27 research outputs found

    Understanding the Mechanism of Abrasive-Based Finishing Processes Using Mathematical Modeling and Numerical Simulation

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    Recent advances in technology and refinement of available computational resources paved the way for the extensive use of computers to model and simulate complex real-world problems difficult to solve analytically. The appeal of simulations lies in the ability to predict the significance of a change to the system under study. The simulated results can be of great benefit in predicting various behaviors, such as the wind pattern in a particular region, the ability of a material to withstand a dynamic load, or even the behavior of a workpiece under a particular type of machining. This paper deals with the mathematical modeling and simulation techniques used in abrasive-based machining processes such as abrasive flow machining (AFM), magnetic-based finishing processes, i.e., magnetic abrasive finishing (MAF) process, magnetorheological finishing (MRF) process, and ball-end type magnetorheological finishing process (BEMRF). The paper also aims to highlight the advances and obstacles associated with these techniques and their applications in flow machining. This study contributes the better understanding by examining the available modeling and simulation techniques such as Molecular Dynamic Simulation (MDS), Computational Fluid Dynamics (CFD), Finite Element Method (FEM), Discrete Element Method (DEM), Multivariable Regression Analysis (MVRA), Artificial Neural Network (ANN), Response Surface Analysis (RSA), Stochastic Modeling and Simulation by Data Dependent System (DDS). Among these methods, CFD and FEM can be performed with the available commercial software, while DEM and MDS performed using the computer programming-based platform, i.e., "LAMMPS Molecular Dynamics Simulator," or C, C++, or Python programming, and these methods seem more promising techniques for modeling and simulation of loose abrasive-based machining processes. The other four methods (MVRA, ANN, RSA, and DDS) are experimental and based on statistical approaches that can be used for mathematical modeling of loose abrasive-based machining processes. Additionally, it suggests areas for further investigation and offers a priceless bibliography of earlier studies on the modeling and simulation techniques for abrasive-based machining processes. Researchers studying mathematical modeling of various micro- and nanofinishing techniques for different applications may find this review article to be of great help

    Development of a machine-tooling-process integrated approach for abrasive flow machining (AFM) of difficult-to-machine materials with application to oil and gas exploration componenets

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    This thesis was submitted for the degree of Doctor of Engineering and awarded by Brunel UniversityAbrasive flow machining (AFM) is a non-traditional manufacturing technology used to expose a substrate to pressurised multiphase slurry, comprised of superabrasive grit suspended in a viscous, typically polymeric carrier. Extended exposure to the slurry causes material removal, where the quantity of removal is subject to complex interactions within over 40 variables. Flow is contained within boundary walls, complex in form, causing physical phenomena to alter the behaviour of the media. In setting factors and levels prior to this research, engineers had two options; embark upon a wasteful, inefficient and poor-capability trial and error process or they could attempt to relate the findings they achieve in simple geometry to complex geometry through a series of transformations, providing information that could be applied over and over. By condensing process variables into appropriate study groups, it becomes possible to quantify output while manipulating only a handful of variables. Those that remain un-manipulated are integral to the factors identified. Through factorial and response surface methodology experiment designs, data is obtained and interrogated, before feeding into a simulated replica of a simple system. Correlation with physical phenomena is sought, to identify flow conditions that drive material removal location and magnitude. This correlation is then applied to complex geometry with relative success. It is found that prediction of viscosity through computational fluid dynamics can be used to estimate as much as 94% of the edge-rounding effect on final complex geometry. Surface finish prediction is lower (~75%), but provides significant relationship to warrant further investigation. Original contributions made in this doctoral thesis include; 1) A method of utilising computational fluid dynamics (CFD) to derive a suitable process model for the productive and reproducible control of the AFM process, including identification of core physical phenomena responsible for driving erosion, 2) Comprehensive understanding of effects of B4C-loaded polydimethylsiloxane variants used to process Ti6Al4V in the AFM process, including prediction equations containing numerically-verified second order interactions (factors for grit size, grain fraction and modifier concentration), 3) Equivalent understanding of machine factors providing energy input, studying velocity, temperature and quantity. Verified predictions are made from data collected in Ti6Al4V substrate material using response surface methodology, 4) Holistic method to translating process data in control-geometry to an arbitrary geometry for industrial gain, extending to a framework for collecting new data and integrating into current knowledge, and 5) Application of methodology using research-derived CFD, applied to complex geometry proven by measured process output. As a result of this project, four publications have been made to-date – two peer-reviewed journal papers and two peer-reviewed international conference papers. Further publications will be made from June 2014 onwards.Engineering and Physical Sciences Research Council (EPSRC) and the Technology Strategy Board (TSB

    Advances and Trends in Non-conventional, Abrasive and Precision Machining

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    The work included in this book pertains to advanced abrasive and nonconventional machining processes. These processes are at the forefront of modern technology, with significant practical significance. Their importance is also made clear by the case studies that are included in the research that is presented in the book, pertaining to important materials and high-end applications. However, the particularities of these manufacturing processes need to be further investigated and the processes themselves need to be optimized. This is conducted in the presented works with significant experimental and modeling work, incorporating modern tools of analysis and measurements

    Surface Finish Control of Inconel 625 Components Produced by Additive Manufacturing Using Combined Chemical-Abrasive Flow Polishing

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    RÉSUMÉ Les secteurs manufacturiers à l’échelle mondiale, particulièrement dans les domaines de l’aérospatial et de l’automobile, expriment de plus en plus le besoin de produire des composants de géométrie complexe en utilisant des approches de fabrication additive plutôt que d’emprunter des voies de fabrication plus traditionnelles. Ainsi, les techniques de fabrication additive de fusion sélective par laser ou faisceau d’électron permettent de réduire le temps de fabrication et la quantité de matière pour produire les pièces tout en améliorant la performance des matériaux. Dans le procédé de fusion sélective par laser, un faisceau laser de haute puissance est utilisé pour fondre localement une poudre métallique pour fabriquer une pièce couche par couche. Cette méthode offre l’avantage de produire des composants à partir de matériaux durs et à haut point de fusion. Bien que les techniques de fabrication additives permettent d’obtenir des caractéristiques uniques du point de vue de la géométrie des pièces, il demeure une problématique au niveau du fini de surface des composants, particulièrement pour les surfaces internes de pièces utilisées pour contenir des écoulements de fluide. La présence de particules partiellement fondues soudées à la surface peut causer une pollution indésirable dans le fluide de même que la rugosité de surface peut limiter l’écoulement du fluide. Ainsi, un des sujets les plus critiques en recherche qui amène une pénalité importante pour les procédés de fabrication additive concerne les opérations secondaires de finition de surface. Peu de résultats de recherche ont été publiés sur les procédés secondaires de polissage de surfaces internes dans les pièces de géométrie complexe. Ceci devient plus important considérant la variété de matériaux utilisés en fabrication additive. Les quelques résultats publiés reliés aux techniques de polissage chimique, électrolytique et mécanique montrent bien les limites de la fabrication additive. Les principaux objectifs des travaux de recherche sont de concevoir, fabriquer et valider une méthode de polissage basée sur la combinaison de produits chimiques et de particules abrasives pour des surfaces internes de pièces aéronautiques en IN-625 produites par fabrication additive. Pour atteindre ce but, on envisage d’étudier : a) l’écoulement de produits chimiques, b) l’écoulement d’abrasifs et c) l’écoulement combiné de produits chimiques et d’abrasifs.----------ABSTRACTABSTRACT ABSTRACTABSTRACTABSTRACT World manufacturing sectors, in particular aerospace and automotive industries, wish to produce highly complex and customized components by adopting additive manufacturing (AM) of products compared to the conventional fabrication methods. This has brought attention to the AM techniques, most commonly selective laser melting (SLM) and electron beam melting (EBM), that have been proven to reduce time to market, decrease buy-to-fly ratio and improve parts performance. In the SLM process, a high-power density laser selectively melts and fuses powders within and between layers to produce a component. Several advantages are offered by SLM such as processing hard materials and production of materials with high melting points. Regardless of excellent features of SLM additive manufacturing technique, the processing conditions lead to some surface problems in the case of internal surfaces of parts designed for fluid flows. This involves appearance of semi-welded particles attached to the surface, causing pollution in the fluid system, and relatively high surface roughness and texture, compromising the fluid flow. Therefore, one of the critical research issues and excessive cost factors penalizing AM approaches is post-processing surface finish. There is a lack of knowledge on the post-AM surface finish techniques that are appropriate for improving the internal surface quality of complex parts. This becomes more complicated when it comes to the wide range of materials produced by AM techniques. According to the review of the literature, some chemical, electrochemical and mechanical techniques have been investigated that deal with the polishing limitations of SLM-built parts. The main objectives of this study were to design, manufacture and validate a post-SLM surface finish technique, used for internal surface polishing of tubular IN-625 parts designed for aerospace industry, employing a combination of chemical and abrasive flow actions. For this purpose, comprehensive experimental studies included: a) chemical flow polishing, b) abrasive flow polishing and c) chemical-abrasive flow polishing. The effect of SLM build orientation and fluid velocity on the surface finish quality for the three polishing techniques was studied. The obtained results showed the feasibility of using the combined chemical-abrasive polishing to reach better polishing efficiency. Indeed, the semi-welded powder particles attached to the surface were removed and surface roughness and texture notably improved

    Elid superfinishing of spherical bearings

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    Driven by a requirement to extend the lifespan of self-aligning lined spherical bearings, this research investigates the use of Elid (electrolytic in-process dressing) as a method of improving ball surface finish. Elid is a continuous and self-regulating electrochemical dressing process that modifies the surface of a grinding, lapping, or superfinishing wheel. It provides improved grit protrusion, impedes wheel loading / glazing and promotes effective cutting. The characteristics of the newly-developed Elid superfinishing process are in many ways fundamentally different to conventional superfinishing. The main difference is that the use of super-abrasives prevents the wheel from self-sharpening; the normal mechanism by which dulled conventional abrasives are removed and a wheel’s surface refreshed. Because the wheel’s performance and condition is continually maintained inprocess by the Elid system, metal resin bonded (MRB) wheels containing very small super-abrasives can be used. It is the utilization of these fine abrasives (30 to 0.12 μm) that enables surface roughness values below 5 nm Ra to be consistently produced on the spherical surface of corrosion-resistant steel balls. This research provides an in-depth understanding of the Elid spherical superfinishing process; investigating the most effective use of the Elid system, wheel dressing requirements and process performance. Optimisation is provided in terms of evaluating the critical operating parameters, the most effective superfinishing cycle and the implications to the complete ball production chain. A range of techniques are used to evaluate processing performance and ball output quality. These include in-process monitoring of Elid and wheel spindle power levels, analysis of wheel condition, rates of ball surface generation and material removal, ball finish and form. Although predominantly concentrated on corrosion-resistant steel, testing is also conducted on titanium and various ball coatings. In investigating various ways of using the Elid system, this work considers electrodischarge truing, pre-process dressing, Elid 1, Elid 2, Elid 3, and Elid combined with electrolytically assisted superfinishing. The initial process solution of Elid 3 (electrodeless) superfinishing provides the capability of working on all standard size balls, however the dressing system lacks stability. The development of a fixturing system that has a small separate electrode enables Elid 1 (conventional) to be used on the majority of ball sizes. Elid 1 allows more aggressive and consistent dressing, a faster rate of ball material removal and thus a substantially reduced processing time. Results with a #12,000 wheel show that surface quality is vastly improved through the use of Elid whilst maintaining current production standards of form accuracy. Surface finishes of 2nm Ra are achieved, which is an order of magnitude better than balls currently produced using barrelling / polishing. Processing times are equivalent or faster when using Elid 1. Alternatively, consistently sub 10 nm Ra finishes can be reached with a #2,000 wheel using Elid 2 (interval dressing). Generally MRB-CBN wheels provide a more effective carbide cutting action than conventional superfinishing wheels. Controlling wheel condition and achieving full and even ball to wheel conformity are the two most significant contributory factors to the success of Elid spherical superfinishing. Insufficient control of these factors results in poor output quality. Monitoring of wheel spindle and Elid power usage provides useful information in assessing the condition of the wheel and identifying potential problems. High spindle power correlates with fast material removal and is a result of high loads and a free cutting action. Elid processing can be employed for improving surface finish after the conventional honing stage, or after cylindrical grinding for improving both ball form and finish.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

    Nano to micrometric grain sized CVD diamond for turning hard and abrasive materials

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    Doutoramento em Ciência e Engenharia de MateriaisO presente trabalho consistiu no desenvolvimento de ferramentas de corte de diamante CVD (Chemical Vapour Deposition) obtido na forma de revestimento em materiais cerâmicos à base de nitreto de silício monolítico (Si3N4) ou compósitos nitreto de silício-nitreto de titânio (Si3N4-TiN). A adição de TiN acima de 23 vol.% conferiu conductividade eléctrica ao compósito, na ordem de 1×10-1 W−1.cm-1, possibilitando a sua maquinagem por electroerosão. Duas técnicas foram utilizadas para o crescimento dos filmes de diamante: deposição química em fase vapor por plasma gerado por microondas, MPCVD (Microwave Plasma Chemical Vapour Deposition), e por filamento quente, HFCVD (Hot Filament Chemical Vapour Deposition). Previamente os substratos cerâmicos sofreram uma preparação superficial por diversos métodos: rectificação por mós diamantadas; polimento com suspensão de diamante (15μm); ataque da superfície por plasma de CF4; riscagem manual ou por ultra-sons com pó de diamante (0.5-1.0 μm). A caracterização das ferramentas revestidas envolveu: o estudo da qualidade e tensões residuais dos filmes de diamante a partir da difracção dos raios X e espectroscopia Raman; a análise da respectiva microestrutura e medida da espessura por microscopia electrónica de varrimento (SEM); a determinação dos valores de rugosidade dos filmes por microscopia de força atómica (AFM); e a avaliação da adesão dos filmes aos substratos por indentação com penetrador Brale. Foram obtidos filmes com granulometria que variaram da gama do diamante nanométrico (< 100 nm) até ao micrométrico convencional (3-12 μm), com consequências na rugosidade superficial do filme. Os filmes de diamante CVD apresentaram espessuras de 15 a 150μm. Os revestimentos apresentaram elevada adesão ao substrato, sendo que o melhor resultado foi atingido pelo diamante micrométrico, suportando um limite de carga aplicada de até 1600 N. O estudo do comportamento em serviço das ferramentas foi efectuado na operação de torneamento de metal duro (WC-Co) e de eléctrodos de grafite, com medição de forças de corte em tempo real por meio de um dinamómetro. Os ensaios foram realizados num torno CNC, em ambiente industrial, na empresa Durit (Albergaria-a-Velha), produtora de metal duro. Os modos de desgaste das ferramentas foram avaliados por meio de observação em microscopia óptica e electrónica de varrimento e o grau de acabamento da superfície maquinada por rugosimetria. A influência destes parâmetros foi estudada em termos das forças envolvidas em operações de torneamento, desgaste das ferramentas e do acabamento conferido à peça maquinada. Os melhores resultados do torneamento de metal duro foram atingidos pelas ferramentas com geometria de aresta em quina-viva, recobertas com os filmes de diamante de 100-200 nm de tamanho de grão, correspondentes às menores forças de corte (<150N), melhor qualidade da peça maquinada (rugosidade aritmética igual a 0,2 μm) e menor desgaste (flanco igual a 110μm). No torneamento de eléctrodos de grafite, as forças de corte foram baixas (< 20N), sendo que o principal modo de desgaste foi a formação de cratera na superfície de ataque (valor máximo igual a 22 μm). O fio da aresta de corte permaneceu inalterado (devido ao mínimo desgaste de flanco), sendo que as diferentes granulometrias do diamante não tiveram influência significativa no comportamento geral das ferramentas.This work consisted on the development of CVD (Chemical Vapour Deposition) diamond cutting tools directly deposited on monolithic silicon nitride (Si3N4) based ceramics and silicon nitride-titanium nitride composites (Si3N4-TiN). A TiN content higher than 23 vol.% confers electric conductivity to the composite in the order of 1×10-1 W−1.cm-1, making possible its machinability by means of electrodischarge machining. Two techniques were used for diamond growth: Microwave Plasma Chemical Vapour Deposition (MPCVD) and Hot Filament Chemical Vapour Deposition (HFCVD). The substrate pre-treatment steps prior to diamond deposition were: grinding with diamond wheels; polishing with diamond suspension (15μm); chemical etching with CF4 plasma; manual scratching or ultrasonic bath scratching with diamond powder (0.5-1.0 μm) for seeding purposes. The diamond cutting tools characterization involved: study of the quality and the residual stress of the films by X ray diffraction and Raman spectroscopy; analysis of respective film microstructure and measurement of film thickness by scanning electron microscopy (SEM); quantification of film surface roughness by atomic force microscopy (AFM); evaluation of adhesion strength of the thin films to Si3N4 substrate by the indentation technique with a Brale indenter. The grain size of the films varied from nanometric (< 100 nm) to conventional micrometric (3-12 μm), therefore giving different surface roughness. The CVD diamond film thickness was in the range of (15-150 μm). The diamond films presented a high adhesion level to the Si3N4 ceramic substrates, the best results being achieved by the micrometric grain sized film, which undergo a normal load of until 1600N. The study of the cutting tool behaviour was performed in turning operations of hardmetal (WC-Co) and graphite electrodes, by real-time acquisition of the cutting forces using a dynamometer. The turning operations were carried out in a CNC lathe, at industrial environment of a hardmetal producer company, Durit (Albergaria-a-Velha). The wear modes of the tested cutting tools were analysed by optical and electronic microscopy observations and the finishing quality of the machined workpiece was measured by surface roughness measurements. The influence of these parameters was studied in terms of the cutting forces developed during turning operations, of tool wear and of the finishing quality of the machined workpieces. The best results attained in hardmetal turning were achieved by the cutting tools with sharp edges, covered with diamond films of 100-200 nm of grain size, which presented the lowest cutting forces (<150N), the best workpiece surface quality (Ra=0.2μm) and the lowest flank wear (110μm). In graphite turning, the cutting forces were very low (<20N) and the main wear mode was the crater one on the rake face (maximum value of 22μm). The cutting edge remained almost intact (due to the minimum flank wear) while the different diamond grain sizes did not have a significant influence on the overall cutting behaviour

    In-Situ Characterization of Burr Formation in Finish Machining of Inconel 718

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    One of the undesirable byproducts that occur during the machining process is the development of burrs, which are defined as rough excess material that forms around the geometric discontinuities of a part. Burrs are especially problematic because they have negative impacts across the triple bottom line: economic, environmental, societal. For one, they are expensive to remove because the deburring process is entirely manual and requires skill. Further, burr material is typically discarded which is adding to the already mounting waste generated from machining such as in coolant and chip disposal. Lastly, there are many societal implications, such as operator injury during assembly and the failure of parts in service because of leftover burrs that turned into stress concentrations. Therefore, optimizing the machining process to minimize burrs and promote sustainable manufacturing is a central challenge for manufacturers today. However, the burr formation mechanism is complex, and research on the phenomenon is scarce. The current state of the art focuses almost exclusively on drilling and micro-milling processes, with very little work investigating burr formation in the conventional machining processes of turning and milling. Research as it pertains to materials that are difficult-to-machine like nickel and titanium-based superalloys is even less common, as most of the literature focuses on softer materials like aluminum and steel alloys. Superalloys are especially crucial to the aerospace industry, comprising most of the components in jet engines. Thus, the objective of this study was to characterize burr formation for nickel-based superalloy Inconel 718 using a custom-built in-situ testbed capable of ultra-high-speed imaging in orthogonal cuts. Experiments were carried out to measure the variation in burr development with respect to several cutting parameters: uncut chip thickness, tool-wear, and cutting speed. Firstly, the exit and side burr geometry were measured after each machining trial for a variety of different metrics. Results showed that all cutting parameters have an influence on the burr geometry, although not every cutting parameter had statistical significance on certain burr metrics. For instance, it was found that side burrs were much more sensitive to tool-wear than exit burrs. Then, by combining digital image correlation (DIC) with a physics-based model, the flow stress was calculated during exit burr formation and results revealed that the stress at the exit burr root was approximately equal to the flow stress. Finally, this study investigates the fracture phenomenon during exit burr formation—it was found that besides the requirement of high strain rate and depth of cut, negative exit burrs, there is a microstructural size effect, which had not been reported by prior work

    Cumulative index to NASA Tech Briefs, 1963-1967

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    Cumulative index to NASA survey on technology utilization of aerospace research outpu
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