In this master thesis, performed at Ovako Group R&D (Hofors) a new machining test method for ranking heats of calcium-treated steels, M-Steels, has been proposed.  A total of six different heats of 42CrMo4-M steel in the quenched-and-tempered (Q+T) condition were tested. The proposed method uses dry turning with coated cemented carbide tools at a cutting speed of 225 m/min, 2 mm depth of cut, and a feed rate of 0.35 rev/min. The machining test is tuned so that M-Steels within medium-sized bar diameters and a small hardness interval can be differentiated by monitoring the flank wear progression of the cutting tool. This method is easily taught to a CNC-operator, it mimics real workshop conditions and can be repeated with relative robustness and ease of execution. It is possible to get a ranking where both the M-Steel treatment and hardness are included.  The major differentiator of tool wear performance was found to be a combination of wear of the outermost Al2O3 coating and the build-up and renewal of protective slag deposits on the tool rake. The rake face wear was found similar between the M-Steels samples, so it is thought that the effect of the slag deposits, as thermal barriers, affect the plastic deformation and wear of the flank face. Given the slag deposits sub-micron thickness, this indirect method of recording the flank wear is highly recommended to showcase the positive effects of the M-Steel in machining The inclusion content was evaluated according to ASTM E45 and with a scanning electron microscope (SEM) automated inclusion assessment. The link between the machinability performance of the M-Steels and their inclusion characteristics could not be clarified in this work.  Teknisk-naturvetenskapliga fakulteten

The Swedish truck industry is looking for new material solutions to achieve lighter engines with increased strength to meet customer demands and to fulfil the new regulations for more environmentally friendly trucks. This could be achieved by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This, however, exposes the engine to higher loads and material physical properties must therefore be enhanced. One material that could meet these demands is Compacted Graphite Iron (CGI). Its mechanical and physical properties make it ideal as cylinder block material, though there are drawbacks concerning its machinability as compared to other materials that are commonly used for the same purpose. Knowledge about machining of the material and its machinability is consequently inadequate. The main goal of this thesis is to identify and investigate the effect of the major factors and their individual contributions on CGI machining process behaviour. When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding of this is developed mainly through experimental analysis as, e.g., machining experiments and material characterization. The machining model presented in this thesis demonstrates the influence of material and process parameters on CGI machinability. It highlights machinability from both design and production planning perspectives. Another important objective of the thesis is an inverse thermo−mechanical FE model for intermittent machining of CGI. Here, experimental results obtained from a developed simulated milling method are used as input data, both to calibrate and validate the model. With these models, a deeper understanding is obtained regarding the way to achieve a stable process, which is the basis for future optimization procedures. The models can therefore be used as a foundation for the optimization of CGI component manufacturing. / <p>QC 20111121</p> / MERA - OPTIMA CGI / FFI - OPTIMA phase two

Les aciers inoxydables sont employés dans des secteurs d’activitéspour lesquels les caractéristiques mécaniques et la résistance à lacorrosion sont primordiaux. Les nuances austéno-ferritiques sansmolybdène (lean-duplex), ont une résistance à la corrosion et despropriétés mécaniques supérieures aux aciers inoxydables austénitiques.Cependant, leur usinabilité est inférieure à celle de leur homologueausténitique. Pour améliorer cette propriété des éléments peuvent êtreajoutés dans les nuances, tel que le niobium. L’objectif de cette étude estd’améliorer l’usinabilité des lean-duplex sans dégrader les autrespropriétés. Différentes teneurs en niobium ont été ajoutées dans un1.4362 pour comprendre comment cet élément affecte la microstructure,la résilience, et la résistance à la corrosion par piqûres. Ces résultatsvont permettre de définir une teneur en niobium optimale. Pour finir, desessais d’usinabilité et de résilience ont été effectués sur des couléesindustrielles de 1.4362 avec et sans niobium après divers traitementsthermiques pour comprendre l’influence d’un ajout de niobium sur cesdeux propriétés. / Stainless steels are used in some industries requiring mechanicalproperties and corrosion resistance. Lean duplex have higher corrosionresistance and mechanical properties than the austenitic stainless steels.However, their machinability is below that of the corresponding austeniticstainless steels. To improve it, some elements can be added in thegrade, like niobium. The aim of this study is to increase machinability oflean duplex grades without degrading their other properties. Differentcontents of niobium were tested in a 1.4362 to understand how thiselement affects the microstructure, the toughness and the pittingcorrosion resistance. With these results optimum niobium content isdefined. Turning and toughness experiments were done on industrial1.4362 grades with and without niobium and with different heatstreatments in order to understand how niobium can influence theseproperties.

<p>The Swedish truck industry is forced to find new material solutions to achieve lighter engines with increased strength. Customers and new environmental regulations demand both higher specific power and more environmentally friendly trucks, and this places a rising pressure on the manufactures. This demand could be met by increasing the peak pressure in the cylinders. Consequently, a more efficient combustion is obtained and the exhaust lowered. This however exposes the engine to higher loads and material physical properties must therefore be enhanced.</p><p>Today, alloyed gray iron is the predominantly used engine material. This material cannot meet the requirements of tomorrow’s engines. Compacted Graphite Iron has good potential to be the replacement; it opens new design opportunities with its superior strength, which can lead to smaller, more efficient engines and additional power. The question is: how will manufacturing be affected?</p><p>The main goal of this thesis is to identify and investigate the main factors’ effect and their individual contributions on CGI machining.  When the relationship between the fundamental features; machinability, material microstructure, and material physical properties, are revealed, then the CGI material can be optimized, both regarding the manufacturing process and design requirements. The basic understanding is developed mainly through experimental analysis. No attempt has been made to optimize the material to be used as engine material in this thesis.</p><p>The thesis demonstrates the importance of having good casting process control. It also illustrates the microstructural properties’ effects on CGI machinability, and what new aspects of machining must be taken into account, compared to gray iron.</p> / OPTIMA CGI

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: There is a strong focus on the use of titanium and its alloys in the aerospace industry due to the high ultimate tensile strength and high strength-to-weight ratio of the material. The high performance nature of the material also makes it difficult and costly to machine. South Africa has the second most abundant titanium resources in the world in the form of rutile and ilmenite but no value chain to produce titanium parts from the ore. Currently, the ore is sold overseas at low prices. There exists an initiative to create a full titanium value chain in South Africa by the Department of Science and Technology. This project forms part of this initiative, where local industry is equipped with knowledge and skills to produce and machine titanium parts. The focus of this study is to determine whether it is possible to machine titanium aerospace parts at a local industry partner and equip the industry partner with knowledge and skills in order to facilitate effective and economical machining of these parts. Daliff Precision Engineering was selected as the local industry partner and specific demonstrator parts were selected on which to base the study. The process the industry partner currently uses to machine aerospace parts from difficult-to-machine alloys was studied and evaluated. It was found that about 70% of the machining time was spent on a single roughing process, hence the decision to study the roughing process in an attempt to establish whether improvement was possible. Pilot tests were done at the facilities of the industry partner and time savings of 95% were realised on the roughing process. A 2-level 3-factor Design of Experiments methodology was followed for experimentation and analysis of titanium machining at the industry partner. The roughing process of the demonstrator part was simulated on the CNC machining centre and the depth of cut, cutting speed and feed per tooth were selected as the factors, and the response was tool wear. A statistical analysis was done using Modde 9.1 design of experiments software and an optimisation model was created in order to determine a feasible set of cutting parameters, maximise material removal rate and have a target amount of tool wear. The findings show that it is possible to economically machine titanium aerospace parts with a selected geometry at the industry partner without the need for significant capital investments. The industry partner can use the knowledge generated in this project to validate their titanium machining capabilities and form part of the titanium value chain that is being developed in South Africa. / AFRIKAANSE OPSOMMING: Daar is ‘n groot fokus op die gebruik van titaan allooie in die lugvaart nywerheid, as gevolg van die material se hoë trek-sterkte en hoë sterkte-tot-gewig verhouding. Die eienskappe wat die material so aantreklik maak, is ook die rede wat dit moeilik en duur maak om te masjineer. Suid-Afrika het die tweede grootste titaan reserwes in die wêreld in die vorm van rutiel en ilmeniet erts, maar geen waarde ketting om titaan onderdele te vervaardig van die erts af nie. Die erts word tans oorsee verkoop teen lae pryse. Daar is tans ‘n inisiatief om ‘n titaan waardeketting in Suid-Afrika te skep deur die Departement van Wetenskap en Tegnologie. Hierdie projek vorm deel van hierdie inisiatief om die plaaslike nywerheid toe te rus met kennis en vaardighede om titaan produkte te vervaardig. The fokus van hierdie studie is om te bepaal of dit moontlik is om titaan lugvaart onderdele te masjineer by ‘n plaaslike industrie-vennoot en om hierdie vennoot met kennis en vaardighede toe te rus om hierdie onderdele effektief en ekonomies te vervaardig. Daliff Precision Engineering is gekies as die plaaslike industrie-vennoot en spesifieke demonstrator onderdele is gekies om die studie op te baseer. Die proses wat die industrie-vennoot tans gebruik om moeilik-om-te-masjineer allooie te masjineer is bestudeer en ge-evalueer. Daar was bevind dat 70% van die masjineringstyd bestee word aan ‘n enkele uitrof-proses. Daar is besluit om vas te stel of die uitrof-proses verbeter kan word. Loods-eksperimente is gedoen by die industrie-vennoot se fasiliteite en ‘n tydsbesparing van 95% is gevind op die uitrof-proses. ‘n 2-Vlak 3-faktor eksperimentele ontwerp metodologie is gevolg om eksperimente by die industrie-vennoot op titaan uit te voer en te analiseer. Die uitrof-proses van die demonstrator onderdeel is gesimuleer op die CNC masjineringsentrum en die diepte van snit, snyspoed en voer per tand is gekies as die faktore en beitel-slytasie is gekies as die respons. ‘n Statistiese analise is gedoen deur Modde 9.1 eksperimentele ontwerp sagteware te gebruik om ‘n moontlike stel van sny-parameters te identifiseer om die materiaal-verwyderingstempo te maksimeer en die teiken waarde vir beitel-slytasie te bereik. Daar is gevind dat dit moontlik is on titaan lugvaart onderdele met ‘n spesifieke geometrie ekonomies te masjineer by die industrie-vennoot, sonder om enige beduidende kapitaal uitgawes aan te gaan. Die industrie-vennoot kan die kennis gebruik wat geskep is deur die projek om hulle titaan masjineringsvaardighede te valideer en om deel te vorm van die titaan waardeketting wat besig is om in Suid-Afrika ontwikkel te word.

Fundação de Amparo a Pesquisa do Estado de Minas Gerais / The aim of this work is to study the effect of silicon content in the machinability of CBA s (Compania Brasileira de Aluminio) 6351 aluminum alloy measured through cutting force and surface finish. In a first moment the effect of depth of cut (ap), cutting speed (vc), feed rate (f) and silicon content (% Si) on the machinability were investigated. The machining process used was turning operation with no cutting fluid. In a second part of the tests it was used MQF (60 l/h) and over head flood in experimental tests with constant depth of cut. For each set of parameters it was acquired values of cutting forces and surface roughness with two repetitions, adopting a 3k design of experiments. The results showed that the silicon content has significant effect in the machinability of the studied alloy compared to the others parameters investigated. Keywords: / O objetivo deste trabalho é a verificação da influência do teor de silício na composição da liga de alumínio 6351 da empresa CBA (Compania Brasileira de Alumínio) na usinabilidade avaliada através da medição da força de corte e do acabamento superficial. Em uma primeira etapa foi analisado estatisticamente o efeito dos parâmetros de corte, profundidade de corte (ap), velocidade de corte (vc), avanço (f) e porcentagem de silício (% Si) na força de corte e rugosidade superficial durante ensaios de torneamento cilíndrico externo sem aplicação do fluido de corte. Em uma segunda etapa dos ensaios utilizou-se fluido de corte aplicado através de MQF (60l/h) e jorro, mantendo constante a profundidade de corte e variando velocidade de corte e avanço. Para cada uma das combinações de parâmetros de corte foram adquiridos valores de força de corte e rugosidade superficial com duas réplicas para cada ensaio, adotando um planejamento fatorial 3k. Analise estatística de variância (ANOVA) mostrou que a porcentagem de silício exerce influência significativa nos parâmetros de usinabilidade avaliados da liga estudada quando comparado com avanço, velocidade de corte e profundidade de corte. / Mestre em Engenharia Mecânica

Conselho Nacional de Desenvolvimento Científico e Tecnológico / Aesthetic and functional excellence in dental prosthetic rehabilitation has been achieved with the increase of advanced ceramics in dentistry. Processing techniques such as heat press injection moulding and CAD/CAM (computer-aided design/computer aided manufacturing) impart decreased porosity to the microstructure, as well as simplicity and automation of the process. In order to examine the machining surface finish of a leucite glass-ceramic produced using Brazilian raw materials, heat-pressed performs were obtained. These preforms had dimensions close to those of the final crown infrastructure in order to allow fast and easy final matching and finish-milling by using a Brazilian milling machine (MTC Robotica), supported by DentMILL (SEACAM) CAM software. As a control and reference manufacturing process, four crown infrastructures were milled by using CEREC®-3 machine. Aimed at achieving a machinable microstruture, two different heating schedule were tested for ceramizing the feldsphatic glass ingots. X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), nanoindentation test and fracture toughness measurement by indentation method were used as characterization methods. Comparison of the properties of the experimental material with those published by other investigator on similar commercial materials conducted to the conclusion that it is a machinable glass-ceramic with acceptable features for application in dental prosthetic rehabilitation. Preforms milling simulation using MTC Robotica machine conducted to the prediction of very long milling time (18h), even considering preforms possessing dimensions similar to those of the desired milling end product, a manufacturing time much greater than those found in commercial CAD/CAM dental milling machines. / A reabilitação protética do elemento dentário com excelência estética e funcional tem sido alcançada através do amplo uso de cerâmicas avançadas na odontologia. Técnicas de processamento como moldagem por injeção a quente e usinagem por CAD/CAM (computer-aided design/computer aided manufacturing) conferem ao material uma microestrutura com menor porosidade, além de simplificar e permitir automação de sua execução. Com o objetivo de avaliar a superfície usinada de uma vitrocerâmica feldspática leucítica produzida a partir de matéria prima nacional, foram confeccionadas pré-formas deste material pela técnica de moldagem por injeção sob pressão a quente. Estas pré-formas têm dimensões aproximadas a da peça final com a finalidade de serem usinadas na fresadora CNC nacional de baixa rotação (MTC Robótica), auxiliada pelo software CAM DentMILL (SEACAM). Além disso, foram usinadas peças do mesmo material no sistema CEREC®, como forma de controle. Para a obtenção de uma microestrutura com melhor usinabilidade, foram testadas duas metodologias de ceramização das pastilhas de vidro feldspático. A caracterização do material foi realizada por meio da difração de raios X (DRX), microscopia eletrônica de varredura (MEV), microscopia de força atômica (AFM), ensaios de nanoindentação e de tenacidade à fratura pelo método da indentação. A partir da comparação das propriedades deste material aos dados obtidos na literatura sobre materiais similares existentes no mercado foi possível classificar o material como usinável e indicar sua aplicação na clínica odontológica reabilitadora. A simulação da usinagem das pré-formas na fresadora MTC Robótica, mesmo com dimensões aproximadas a da peça final, apresentou um tempo de usinagem muito longo (18h), o que a tornou inviável comparada aos sistemas CAD/CAM consolidados no mercado.

Cette étude porte sur l'usinage de l'alliage de titane Ti17 avec une assistance jet d'eau haute pression. Une attention particulière a été portée à l'analyse des mécanismes de dégradation et d'usure des outils lors de l'usinage avec et sans assistance. Le suivi de l'usure est réalisé par des observations régulières au microscope électronique à balayage (MEB) et par des analyses chimiques (technique EDS) afin de déterminer les zones de dépôt de matière sur l'outil. Toutes ces observations ont permis d'expliquer les mécanismes d'usure pour une opération d'ébauche et de finition. Il a été montré que les mécanismes d'usure sont différents entre l'usinage conventionnel et l'usinage assisté. En effet, lors de l'assistance jet d'eau haute pression, certains mécanismes ne sont plus activités mais d'autres mécanismes sont accélérés. Il existe donc une pression de jet d'eau optimale pour minimiser l'usure de l'outil.Afin de mettre en évidence l'effet du jet d'eau sur les phénomènes thermomécaniques dans les zones de formation du copeau, une modélisation par éléments finis est réalisée. Un couplage fluide / structure a dû être mis en place afin de prendre en compte les actions mécaniques et thermiques du jet d'eau sur la zone de coupe. Pour cela, la loi de comportement et le modèle d'endommagement de Johnson-Cook, ont été identifiés pour le Ti17 dans des conditions extrêmes sur une large gamme de températures et de vitesses de déformation. Cette modélisation a permis de mettre en évidence, pour l'usinage assisté haute pression, la diminution de la zone de contact outil/copeau, de retrouver la fragmentation du copeau et de quantifier le refroidissement des différentes zones de cisaillement.En revanche, cette modélisation ne permet pas de connaître l'effet de l'hétérogénéité microstructurale du matériau sur la zone de coupe. Ce constat est d'autant plus important que le matériau étudié présente une taille de grain importante (de l'ordre du millimètre). Pour cela, une nouvelle modélisation (multi-échelle) a été développée afin de prendre en compte la microstructure du matériau. Le matériau est donc modélisé comme un polycristal qui prend en compte des lois de la plasticité cristalline. Cette nouvelle approche permet alors de simuler la formation du copeau en prenant en compte les orientations cristallines des grains et les changements de phase qui apparaissent lors de l'usinage. / This study focuses on the machining of the Ti17 titanium alloy using high-pressure water jet assistance. Special emphasis is placed on the analysis of degradation mechanisms and tool wear during machining, with and without assistance. Wear monitoring was achieved by regular observations using both scanning electron microscope (SEM) and chemical analysis (EDS technique) to determine the areas of material deposition on the tool. These observations made it possible to explain the wear mechanisms for roughing and finishing conditions. Wear mechanisms for conventional machining and for assisted machining were found to be significantly different. Indeed, with high-pressure water jet assistance, some tool wear mechanisms are no longer activated, whereas others are accelerated. Hence, there exists an optimum water jet pressure which minimizes tool wear.To highlight the effect of water jet assistance on the thermomechanical phenomena in the chip formation zone, finite-element modeling has been performed. Fluid/structure coupling was developed to take into account the mechanical and thermal effects of the water jet. For this to be possible, the Johnson-Cook constitutive law and damage model have been identified for the Ti17 titanium alloy, under extreme conditions, over a wide range of temperatures and strain rates. This modeling has highlighted the fact that, for high-pressure assisted machining, the tool/chip contact zone is reduced. In addition, the simulation of chip fragmentation as well as the cooling effect on the tool and workpiece is possible.However, this model does not shed light on the effect of the microstructural heterogeneity of the material in the cutting zone. This is an important observation because the material studied has a very large grain size (of the order of a millimeter). For this reason, a new (multi-scale) modeling approach has been developed to take into consideration the microstructure of the material. The material is subsequently modeled as a polycrystal which obeys crystal plasticity constitutive laws. This new approach is then used to simulate chip formation, taking into account the grain orientations and phase changes that occur during the machining process.

De nombreux paramètres interviennent dans la longévité des inlays/onlays réalisés par CFAO tels que l’usinabilité et les propriétés mécaniques des matériaux utilisés, l’adaptation de la restauration ainsi que la qualité de l’interface entre le matériau de restauration en céramique ou en composite et le matériau d’assemblage. Dans un premier temps, au travers d’une revue systématique de la littérature, nous avons sélectionné les méthodes expérimentales et les paramètres permettant d’évaluer l’adaptation de ces restaurations. Il existe des techniques en 2D qui mesurent l’espace dent-matériau à des points de référence présélectionnées et des techniques en 3D (Triple-scan, micro-CT) qui mesurent l'ensemble de l'interface. Cette revue de la littérature nous a permis de mettre en évidence que : le matériau de restauration, le type de préparation, le vieillissement, le collage ou non de la restauration et des paramètres propres à la CFAO ont une influence sur l’adaptation. Dans un deuxième temps, nous avons étudié les propriétés mécaniques de blocs en céramique et en composite et l’adaptation interne in vitro d’inlays usinés à partir de ces mêmes matériaux. L’influence de la nature du matériau de restauration et de son usinabilité sur l’adaptation a été mise en évidence. La troisième partie de notre travail a porté sur la qualité de cette interface par un test de résistance en microtraction et une analyse du type de fracture. Une relation étroite a été démontrée entre la microstructure du bloc testé et le type de traitement de surface utilisé. Ce travail a souligné l’importance d’utiliser plusieurs méthodologies et de les croiser entre elles afin de mieux corréler nos résultats. L’étude du vieillissement de ce joint dento-prothétique constitue un travail à part entière dans laquelle certaines méthodologies utilisées dans cette thèse (profils de rupture, essais mécaniques) peuvent être transposées / Several parameters are involved in the longevity of CAD-CAM inlays/onlays restorations such as the machinability and mechanical properties of the materials used, the adaptation of the restoration and the quality of the resin cement-ceramic or composite interface. Initially, through a systematic review of the literature, the experimental methodologies and parameters to evaluate the adaptation of these restorations were selected. The gap between the tooth and the material, at preselected reference points, is measured by 2D techniques. 3D techniques (Triple-scan, micro-CT) are able to measure the entire interface. This review of the literature allowed us to highlight that: the restorative material, the preparation design, aging, the use of a bonding-system and parameters regarding the CAD-CAM technology have an influence on the marginal adaptation. Afterwards, we assessed the mechanical properties of CAD-CAM ceramic and composite blocks and the internal adaptation in vitro of inlays milled with these same materials. The influence of the nature of the restorative material and its machinability on adaptation was put forward. The third part of our work focused on the quality of this interface using a microtensile bond strength test and a fracture type analysis. A tight association has been shown between the microstructure of the tested blocks and the type of surface treatment applied. This work underlined the importance of using several methodologies and crossing them to better correlate our results. Studying the aging of this dento-prosthetic joint constitutes a whole work in which some approaches used in this thesis (fracture profiles, mechanical tests) can be implemented and transposed

The thesis is focused on machining of hard-to-machine materials. In the theoretical part hard-to-machine materials are divided and characterized. Furthermore, the thesis specifies hardened steels and their heat treatment, machinability and mechanism of wear and chip formation. There are tool materials and their classes suitable for machining hardened steels. The practical part deals with the influence of the cutting conditions on the roughness of the machined surface when turning hardened steel.