Méthodes de compensation des erreurs d'usinage utilisant la mesure sur machines-outils

"RÉSUMÉ:" Cette thèse vise à développer des modèles mathématiques qui utilisent les données d'inspection en semi-finitions pour formuler la compensation de la passe de finition afin d’améliorer la précision d’usinage. Pour la rentabilité industrielle, les tâches de mesure et de compensation doivent être effectuées sous la condition de l’usinage à porte fermée sans interventions humaines. La mesure sur machines-outils est utilisée pour inspecter la pièce immédiatement après la coupe toute en gardant le même montage. Elle détecte les défauts de fabrication vus par la machine-outils. Le fléchissement du système machine-outil-pièce et l'imprécision des dimensions de l’outil de coupe sont les sources les plus importantes de ces défauts. La pièce usinée peut ainsi être inspectée en semi-finitions pour prédire les déviations systématiques qui pourraient survenir plus tard à la passe de finition. Donc, afin de produire une pièce avec une précision acceptable, des actions de correction peuvent être dérivées pour anticiper l'erreur attendue. L’erreur est modélisée comme étant la somme de deux composantes. Une composante indépendante de la profondeur de coupe et liée à la dimension de l'outil tel que l'usure. L'autre dépend de la profondeur de coupe telle que le fléchissement. Un modèle général est présenté, qui relie seulement les résultats d’inspection sur machine-outils pour compenser la passe finale. Le coefficient variable de la compliance de coupe relie, en mode multi-passe, le fléchissement total à la profondeur de coupe. Il est utilisé pour estimer la compensation de la trajectoire. Le modèle est capable de prendre en compte l'effet de la variation de la profondeur de coupe et de l'enlèvement de la matière dans l'estimation de la compensation. Afin de générer la trajectoire compensée sous forme continue à partir de mesures discrètes, une technique de déformation de B-Spline est adoptée pour les données disponibles et appliquées pour calculer la trajectoire compensée à partir d’un nombre limité de vecteurs de compensation discrètes. Les résultats montrent que les erreurs mesurées sur machine-outils peuvent être réduites significativement en utilisant le modèle de compensation proposé. La machine à mesurer tridimensionnelle est utilisée pour vérifier la mesure sur machine de bague étalon. Pour une plaque mince, une erreur de 78 μm est réduite à moins de ± 3 μm. Pour une paroi circulaire avec une raideur variable l'erreur est réduite de -60 à ± 6 μm. Pour une plaque mince de forme libre semblable à un profil aérodynamique, représenté par B-Spline, l'amélioration est de 140 μm à ± 20 μm.----------"ABSTRACT:" On-machine measurement process is used to inspect the part immediately after the cut without part removal and additional setups. It detects the machining defects visible to the machine tool. The system machine-tool-part deflection and the cutting tool dimension inaccuracy are the most important sources of these defects. The machined part can be inspected, at the semi-finishing cut level to identify systematic defects that may occur later at the finishing cut. Therefore, corrective actions can be derived to anticipate the expected error in order to produce a part with acceptable accuracy. For industrial profitability, the measurement and the compensation tasks must be done under the closed door machining requirement without human interventions. This thesis aims to develop mathematical models that use the data inspection of previous cuts to formulate the compensation of the finishing-cut. The goal of the compensation is to anticipate the expected error which is identified under two components. One is independent on the depth of cut and is related to the cutting tool dimension such as the wear. The other is dependent on the cutting depth such as the deflection. A general model is presented which relies solely on-machine probing data from semi-finishing cuts to compensate the final cut. A variable cutting compliance coefficient relates the total system deflection to the depth of cut in multi-cut process. It is used to estimate the compensation of the tool path. The model is able to take into account the effect of the cutting depth variation and the material removal in the estimation of the error at the finishing-cut. In order to generate the continuous compensated tool path from discrete measurements, a B-Spline deformation technique is adapted to the available data and applied to compute the compensated tool path according to a restricted number of discrete compensation vectors. The results show that the on-machine probed errors can be significantly reduced using the proposed compensation model. The coordinate measurement machine is used to verify the on machine measurement of a ring gauge. For a simple straight thin wall, an error of 78 μm is reduced to less than ± 3 μm. For a circular wall with variable stiffness using a multi-cut process, the error is reduced from -60 μm to ±6 μm. For a free form thin wall similar to airfoil profile represented with the B-Spline, the improvement is from +140 μm to ±20 μm

Influence of feed drives on the structural dynamics of large-scale machine tools

Milling is one of the most widely used processes in the manufacturing industry and demands machines with high productivity rates. In large machine tool applications, the cutting capability is mainly limited by the appearance of structural chatter vibrations. Chatter arises from the dynamic interaction of the machining system compliance with the cutting process. For the specific case of large-scale machine tools, the low frequency resonances have modal shapes that generate relative displacements in the machine joints. This thesis presents new approaches to minimize the appearance of chatter vibrations by targeting and understanding the machine tool compliance, in particular, from the feed drive of the machine tool. A detailed model of the double pinion and rack feed drive system and the master-slave coupling improves the large machine tools modeling. As the vibrations are measured by the axes feedback sensors, a new strategy for feed drive controller tuning allows increasing the chatter stability using a judicious selection of the servo parameters. Then, in-motion dynamic characterizations demonstrate the important influence of the nonlinear friction on the machine compliance and improve the chatter stability predictions. Finally, an operational method for characterizing both tool and workpiece side dynamics while performing a cutting operation is developed. All the contributions of the thesis have been validated experimentally and tend to consider the influence of the feed drives on the structural dynamics of large-scale machine tools

From CAD-Design to Force Controlled Robot Manufacturing

This Master Thesis presents the necessary steps to manufacture a piece, starting from the draw in the software Pro/ENGINEER and then processing the generated G-code to create a RAPID program understandable for the robot. Some additions required to make the code work on the Teach Pendant of the IRB 2400-16 are explained in detail. Apart from the RAPID program, the robot is also controlled with the help of a Simulink controller created to avoid collisions and to assure a compliant behaviour with the environment. An extra application is included in order to obtain information about the shape of the workpiece that the robot will machine

Intelligent Machining Systems

Machining is one of the most widespread manufacturing processes and plays a critical role in industries. As a matter of fact, machine tools are often called mother machines as they are used to produce other machines and production plants. The continuous development of innovative materials and the increasing competitiveness are two of the challenges that nowadays manufacturing industries have to cope with. The increasing attention to environmental issues and the rising costs of raw materials drive the development of machining systems able to continuously monitor the ongoing process, identify eventual arising problems and adopt appropriate countermeasures to resolve or prevent these issues, leading to an overall optimization of the process. This work presents the development of intelligent machining systems based on in-process monitoring which can be implemented on production machines in order to enhance their performances. Therefore, some cases of monitoring systems developed in different fields, and for different applications, are presented in order to demonstrate the functions which can be enabled by the adoption of these systems. Design and realization of an advanced experimental machining testbed is presented in order to give an example of a machine tool retrofit aimed to enable advanced monitoring and control solutions. Finally, the implementation of a data-driven simulation of the machining process is presented. The modelling and simulation phases are presented and discussed. So, the model is applied to data collected during an experimental campaign in order to tune it. The opportunities enabled by integrating monitoring systems with simulation are presented with preliminary studies on the development of two virtual sensors for the material conformance and cutting parameter estimation during machining processes

Industrial Robotics for Advanced Machining

This work presents a literature review of the current state of robotic machining with industrial machining robots, primarily those with 6-axis end effectors and serial link (anthropomorphic) construction. Various disadvantages of robotic machining in industry are presented, as well as the methods applied to mitigate them and discussions of their effects. From this review, the methods of dynamic modelling, stability prediction and configuration control are selected for application to the task of optimisation of a robotic machining cell for drilling operations. Matrix Structural Analysis (MSA) and methods developed by Klimchik et al. are used for compliance modelling, stability prediction methods developed by Altintas et al. and machining stability lobe prediction are then applied to a robotic drilling process, as explored by Mousavi et al. This optimisation method is applied using the measured and estimated properties of an ABB IRB 6640 robot and results are presented in comparison with previous experimentation with the physical robot, and analytical stability predictions from the same cutting parameters with Cutpro software. Results are discussed in the concluding chapters, as well as discontinued parts of the project and suggestions for future work

Measurement Accuracy Investigation of Touch Trigger Probe with Five-Axis Machine Tools

The touch trigger probe plays an important role in modern metrology because of its robust and compact design with crash protection, long life and excellent repeatability. Aside from coordinate measuring machines (CMM), touch trigger probes are used for workpiece location on a machine tool and for the accuracy assessment of the machine tools. As a result, the accuracy of the measurement is a matter of interest to the users. The touch trigger probe itself as well as the measuring surface, the machine tool, measuring environment etc. contribute to measurement inaccuracies. The paper presents the effect of surface irregularities, surface wetness due to cutting fluid and probing direction on probing accuracy on a machine tool

A Metrics-based Sustainability Assessment of Cryogenic Machining Using Modeling and Optimization of Process Performance

The development of a sustainable manufacturing process requires a comprehensive evaluation method and fundamental understanding of the processes. Coolant application is a critical sustainability concern in the widely used machining process. Cryogenic machining is considered a candidate for sustainable coolant application. However, the lack of comprehensive evaluation methods leaves significant uncertainties about the overall sustainability performance of cryogenic machining. Also, the lack of practical application guidelines based on scientific understanding of the heat transfer mechanism in cryogenic machining limits the process optimization from achieving the most sustainable performance. In this dissertation, based on a proposed Process Sustainability Index (ProcSI) methodology, the sustainability performance of the cryogenic machining process is optimized with application guidelines established by scientific modeling of the heat transfer mechanism in the process. Based on the experimental results, the process optimization is carried out with Genetic Algorithm (GA). The metrics-based ProcSI method considers all three major aspects of sustainable manufacturing, namely economy, environment and society, based on the 6R concept and the total life-cycle aspect. There are sixty five metrics, categorized into six major clusters. Data for all relavant metrics are collected, normalized, weighted, and then aggregated to form the ProcSI score, as an overall judgment for the sustainability performance of the process. The ProcSI method focuses on the process design as a manufacturer’s aspect, hoping to improve the sustainability performance of the manufactured products and the manufacturing system. A heat transfer analysis of cryogenic machining for a flank-side liquid nitrogen jet delivery is carried out. This is performed by micro-scale high-speed temperature measurement experiments. The experimental results are processed with an innovative inverse heat transfer solution method to calculate the surface heat transfer coefficient at various locations throughout a wide temperature range. Based on the results, the application guidelines, including suggestions of a minimal, but sufficient, coolant flow rate are established. Cryogenic machining experiments are carried out, and ProcSI evaluation is applied to the experimental scenario. Based on the ProcSI evaluation, the optimization process implemented with GA provides optimal machining process parameters for minimum manufacturing cost, minimal energy consumption, or the best sustainability performance