Etude de vibrations auto-entretenues en coupe tridimensionnelle : nouvelle modélisation appliquée au tournage

Dans la mise en forme par enlèvement de matière, pour certaines morphologies de pièces et sous certaines conditions de coupe, l’apparition de vibrations auto-entretenues est inévitable. Pour remédier à ce phénomène en tournage des matériaux, une étude expérimentale originale exploitant la notion de torseur d’efforts est mise en place pour déterminer, très précisément, le comportement dynamique du système usinant (pièce/outil/machine). Les principaux paramètres relatifs au comportement dynamique du système usinant sont identifiés. La localisation des déplacements de la pointe de l’outil dans un plan caractéristique est démontrée. L’existence de ce plan et les corrélations avec les caractéristiques élastiques du système usinant permettent de simplifier le modèle dynamique 3D et de proposer un modèle en accord avec les résultats expérimentaux tout en restant dans une configuration tridimensionnelle de la coupe. La simulation numérique issue de ce modèle simplifié fournit des résultats en bon accord avec l’expérience.In machining by removal of material, for specific design of parts and under specific cutting conditions, self-excited vibrations are inevitable. To try to cure this phenomenon in turning of materials, an original experimental study based on the concept of torque of forces is set up to determine, very precisely, the dynamic behavior of the machining system (part/tool/machine). The main parameters relating to the dynamic behavior of the machining system are identified. The localization of displacements of the point of the tool in a characteristic plan is demonstrated. The existence of this plan and the correlations with the elastic characteristics of the machining system make it possible to simplify the dynamic model 3D and to propose a model in agreement with the experimental results while remaining in a three-dimensional configuration of the cut. The numerical simulation resulting from this simplified model provides results in perfect agreement with the experiment

Dynamic behavior analysis for a six axis industrial machining robot

The six axis robots are widely used in automotive industry for their good repeatability (as defined in the ISO92983) (painting, welding, mastic deposition, handling etc.). In the aerospace industry, robot starts to be used for complex applications such as drilling, riveting, fiber placement, NDT, etc. Given the positioning performance of serial robots, precision applications require usually external measurement device with complexes calibration procedure in order to reach the precision needed. New applications in the machining field of composite material (aerospace, naval, or wind turbine for example) intend to use off line programming of serial robot without the use of calibration or external measurement device. For those applications, the position, orientation and path trajectory precision of the tool center point of the robot are needed to generate the machining operation. This article presents the different conditions that currently limit the development of robots in robotic machining applications. We analyze the dynamical behavior of a robot KUKA KR240-2 (located at the University of Bordeaux 1) equipped with a HSM Spindle (42000 rpm, 18kW). This analysis is done in three stages. The first step is determining the self-excited frequencies of the robot structure for three different configurations of work. The second phase aims to analyze the dynamical vibration of the structure as the spindle is activated without cutting. The third stage consists of vibration analysis during a milling operation