Dans l’industrie de la mise en forme des matériaux métalliques, le frottement joue un rôle très important. Cependant, il est difficile à contrôler totalement, notamment dans les procédés complexes où le taux de nouvelles surfaces générées lors de la déformation plastique est important. La thèse propose d’identifier par analyse inverse les propriétés tribologiques du matériau, directement à partir de la courbe donnant la force en fonction du déplacement pour un procédé d'extrusion directe. La conception d’une filière d’extrusion, avec des dimensions optimales pour maximiser l’influence du frottement a été faite à l’aide de calculs analytiques en se basant sur des critères particuliers tels que: la capacité maximale de la presse, la maximisation de la longueur de frottement, le rapport entre la puissance de frottement et la puissance de déformation et la limite du taux de réduction pour éviter l’endommagement du matériau. Comme dans le procédé d’extrusion il existe un certain couplage entre l’influence des paramètres rhéologiques et des paramètres tribologiques, des tests de compression d’éprouvettes «haltères» ont été réalisés dans une première étape afin d’identifier la loi de comportement rhéologique du matériau. La conception du test proposé a été validée par des simulations numériques avec FORGE2®. Les simulations numériques ont été également effectuées pour analyser la sensibilité des paramètres rhéologiques et tribologiques du matériau sur la force d’extrusion. L’influence de la géométrie de la filière sur la courbe de force a été examinée en détail. Une campagne d’essais a été réalisée pour l’alliage d’aluminium AA5083. La loi de comportement du matériau a été en conséquence identifiée par analyse inverse à partir de la courbe expérimentale donnant la force de compression des éprouvettes «haltères». Dans une deuxième étape, les propriétés tribologiques du matériau pour différents modèles de frottement ont été ensuite identifiées par analyse inverse à partir de la courbe donnant la force d’extrusion. La méthode d’identification par analyse inverse a été enfin validée par la simulation d’un procédé industriel d’extrusion. La campagne d’études expérimentales a été complétée par la caractérisation du matériau par des mesures de dureté, des mesures de diffraction des rayons X et des mesures de diffraction des électrons rétrodiffusés (EBSD) afin de mettre en évidence l’évolution de la surface des pièces après la déformation plastique. Les résultats indiquent que le frottement a une influence importante sur l’évolution des orientations cristallines de la surface du matériau extrudé. / In the industry of metal forming, friction plays a very important role. However, it is difficult to control completely this phenomenon, especially in the complex processes where the rate of the new surface generated during the plastic deformation is important. The thesis proposes to identify by inverse analysis the tribological properties of material, directly starting from the curve of the load versus the displacement of a direct extrusion process. The design of an extrusion die, with optimal dimensions to maximize the influence of friction, was carried out using analytical calculations based on particular criteria such as: the maximum capacity of the press, the maximization of the friction length and of the ratio between the friction power and the deformation power, the limit of the reduction rate to avoid damage of the material. Since in the extrusion process there is a certain coupling between the influence of the rheological parameters and the tribological parameters, compression tests using "dumbbells" specimens were carried out in a first stage in order to identify the rheological behavior law of the material. The design of the proposed test has been validated by numerical simulations using FORGE2®. The numerical simulations were also performed in order to analyze the sensitivity of rheological and tribological parameters of the material on the extrusion load. The influence of the geometry of the die on the extrusion load curve has been examined in detail. A campaign of tests was carried out for the AA5083 aluminum alloy. The behavior law of the material was consequently identified by inverse analysis starting from the experimental load curve of compression tests using "dumbbells" specimens. In a second step, the tribological properties of the material for different friction models were then identified by inverse analysis starting from the extrusion load curve. The method of identification by inverse analysis was finally validated by the simulation of an industrial extrusion process. The campaign of experimental studies has been completed by the characterization of the material by measurements of hardness, X-ray diffraction measurements and electron backscattered diffraction (EBSD) measurements in order to highlight the evolution of the surface of the extruded specimen after the plastic deformation. The results indicate that friction has an important influence on the evolution of crystal orientations of the surface of the extruded material.

A series of experiments was performed on groups of samples made from materials currently used to manufacture tooling for extruders to determine if the ASTM G65 dry sand rubber wheel abrasion test could be used as an accelerated test to evaluate candidate materials. Samples were tested in the heat treated condition and after surface modification by plasma ion nitriding. The range of materials tested included medium and high alloy steels and steel bonded carbide composites. The abrasives used were AFS 50/70 test sand and Dresser Glasgrain crushed fused silica. Evaluation of test wear scars and wear debris from the tests using AFS 50/70 showed that delamination was the primary wear mechanism for the composite materials, with some ploughing and microcutting, while ploughing and microcutting were the primary mechanisms in the wear of the steels. Evaluation of parts made from a composite material which were removed from service indicated that matrix erosion was the primary wear mechanism. Tests with Glasgrain fused silica as the abrasive yielded wear scars with the same morphology as the parts returned from service, but the very poor flow characteristics of this material caused inconsistency in the supply of this abrasive to the contact region. Interrupted tests showed that the wear rate was constant for the steels in the non-nitrided condition. After nitriding, the wear rate increased with test duration. The nitriding was found to act as a barrier coating providing an initial period of very low wear until the nitride layer is broached. The wear rate then increases to approximate the wear rate of the non-nitrided samples. It was found that the friction force alters the location of the maximum normal force, shifting the point of greatest contact force toward the entry end of the wear scar. / Master of Science

CPU heat sinks with high efficiency of heat transfer are greatly demanded for a personal computer with high-speed computational ability. In recent years, the manufacturing technology of CPU heat sinks has got much attention and becomes indispensable for developing the high-performance CPUs.In this study, some different design criteria for the flow guide and die are proposed during an extrusion process with complex cross-sectional shapes, such as CPU heat sinks. The plastic flow pattern of the billet inside the die cavity is analyzed by using a commercial finite element package ¡§DEFORM 3D¡¨.The extrusion load, the stress and strain distribution of die, and the curvature of the product are investigated. Taguchi method is used to find the optimum extrusion condition of the die parameters. In addition, the experiments of extrusion using Al 6061 were carried out. The plastic flow pattern of the billet within the die and the dead metal zones were observed. The experimental data were compared with the analytical values to verify the validity of the proposed analytical models.

Extruded products with precision shape have been used widely to 3C products, electronic equipment, communicatory installation, precision instrument, automobile industry. The tolerance for this kind of asymmetric products with small size is strictly required. During extrusion, the plastic flow of the billet inside the die cavity is complicated. The temperature distribution of the billet, the elastic deformation of the die, and the design of the flow guide affect the final dimension of the product. This paper uses the finite element code ¡§DEFORM 3D¡¨ to simulate the plastic flow of the billet inside the die cavity and the stress, strain, temperature distributions of the die during extrusion of a 3C product, Clip and Housing. From the simulation results, a die design guideline is proposed and the temperature, stress, strain distributions are discussed systematically. Furthermore, extrusion experiments are conducted. From the comparisons of the temperature at the die exit, the product sizes and the extrusion force, the validity of the die design rule is verified.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 165-183). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 151-159). Also available on the Internet.

No description available.

No description available.

Thesis (M.S.)--University of Missouri-Columbia, 2007. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on January 16, 2008) Includes bibliographical references.

Thesis (Ph.D.)--McMaster University, 2005. / Supervisor: Andrew Hrymak. Includes bibliographical references (leaves 157-168). Also available online.