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In the current research, an analytical chip formation model and the methodology to determine material flow data have been developed. The efforts have been made to address work hardening and thermal softening effects and allow the material to flow continuously through an opened-up deformation zone. Oxley's analysis of machining is extended to the application of various engineering materials. The basic model is extended to the simulation of end milling process and validated by comparing the predictions with experimental data for AISI1045 steel and three other materials (AL-6061, AL7075 and Ti-6Al-4V) from open literatures. The thorough boundary conditions of the velocity field in the primary shear zone are further identified and analyzed. Based on the detailed analysis on the boundary conditions of the velocity and shear strain rate fields, the thick “equidistant parallel-sided” shear zone model was revisited. A more realistic nonlinear shear strain rate distribution has been proposed under the frame of non-equidistant primary shear zone configuration, so that all the boundary conditions can be satisfied. Based on the developed model, inverse analysis in conjugation of genetic algorithm based searching scheme is developed to identify material flow stress data under the condition of metal cutting. ii On the chip-tool interface, The chip-tool interface is assumed to consist of the secondary shear zone and elastic friction zone(i.e. sticking zone and sliding zone). The normal stress distribution over the entire contact length is represented by a power law equation, in which the exponent is determined based on the force and moment equilibrium. The shear stress distribution for the entire contact length is assumed to be independent of the normal stress. The shear stress is assumed to be constant for the plastic contact region and exponentially distributed over the elastic contact region, with the maximum equal to the shear flow stress at the end of sticking zone and zero at the end of total contact. The total contact length is derived as a function governed by the shape of normal stress distribution. The length of the sticking zone is determined as the distance from the cutting edge to the location where the local coefficient of friction reaches a critical value that initiates the bulk yield of the chip. Considering the shape of the secondary shear zone, the length of the sticking zone can also be determined by angle relations. The maximum thickness of the secondary shear zone is determined by the equality of the sticking lengths calculated by two means. With an arbitrary input of the sliding friction coefficient, various processing parameters as well as contact stress distributions during orthogonal metal cutting can be obtained. / UOIT

Over the last two decades or so, metal matrix composites (MMCs) have been drawing the attention of the industry due to their potentials in fulfilling demands for high performance industrial materials, products and advanced engineering applications. On the other hand, the high precision machining is becoming one of the most effective methods for enabling these difficult-to-machine composites to be applied particularly in precision engineering. Therefore, in-depth scientific understanding of MMC precision machining is essential and much needed so as to fulfil the gap between fundamental issues in precision machining of MMCs and their industrial scale applications. This thesis focuses on development of a multiscale multiphysics based approach to investigating the machinability of particulate MMCs and the machining process optimisation. In order to investigate the surface generation in relation to the process variables, this PhD study covers the key fundamental issues including chip formation process, dynamic cutting force, cutting temperature partition and tool wear by means of combining modelling, simulation and experimental study. The chip formation mechanisms and the minimum chip thickness in precision machining of SiCp/Al and B4Cp/Al MMCs by using PCD tools are investigated through a holistic approach. Minimum chip thickness (MCT) value is firstly identified based on the modified mathematical model. The certain threshold of the uncut chip thickness, i.e. chips starting to form at this chip thickness point, is then established. The chip formation process including the matrix material breakage, particles fracture, debonding, sliding or removal and their interfacial interactions are further simulated using finite element analysis (FEA). The minimum chip thickness and chip formation simulations are evaluated and validated via well-designed experimental trials on a diamond turning machine. The chips and surface profiles formed under varied process variables in periodic material removals are inspected and measured in order to obtain a better understanding on MMC chip formation mechanisms. The improved dynamic cutting force model is developed based on the micro cutting mechanics involving the size effect, undeformed chip thickness effects and the influence of cutting parameters in the micro scale. Cutting process variables, particle form, size and volume fraction at different scales are taken into account in the modelling. The cutting force multiscale modelling is proposed to have a better understanding on the MMCs cutting mechanics and to predict the cutting force accurately. The cutting forces are modelled and analysed in three cutting regimes: elastic recovery zone, ploughing zone and shearing zone. A novel instantaneous chip thickness algorithm including real chip thickness and real tool trajectory is developed by taking account of the tool runout. Well-designed cutting trials are carried out under varied process variables to evaluate and validate the force model. In order to obtain the actual cutting forces accurately, transfer function technique is employed to compensate the measured cutting forces. The cutting force model is further applied to correlate the cutting tool wear and the prediction of the machined surface generation. Multiphysics coupled thermal-mechanical-tribological model and FE analysis are developed to investigate the cutting stress, cutting temperature, tool wear and their intrinsic relationships in MMCs precision machining process. Heat generation, heat transfer and cutting temperature partition in workpiece, chips and cutting tool are simulated. A modified tool wear rate model is proposed, tool wear characteristics, wear mechanisms and dominate tool wear are further investigated against the real machining process. Cutting tool wear is monitored and assessed offline after machining experiments. The experimental study on the machined surface generation is presented covering cutting force, tool wear, tool life, surface roughness and machining efficiency. Process optimisation is explored by considering the variation of cutting parameters, cutting tool conditions and workpiece materials in order to achieve the desired outcomes and machinability.

Particleboard (PB) is a widely used panel material because of its physical properties and low cost. Unfortunately, cutting can degrade its surface creating rejects and increasing manufacturing costs. A major challenge is PB’s internal variability. Different particle and glue bond strength combinations can sometimes create high quality surfaces in one area and defects such as edge chipping in nearby areas. This research examines methods of improving surface quality by examining PB characteristics and their interactions with the cutting tool. It also develops an analytical model and software tool that allows the effects of these factors to be simulated, thereby giving practical guidance and reducing the need for costly experiments. When PB is cut and the glue bond strength is weaker than the particle strength, particles are pulled out, leading to surface defects. When instead the glue bond strength is stronger than the particle strength, particles are smoothly cut, leading to a high quality surface. PB is modeled as a matrix of particles each with stochastically assigned material and glue bond strengths. The PB model is layered allowing particles to be misaligned. Voids are modeled as missing particles. PB cutting is modeled in three zones. In the finished material and tool tip zones, particles are compressed elastically and then crushed at constant stress. After failure, chip formation occurs in the chip formation zone. At large rake angles, the chip is modeled as a transversely loaded beam that can fail by cleavage at its base or tensile failure on its surface. At small rake angles, the chip is modeled as the resultant force acting on the plane from the tool tip through to the panel surface. Experimental and simulation results show that cutting forces increase with depth of cut, glue content and particle strength. They decrease with rake angle. Glue bond strength can be increased to the equivalent particle strength through the selection of particle geometry and the subsequent increased glue bond efficiency, which increases the cut surface quality without the need for additional glue. Minimizing the size and frequency of voids and using larger rake angles can also increase surface quality.

Particleboard (PB) is a widely used panel material because of its physical properties and low cost. Unfortunately, cutting can degrade its surface creating rejects and increasing manufacturing costs. A major challenge is PB’s internal variability. Different particle and glue bond strength combinations can sometimes create high quality surfaces in one area and defects such as edge chipping in nearby areas. This research examines methods of improving surface quality by examining PB characteristics and their interactions with the cutting tool. It also develops an analytical model and software tool that allows the effects of these factors to be simulated, thereby giving practical guidance and reducing the need for costly experiments. When PB is cut and the glue bond strength is weaker than the particle strength, particles are pulled out, leading to surface defects. When instead the glue bond strength is stronger than the particle strength, particles are smoothly cut, leading to a high quality surface. PB is modeled as a matrix of particles each with stochastically assigned material and glue bond strengths. The PB model is layered allowing particles to be misaligned. Voids are modeled as missing particles. PB cutting is modeled in three zones. In the finished material and tool tip zones, particles are compressed elastically and then crushed at constant stress. After failure, chip formation occurs in the chip formation zone. At large rake angles, the chip is modeled as a transversely loaded beam that can fail by cleavage at its base or tensile failure on its surface. At small rake angles, the chip is modeled as the resultant force acting on the plane from the tool tip through to the panel surface. Experimental and simulation results show that cutting forces increase with depth of cut, glue content and particle strength. They decrease with rake angle. Glue bond strength can be increased to the equivalent particle strength through the selection of particle geometry and the subsequent increased glue bond efficiency, which increases the cut surface quality without the need for additional glue. Minimizing the size and frequency of voids and using larger rake angles can also increase surface quality.

Particleboard (PB) is a widely used panel material because of its physical properties and low cost. Unfortunately, cutting can degrade its surface creating rejects and increasing manufacturing costs. A major challenge is PB’s internal variability. Different particle and glue bond strength combinations can sometimes create high quality surfaces in one area and defects such as edge chipping in nearby areas. This research examines methods of improving surface quality by examining PB characteristics and their interactions with the cutting tool. It also develops an analytical model and software tool that allows the effects of these factors to be simulated, thereby giving practical guidance and reducing the need for costly experiments. When PB is cut and the glue bond strength is weaker than the particle strength, particles are pulled out, leading to surface defects. When instead the glue bond strength is stronger than the particle strength, particles are smoothly cut, leading to a high quality surface. PB is modeled as a matrix of particles each with stochastically assigned material and glue bond strengths. The PB model is layered allowing particles to be misaligned. Voids are modeled as missing particles. PB cutting is modeled in three zones. In the finished material and tool tip zones, particles are compressed elastically and then crushed at constant stress. After failure, chip formation occurs in the chip formation zone. At large rake angles, the chip is modeled as a transversely loaded beam that can fail by cleavage at its base or tensile failure on its surface. At small rake angles, the chip is modeled as the resultant force acting on the plane from the tool tip through to the panel surface. Experimental and simulation results show that cutting forces increase with depth of cut, glue content and particle strength. They decrease with rake angle. Glue bond strength can be increased to the equivalent particle strength through the selection of particle geometry and the subsequent increased glue bond efficiency, which increases the cut surface quality without the need for additional glue. Minimizing the size and frequency of voids and using larger rake angles can also increase surface quality. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

This research develops an analytical scientific approach for investigating the high precision surface generation and the quantitative analysis of the effects of direct factors in precision machining. The research focuses on 3D surface characterization with particular reference to the turning process and associated surface generation. The most important issue for this research is surface functionality which is becoming important in the current engineering industry. The surface functionality should match with the characterization parameters of the machined surface, which can be expressed in formula form as proposed in chapter 4. Modelling and simulation are extensively used in the research. The modelling approach integrates the cutting forces model, thermal mode% vibration model, tool wear model, machining system response model and surface topography model. All of those models are integrated as a whole model. The physical model with such as direct inputs is formed. The major inputs to the model are tooling geometry and the process variables. The outputs from the modelling approach are cutting force, surface texture parameters, dimensional errors, residual stress and material removal rate. MATLAB and Simulink are used as tools to implement the modelling and simulation. According to the simulation results, it is found that the feed rate has the most profound effect on in surface generation. The influence of the vibrations between the cutting tool and the workpiece on the surface roughness may be minimised by the small feed rate and large tool nose radius. Surface functionality simulation has been developed to model and simulate the surface generation in precision turning. The surface functionality simulation model covers the material and tool wear as well. It shows that chip formation is resulted from cutting forces. Cutting trials are conducted to validate the modelling and simulation developed. There are positive results that show the agreement between the simulation and experimental results. The analysis of the results of turning trials and simulations are conducted in order to find out the effects of process variables and tooling characteristics on surface texture and topography and machining instability. From the research, it can be concluded that the investigation on modelling and simulation of precision surfaces generation in precision turning is performed well against the research objectives as proposed. Recommendations for future work are to improve the model parameters identification, including comprehensive tool wear, chip formation and using Neural Networks modelling in the engineering surface construction system.

O presente trabalho tem como objetivo comparar um modelo de formação de cavacos obtido pelo Método dos Elementos Finitos (MEF) com resultados experimentais obtidos em processos de fresamento ortogonal. A comparação se concentra na distribuição de temperatura na peça. O trabalho desenvolve um modelo para a formação de cavacos com a distribuição de temperatura na região de corte usando o software ABAQUS. Inicialmente, o modelo desenvolvido utiliza o Método Explícito de solução para a formação de cavacos durante uma interação da aresta da fresa de topo com a peça. Para a simulação da operação completa de fresamento ortogonal de uma peça com a extensão de 80 mm e espessura de 5 mm em aço AISI 4340 endurecido, o método implícito é utilizado. O material da peça é modelado como isotrópico-elasto-plástico segundo a proposta de Johnson-Cook. A comparação é realizada com velocidades de corte de 80, 100 e 150 m/mim e avanço por dente de 0,17 mm/rev para que as influências da velocidade na temperatura possam ser avaliadas. A partir da comparação desses resultados, é possível analisar a eficiência do modelo desenvolvido pelo MEF para simulação de processos de Usinagem em Altas Velocidades de Corte (HSC - High Speed Cutting). / The goal of this study is to compare a model of chip formation obtained by the Finite Element Method (FEM) with experimental results in orthogonal milling process. The comparison focuses on the temperature distribution in the workpiece. The present work develops a model for chip formation with the temperature distribution in the cutting zone using the software ABAQUS. The model starts using the explicit method of solution for the chip formation during one interaction between the insert and the workpiece. To simulate a complete operation of orthogonal milling on a workpiece 80 mm long and 5 mm thick made of AISI 4340 hardened steel, it was used the implicit method. The workpiece material is modeled as an isotropic-elastic-plastic according to the Johnson-Cook proposal. The comparison is made using cutting speeds of 80, 100 and 150 m/min and feed rate of 0.17 mm/rev to check the in uences of cutting speed on the temperature. From the comparison of these results, it is possible to assess the eciency of the model developed by FEM simulation when machining using High Speed Cutting (HSC) conditions.

O presente trabalho tem como objetivo comparar um modelo de formação de cavacos obtido pelo Método dos Elementos Finitos (MEF) com resultados experimentais obtidos em processos de fresamento ortogonal. A comparação se concentra na distribuição de temperatura na peça. O trabalho desenvolve um modelo para a formação de cavacos com a distribuição de temperatura na região de corte usando o software ABAQUS. Inicialmente, o modelo desenvolvido utiliza o Método Explícito de solução para a formação de cavacos durante uma interação da aresta da fresa de topo com a peça. Para a simulação da operação completa de fresamento ortogonal de uma peça com a extensão de 80 mm e espessura de 5 mm em aço AISI 4340 endurecido, o método implícito é utilizado. O material da peça é modelado como isotrópico-elasto-plástico segundo a proposta de Johnson-Cook. A comparação é realizada com velocidades de corte de 80, 100 e 150 m/mim e avanço por dente de 0,17 mm/rev para que as influências da velocidade na temperatura possam ser avaliadas. A partir da comparação desses resultados, é possível analisar a eficiência do modelo desenvolvido pelo MEF para simulação de processos de Usinagem em Altas Velocidades de Corte (HSC - High Speed Cutting). / The goal of this study is to compare a model of chip formation obtained by the Finite Element Method (FEM) with experimental results in orthogonal milling process. The comparison focuses on the temperature distribution in the workpiece. The present work develops a model for chip formation with the temperature distribution in the cutting zone using the software ABAQUS. The model starts using the explicit method of solution for the chip formation during one interaction between the insert and the workpiece. To simulate a complete operation of orthogonal milling on a workpiece 80 mm long and 5 mm thick made of AISI 4340 hardened steel, it was used the implicit method. The workpiece material is modeled as an isotropic-elastic-plastic according to the Johnson-Cook proposal. The comparison is made using cutting speeds of 80, 100 and 150 m/min and feed rate of 0.17 mm/rev to check the in uences of cutting speed on the temperature. From the comparison of these results, it is possible to assess the eciency of the model developed by FEM simulation when machining using High Speed Cutting (HSC) conditions.

<p>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.</p>