eco-Indicators. The energy perspective alone was considered and a Total Energy Indicator (TEI) value was calculated using various parameters to quantify process sustainability: process productivity, energy consumption rate, etc. Precise thermal control of selective laser sintering (SLS) is desirable for improving geometric accuracy, mechanical properties, and surface finish of parts produced. An experimental setup to monitor the temperature distribution was designed using Resistance Temperature Detectors (RTD) as a part of this study. Discrepancies in temperature profiles were investigated and recommendations were made to improve thermal characteristics of the SLS process.Item Topology optimization for additive manufacturing of customized meso-structures using homogenization and parametric smoothing functions(2010-12) Sundararajan, Vikram Gopalakrishnan; Seepersad, Carolyn C.; Crawford, Richard H.Topology optimization tools are useful for distributing material in a geometric domain to match targets for mass, displacement, structural stiffness, and other characteristics as closely as possible. Topology optimization tools are especially applicable to additive manufacturing applications, which provide nearly unlimited freedom for customizing the internal and external architecture of a part. Existing topology optimization tools, however, do not take full advantage of the capabilities of additive manufacturing. Prominent tools use micro- or meso-scale voids or artificial materials to parameterize the topology optimization problem, but they use filters, penalization functions, and other schemes to force convergence to regions of fully dense (solid) material and fully void (open) space in the final structure as a means of accommodating conventional manufacturing processes. Since additive manufacturing processes are capable of fabricating intermediate densities (e.g., via porous mesostructures), significant performance advantages could be achieved by preserving and exploiting those features during the topology optimization process. Towards this goal, a topology optimization tool has been created by combining homogenization with parametric smoothing functions. Rectangular mesoscale voids are used to represent material topology. Homogenization is used to analyze its properties. B-spline based parametric smoothing functions are used to control the size of the voids throughout the design domain, thereby smoothing the topology and reducing the number of required design variables relative to homogenization-based approaches. Resulting designs are fabricated with selective laser sintering technology, and their geometric and elastic properties are evaluated experimentally.