Dissertations / Theses on the topic 'Process parameters during AM'

Additive Manufacturing (AM) is an innovative manufacturing process which offers near-net shape fabrication of complex components, directly from CAD models, without dies or substantial machining, resulting in a reduction in lead-time, waste, and cost. For example, the buy-to-fly ratio for a titanium component machined from forged billet is typically 10-20:1 compared to 5-7:1 when manufactured by AM. However, the production rates for most AM processes are relatively slow and AM is consequently largely of interest to the aerospace, automotive and biomedical industries. In addition, the solidification conditions in AM with the Ti alloy commonly lead to undesirable coarse columnar primary β grain structures in components. The present research is focused on developing a fundamental understanding of the influence of the processing conditions on microstructure and texture evolution and their resulting effect on the mechanical properties during additive manufacturing with a Ti6Al4V alloy, using three different techniques, namely; 1) Selective laser melting (SLM) process, 2) Electron beam selective melting (EBSM) process and, 3) Wire arc additive manufacturing (WAAM) process. The most important finding in this work was that all the AM processes produced columnar β-grain structures which grow by epitaxial re-growth up through each melted layer. By thermal modelling using TS4D (Thermal Simulation in 4 Dimensions), it has been shown that the melt pool size increased and the cooling rate decreased from SLM to EBSM and to the WAAM process. The prior β grain size also increased with melt pool size from a finer size in the SLM to a moderate size in EBSM and to huge grains in WAAM that can be seen by eye. However, despite the large difference in power density between the processes, they all had similar G/R (thermal gradient/growth rate) ratios, which were predicted to lie in the columnar growth region in the solidification diagram. The EBSM process showed a pronounced local heterogeneity in the microstructure in local transition areas, when there was a change in geometry; for e.g. change in wall thickness, thin to thick capping section, cross-over’s, V-transitions, etc. By reconstruction of the high temperature β microstructure, it has been shown that all the AM platforms showed primary columnar β grains with a <001>β.

In this project we present a machine vision system to measure the geometrical parametersand dimensional defects of steel billets (blooms/slabs). Geometrical parameters includewidth, height and length and dimensional defects include camber, rhomboid difference andtorsion. The system has been equipped with a color camera, an industrial computer andother peripheral equipments such as lens, Ethernet Cat-5 cable and camera housing. Digitalimage processing techniques have been used to analyze the single view images. To do so,the image is enhanced first and then it is reregistered with a constant background. Afterthat the billet’s motion is calculated and the image is segmented. The billet boundary linesare then estimated using billets geometrical features. Then the Hough transform isfollowed by the canny edge detector to detect and link the exact sides of billets. Twocalibration methods have been used to transform the measured values in pixel to wordreference values in centimeter. These techniques result in removing the necessity of multicameras that have been used in the same projects by keeping the accuracy.
در اين پروژه سيستمي را براي اندازه گيري ابعاد هندسي و نقصهاي ابعادي شمشهاي فولادي ارائهميدهيم. براي اندارهگيري عرض، ارتفاع و طول شمش در كنار اندازهگيري خميدگي، لوزيشدگي وو IPC پيچش شمش از سيستم ماشين بينايي استفاده ميكنيم كه از يك دوربين رنگي ، كامپيوتر صنعتيساير تجهيزات جانبي مثل لنز ,كابل شبكه و محفظه دوربين تشكيل شده است. تصاوير يكنمايي برداشتهشده مورد آناليز قرار ميگيرند و با تكنيكهاي پردازش تصوير اضلاع شمش در آنها پيدا مي شوند. براياين منظور ابتدا كيفيت تصوير بهبود يافته وسپس نسبت به يك مرجع ثابتي ثبت ميشود سپس مقدارحركت شمش در بين دو تصوير متوالي محاسبه ميشود. در ادامه تصوير بخشبندي شده و اضلاعدر اطراف اين اضلاع تقريبي Canny تقريبي شمش از روي مشخصات كلي شمش پيدا مي شوند. روشبه كار گرفته ميشود تا لبه هاي شمش تشخيص داده شوند. براي حذف اثر نويز وگسستگي لبهها ازاستفاده ميشود تا محتملترين خطوط را در تصوير به عنوان اضلاع شمش در نظر بگيرد. Hough تبديلبراي تبديل ابعاد پيكسلي محاسبه شده به مقادير واقعي كه بر حسب سانتيمتر هستند از دو تكنيككاليبراسيون به طور همزمان استفاده ميشود تا ضمن حفظ دقت، نياز به دوربينهاي بيشتر كه در پروژهاي مشابه مورداستفاده قرار ميگيرند از بين برود.

An obstacle to the wide spread use of additive manufacturing (AM) is the difficulty in estimating the effects of process parameters on the mechanical properties of the manufactured part. The complex relationship between the geometry, parameters and mechanical properties makes it impractical to derive an analytical relationship and calls for the use of a numerical model. An approach to formulate a numerical model in developed in this thesis. The AM technique focused in this thesis is fused filament fabrication (FFF). A numerical model is developed by recreating FFF build process in a simulation environment. Machine instructions generated by a slicer to build a part is used to create a numerical model. The model acts as a basis to determine the effects of process parameters on the stiffness and the strength of a part. Determining the stiffness of the part is done by calculating the response of the model to a uniformly distributed load. The strength of the part depends on it's thermal history. The developed numerical model serves as a basis to implement models describing the relation between thermal history and strength. The developed model is suited to optimize FFF parameters as it encompass effects of all FFF parameters. A genetic algorithm is used to optimize the FFF parameters for minimum weight with a minimum stiffness constraint.
Ett hinder för att additiv tillverkning (AT), eller ”3D-printing”, ska få ett bredare genomslag är svårigheten att uppskatta effekterna av processparametrar på den tillverkade produktens mekaniska prestanda. Det komplexa förhållandet mellan geometri och processparametrar gör det opraktiskt och komplicerat att härleda analytiska uttryck för att förutsäga de mekaniska egenskaperna. Alternativet är att istället använda numeriska modeller. Huvudsyftet med denna avhandling har därför varit att utveckla en numerisk modell som kan användas för att förutsäga de mekaniska egenskaperna för detaljer tillverkade genom AT. AT-tekniken som avses är inriktad på Fused Filament Fabrication (FFF). En numerisk modell har utvecklats genom att återskapa FFF-byggprocessen i en simuleringsmiljö. Instruktioner (skriven i GCode) som används för att bygga en detalj genom FFF har här översatts till en numerisk FE-modell. Modellen används sen för att bestämma effekterna av processparametrar på styvheten och styrkan hos den tillverkade detaljen. I detta arbete har strukturstyvheten hos olika detaljer beräknats genom att utvärdera modellens svar för jämnt fördelade belastningsfall. Styrkan, vilket är starkt beroende på den tillverkade detaljens termiska historia, har inte utvärderats. Den utvecklade numeriska modellen kan dock fungera som underlag för implementering av modeller som beskriver relationen mellan termisk historia och styrka. Den utvecklade modellen är anpassad för optimering av FFF-parametrar då den omfattar effekterna av alla FFF-parametrar. En genetisk algoritm har använts i detta arbete för att optimera parametrarna med avseende på vikt för en given strukturstyvhet.

In the iron production processes, sinters and pellets are mostly used as raw materials due to their consistency with respect to physical and chemical properties. However, natural iron ores, as mined, are rarely used directly as a feed material for iron processing. This is mainly due to the fact that they have small contents of iron and high concentration of impurities. Moreover, they swell and disintegrate during the descent in the furnace as well as due to low melting and softening temperatures. This work involves an investigation of the parameters that influence the use of natural iron ores as a direct feed material for iron production. Furthermore, it points out ways in which these can be mitigated so as to increase their direct use in iron production. Natural iron ore from Muko deposits in south-western Uganda was used in this study. Initially, characterisation of the physical and chemical properties was performed, to understand the natural composition of the ore. In addition, investigations were done to study the low temperature strength of the ore and its behaviour in the direct reduction zone. Also, simulations were performed with three models using the experimental data from the direct reduction experiments in order to determine the best model for predicting the direct reduction kinetics of natural iron ores. Chemical analyses showed that the Muko ore represents a high grade of hematite with an Fe content of 68% on average. The gangue content (SiO2+Al2O3) in 5 of the 6 investigated iron ore samples was < 4%, which is within the tolerable limits for the dominant iron production processes. The S and P contents were 0001-0.006% and 0.02-0.05% respectively. These can be reduced in the furnace without presenting major processing difficulties. With respect to the mechanical properties, the Muko ore was found to have a Tumble Index value of 88-93 wt%, an Abrasion Index value of 0.5-3.8 wt% and a Shatter Index value of 0.6-2.0 wt%. Therefore, the ore holds its form during the handling and charging processes. Under low temperature investigations, new parameters were discovered that influence the low temperature strength of iron oxides. It was discovered that the positioning of the samples in the reduction furnace together with the original weight (W0) of the samples, have a big influence on the low temperature strength of iron oxide. Higher mechanical degradation (MD) values were obtained in the top furnace reaction zone samples (3-25% at 500oC and 10-21% at 600oC). These were the samples that had the first contact with the reducing gas, as it was flowing through the furnace from top to bottom. Then, the MD values decreased till 5-16% at a 500oC temperature and 6-20% at a 600oC temperature in the middle and bottom reaction zones samples. It was found that the obtained difference between the MD values in the top and other zones can be more than 2 times, particularly at 500oC temperature. Furthermore, the MD values for samples with W0 < 5 g varied from 7-21% well as they decreased to 5-10% on average for samples with W0 ≥ 5 g. Moreover, the MD values for samples taken from the top reaction zone were larger than those from the middle and bottom zones. During direct reduction of the ores in a H2 and CO gas mixture with a ratio of 1.5 and a constant temperature, the reduction degree (RD) increased with a decreased flow rate until an optimum value was established. The RD also increased when the flow rate was kept constant and the temperature increased. An optimum range of 3-4g was found for natural iron ores, within which the highest RD values that are realised for all reduction conditions. In addition, the mechanical stability is greatly enhanced at RD values > 0.7. In the case of microstructure, it was observed that the original microstructure of the samples had no significant impact on the final RD value (only 2-4%). However, it significantly influenced the reduction rate and time of the DR process. The thermo-gravimetric data obtained from the reduction experiments was used to calculate the solid conversion rate. Three models: the Grain Model (GM), the Volumetric Model (VM) and the Random Pore Model (RPM), were used to estimate the reduction kinetics of natural iron ores. The random pore model (RPM) provided the best agreement with the obtained experimental results (r2 = 0.993-0.998). Furthermore, it gave a better prediction of the natural iron oxide conversion and thereby the reduction kinetics. The RPM model was used for the estimation of the effect of original microstructure and porosity of iron ore lumps on the parameters of the reduction process.

QC 20130531

Sustainable Technology Development in the Lake Victoria Region

Three batches of milk were ultrafiltered to 60, 65, or 70% volume reduction before diafiltration. Starting diafiltration at 70% volume reduction took less time and water without affecting nutrient recovery. Whole milk was heated to 60, 72, and 82°C for 16 s. Milk representing each heat treatment was divided into three batches, one unacidified (pH 6.6), the others acidified to pH 6.2 and 5.8. The milk was ultrafiltered, diafiltered, and concentrated to 5x (80% volume reduction). Retentate was inoculated with .5% lactic culture and incubated at 28°C to pH 5.1. Each lot of fermented retentate was evaporated under 76 kPa vacuum until moisture was reduced to 35-38%, then made into pasteurized process cheese food by cooking to 82°C. The final product contained 43-44% moisture, 24-28% fat, 1.7% salt, and 2.5% sodium citrate. Fat and protein recovery were not affected by heat treatment or pH adjustment of the milk. Recovery of calcium, phosphorus, and riboflavin were significantly reduced following acidification of milk. Riboflavin recovery was higher when milk was preheated to 60°C as opposed to 72 or 82°C. Effect of cooking temperature on meltability of process cheese food was evaluated by repeating the above experiment at three cooking temperatures, 70, 76, or 81 °C. Cooking temperature significantly affected meltability. Cheese cooked to 70°C melted best for all treatments. At all cooking temperatures, cheese from unacidified milk (pH 6.6) had greater meltability than cheese from milk acidified to pH 5.8 or 6.2. Cooking temperature had a greater effect on meltability of process cheese food made from ultrafiltered retentate than calcium content. Preheating milk before ultrafiltration did not significantly affect meltability of pasteurized process cheese food. Meltability of pasteurized process cheese food was best when made from retentate heated (following ultrafiltration) to 61°C for 16 sand poorest when retentate was heated to 72 or 83°C. During ultrafiltration without diafiltration, amino acid analysis was on samples taken at 0, 20, 40, 60, and 80% volume reduction. There were no differences in amino acid composition (g/100 g protein) between milk and 5x retentate. Soluble nitrogen at pH 4.6 in pasteurized process cheese food was an approximate measure of undenatgred whey protein. As processing temperature increased from 66 to 82°C, undenatured whey protein decreased. Decrease in meltability due to increased processing temperature was related to denaturation of whey protein. Process cheese food made from blends of UF curd and Cheddar cheese had acceptable meltability with up to 66% UF curd when the final processing temperature was 68°C. Milk with high bacterial numbers (7.8 x 106 CFU/ml) was heated to 72°C for 16 s, acidified to pH 5.8 and ultrafiltered to a 5x concentration. Ultrafiltration proceeded normally and no processing difficulties were encountered.

La present tesi doctoral s’ha centrat en el repte d’aconseguir, mitjançant Fabricació Additiva (FA), models per a assaig quirúrgic, sota la premissa que els equips per fer-los haurien de ser accessibles a l’àmbit hospitalari. L’objectiu és facilitar l’extensió de l’ús dels prototips com a eina de preparació d’operacions quirúrgiques, transformant la pràctica mèdica actual de la mateixa manera que en el seu moment ho van fer tecnologies com les que van facilitar l’ús de radiografies. El motiu d’utilitzar FA, en lloc de tecnologies més tradicionals, és la seva capacitat de materialitzar de forma directa les dades digitals obtingudes de l’anatomia del pacient mitjançant sistemes d’escanejat tridimensional, fent possible l’obtenció de models personalitzats. Els resultats es centren en la generació de nou coneixement sobre com aconseguir equipaments d’impressió 3D multimaterials accessibles que permetin l’obtenció de models mimètics respecte als teixits vius. Per facilitar aquesta buscada extensió de la tecnologia, s’ha focalitzat en les tecnologies de codi obert com la Fabricació per Filament Fos (FFF) i similars basades en líquids catalitzables. La recerca s’alinea dins l’activitat de desenvolupament de la FA al CIM UPC, i en aquest àmbit concret amb la col·laboració amb l’Hospital Sant Joan de Déu de Barcelona (HSJD). El primer bloc de la tesi inclou la descripció de l’estat de l’art, detallant les tecnologies existents i la seva aplicació a l’entorn mèdic. S’han establert per primer cop unes bases de caracterització dels teixits vius -sobretot tous- per donar suport a la selecció de materials que els puguin mimetitzar en un procés de FA, a efectes de millorar l’experiència d’assaig dels cirurgians. El caràcter rígid dels materials majoritàriament usats en impressió 3D els fa poc útils per simular tumors i altres referències anatòmiques. De forma successiva, es tracten paràmetres com la densitat, la viscoelasticitat, la caracterització dels materials tous a la indústria, l’estudi del mòdul elàstic de teixits tous i vasos, la duresa d’aquests, i requeriments com l’esterilització dels models. El segon bloc comença explorant la impressió 3D mitjançant FFF. Es classifiquen les variants del procés des del punt de vista de la multimaterialitat, essencial per fer models d’assaig quirúrgic, diferenciant entre solucions multibroquet i de barreja al capçal. S’ha inclòs l’estudi de materials (filaments i líquids) que serien més útils per mimetitzar teixits tous. Es constata com en els líquids, en comparació amb els filaments, la complexitat del treball en processos de FA és més elevada, i es determinen formes d’imprimir materials molt tous. Per acabar, s’exposen sis casos reals de col·laboració amb l’HJSD, una selecció d’aquells en els que el doctorand ha intervingut en els darrers anys. L’origen es troba en la dificultat de l’abordatge d’operacions de resecció de tumors infantils com el neuroblastoma, i a la iniciativa del Dr. Lucas Krauel. Finalment, el Bloc 3 té per objecte explorar nombrosos conceptes (fins a 8), activitat completada al llarg dels darrers cinc anys amb el suport dels mitjans del CIM UPC i de l’activitat associada a treballs finals d’estudis d’estudiants de la UPC, arribant-se a materialitzar equipaments experimentals per validar-los. La recerca ampla i sistemàtica al respecte fa que s’estigui més a prop de disposar d’una solució d’impressió 3D multimaterial de sobretaula. Es determina que la millor via de progrés és la de disposar d’una pluralitat de capçals independents a fi de capacitar la impressora 3D per integrar diversos conceptes estudiats, materialitzant-se una possible solució. Cloent la tesi, es planteja com seria un equipament d’impressió 3D per a models d’assaig quirúrgic, a fi de servir de base per a futurs desenvolupaments.
La presente tesis doctoral se ha centrado en el reto de conseguir, mediante Fabricación Aditiva (FA), modelos para ensayo quirúrgico, bajo la premisa que los equipos para obtenerlos tendrían que ser accesibles al ámbito hospitalario. El objetivo es facilitar la extensión del uso de modelos como herramienta de preparación de operaciones quirúrgicas, transformando la práctica médica actual de la misma manera que, en su momento, lo hicieron tecnologías como las que facilitaron el uso de radiografías. El motivo de utilizar FA, en lugar de tecnologías más tradicionales, es su capacidad de materializar de forma directa los datos digitales obtenidos de la anatomía del paciente mediante sistemas de escaneado tridimensional, haciendo posible la obtención de modelos personalizados. Los resultados se centran en la generación de nuevo conocimiento para conseguir equipamientos de impresión 3D multimateriales accesibles que permitan la obtención de modelos miméticos respecto a los tejidos vivos. Para facilitar la buscada extensión de la tecnología, se ha focalizado en las tecnologías de código abierto como la Fabricación por Hilo Fundido (FFF) y similares basadas en líquidos catalizables. Esta investigación se alinea dentro de la actividad de desarrollo de la FA en el CIM UPC, y en este ámbito concreto con la colaboración con el Hospital Sant Joan de Déu de Barcelona (HSJD). El primer bloque de la tesis incluye la descripción del estado del arte, detallando las tecnologías existentes y su aplicación al entorno médico. Se han establecido por primera vez unas bases de caracterización de los tejidos vivos – principalmente blandos – para dar apoyo a la selección de materiales que los puedan mimetizar en un proceso de FA, a efectos de mejorar la experiencia de ensayo de los cirujanos. El carácter rígido de los materiales mayoritariamente usados en impresión 3D los hace poco útiles para simular tumores y otras referencias anatómicas. De forma sucesiva, se tratan parámetros como la densidad, la viscoelasticidad, la caracterización de materiales blandos en la industria, el estudio del módulo elástico de tejidos blandos y vasos, la dureza de los mismos, y requerimientos como la esterilización de los modelos. El segundo bloque empieza explorando la impresión 3D mediante FFF. Se clasifican las variantes del proceso desde el punto de vista de la multimaterialidad, esencial para hacer modelos de ensayo quirúrgico, diferenciando entre soluciones multiboquilla y de mezcla en el cabezal. Se ha incluido el estudio de materiales (filamentos y líquidos) que serían más útiles para mimetizar tejidos blandos. Se constata como en los líquidos, en comparación con los filamentos, la complejidad del trabajo en procesos de FA es más elevada, y se determinan formas de imprimir materiales muy blandos. Para acabar, se exponen seis casos reales de colaboración con el HJSD, una selección de aquellos en los que el doctorando ha intervenido en los últimos años. El origen se encuentra en la dificultad del abordaje de operaciones de resección de tumores infantiles como el neuroblastoma, y en la iniciativa del Dr. Lucas Krauel. Finalmente, el Bloque 3 desarrolla numerosos conceptos (hasta 8), actividad completada a lo largo de los últimos cinco años con el apoyo de los medios del CIM UPC y de la actividad asociada a trabajos finales de estudios de estudiantes de la UPC, llegándose a materializar equipamientos experimentales para validarlos. La investigación amplia y sistemática al respecto hace que se esté más cerca de disponer de una solución de impresión 3D multimaterial de sobremesa. Se determina que la mejor vía de progreso es la de disponer de una pluralidad de cabezales independientes, a fin de capacitar la impresora 3D para integrar diversos conceptos estudiados, materializándose una posible solución. Para cerrar la tesis, se plantea cómo sería un equipamiento de impresión 3D para modelos de ensayo quirúrgico, a fin de servir de base para futuros desarrollos.

碩士
國立高雄第一科技大學
機械與自動化工程研究所
103
With a seriously increasing deficiency in energy sources and a growing interest in environmental protection, a trend in the development of renewable sources of energy, energy saving, and resource recovery has been spreading worldwide, which can consequently slow down the consumption of energy resources. The development of high-frequency induction heating as a strategy to manufacture foaming aluminum is studied. This experiment used a low-carbon steel SS400 as a mold and used CNC machine table as a vehicle. In this study, the control factors selected geometries and layouts, pre-heating time, induction pre-heating coil current, induction heating coil current, workpiece speed, heating pause time, cooling gas and cooling gas speed. then application Taguchi principal component analysis for cell size, porosity, unifority and compressive strength of porous aluminum alloy, inferences high frequency induction heating process, and development of multi-objective optimization foaming parameter combinations, in order to enhance various properties significantly. In brief, the current study draws the following conclusions: (1) Foaming direction and binding sites have a very important impact on the pore characteristics. (2) Induction pre-heating coil current is control of heating rate; the results show that the slower heating rate of foaming effect is better, but too slow will result in incomplete foaming effect. Pre-heating time is control foaming stage; the results show that the longer pre-heating time is combined with holes faster. (3) Workpiece speed is control of the moving speed of heating area; the results show that the faster speed of foaming effect is better, but too slow will result in incomplete foaming effect. Induction heating coil current is control of the temperature field of heating area; the results show that the greater current of foaming effect is poor, but the foaming speed can be increased. Heating pause time is control of the foaming characteristics, the results show that the longer heating pause time of foaming effect is better, but too long will result in incomplete foaming effect. Cooling gas speed is control aluminum foam for solidified; the results show that the greater cooling gas speed of foaming effect is better. Cooling gas is control aluminum foam for solidified; the results show that the faster cooling speed of He, Ar and foaming effect is better. (4) In L18 experiment, L7 is the best test piece; the results show that the average cell size of 2.47mm, uniformity of 0.52 (5) The optimized parameter combination in the production process of high frequency induction heating with foaming aluminum is as follows: geometries and layouts of A1, induction heating coil current of 240 A, induction pre-heating coil current of 200 A, heating pause time of 0 s/50mm, pre-heating time of 300s, workpiece speed of 80 mm/min, cooling gas of He, and cooling gas speed of 20 L/min. (6) The results of the variance analysis show that the most important controlling factors that influence the production process of high frequency induction heating with foaming aluminum inside include induction pre-heating coil current, pre-heating time, and geometries and layouts, with a total contribution rate of 59.68%.

碩士
國立虎尾科技大學
動力機械工程研究所
94
Abstract Due to the light weight and magnetic ray insulation characteristics in magnesium alloy material, it is widely utilized in 3C electronic components and automobile parts. However, its formability is very poor due to the phenomenon of negative rate strain hardening appeared as the deformation in large strain range, so it is usually formed as die casting or casting manner, leads to much scrap and the manufacturing cost is thus increased. The purpose of this study is to construct a series of process parameters for magnesium alloy tube components during hydro-forming and may offer the data resulting from theanalysis as a guideline for magnesium alloy forming in industry. AZ31 magnesium alloy tube is used as the billet for hydro-forming with hydraulic pressure as the main forming power combining with the mechanical auxiliary force to fabricate the tubing products. Finite element software DEFORM-2D/3D is adopted to investigate the forming situations for some in common use fitting tubes, which include T type fitting, rectangle tube, tube bulge forming and irregular tube forming etc.. By changing process parameter, such as punch speed, hydraulic pressure, die-workpiece interface friction and die geometry shape etc. to investigate the material flow of tube fitting, wall thickness variations, and stress and strain distributions. By qualifying the smallest wall thickness of tube fitting requirement and forming sequences completed or not, analysis synthesis and overall judgment to establish an admissible level of process parameter range for complete tube manufacture, or getting optimal process conditions. The results show that suitable mechanical force can help material flow, avoid large strain deformation falling into the area of negative rate strain hardening and enhance magnesium alloy become easy forming, make tube fitting may be formed successfully.

博士
國立臺灣科技大學
機械工程系
103
Recently, severe material flow is caused to obtain successful joints by an innovative joining process, called friction stir spot welding (FSSW). Because of its thermomechanical characteristic, the interaction between process parameters and tool geometry makes the process complicated and leads to temperature and pressure difference in welds, resulting in variation of material flow and joint strength of welds. In this study, aluminum alloy sheets were joined by the FSSW process using various threaded tools. The influences of tool geometry and process parameters on material flow evolution, welding force, work, power, weld temperature and joint strength during FSSW were analyzed. In addition, numerical simulation of weld temperature was also discussed. The results indicated that rotational speed and dwell time increase process work and weld temperature, lowering weld torque and material flow resistance. Additionally, threaded locations had little effect on weld temperature in local regions. The highest temperature was shown in the upper sheet region, which was nearest to the shoulder. During tool plunging, the lower sheet penetrated into the upper sheet. A sheet interface and rotational speed was beneficial for promoting the penetration behavior. In a dwell period, sink and source of material were formed at the ends of threads. Material flowed into threaded sections via material sink, following moving forward to material source to form a stir zone (SZ). The growth of SZ squeezed the sheet interface, resulting in the variations of weld morphology and joint strength. The reduction in upper sheet thickness was suppressed in the T-tool welds, thus exhibiting superior joint strength. In addition, the welds joined by tools with 900 rpm, 9 s and counterclockwise rotation showed superior joint strength.

碩士
國立聯合大學
材料科學工程學系碩士班
104
SiC, with low thermal expansion, high thermal conductivity and hardness, well chemical resistance and high temperature oxidation resistance, has been used for the substrate protection under high temperature such as LED epitaxy, graphite heat sink, carbonic mold, etc. In generally, SiC film has been produced by chemical vapor deposition (CVD). The deposition rate of SiC film is strongly affected by temperature, pressure, gas flow rate, and intermediates adsorption on the substrate surface. The coating uniformity is relative to the difference of deposition rate each site on substrate. In order to achieve the better double-side deposition rate and uniformity, the numerical simulation model based on thermal flux was constructed by Fluent software in this study. The transport equations for fluid dynamics, heat transfer and mass transfer are simultaneously solved by employing the finite element method. The effects of process parameters and substrate arrangements on deposition were studied. From the simulation results, increasing reactor heating temperature could get not only the excellent deposition rate but also the great uniformity of SiC film. The higher operating pressure would obtain the rapid deposition rate, but the uniformity became worse. The larger species flow rate diminished the deposition rate, and the uniformity shown the opposite tendency on double-side of substrate. However, the film uniformity of entire substrate still increased with the gas flow rate. Although increasing the incline angle of substrate could not achieve the same tendency of deposition rate each single-side on substrate, the uniformity of deposition could be increased on whole substrate. Even though the deposition rate and uniformity might be reduced by adding substrate numbers, the higher productivity and low cost should be obtained in multi-substrate design and could benefit industrial work. From the above, the best deposition rate and uniformity could achieve where the reactor heating temperature is 1800 K, the operating pressure is 10 kPa, the SiCl4, CH4 and H2 flow rate are 1.2, 1.2 and 10 slm and the reactor arrangement is vertical single substrate design.

碩士
國立成功大學
材料科學(工程)學系
86
Chemical-mechanical polishing (CMP) for the planarization of multilevel interconnection has become an emerging key technology in IC manufacturing. For the most widely used aluminum conductors, however, researches on the mechanism during CMP is still limited. The lack of information in the literature regarding the mechanism of Al CMP may be due to the soft nature of Al and the complicated electrochemistry of Al in slurry, besides the secret involved in the new technology. In this study, the effect of different condition in Al CMP process were explored using electrochemical technique. First, the study is basis on chemical reaction, the effect of pH and H2O2 on the electrochemical behaviors and chemical dissolution rate at static state and under grinding condition. Second,the study is basis on mechanical grinding, the effect of polishing pressure and platen speed on the electrochemical behaviors and removal rate.The experimental results showed that, Al exhibits a stable passivation behavior in the slurry investigated at stress free condition. Both the corrosion potential and current density increase by reducing slurry pH or by adding H2O2. Under polishing condition, however, passivation behavior can no longer exist. The removal rate decrease a little by increasing pH, but a increase in the dissolution current density is observed. Wherever the electrochemical results also show that eith platen speed or polishing pressure has no effect on the feature of potentiodynamic polarization curve under polishing condition, demonstrating the negligible effect of mechanical factor on the electrochemical reaction. Furthermore, the results clearly show that Preston''s equation is not obeyed as far as removal rate is considered. But the removal rate still increase by increasing polishing pressure and platen speed.The XPS analyses reveal that the formations of Al2O3 and AlPO4 are prevailed when the slurry pH is increased, which is in good agreement with the potentiodynamic polarization measurement.

碩士
中原大學
機械工程研究所
95
Micro electroforming technology of the LIGA process is very important and has a great effect on the replication of micro-structure. In this study, the effects of processing and adding Ni semi-bright during electroforming process on disc stamp quality were been investigated. From the result of study, the stamp of electroforming with Ni semi-bright has bigger hardness. The hardness of stamp has increased 76.58% and reaches the maximum when solution temperature, current density and Ni semi-bright are 60℃, 13.5ASD and 15ml, respectively. The improving of hardness is Ni deposit transition form pillar to layer forms that can be observed the cross section via a metallographic. For the hardness and surface roughness of the stamp, the higher hardness and lower surface roughness need high solution temperature, low current density and adding Ni semi-bright. The higher solution temperature, higher current density and adding Ni semi-bright will get thicker and not uniform stamp. Form this study, it will lead to a better understanding on the electroforming characteristics. We can choose and adjust the parameters to get suitable and economic efficiency way during electroforming process.

碩士
中原大學
機械工程研究所
95
This study is focusing on the process influence when making the blu-ray disc stamp. Including the micro-structure and roughness of the blu-ray disc stamp are the key issues of the stamp quality. The experiment parameters have developing time, sputtering time, electroforming current and the ion aching time. The contribution of each parameter to the micro-structure and roughness has been discussed and investigated. The experiment steps have: 1. expose the photoresist by the excimer laser mechine. 2.use ion aching the photoresist to develop the micro structure. 3.sputter the conductive layer. 4.dipping in electroforming machine. The results show that the developing and aching process have great effect on the micro-structure and roughness. The sputter time and the electroforming also have relatively effect on the roughness of the stamp. As analyzing the micro-structure and roughness of the stamp by the atomic force micrometer, the result indicated that the developing aching process have key effect on the groove width and groove angle. But all the processes have the effect on the roughness. We find that the optimal blu-ray disc stamp making process could be as following: the developing time set to 20 seconds, the sputtering time set to 450 seconds, the current of electroforming process set to 50 ampere , and the ion aching time set to 80 seconds.

Purdue School of Engineering and Technology, Indianapolis
Powder Bed Fusion Additive Manufacturing enables the fabrication of metal parts with complex geometry and elaborates internal features, the simplification of the assembly process, and the reduction of development time. However, the lack of consistent quality hinders its tremendous potential for widespread application in industry. This limits its ability as a viable manufacturing process particularly in the aerospace and medical industries where high quality and repeatability are critical. A variety of defects, which may be initiated during the powder-bed fusion additive manufacturing process, compromise the repeatability, precision, and resulting mechanical properties of the final part. The literature review shows that a non-uniform temperature distribution throughout fabricated layers is a significant source of the majority of thermal defects. Therefore, the work introduces an online thermography methodology to study temperature distribution, thermal evolution, and thermal specifications of the fabricated layers in powder-bed fusion process or any other thermal inherent AM process. This methodology utilizes infrared technique and segmentation image processing to extract the required data about temperature distribution and HAZs of the layer under fabrication. We conducted some primary experiments in the FDM process to leverage the thermography technique and achieve a certain insight to be able to propose a technique to generate a more uniform temperature distribution. These experiments lead to proposing an innovative chessboard scanning strategy called tessellation algorithm, which can generate more uniform temperature distribution and diminish the layer warpage consequently especially throughout the layers with either geometry that is more complex or poses relatively longer dimensions. In the next step, this work develops a new technique in ABAQUS to verify the proposed scanning strategy. This technique simulates temperature distribution throughout a layer printed by chessboard printing patterns in powder-bed fusion process in a fraction of the time taken by current methods in the literature. This technique compares the temperature distribution throughout a designed layer printed by three presented chessboard-scanning patterns, namely, rastering pattern, helical pattern, and tessellation pattern. The results confirm that the tessellation pattern generates more uniform temperature distribution compared with the other two patterns. Further research is in progress to leverage the thermography methodology to verify the simulation technique. It is also pursuing a hybrid closed-loop online monitoring and control methodology, which bases on the introduced tessellation algorithm and online thermography in this work and Artificial Neural Networking (ANN) to generate the most possible uniform temperature distribution within a safe temperature range layer-by-layer.