The metal cutting industry today is highly automated and, as a step towards Europe's ability to compete on the world market, an increased level of automation can be expected in the future. Therefore, much attention has been paid to the use of automated monitoring systems within the maintenance strategies designed to prevent breakdown. This research focuses on the condition monitoring of cutting tools in CNC turning, using airborne acoustic emission, (AAE). A structured approach for overcoming the problems associated with changing cutting parameters is presented with good results. A reverse and novel approach in estimating gradual tool wear in longitudinal roughing has been made by predicting cutting parameters directly from the acoustics emitted from the process. Using the RMS as a representation of the energy in the signal, where the spectral distributions are working as divisional operators, it has been possible to accurately extract a representation of feed rate, depth of cut and cutting speed from the signal. Using a simplified relationship to estimate tangential cutting force, a virtual force can be calculated and related to a certain amount of flank wear using non-linear regression. Furthermore, this research presents a monitoring solution where disturbances are eliminated by recognising the sound signatures where it, afterwards, is possible to evaluate the reliability of the wear decision. This is done by describing irregularities in the signal , where surface parameters used on a sound waveform, combined in a neural network, has been used to trigger outputs for several defined classes of disturbances. An investigation of the two wear types flank and crater wear, has been conducted and is has been concluded, that although crater wear has an effect on the AAE, it is difficult to recognise this. AAE has shown to an efficient tool to detect flank wear, where a direct relationship is shown between the changes in the cutting parameters, tool wear and AAE. This approach has resulted in a precise monitoring so lution, where flank wear can be estimated within an error of I0%.

The objective of the present thesis is the investigation of the generation mechanism of the ultrasonic vibrations, commonly called acoustic emissions (AE), detected during the course of metal cutting, since, although quite a lot of research effort has been put into the use of AE to monitor metal cutting condition, the mechanism by which AE is generated is still not fully understood. If chip generation is continuous, without built-up edge, and a sharp tool is used, continuous type AE is normally assumed. Most published models relate the energy of AE to the total cutting power, but this can be shown to be rather incorrect. Consequently, as continuous-type AE is mostly generated due to plastic deformation, and as dislocation motion is the main mechanism of plastic deformation of metals, a relationship between AE and dislocation motion is developed for the typical plastic deformation regimes encountered in metal cutting (due to the high temperatures, flow stress decreases with temperature in the so-called diffusion controlled regime, and due to the high strain rates, opposing viscous damping becomes the dominant mechanism governing dislocation movement). Although viscous damping governs the mechanics of deformation in metal cutting, it is proposed that AE is generated due to the interaction between dislocations and obstacles, since as a dislocation approaches an obstacle, strain energy is stored, which is rapidly released as soon as the dislocation surmounts the obstacle, resulting in the emission of an AE event. The detected AE is a result of many consequential likewise events. Consequently, a qualitative original model of AE generation is developed, in which the energetic level of AE is predicted to increase with strain and strain rate, but decrease with temperature, and the frequency content of AE is predicted to increase with strain rate, decrease with temperature, and remain unchanged with strain. In order to access the validity of the above-mentioned model, two sets of metal cutting experiments were accomplished for four different work materials, in which the cutting conditions were varied over a wide range, and the workpiece temperature was artificially modified. Both energy and frequency information were computed from the experimental data using the most appropriate data processing technics, i.e. AE mode and mean frequency, respectively. In addition, a semi-empirical metal cutting theory was utilized to predict basic metal cutting parameters. As the experimental results are in close agreement with the predictions provided by the qualitative model, it is concluded that the main source of AE in metal cutting comes from the interaction of moving dislocations with obstacles, whose dynamics is, however, dictated by viscous damping.

Abrasive waterjet (AWJ) cutting is one of the most promising fast emerging non-traditional cutting technologies. It is highly competitive for machining difficult-to-cut materials like ceramics, composites and titanium alloys as compared to other nonconventional processes (e.g. laser, EDM) which are either technologically inappropriate or fail to be cost-effective. However, at the moment most of the usage of the AWJ machining lies in the area of the through cutting applications and to perform controlled depth cutting (milling) is still at craftsmanship level. This is due to the facts that: (i) AWJ machining is based on employing a jet plume as a "soft body" tool, the footprint of which not only depends on the jet energy parameters (e.g. pressure, abrasive mass flow rate, etc) but also on the jet kinematic parameters (e.g. jet traverse speed) which make controlling of the jet penetration depth very difficult; (ii) there is absence of the appropriate and reliable models that can simulate and predict the AWJ milled footprints and this is one of the major obstructions constraining the use of the AWJ milling applications. The aim of this thesis is to develop accurate models for predicting the A WJ milled footprints. The workpiece material considered is a titanium based superalloy (Ti-6Al- 4V) which is extensively used in the aerospace and medical industry. Two modelling approaches; finite element (FE) modelling and mathematical modelling are presented in this work. Considerable numbers of experiments are conducted to generate the data for validating the results from the models. The models presented in the current study are closer to the real life conditions occurring during the A WJ machining as compared to the state of the art in modelling of AWJ machining. Regarding the FE modelling, the abrasive particles (i.e. garnet) are modeled as elastic with a tensile failure criterion with various non-spherical shapes (rhombic, triangular and trapezoidal) and sharp cutting edges in contrast to the usual approach of assuming them as rigid spherical particles. The effects of mass flow rate of the abrasive particles, traverse speed of the AWJ plume across the workpiece and Gaussian spatial distribution of the abrasive particles in the jet plume are also incorporated in the FE model. The FE model is developed to an extent that it can simulate the footprints as a result of overlapping passes of the AWJ. The simulated jet footprints from the FE models are in good agreement (maximum errors ≤ 15%) with the experimental results. From the mathematical modelling point of view, a model is developed that can accurately predict the AWJ milled footprints with root-mean-squared errors less than 9%. The model takes into account the effects of jet incidence angles, traverse speeds and arbitrarily-moving jet-paths within the target surface. The model is computationally inexpensive and can be used for real time predictions of footprints during CNC machining. The current study provides the reliable models that can be employed for accurate prediction of the abrasive waterjet milled footprints at various process parameters which is a necessary step towards the exploitation of the A WJ machining for controlled depth cutting applications and its automation.

Depuis une dizaine d'années, la découpe par jet hybride où un jet d'eau fait office de guide d'onde pour le laser est utilisée avec succès dans le domaine de la microélectronique. Afin de développer cette technologie pour l'amener vers d'autres marchés tels que l'automobile, la chaudronnerie ou l'aéronautique, il est nécessaire d'augmenter la puissance des lasers et la pression du jet. A ces hauts niveaux énergétiques, les nouvelles interactions qui apparaissent entre la lumière et le fluide ainsi que les modifications du matériau engendrées par le jet hybride n'ont encore jamais été étudiées d'un point de vue physico-chimique. Nous avons donc d'abord mis au point un système permettant de mesurer les propriétés optiques de l'eau à très haute pression dont une application directe pourrait être un capteur optique de pression des fluides. Ainsi et de façon originale, ce travail a permis de mesurer l'indice de réfraction et la polarisabilité de l'eau jusqu'à 250 MPa en modélisant leurs évolutions à l'aide des équations de Tait, de Sellmeier et de Lorentz-Lorenz. Cette étude a débouché sur la création d'un modèle reliant directement la densité du fluide à la mesure de son indice de réfraction. Suite à ces résultats, nous avons pu, après des simulations d'hydrodynamisme, concevoir une tête permettant le couplage d'un laser haute puissance guidé par jet d'eau haute pression. Nous avons alors testé diverses formes de chambres permettant le couplage d'un jet hybride de nouvelle génération. En parallèle, nous avons étudié l'impact physico-chimique d'un jet hybride découplé où le laser et le jet d'eau sont focalisés, pour la découpe, à la surface d'échantillons en acier 301L et en alliage de titane TA6V. Les résultats ont été obtenus par spectroscopie Raman, Diffraction des Rayons X (DRX), microscopie optique et microscopie électronique à balayage couplé à de l'analyse EDS (Energy Dispersive Spectroscopy) et à de l'analyse d'orientation cristallographique (EBSD). Lors de la découpe, des transformations de phases et une couche oxydée apparaissent à la surface des échantillons. Nous avons montré notamment que ces couches d'oxydes ainsi que les résidus de coupe sont en majeure partie constitués de magnétite (Fe3O4) et de rutile (TiO2) / For a decade, the hybrid jet cutting where a water jet acts as waveguide for the laser has been successfully used in the field of microelectronics. To develop this technology and bring it up to other markets such as automotive, boiler or aerospace, it is necessary to increase both the laser energy and the water jet pressure. At these high energy levels, new interactions that occur between light and fluid as well as the material changes caused by the hybrid jet have never been studied from a physicochemical point of view. So, at first, we have devised a system allowing measurements of optical properties of water at high pressure with a possible direct application in optical sensor for fluid pressure. In an original way, this work has allowed us to measure the refractive index and polarizability of water up to 250 MPa and model their evolution using Tait, Sellmeier and Lorentz-Lorenz equations, respectively. A direct result of this study is the creation of a model linking directly the fluid density to the measurement of its refractive index. Following these developments and after hydrodynamics simulations, we have designed a specific head for coupling a high power laser guided by high pressure water jet. Then we have tested various head types allowing the coupling of a new generation hybrid jet. In the same time, we have studied the physicochemical impact of decoupled hybrid jet where the laser and water jet are both focused, for cutting, at the surface of 301L steel and titanium alloy TA6V samples. The analysis have been done by Raman spectroscopy, X-ray diffraction (XRD), optical microscopy and scanning electron microscopy coupled with EDS (Energy Dispersive Spectroscopy) analysis and the crystallographic orientation (EBSD) analysis. During cutting, a phase transformation and an oxidized layer appear on the surface of the samples. We have shown in particular that these oxide layers and cutting residues are mainly composed of magnetite (Fe3O4) and rutile (TiO2)