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. / text

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. / text

Selective laser sintering (SLS) is a rapid prototyping method in which three-dimensional objects are constructed by sintering thin layers of a variety of powdered materials via laser beam. In SLS, as in most other Rapid Prototyping methods, the produced parts exhibit varying degrees of intrinsic porosity due to the discrete nature of layer-by-layer production. Selective scanning and discrete bonding of individual particles or clusters of particles impart local porosity, which is mostly an undesired trait as the part integrity decreases with increased porosity. However, there are a number of emerging or potential applications as in tissue engineering and composite/functionally graded materials, in which part porosity and its control during production are needed. In this study, the manufacturing capabilities of selective laser sintering are investigated towards producing predesigned porous structures using a polymeric powder. The porous structures are characterized in two main categories: regular porous structures, which involve geometries such as predesigned holes and lattice structures that have orderly porous architecture, and irregular porous structures, which exhibit random pore architecture that is intrinsic in all SLS parts. The limitations of producing regular porous structures are investigated, identified and quantified, based on hole size and dimensional accuracy. An experimental analysis based on design of experiments is employed to investigate the effects of processing parameters on the resulting macroscopic pore properties of irregular porous structures. A mathematical relation is developed to quantify and predict the relations between the SLS process parameters: Laser power, hatching distance, laser scan spacing, and the resulting apparent mass density (as a measure of porosity). The subsequent tests verify accuracy of the developed empirical model.

Thesis (MEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Rapid prototyping (RP) technologies have expanded vastly over recent years. With the advent of new materials along with new processes, each technology has been contributing to the diversities in different fields of application for the growing technologies. In the course of improvement, it is however critical to understand exactly what the capability of each individual technology is in order to compare future improvements, or even to compare current processes and technologies. The objective of this research has been to develop capability profiles of prominent RP technologies: 3D-Printing (3DP), Selective Laser Sintering (SLS), and Laminated Object Manufacturing (LOM) - in which different characteristics of each technology are measured and quantified. A capability profile may be regarded as a set of building blocks that give a representation of the RP technology's ability and is defined by quantifying the following characteristics: Accuracy (both dimensional- and geometrical accuracy) Surface finish measures Strength and elongation Build time, and Cost The significance behind developing capability profiles lies in the need to more accurately describe and compare each of the different processes - especially Z Corporation's 3DP, since although this process is regarded as very capable in many areas, little has been published to substantiate this opinion. When users of these technologies are pushing the limits of their machines, it becomes critical to know exactly what these boundaries are in order to know with some measure of certainty that they will be able to fulfil a certain customer demand or expectation. For South Africa in particular, the industry's growing interest in rapid prototyping is triggering inevitable questions as to whether a certain RP technology can produce the desired solutions to their problems. The South African industry's growing awareness about rapid prototyping is opening new doors for better solutions to new and existing problems - but ultimately, before investing money, customers want to know if RP is going to meet the standards needed to solve their solutions. On a more general level, this study can also be seen to bear significance in contributing to research in what has become known as rapid manufacturing (RM). This term is defined as the manufacture of end-use products using additive manufacturing techniques. RM must guarantee long-term consistent component use for the entire product life cycle or for a defined minimal period for wearing parts [1]. However, before it is possible to guarantee long-term consistency of components, one must first ensure consistency of the process. Once a process is consistent, the next question becomes: What is it capable of doing consistently? This study aims to answer this question for the three processes (3DP, SLS and LOM) mentioned earlier. In doing so, this study and its development of capability profiles, seeks to contribute and be of value in both academic circles as well as for industry partners and system manufacturers. / AFRIKAANSE OPSOMMING: Snelle Prototipering (SP) tegnologieë het die afgelope jare ongelooflike groei ondervind. Met die ontwikkeling van nuwe materiale tesame met nuwe prosesse, het elke tegnologie bygedra tot 'n diversiteit in moontlike toepassings vir 'n verskeidenheid van velde. Met 'n mikpunt van aaneenlopende verbetering, is dit egter krities om te verstaan presies wat elke individuele tegnologie se vermoëns is. Dit maak dit dan moontlik om toekomstige verbeteringe te vergelyk, of om selfs huidige prosesse met mekaar te vergelyk. Die doel van hierdie navorsing was om vermoënsprofiele van prominente SP tegnologieë te ontwikkel: 3D-Printing (3DP), Selective Laser Sintering (SLS) en Laminated Object Manufacturing (LOM) - waarin verskillende karaktereienskappe van elke tegnologie gemeet en gekwantifiseer word. 'n Vermoënsprofiel mag beskou word as 'n stel boustene wat 'n weerspieëling gee van die SP tegnologie se vermoë en word gedefinieer deur die kwantifisering van die volgende karaktereienskappe: Akkuraatheid (beide dimensionele- en geometriese akkuraatheid) Oppervlakgehalte metings Treksterktes en verlengings Bou- of vervaardigingstye, en Kostes Die rede waarom dit belangrik is om vermoënsprofiele te ontwikkel berus by die behoefte om die verskillende prosesse met meer akkuraatheid te beskryf en te vergelyk - veral Z Corporation se 3DP. Alhoewel hierdie proses algemeen beskou word as baie bevoeg in vele areas, is min informasie al gepubliseer om hierdie opinie te ondersteun. Wanneer gebruikers van hierdie tegnologieë hul masjiene tot die limiete druk, begin dit krities raak om presies te weet wat daardie grense is, sodat hulle met 'n sekere mate van sekerheid sal kan sê of hulle sal kan voldoen aan kliënte se behoeftes of verwagtinge. Die Suid-Afrikaanse industrie se belangstelling in SP tegnologieë begin al hoe meer groei, en daarmee saam, begin vrae ontstaan tot watter mate snelle prototipering wel werkbare oplossings kan produseer vir hul probleme. Hierdie groeiende bewustheid van die Suid-Afrikaanse industrie begin dus ook nou nuwe paaie openbaar vir beide nuwe en ou probleme - maar uiteindelik, voordat kliënte egter bereid sal wees om geld te belê, sal hulle wil weet of snelle prototipering die standaarde gaan behaal wat nodig sal wees om juis hierdie oplossings te verwesenlik. Op 'n meer breë vlak, beoog hierdie studie om ook 'n bydrae te maak in die groeiende navorsingsveld van snelle vervaardiging (SV). Hierdie is 'n term wat gedefinieer word as die vervaardiging van endgebruiker produkte, met die benutting van byvoegings-vervaardigings tegnieke. SV moet versekering bied vir komponente se werkverrigting op die lange duur vir die hele produk se lewenssiklus, of ten minste vir 'n gedefinieerde minimale tydperk in die geval van slytasie-parte [1]. Maar voordat dit moontlik sal wees om hierdie versekering te bied, moet mens eers die versekering kan bied van 'n proses se werkverrigting. Wanneer die prosesse betroubaar en deurlopende resultate lewer, word die volgende logiese vraag gestel: Wat presies, is hierdie proses in staat om betroubaar te lewer? Hierdie studie beoog om juis hierdie vraag te beantwoord vir die drie prosesse (3DP, SLS en LOM) wat vroeër genoem is. Dienooreenkomstig, met die ontwikkeling van vermoënsprofiele van hierdie prosesse, behoort hierdie studie van waarde te wees vir beide akademici, sowel as industrie-lede en vervaardigers van SP tegnologieë.

The diploma thesis deals with design and realization of experimental 3D printer for selective laser sintering of plastic powders. The output of the work is a device that can create the main process conditions for laser sintering. A diode laser is used in the device, which allows aluminum composite powders to be processed. The printer allows you to heat up the applied layer of powder and set-up space. The research section focuses on similar equipment, process parameters, laser technology and control system. The design section contains solution variants and a description of the chosen solution.

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The focus of this thesis is the critical review of Additive Printing (AP) or 3D-printing, and optimization strategies for the introduction of new materials. During the course of tenure, four classes of solids were investigated to determine the hurdles presented from each system. Specifically, the investigation developed techniques for optimization of ink production, green-film deposition, and laser sintering parameters surrounding the Optomec AJP system (AJP). In the assessment, statistical experimental design, analysis and material characterization techniques have been utilized. Final recommendations disseminate current best practices for new ink and material development, along with factor analysis of input variables for phase and material properties, along with insights for future research of these systems. The first chapter provides a general introduction to the field of AP. The second chapter focuses specifically on Optomec aerosol-jet process (AJP) techniques, and expands the discussion to process parameters, information concerning the fabrication/characterization procedure followed for each system, and includes: a detailed description of the materials investigated. This is important because printing parameters, optimization, and approach may be divergent for optimization within each strain; and is meant as an aid to resolve some technical issues for future investigators. The third chapter is fully dedicated to the results concerning the fabrication and the characterization of amorphous boron powder to film. Chapter four discusses future research options, ideas and directions. Appendices are provided for any which wish to investigate the orthogonal arrays used, or the combinatorial effects resulting in the attributes of the material system final products. / Master of Science

Great improvements are continuously being made in the solid free form fabrication (SFF) industry in terms of processes and materials. Fully functional parts are being created directly with little, if any, finishing. Parts are being directly fabricated with engineering materials such as ceramics and metals. This thesis aims to facilitate a substantial advance in rapid prototyping capabilities, namely that of fabricating parts with continuously heterogeneous material compositions. Because SFF is an additive building process, building parts layer-by-layer or even point-by-point, adjusting material composition throughout the entire part, in all three dimensions, is feasible. The use of fine powders as its build material provides the potential for the Selective Laser Sintering (SLS), ThreeDimensional Printing (3DP), and Freeform Powder Molding (FPM) processes to be altered to create continuously heterogeneous material composition. The current roller distribution system needs to be replaced with a new means of delivering the powder that facilitates selective heterogeneous material compositions. This thesis explores a dense phase pneumatic conveying system that has the potential to deliver the powder in a controlled manner and allow for adjustment of material composition throughout the layer. / Master of Science

A prosthetic socket worn by an amputee must serve a wide variety of functions, from stationary support to the transfer of forces necessary to move. Fit and comfort are important factors in determining the therapeutic effectiveness of a socket. A socket that does not fit the subject well will cause movement problems and potentially long-term health issues. Because a subject's residual limb changes volume throughout the day, it is desirable that the socket adapt to accommodate volume changes to maintain fit and comfort. This thesis presents research to manufacture adaptive sockets using selective laser sintering (SLS). This additive manufacturing process allows freedom to design a socket that has both compliant areas that can adapt to changes to the residual limb, as well as rigid regions to provide necessary support for the limb. A variety of concepts are discussed that are intended for manufacture by SLS, and that feature flexible inner membranes in various configurations. For each concept the membrane will be inflated or deflated to match the limb’s change in volume and the thesis also presents a study to determine SLS machine parameters for optimal build results. A series of experiments was created to understand the ability of SLS manufactured plastics to be inflated and the possible performance. / text

Constrained negative stiffness elements in volume concentrations (1% to 2%) embedded within viscoelastic materials have been shown to provide greater energy absorption than conventional materials [Lakes et al., Nature (London) 410, 565–567 (2001)]. This class of composite materials, called meta-materials, could be utilized in a variety of applications including noise reduction, anechoic coatings and transducer backings. The mechanism underlying the meta-material's behavior relies on the ability of the negative stiffness element to locally deform the viscoelastic material, dissipating energy in the process. The work presented here focuses specifically on the design of the negative stiffness elements, which take the form of buckled beams. By constraining the beam in an unstable, S-shaped configuration, the strain energy density of the beam will be at a maximum and the beam will accordingly display negative stiffness. To date, physical realization of these structures has been limited due to geometries that are difficult to construct and refine with conventional manufacturing materials and methods. By utilizing the geometric freedoms allowed by the Selective Laser Sintering (SLS) machines, these structures can be built and tuned for specific dynamic properties. The objective of this research was to investigate the dynamic behavior of SLS-constructed meso-scale negative stiffness elements with the future intention of miniaturizing the elements to create highly absorptive meta-materials. This objective was accomplished first through the development and analysis of a mathematical model of the buckled beam system. A characterization of the Nylon 11 material was performed to obtain the material properties for the parts that were created using SLS. Applying the mathematical model and material properties, a tuned meso-scale negative stiffness structure was fabricated. Transmissibility tests of the meso-scale structure revealed that the constrained negative stiffness system was able to achieve overall higher damping and vibration isolation than an unconstrained system. Quasistatic behavior of the system indicated that these elements would be ideal for implementation within meta-materials. Based on the results of the meso-scale system, a method to test a representative volume element for a negative stiffness meta-material was developed for future completion. / text