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. / text

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. / text

Existing laser sintering systems have several advantages over alternate additive manufacturing technologies but suffer from limitations inherent to the use of a single, self-contained powder bed. This powder bed design limits the ability of the machine to print multiple materials in a single print cycle, obscures the part during printing which can lead to material waste, and presents significant obstacles to embedding during printing. I present here an additive manufacturing process that uses an upward-directed laser to fuse monolayers of material powder onto a substrate through a clear surface. The powder on the glass can then be replenished or replaced, and new powder can be fused to the previous powder layer. This is repeated until a solid, multi-layer hanging print is formed. This process eliminates the need for a large powder bed as well as allows the sintering of different powders in a single layer. I demonstrate this method by using a 445 nm laser to fabricate a multi-material pattern of Nylon-12 and TPU as well as producing direct metal laser sintered (DMLS) copper components. I also demonstrated the ability of this technology to print hybrid powder/resin components and embed during the printing process.

Published Article / Until recently solid freeform fabrication (SFF) technology has been used mostly for production of prototype parts. However, as this technology matures, the initiative of utilising it for the manufacture of end-use products is establishing itself. As this tendency to use SFF for actual production runs increases, a demand is developing for sets of process-specific design for manufacture (DFM) guidelines that will assist designers who are designing parts for manufacture by a specific rapid manufacturing (RM) process. The purpose of this paper is to provideRMdesigners with such a series of processspecific design for manufacture guidelines.

Laser Sintering (LS) is a powder based Additive Manufacturing (AM) technology capable of producing near-net shape objects from 3D data. The benefits of LS include almost unlimited design freedom and reduced material waste, however the number of commercially available materials are limited, with materials traditionally being optimised for the process using a trial and error method and material development being led by previous research into polyamide (PA). There is a desire for greater material choice in LS, particularly high performance polymers. The EOSINT P800 by AM systems manufacturer EOS GmbH is the first commercially available high temperature laser sintering (HT-LS) system capable of working high performance polymers; a PolyEtherKetone (PEK) known by the trade name HP3 PEK is the first material offered by EOS for use with the system. This research project undertakes to characterise the EOSINT P800 and HP3 PEK material with different thermal histories. Experimental work focusses on establishing material properties such as size and shape, crystallinity and decomposition. Characterisation of coalescence behaviour and comparison with theoretical models for viscous sintering is presented as a less experimentally intensive method of understanding how a material will behave during the LS process. A map of temperatures inside the powder bed in the EOSINT P800 is created for the first time and compared with output from on-board temperature sensors in the system, demonstrating the thermal distribution within the bed during building, and explaining differences between as-received and used powder. The results demonstrate that material and process characterisation methods are useful for understanding how and why a high temperature laser sintering material behaves the way it does. The behaviour of HP3 PEK observed during experimental work indicates that guidelines based on LS of PA are too restrictive as indicators of suitability for LS and newer systematic approaches are potentially better suited for qualification of HT-LS polymers. The novel method for mapping thermal distribution inside the LS system documented here shows the limitations of current hardware to effectively process high performance polymers. Overall, the finding of this research project is that understanding of material and process cannot be considered in isolation but combined have the potential to reduce the amount of trial and error required during qualification of new materials and increase the range and variety of polymers available for LS and HT-LS.

Direct Metal Laser Sintering (DMLS) is a rapid prototyping technique that allows for direct and rapid manufacturing of complex components. DMLS is however an intricate process and the quality of the final product is influenced by multiple manufacturing parameters (or DMLS settings) and powder characteristics. The effect which each of these manufacturing parameters and powder characteristics has on the final parts is not well understood and the success of process manufacturing mainly relies on empirical knowledge. Consequently high dimensional deformation and relatively poor mechanical properties are still experienced in many DMLS products, in particular in copper-based laser sintered parts. A need therefore exists to systematically examine the effect of process parameters on the quality of final parts in order to determine the most appropriate manufacturing parameters for specific applications of copper-based laser sintered parts. This document summarises the effect of different process parameters on the quality of Direct Metal 20 laser sintered parts produced with a EOSINT M250 Xtended laser sintering machine from powder consisting of Ni5Cu, Cu15Sn – Cu5Sn and Cu8P – Cu2P material grains. The quality of the sintered parts is defined in terms of the microstructures, porosities and dimensional deformations obtained. The effects of three different geometric sintering strategies currently in standard use namely Solid Skin, Skin Stripes and Skin Chess were examined, and the more appropriate process parameters and scanning technique for the available set-up is presented. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Direct Metal Laser Sintering (DMLS) is a rapid prototyping technique that allows for direct and rapid manufacturing of complex components. DMLS is however an intricate process and the quality of the final product is influenced by multiple manufacturing parameters (or DMLS settings) and powder characteristics. The effect which each of these manufacturing parameters and powder characteristics has on the final parts is not well understood and the success of process manufacturing mainly relies on empirical knowledge. Consequently high dimensional deformation and relatively poor mechanical properties are still experienced in many DMLS products, in particular in copper-based laser sintered parts. A need therefore exists to systematically examine the effect of process parameters on the quality of final parts in order to determine the most appropriate manufacturing parameters for specific applications of copper-based laser sintered parts. This document summarises the effect of different process parameters on the quality of Direct Metal 20 laser sintered parts produced with a EOSINT M250 Xtended laser sintering machine from powder consisting of Ni5Cu, Cu15Sn – Cu5Sn and Cu8P – Cu2P material grains. The quality of the sintered parts is defined in terms of the microstructures, porosities and dimensional deformations obtained. The effects of three different geometric sintering strategies currently in standard use namely Solid Skin, Skin Stripes and Skin Chess were examined, and the more appropriate process parameters and scanning technique for the available set-up is presented. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2015

Published Article / e-Manufacturing means the fast, flexible and cost-effective production of parts directly from electronic data, which can include rapid prototyping, rapid tooling, (spare) parts on demand etc. Especially interesting is the direct manufacture of enduse parts. In this paper, recent case studies will be presented showing commercial e-Manufacturing projects including small production batches and mass customized series production from various industrial branches. The paper also discusses the relevance of several recent technological innovations in laser-sintering for e- Manufacturing, especially how increasing the productivity of machines and process chains has increased the range of applications which are cost-effective using lasersintering. <br>Case studies include: <ul> <li> small series production (up to a few thousand p.a.) of products</li> <li> production of customized (one-off) products</li> <li> mass production of customer-specific (mass customized) products</li> <li> optimized tooling concepts for production of up to millions of products</li> </ul>

Laser Sintering is an Additive Manufacturing technology that uses digital files to construct 3-dimensional parts by depositing and consolidating layers of powdered material. Application of the technology for metal and ceramic powders is common but the focus of this work was on polymer laser sintering. A significant drawback for polymer laser sintering is the limited selection of materials currently available for use compared with more conventional processes such as injection moulding. This constrains the usefulness of the technology for designers and engineers. A primary reason for this is a lack of detailed understanding of the development process for new materials for laser sintering. This PhD investigation examines some of the key attributes and requirements needed for successfully implementing new polymer-based laser sintering materials. A strategic method for characterizing and identifying new polymer materials was created utilizing thermal measurements, practical and analytical methods to quantify sintering rate, and degradation studies. Validation of this work occurred through the successful integration of a new laser sintering material at industrial project partner Burton Snowboards. Thermal degradation as a result of the laser sintering process was studied in detail and resulted in the creation of a proposed new parameter: Stable Sintering Region (SSR). The term acknowledges and defines the region above the melting point that is the minimum requirement for sintering to occur and an upper limit beyond which polymer deterioration impedes on mechanical properties. A quantitative approach to define the SSR was developed and explored with three different laser sintering materials, two of which were flexible elastomers. The ability to specifically interpret laser sintering process parameters from thermal degradation characterization was created and used to explore the effects of high energy input on tensile properties and molecular weight. The results of these tests showed the potential to identify an Optimum Sintering Range based on maximizing mechanical properties through the control of energy input and molecular weight. This thesis makes a significant contribution to the knowledge and understanding of polymer laser sintering, especially in the context of materials development. Novel concepts such as the Stable Sintering Region were developed using a theoretical approach and practical measurements and were also thoroughly explored for verification. Additionally, a new method to use a powder characterization technique to predict the actual machine parameters of a material in the laser sintering process was quantified. This has several implications for testing new materials for laser sintering and efficiently identifying appropriate processing conditions.

Os objetivos deste trabalho foram a implantação e a otimização da técnica de sinterização por varredura a laser de filmes espessos, o estudo da cinética do processo e a avaliação das propriedades do composto BaTi0.85Zr0.15O3 (BTZ) sinterizado a laser, em comparação com os filmes sinterizados em forno. Pós nanocristalinos de BTZ foram sintetizados em baixas temperaturas com sucesso pela primeira vez (600ºC), por meio do método dos precursores poliméricos modificado. Foram obtidos pós nanométricos com tamanho de partículas primárias de ~20 nm e com aglomeração controlada, uma inovação para pós de BTZ preparados por rotas químicas. Para a deposição dos filmes, a estabilidade das suspensões de partida foi estudada e filmes espessos com excelente homogeneidade foram depositados utilizando a técnica de eletroforese (EDP). O desenvolvimento da técnica permitiu o controle da espessura do filme a partir dos parâmetros de deposição. A montagem experimental para a sinterização a laser foi otimizada de modo a permitir a sinterização de filmes com dimensões de até 70 mm de comprimento por 10 mm de largura e espessuras variáveis. Os tempos de patamares em cada etapa foram dependentes da velocidade e do número de varreduras. A temperatura máxima que se pode atingir no filme espesso, durante cada varredura e para uma potência nominal do laser fixa, foi correlacionada com a densidade relativa. Os processos térmicos envolvidos durante a varredura a laser atuaram de modo similar á sinterização em duas etapas (two step sintering). Com o intuito de melhorar a densificação dos filmes, passamos a adicionar o composto Bi4Ti3O12 (BIT) (1 e 2 mol %) ao BTZ durante a deposição. A utilização do sistema desenvolvido para a sinterização por varredura a laser em conjunto com o acréscimo do aditivo BIT resultou em uma diminuição no tamanho de grão dos filmes e uma importante diminuição da porosidade aparente. Para a aditivação com 2 mol% de BIT obtivemos filmes de ótima densidade (porosidade aparente de ~4%) e reduzido tamanho de grão (~200 nm), resultado inédito em se tratando de filmes espessos. A sinterização a laser resultou em filmes com maior permissividade dielétrica em relação ao filme sinterizado em forno elétrico. As reações que ocorrem entre o BTZ e o BIT foram exploradas usando conjuntamente as técnicas de espectroscopia de impedância, análise térmica e difratometria de raios-X. / The goals of this work were the implantation and optimization of the technique of sintering by laser scan of thick films, the kinetic study of the process and the evaluation of the physical properties of the laser sintered compound BaTi0.85Zr0.15O3 (BTZ), compared to thick films sintered in conventional furnace. Nanocrystalline powders of BTZ were for the first time, successfully synthesized at low temperatures (600ºC) using the modified polymeric method. Nanometric powders with primaries particles of ~20nm sizes and controlled agglomeration were obtained which was an innovation for BTZ powders prepared by chemical methods. For the films deposition, the suspensions stability was studied and thick films with excellent homogeneity were deposited using the electrophoresis technique (EDP). The developing of the technique allowed the thicknesses control using the deposition parameters. The characteristics of the experimental apparatus were optimized in such a way as to allow the sintering of thick films whose dimensions were up to 70mm in length, 10mm in width and variable thicknesses. The step times in each stage were dependent on the velocity and scan number. The maximum temperature that can be achieved in the thick film, during each scan, and for a fixed rated laser power was correlated with the relative density. The related thermal process during the continuous laser scan acted in a similar way as a two-step sintering. To improve the densification of the films, we started to add the compound Bi4Ti3O12 (BIT) (1 e 2 mol %) to BTZ during the deposition. The utilization of the system developed for the sintering by laser scan alongwith the adding of the BIT resulted in a grain size decrease and a significant decrease in apparent porosity. For the 2mol% additivation we obtained films with excellent density (apparent porosity of ~4%) and reduced grain size (~200nm), which is an unpublished result for thick films. The laser sintering resulted in films with a higher dielectric permittivity in relation to the conventionally sintered film. The reactions between BTZ and BIT were explored using the techniques of impedance spectroscopy, thermal analysis and X-ray diffraction.