Desarrollo de trayectorias para mecanizado y verificación de engranajes

A lo largo de la Historia de la Humanidad se han utilizado diversos métodos para solucionar los problemas de transmisión de movimiento y potencia, siendo tradicionalmente muy utilizados los engranajes. En la actualidad su uso está extendido en aplicaciones tales como la industria automovilística, la industria del transporte y elevación, energía eólica, y solar, en antenas y también en aplicaciones de precisión como transmisiones de pequeñas dimensiones.Los procesos de fabricación de estos mecanismos requieren el cumplimiento de diversas especificaciones. El objetivo es obtener un producto con cero defectos en su producción. Sin embargo, los métodos de diseño, fabricación y verificación de engranajes suelen ser complejos, por lo que son de utilidad herramientas que agilicen los procesos de cada una de estas etapas.La motivación de esta tesis surge a partir del deseo de desarrollar una línea de investigación en la cual se generen nuevos métodos de fabricación y verificación que permitan agilizar el trabajo de diseñadores, investigadores y operarios. Su objetivo es recorrer los pasos que componen el proceso productivo y aportar mejoras en las diversasetapas de producción que sean útiles para su aplicación en la industria.Los hitos que se pretenden conseguir a lo largo del trabajo de esta Tesis Doctoral sonlos siguientes:1. Estudiar en primer lugar los métodos y herramientas que existen actualmente para digitalizar perfiles. Analizar la importancia que tiene el número de puntos que componen el perfil en los tiempos de fabricación y desarrollar un método que consiga identificar los puntos que más información aporten al perfil, para de esta manera seleccionar los puntos más significativos y que dicho perfil sea más ágil de procesar. Generar algoritmos que identifiquen estos puntos y desarrollar un programa informático implementando este modelo matemático. Finalmente, evaluar la eficacia de este algoritmo mediante experimentos en el laboratorio.2. A continuación se propone estudiar los métodos CAM existentes y analizar las trayectorias que sigue la máquina-herramienta para mecanizar un perfil digitalizado. Evaluar la influencia de las trayectorias en el mecanizado en los tiempos de producción. Desarrollar un algoritmo basado en estudios anteriores para su implementación en un programa informático que permita reducir los tiempos de mecanizado. Evaluar la eficacia de este algoritmo mediante experimentos en el laboratorio.3. Tras el desarrollo de las herramientas en los apartados anteriores orientadas a la fabricación, se pretende a continuación crear una herramienta informática que apoye el proceso de control de calidad. Se propone programar una aplicación informática que, a partir de un engranaje fabricado y cuyas características geométricas son conocidas, sea capaz de verificar su calidad dimensional. Así, se asegura que la calidad de la producción cumple con las especificaciones requeridas.4. Con los conocimientos adquiridos en los apartados anteriores de digitalización, limpieza de puntos, trayectorias y programación de herramientas de diseño y verificación de engranajes, se propone estudiar engranajes no circulares y desarrollar herramientas y métodos alternativos de producción para su fabricación. Se analizarán engranajes elípticos y ovales debido a su amplio uso en gran variedad de aplicaciones. Se desarrollarán modelos matemáticos que definan el perfil de estos engranajes. A continuación se seleccionará un método de fabricación adecuado para utilizar con los modelos matemáticos. Finalmente se mecanizarán y se verificarán prototipos para evaluar la adecuación del método propuesto<br /

Uniform Micro-Patterning of an Arbitrary Surface

According to the literature, creating specific micro-level patterns on some surfaces can significantly reduce friction. To this effect, a method is presented to create a regular pattern of micro-level indentations on any irregular surface. Creating a uniform pattern on a regular surface is possible using commercial CAD software, where regular surface is the surface obtained by extrusion or revolution of a 2D sketch along any curve. But, it is complicated and often incorrect for irregular surfaces. The thesis presents the approach followed to create parameterized regular patterns on arbitrary surfaces. Three different algorithms are presented, each achieving a progressively increased quality solution. The last and best method provides a set of points with their corresponding normals to the surface to enable the creation of the patterning feature. The algorithm reads an STL file, a format neutral output of any CAD software and implements the method on the approximated surface. Each facet surface upon which the pattern has to be created is sliced by planes at specific distances from each other. The intersections of the facets and the planes are calculated and chains are formed from the intersections in each plane. Points are interpolated at the required pitch in different chains formed at the intersection of a single plane and the facets. This procedure is repeated for each plane. Thus, a pattern of points of specified pitch distance that can be as low as microns can be generated. Given specifications of a machine, this method generates the X, Y, and Z translations and the axis rotation angles needed to generate a g-code specific to a micro-milling machine. This code can be used directly for any metal removing process that has to create micro-level indentations on an arbitrary surface. If instead, the features are protrusions on some irregular surface, then the resultant points obtained with the developed approach can be used to apply the pattern at each of the identified locations

A review of geometry representation and processing methods for cartesian and multiaxial robot-based additive manufacturing

Nowadays, robot-based additive manufacturing (RBAM) is emerging as a potential solution to increase manufacturing flexibility. Such technology allows to change the orientation of the material deposition unit during printing, making it possible to fabricate complex parts with optimized material distribution. In this context, the representation of parts geometries and their subsequent processing become aspects of primary importance. In particular, part orientation, multiaxial deposition, slicing, and infill strategies must be properly evaluated so as to obtain satisfactory outputs and avoid printing failures. Some advanced features can be found in commercial slicing software (e.g., adaptive slicing, advanced path strategies, and non-planar slicing), although the procedure may result excessively constrained due to the limited number of available options. Several approaches and algorithms have been proposed for each phase and their combination must be determined accurately to achieve the best results. This paper reviews the state-of-the-art works addressing the primary methods for the representation of geometries and the subsequent geometry processing for RBAM. For each category, tools and software found in the literature and commercially available are discussed. Comparison tables are then reported to assist in the selection of the most appropriate approaches. The presented review can be helpful for designers, researchers and practitioners to identify possible future directions and open issues

Spiral tool paths for high-speed machining of 2D pockets with or without islands

We describe new methods for the construction of spiral tool paths for high-speed machining. In the simplest case, our method takes a polygon as input and a number δ>0 and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is G1 continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most δ. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in some polygons with no islands than what is obtained by conventional spiral tool paths. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island. Keywords: Spiral-like path, Medial axis, Smoothing, High-speed machinin

Spiral Toolpaths for High-Speed Machining of 2D Pockets with or without Islands

We describe new methods for the construction of spiral toolpaths for high-speed machining. In the simplest case, our method takes a polygon as input and a number $\delta>0$ and returns a spiral starting at a central point in the polygon, going around towards the boundary while morphing to the shape of the polygon. The spiral consists of linear segments and circular arcs, it is $G^1$ continuous, it has no self-intersections, and the distance from each point on the spiral to each of the neighboring revolutions is at most $\delta$. Our method has the advantage over previously described methods that it is easily adjustable to the case where there is an island in the polygon to be avoided by the spiral. In that case, the spiral starts at the island and morphs the island to the outer boundary of the polygon. It is shown how to apply that method to make significantly shorter spirals in polygons with no islands. Finally, we show how to make a spiral in a polygon with multiple islands by connecting the islands into one island.Comment: 22 pages, 13 figure

Lab-on-a-Chip Integration of Size-based Separation Techniques for Isolation of Bacteria from Blood

Clinical sample preparation is an essential process in modern diagnostics for maximizing sensitivity and specificity of detection and for ensuring reliability of assay readout. In general, sample preparation typically involves isolating and concentrating a population of target molecules, cells, or particles together with the removal of undesired components from specimen that could otherwise interfere with target detection. The identification of bacteria from complex clinical matrices such as blood presents a particular sample preparation challenge. Conventional culture-based methods typically require at least 24 h of incubation time, making this approach unsuitable for use in rapid diagnostics. Therefore, the development of sample preparation methods for bacteria with rapid processing time, high purification efficiency, and large volumetric throughput to enable analysis of low bacteria concentrations in blood remains a key challenge. This dissertation is focused on realizing a universal platform for preparing microbial sample from blood that is free lysis buffer, electric field, or affinity-based capture methods. First, we developed the porous silica monolith elements integrated into thermoplastic devices for isolation of intact bacteria from blood, enabling the application of emerging detection methods that supports bacterial identification from purified cell populations. Second, to support high throughput analysis of blood samples procured in resource-limited environments, microfluidics elements integrated directly into a syringe are demonstrated by utilizing the deterministic lateral displacement technique and the Dean flow focusing methods. Through these approaches blood cell reduction prior to bacteria isolation can be achieved, thereby increasing the overall sample volume that may be processed by the system. Additionally, a miniaturized hydrocylone capable of operating at tens of milliliters per minute feed rate is presented. Complex microstructures successfully realized at a hundred-micron scale by 3D printing technique presented a promising route to the unconventional microfluidic systems. Lastly, we demonstrated ancillary microfluidic components required to enable full operation of the system in a low-cost lab-on-a-chip format suitable for implementation in resource-limited environments and optimize overall operation of the platform to achieve throughput, sensitivity, and selectivity suitable for clinical application when coupling the platform with downstream detection methods designed for assay readout from intact bacteria

X-ray computed microtomography applications for complex geometries and multiphase flow

In all fields, fundamental and applied research seek to produce experimental measurements without causing interferences to the process being observed. This capability is of paramount importance, since small perturbations of the phenomenon can alter it to the point of producing biased or even incorrect results. Xray techniques, based on synchrotron or laboratory X-ray sources, have attracted the attention of the research and industrial R&D community thanks to their characteristic of having little to no detectable influence on the subject under study. Moreover, if declined as tomography, this technique can provide localized full volume information at the micrometre scale, from which arbitrary shaped geometries and material densities can be deduced. During this thesis an X-ray microtomography instrument, based on a laboratory X-ray source, has been exploited to gain three main objectives. The first one is the analysis of how a liquid drop, of water or glycol, adapts its shape to reach an equilibrium state when gently deposed on a flat or patterned surface. So far this has been done using 2D techniques but introducing the knowledge of the third dimension and being able to see the drop shape even in not optically accessible locations, opens new possibilities to better understand the physics that regulate it. The second one is the reconstruction of the internal geometries of automotive diesel injectors with high resolution to detect and highlight differences between nominal and real geometries, key information to produce more realistic CFD simulations of the flow inside production grade injectors geometries. A scaled -up model made of PEEK was also studied, producing successive tomographies, to detect small geometrical changes induced by part usage, giving an in-depth view of the locations more prone to be damaged by cavitation flow. The third one is the study of a multiphase flow inside the same scaled-up model injection channel with flowing conditions exhibiting cavitation. The geometry of the non-axisymmetric model mimics the flow pattern of a real diesel injection channel and automotive grade diesel was consequently selected as fluid. Understanding the dependence of cavitation development on flow characteristics in a three-dimensional way, through the determination of the localized void fraction of the multiphase flow, can lead to improvements in the knowledge of such a phenomenon that can guide the design of future fuel injection equipment