Cutting tool edges are honed to an edge radius of about 15-30 micrometers for enhancing tool performance. During honing, defects left by prior manufacturing processes such as grinding and pressing are removed to achieve a higher quality edge. Recently, researchers have shown that tailoring the edge microgeometry to comprise an asymmetric shape and/or a gradient edge microgeometry is beneficial. Conventional edge honing processes such as brush honing and abrasive micro-blasting are limited in terms of reliably generating such geometries in a productive manner. To this end, this research explored the application of non-Newtonian aqueous suspensions of cornstarch and abrasives, for the edge honing of cutting tools. This thesis details the science, technology, characteristics and capabilities of this innovative process. / Thesis / Master of Applied Science (MASc)

Le procédé de rodage par pierres abrasives est actuellement utilisé pour produire en grande série des chemises de carter cylindre avec des propriétés fonctionnelles spécifiques. La qualité de forme, la rugosité et l'aspect des surfaces ainsi rodées déterminent grandement les performances mécaniques et écologiques des moteurs. Le processus de rodage, mécaniquement complexe, fait intervenir des machines complètement dédiées et optimisées pour les rodages classiques. Après une étude détaillée des machines de production actuelles, de leurs performances et de leurs limites, l'objectif de recherche de flexibilité du procédé pour l'industriel Renault s'est traduit par deux développements : une modélisation de l'abrasion avec une simulation du procédé pour mieux le comprendre et la conception d'un prototype de machine de rodage à hautes performances pour tester d'autres méthodes de rodage.La simulation est basée sur la double discrétisation de l'espace-et du temps et sur un modèle de coupe original. La discrétisation de l'espace permet de représenter à une échelle macroscopique le rodoir et la pièce à usiner et de tenir compte des contacts locaux entre eux. Les propriétés microscopiques et mésoscopiques de la surface rodée sont étudiées à cette échelle. La discrétisation temporelle autorise la prise en compte de la cinématique de la machine. Le modèle de coupe repose sur l'interaction des courbes de portance du rodoir et de la chemise. Son exploitation au niveau macroscopique permet de prédire l'enlèvement de matière, la force de contact locale ainsi que l'aspect de la surface rodée et leurs évolutions au cours du rodage. Cette simulation est validée par de nombreuses expériences.Ce document présente la conception, la réalisation et la mise au point d'un prototype de machine de rodage avec des actionneurs électriques à performances dynamiques élevées. Une commande numérique permet le pilotage synchronisé de la rotation et du battement et autorise l'interpolation de trajectoires. L'expansion radiale peut être pilotée en position ou en force. Nous avons proposé de nouvelles trajectoires originales dans l'objectif d'augmenter la productivité du procédé et dans le but de générer de nouvelles textures. / The honing process with abrasive stones is currently used to mass produce the liners cylinder block with specific functional properties. The quality of shape, the roughness and the textural appearance of honed surface determine the mechanical performance and ecological engines. The honing process is mechanically complex and involves machines completely dedicated and optimized for classical honing operations. After a detailed study of current production machines, their performance and their limitations, the research goal of flexible process for industrial Renault has led to two developments: a model of the abrasion with a process simulation to better understand and design of a prototype machine with high performance to test other methods of honing.The simulation is based on a space-time discretization and an original model of stock cutting. The space discretization is used to represent a macroscopic scale the honing tool and the workpiece and to take into account local contacts between them. Microscopic and mesoscopic properties of the honed surface are studied at this level. Time discretization allows taking into account the kinematics of the machine. The cutting model is based on the interaction of the bearing area ratio curves of the honing tool and the liner. Operation at the macroscopic level predicts the removal of material, the contact force and the local aspect of the honed surface and their changes during the operation. This simulation is validated by numerous experiments.This paper presents the design, the implementation and the development of a prototype machine with electric actuators for high dynamic performance. A digital controller allows the synchronized control of the rotation and stroke to allow trajectories interpolation. The radial expansion can be controlled in position or force. We proposed new original trajectories in the objective of increasing the productivity of the process and to generate new surface textures.

<p>This thesis presents the proof-of-concept of electro-erosion edge (EE) honing as a novel edge preparation process that is based on micro-shaping of the cutting edges of metal cutting tools by electro discharge machining (EDM). This process in its simplest form is first applied to straight edge high speed steel cutting tools which results in a four-fold enhancement in the lives of these tools as compared to the sharp unprepared ones. In the next step the EE-honing application is expanded to hone carbide tools of a complex geometry through the innovative idea of using foil counterfaces. Foil counterface ensures the uniform processing of the entire edge length irrespective of macrogeometric complexities such as curvilinear cutting edges and nose radii. By employing this technique, cutting tools of a complex geometry can be prepared with only 13% edge radius variation which is significantly lower than 40% variation reported for conventional edge preparation processes. ED-machining of cemented carbides necessitates the systematic identification of optimal process parameters to preserve process stability and surface integrity. It is shown that by the application of optimal EE-honing process parameters, EE-honed tools achieved the same life of conventionally prepared ones with the same radii. The advent of advanced edge preparation techniques like EE-honing process has led to the emergence of engineered cutting edge microgeometries most of which cannot be represented by a single edge radius value. In this regard, a novel idea of using parametric quadratic curves for comprehensive cutting edge characterization is presented in the next part of this thesis. The free-knot B-spline approximation enables the unique identification of cutting edge separation points from the clearance and rake faces. Subsequent to the edge identification, quadratic parametric polynomials are employed to characterize the cutting edge by four characterization parameters. These parameters are contour-based and easy to visualize. As the final part of the thesis, the EE-honing process is simulated numerically to gain a better insight into the process. Simulation can model the generation of symmetrical and asymmetrical edges and predict edge geometry with the maximum of 14% error.</p> / Doctor of Philosophy (PhD)

Internal combustion (IC) engines used in road transport applications employ pistons to convert gas pressure into mechanical work. Frictional losses abound within IC engines, where only 38- 51% of available fuel energy results in useful mechanical work. Piston-bore and ring-bore conjunctions are fairly equally responsible for circa 30% of all engine friction - equivalent to 1.6% of the input fuel each. Therefore, reduction in piston assembly friction would have a direct impact on specific performance and / or fuel consumption. In motorsport, power outputs and duty cycles greatly exceed road applications. Consequently, these engines have a shorter useful life and a high premium is placed on measures which would increase the output power without further reducing engine life. Reduction of friction offers such an opportunity, which may be achieved by improved tribological design in terms of reduced contact area or enhanced lubrication or both. However, the developments in the motorsport sector are typically reactive due to a lack of relative performance or an ad-hoc reliance, based upon a limited number of actual engine tests in order to determine if any improvement can be achieved as the result of some predetermined action. A representative scientific model generally does not exist and as such, investigated parameters are often driven by the supply chain with the promise of improvement. In cylinder investigations are usually limited to bore surface finish, bore and piston geometrical form, piston skirt coatings and the lubricant employed. Of these investigated areas newly emerging surface coatings are arguably seen as predominate. This thesis highlights a scientific approach which has been developed to optimise piston-bore performance. Pre-existing methods of screening and benchmarking alterations have been retained such as engine testing. However, this has been placed in the context of validation of scientifically driven development. A multi-physics numerical model is developed, which combines piston inertial dynamics, as well as thermo-structural strains within a thermoelastohydrodynamic tribological framework. Experimental tests were performed to validate the findings of numerical models. These tests include film thickness measurement and incylinder friction measurement, as well as the numerically-indicated beneficial surface modifications. Experimental testing was performed on an in-house motored engine at Capricorn Automotive, a dynamometer mounted single-cylinder 'fired' engine at Loughborough University, as well as on other engines belonging to third party clients of Capricorn. The diversity of tests was to ascertain the generic nature of any findings. The multi-physics multi-scale combined numerical-experimental investigation is the main contribution of this thesis to knowledge. One major finding of the thesis is the significant role that bulk thermo-structural deformation makes on the contact conformity of piston skirt to cylinder liner contact, thus advising piston skirt design. Another key finding is the beneficial role of textured surfaces in the retention of reservoirs of lubricant, thus reducing friction.

Orientador: Amauri Hassui / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-26T13:17:57Z (GMT). No. of bitstreams: 1 Araujo_GilbertodeLima_M.pdf: 4592521 bytes, checksum: 2e679dc1a192c0f7897695fb43c81107 (MD5) Previous issue date: 2014 / Resumo: Os processos de brunimento visam buscar precisão de usinagem mais acentuada em superfícies cilíndricas, principalmente em diâmetros internos, em que tais tolerâncias não podem ser obtidas por um processo de retificação cilíndrica. As operações anteriores deste processo também contribuem na qualidade final em termos de obtenção de características geométricas mais precisas. A determinação dos parâmetros de corte de usinagem, o tipo de ferramenta, neste caso a pedra de brunimento ou brunidor, as condições de fixação da peça a ser usinada e o fluido de corte também afetam tais requisitos de especificação geométrica no produto final. Quando as especificações do produto em erros de forma de circularidade e retilineidade demandam valores abaixo de 0,001mm e rugosidade média máxima de 0,10 µm Ra, para sua produção seriada é necessário a realização de uma operação complementar de lapidação, que em muitas aplicações são manuais e utilizam pastas de difícil remoção na superfície da peça. O presente trabalho busca estudar as operações de brunimento e lapidação, tendo como objetivo: realizar experimentos em busca de alternativas de processo para substituir a operação de lapidação diretamente pelo brunimento de precisão, aplicado em aços-liga de alta dureza. Como resultado final, obter erros de forma estatisticamente aceitáveis em produção seriada, inferiores à 0,001mm e rugosidade média abaixo de 0,10 µm Ra, através de experimentos planejados de todo sistema máquina e ferramenta. Os primeiros ensaios comprovaram a forte influência da baixa granulometria dos brunidores na rugosidade da peça, alcançando valores similares ao da lapidação. Os demais ensaios mostraram que a rotação do fuso da brunidora e o avanço dos brunidores em valores baixos, nos limites inferiores dos que foram definidos nos ensaios, proporcionaram melhores características geométricas de circularidade e retilineidade. A estabilidade dimensional do diâmetro da peça também foi melhorada nestas condições. A conclusão desta pesquisa foi de que é possível substituir uma operação de lapidação pelo brunimento de precisão. Palavras Chave: Brunimento, brunidor, brunidora, lapidação, circularidade, retilineidade, rugosidade / Abstract: Honing process is used when a high precision machining is required to correct bore errors on a cylindrical surface, mainly in internal diameters, which is more accurate than grinding process. The operations carried out before honing affect directly the final quality in order to achieve tighter tolerances. The specification of the cutting parameters, such as the tool type, in this case the honing stone, the fixturing condition and the honing coolant affect the geometric results on the final product. In some products applications when roundness and straightness specification is very tight, around or less than 0,001mm and surface finishing of 0,10 ?m Ra maximum, it is necessary a complementary operation of lapping, which is manual and uses the lapping paste, difficult to remove from the piece surface. The objective of this research is to analyze the behavior of the above parameters on precision honing process for hardened steels and suggest process alternatives to achieve the above tolerances directly from honing without lapping. The results must be statistically accepted in production environment by planned experiments in the machine and tooling system. The experiments confirmed the influence of lower honing stones grit size in the roughness quality and it was achieved equivalent surface from the lapping operation. In addition, it was demonstrated that lower spindle speed and stones feedrate figures, in the bottom limit from the range adopted in the trials resulted in a better geometry quality in the roundness and straightness. Also the diameter capability improved with this cutting condition. The conclusion of this research was that it is possible to replace a lapping operation to a precision honing. Keywords: Honing, honing stones, honing machine, lapping, cylindricity, roundness, straightness, surface finishing / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

No description available.

Le rodage mécanique demeure encore le procédé industriel de référence pour la finition des cylindres de moteurs dans le cadre des productions de grande série. La voie actuelle de fabrication en rodage procède par frottement et abrasion à vitesse réduite pour imprimer une texture anisotrope et multi-échelle sur la surface du cylindre. La signature de cette texture a la particularité de satisfaire des exigences multifonctionnelles du cylindre (frottement, lubrification, usure, consommation d'huile, etc.). Elle est cependant générée par un rodage stratifié en production industrielle qui consiste en trois étapes successives avec effet d'échelle: ébauche (échelle macroscopique), finition (échelle mésoscopique) et superfinition (échelle microscopique). Plusieurs méthodes de rodage ont émergé cette dernière décennie et dont la différentiation technologique et économique se fait essentiellement par le choix des attributs texturaux et topographiques de surface de rodage. La présente étude analyse les processus de rodage industriel, du choix d'anisotropie possibles et paramètres texturaux dans une optique de fonctionnalisation de la surface rodée du cylindre. Une approche méthodologique sur la tribo-fonctionnalité multi-échelle de la surface de rodage du cylindre a été développée, puis validée par simulation numérique dans le cas du tribo-contact segment-cylindre. Elle s'appuie sur le triptyque suivant :- le couplage entre le processus de rodage et la fonctionnalité via la caractérisation de sa signature texturale multi-échelle,- l'exploitation de l'anisotropie contrôlée par simulation numérique qui conduit à la texture de fonction,- l'interaction surface – procédé de rodage qui devient indissociable, notamment dans la fabrication de la texture de fonction et sa qualification tribo-fonctionnelle par des essais tribométriques.Cette démarche méthodologique a été appliquée aux procédés de rodage industriel tel que le rodage plateau (PH), glissant (SH) et hélico-glissant (HSH). Cela a permis de démontrer qu'une texture anisotrope fine de type PH composée de plateaux et vallées de faible amplitude présente les meilleurs attributs fonctionnelles en frottement. Cependant, une texture anisotrope de type HSH avec un angle de striation de 130° est moins sensible en frottement à l'aspect plateau obtenu par écrêtage des pics de rugosité. Ce résultat ouvre une évolution potentielle du process HSH où la dernière étape de rodage peut être réduite voire supprimée. Par la suite, la démarche développée a été étendue aux textures innovantes à bas frottement de rodage en développement avec une anisotropie circulaire, ondulatoire, stratifiée mixte, ou assistée en trajectoire. Les résultats ont montré que des textures HSH optimisées en trajectoire (avec suppression de stries d'inversion au niveau des points mort haut (PMH) et point mort bas (PMB) du cylindre) ainsi que des textures stratifiées mixtes 45°-130°-45° (stries à 45° au PMB et PMH et 130° au milieu du cylindre) permettent une réduction significative du frottement segment-fût en régime de lubrification mixte en comparaison par rapport au texture de rodage HSH conventionnel. / Mechanical honing process is still the reference industrial process for high production engine liners. The current manufacturing way use reduced velocity friction and abrasion mechanisms to print a multiscale and anisotropic texture on the liner surface. The texture signature characteristics satisfy multifunctional requirements of the liner (friction, lubrication, wear, oil consumption etc.). It is generated by a stratified honing process for industrial production which consists of three stages with scale effect: rough (macroscopic scale), finish (mesoscopic scale) and super-finish honing (microscopic scale). Different honing methods emerged during last decade in which the technological and economic differentiation is essentially based on textural attributes of honed surfaces. The present study analyses the industrial honing processes, the possible surface anisotropy choices and texture parameters with a view to honed liner surface functionalisation. A methodological approach about multiscale honed surface tribofunctionality has been developed and then validated by numerical simulation in the case of ring-liner tribocontact. It builds on the following triptych:- the coupling between honing process and functionality through its multiscal textural signature,- the exploitation of the controlled anisotropy by numerical simulation which conducts to fonctionality,- the surface-process interaction which becomes indivisible, particularly in texture manufacturing and its tribofunctional qualification though tribometric trials.The methodology has been applied to industrial honing processes (plateau honing (PH), slide honing (SH) and helical slide honing (HSH)). The results show that smooth texture with lower plateau roughness and valley depth contributes to reduce frictional performances of honed surfaces. Nevertheless, Helical slide honed surfaces are less sensitive in friction to the plateaudness i.e., to superficial roughness comparatively to PH textures. This is promising for HSH process optimization, in which the third stage can be reduced or deleted. Then the developed approach has been extended to honing development for innovative texture anisotropy (circular, undulatory, mixed, trajectory assisted) for low-friction performances. The results show that assisted trajectory (without inversion grooves at top dead (TDC) and bottom dead centers (BDC)) and 45-130-45 mixed textures (with 45° cross-hatched grooves at TDC and BDC, 130° cross-hatched grooves at mid-height) enhance significantly frictional performances in comparison to HSH conventional process.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The purpose of this work is to evaluate the geometrical and dimensional quality of block cylinders used in hermetic compressors machined by conventional and flexible honing. The conventional honing was done by EMBRACO, while the flexible honing was conducted at Federal University of Uberlândia using a CNC mill and a flexible honing which consists of a metal rod and nylon bristles with abrasive lobes at the ends. The evaluation of geometrical and dimensional quality was done by the measurement of: i) the cylinder diameter using a three coordinates measuring machine and a micrometer, ii) the circularity and cylindricity deviations using a shape deviation measuring machine and iii) the roughness (Ra, Rq, Rt, Rsk, Rku, Rk, Rpk e Rvk) using a electromechanical rugosimeter and a interferometer. For each measurand, it was estimated the related measurement uncertainty using the GUM methodology except for the roughness, where the Monte Carlo method was applied. The results showed that the flexible burnishing provides a significant improvement of the values of roughness parameters and the circularity deviation, while diameter values remained nearly constant. The flexible burnishing reduces the peak heights and eliminates the isolated occurrence of those without modify the valley depths, so providing improvements in proprieties such as surface softening, lubricant retention, mechanical strength and capacity to withstand loads in contact operations, meeting the desired tolerances. / O objetivo deste trabalho é avaliar a qualidade dimensional e geométrica de cilindros de blocos de compressores herméticos usinados pelo brunimento convencional e flexível. O brunimento convencional foi realizado pela EMBRACO, enquanto o brunimento flexível foi realizado na Universidade Federal de Uberlândia utilizando uma fresadora CNC e um brunidor flexível que é composto por uma haste metálica e cerdas de nylon com lóbulos abrasivos nas pontas. A avaliação da qualidade dimensional e geométrica foi efetuada por meio da medição do diâmetro do cilindro utilizando uma máquina de medir a três coordenadas e um micrômetro, dos desvios de cilindricidade e de circularidade por meio de uma máquina de medir desvios de forma e da rugosidade (Ra, Rq, Rt, Rsk, Rku, Rk, Rpk e Rvk), utilizando um rugosímetro eletromecânico e um interferômetro. Para cada mensurando foi estimada sua respectiva incerteza de medição, aplicando a metodologia proposta no GUM, exceto para a rugosidade, que foi utilizado o Método de Monte Carlo. Os resultados indicaram que o processo de brunimento flexível proporciona uma melhoria significativa dos valores dos parâmetros de rugosidade e do desvio de circularidade, enquanto que os valores de diâmetro permaneceram praticamente constantes. O brunimento flexível reduz a altura dos picos e elimina a presença isolada destes sem alterar a profundidade dos vales, proporcionando melhorias nas propriedades de amaciamento da superfície, retenção de lubrificante, na resistência mecânica e na capacidade de suportar cargas em operações de contato, atendendo as tolerâncias desejadas. / Mestre em Engenharia Mecânica

O presente trabalho discute a influência da microestrutura dos ferros fundidos, cinzento (FFC) e vermicular (FFV), na ocorrência de metal dobrado (FM) em superfícies brunidas e no comportamento tribológico em ensaio lubrificado do tipo anel sobre cilindro. As amostras de ferro fundido foram extraídas diretamente de um bloco de motor de combustão interna, em regiões de diferentes espessuras. O anel de pistão utilizado foi de aço inoxidável martensítico nitretado com perfil assimétrico e o óleo lubrificante foi o SAE 30 CF monoviscoso. A quantificação de sulcos e de metal dobrado (FM) foi realizada empregando-se uma metodologia baseada na literatura. Para a execução dos ensaios tribológicos foi projetada e construída uma adaptação para a montagem das amostras e controle de temperatura do óleo lubrificante. Um parâmetro para avaliação do desempenho tribológico foi proposto – índice de mérito tribológico (IMT) – que leva em conta coeficiente de atrito (COF) e alterações de topografia. Os ferros fundidos apresentaram microestruturas típicas. Contudo, observaram-se diferenças de morfologia e distribuição da grafita; com maior número de grafitas e menor fração de grafita para os materiais de parede fina. Observou-se FM nos platôs e nos sulcos das superfícies brunidas em todas as amostras. Quantificações mostraram que as larguras dos sulcos foram estatisticamente iguais e com alto percentual de obstrução. A quantificação de FM dos materiais mostrou maiores valores presentes na região do Spk (FMspk) para os FFC's. Os materiais de parede grossa apresentaram maiores valores de % FM dentro do sulco (%FM/Sulco) e este parâmetro teve forte e positiva correlação estatística com a fração de grafita. Evidências, obtidas em avaliações de seções transversais, corroboraram a relação entre FM e grafita. Constatou-se que o FM pode ser formado diretamente sobre a grafita ou, ainda, de forma indireta devido à extrusão desta fase. Ademais, verificou-se que a morfologia e orientação da grafita têm influência na formação do FM. Realizaram-se ensaios preliminares de curta duração de anel sobre cilindro para a avaliação da repetibilidade dos resultados de COF, os quais indicaram menor dispersão para condições com menores frequências e maiores forças normais. Avaliações da dinâmica do ensaio tribológico permitiram apontar relações de redução de COF durante os semi-ciclos de movimento e associá-las à teoria de lubrificação hidrodinâmica. O COF para ensaios de longa duração apresentou comportamento cíclico com transições. Estas transições foram associadas a mecanismos de formação-remoção-formação de tribofilmes de ZDDP. Os ensaios impuseram alterações nos parâmetros de rugosidade (principalmente com alisamento das superfícies) e redução do parâmetro de filme. O IMT evidenciou pouca influência da espessura do material; e melhor desempenho tribológico para os FFV's. A rotina de quantificação de FM mostrou limitação técnica devido ao alisamento da superfície, o que causa mudança na referência de alturas das superfícies brunidas. Ainda assim, verificou-se redução do %FM/Sulco e tendência de desobstrução do sulco. Contatou-se pouca influência do FM no comportamento do COF devido à similaridade dos parâmetros de FM entre os materiais. Contudo, o FM foi associado a um agente de abrasão à três corpos e apresentou forte correlação positiva do parâmetro de FMspk (no início do ensaio) com o parâmetro do IMT relacionado com a alteração de topografia. / The present work discusses the influence of the microstructure of gray cast iron (GCI) and compacted graphite iron (CGI) on the occurrence of folded metal (FM) on honed surfaces and its tribological behavior in ring-on-cylinder test under lubrication. The cast iron samples were taken directly from an internal combustion engine block in regions of different thicknesses. The piston ring used was a nitrided martensitic stainless steel with asymmetrical profile and the lubricant oil was the SAE 30 CF. The quantification of grooves and folded metal (FM) was carried out using a methodology based on the literature. For the execution of the tribological tests an adaptation was designed and built for assembling the samples and for controlling the oil temperature. One parameter to evaluate the tribological performance was proposed - tribological merit index (TMI) - which considers the coefficient of friction (COF) and changes in topography. Each cast iron presented typical microstructures. However, differences in morphology and graphite distribution were observed; the samples from thinner wall presented higher number of graphite and less fraction of graphite. FM was observed on the plateaus and grooves of the honed surfaces in all samples. Quantification showed that the widths of the grooves were statistically similar and with a high percentage of obstruction. GCIs present a higher amount of FM in the Spk region (FMspk).The thicker wall samples presented a higher amount of FM in the grooves (% FM / Groove) and this parameter had a strong and positive statistical correlation with the graphite fraction. Evidences, obtained in cross section evaluations, corroborated the relationship between FM and graphite. It was verified that FM can be formed directly on graphite or indirectly due to the extrusion of this phase. In addition, its morphology and orientation influenced the occurrence of FM. Preliminary short-term tests were performed to evaluate the repeatability of COF results. These tests indicated less dispersion for conditions with lower frequencies and higher normal forces. Evaluations of the dynamics of the tribological test allowed to point out conditions to reduce the COF during the half-cycles of movement and to associate them to the theory of hydrodynamic lubrication. The COF for long-term tests presented cyclical behavior with transitions. These transitions were associated with formation-removal-formation mechanisms of ZDDP tribofilms. The tribological tests imposed changes on the roughness parameters (mainly with smoothness of the surfaces) and reductions on the film parameter. The thickness of samples affected little the TMI; and a better tribological performance of CGIs was detected. The FM quantification routine showed a technical limitation due to surface smoothing, which causes a change in the reference of heights of honed surfaces. Nevertheless, there was a reduction in %FM/Groove and tendency to clear the grooves. There was little influence of FM in COF behavior due to the similarity of FM parameters among the materials. However, FM was associated as a three-body abrasive agent and a strong positive correlation between the FMspk parameter (at the beginning of the test) and the TMI parameter was described.

O presente trabalho discute a influência da microestrutura dos ferros fundidos, cinzento (FFC) e vermicular (FFV), na ocorrência de metal dobrado (FM) em superfícies brunidas e no comportamento tribológico em ensaio lubrificado do tipo anel sobre cilindro. As amostras de ferro fundido foram extraídas diretamente de um bloco de motor de combustão interna, em regiões de diferentes espessuras. O anel de pistão utilizado foi de aço inoxidável martensítico nitretado com perfil assimétrico e o óleo lubrificante foi o SAE 30 CF monoviscoso. A quantificação de sulcos e de metal dobrado (FM) foi realizada empregando-se uma metodologia baseada na literatura. Para a execução dos ensaios tribológicos foi projetada e construída uma adaptação para a montagem das amostras e controle de temperatura do óleo lubrificante. Um parâmetro para avaliação do desempenho tribológico foi proposto – índice de mérito tribológico (IMT) – que leva em conta coeficiente de atrito (COF) e alterações de topografia. Os ferros fundidos apresentaram microestruturas típicas. Contudo, observaram-se diferenças de morfologia e distribuição da grafita; com maior número de grafitas e menor fração de grafita para os materiais de parede fina. Observou-se FM nos platôs e nos sulcos das superfícies brunidas em todas as amostras. Quantificações mostraram que as larguras dos sulcos foram estatisticamente iguais e com alto percentual de obstrução. A quantificação de FM dos materiais mostrou maiores valores presentes na região do Spk (FMspk) para os FFC's. Os materiais de parede grossa apresentaram maiores valores de % FM dentro do sulco (%FM/Sulco) e este parâmetro teve forte e positiva correlação estatística com a fração de grafita. Evidências, obtidas em avaliações de seções transversais, corroboraram a relação entre FM e grafita. Constatou-se que o FM pode ser formado diretamente sobre a grafita ou, ainda, de forma indireta devido à extrusão desta fase. Ademais, verificou-se que a morfologia e orientação da grafita têm influência na formação do FM. Realizaram-se ensaios preliminares de curta duração de anel sobre cilindro para a avaliação da repetibilidade dos resultados de COF, os quais indicaram menor dispersão para condições com menores frequências e maiores forças normais. Avaliações da dinâmica do ensaio tribológico permitiram apontar relações de redução de COF durante os semi-ciclos de movimento e associá-las à teoria de lubrificação hidrodinâmica. O COF para ensaios de longa duração apresentou comportamento cíclico com transições. Estas transições foram associadas a mecanismos de formação-remoção-formação de tribofilmes de ZDDP. Os ensaios impuseram alterações nos parâmetros de rugosidade (principalmente com alisamento das superfícies) e redução do parâmetro de filme. O IMT evidenciou pouca influência da espessura do material; e melhor desempenho tribológico para os FFV's. A rotina de quantificação de FM mostrou limitação técnica devido ao alisamento da superfície, o que causa mudança na referência de alturas das superfícies brunidas. Ainda assim, verificou-se redução do %FM/Sulco e tendência de desobstrução do sulco. Contatou-se pouca influência do FM no comportamento do COF devido à similaridade dos parâmetros de FM entre os materiais. Contudo, o FM foi associado a um agente de abrasão à três corpos e apresentou forte correlação positiva do parâmetro de FMspk (no início do ensaio) com o parâmetro do IMT relacionado com a alteração de topografia. / The present work discusses the influence of the microstructure of gray cast iron (GCI) and compacted graphite iron (CGI) on the occurrence of folded metal (FM) on honed surfaces and its tribological behavior in ring-on-cylinder test under lubrication. The cast iron samples were taken directly from an internal combustion engine block in regions of different thicknesses. The piston ring used was a nitrided martensitic stainless steel with asymmetrical profile and the lubricant oil was the SAE 30 CF. The quantification of grooves and folded metal (FM) was carried out using a methodology based on the literature. For the execution of the tribological tests an adaptation was designed and built for assembling the samples and for controlling the oil temperature. One parameter to evaluate the tribological performance was proposed - tribological merit index (TMI) - which considers the coefficient of friction (COF) and changes in topography. Each cast iron presented typical microstructures. However, differences in morphology and graphite distribution were observed; the samples from thinner wall presented higher number of graphite and less fraction of graphite. FM was observed on the plateaus and grooves of the honed surfaces in all samples. Quantification showed that the widths of the grooves were statistically similar and with a high percentage of obstruction. GCIs present a higher amount of FM in the Spk region (FMspk).The thicker wall samples presented a higher amount of FM in the grooves (% FM / Groove) and this parameter had a strong and positive statistical correlation with the graphite fraction. Evidences, obtained in cross section evaluations, corroborated the relationship between FM and graphite. It was verified that FM can be formed directly on graphite or indirectly due to the extrusion of this phase. In addition, its morphology and orientation influenced the occurrence of FM. Preliminary short-term tests were performed to evaluate the repeatability of COF results. These tests indicated less dispersion for conditions with lower frequencies and higher normal forces. Evaluations of the dynamics of the tribological test allowed to point out conditions to reduce the COF during the half-cycles of movement and to associate them to the theory of hydrodynamic lubrication. The COF for long-term tests presented cyclical behavior with transitions. These transitions were associated with formation-removal-formation mechanisms of ZDDP tribofilms. The tribological tests imposed changes on the roughness parameters (mainly with smoothness of the surfaces) and reductions on the film parameter. The thickness of samples affected little the TMI; and a better tribological performance of CGIs was detected. The FM quantification routine showed a technical limitation due to surface smoothing, which causes a change in the reference of heights of honed surfaces. Nevertheless, there was a reduction in %FM/Groove and tendency to clear the grooves. There was little influence of FM in COF behavior due to the similarity of FM parameters among the materials. However, FM was associated as a three-body abrasive agent and a strong positive correlation between the FMspk parameter (at the beginning of the test) and the TMI parameter was described.