Thesis (M.S.)--University of Michigan, 1966.

[ES] La tesis doctoral presenta y analiza la técnica de la cáscara cerámica, desde la creación del modelo en cera hasta la elaboración completa del molde de fundición específico de esta técnica. Se aportan referencias originales históricas y técnicas. Se realizan pruebas de porosidad y resistencia en función de los refractarios empleados y el número de capas, con conclusiones aclaratorias en cada capítulo. / [EN] This doctoral dissertation explains and analyzes the ceramic shell technique as a whole, starting from the creation of the wax model until the elaboration of the casting mold specific for this technique is finished. Original historical and technical references are provided. Different porosity and resistance tests are carried out depending on the refractory materials used and the number of layers. Clarifying conclusions are included in each chapter. / A Mr. David Reid, maestro de la técnica de la cáscara cerámica adaptada al taller de los escultores. Al Dr. Juan Carlos Albaladejo, director de la tesis doctoral, generoso maestro difusor de la técnica en las universidades españolas. Al Departamento de Ingeniería de los materiales (D. José Monzó y D. Pascual Hernández); al Dpto. de Pintura (Dr. Domingo Oliver y D. Manuel Guillén); al Institut de Ciències del Materials de la UV (Dra. Carmen Guillém); al IDM de la UPV (Dr. Ramón Martínez Mañez, Dr. Juan Soto y Dra. Mª Dolores Marcos); y al Departamento de Escultura (Paco P. Benavent y Dr. Pablo Sedeño) A Toni Tomás, Beatriz Piñero, Ángeles Afonso, Soledad del Pino, Mª Mar Caballero, familia Crespo Ricart y a Marian Alonso. / Marcos Martínez, MDC. (2001). Fundición a la cera perdida: Técnica de la Cascarilla Cerámica [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/157239 / TESIS

For over 30 years research has been done concerning the solidification and quenching of light metal alloys for the purpose of improving material properties. This thesis is concerned with an interesting new process for casting metals, by spraying water onto a sand mould, removing the sand and the directly quenching the part. This process is challenging since the component during solidification is extremely fragile, and the rate of cooling that is needed could seriously damage it. The water flow rate to the component needs to be quickly and precisely controlled. Additionally as this a new method there is very little prior art. The purpose of this thesis to develop a control system for the water sprayers flow rates. With this system the flow rate through the nozzles will be controlled indirectly using pressure feedback. The material properties and casting process, and how they influenced the design and construction of the spraying apparatus, are explained first. The hydraulic plant being controlled consists of three proportional valves connected to six spray nozzles. Based on experiments, the plant is extremely nonlinear making it difficult to control. Several controllers were developed and compared experimentally. The best performance was produced by extending a proportional plus integral plus derivative controller by adding an empirical nonlinear feedforward component; smoothing the setpoint; bounding the integration term; adding one bias at time zero and a 2nd bias for the remaining time (to mitigate valve stiction and to prime the hoses). This extended PID controller produced a 0.7% mean error and 1.9% mean absolute error for a multi-step setpoint covering a range of 0 to 80 PSI. Its performance was also highly repeatable. The standard deviations of the mean error, mean absolute error and maximum absolute error were less than 0.2 PSI over five runs. / Thesis / Master of Applied Science (MASc) / During the sand casting of aluminium and magnesium rapid cooling will greatly improve the material properties. By containing the liquid metal in a water soluble sand mould, and spraying it with water; the desired part shape and rapid cooling can be achieved. Removing the mould requires a powerful high flow rate jet. During the solidification of the metal, the flow rate must be reduced or the part would be demolished. This necessitated the development of a high speed, high flow rate controller to adjust the flow rate to remove the sand but not damage the part, and to maintain a smooth continuous cooling rate. The hydraulic system being controlled consists of three electronic valves connected to six spray nozzles. Several controllers are developed and compared experimentally. The best controller is shown to provide a quick and precise response.

The primary focus of the present work is to model the entire casting process from filling stage to complete solidification. The model takes into consideration any phase change taking place during the filling process. An implicit volume of fluid (VOF) based algorithm has been employed for simulating free surface flows during the filling process and the model for solidification is based on a fixed-grid enthalpy-based control volume approach. Solidification modelling is coupled with VOF through User Defined Functions (UDF) developed in commercial fluid dynamics (CFD) code FLUENT 6.3.26. The developed model is applied for the simultaneous filling and solidification of pure metals and binary alloy systems to study the effects of filling process on the solidification characteristics, evolution of mushy zone and the final macrosegregation pattern in the casting. The numerical results of the present analysis are compared with the conventional analysis assuming the initial conditions to be a completely filled mould cavity with uniform temperature, solute concentration and quiescent melt inside the cavity. The effects of process parameters, namely the degree of superheat, cooling temperature and filling velocity etc. are also investigated. Results show significant differences on the evolution of mushy zone and macrosegregation between the present analysis and the conventional analysis. The application of present model to simulate three dimensional sand casting is also demonstrated. The three dimensional competetive effect of filling generated residual flow and the buoyancy-induced convective flow pattern cause significant difference in macrosegregation pattern in casting.

Thesis (MScEng (Industrial Engineering))--University of Stellenbosch, 2008. / This thesis forms part of the AMTS Project on Investment Casting Capabilities for Light Metal Alloys in South Africa, the focus area being Rapid Tooling Development. Various issues of the investment casting process are being discussed from an industrial engineering point of view. These issues are related to the possibilities of improving the investment casting process’ lead times by shortening it while still maintaining affordable costs and required quality. Hereby the possibilities given by the newly developed “rapid technologies” are investigated. The focus is on Rapid Pattern Making as one of the most essential components for accelerated development of new products. Three of the most widely used layer manufacturing processes available in South Africa are selected for the study, namely Three Dimensional Printing – Drop-on-Bed (ZCorporation), Selective Laser Sintering (EOS) and Three Dimensional Printing – Drop-on-Drop (ThermoJet - 3D Systems). These three methods represent different materials; therefore different mechanical properties, different process economics as well as different technological characteristics. A standard benchmark part is used as a study base. Four patterns are produced by these three methods. A comprehensive measurement programme is conducted, followed by an appropriate statistical analysis and evaluation regarding accuracy and surface finish. Rapid Die Making is analysed with the possibilities of using additive methods for rapid tooling. Two dies are built with the same technology – Selective Laser Sintering (EOS), but in different materials. The same evaluation methodology is used for the statistical analysis and comparison. The two dies are injected with wax in order to produce the original benchmark part. The best wax patterns from each die are selected and evaluated, using the same methodology for analysis and comparison. The current state of Direct Shell Production is shortly discussed. The research concludes that RP&T techniques can successfully be used for creating accurate patterns and dies in order to shorten lead times in the investment casting process chain. Each RP&T process has its own set of advantages and disadvantages. All users should evaluate their requirements and the capabilities of the variety of techniques before deciding on a process to apply.

Published Article / This article looks at the role that vacuum casting plays in the rapid prototyping and rapid manufacturing process. The accuracy to which components can be reproduced, by looking at the controllable factors in the casting process and the different types of materials that are available, were investigated and the process was also compared to other rapid prototyping and manufacturing processes in terms of cost effectiveness. Castings were made from a typical component under different operating conditions and the characteristics of the cast component, dimensions strength and surface hardness, were measured and plotted to determine the characteristics and accuracy of the process.

Published Article / Spin casting is widely used as a batch manufacturing process for decorative products. In the process, moulds are filled by taking advantage of the centrifugal effect, which is used to increase the pressure within the moulds, resulting in more detailed products. In this study, we analyse the different parameters that could affect the casting of mechanical parts through spin casting. Through this study, the user will be guided in the selection of parameters that will result in a certain degree of accuracy. The parameters were determined by performing numerous experiments using zinc alloy and tin-based pewter as casting materials. Results were obtained by casting approximately 15 000 parts in various positions, and at various clamping pressures, rotational speeds and temperatures in both the mould and the material. The experiments were undertaken by varying one parameter at a time, and with each set parameter repeated once, resulting in 100 test pieces per parameter for evaluation. From the results obtained, a series of critical factors and parameters, which are driven by part characteristics or features, has been studied. Contrary to following a modelling approach, the research was conducted following an action-research approach, with planned activities, but where actual results have defined the follow-up procedures. These guidelines will help industrial users ensure the accuracy of parts produced by spin casting. Also, since this project attempted to create a database of results that can be applied in future, it furthermore implies that the data created for the first time can be used in a numerical modelling approach in further / follow-up research. No such data was available from any previous research.

Two direct consolidation methods usually used for advanced ceramics have been combined in this project in order to develop a novel fabrication route for traditional ceramics. Specifically the method used is based on the Additive Manufacturing extrusion process using direct writing of high solid loading ceramic pastes and then freeze-casting to solidify the deposited material. This novel fabrication method, for which a patent has been granted, has been christened “Direct Writing Freeze-Casting” (DWFC). Although the DWFC process is the subject of investigation by other researchers for a range of different applications, including the production of medical implants with alumina, the research presented in this thesis focuses on its use in the manufacture of white wares, giftware, and applied arts and crafts in general. This new system will provide designers, potters, artists, craft makers and manufacturers with a flexible and automated way of manufacturing porcelain objects. One of the major challenges to be overcome to exploit the DWFC process is the development of suitable slurry material formulations. Initial trials demonstrated that it is not possible to use conventional clay based porcelain materials with a platelet shaped microstructure which inhibits freeze casting. In this thesis the development and characterisation of non plastic porcelain slurry, based on substitution of kaolin (clay) with a calcined clay material (molochite), which can be processed using this new method is presented. The new non plastic porcelain formulation, which has a high solid load of 75.47% wt., has been subjected to detailed analysis to assess its suitability at each stage of the process; extrusion, freeze-casting (solidification) and firing.

No description available.

Solidification during horizontal continuous casting of low carbon steel billets with cyclic withdrawal was simulated and the wavy profile of the solidifying shell characteristic of this process was reproduced. Effects of rate of withdrawal cycle, superheat and casting speed were determined. In order to carry out this simulation in a personal computer, efficient numerical techniques had to be developed for mesh refinement by coordinate transformation, interfaces with temperature discontinuities and re-entrant corners. A flexible means of mesh generation involving polynomials was also developed. From the transient heat transfer model finite difference equations peculiar to each gridpoint in the solution field were derived and solved by the Alternating Direction Implicit (ADI) method. Graphics software were developed to view the results with 3-D as well as contour plots. The heat transfer model was verified with published results of vertical continuous casting of Mg alloys and steel. Due to its ability to deal with interfaces, unlike previous work, the present model could solve temperature at both casting and mold simultaneously. A model for the shell growth, rupture and healing at the break-ring of horizontal continuous casting molds was incorporated into the heat transfer model. An interesting result of this simulation was the presence of transient hot spots in the hot face of the mold. Elimination of such hot spots should aid shell strength and hence the casting rate. A semi-quantitative dependence of the depth of the primary witness mark on cycle rate was also established.