In both the chemical and mechanical pulping process, the logs are cut into wood chips by a disc chipper before fibre separation. To make the wood chipping process more efficient, one have to investigate in detail the coupling between theprocess parameters and the quality of the chips. The objective of this thesis is to obtain an understanding of the fundamental mechanisms behind the creation of wood chips. Both experimental and analytical/numerical approaches have been taken inthis work. The experimental investigations were performed with an in‐house developed equipment and a digital speckle photography equipment. The results from the experimental investigation showed that the friction between the log and chipping tool is probably one crucal factor for the chip formation. Further more it was found that the indentation process is approximately self‐similar, and that the stress field over the entire crack‐plane is critical for chip creation. The developed analytical model predicts the normal and shear strain distribution. The analytical distributions are in reasonable agreement with the corresponding distributions obtained from a finite element analysis.

Within manufacturing of metallic components, machining plays an important role and is of vital significance to ensure process reliability. From a cutting tool design perspective,  tool macro geometry  design  based on physics based  numerical modelling  is highly needed  that can predict chip morphology.  The chip morphology describes the chip shape geometry and the chip curl geometry. The prediction of chip flow and chip shape is vital in predicting chip breakage, ensuring good chip evacuation and lower surface roughness.  To this end, a platform where such a  numerical model’s chip morphology prediction  can be compared with experimental investigation is needed and is the focus of this work. The studied cutting processes are orthogonal cutting process and nose turning process. Numerical models that simulate the chip formation process are employed to predict the chip morphology and are accompanied by machining experiments. Computed tomography is used  to scan the chips obtained from machining experiments and its ability to capture the variation in  chip morphology  is evaluated.  For nose turning process,  chip  curl parameters during the cutting process are to be calculated. Kharkevich model is utilized in this regard to calculate the  ‘chip in process’ chip curl parameters. High speed videography is used to measure the chip side flow angle during the cutting process experiments and are directly compared to physics based model predictions. The results show that the methodology developed provides  the framework where advances in numerical models can be evaluated reliably from a chip morphology prediction capability view point for nose turning process. The numerical modeling results show that the chip morphology variation for varying cutting conditions is predicted qualitatively. The results of quantitative evaluation of chip morphology prediction shows that the error in prediction is too large to be used for predictive modelling purposes.

This thesis presents the simulation of chip formation in orthogonal metal cutting to evaluate the predictive capabilities of finite element code DYNA 3D. The Johnson and Cook constitutive model for materials, OFHC Copper, Aluminum 2024 T351, and Aluminum 6061 T6 alloy were incorporated into the simulation to account for the effects of strain hardening, strain rate hardening, and thermal softening effects during machining. Calculated values for the Johnson and Cook constitutive constants for Aluminum 6061 T6 alloy were determined from the literature. The model was compared to experimentally measured shear angles, chip thickness, chip velocity, and forces from the literature to evaluate the accuracy of the finite element code for a range machining strain rates. In an attempt to determine the predictive capabilities of DYNA 3D a strain rate regime of 10+3 s-1 to 10+4 s-1 was defined as the optimal strain rate regime for the orthogonal metal cutting application.

Titanium alloys are major materials used in the airplane industry, and prospects show that airplane production will double in the next 20 years. Consequently, the demand for cutting tools for machining of titanium alloys will increase. The primary problem when machining titanium alloys is their low thermal conductivity. Crater wear is the main factor limiting tool life, and is generally caused by thermal diffusion due to high temperatures in the tool-chip interface. This master’s thesis was performed in collaboration with Sandvik Coromant, with the prospect to increase knowledge of how diffusion and chip formation influences crater wear progression. The aim was to study tool wear of cutting tools when turning Ti–6Al–4V. This was done by testing two different rake face geometries, both coated and uncoated, at cutting speeds of 30–115 m/min. Diffusion was investigated to learn about the impact it has on crater wear. Chips were examined to investigate chip formation and shear strain. The coated modified rake face insert showed less crater wear only for the initial few seconds of machining. Uncoated inserts with a modified rake face showed higher diffusion rate and faster crater wear progression than did standard inserts. The standard inserts showed twice as long tool life as did the modified inserts. No significant differences in the chip formation mechanism were found between modified and standard inserts. Cracks were found within shear bands that were thinner than usual, which suggest that the generation of cracks allows less shear deformation.

L’usinage des pièces en alliages de titane, notamment en Ti6Al4V qui a une faible usinabilité, a été toujours parmi les préoccupations majeures des entreprises du secteur de l’aéronautique. Toutefois, il est difficile, en se basant seulement à des essais expérimentaux, de bien comprendre les mécanismes participants à la formation du copeau. Il est alors nécessaire d’avoir recours à des modélisations numériques fiables permettant d’avoir accès à des grandeurs physiques instantanées et très localisées. Le travail présenté porte sur la fiabilisation de la modélisation de la coupe. Des simulations numériques 2D et 3D ont été mises en place. Le modèle de comportement de Johnson-Cook et le critère énergétique d’évolution d’endommagement ont été utilisés. L’étude préliminaire 2D de l’effet du maillage, notamment la taille, le type et la fonction d’interpolation des éléments finis, a souligné l’importance d’une discrétisation convenable du modèle qui tient compte du coût de calculs. De plus, il a été montré qu’un choix convenable du type de la formulation est crucial. L’effet des coefficients rhéologiques et d’endommagement (initiation et évolution) sur la formation du copeau (morphologie, champ de déformation et de température) a été déterminé. Des essais expérimentaux de la coupe orthogonale du Ti6Al4V à différentes conditions de coupe ont été effectués. La dépendance de la géométrie du copeau et des efforts à la vitesse de coupe et à l’avance a été étudiée. Les résultats expérimentaux ont été utilisés pour la validation des modèles numériques 3D qui permettent une étude fine de la formation du copeau. Cette approche a permis de reproduire fidèlement les phénomènes physiques se produisant au niveau du plan médian de la pièce tout en tenant compte de l’écoulement de la matière sur les bords. Les résultats prédits ont mis en évidence que, même dans le cas d’une coupe orthogonale, la formation du copeau est bien un phénomène 3D. Afin d’augmenter la fiabilité des modèles numériques 3D, une nouvelle loi thermo-viscoplastique a été proposée. Cette loi, identifiée et implémentée dans le logiciel Abaqus® à travers la routine VUMAT©, a été utilisée pour la simulation de l’usinage du Ti6Al4V. Elle a conduit à une amélioration notable des résultats numériques. / Machining of titanium alloys workpieces, especially in Ti6Al4V which has a low machinability, has always been among the major preoccupations of the companies in the aeronautics sector. However, it is difficult, basing only on experimental tests, to well understand the mechanisms involved during the chip formation. In fact, the use of reliable numerical models that allow the access to instantaneous and very localized physical quantities is required. The presented work consists on the increase of the cutting modeling reliability. 2D and 3D numerical simulations have been performed. The Johnson-Cook constitutive model and the damage evolution criterion have been used. The preliminary 2D study focused on the mesh effect, especially the size of the finite element, its type and its interpolation function, has highlighted the importance of a convenient discretization of the model that takes into account the machining computing cost. In addition, it has been shown that a suitable choice of the formulation type is crucial. The effect of the rheological and damage (initiation and evolution) coefficients on the chip formation (morphology, strain and temperature field) has been determined. Experimental orthogonal cutting tests of the Ti6Al4V at different cutting conditions have been performed. The dependency of the chip geometry and the efforts to the cutting speed and the feed rate has been studied. Experimental results have been used in the validation of the 3D numerical models, which allow a deep study of the chip formation process. This approach has allowed an accurately reproduction of the physical phenomena that occurs in the median plan of the workpiece as well as in its sides. The predicted results have highlighted that, even in the case of orthogonal cutting process, the chip formation is a 3D phenomenon. In order to increase the reliability of 3D numerical models, a new thermo-visco-plastic law has been proposed. This law, identified and implemented in the software Abqus® through the subroutine VUMAT©, has been used to model machining process of the Ti6Al4V. It has resulted in a notable improvement of numerical results.

A usinagem é caracterizada pela grande quantidade de deformação plástica localizada no material devido à formação do cavaco, de forma que existe um compromisso entre o processo de deformação, encruamento e amolecimento, pelo aumento da temperatura, gerando bandas de cisalhamento. A compreensão destas zonas cisalhamento se faz importante, por conter informações que podem ser aplicadas ao aperfeiçoamento das técnicas de usinagem relacionadas à melhoria do processo e a e à busca da inovação em materiais e ferramentas. Nesse contexto, os aços inoxidáveis, que em geral, são caracterizados como materiais de baixa usinabilidade, em consequência do elevado grau de encruamento e baixa condutividade térmica durante a usinagem, podem facilitar investigações da formação do cavaco pós-processo em razão da morfologia segmentada de seus cavacos. Para tanto, o objetivo deste trabalho foi abordar a usinagem sob a ótica da ciência do comportamento mecânico dos materiais através da avaliação das características e propriedades de três classes de aços inoxidáveis com diferentes estruturas cristalianas e microestruturas. A análise foi feita utilizando respostas de deformação, taxa de deformação, tensão, encruamento e temperatura na zona de cisalhamento primária, determinados a partir do monitoramento das forças de usinagem e caracterização do cavaco (morfologia e microestutura) em ensaios de torneamento semi-ortogonal, visando o levantamento e a relação dos parâmetros fundamentais do sistema de corte, que possam ser fatores significativos na modelagem do processo de usinagem. Os resultados mostraram que aços inoxidáveis apresentaram comportamentos distintos na usinagem, mostrando uma grande dependência da estrutura cristaliana, responsável pelos planos de deslizamento preferenciais, contribuindo para uma maior deformação e reduzindo a tensão de cisalhamento, além da difusividade térmica e dureza do material, que foram fortes indicadores da susceptibilidade dos aços inoxidáveis ao cisalhamento adiabático com formação de cavaco contínuo ou segmentado. A resposta à tensão e deformação dos aços inoxidáveis austenítico e duplex mostraram similaridade quando comparados com a classe martensítica. Não foi evidenciada presença de martensita induzida por deformação na usinagem do aço inoxidável austenítico. Por meio do planejamento composto central foi possível gerar modelos empíricos para cada classe de material relacionando as respostas de deformação, taxa de deformação, tensões, encruamento e temperatura na zona de cisalhamento primária com as condições de corte. / Machining is characterized by large amount of located plastic strain on material due to chip formation, so that there is a link between strain process, strain hardening, and heat softening, thus generating shear bands. Understanding these shear zones becomes important because it contains information that can be applied to machining technique improvements related to process optimizing, and the materials and tools innovations. In this context, stainless steels are regarded as poor machinability materials, due to high work hardening and low thermal conductivity; however, their segmented chip morphology is helpful for facilitating the post-process chip formation researches. Therefore, the aim was to approach machining from the viewpoint of the mechanical behavior science by comparing three stainless steels grades with dissimilar crystalline structures and microstructures during cutting. Strain, strain rate, stress, strain hardening, and primary shear plane temperature were the output variables analyzed. These output variables were determined from cutting forces monitoring and chip characterization (morphology and microstructure) in semiorthogonal turning tests. The results showed the stainless steels machining behavior was different depending on the lattice structure, which is responsible for preferential slipping planes, contributing to amount of strain and reducing the shear stress. Thermal conductivity and hardness were also strong indicators of stainless steels adiabatic shear susceptibility by continuous or segmented chip formation. The stress and strain response of austenitic and duplex stainless steel grades were similar compared to martensitic grade. Strain-induced martensite formation was not evidenced in austenitic stainless steel machining. Empirical models of strain, strain rate, stress, strain hardening and primary shear plane temperature as a function of cutting conditions were obtained by means of the central composite design.

Classical orthogonal and oblique cutting are the fundamental material removal or machining processes to which other practical machining processes can be related in the study and modelling of the machining processes. In the last century, a large amount of research and development work has been done to study and understand the various machining processes with a view to improving the processes for further economic (cost and productivity) gains. However, many aspects of the cutting processes and cutting performance remains to be fully understood in order to increase the cutting capability and optimize the cutting processes; in particular, there is little study to understand the effects of the inevitable tool wear on the machining processes. This thesis includes an extensive literature review on the mechanics of cutting analysis. Considerable work has been carried out in past decades on the fundamental analysis of 'sharp' tool cutting. Although some work has been reported on the effects of tool flank wear on the cutting performance, there is a general lack of the fundamental study of the effects of the flank wear on the basic cutting or chip formation process. It has been well documented that tool flank wear results in an increase in the cutting forces. However, it was not known if this force increase is a result of the change in the chip formation process, and/or the rubbing or ploughing forces between the tool flank and the workpiece. In work carried out since the early 1980s, the effects of the so-called edge forces have been considered when the tool is not absolutely sharp. Little has been reported to further develop fundamental cutting theories to understand applications to more relevant the practical situation, i.e. to consider the tool wear effects. Based on the findings of the literature review, an experimental investigation is presented in the first part of the thesis to study the effects of tool flank wear on the basic cutting or chip formation process by examining the basic cutting variables and performance in the orthogonal cutting process with tool flank wear. The effects of tool flank wear on the basic cutting variables are discussed by a comprehensive analysis of the experimental data. It has been found that tool flank wear does not affect the basic cutting variables (i.e. shear angle, friction angle and shear stress). It is therefore deduced that the flank wear does not affect the basic chip formation process in the shear zone and in the tool-chip interface. The study also finds that tool flank wear causes an increase in the total cutting forces, as can be expected and such an increase is entirely a result of the rubbing or ploughing forces on the tool wearland. The significance of this finding is that the well-developed machining theories for 'sharp' tools can be used in modelling the machining processes when tool flank wear is present, rather than study the machining process and develop machining theories from scratch. The ploughing forces can be modelled for incorporation into the overall cutting force prediction. The experimental study also allows for the forces on the wearland (or wearland force) and edge forces to be separated from the total measured forces. The wearland force and edge force models are developed in empirical form for force prediction purpose. In addition, a database for the basic cutting variables or quantities is established for use in modelling the cutting forces. The orthogonal cutting force model allowing for the effects of flank wear is developed and verified by the experimental data. A comprehensive analysis of the mechanics of cutting in the oblique cutting process is then carried out. Based on this analysis, predictive cutting force models for oblique cutting allowing for the effects of flank wear are proposed. The wearland force and edge force are re-considered by analysing the oblique cutting process and the geometrical relation. The predictive force models are qualitatively and quantitatively assessed by oblique cutting tests. It shows that the model predictions are in excellent agreement with the experimental data. The modelling approach is then used to develop the cutting force models for a more general machining process, turning operation. By using the concept of an equivalent cutting edge, the tool nose radius is allowed for under both orthogonal and oblique cutting conditions. The wearland forces and edge forces are taken into consideration by the integration of elemental forces on the tool flank and the cutting edge, respectively. The cutting forces in turning operations are successfully predicted by using the basic cutting quantity database established in the orthogonal cutting analysis. The models are verified by turning operation tests. It shows that the model predictions are in excellent agreement with the experimental results both qualitatively and quantitatively. The major findings, research impacts and practical implications of the research are finally highlighted in the conclusion. The modelling approach considering the flank wear effects in the classical orthogonal and oblique cutting and turning operations can be readily extended to other machining operations, such as drilling and milling.

A usinagem é caracterizada pela grande quantidade de deformação plástica localizada no material devido à formação do cavaco, de forma que existe um compromisso entre o processo de deformação, encruamento e amolecimento, pelo aumento da temperatura, gerando bandas de cisalhamento. A compreensão destas zonas cisalhamento se faz importante, por conter informações que podem ser aplicadas ao aperfeiçoamento das técnicas de usinagem relacionadas à melhoria do processo e a e à busca da inovação em materiais e ferramentas. Nesse contexto, os aços inoxidáveis, que em geral, são caracterizados como materiais de baixa usinabilidade, em consequência do elevado grau de encruamento e baixa condutividade térmica durante a usinagem, podem facilitar investigações da formação do cavaco pós-processo em razão da morfologia segmentada de seus cavacos. Para tanto, o objetivo deste trabalho foi abordar a usinagem sob a ótica da ciência do comportamento mecânico dos materiais através da avaliação das características e propriedades de três classes de aços inoxidáveis com diferentes estruturas cristalianas e microestruturas. A análise foi feita utilizando respostas de deformação, taxa de deformação, tensão, encruamento e temperatura na zona de cisalhamento primária, determinados a partir do monitoramento das forças de usinagem e caracterização do cavaco (morfologia e microestutura) em ensaios de torneamento semi-ortogonal, visando o levantamento e a relação dos parâmetros fundamentais do sistema de corte, que possam ser fatores significativos na modelagem do processo de usinagem. Os resultados mostraram que aços inoxidáveis apresentaram comportamentos distintos na usinagem, mostrando uma grande dependência da estrutura cristaliana, responsável pelos planos de deslizamento preferenciais, contribuindo para uma maior deformação e reduzindo a tensão de cisalhamento, além da difusividade térmica e dureza do material, que foram fortes indicadores da susceptibilidade dos aços inoxidáveis ao cisalhamento adiabático com formação de cavaco contínuo ou segmentado. A resposta à tensão e deformação dos aços inoxidáveis austenítico e duplex mostraram similaridade quando comparados com a classe martensítica. Não foi evidenciada presença de martensita induzida por deformação na usinagem do aço inoxidável austenítico. Por meio do planejamento composto central foi possível gerar modelos empíricos para cada classe de material relacionando as respostas de deformação, taxa de deformação, tensões, encruamento e temperatura na zona de cisalhamento primária com as condições de corte. / Machining is characterized by large amount of located plastic strain on material due to chip formation, so that there is a link between strain process, strain hardening, and heat softening, thus generating shear bands. Understanding these shear zones becomes important because it contains information that can be applied to machining technique improvements related to process optimizing, and the materials and tools innovations. In this context, stainless steels are regarded as poor machinability materials, due to high work hardening and low thermal conductivity; however, their segmented chip morphology is helpful for facilitating the post-process chip formation researches. Therefore, the aim was to approach machining from the viewpoint of the mechanical behavior science by comparing three stainless steels grades with dissimilar crystalline structures and microstructures during cutting. Strain, strain rate, stress, strain hardening, and primary shear plane temperature were the output variables analyzed. These output variables were determined from cutting forces monitoring and chip characterization (morphology and microstructure) in semiorthogonal turning tests. The results showed the stainless steels machining behavior was different depending on the lattice structure, which is responsible for preferential slipping planes, contributing to amount of strain and reducing the shear stress. Thermal conductivity and hardness were also strong indicators of stainless steels adiabatic shear susceptibility by continuous or segmented chip formation. The stress and strain response of austenitic and duplex stainless steel grades were similar compared to martensitic grade. Strain-induced martensite formation was not evidenced in austenitic stainless steel machining. Empirical models of strain, strain rate, stress, strain hardening and primary shear plane temperature as a function of cutting conditions were obtained by means of the central composite design.

In live we often involve monitoring of very fast actions, that are not observable by the human eye. The thesis focuses on possibilities of high speed digital cameras, their application in industry, and the mechanism of chip formation. The experiment part aims to record the chosen process of chip machining and the problems of necessary illumination during the process of object imaging.

The diploma thesis focuses on analysis of mechanism of chip formation during machining of titan alloys. Application of titan alloys in metal-working and engineering industry is currently very significant topic. The mechanism of titan chip formation is dissimilar to steel and its foundation plays an important role in optimization of cutting process.