Дисертації з теми "Machining finishing"

The current scenario of industrialization requires need for higher productivity which is met by advanced material removal process, i.e., abrasive flow machining (AFM) in which the internal surfaces of the workpiece is machined to higher accuracy level with the help of abrasive laden media. In this paper, the conventional AFM setup has been made hybrid using electrolytic and magnetic force arrangement alongwith rotational effect in order to achieve better results in terms of material removal and surface roughness. The newly developed in-house polymer media were utilized in the process and the input parameters taken during experimentation were magnetic flux, electrolytic rod size and shape, rotational speed, polymer media, abrasive particles and extrusion pressure. It was found that the material removal and surface roughness improvement were more in electrochemo magneto rotational AFM process compared to conventional AFM process. The experimental values were in confirmation with those obtained in the optimization techniques applied, i.e., Taguchi L9 OA, Matlab fuzzy logic and GRA-PCA. In addition, the hybrid mathematical model was developed and effect of different forces occurring in the process and computational flow analysis of media have been explained. With advent of need for fast productivity in terms of material removal and surface roughness of the workpiece, abrasive flow machining (AFM) process is gaining rapid importance in the industries. In this process, the fine finishing of the internal surfaces is done that are difficult to reach spaces using abrasive laden polymer media. The media is extruded past the surface under high pressure with the help of two sets of extrusion piston cylinder arrangements. Further various innovations done in the field of abrasive flow machining have been studied in detail in a tabulated form. It included the applications of the process and the different variant forms of AFM process. Hence it can be concluded that this form of non conventional machining process is efficient both in terms of surface roughness and material removal. The SBR media resulted in maximum material removal during experimentation, i.e., 3.88 mg when input parameters, i.e., electrolytic voltage, number of extrusion cycles and pressure were taken as 18 V, 4 and 10 bar respectively. The NR, NTR and SR media had intermediate effect of material removal but minimum removal of material was achieved in case of PBS media, i.e., 2.39 mg at 6 V voltage, 6 number of cycles and 30 bar pressure. The material removal was first increased with higher rod size but afterwards its increase was lesser. The surface plots obtained from RSM technique showed that MR obtained was 2.25 mg at 21 bar pressure and 7 number of cycles. As compared to conventional AFM setup, it was found that in EMR-AFM setup, 34.5 % and 17.8 % improvement in % Ra and material removal, respectively, was obtained. It was found that MR was approximately 2.9 mg on an average when machining was done on traditional AFM process, while it increased upto 4.5 mg in prepared hybrid machine setup.

Brittle materials such as silicon, germanium, glass and ceramics are widely used in semiconductor, optical, micro-electronics and various other fields. Traditionally, grinding, polishing and lapping have been employed to achieve high tolerance in surface texture of silicon wafers in semiconductor applications, lenses for optical instruments etc. The conventional machining processes such as single point turning and milling are not conducive to brittle materials as they produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where the material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a comprehensive predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness required to achieve ductile-regime machining. The input to the model includes tool geometry, workpiece material properties and machining process parameters. The fact that the scale of ductile regime machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions. This research would aid in predicting forces and undeformed chip thickness values for micro-machining brittle materials given their material properties and process conditions. The output could be used to machine brittle materials without fracture and hence preserve their surface texture quality. The need for resorting to experimental trial and error is greatly reduced as the critical parameter, namely undeformed chip thickness, is predicted using this approach. This can in turn pave way for brittle materials to be utilized in a variety of applications.

Additive Manufacturing, and specifically powder bed fusion processes, have advanced rapidly in recent years. Selective Laser Melting in particular has been adopted in a variety of industries from biomedical to aerospace because of its capability to produce complex components with numerous alloys, including stainless steels, nickel superalloys, and titanium alloys. Post-processing is required to treat or solve metallurgical issues such as porosity, residual stresses, and surface roughness. Because of the geometric complexity of SLM produced parts, the reduction of surface roughness with conventional processing has proven especially challenging. In this Thesis, two processes, abrasive flow machining and ultrasonic shot peening, are evaluated as surface finishing processes for selective laser melted 316L. Results of these experiments indicate that AFM can reliably polish as-built internal passages to 1 µm Ra or better but is unsuitable for passages with rapidly expanding or contracting cross-sections. AFM can also polish relatively small passages, but lattice components may prove too complex for effective processing. USP cannot achieve such low surface roughness, but it is a versatile process with multiple advantages. Exterior surfaces were consistently processed to 1.7 to 2.5 µm Ra. Interior surfaces experienced only partial processing and demonstrated high geometric dependence. USP significantly hardened the surface, but steel media hardened the surface better than ceramic media did. Both AFM and USP are recommended processes for the surface finishing of SLM manufactured parts. Good engineering judgement is necessary to determine when to use these processes and how to design for post-processing.

Este trabalho discute as alterações micro-estruturais superficiais nos aços usinados por torneamento duro. Uma estrutura não aceita metalurgicamente, chamada de Camada Branca (\"White Layer\" - WL), é freqüentemente encontrada na superfície torneada. A presença desta camada branca depende dos parâmetros do processo de corte, especialmente do desgaste da ferramenta e da velocidade do corte. A formação da camada branca foi investigada no presente trabalho na face plana inferior de um anel de rolamento fabricada com o aço DIN 100Cr6, usinada por torneamento duro no estado temperado e revenido (dureza 60HRC). A profundidade foi medida usando as técnicas padrões metalográficas. As propriedades mecânicas da camada superficial (módulo de rigidez, E, e microdureza Vickers, HV) foram estimadas pelo método de microidentação instrumentada em uma amostra isenta da camada branca e em duas outras amostras, com camadas brancas de diferentes espessuras (respectivamente 7 e 12 mm de espessura). De acordo com a literatura a profundidade da camada branca aumenta de acordo com o desgaste da aresta da ferramenta. Este por sua vez aumenta com a velocidade de corte, mas atinge a saturação. Em outras palavras, a profundidade de corte tem pouco efeito sobre a profundidade da camada branca; porém aumentando o avanço da ferramenta de corte ocorre o aparecimento da mesma. Os presentes resultados confirmam um efeito do avanço da ferramenta sobre a espessura da WL, tal que quanto menor o avanço, maior é a espessura, porém não confirmam o efeito do desgaste da ferramenta. A formação desta camada é discutida no contexto da sua influência sobre a rugosidade das peças.
This work deals with the microstructural changes in the surface of steels machined by hard turning. A non-acceptable microstructure, called White Layer - WL, is usually found in the hard turned surface. The presence of the white layer depends on hard turning parameters, especially on the wear of the machining tool and cutting speed. The formation of the white layer was investigated in the present work by hard turning the inferior face of a roller-bearing ring fabricated with DIN 100Cr6 steel quenched and tempered (60 HRC hardness). The depth of the WL was measured by standard metallographic procedures. The mechanical properties (stiffness modulus, E, and Vickers hardness) of the surface layer were measured by intrumented indentation in three samples: one with no WL, and two containing a WL of respectively 7 and 12 mm. According to the literature the depth of the WL increases with the wear of the machining tool. This increased with cutting speed, but reaches saturation. The presentresults confirm an effect of tool advance upon the depth of the WL, such that decreasing the advance leads to an increase in its depth, but an effect of tool wear could not be recognized. The formation of the WL is discussed in the context of its effect on surface roughness.

Orientador: Anselmo Eduardo Diniz
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica
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Resumo: Normalmente, a utilização de aços ferramenta endurecidos, juntamente com as formas complexas típicas das peças utilizadas na área de moldes e matrizes, oferecem dificuldade na usinagem por fresamento, principalmente nas operações de acabamento que exijam o uso de ferramentas longas. A técnica de fresamento HSM (High Speed Machining - usinagem em altas velocidades, ou ainda High Speed Milling - fresamento em altas velocidades) tem se tornado uma alternativa para realizar este tipo de usinagem, reduzindo, ou às vezes até eliminando operações de eletro-erosão e polimento. Tipicamente, as fresas de pastilhas de metal duro intercambiáveis tem sido usadas em operações de desbaste e semi-acabamento, enquanto nas operações de acabamento ou em usinagem de geometrias que exijam ferramentas com pequenos diâmetros ainda predomina o uso de fresas inteiriças. O objetivo principal deste estudo é avaliar a influência de cinco variáveis de processo de fresamento com alta velocidade de corte, sobre o acabamento da superfície usinada. A influência do desgaste das ferramentas sobre o acabamento superficial, ao longo de 400 minutos de usinagem, também foi avaliado, além de uma comparação entre ferramentas inteiriças de metal duro e ferramentas de pastilha intercambiável montada em corpo de metal duro, a fim de avaliar a viabilidade técnica do uso deste segundo tipo de ferramenta, em substituição às tradicionais fresas inteiriças utilizadas em operações de acabamento. Na maioria dos experimentos realizados, pequenos valores de rugosidade foram mantidos, demonstrando que operações de acabamento em aço ABNT H13 IM com dureza de 50 HRC é possível com vida longa de ferramenta, mesmo utilizando-se valor de 500 m/min para velocidade de corte. Além disto, a análise da influência das variáveis de processo utilizadas neste trabalho mostrou que é possível, sob algumas condições, utilizar tanto ferramentas inteiriças, quanto de pastilha intercambiável montada em corpo de metal duro em operações de acabamento
Abstract: Typically, the use of hardened tool steels, along with complex shapes typical of the parts used in the field of molds and dies, offer difficulty in machining by milling, mainly in finishing operations that demand the use of long tool. The HSM (High Speed Machining or High Speed Milling) has become a possible alternative for making this type of machining, reducing, or sometimes eliminating electric discharge machining and polishing operations. Usually, indexable carbide insert mills has been used for roughing and semi-finishing, while in finishing operations or when the machining geometries that require tools with small diameters the integral tools are used yet. The main objective of this study is to evaluate the influence of five process variables, with high cutting speed, on the finish of the machined surface. The influence of tool wear on surface finish through 400 minutes of milling was also evaluated, as well as a comparison between integral carbide mills and indexable insert mounted at cemented carbide toolholder endmills, in order to evaluate the technical feasibility of using this second type of tool, replacing the traditional integral carbide endmills used in finishing operations. In most experiments, small roughness values were maintained, showing that finishing operations on AISI H13 IM with a hardness of 50 HRC is possible with long tool life, even using the cutting speed of 500 m/min. Furthermore, the analysis of the influence of process variables used in this study showed that is possible, under some conditions, the use either integral carbide tools, or indexable insert mounted at cemented carbide toolholder endmills on finishing operations
Mestrado
Materiais e Processos de Fabricação
Mestre em Engenharia Mecânica

The Master‘s thesis focuses on processing of hard-to-machine materials by the finishing machining methods. The first chapter comprises division and characteristics of finishing technologies in the field of machining processes. The chapter following includes division and characteristics of the hard-to-machine materials. The experimental part – another significant part of the thesis – is focused on grinding of mostly bearing rings made of hard-to-machine materials. The aim of the experimental part is to compare and subsequently assess the use of various kinds of grinding wheels in the grinding process of a given workpiece material. Several parameters are examined from the technological and economic point of view. The assessment of the experimental part provides an overview on the advantages and disadvantages of the use of the grinding wheels in the grinding process of a given material for large-scale production. The conclusion is a summary of the results obtained in the experimental part.

L'étude présentée dans ce mémoire se focalise sur l'usinage de moules en matériaux composites, en considérant les problèmes d'état de surface et de gamme d'usinage. Les pièces de structure aéronautiques peuvent être obtenues par les procédés de fabrication de la famille LCM (Liquid Composite Molding). Ce procédé impose une température de fonctionnement élevée qui conduit à une dilatation du moule néfaste à la qualité de la pièce injectée. Pour remédier à ce problème, il est nécessaire de réaliser l'outillage dans un matériau à faible dilatation ou se comportant comme le matériau injecté. Pour cela, un matériau composite (Hextool™) est proposé en remplacement des moules métalliques conventionnels. L'étape d'usinage de forme est indispensable car elle donne les dimensions finales de l'outillage et conditionne le temps de polissage manuel nécessaire pour atteindre la rugosité arithmétique visée. Ce travail propose deux voies d'amélioration à travers l'étude micro-géométrique de l'opération de finition par outil coupant puis par outil abrasif. La première voie met en évidence l'existence d'une valeur minimale de rugosité accessible lors d'un usinage avec un outil coupant. L'analyse de ce phénomène permet de proposer une valeur de prise de passe radiale optimisant le ratio rugosité du moule / temps d'usinage. La deuxième conduit à la définition d'un outil abrasif utilisable sur un centre d'usinage. La faisabilité d'une telle opération et les capacités de cette technologie innovante sont discutées. Enfin, le choix des outils, des stratégies d'usinage et de la machine outil sont discutés et aboutissent à la proposition d'une gamme de référence pour l'usinage d'ébauche et de finition de moules en matériaux composites.

This eleborate study is aimed at analysis of complete methods machining. There are characterized particular methods and their effect on the surface´s quality of machined area in this study. Concluding part of the study includes practical demonstration of machining by using cemented carbide-tipped tool and polycrystalline diamond and evaluation of this demonstration.

La Fabrication Additive Arc-Fil (Wire Arc Additive Manufacturing) est une technologie de fabrication qui utilise du fil métallique comme matière première et un arc électrique comme source d’énergie. Le fil est déposé à une vitesse prédéfinie et fusionné grâce à l'arc électrique, soit sur un substrat, soit sur une couche préexistante. Cette recherche se concentre sur l'utilisation du procédé Cold Metal Transfer (CMT) appliqué à l'acier inoxydable austénitique 316L. Bien que cette technologie soit couramment employée avec succès pour la réparation, le défi actuel réside dans la production en série de pièces fonctionnelles, nécessitant ainsi la résolution de problèmes de conception et de fabrication spécifiques.Le premier objectif de cette thèse est d'évaluer l'impact des paramètres du procédé, en particulier la vitesse d'avance et le temps d'inter-passe, sur les dimensions, la qualité de surface des pièces et sur le parachèvement par usinage. Pour ce faire, un plan d'expériences a été mis en place, impliquant la fabrication de murs multicouches et multi cordons sur un substrat monté sur un support en aluminium. Ensuite, une face de chaque mur fabriqué a été usinée afin de déterminer la profondeur d'usinage nécessaire pour obtenir une surface exempte d'ondulations, et d'analyser la rugosité de surface ainsi que la dureté de ces zones. Enfin, une nouvelle méthode de recouvrement a été développée.Le deuxième objectif consiste à exploiter les résultats obtenus pour développer des méthodes et des règles permettant de passer de la conception 3D à la réalisation d'une pièce finale. Ces méthodes s’appuient sur une phase de fabrication additive et une phase de parachèvement par usinage. Ce processus vise à éliminer les dispersions géométriques et d’état de surface inhérentes au procédé WAAM, à déterminer la surépaisseur d’usinage nécessaire, et à intégrer les problématiques liées aux contraintes générées par le procédé primaire.Le dernier objectif est de comprendre les mécanismes de génération des contraintes résiduelles et des déformations induites par le procédé primaire. Pour ce faire, une modélisation thermomécanique du procédé a été développée. Elle a mis en évidence l'influence de la vitesse d'avance et du temps d'inter-passe sur le comportement thermomécanique
Wire Arc Additive Manufacturing is a manufacturing technology that uses metal wire as the raw material and an electric arc as the energy source. The wire is deposited at a predefined rate and fused by the arc, either onto a substrate or onto a pre-existing layer. This research focuses on the use of the Cold Metal Transfer (CMT) process applied to austenitic 316L stainless steel. While this technology is widely and successfully used for repair, the current challenge lies in the mass production of functional parts, requiring the resolution of specific design and manufacturing issues.The first objective of this thesis is to evaluate the impact of process parameters, in particular travel speed and interpass time, on part dimensions, surface quality and machining finish. To accomplish this, a design of experiments was set up, involving the manufacture of multi-layer, multi-bead walls on a substrate mounted on an aluminum support. Next, one face of each fabricated wall was machined to determine the machining depth required to achieve a waviness-free surface, and to analyze the surface roughness and hardness of these areas. Finally, a new overlapping method was developed.The second objective is to use the results obtained to develop methods and rules for moving from 3D design to the production of a final part. These methods rely on an additive manufacturing phase and a machining finishing phase. This process aims to eliminate geometric and surface finish variations inherent to the WAAM process, determine the necessary machining allowance, and incorporate issues related to the primary process.The final objective is to understand the mechanisms behind the generation of residual stresses and deformations induced by the primary process. To achieve this, a thermomechanical modeling of the process was developed, highlighting the influence of Travel speed and interpass time on the thermomechanical behavior

碩士
華梵大學
機電工程研究所
90
A new internal magnetic-abrasive machining process of the 6061-T6 aluminum alloy rectangular tube is developed and investigated. In this study, a new finishing apparatus and auxiliary fixtures are designed and developed to simulate the internal finishing process, the magnetic abrasive particle that the finishing ability abrasive grains (Al2O3) are sintered with a ferromagnetic substance (iron powder) by hot pressed, and, the working parameters and their finishing performances are investigated and reported. The Taguchi-Method is adopted for the experimental plan, magnetic field strength, quantity of magnetic abrasives, particle size of magnetic abrasives, rotating speed of magnetic pole, feed rate, vibration frequency, vibration amplitude and the coolant are to be used as the control parameters, internal surface finishing performances, such as the stock removal, the polishing efficiency, and the surface roughness, are studied and verified experimentally. In the present case, by applying the optimal working conditions, a 19.33mg stock removing and 1.91mg/min optimal polishing efficiency were found, and the surface roughness was improved from Ra 0.52mm、Rz(DIN) 2.8mm to Ra 0.09mm、Rz(DIN) 0.66mm. In this paper, the effects of some major parameters on the surface finishing performances are also clarified experimentally.

碩士
國立臺灣大學
機械工程學研究所
99
Surface quality of machined products do not only determines the appearance of the products, but also determines the features of products. Novel three-axis milling CNC machines have advantages of high efficiency, high flexibility, high rigidity and high accuracy. Therefore, improving the efficiency and quality of the surface finishing by using three-axis CNC milling machine is a essential issue. This study will use a three-axis CNC milling machine to research the finishing oblique surface and curved surface. Considering the toolpath stepover, stepdown, height of scallop, spindle speed, cutting speed, feed rate, tool radius, slope gradient, radius of curvature, end mills and ball end mills effect on the machined surface. The experimental results show that feed rate and spindle speed effect surface roughness in the feed direction. The scallop is caused by toolpath and tool radius, and effect surface roughness in cross feed direction. Ball end mills is easier than end mills to get low surface roughness in oblique surface finishing. Furthermore, the surface roughness of oblique in feed direction made by contour toolpath is better than parallel toolpath. For curved surface finishing, using ball end mills with parallel toolpath will produce surface waviness caused by small shape errors of tool. Surface waviness is related to radius of curvature, and can be removed by second processing.

碩士
國立中央大學
機械工程研究所
100
With the development of micro machining or measurement technology, the demand for micro-spherical tools or probes such as using for micro-hole machining, coordinate measuring machine (CMM) and chip test has been rapidly increasing. Electrochemical micro machining (ECMM) is one of nonconventional micromachining processes; its material removal is an anode electrochemical dissolution process. The anodic electrochemical dissolution occurs when a voltage is applied between anode and cathode placed in electrolyte. This paper demonstrates a finishing process using ECMM (ECMF) to build an accurate and smooth micro-spherical tungsten electrode. A micro tungsten electrode is made by several processes including wire electro-discharge grinding (WEDG), electric discharge machining (EDM) spherical forming, and ECMF. The influence of ECMF parameters on the EDMed surface and tool diameter is presented. The experimental result shows a smooth micro-spherical tungsten electrode can be successfully finished and brightened with suitable ECMF parameters that are a voltage of 16 V, electrolyte concentration of 2 wt% and machining time of 0.5 second. When using this method, not only the micro tungsten electrode has a smooth surface and but also its diameter can be fine-tuned to get the high accuracy via the machining time control. Finally, the electrode is tested to drill a micro hole to compare with the machining performance by using conventional cylindrical electrode.

Abrasive flow machining is a nontraditional finishing process and is used to polish metallic components, internal inaccessible cavities or recesses using a semi liquid paste. It was developed to deburr, polish, and radius surfaces having complex geometries and edges by flowing abrasives with a viscoelastic polymer (called as media) over them. Abrasion occurs wherever the medium passes through the highly restrictive passage. In this work, two way abrasive flow machining is used to optimize the material removal and % improvement in surface roughness on brass material. In this study three parameter are used level of carbon nano tube, level of pressure, number of cycle. The abrasive media is formed with the combination of polymer and gel, abrasive particle and carbon nano tube (CNT). Polymer is made with the help of some chemical like as silicon oil , boric acid and ferric chloride (FeCl3.6H2o) and ammonia carbonates (NH4CO3). This media is mixed with the level of CNT and experiment is conducted on brass work-piece. Three process parameter level of CNT, Extrusion pressure and Number of cycle have been used for experiment to study the effect of these process parameter on % improvement in surface roughness and material removal of brass work-piece. L9 orthogonal array based on Taguchi method has been used to study the effect of various process parameter on selected on response parameter. All three parameter affects the material removal and surface finish, by using level of CNT material removal continuosly increased among other parameter while surface roughness is improved up to second level after decreases. In case of No of cycle from first level to second level material is decreased after that increased but for surface roughness improvement is little bit significant. Third parameter extrusion pressure have little bit significant on MR but highly significant for surface roughness improvement. Effect of CNT on material removal is continuosly increases. The percentage contribution of CNT is 14.98%.and the effect of other parameter on MR are percentage contribution of Extrusion pressure is 15.56% and the percentage contribution of Number of cycle is 21.22%. Optimum level is selected for material removal is C3 P1 N3. Effect of CNT on improvement on surface finish the percentage contribution of CNT is maximum is 23.84%.The percentage contribution of number of cycle is 23.14% and extrusion pressure which contribute 15.90%.

碩士
修平科技大學
精密機械與製造科技碩士班
106
This research presents the finishing grinding process for the surface processing of Bolt of Inconel 718 Nickel base alloy. Feed rate and grinding depth, types of grinding wheels, grinding fluid used as the processing parameters to observe the processing characteristics, such as machined surface and surface texture, chip. Using the response surface method (RSM) to generate second order mathematical module explained the relationship between the processing parameters and quality characteristics. The results show the higher feed rate, lower grinding depth and using grinding fluid to reduce the surface roughness values and to obtain better surface quality. The lower toughness and higher the hardness and grin size of wheel is more suitable for milling Inconel 718 nickel-based alloys, and using the grinding fluid minimizes the surface roughness value. Optimum processing parameters obtain its optimal surface roughness values compared with the initial surface roughness values reduced 62.2%.