New Methodology for Automatic Process Parameters Optimization in Selective Laser Melting

Selective laser melting is one of the most promising additive manufacturing technologies, thanks to its capability to manufacture complex shaped parts with good dimensional accuracy and high mechanical performance. In recent years, this technique is starting to be adopted for the production of end-use parts, addressing high quality requirements. To achieve the desired quality of the final product it is necessary to optimize the process parameters, possibly by reducing the build time needed for its production. However, the currently available process optimization methodologies are very time consuming and there is a lack of standards. The aim of this work is to develop an automatic, reliable and objective process optimization technique, which can be employed to find optimal parameters combinations for different process conditions. Therefore, it has been developed an experimental approach, based on single tracks analysis and on 3D benchmarks characterization. The main novelty of this optimization method is the automatization of samples analysis, which entailed the adoption of innovative surface metrology techniques and of novel algorithmic frameworks developed in MATLAB environment. According to the novel method, the effects of laser power (P), scan speed (v) and laser spot size (ds) have been investigated for the two most used materials; the extra-low-interstitial grade of Ti6Al4V alloy and the 316L stainless steel. Hence, P-v optimal combinations has been defined for each spot size level investigated, finding a first optimal region in single tracks analysis and then identifying the optimal parameter set for 3D components production. This methodology has allowed the definition of multiple optimal parameter sets in an automatic way, limiting time and material waste. Therefore, it can be adopted in all existent production strategies that require more than one process parameter set and could allow the development of new production approaches

High-resolution fluorescence endomicroscopy for rapid evaluation of breast cancer margins

Breast cancer is a major public health problem world-wide and the second leading cause of cancer-related female deaths. Breast conserving surgery (BCS), in the form of wide local excision (WLE), allows complete tumour resection while maintaining acceptable cosmesis. It is the recommended treatment for a large number of patients with early stage disease or, in more advanced cases, following neoadjuvant chemotherapy. About 30% of patients undergoing BCS require one or more re-operative interventions, mainly due to the presence of positive margins. The standard of care for surgical margin assessment is post-operative examination of histopathological tissue sections. However, this process is invasive, introduces sampling errors and does not provide real-time assessment of the tumour status of radial margins. The objective of this thesis is to improve intra-operative assessment of margin status by performing optical biopsy in breast tissue. This thesis presents several technical and clinical developments related to confocal fluorescence endomicroscopy systems for real-time characterisation of different breast morphologies. The imaging systems discussed employ flexible fibre-bundle based imaging probes coupled to high-speed line-scan confocal microscope set-up. A preliminary study on 43 unfixed breast specimens describes the development and testing of line-scan confocal laser endomicroscope (LS-CLE) to image and classify different breast pathologies. LS-CLE is also demonstrated to assess the intra-operative tumour status of whole WLE specimens and surgical excisions with high diagnostic accuracy. A third study demonstrates the development and testing of a bespoke LS-CLE system with methylene blue (MB), an US Food and Drug Administration (FDA) approved fluorescent agent, and integration with robotic scanner to enable large-area in vivo imaging of breast cancer. The work also addresses three technical issues which limit existing fibre-bundle based fluorescence endomicroscopy systems: i) Restriction to use single fluorescence agent due to low-speed, single excitation and single fluorescence spectral band imaging systems; ii) Limited Field of view (FOV) of fibre-bundle endomicroscopes due to small size of the fibre tip and iii) Limited spatial resolution of fibre-bundle endomicroscopes due to the spacing between the individual fibres leading to fibre-pixelation effects. Details of design and development of a high-speed dual-wavelength LS-CLE system suitable for high-resolution multiplexed imaging are presented. Dual-wavelength imaging is achieved by sequentially switching between 488 nm and 660 nm laser sources for alternate frames, avoiding spectral bleed-through, and providing an effective frame rate of 60 Hz. A combination of hand-held or robotic scanning with real-time video mosaicking, is demonstrated to enable large-area imaging while still maintaining microscopic resolution. Finally, a miniaturised piezoelectric transducer-based fibre-shifting endomicroscope is developed to enhance the resolution over conventional fibre-bundle based imaging systems. The fibre-shifting endomicroscope provides a two-fold improvement in resolution and coupled to a high-speed LS-CLE scanning system, provides real-time imaging of biological samples at 30 fps. These investigations furthered the utility and applications of the fibre-bundle based fluorescence systems for rapid imaging and diagnosis of cancer margins.Open Acces

Laser powder bed fusion of cemented tungsten carbide cutting tools

Thesis (PhD)--Stellenbosch University, 2022.ENGLISH ABSTRACT: Cemented carbides are extremely hard, wear resistant materials, and one of the most widely used tool materials in numerous manufacturing industries. Metal cutting tools are commonly manufactured from cemented carbides using standard powder metallurgy processes such as the press and sinter process. The tooling market is highly competitive and the companies with the best research and development departments have the competitive advantage when it comes to cutting edge technology. However, historically, the development process for a new cutting tool or production technology is a lengthy and costly venture. The use of laser powder bed fusion (L-PBF) for research, development, and small-batch production of cemented tungsten carbide cutting tools has not been extensively reported, and commercialisation does not seem apparent as yet. While the usage of L-PBF to produce cutting tools may be beneficial to advancing cutting tool technology, the process has many inherent drawbacks that affect part quality. However, there are many changes to the current L-PBF process that can be investigated to improve the final quality of L-PBF-produced tools before post-processing. The successful application of L PBF technology could help develop and manufacture cutting tools at an improved rate. The aim of this study was to determine and manage the influences of certain factors encountered during L-PBF of tungsten carbide cobalt (WC-Co) and their effects on specific cutting tool properties and cutting performance to produce L-PBF cutting tools that could be comparable to a conventionally produced tool. To accomplish this, three powders were analysed and investigated for their use in the L-PBF process. Then, characterisation of an existing cutting tool was performed to be used as a quality benchmark for L-PBF cutting tools. After a reasonable understanding of powders and conventional cutting tools was obtained, single track scans were performed on a tool steel base plate to understand adhesion and the feasibility of using a conventional base plate. The next stage of the study involved understanding the effects of different laser parameters and scanning strategies on the track morphology, density, hardness, and cobalt content of L-PBF produced WC-12wt%Co samples. Various parameter optimisation methods and strategies were tested and L-PBF-produced cutting tools were utilised in preliminary cutting tests to determine their cutting ability and to deduce which factors had the greatest effects on cutting contact time. The L-PBF scanning strategy was observed to be the most significant factor for successful cutting operations. A diagonal raster strategy with an 80-degree alternating rotation produced the best cutting inserts for the specific insert geometry and grade. Verification WC-12wt%Co inserts were produced with L-PBF for final cutting tests. These inserts were comparable to conventionally produced tungsten carbide inserts with respect to cutting performance indicators such as contact time and workpiece surface roughness. On average, after roughly 16M30S contact time, the L-PBF cutting tools exhibited 0.7 mm maximum flank wear versus 0.4 mm for similar conventional inserts. These results suggest that L-PBF could, one day, be a viable solution for research, developments, and small-batch production of WC-Co cutting tools.AFRIKAANSE OPSOMMING: Sinterkarbiede is uiters hard, slytasiebestand en een van die gereedskapsmateriale wat die algemeenste in talle vervaardigingsbedrywe gebruik word. Metaalsnygereedskap word gewoonlik met behulp van standaard poeiermetallurgieprosesse, soos die pers- en sinterproses, uit sinterkarbiede vervaardig. Die werktuigmark is baie mededingend en ondernemings met die beste navorsingen ontwikkelingsdepartemente, het die mededingende voordeel as dit by die nuutste tegnologie kom. Histories is die ontwikkelingsproses vir ʼn nuwe snybeitel of produksietegnologie egter ʼn lang en duur proses. Die gebruik van laser- poeierbedsamesmelting (L-PBF) vir navorsing, ontwikkeling en kleinskaalproduksie van gesementeerde-wolframkarbiedsnygereedskap is nog nie wyd gerapporteer of gekommersialiseer nie. Hoewel die gebruik van L-PBF voordelig vir die bevordering van snygereedskaptegnologie kan wees, het die proses baie inherente nadele wat die gehalte van die onderdele beïnvloed. Daar is egter baie veranderinge aan die huidige L-PBF-proses wat ondersoek kan word om die finale gehalte van L-PBF-vervaardigde gereedskap voor ná-vervaardiging te verbeter. Die suksesvolle toepassing van L-PBF-tegnologie kan help om snygereedskap vinniger te ontwikkel en te vervaardig. Die doel van hierdie studie was om die invloed van sekere faktore tydens die L-PBF van wolframkarbied-kobalt (WC-Co), en die uitwerking daarvan op spesifieke snygereedskapseienskappe en -snyprestasie te bepaal en te bestuur, om uiteindelik L-PBF-snygereedskap te vervaardig wat met ʼn konvensioneel vervaardigde werktuig vergelykbaar is. Om dit te bewerkstellig, is drie poeiers vir gebruik in die L-PBF-proses ontleed en ondersoek. Vervolgens is karakterisering van ʼn bestaande snybeitel uitgevoer om as ʼn gehaltenorm vir L-PBF-snygereedskap te dien. Nadat ʼn redelike begrip van poeiers en konvensionele snygereedskap verkry is, is enkelbaanskanderings op ʼn basisplaat van gereedskapstaal uitgevoer om die aanklewing en dus die haalbaarheid van die gebruik van ʼn konvensionele staalbasisplaat te ondersoek. Die volgende fase van die werk het die bestudering van die effekte van verskillende laserparameters en skanderingstrategieë op die baanmorfologie, digtheid, hardheid en kobaltinhoud van L-PBF geproduseerde WC-12wt%Co-monsters behels. Verskeie parameter-optimaliseringsmetodes en - strategieë is getoets en L-PBF-vervaardigde snygereedskap is in voorlopige snytoetse gebruik om hulle snyvermoë te bepaal en af te lei watter faktore die grootste effek op die snykontaktyd het. Waarneming het aangedui dat die L-PBF-skanderingstrategie die belangrikste faktor vir suksesvolle snywerk is. ʼn Diagonale rasterstrategie met ʼn wisselrotasie van 80 grade het die beste snyinvoegstukke opgelewer vir die spesifieke invoegstukgeometrie en -graad wat bestudeer is. Verdere WC-12wt%Co-snyinvoegstukke is ter bevestiging vir finale snytoetse met behulp van L PBF vervaardig. Hierdie invoegstukke was met betrekking tot snyprestasie, soos kontaktyd en oppervlakruheid van die werkstuk, met konvensioneel vervaardigde wolframkarbied-invoegstukke vergelykbaar. Na ongeveer 16M30S se kontaktyd vertoon die L-PBF-snybeitel ʼn gemiddelde flankslytasie van 0.7 mm teenoor 0.4 mm vir soortgelyke konvensionele invoegstukke. Hierdie resultate dui daarop dat L-PBF in die toekoms wel ʼn lewensvatbare oplossing vir die navorsing, ontwikkeling en kleinskaalproduksie van WC-Co-snygereedskap kan wees.Doctora

Kaleidoscopic imaging

Kaleidoscopes have a great potential in computational photography as a tool for redistributing light rays. In time-of-flight imaging the concept of the kaleidoscope is also useful when dealing with the reconstruction of the geometry that causes multiple reflections. This work is a step towards opening new possibilities for the use of mirror systems as well as towards making their use more practical. The focus of this work is the analysis of planar kaleidoscope systems to enable their practical applicability in 3D imaging tasks. We analyse important practical properties of mirror systems and develop a theoretical toolbox for dealing with planar kaleidoscopes. Based on this theoretical toolbox we explore the use of planar kaleidoscopes for multi-view imaging and for the acquisition of 3D objects. The knowledge of the mirrors positions is crucial for these multi-view applications. On the other hand, the reconstruction of the geometry of a mirror room from time-of-flight measurements is also an important problem. We therefore employ the developed tools for solving this problem using multiple observations of a single scene point.Kaleidoskope haben in der rechnergestützten Fotografie ein großes Anwendungspotenzial, da sie flexibel zur Umverteilung von Lichtstrahlen genutzt werden können. Diese Arbeit ist ein Schritt auf dem Weg zu neuen Einsatzmöglichkeiten von Spiegelsystemen und zu ihrer praktischen Anwendung. Das Hauptaugenmerk der Arbeit liegt dabei auf der Analyse planarer Spiegelsysteme mit dem Ziel, sie für Aufgaben in der 3D-Bilderzeugung praktisch nutzbar zu machen. Auch für die Time-of-flight-Technologie ist das Konzept des Kaleidoskops, wie in der Arbeit gezeigt wird, bei der Rekonstruktion von Mehrfachreflektionen erzeugender Geometrie von Nutzen. In der Arbeit wird ein theoretischer Ansatz entwickelt der die Analyse planarer Kaleidoskope stark vereinfacht. Mithilfe dieses Ansatzes wird der Einsatz planarer Spiegelsysteme im Multiview Imaging und bei der Erfassung von 3-D-Objekten untersucht. Das Wissen um die Spiegelpositionen innerhalb des Systems ist für diese Anwendungen entscheidend und erfordert die Entwicklung geeigneter Methoden zur Kalibrierung dieser Positionen. Ein ähnliches Problem tritt in Time-of-Flight Anwendungen bei der, oft unerwünschten, Aufnahme von Mehrfachreflektionen auf. Beide Problemstellungen lassen sich auf die Rekonstruktion der Geometrie eines Spiegelraums zurückführen, das mit Hilfe des entwickelten Ansatzes in allgemeinererWeise als bisher gelöst werden kann

Infrared stereolithography

Tese de doutoramento em Ciência e Engenharia de Polímeros e CompósitosStereolithography is an important rapid prototyping process that creates three-dimensional solid objects in a multi-layer procedure. This technology involves the curing or solidification of a liquid photo or thermo sensitive polymer through the use of an irradiation light source, which supplies the energy needed to induce a chemical reaction, bonding large numbers of small molecules and forming a highly cross-linked polymer. This reaction determines the resin morphology that, in turn, defines the physical, electrical, and mechanical properties of the cured material. The cure reaction is highly exothermic and, the temperature and the reaction rate can vary considerably within the curing material due to polymers low thermal conductivity. The main goal of this thesis is to study the process of microstereolithography by infrared radiation and the corresponding polymeric systems. Thermal effects were used over an appropriated polymeric resin to induce a phase change in the material, known as cure reaction, and consequently to obtain solid shapes or patterns. Cure kinetics was characterised and the effects of resin composition were determined. The knowledge of parameters and material composition influence over the process is of great importance to predict both the final geometry and mechanical properties.A estereolitografia é um importante processo de prototipagem rápida que permite criar objectos sólidos tridimensionais através de um processo camada a camada. Esta tecnologia envolve a cura ou solidificação de uma resina polimérica líquida, termo ou foto sensível através da utilização de uma fonte de irradiação, que fornece a energia necessária para provocar uma reacção química, ligando um grande número de pequenas moléculas e levando à formação de um polímero altamente reticulado. Esta reacção determina a morfologia de resina que, por sua vez, define as propriedades físicas, eléctricas e mecânicas do material curado. A reacção de cura é altamente exotérmica e a temperatura e velocidade da reacção podem variar consideravelmente no interior do material curado devido à baixa condutividade térmica dos polímeros. O objetivo principal deste trabalho é estudar o processo de micro estereolitografia por radiação infravermelha e os sistemas poliméricos correspondentes. Efeitos térmicos foram utilizados sobre uma resina polimérica apropriada para induzir uma mudança de fase no material, conhecido como reacção de cura, e, consequentemente, para obter formas ou padrões sólidos. A cinética da cura foi caracterizada e os efeitos da composição da resina foram determinados. O conhecimento da influência dos parâmetros e da composição do material no processo é de grande importância para prever a geometria final e as propriedades mecânicas

Optical In-Process Measurement Systems

Information is key, which means that measurements are key. For this reason, this book provides unique insight into state-of-the-art research works regarding optical measurement systems. Optical systems are fast and precise, and the ongoing challenge is to enable optical principles for in-process measurements. Presented within this book is a selection of promising optical measurement approaches for real-world applications

On the integration of deformation and relief measurement using ESPI

The combination of relief and deformation measurement is investigated for improving the accuracy of Electronic Speckle-Pattern Interferometry (ESPI) data. The nature of sensitivity variations within different types of interferometers and with different shapes of objects is analysed, revealing significant variations for some common interferometers. Novel techniques are developed for real-time measurement of dynamic events by means of carrier fringes. This allows quantification of deformation and relief, where the latter is used in the correction of the sensitivity variations of the former

Advanced LIDAR-based techniques for autonomous navigation of spaceborne and airborne platforms

The main goal of this PhD thesis is the development and performance assessment of innovative techniques for the autonomous navigation of aerospace platforms by exploiting data acquired by electro-optical sensors. Specifically, the attention is focused on active LIDAR systems since they globally provide a higher degree of autonomy with respect to passive sensors. Two different areas of research are addressed, namely the autonomous relative navigation of multi-satellite systems and the autonomous navigation of Unmanned Aerial Vehicles. The global aim is to provide solutions able to improve estimation accuracy, computational load, and overall robustness and reliability with respect to the techniques available in the literature. In the space field, missions like on-orbit servicing and active debris removal require a chaser satellite to perform autonomous orbital maneuvers in close-proximity of an uncooperative space target. In this context, a complete pose determination architecture is here proposed, which relies exclusively on three-dimensional measurements (point clouds) provided by a LIDAR system as well as on the knowledge of the target geometry. Customized solutions are envisaged at each step of the pose determination process (acquisition, tracking, refinement) to ensure adequate accuracy level while simultaneously limiting the computational load with respect to other approaches available in the literature. Specific strategies are also foreseen to ensure process robustness by autonomously detecting algorithms' failures. Performance analysis is realized by means of a simulation environment which is conceived to realistically reproduce LIDAR operation, target geometry, and multi-satellite relative dynamics in close-proximity. An innovative method to design trajectories for target monitoring, which are reliable for on-orbit servicing and active debris removal applications since they satisfy both safety and observation requirements, is also presented. On the other hand, the problem of localization and mapping of Unmanned Aerial Vehicles is also tackled since it is of utmost importance to provide autonomous safe navigation capabilities in mission scenarios which foresee flights in complex environments, such as GPS denied or challenging. Specifically, original solutions are proposed for the localization and mapping steps based on the integration of LIDAR and inertial data. Also in this case, particular attention is focused on computational load and robustness issues. Algorithms' performance is evaluated through off-line simulations carried out on the basis of experimental data gathered by means of a purposely conceived setup within an indoor test scenario