Dissertations / Theses on the topic 'Metal cladding'

Thesis (MTech (Mechanical Engineering))--Peninsula Technikon, 2003
Systematic laser cladding experiments were performed using a mixture of a Nickel base alloy powder mixed with tungsten carbide powder (percentage contents of tungsten carbide from 10% to 40%) on EN8 steel substrate with pre-placed powder method. Laser cladding of the Nickel base alloy powder + 50% tungsten carbide powder on EN9 steel substrate was performed with powder injection method as well. A Finite Element Method for calculating the surface temperature distribution was used to help prediction of temperature distribution laser cladding results. Composition of cladding materials was designed; a sticking agent was chosen for the pre-placed powder method. Clad coatings were obtained for different process parameters for laser cladding, and a detailed study of the affects of these parameters has been carried out. The characteristic microstructure and properties of the clad layers and interface were investigated by using an optical microscope, a micro hardness tester and a makeshift wear test. A comprehensive review is presented on the dilution of the coating and the typical problems experienced with the coating substrate interface. The results show that microstructure of clad layers comprise three zones: the cladding layer, bonding zone and heat-affected zone. The results showed that tungsten carbide particles increased the hardness and wear resistance as expected. Wear resistance of laser cladding coating is 3.5 times than that of substrate. The micro hardness range of the cladding layer is from RV 981.5 to RV 1187, which is 2-3 times than that of substrate. The micro hardness varies from cladding coating to transition layer then to heat affected zone and substrate along a gradient.

Surface engineering provides solutions to wear and corrosion degradation of engineering components. Laser cladding is a surfacing process used to produce wear and corrosion resistant surfaces by covering a particular part of the substrate with another material that has superior properties, producing a fusion bond between the two materials with minimal dilution of the clad layer by the substrate. The advantages of laser cladding compared to conventional techniques include low and controllable heat input into the workpiece, a high cooling rate, great processing flexibility, low distortion due to the low heat input to the workpiece and minimal post-treatment. The main processing parameters of laser cladding include laser power, laser spot size, processing speed, and powder feed rate. Within an optimized operational window, all these variables have some effect on the temperature of the clad interaction zone. The laser cladding technique is very complicated because it involves metallurgical and physical phenomena, such as laser beam-materials interaction, heat transfer between the clad and the substrate, and the interdiffusion of the clad and the substrate materials. Laser cladding is currently an open-loop process, relying on the skills of the operator and requiring dedication to specialty to make it successful. Unless the required expertise is provided, attempts to make the process successful will be futile. The objective in conducting the project was to investigate and develop prototype sensors to monitor and control Nd:YAG laser cladding process. Through a LabVIEW software based monitoring program, real-time process monitoring of optical emissions in the form of light and heat radiation was carried out, and correlated with the properties of the produced clad layers. During various experiments, single- and multiple-track laser cladding trials were performed. The responses of such sensors to the selected conditions were examined and an in depth analysis of detected heat and optical radiation signals was carried out. The results of these experiments showed the ability of such sensors to recognize changes in process parameters, and detected defects on layer surfaces along with the presence of oxides. A multi-function closed-loop laser power and CNC motion table feed rate control interface based on a LabVIEW platform has been designed and built, which is capable of accepting and interpreting sensors� data and adjusting accordingly the laser power and CNC motion table feed rate to produce sound clad layers. The developed dual control strategy utilized in this study forms a relatively inexpensive and less-complicated system that allows end-users to achieve lower failure rates during laser cladding (within its own limitations) and, therefore, through successful concurrent control of melt pool temperature and motion table feed rate provide better productivity and quality in the experimentally produced clad layers.

Thesis (MscEng)--Stellenbosch University, 2013.
ENGLISH ABSTRACT: Low-rise buildings with crest fastenedmetal cladding are susceptible to failures in the vicinity of the fasteners during strongwind uplift conditions. These localised failures often lead to the progressive removal of cladding, which can cause disastrous building damage. In South Africa, the current metal cladding design approach is inadequate, since it solely relies upon manufacturer design specifications. These specifications are typically designated as broad design guidelines for the maximum allowable cladding support spacings which are independent from any specified design loads. This research focuses on the investigation of 0.50 mm ISQ550 IBR cladding systems to understand basic cladding behaviour during static wind uplift conditions and to quantify the uplift performance of IBR systems. The research investigation also included the improvement and performance evaluation of a full-scale cladding test method which applies an air-bag loading method to simulate static wind uplift conditions according to the revised SANS 10237:201X code of practice. This thesis may serve as a basis for further cladding research, and the development of suitable standardised metal cladding test methods in South Africa. Several experimental investigation methods and limited finite element analyses (FEA) were used to investigate IBR and the performance of the test methods. Tensile testing was used to determine the material properties of the cladding metal. The full-scale cladding assembly testing was used to investigate the behaviour of IBR and to evaluate the performance of the air-bag test rig. The localised behaviour of the cladding around the fasteners was also investigated with a small cladding subassembly test method. The FEA served as a supplementary investigation for IBR performance evaluation. The experimental investigation confirmed that the static wind uplift resistances of IBR systems are mainly governed by localised deformations of their fastened crests and fastener pull-through failures. The behaviour and performance of IBR systems are heavily dependent on the crest fastening arrangement. IBR systems with every crest fastening demonstrated a considerably higher wind uplift resistance than IBR systems with the standard alternate crest fastening arrangement. The measured fastener loads were independent from span length, whereas the overall uplift resistance of IBR reduced with increased span lengths. Load-span resistance data for 0.50 mm ISQ550 IBR was derived from testing to provide a rational framework for design. The FEA provided a reasonable simulation of IBR subjected to static wind uplift and confirmed the presence of high stress and strain concentrations around the fastener holes which cause fastener pull-through failures. Therefore, FEA can be used as an effective tool to investigate the behaviour of IBR. In conclusion, the air-bag test method used in this research investigation provided an effective method for evaluating the uplift performance of crest fastened metal cladding. However, the air-bag load method is not capable of accurately simulating a true uniformly distributed uplift load. It is recommended that direct air pressure testing be adopted for any further research or commercial testing ofmetal cladding because direct air pressure testing is an effective and proven test method for accurate simulation of static and cyclic wind uplift conditions.
AFRIKAANSE OPSOMMING: Metaalbekleding met kruinvashegting op lae geboue is geneig om te faal by die vashegters tydens toestande van sterkwind-opheffing. As vashegters faal kan bekleding progressief verwyderwordomrampspoedige skade aan die gebou te veroorsaak. Die huidige ontwerpmetode vir metaalbekleding in Suid-Afrika is onvoldoende, aangesien dit slegs gegrond is op vervaardigers se ontwerpspesifikasies. Spesifikasies word gewoonlik verklaar as breë ontwerpriglyne vir die maksimum toelaatbare spasiërings van ondersteunings sonder enige oorwegings vir ontwerpbelastings. Hierdie navorsing fokus dus op 0.50mm ISQ550 IBR metaalbekleding omdie basiese gedrag van bekleding tydens wind-opheffing beter te verstaan en die ophefweerstand van IBR te kwantifiseer vir ontwerpdoeleindes. Verder ondersoek hierdie navorsing ook die verbetering en evaluasie van ’n volskaalse bekledingstoetsmetode wat statiese wind-opheffing naboots met verspreide lugsakbelasting volgens die hersiende SANS 10237:201X gebruikskode. Hierdie proefskrif kan dien as ’n grondslag vir verdere navorsing en die ontwikkeling van geskikte standaard-toetsmetodes vir metaalbekleding in Suid-Afrika. Verskeie eksperimentele toetsmetodes en beperkte eindige-element-analises (EEA) is gebruik om die gedrag van IBR en die toets-opstellings te ondersoek. Trektoetse is gebruik om die meganiese eienskappe van die bekledingsmetaal te bepaal. Volskaalse toets-opstellings is gebruik om die weerstand van IBR te ondersoek en die lugsaktoetsmetode te evalueer. Die gelokaliseerde gedrag van die bekleding rondom die vashegters was ook ondersoek met klein toets-opstellings. EEA het gedien as ’n aanvullende ondersoek om die gedrag van IBR te evalueer. Die eksperimentele ondersoek het bevestig dat die wind-ophefweerstande van IBR-stelsels hoofsaaklik bepaal word deur gelokaliseerde deformasies van die vasgehegde kruine en die vashegters se deurtrekweerstand. Die gedrag en weerstand van IBR-stelsels is ook grootliks afhanklik van die toegepaste vashegtingsmetode. IBR stelsels met vashegting deur elke kruin het ’n hoër ophefweerstand verskaf as IBR-stelsels met die standaard vashegtingsmetode deur elke tweede kruin. Die gemete vashegterbelastings was onafhanklik van die spanlengtes, terwyl die algehele ophefweerstand van IBR verminder het vir langer spanlengtes. Toetsdata is gebruik om ophefweerstande vir 0.50mm ISQ550 IBR oor verskeie spanlengtes af te lei sodat ’n rasionele raamwerk vir ontwerp bewerkstellig kan word. Die EEA het die gedrag van IBR tydens toestande van statiese wind-opheffing redelik goed nageboots en het ook die teenwoordigheid van hoë spannings- en vervormingskonsentrasies rondom die vashegtergate, wat vashegters laat deurtrek, bevestig. Daarom kan EEA as ’n effektiewe instrument gebruik word om die gedrag van IBR te ondersoek. Ten slotte word dit afgelei dat die lugsaktoetsmetode van hierdie navorsingsondersoek ’n effektiewe metode verskaf het vir die gedrag-evaluering van kruinvasgehegte bekleding tydens wind-opheffing. Die lugsaktoetsmetode kan egter nie ’n ware gelykverspreide ophefbelasting naboots nie. Daarom word dit voorgestel dat toetsmetodes wat direkte lugdruk aanwend gebruik moet word vir enige verdere navorsing of kommersiële toetse van metaalbekleding, aangesien dit ’n effektiewe en bevestigde toetsmetode is wat statiese en sikliese opheftoestande akkuraat kan naboots.

Thesis (M. S.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Klein, Benjamin; Committee Member: Alavi, Kambiz; Committee Member: Allen, Janet K.; Committee Member: Buck, John; Committee Member: Gaylord, Tom; Committee Member: Yoder, Douglas.

Thesis (M.S.)--University of Missouri--Rolla, 2007.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed December 6, 2007) Includes bibliographical references.

Laser metal deposition is one of the most versatile methods in the expanding field of additive manufacturing. Its outstanding advantage is its capability to process a variety of metallic materials for the freeform fabrication of objects having sound mechanical properties. The process is used in applications of rapid manufacturing, components repair and surface coating. During recent years, modelling has been increasingly used to study and improve the laser metal deposition process. However, most models have focused on analysing individual stages of the deposition process and thus have not thoroughly dealt with the occurrence of mutually-influencing phenomena. This work presents a new numerical model that, starting from the simulation of powder particles in the deposition head, integrates the important phenomena and interactions that govern the dynamics of a powder stream and a deposition melt pool, within a single model for the first time.The resulting model is comprehensive enough to allow the prediction of the morphology of deposited tracks and structures and the heat flows during their creation; as well as the flexibility to simulate, in principle, any deposition shape. The model has been demonstrated using the settings of an actual laser metal deposition system, and has been applied to study clad formation in the deposition of single tracks, layers, walls and simple three-dimensional structures. Moreover, the model has been used to study the formation of irregularities and excessive mass deposition. A new sensor-less deposition control technique based on the simulation and testing of different deposition strategies prior to actual deposition, is proposed. As a demonstration of this control technique, the model has also been used to study the case where excessive deposition develops at intersecting or cornered tracks. Improved deposition strategies have been tested using the model and applied to real deposits. A two fold improvement in layer height control has been achieved in the case of cornered layers.The outcome of the work presented in this thesis can be applied in further studies and prediction of laser deposited shapes for real applications. Furthermore, it can be potentially used for improvement of the laser metal deposition technology through the simulation of deposition strategies prior to actual processing.

The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald nuclear power plant representing the first generation of Russian-type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs of 4 units represent different material conditions as follows: • Irradiated (Unit 4), • irradiated and recovery annealed (Units 2 and 3), and • irradiated, recovery annealed and re-irradiated (Unit1). The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam. Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall. This report presents test results measured on the trepans from the beltline welding seam No. SN0.1.4. and forged base metal ring No. 0.3.1. of the Units 1 2 and 4 RPVs. The key part of the testing is focussed on the determination of the reference temperature T0 of the Master Curve (MC) approach following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined: • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed. • KJc values of the weld metals generally followed the course of the MC though with a large scatter. • There was a large variation in the T0 values evaluated across the thickness of the multilayered welding seams. • The T0 measured on T-S oriented SE(B) specimens from different thickness locations of the welding seams strongly depended on the intrinsic structure along the crack front. • The reference temperature RT0 determined according to the “Unified Procedure for Lifetime Assessment of Components and Piping in WWER NPPs - VERLIFE” and the fracture toughness lower bound curve based thereon are applicable on the investigated weld metals. • A strong scatter of the fracture toughness KJc values of the recovery annealed and re-irradiated and the irradiated base metal of Unit 1 and 4, respectively is observed with clearly more than 2% of the values below the MC for 2% fracture probability. The application of the multimodal MC-based approach was more suitable and described the temperature dependence of the KJc values in a satisfactory manner. • It was demonstrated that T0 evaluated according to the SINTAP MC extension represented the brittle fraction of the data sets and is therefore suitable for the nonhomogeneous base metal. • The efficiency of the large-scale thermal annealing of the Greifswald WWER 440/V230 Unit 1 and 2 RPVs could be confirmed.

The research is divided into four related sections of work. The first relates to the rim wall wear of the existing unlubricated steel, and polyethylene centre bearing components. Based on these findings, the second and third sections of work includes materials characterisation of alternative centre bearing surfaces - plasma nitrided molybdenum steel and stellite 6 laser clad layers, respectively. Finally, in the last section of work, the reciprocating pin-on-plate wear test method is used to evaluate the friction and wear of the existing and alternative centre bearing materials. The worn dimensions of the AISI 1053 steel, Hadfield steel, and polyethylene centre bearing components were determined. The wear of the high density polyethylene centre bowl liner was negligible. The rim wall wear of the unlubricated steel components was greatest in the longitudinal direction, whilst there was negligible wear in the lateral direction. The average wear depth rate for the AISI 1053 steel top centre was approximately twice that of the Hadfield steel centre bowl liner. The cross-sectional microhardness and microstructure of one worn AISI 1053 steel top centre and two worn Hadfield steel centre bowl liners were determined. The worn Hadfield steel centre bowl liners showed significant near surface work hardening. The wear mechanism for the AISI 1053 steel top centre was plastic strain accumulation in conjunction with low cycle fatigue. The quench and tempered AISI 4016 molybdenum steel samples were plasma nitrided at 450, 500, 550 and 580 C using 75% N2: 25% H2 mixture gas for 5 hours. The microstructures of the coatings were determined using optical microscopy, and scanning electron microscopy. The treated samples were characterised using x-ray diffraction and vi microhardness. The optimum condition for this material was achieved at the temperature of 500 0C. Stellite 6 multi-track layers were laser clad onto mild and AISI 4016 steel substrates with a continuous wave Nd:YAG laser at 1800 W laser source power using four different processing speeds: 600, 900, 1200, and 1500 mm/min. The laser power, defocused laser spot size, and powder feed rate were held constant. The clad samples were characterised using optical microscopy and scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS). Microhardness profiles of the clad layers and heat affected zones were determined. For both substrates the optimum processing speed is between 600 and 900 mm/min. Wear testing of Hadfield pin - AISI 1053 steel plate, Hadfield pin - untreated AISI 4016 steel plate, HDPE pin – Hadfield steel plate, Hadfield pin - plasma nitrided AISI 4016 steel (500 °C) plate, and Hadfield pin – laser clad Stellite 6 (600 mm/min) plate material pairs was conducted using the pin-on-plate reciprocating wear test method. The wear test conditions provided a good simulation of the rim wall operating conditions for the Hadfield steel pin – plasma nitrided AISI 4016 steel (500 °C) plate and Hadfield steel pin – laser clad Stellite 6 (600 mm/min) plate material pairs. The Hadfield steel pin – nitrided AISI 4016 steel (500 °C) plate material pair had the lowest wear under these wear test conditions, whilst it’s co-efficient of friction of 0.57 would make it suitable for use in lightly loaded (50 ton wagon mass) 3-piece freight bogies.

The purpose of the project work was to build knowledge of the tribological behaviour of self-lubricating laser cladding, with and without external solid lubricant during conditions relevant for hot metal forming of aluminium. The materials used during the project were plates coated with a Ni-based self-lubricating clad and a reference sample of work tool steel. The self-lubricating laser clad was applied using a high power direct diode laser. The external solid lubricant used was a graphite dispersion. The external solid lubricant was applied on the samples using a spraying technique, leaving a dry layer of solid graphite on the plates. To test the tribological behaviour of the plates, linear reciprocating friction and wear tests were performed both under lubricated and dry conditions. During the dry tests, different surface roughness of the plates where investigated. The pins for the tribological test were made of AA7075. Parameters chosen for the tribological tests were based on conditions during hot forming of aluminium. After having taken images of the plates using scanning electron microscopy, and using a 3D optical profiler, the wear volume and material transfer was evaluated, and wear mechanism analysis was performed.   The tribological behaviour of polished Ni-based laser clad under dry conditions is comparable to that of the reference sample at its best performance. Using a mirror polished Ni-based laser clad under dry condition can be an option to not using external solid lubricant during hot forming of aluminium. Also, the surface roughness of the self-lubricating clad under dry conditions does not affect the coefficient of friction.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O desgaste abrasivo é uma das causas de falhas em equipamentos e responsável por prejuízos nos processos industriais. Uma técnica capaz de minimizar os efeitos deste fenômeno é a aplicação de revestimentos duros nas superfícies críticas. Recentemente foram desenvolvidos revestimentos contendo carbonetos de titânio formados pela fusão de misturas contendo cavacos das ligas ASTM F67 e ASTM F136 sobre peças de aço-carbono ASTM A-36. Após a aplicação do processo de soldagem GTAW obteve-se significativa fração volumétrica de TiC grosseiro com elevada dureza. No presente trabalho foi investigada a refusão dessas soldas pelo processo de soldagem a Laser Nd:YAG pulsado. A microestrutura das amostras foi analisada por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV) e microdureza Vickers. A caracterização microestrutural mostrou que houve refinamento dos carbonetos de titânio (TiC) na matriz ferrítica refundida com o Laser, cujo principal efeito foi um endurecimento do metal de solda. A caracterização mecânica demonstrou um aumento na microdureza da superfície do material. Este comportamento favorece o uso da refusão a Laser para a melhoria da qualidade das superfícies que demandam maior resistência ao desgaste abrasivo.
The abrasive wear is one of the causes of failures in equipment and responsible for damages in industrial processes. A technique capable of minimizing the effects of this phenomenon is the application of hard coatings on critical surfaces. Recently, coatings containing titanium carbides produced by melting mixtures containing ASTM F67 and ASTM F136 chip blends on ASTM A-36 carbon steel parts have been developed. After an application of the GTAW get process, an important volumetric fraction of coarse TiC with high hardness was obtained. In the present work the remelts is investigated for welds by the pulsed Nd: YAG Laser process. A microstructure of the samples was analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Vickers microhardness. The microstructural characterization showed that there was a refinement of the titanium carbides (TiC) in the ferritic matrix remelt with the Laser, whose main effect was a hardening of the weld metal. The mechanical characterization showed an increase in the microhardness of the material surface. This behavior favors the use of laser cladding to improve the quality of surfaces that require high abrasive wear resistance.

Orientador: Juno Gallego
Resumo: O desgaste abrasivo é uma das causas de falhas em equipamentos e responsável por prejuízos nos processos industriais. Uma técnica capaz de minimizar os efeitos deste fenômeno é a aplicação de revestimentos duros nas superfícies críticas. Recentemente foram desenvolvidos revestimentos contendo carbonetos de titânio formados pela fusão de misturas contendo cavacos das ligas ASTM F67 e ASTM F136 sobre peças de aço-carbono ASTM A-36. Após a aplicação do processo de soldagem GTAW obteve-se significativa fração volumétrica de TiC grosseiro com elevada dureza. No presente trabalho foi investigada a refusão dessas soldas pelo processo de soldagem a Laser Nd:YAG pulsado. A microestrutura das amostras foi analisada por difração de raios-X (DRX), microscopia eletrônica de varredura (MEV) e microdureza Vickers. A caracterização microestrutural mostrou que houve refinamento dos carbonetos de titânio (TiC) na matriz ferrítica refundida com o Laser, cujo principal efeito foi um endurecimento do metal de solda. A caracterização mecânica demonstrou um aumento na microdureza da superfície do material. Este comportamento favorece o uso da refusão a Laser para a melhoria da qualidade das superfícies que demandam maior resistência ao desgaste abrasivo.
Mestre

The repair of worn or damaged components is becoming more attractive to manufacturers, since it enables them to save resources, like raw material and energy. With that costs can be reduced, and profit can be maximised. When enabling the re-use of components, the lifetime of a component can be extended, which leads to improved sustainability measures. However, repair is not applied widely, mainly because costs of repairing are overreaching the costs of purchasing a new component. One of the biggest expense factors of repairing a metal component is the labourintense part of identifying and quantifying worn or damages areas with the use of various external measurement systems. An automated measuring process would reduce application cost significantly and allow the applications to less cost intense component. To automate the repair process, in a one-machine solution, it is prerequisite that a measuring device is included in the machine enclosure. For that, different measuring solutions are being assessed towards applicability on the “Trumpf TruLaser Cell 3000 Series”. A machine that uses the Laser Metal Deposition (LMD) technology to print, respectively weld, metal on a target surface. After a theoretical analysis of different solutions, the most sufficient solution is being validated by applying to the machine. During the validation a surface models from a test-component is generated. The result is used to determine the capability of detecting worn areas by doing an automated target-actual comparison with a specialised CAM program. By verifying the capability of detecting worn areas and executing a successful repair, the fundamentals of a fully automated repair process can be proven as possible in a one-machine solution.
Tillverkare har börjat se stora möjligheter i att reparera slitna eller skadade komponenter som ett sätt att spara resurser, så som råmaterial och energi. Med den besparingen minskar kostnaderna och vinsten kan således maximeras. Reparation möjliggör även återanvändning av komponenter, vilket förlänger komponentens livslängd och leder till förbättrade hållbarhetsåtgärder. Dock tillämpas reparation inte i någon stor utsträckning i nuläget, främst eftersom kostnaderna för reparation överstiger kostnaderna för att köpa en ny komponent. En av de största kostnaderna för att reparera en metallkomponent är att identifiera och kvantifiera slitna eller skadade områden med hjälp av olika externa mätsystem, som är en väldigt arbetsintensiv process. En automatiserad mätprocess skulle minska avsökningskostnaden avsevärt och således reducera den totala kostnaden för komponenten. För att möjliggöra en automatiserad reparationsprocess i en enda maskinlösning är det en förutsättning att en mätanordning ingår i maskinhöljet. Därför har olika mätningslösningar utvärderats med avseende på användbarhet i "TRUMPF TruLaser Cell 3000 Series", vilket är en maskin som använder Laser Metall Deposition-teknik (LMD-teknik) för att skriva ut och svetsa metall på en definierad yta. En teoretisk analys av olika lösningar har utförts, där den teoretiskt mest lämpliga lösningen validerades genom att appliceras till maskinen. Valideringen genererade en modell av ytan av en testkomponent. Sedan utfördes en automatiserad, målrelaterad jämförelse med ett specialiserat CAM-program baserat på modellresultatet, för att bestämma möjligheten att upptäcka slitna områden. Genom att verifiera förmågan att upptäcka slitna områden samt genomförandet av en lyckad reparation kan grunden för en helt automatiserad reparationsprocess bevisas som möjlig i en enda maskinlösning.
Das reparieren von abgenutzten oder beschädigten Komponenten wird immer attraktiver für Hersteller. Es ermöglicht es Ressourcen einzusparen wie beispielsweise Rohmaterial und Energie, was die Lebenszeit einer Komponente verlängert und damit die Nachhaltigkeit verbessert. Allerdings ist Reparieren nach wie vor nicht weit verbreitet, hauptsächlich dadurch bedingt, dass die Reparaturkosten die Kosten für eine neue Komponente übersteigen. Einer der größten Kostenfaktoren des reparieren einer Metallkomponente ist der Arbeitsintensive Teil der Identifizierung und Quantifizierung des abgenutzten oder beschädigten Bereichs mit verschiedensten externen Vermessung Systemen. Ein automatisierter Vermessungsprozess würde die Kosten signifikant reduzieren und neue Applikationen ermöglichen. Das automatisieren der gesamte Prozesskette – in einer Single-Maschinenlösung – erfordert, dass eine Messeinrichtung im Bearbeitungsraum der Maschine angebracht wird. Dafür werden verschiedene Lösungen nach Anwendbarkeit an der Trumpf Laser Cell 3000 Serie hin beurteilt. Eine Maschine, welche Laser Metal Deposition (LMD) als Technologie anwendet um Material auf Oberflächen aufzubringen. Nach einer theoretischen Analyse verschiedener Lösungen wird die beste Lösung va durch anbringen an die Maschine validiert. Bei der Validierung wird ein Oberflächenmodel erzeugt. Das Ergebnis wird dann genutzt um die Fähigkeit zu belegen, dass beschädigte Stellen, durch einen Soll-Ist-Vergleich in einem speziellen CAM Programm, automatisch detektiert werden können. Basierend auf diesem Beleg und mit dem Ergebnis eine Komponente erfolgreich reparieren zu können, gilt die These eines automatisierten Reparaturprozesses in einer Single-Maschinenlösung als beweisen.

Clad metals are extensively used for their multi-functionality and their optimal combination of quality and cost. Roll bonding is an effective and economic processing approach to making clad metals. This dissertation presents an experimental investigation of the roll cladding process as well as thermo-mechanical modeling of mechanism for roll bonding of clad metals. The objectives of this research are to investigate the bonding mechanism of dissimilar metals in a warm rolling process and to advance the knowledge of the roll cladding process. To accomplish the objectives, aluminum 1100 sheet (Al 1100) and stainless steel 304 sheet (SST 304) are bonded by warm rolling under controlled conditions. The 180 degrees peel test is used to determine the bonding property of those clad metals. The experimental results show that the rolling thickness reduction and the entry temperature are two major factors of bonding strength. Minimum thickness reduction at a particular entry temperature is required to bond Al 1100 and SST 304. Increasing of either thickness reduction or entry temperature significantly improves the bonding strength between the two metals. X-ray microanalysis is also performed to characterize the diffusion state at the bonding interface. The diffusion coefficients of aluminum and iron are estimated through experimental method. A thermo-mechanical model was developed to describe the rolling plastic deformation of component metal sheets and the diffusion evolution during a roll bonding process of dissimilar metals. The effect of various rolling conditions on the contact area ratio was quantitatively discussed. Finite element simulation of 2-D diffusion under the rolling created boundary conditions was performed. The peel strength during the diffusion evolution was predicted by the integrated roll bonding model. The modeling predictions correspond to the experimental results well. The correspondence validates the effectiveness of the thermo-mechanical roll bonding model. Based on experimental observation, this research presents a bonding mechanism for the roll cladding process of dissimilar metals. The roll bonding model can help optimize rolling parameters for varying bonding strength depending on the demands of the application. It can also provide insights into design and analysis of rolling bonding process of other groups of dissimilar metal sheets.

The roof of a low rise building (e.g., house, industrial shed) is subjected to intense fluctuating wind pressures during a tropical cyclone. A failure of the building’s roof is not only a life safety issue but also impacts greatly on the community’s resilience during and after wind storms. Low cycle fatigue cracking of roof and wall cladding, fixings, and supports during tropical cyclones is a complex process, where small changes in load, geometry or material properties can significantly affect the fatigue performance of the cladding system. Investigating the performance of the building envelope when subjected to cyclonic winds is of importance to the manufacturing and construction industry, and standards communities. A better understanding of the fatigue mechanisms of cladding systems will provide industry with a means to optimise the cladding design and to improve the assessment of vulnerability of building stock. The research was conducted to analyse the performance of light gauge but high yield strength corrugated metal cladding subjected to cyclonic wind loads. The experimental methods involved tensile coupon tests and static point load tests as well as static pressure, cyclic pressure and dynamic wind pressure tests on double 900 mm span 0.42 mm BMT G550 corrugated cladding specimens. The air pressure tests, including the simulated cyclonic wind pressures, were carried out by using a Pressure Loading Actuator (PLA) that was able to apply a positive and negative (suction) pressure via an air-chamber. Reactions in the X, Y and Z directions were measured at the cladding screws, along with lateral movement of the screws and crack growth in the cladding under the range of fluctuating loads. Wind tunnel test data and full scale measurements show that the wind pressures are highly fluctuating and temporally and spatially varying across the building envelope. Yet the line load testing and typical product testing applies the “same load” to all fasteners in the test specimen. The thesis has shown, by measuring fastener reactions to point loads applied at various points across the cladding, that there is minimal influence on the reaction in one screwed crest to an adjacent screwed crest, justifying the assumption of applying a uniform load across the test specimen. Different shaped cyclic pressure traces, such as sinusoidal, sawtooth and spike were used. The numbers of cycles to failure for these pressure traces with similar load cycle ranges showed it was the peak load per cycle and load ratio that governed number of cycles to failure and not the RMS of the trace or the duration of the peak. The application of fluctuating pressures representing wind loads enabled the assessment of cladding response to these dynamic pressures and a comparison to cyclic load tests. Cladding crack patterns generated with the simulated wind trace from the PLA were similar in shape and length to crack patterns reported in damage surveys and the loads at which the claddings deformed and buckled, were of similar magnitude to those in the cyclic load tests. Analysis of the applied fluctuating pressures and resultant screw reactions showed that the cladding specimens responded in a quasi-static manner. That is, there was no resonance in the cladding from the fluctuating pressures. A Damage Index metric based on Smax-N cyclic test data is proposed that could be used as an indicator of extensive cladding damage and possible cladding failure for generated cyclonic traces. The DI could also be used to indicate possible crack initiation for crease type cracks following low intensity cyclone crossings. The outcomes of this study have demonstrated (a) the relevance of the experimental basis of the current test standard (i.e., L-H-L), (b) the improved resilience of the building envelope if designed to the L-H-L standard over the previous test criteria, (c) potential areas to be strengthened in current building stock, and (d) the need for increased design pressures on cladding elements in the Australian Wind Actions Standard.

I propose to develop a new method for the synthesis of metal matrix composites (MMC) using aerosol reactants in a radio frequency (RF) plasma torch. An inductivelycoupled RF plasma torch (ICPT) may potentially be designed to maintain laminar flow and a radial temperature distribution. These two properties provide a method by which a succession of metal layers can be applied to the surface of SiC fibers. In particular, the envisaged method provides a means to fully bond any desired metal to the surface of the SiC fibers, opening the possibility for MMCs in which the matrix metal is a highstrength steel. A crucial first step in creating the MMC is to test the feasibility of constructing an ICPT with completely laminar flow in the plasma region. In this work, a magnetohydrodynamic (MHD) model is used along with a computational fluid dynamic (CFD) software package called FLUENT© to simulate an ICPT. To solve the electromagnetic equations and incorporate forces and resistive heating, several userdefined functions (UDF) were written to add to the functionality of FLUENT©. Initially, an azimuthally-symmetric, two-dimensional model was created to set a test baseline for operating in FLUENT© and to verify the UDF. To incorporate coil angle and current leads, a fully three dimensional model UDF was written. Preliminary results confirm the functionality of the code. Additionally, the results reveal a non-mixing, laminar flow outer region for an axis-symmetric ICPT.

碩士
國立成功大學
機械工程學系碩博士班
100
The purpose of this thesis is to characterize the metal powder/resin cladding system with the Nd-YAG laser numerically and experimentally. In the numerical simulation, the FLUENT software was applied to simulate the flow field of the resin output from a feeder nozzle on a substrate with various outlet heights and output times. In the experiment, the distribution of the metal powder/resin composite layer has been visualized. The multi-pulse cladding was made by the pulsed Nd-YAG laser. Furthermore the cladding specimen was verified by micro tensile test and metallurgical observation. Both the numerical simulation and experimental results show that an optimum cladding profile could be obtained with proper selection of the composite outlet height. According to the micro tensile test, the strength of the multi-pulse cladding layer is higher than the base material. It can be found the cladding microstructure is similar to that of the conventional laser cladding but with fine bonding structure.

M. Tech. Metallurgical Engineering
Titanium alloys exhibit poor tribological characteristic which include abrasion resistance, metal to metal wear resistance and solid particle erosion and cavitation due to low surface hardness and high coefficient of friction. These poor properties have limited the application of titanium alloys as engineering tribological components, tools and parts that operate in severe wear and friction conditions. Laser processing defects such as pores, cracks and segregation pose a huge threat to the quality and the microstructure of the deposited layer. Defects caused by the parameters lead to severe wear and corrosion occurrence, hence, precise control of the parameters are crucial and it depends on the properties of the material used. It is postulated that Nickel Titanium (NiTi) is a promising candidate as reinforcement matrix material for wear resistant alloy. The wear resistance would be further enhanced if NiTi is in-situ incorporated onto titanium matrix by laser cladding to yield hard intermetallic phases. The main goal of the study is to develop corrosive-wear resistant thin surface coatings on Ti-6Al-4V alloy for automotive and aerospace applications by depositing Titanium and Nickel elemental powders to form in-situ NiTi intermetallic using laser cladding technique.

碩士
國立交通大學
光電工程研究所
103
In this thesis we have two parts. In the first part, we have demonstrated a room temperature plasmonic nanolaser at UV region using ZnO NW-based structure by utilizing the large dispersive characteristics due to the intrinsic interband absorption of silver. The lasing energy is about 3.324 eV (373 nm) with a threshold power of 69 MW/cm2 and a linewidth of 0.4 nm. We believe refined nanocavity geometry and fabrication process can bring the ZnO plasmon nanolaser to be operated at even above the room temperature. In the second part, we do some optimization on GaAs nanocavity. We change rectangular pillar into cylinder pillar and do sidewall repair. By using the O2 plasma oxidization and phosphoric acid etching, we successfully reduce the surface defect created from dry ecthing of GaAs. We will discuss those two optimization and put them in to process flow in order to produce electrical driven GaAs-based Metallic cavity laser. Finally, we will analysis and discuss the measurement result.