Laser metal deposition (LMD) offers a unique combination of process flexibility, time savings, and reduced cost in producing titanium alloy components. The current challenge in processing titanium alloys using LMD methods is understanding the complex microstructure evolution as a part is fabricated layer by layer. The current work focuses on the characterization, thermal, and microstructural modeling of multilayered Ti-6Al-4V deposits. A thermal model has been developed using finite difference techniques to predict the thermal history of LMD processes. A microstructure model that predicts the alpha phase fraction and morphology evolution was constructed to quantify the effect of thermal cycling on the as-deposited microstructure evolution. Alpha dissolution and growth are modeled assuming one-dimensional plate dissolution according to a parabolic rate law, and a Johnson-Mehl-Avrami-Kolmorgorov (JMAK) nucleation and growth model, respectively. Alpha morphology (colony-alpha and basketweave-alpha) evolution is tracked using a simplistic approach. Characterization of the deposit has shown that a complex microstructure evolves consisting of a two distinct regions: a transient region of undeveloped microstructure and a characteristic layer that is periodically repeated throughout the deposit. The transient region contains a fine basketweave and colony-alpha morphology. The characteristic layer contains a two phase mixture of alpha+beta, with the alpha phase exhibits regions of colony-alpha (layer band) and basketweave-alpha morphology. The different regions of microstructural contrast in the deposit are associated with thermal cycling. The thermal model results show that a heat affected zone defined by the beta transus extends approximately 3 layers into the deposit. The phase fraction model predicts the greatest variation in microstructural evolution to occur in a layer n after the deposition of layer n+3. The results of the morphology model show that increased amounts of colony-alpha form near the top of a characteristic layer. It follows that a layer band (colony-alpha region) forms as a result of heating a region of material to a peak temperature just below the beta transus, where a large amount of primary-alpha dissolves. Upon cooling, colony-alpha forms intragranularly. The coupled thermal and microstructure models offer a way to quantitatively map microstructure during LMD processing of Ti-6Al-4V. / Ph. D.

Widespread use of solid oxide fuel cells is hindered by a lack of long-term durability of seals between metallic and ceramic components caused by thermal expansion mismatch induced cracking. A novel gas seal design incorporating an engineered thermal expansion gradient in a SrO-La₂O₃-A₂O₃-B₂O₃-SiO₂ glass matrix with a TiNiHf shape memory alloy mesh for active stress relief and crack healing is being developed. Coefficient of thermal expansion (CTE) measurements of the seal and fuel cell components shows the possibility for a thermal expansion gradient. Differential scanning calorimetry and microscopy have shown that the TiNiHf alloy has a shape memory transition in the desired range of 200-250ºC. The oxide glass partially crystallizes during thermal cycling which has been observed through X-ray diffraction and dilatometry. The CTE decreases from 9.3Ã 10-6/°C to 6.6Ã 10-6/°C after thermal cycling. Neutron diffraction data from TiNiHf /glass composite samples reveals that the TiNiHf alloy has the ability of absorbing residual stresses from a glass matrix during martensitic phase transition. There is evidence from microscopy that the glass composition is important in determining if reaction will occur with the TiNiHf alloy. The TiNiHf alloy mesh structures can be created using the 3D printing process. This process has been adapted to allow for printing of very thin wire mesh structures of Ni and NiTi powders with a more suitable binder solution. A bi-layer test fixture has been developed which will be useful for assessing leak rate through seal materials. / Master of Science

Thesis (M. Tech. (Engineering: Mechanical)) -- Central University of Technology, Free State, 2013 / This research examines the suitability of Additive Manufacturing (AM) for manufacturing dies used in aluminium high pressure die casting. The study was guided by the following objectives: • The reviews of applicable literature sources that outline technical and application aspects of AM in plastic injection moulds and the possibilities of applying it to high pressure casting die. • To introduce AM grown die components in die manufacture. Further, to develop a methodology that will allow industry to apply AM technology to die manufacture. • Revolutionise the way die manufacture is done. The potential for AM technologies is to deliver faster die manufacture turnaround time by requiring a drastically reduced amount of high level machining accuracy. It also reduces the number of complex mechanical material removal operations. Fewer critical steps required by suitable AM technology platforms able to grow fully dense metal components on die casting tools able to produce production runs. • Furthermore, promising competitive advantages are anticipated on savings to be attained on the casting processing side. AM technology allows incorporation of features in a die cavity not possible to machine with current machining approaches and technology. One such example is conformal cooling or heating of die cavities. This approach was successfully used in plastic injection mould cavities resulting in savings on both the part quality as well as the reduction on cycle time required to produce it (LaserCUSING®, 2007). AM technology has evolved to a point where as a medium for fast creation of an object, it has surpassed traditional manufacturing processes allowing for rapidly bridging the gap between ideas to part in hand. The suitability of the AM approach in accelerating the die manufacturing process sometime in the near future cannot be dismissed or ignored. The research showed that there is promise for application of the technology in the not too distant future. In the South African context, the current number and affordability of suitable AM platforms is one of the main stumbling blocks in effecting more widespread applied research aimed at introduction of the technology to die manufacture.

Thesis (M. Tech.) -- Central University of Technology, Free State, 2008 / As the tendency to use sol id freeform fabrication (SFF) technology for the manufacture of end use parts grew, so too did the need for a set of general guidelines that would aid designers with designs aimed specifically for rapid manufacture. Unfortunately, the revolutionary additive nature of SFF technology left certain fundamental principles of conventional design for manufacture and assembly outdated. This implied that whole chapters of theoretical work that had previously been done in this field had to be revised before it could be applied to rapid manufacturing. Furthermore, this additive nature of SFF technology seeded a series of new possibilities and new advantages that could be exploited in the manufacturing domain, and as a result drove design for rapid manufacturing principles even further apart from conventional design for manufacture and assembly philosophy. In this study the impact that rapid manufacture had on the conventional product development process and conventional design for manufacture and assembly guidelines were investigated. This investigation brought to light the inherent strengths and weaknesses of SFF, as well as the design for manufacture and assembly guidelines that became invalid, and consequently lead directly to the characterization of a set of design for rapid manufacture guidelines.

Additive manufacturing is an industrial process, developed in the early 1980s and currently used in several industries such as the medical, aircraft and automotive industries. In the first place,additive manufacturing was mostly usedby manufacturing industries to produce prototypes, models and patterns. Nowadays, this technology can be used at any point in the lifecycle of a product from pre-production(rapid prototyping and rapid tooling) to production (direct manufacturing). This technology is especially adapted for the production of limited series of small and geometrically complex components.The purpose of this study is to identify howadditive manufacturing affects operational performance during the development and production phases, specifically in the case of the automotive industry.With this purpose in mind, I have collected primary and secondary data through a qualitative study using both in-depth semi-structured interviewsand archival records found on automotive companies’ websites. The objective of collecting multiple sources datawas to gain a reliable and comprehensive perception of the situation and understand the effects of additive manufacturing on operational performance, and more precisely on the seven production wastesdefined on lean practices, to be able to answer my research question. The data are analyzed using an inductive thematic analysis approach and testthe presupposition that emerged from the empirical findings. Through the analysis of the data collected, I came to the conclusion that additive manufacturing is mostly used during the prototyping phase and sometimes also used for rapid tooling. But it appears that this technology is only used for direct manufacturing in some specific niche markets such as luxury carmakers. Another interesting finding concerns the use of additive manufacturing for marketing purpose. Concerning operational performance, the impacts of additivemanufacturing remainlimited, and contrary to what some authors said, the use of this technology is still marginal in the automotive industry compared to traditional manufacturing.

This dissertation has three parts which are distinctive from the perspective of their frequency regime of operation and from the nature of their contributions to the science and engineering communities. The first part describes work that was conducted on a vertical-external-cavity surface emitting-laser (VECSEL) in the optical frequency regime. We designed, fabricated, and tested a hybrid distributed Bragg reflector (DBR) mirror for a VECSEL sub-cavity operating at the laser emission wavelength of 1057 nm. The DBR mirror was terminated with a highly reflecting gold surface and integrated with an engineered pattern of titanium. This hybrid mirror achieved a reduction in half of the number of DBR layer pairs in comparison to a previously reported, successful VECSEL chip. Moreover, the output power of our VECSEL chip was measured to be beyond 4.0Wwith an optical-to-optical efficiency of 19.4%. Excellent power output stability was demonstrated; a steady 1.0 W output at 15.0 W pump power was measured for over an hour. The second part reports on an ultrafast in situ pump-probing of the nonequlibrium dynamics of the gain medium of a VECSEL under mode-locked conditions. We proposed and successfully tested a novel approach to measure the response of the inverted carriers in the active region of a VECSEL device while it was operating under passively mode-locked conditions. We employed the dual-frequency-comb spectroscopy (DFCS) technique using an asynchronous optical sampling (ASOPS) method based on modified time-domain spectroscopy (TDS) to measure the nonequilibrium dynamics of the gain medium of a phase-locked VECSEL that we designed and fabricated to operate at the1030 nm emission wavelength. Our spectroscopic studies used a probe pulse of 100 fs and an in situ pump pulse of 13 ps. We probed the gain medium of the VECSEL and recorded a depletion time of 13 ps, a fast recovery period of 17 ps, and 110 ps for the slow recovery time. Our scans thus demonstrated a 140 ps full depletion-recovery cycle in the nonequilibrium state. The third part discusses work in the microwave and millimeter wave frequency regimes. A new method to fabricate Luneburg lenses was proposed and demonstrated. This type of lens is well known; it is versatile and has been used for many applications, including high power radars, satellite communications, and remote sensing systems. Because the fabrication of such a lens requires intricate and time consuming processes, we demonstrated the design, fabrication and testing of a Luneburg lens prototype using a 3-D printing rapid prototyping technique both at the X and Ka-V frequency bands. The measured results were in very good agreement with their simulated values. The fabricated X-band lens had a 12 cm diameter and produced a beam having a maximum gain of 20 dB and a beam directivity (half-power beam width (HPBW)) ranging from 12° to 19°). The corresponding Ka-V band lens had a 7 cm diameter; it produced a beam with a HPBW about the same as the X-band lens, but with a maximum gain of more than 20 dB.

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / Use of top-down design principles and standard interface techniques provides the basis for a global telemetry data collection, analysis, and satellite control network with a high degree of survivability via use of distributed architecture. Use of Commercial Off-The-Shelf (COTS) hardware and software minimizes costs and provides for easy expansion and adaption to new satellite constellations. Adaptive techniques and low cost multiplexers provide for graceful system wide degradation and flexible data distribution.

由於大環境的改變，公司間的競爭越來越激烈；顧客對新產品的需求也因為新技術的出現日益增加。為了因應全球化競爭及產品生命週期縮短的大環境，迅速及優異的新產品發展成為公司重要的競爭優勢。為了強化公司的競爭優勢，新產品發展已成為一重要議題。本論文著重於研究改善新產品發展的過程，探討影響新產品發展的關鍵因素，尤其是生產與研發間的關係。 本論文分為五個部分，第一章探討新產品發展的概念及基礎理論，說明新產品發展從單一功能政策進化為今日的跨功能性政策的一環。第二章對影響新產品發展的關鍵因素做詳盡介紹，說明跨功能性的整合將會是新產品發展成功的關鍵方法。第三章仔細討論研發與製造間的關係，並將兩者的角色由傳統的分別為單一部門功能的觀點打破，且將產品的設計與製程均視為新產品發展的重要功能，試圖詮釋將單一個人╱部門的知識與成功的新產品發展連結的可能性。第四章將探討知識傳遞的限制、知識管理及組織學習的基本理論。第五章將介紹重要的管理上、組織上及技術上的支援工具，並希望藉由這樣的分析能夠瞭解新產品開發過程中各關鍵因素間的關係。第六章將介紹實務上所使用的新產品開發觀念，這部分的資料是由個案訪問而來，選了三家不同產業具國際營運的公司為例，對實務做驗證。最後，提出一新產品開發的「最佳實務」，包括了重新定義新產品開發過程中的功能，並提出一良好管理新產品開發的建議。 / Nowadays the competitions among companies become more and more fierce due to the dramatic change of competitive environment. The demands of new products are accelerated by the emerging new technologies. The rapid and excellent new product development (NPD) has become a great strategic advantage to be accommodated to the global competition with shorter product life cycle. In order to enhance the competitive advantage, improving NPD has become a vital issue for companies. This thesis focuses on improving the NPD process. Factors influencing the NPD process are discussed in detail, especially the interface between R&D and production. The thesis is divided into five parts, starting with a general view on NPD in the first chapter. There it will be shown, how NPD has changed over the last decades from a traditional approach of functional-development to a cross-functional process today. Factors influencing this effective collaboration are presented in chapter two. In chapter three, the interface between R&D and production is directly scanned. It will be distinguished between the individual knowledge bases of the different departments. Process and product knowledge can be identified as the parts to be matched and will be illustrated. Consequently, the possibilities of linking those knowledge bases during NPD are shown. Chapter four will focus on the limitations of knowledge transfer and the fundamentals of knowledge management and organizational learning will be presented. In chapter five, supportive organizational, managerial and technological tools will be analyzed. The multiple views on NPD assure that all factors influencing the process are analyzed and proven according to their leverage on the process. In chapter six, currently used NPD concepts are outlined. The information presented was gathered through interviews carried out at globally operating companies who have technological centers and production sites in Sweden. To avoid focusing on NPD practices in an industry, the companies were chosen according to their product lines and customer segments. The final part will present best practices in NPD. This includes reconsidering all the discussed aspects and presenting a recommendation about how to organize NPD superiorly.

La carotide est une artère très importante, car elle a pour fonction, principale avec le tronc basilaire d'irriguer le cerveau. Le flux sanguin dans cette région est complexe durant un cycle cardiaque. Les différentes formes de flux et en particulier le vortex ont rarement été discutés auparavant, et le battement de la paroi n'est pas pris en compte. Ce travail de thèse est une contribution pour comprendre l'évolution du vortex et les éléments qui l'influencent, en particulier les battements de parois, pour une recherche expérimentale au niveau de modèles de la bifurcation carotidienne. Les fantômes de carotide avec une transparence et une élasticité des parois artérielles proches de la réalité ont été réalisés par la technique de prototypage rapide. La description des phénomènes de flux et de vortex ont été réalisée dans les fantômes rigide et souple des carotides essentiellement de deux manières : longitudinalement par caméra rapide et transversalement par IRM. Une plateforme économique de PIV a été établie pour quantifier précisément le comportement du vortex avec des vecteurs de vitesse. Une méthode de segmentation de région de vortex et une analyse quantitative ont été mises au point pour étudier leur évolution durant le cycle cardiaque par IRM. La reproductibilité du vortex a été validée par une approche statistique. Les paramètres influençant le comportement des vortex dans les fantômes souple et rigide ont été étudiés. Enfin, une étude de faisabilité sur les vortex dans les fantômes en forme de carotide réelle a été réalisée pour la première fois. / The carotid artery is very important because its main function, with the basilar artery, is to irrigate the brain. The blood flow in this region is complex during a cardiac cycle. The various shapes of flow, in particular, the vortex, has rarely been discussed before and the beating of the arterial wall has not been taken into account. This thesis is a contribution to understand the evolution of the vortex and its factors, in particular the beating of arterial wall in experimental research at the carotid bifurcation. The elastic carotid phantoms with transparency and similar elasticity to real arterial walls properties have been made by rapid prototyping technique. The descriptions of vortex in the rigid and elastic carotid phantoms have been studied in two ways : longitudinal by a high-speed frame camera and tranversal by MRI sequences. An economic PIV platform that can accurately quantify the vortex by velocity vectors has been mounted. Asegmentation method to quantify and analyze the area of the vortex has been developed to study its evolution during the cardiac cycle by MRI. The reproducibility of the vortex has been validated by a statistical approach. The parameters influencing the behavior of vortex have been investigated in rigid and elastic phantoms. At the end, the study of vortex in real-carotid-shaped phantom has been tested for the first time.

O presente trabalho trata da manufatura direta de implantes de hidroxiapatita mediante a técnica de prototipagem rápida. A hidroxiapatita proveniente de estrutura óssea mineral bovina possui grande importância dentre os biomateriais devido a sua biocompatibilidade e grande similaridade com a estrutura óssea humana. A prototipagem rápida permite a obtenção de modelos com dimensões e formato miméticos ao do defeito ósseo do paciente e possibilita a obtenção de implantes com porosidade desejada e geometria complexas. Este trabalho tem como objetivo o estudo da obtenção de implantes por três diferentes técnicas de prototipagem rápida: usinagem a verde, 3DPrint e uma inovadora técnica de prototipagem rápida obtida pela polimerização da resina acrílica (fase líquida da barbotina) por luz ultravioleta presente em uma faixa da banda do espectro de luz emitido pelo laser azul (SLB). A diminuta pressão de conformação, típicas das técnicas de prototipagem rápida aditiva, exige pós altamente reativos para efetiva sinterização, dessa forma a hidroxiapatita obtida a partir do fêmur bovino foi calcinada e moída em moinhos de bolas e vibratório na busca de pós submicrométricos. A usinagem a verde de compactados foi considerada como padrão ouro da manufatura e foi aplicada para obtenção de corpos de prova cilíndricos, previamente conformados por prensagem isostática a 100 e 200 MPa e ensaiados por densificação, flexão, dureza e tenacidade à fratura. Introdução de partículas de alumina e whiskers de alumina foram ensaiados na busca de otimização das propriedades mecânicas. Para prototipagem rápida pelo método de SLB, misturas de hidroxiapatita e resina foram submetidas à emissão do laser azul com percurso direcionado em equipamento CNC, onde peças tridimensionais foram prototipadas e sinterizadas. A hidroxiapatita proveniente do osso bovino apresentou características de íons substitucionais de carbonato e após moagens em moinho de bolas seguido de vibratório foi obtida partículas de diâmetro médio equivalente de 0,35 µm que se mostraram reativas para promoção da sinterização. A sinterização a 1300 ºC-2h forneceu as melhores características cristalográfica e de propriedades mecânicas, resultando em corpos referências com hidroxiapatita sem decomposição em outros fosfatos de cálcio com 99,8 % da densidade, resistência mecânica à flexão de 100 MPa, dureza de 483 HV e tenacidade à fratura de 0,6 MPa.m1/2. A introdução de 1 vol% de alumina e whiskers de alumina elevaram a resistência mecânica do corpo para aproximadamente 140 MPa com tenacidade de 0,61 MPa.m1/2. Para a técnica 3DPrint aglomerados esféricos da composição cerâmica deve ter dimensões entre as malhas de 200 e 400 mesh (75 a 38 µm) e o binder deve ter resistividade superior à 290 kΩ, componentes reativos, emolientes, lubrificantes e estabilizantes. Na manufatura pela técnica SLB a incidência do laser com fluência de 170 mW.s/mm2 promoveu a cura da resina no diâmetro de 0,5 mm e profundidade próxima a 0,5 mm o que, permitiu a prototipagem de scaffolds com camadas de espessura de 0,5 mm resistente ao manuseio para remoção da barbotina não curada. / The study deals with the direct manufacturing of hydroxyapatite implants using rapid prototyping. Hydroxyapatite structure originated from bovine mineral bone has great importance among the biomaterials and biocompatibility due to its great similarity with the human bone structure. Rapid prototyping allows obtaining models with dimensions and shaping mimetics to the patient\'s bone defect and enables the achievement of implants with complex geometry and porosity desired. This study aims to obtain scaffolds for three rapid prototyping techniques: the green machining, 3DPrint and an innovative rapid prototyping technique, obtained by polymerization of acrylic resin (liquid phase of slurry) by ultraviolet light present in a range of the spectrum band a blue light emitted by the laser (SLB). The small conformation pressure, typical of additive rapid prototyping techniques requires highly reactive powders for effective sintering, and then hydroxyapatite obtained from bovine femur was calcined and milled in ball mill and vibratory mill for obtention of sub micrometrics powders. The green machining was considered as the standard of mechanical properties and was used to obtain cylindrical specimens, previously shaped by isostatic pressing at 100 and 200 MPa, and tested by densification, bending, hardness and toughness fracture. Introduction of particles of alumina and alumina whiskers were tested in search engine optimization of the mechanical properties. For rapid prototyping by the method of SLB, mixtures of hydroxyapatite and resin were subjected to blue laser emission directed in CNC equipment where three-dimensional pieces were prototyped and sintered. Hydroxyapatite derived from bovine bone showed characteristics of substitutional carbonate ions and non-stoichiometry, after grinding in a ball mill followed by vibratory mill, particles obtained was equivalent average diameter of 0.35 micrometers that proved reactive to promote sintering. Sintering at 1300 °C-2h gave the best crystallographic characteristics and mechanical properties, resulting in references bodies with hydroxyapatite without decomposition of other calcium phosphates with 99.8 % of density, flexural strength of 100 MPa, hardness of 483 HV and fracture toughness of 0.6 MPa.m1/2. The introduction of 1 vol% alumina and alumina whiskers increased the mechanical strength of the body with approximately 140 MPa and toughness fracture of 0.61 MPa.m1/2. For technical 3DPrint spherical agglomerates of ceramic composition should have dimensions between 200 and 400 mesh (75-38 µm) and the binder should have resistivity higher than 290 kΩ and components reactive, emollients, lubricants and stabilizers. In the manufacturing technique SLB incidence of the laser with a fluency of 170 mW.s/mm2 promoted curing of the resin of 0.5 mm in diameter and depth about 0.5 mm, which enabled the prototyping of scaffolds with thick layers 0.5 mm resistant to handle for removal of slurry uncured.