Thesis (M.S.)--University of Michigan, Ann Arbor, 1976. / Typescript (photocopy). Includes bibliographical references (leaves 69-71). Also issued in print.

Thesis (M.S.)--University of Michigan, Ann Arbor, 1976. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 69-71).

Thesis (M.S.)--University of Michigan, Ann Arbor, 1982. / Typescript (photocopy). eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 41-43).

Thesis (M.App.Sc.) - Carleton University, 2007. / Includes bibliographical references (p. 101-105). Also available in electronic format on the Internet.

Thesis (M.Eng.)(Mechanical)--University of Pretoria, 2005. / Title form opening screen (viewed March 20 2006). Summaries in English and Afrikaans. Includes bibliographical references.

abstract: When manufacturing large or complex parts, often a rough operation such as casting is used to create the majority of the part geometry. Due to the highly variable nature of the casting process, for mechanical components that require precision surfaces for functionality or assembly with others, some of the important features are machined to specification. Depending on the relative locations of as-cast to-be-machined features and the amount of material at each, the part may be positioned or ‘set up’ on a fixture in a configuration that will ensure that the pre-specified machining operations will successfully clean up the rough surfaces and produce a part that conforms to any assigned tolerances. For a particular part whose features incur excessive deviation in the casting process, it may be that no setup would yield an acceptable final part. The proposed Setup-Map (S-Map) describes the positions and orientations of a part that will allow for it to be successfully machined, and will be able to determine if a particular part cannot be made to specification. The Setup Map is a point space in six dimensions where each of the six orthogonal coordinates corresponds to one of the rigid-body displacements in three dimensional space: three rotations and three translations. Any point within the boundaries of the Setup-Map (S-Map) corresponds to a small displacement of the part that satisfies the condition that each feature will lie within its associated tolerance zone after machining. The process for creating the S-Map involves the representation of constraints imposed by the tolerances in simple coordinate systems for each to-be-machined feature. Constraints are then transformed to a single coordinate system where the intersection reveals the common allowable ‘setup’ points. Should an intersection of the six-dimensional constraints exist, an optimization scheme is used to choose a single setup that gives the best chance for machining to be completed successfully. Should no intersection exist, the particular part cannot be machined to specification or must be re-worked with weld metal added to specific locations. / Dissertation/Thesis / Masters Thesis Engineering 2016

No description available.

Engineering applications of the recently developed zinc-aluminium casting alloys have been restricted due to certain inherent disadvantages such as segregation. However, segregation can be overcome by thorough mh:!ng of the melt and close temperature control or by rapid solidification of the melt, which can be achieved by squeeze casting. A more serious problem exists in service if components are subjected to a modest temperature increase to about 80°C, when there is a drastic loss of strength. It was therefore thought that the incorporation of ceramic fibres in the matrix could improve the properties of the material at modestly elevated temperatures. In the majority of engineering applications, stresses exist in more than one direction, so castings with isotropic properties are preferred and consequently reinforcement of composite in three dimensions would be necessary to maintain isotropic properties. An investigation was conducted to establish the influence of squeeze casting on the mechanical properties and structure of ZA-8, ZA-12 and ZA-27 alloys. The relationship between these factors and controlled process variables such as die temperature and applied squeeze pressure was established. The mechanical properties of the castings at room temperature and the effect of ageing at 95°C on tensile strength and dimensional changes were established. The results showed a substantial improvement in the tensile strength of the 'as-cast' squeeze cast alloys when compared with the 'as-cast' gravity die cast alloys. In the case of ZA-27 alloy, squeeze casting significantly improved ductility, which is a feature of benefit for all composite systems. The results also showed that pressure and die temperature substantially affect dimensional changes of the alloys when aged at 95°C. A major aspect of the research was the evaluation of the mechanical properties of the fibre reinforced ZA-27 alloy at elevated temperatures. Short silicon carbide fibres were randomly oriented in the matrix to obtain isotropic properties by a technique involving squeeze infiltration, followed by remelting and dispersal in the melt using specially designed equipments. Squeeze casting was used in the final stage of the composite fabrication. Castings of squeeze cast composite (with up to 10% volume fibre) and squeeze infiltrated composite (with up to 18-20% volume fibre) were produced with a sound structure and with fibres that were uniformly distributed and randomly oriented in three dimensions. It was found that the reaction between the fibres and molten alloy must be closely controlled for optimum properties of the composite. In this respect, the optimum time of contact between the fibre and the molten alloy was experimentally determined. It was found that the fibre supplied was of inferior tensile strength, which resulted in poor tensile strength of the tested composite up to a temperature of 100°C. However, the fibre brought substantial Improvement ln the tensile strength of the composite when tested at temperatures of 150 to 250°C. The modulus of elasticity of the composite was substantially improved at room temperature as well as at elevated temperature. The fatigue life of the squeeze cast composite was improved compared with squeeze cast matrix alloy (fibre-free). Squeeze cast composites with 3% volume fibre showed an Improvement in tribological properties compared with squeeze cast matrix alloy and squeeze cast and squeeze infiltrated composites with higher volume percentage of fibre. Wear of cutting tools was adversely affected by the presence of fibre.

In the continuous casting of steels, clogging of the submerged entry nozzle has long been a persistent and costly issue. Previous modelling attempts have assumed that inclusions of different types exhibit the same degree of adhesion when colliding with the nozzle wall - an assumption not borne out by evidence in the literature. In this thesis, a dynamic clogging model is proposed which accounts for the effects of different degrees of inclusion-wall and inclusion-clog adhesion on clog formation and growth. The overall clogging model consists of several sub-models in order to account for the different physics. The melt flow and inclusion motion are modelled using an Eulerian-Lagrangian approach. The inclusion adhesion behavior is determined by the use of a stochastic model activated when an inclusion collides with a surface. A user defined sticking probability is used to determine if an inclusion sticks to a surface (Swall for wall collision or Sclog for clog collision) or instead bounces off. A macroscopic model is used to determine clog growth, where the volume of clog in a cell is tracked and used to determine when the clog grows into adjacent cells. Finally, a modified Kozeny-Carmen equation is used as a porosity model so that the presence of the clog affects and diverts the melt flow. The modified melt flow then alters subsequent inclusion deposition and clog growth. The model is used to investigate the effects of different degrees of inclusion adhesion on inclusion deposition and clog growth. Three scenarios are examined - 1) Inclusion deposition in a pilot scale nozzle, 2) Inclusion deposition in an industrial scale slide-gate controlled nozzle and 3) Clog formation and growth in a pilot scale nozzle. The deposition studies indicate that in a pilot scale nozzle, only a minority of inclusions ever collide with the nozzle (≈ 10%). In contrast, in the industrial scale nozzle there are far more inclusion collisions with the nozzle wall, ranging from 80% when the slide-gate is 20% open to 30% when the slide-gate is 100% open. Despite the differences in nozzle geometry and flow conditions, a similar effect on inclusion deposition is seen when Swall is varied. The effects of Swall can be divided into two regimes. When 0 ≥ Swall < 0.05 there is a sharp increase in the deposition ratio as Swall increases. When Swall > 0.05 there is a small and linear increase in the deposition ratio as Swall increases. This pattern is also seen in the study of clog formation and growth in a pilot scale nozzle. The effects of Swall or Sclog on clog volume can be divided into two regimes. As Swall or Sclog increases, there is a large increase in clog volume, until the sticking probability increases above 1E-2, then any further increase results in only a small increase in clog volume. In comparison to literature data the model successfully simulates the location of clog formation, the initial jump in clogging factor and the clogging factor growth rate in the later stages of clogging. However, the model underestimates the overall increase in clogging factor, resulting in a clogging factor at the end of the simulation which is half of that seen in the experiment. / Thesis / Doctor of Philosophy (PhD) / One of the ongoing challenges in the continuous casting industry is the occurrence of nozzle clogging. Over time, a buildup of material occurs within the submerged entry nozzle, called a clog. The clog leads to the partial or complete blockage of the nozzle, resulting in increased production costs. Since studying this phenomena experimentally is difficult due to the high temperature and opacity of the molten steel, modelling provides a useful alternative approach. However, previous modelling efforts regarding nozzle clogging have treated all inclusions as exhibiting the same adhesion behavior. This thesis aims to address this issue by presenting a dynamic nozzle clogging model which accounts for the effects of different degrees of inclusion adhesion. The model is used to study both inclusion deposition and clog formation. Results indicate that even a small amount of sticking probability results in a significant degree of inclusion deposition and clogging. The effect of sticking probability on clogging can be divided into two regimes, one where the clogging is very sensitive to the sticking probability and one where it is insensitive. Finally, the model was shown to run adequately even on coarser meshes (meshes with a smaller number of larger cells), indicating its utility in industrial applications, where it can be used to predict the location of clog formation and the clog growth rate.

Within industrial product development processes there is an increasing demand towards reliable predictions of the material behavior, which aims to promote a property driven development that can reduce the lead times. The implementation of simulation based product development with integrated casting simulation may enable the design engineers to gain an early understanding of the products with relation to castability, and orient the subsequent design refinement so as to achieve the desired mechanical properties. This work investigates the suitability of three commercial casting simulation softwares –MAGMA 5.2, NovaFlow &amp; Solid 4.7.5 (NFS) and Click2Cast 3.0 (C2C)–, with respect to the needs of design engineers, such as prediction of shrinkage porosity and mechanical properties with relation to the design. Simplified solidification simulations suitable for this stage were thus performed for three high pressure die cast components with different geometrical constraints. The comparability between the solidification and cooling behaviour predicted by the three softwares was studied, and showed that a reasonably good agreement between predicted solidification times by MAGMA and NFS could be obtained, albeit not between predictions by MAGMA and C2C. Predictions by the three softwares of the hot spot/porosity areas showed to have a good agreement. The calculation times by each software were compared, and MAGMA was seen to have the best performance, yielding significantly shorter times than NFS and C2C. The results obtained were also compared to experimental investigations of porosity, microstructural coarseness, and mechanical properties. There was a good agreement between the predicted hot spot areas –i.e. areas in the geometry that solidify last– and the findings of porosities in the actual castings, meaning that solidification simulations might be able to provide important information for the prediction of most of shrinkage related porosity locations that are related to the casting geometry. However, the lack of a detailed knowledge at the design stage of the casting process limits the possibilities to predict all porosities. The predicted microstructure and mechanical properties by MAGMA non-ferrous were seen to have a good agreement in trend with the experimental data, albeit the predicted values showed large differences in magnitude with the experimental data. Although, the MAGMA non-ferrous module was not developed for HPDC components, it was interesting to study if it could be applied in this context. However, the models seem to need adoption to the HPDC process and alloys. In conclusion, with a limited knowledge of the manufacturing parameters, simplified solidification simulations may still be able to provide reasonably reliable and useful information during early development stages in order to optimise the design of castings.