Five-axis CNC machining presents high efficiency and unparallel flexibility in the machining of complex curved surfaces. However, generation of gouge-free CNC tool path and cutter orientation in 5-axis CNC machining remains a challenge due to the complex nature of the geometry problem encountered and the wide variations of surface geometry. In particular, curvature gouge is the biggest obstacle that hinders the advantages of 5-axis CNC machining. At present to avoid curvature gouge. a ball mill cutter with simple cutter geometry is mostly used in machining complex curved surfaces, although this either leads to lengthy machining time or poor surface finish with larger cusps which require extensive amount of hand polishing later on. An end and/or torus mill cutters with better cutter-surface curvature match can considerably improve the efficiency of the machining and the quality of the machined surface. But generation of appropriate tool paths and orientations for the more complex cutter geometry in gouge-free 5-axis CNC machining of curved surface requires a better understanding and a rigorous model of cutter-surface interaction, which do not exist at present. In this work, a rigorous mathematical model of cutter-surface geometry that facilitate better understanding on the interactions between various mill cutters. including ball. torus and end mills. and curved surface is introduced. The model is based on the new Euler-Meusnier Sphere (EMS) concept from a generic mathematical and geometric model of the cutter and surface geometry. The EMS model determines the curvature gouge constraints with varying cutter size and maximum cutter tilting angle for any given surfaces. A generic. global curvature gouge detection and avoidance method for the 5-axis CNC machining of concave, curved surfaces has been introduced. The method also improves curvature match between the cutter and the machined surface by facilitating the use of torus and end mill cutters. Computer simulation tests and real part machining have been carried out to assess the effectiveness of the new theory and newly introduced curvature gouge detection and avoidance criteria. Five-axis CNC machining experiments on curved surface, e.g. ellipse and exponent surfaces, are carried out. The machined surfaces following different tool path and cutter orientation strategies are measured using a CMM to appraise the real benefit of the introduced approach. The method has been applied to all three types of commonly used mill cutters: end. torus and sphere, for concave curved surfaces with limited curvature variation. The machining experiments have demonstrated the superior capability of the new method in providing guaranteed gouge elimination. better surface quality, and simple implementation. in comparing with 5-axis tool path and cutter orientation planning methods. The new EMS concept and curvature gouge detection/elimination method form the foundation for generating highly efficient, high quality surface producing 5-axis CNC tool path. and cutter orientation planning, programming and optimization for machining curved surfaces.

Due to increasing trends of miniaturization, components with microscale features are in high demand. Accordingly, manufacturing and measurement of small components as small as a few microns became new challenges. Micro milling and femtosecond laser machining are the most common in use cutting operations providing high accuracy and productivity. Micro milling has unique features different from traditional milling including high ratio of tool size to feature size, and constant ratio of tool edge radius to tool size [1]. Due to the mentioned differences, low stiffness of the micro mill and the complexity of the cutting mechanism at the macroscale, selection of cutting parameters are difficult [2]. Therefore, process performance in micro milling, which affects surface quality and tool life, depends on the selected cutting parameters. Also, for measuring micro components, the available dimensional control systems in the market are atomic force microscopes (AFMs) and a combination of coordinate measuring machines (CMMs) and vision systems. These are confined to the scopes of nanoscale and macroscale parts, respectively. It is difficult to justify the high cost and large size of these systems for measurement of mesoscale/microscale features and components and dimensional verification of miniature parts with 3D features. Therefore, a new cost-effective way is needed for measuring components and features in these scales. Additionally, lack of advanced CAD/CAM software for micro laser machining providing constant velocity along the tool path, is the main problem in femtosecond laser machining. In this thesis, to address the mentioned challenges, different software packages are presented to improve micro machining productivity, to provide an accurate and cost effective way of micro scanning and to bring CAD/CAM capability for micro laser machining. / Graduate / 0548 / abdolreza.bayesteh@gmail.com

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In this study, the new predictive model for the micro-grinding process was developed by consolidating mechanical and thermal effects within the single grit interaction model at microscale material removal. The size effect of micro-machining was also included in the proposed model. In order to assess thermal effects, the heat partition ratio was experimentally calibrated and compared with the prediction of the Hahn model. Then, on the basis of this predictive model, a comparison between experimental data and analytical predictions was conducted in view of the overall micro-grinding forces in the x and y directions. Although there are deviations in the predicted micro-grinding forces at low depths of cut, these differences are reduced as the depth of cut increases. On the other hand, the optimization of micro machine tools was performed on the basis of the proposed design strategy. Individual mathematical modeling of key parameters such as volumetric error, machine working space, and static, thermal, and dynamic stiffness were conducted and supplemented with experimental analysis using a hammer impact test. These computations yield the optimal size of miniaturized machine tools with the technical information of other parameters.

This thesis presents a method for the prediction of final peak-to-valley (PTV) surface profile variation for face turning of rings of non-uniform cross section. An analytical method relates initial part form, part deflection during workholding and machining, and part elastic recovery to final PTV surface profile variation. Finite element method is used to supplement the analytical model, and experiments are conducted to validate both the analytical and finite element approaches. Analytical and finite element results correspond well with experimental observations, with average relative errors of 11.6 and 7.2 percent, respectively.

Excessive vibrations continue to be a major hurdle in improving machining efficiency and achieving stable high speed cutting. To overcome detrimental vibrations, an enhanced understanding of the underlying nonlinear dynamics is required. Cutting instability is commonly studied through modeling and analysis which incorporates linearization that obscures the true nonlinear characteristics of the system which are prominent at high speeds. Thus to enhance cutting dynamics knowledge, a comprehensive nonlinear turning model that includes tool-workpiece interaction is experimentally validated using a commercial laser vibrometer to capture tool and workpiece vibrations. A procedure is developed to use instantaneous frequency for experimental time-frequency analysis and is shown to thoroughly characterize the underlying dynamics and identify chatter. For the tests performed, chatter is associated with changing spectral components and bifurcations which provides a view of the underlying dynamics not experimentally observed before. Validation of the turning model revealed that the underlying dynamics observed experimentally are accurately captured, and the coupled tool-workpiece chatter vibrations are simulated. The stability diagram shows an increase in the chatter-free limit as the spindle speed increases until 1500rpm where it begins to level out. At high speeds the workpiece dominates the dynamics, and excessive workpiece vibrations create another stability limit to consider. Thus, workpiece dynamics should not be neglected in analyses for the design of machine tools and robust control laws. The chip formation mechanisms and high speeds make micro-milling highly non-linear and capable of producing broadband frequencies that negatively affect the tool. A nonlinear dynamic micro-milling model is developed to study the effect of parameters on tool performance through spectral analysis using instantaneous frequency. A lumped mass-spring-damper system is assumed for modeling the tool, and a slip-line force mechanism is adopted. The effective rake angle, helical angle, and instantaneous chip thickness are accounted for. The model produced the high frequency force components seen experimentally in literature. It is found that increasing the helical angle decreased the forces, and an increase in system stiffness improved the dynamic response. Also, dynamic instability had the largest effect on tool performance with the spindle speed being the most critical parameter.

La selección de centros de mecanizado de alta velocidad es un proceso complejo que requiere de mucha experiencia, puesto que en él intervienen un gran número de variables, tanto tecnológicas como económicas. Existen metodologías orientadas a seleccionar el centro de mecanizado óptimo, considerando únicamente una de estas dos tipologías de variables, sin embargo, esta tesis propone una metodología que contempla ambos tipos. Para ello se identifican las variables que tienen mayor influencia sobre los resultados del proceso de mecanizado, tanto desde un punto de vista de calidad de las piezas fabricadas como de la economía de la fabricación, y se propone un modelo de selección basado en los resultados de un trabajo experimental realizado sobre piezas de aluminio. Dicho modelo se implementa mediante redes neurales, cuyo entrenamiento se realiza en base a los resultados del trabajo experimental mencionado.

Vibration problems are still the major constraint in modern machining processes that seek higher material removal rate, shorter process time, longer tool life and better product quality. Depending on the process, the weaker structure element can be the tool/tool holder, workpiece/fixture or both. When the tool/tool holder is the main source of vibration, the stability limit is determined in most cases by the ratio of length-to-diameter. Regenerative chatter is the most significant dynamic phenomenon generated through the interaction between machine tool and machining process. As a rule of thumb, the ratio between the tool’s overhang length and the tool’s diameter shouldn’t exceed 4 to maintain a stable machining process while using a conventional machining tool. While a longer tool overhang is needed for specific machining operations, vibration damping solutions are required to ensure a stable machining process. Vibration damping solutions include both active and passive damping solutions. In the passive damping solutions, damping medium such as viscoelastic material is used to transform the vibration strain energy into heat and thereby reduce vibration amplitude. For a typical cantilever tool, the highest oscillation displacement is near the anti-node regions of a vibration mode and the highest oscillation strain energy is concentrated at the node of a vibration mode. Viscoelastic materials have been successfully applied in these regions to exhibit their damping property. The node region of the 1st bending mode is at the joint interfaces where the cantilever tools are clamped. In this thesis, the general method that can be used to measure and characterize the joint interface stiffness and damping properties is developed and improved, joint interfaces’ importance at optimizing the dynamic stiffness of the joint interface is studied, and a novel advancing material that is designed to possess both high young’s modulus and high damping property is introduced. In the joint interface characterization model, a method that can measure the joint interface’s stiffness and damping over the full frequency range with only the assembled structure is presented. With the influence of a joint interface’s normal pressure on its stiffness and damping, an optimized joint interface normal pressure is selected for delivering a stable machining process against chatter with a boring bar setting at 6.5 times overhang length to diameter ratio in an internal turning process. The novel advancing material utilizes the carbon nano particles mixed in a metal matrix, and it can deliver both high damping property and high elastic stiffness to the mechanical structure. / <p>QC 20130521</p> / PoPJIM, HydroMod, XPRES, NanoComfort

Condition monitoring of critical machine tool components and machining processes is a key factor to increase the availability of the machine tool and achieving a more robust machining process. Failures in the machining process and machine tool components may also have negative effects on the final produced part. Instabilities in machining processes also shortens the life time of the cutting edges and machine tool. The condition monitoring system may utilise information from several sources to facilitate the detection of instabilities in the machining process. To avoid additional complexity to the machining system the use of internal sensors is considered. The focus in this thesis has been to investigate if information related to the machining process can be extracted directly from the internal sensors of the machine tool. The main contibutions of this work is a further understanding of the direct response from both linear and angular position encoders due the variations in the machining process. The analysis of the response from unbalance testing of turn tables and two types of milling processes, i.e. disc-milling and slot-milling, is presented. It is shown that operational frequencies, such as cutter frequency and tooth-passing frequency, can be extracted from both active and inactive machine axes, but the response from an active machine axis involves a more complex analysis. Various methods for the analysis of the responses in time domain, frequency domain and phase space are presented. / QC 20100518

To survive in today's manufacturing environments companies must push the standards of accuracy and speed to the highest levels possible. Electro Discharge Machining (EDM) has been used for over 50 years and recent developments have seen the use of EDM become much more viable. The goal of this research is to produce and evaluate electrodes produced by different manufacturing methods. The use of electroforming and spray-metal deposition has only recently become viable methods of producing usable rapid tooling components. The speed and accuracy as well as the cost of manufacture play a vital role in the tool and mould manufacturing process. Electroforming and spray-metal deposition offer an alternate option to traditional machining of electrodes. Electroforming is one method of producing electrodes for EDM. The fact that electroforming can be used to produce multiple electrodes simultaneously gives it the advantage of saving on costs when multiple electrodes are needed. Spray-metal deposition offers another alternative that is much cheaper and relatively faster to manufacture. The used of these non-traditional manufacturing methods in this research are compared to the performance of traditional solid electrodes in terms of machining time, material removal rate, tool wear rates and surface roughness at several standard machining settings. The results of this research are presented in this thesis along with conclusions and comments on the performance of the different methods of electrode manufacture. The major findings of the research include the solid electrodes performed better than the electroformed electrodes in Material Removal Rate (MRR), Tool Wear Rate (TWR), and Surface Roughness (Ra) at all machine settings. However it was found that the production cost of the solid electrodes was six times that of the electroformed electrodes. The production of spray metal electrodes was unsuccessful. The electrode shell walls were not an even thickness and the backing material broke through the shell making them unusable. It is concluded that with further refinements and research, electroforming and spray metal processes will become an extremely competitive method in electrode manufacture and other rapid tooling processes.