arXiv subjects

Jean-Yves K'Nevez

Publications and source records attributed to Jean-Yves K'Nevez.

13 recordsLinked to original sources

arXiv2012

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.

cs.RO↗

arXiv2012

Experimental Characterization of Robot Arm Rigidity in Order to Be Used in Machining Operation

Attempts to install a rotating tool at the end of a robot arm poly-articulated date back twenty years, but these robots were not designed for that. Indeed, two essential features are necessary for machining: high rigidity and precision in a given workspace. The experimental results presented are the dynamic identification of a poly-articulated robot equipped with an integrated spindle. This study aims to highlight the influence of the geometric configuration of the robot arm on the overall stiffness of the system. The spindle is taken into account as an additional weight on board but also as a dynamical excitation for the robot KUKA KR_240_2. Study of the robotic machining vibrations shows the suitable directions of movement in milling process

cs.RO↗

arXiv2010

Self-excited vibrations in turning: cutting moment analysis

This work aims at analysing the moment effects at the tool tip point and at the central axis, in the framework of a turning process. A testing device in turning, including a six-component dynamometer, is used to measure the complete torsor of the cutting actions in the case of self-excited vibrations. Many results are obtained regarding the mechanical actions torsor. A confrontation of the moment components at the tool tip and at the central axis is carried out. It clearly appears that analysing moments at the central axis avoids the disturbances induced by the transport of the moment of the mechanical actions resultant at the tool tip point. For instance, the order relation between the components of the forces is single. Furthermore, the order relation between the moments components expressed at the tool tip point is also single and the same one. But at the central axis, two different order relations regarding moments are conceivable. A modification in the rolling moment localization in the (y, z) tool plan is associated to these two order relations. Thus, the moments components at the central axis are particularly sensitive at the disturbances of machining, here the self-excited vibrations.

physics.gen-ph↗

arXiv2009

Using Tracking Analysis and Predictive Maintenance in Order to Obtain Dynamics of Machine Tool Spindle

Predictive maintenance is directed towards recognizing the earliest significant changes in machinery condition. Contrasted with protective condition monitoring in which fast response is the primary requirement, predictive monitoring is not limited by time and may use a greather range of complex characteristics. Vibration analysis has long been used for the detection and identification of machine tool condition. Main focus is to identify a procedure to obtain eigenvalue frequencies for machine tool spindle using tracking analysis.

physics.class-ph↗

arXiv2009

Optimization and Dynamic Characterization System Part in Turning

The appearance of the self-sustained vibrations corresponds to the dynamic instability of the machine tool. An experimental device and a model were designed to characterize the cutting system, the block part. This analysis shows the need for knowing more details of it the behavior of the coin at the time of the cut, and for envisaging for the continuation the appearance of vibrations.

physics.class-ph↗

arXiv2009

Analyzes Geometry of Part and Chips at the Time of Regeneratives Vibrations

The actions of cut applied to the elastic system cause relative displacements tool/part, which induce a rise in the temperature in the components of the machine tools, its environment, the system-tools-part and generate vibrations. The experimental procedures installation, at the dynamic level, made it possible to determine the elements necessary to a rigorous analysis of the influence of the geometry of the tool, its displacement and evolution of the contacts tool/part and tool/chip on surface carried out

physics.class-ph↗

arXiv2009

The Regenerative Vibrations Influence on the Mechanical Actions in Turning

In manufacturing during the cutting process the appearance of vibrations can not be avoided. These vibrations constitute a major obstacle to obtain a greater productivity and a better quality of the workpiece. It is thus necessary to develop models which make it possible to study, the totality of the 3D dynamic phenomena. Thanks to an experimental approach the complete torque of the mechanical actions is measured in the presence of the vibrations during a turning operation. This study makes it possible to analyze the variations of the central axis which is a significant parameter of the vibratory phenomena.

physics.class-ph↗

arXiv2009

Self-excited vibrations in turning : Forces torsor analysis

The present work deals with determining the necessary parameters considering a three dimensional model to simulate in a realistic way the turning process on machine tool. This paper is dedicated to the study of the self-excited vibrations incidence on various major mechanics characteristics of the system workpiece / tool / material. The efforts (forces and moments) measurement using a six components dynamometer confirms the tool tip moments existence. The fundamental frequency of 190 Hz proves to be common to the tool tip point displacements, the action application point or at the torque exerted to the tool tip point. The confrontation of the results concerning displacements and efforts shows that the applications points of these elements evolve according to similar ellipses located in quasi identical planes. The large and the small axes of these ellipses are increasing with the feed rate motion values accordingly to the mechanical power injected into the system. Conversely, the respective axes ratios of these ellipses are decreasing functions of the feed rate while the ratio of these ratios remains constant when the feed rate value is increasing. In addition, some chip characteristics are given, like the thickness variations, the width or the hardening phenomenon.

physics.class-ph↗

arXiv2009

Displacements analysis of self-excited vibrations in turning

The actual research deals with determining by a new protocol the necessary parameters considering a three-dimensional model to simulate in a realistic way the turning process on machine tool. This paper is dedicated to the experimental displacements analysis of the block tool / block workpiece with self-excited vibrations. In connexion with turning process, the self-excited vibrations domain is obtained starting from spectra of two accelerometers. The existence of a displacements plane attached to the tool edge point is revealed. This plane proves to be inclined compared to the machines tool axes. We establish that the tool tip point describes an ellipse. This ellipse is very small and can be considered as a small straight line segment for the stable cutting process (without vibrations). In unstable mode (with vibrations) the ellipse of displacements is really more visible. A difference in phase occurs between the tool tip displacements on the radial direction and on the cutting one. The feed motion direction and the cutting one are almost in phase. The values of the long and small ellipse axes (and their ratio) shows that these sizes are increasing with the feed rate value. The axis that goes through the stiffness center and the tool tip represents the maximum stiffness direction. The maximum (resp. minimum) stiffness axis of the tool is perpendicular to the large (resp. small) ellipse displacements axis. FFT analysis of the accelerometers signals allows to reach several important parameters and establish coherent correlations between tool tip displacements and the static - elastic characteristics of the machine tool components tested.

physics.class-ph↗

arXiv2009

New method to characterize a machining system: application in turning

Many studies simulates the machining process by using a single degree of freedom spring-mass sytem to model the tool stiffness, or the workpiece stiffness, or the unit tool-workpiece stiffness in modelings 2D. Others impose the tool action, or use more or less complex modelings of the efforts applied by the tool taking account the tool geometry. Thus, all these models remain two-dimensional or sometimes partially three-dimensional. This paper aims at developing an experimental method allowing to determine accurately the real three-dimensional behaviour of a machining system (machine tool, cutting tool, tool-holder and associated system of force metrology six-component dynamometer). In the work-space model of machining, a new experimental procedure is implemented to determine the machining system elastic behaviour. An experimental study of machining system is presented. We propose a machining system static characterization. A decomposition in two distinct blocks of the system "Workpiece-Tool-Machine" is realized. The block Tool and the block Workpiece are studied and characterized separately by matrix stiffness and displacement (three translations and three rotations). The Castigliano's theory allows us to calculate the total stiffness matrix and the total displacement matrix. A stiffness center point and a plan of tool tip static displacement are presented in agreement with the turning machining dynamic model and especially during the self induced vibration. These results are necessary to have a good three-dimensional machining system dynamic characterization.

cs.CE↗

arXiv2009

Determination Du Centre De Raideur Pour Les Machines-Outils - Application Au Tournage

The determination of the stiffness center of a machine tool is a major element for knowing the dynamic behavior of this one. This stiffness center can be obtained from a static characterization of the machine tool. For an operation of turning, we present an experimental protocol to determine the stiffness matrix, then by inversion, the associated flexibility matrix. This step makes it possible to establish the privileged directions of the movement associated with the maximum and minimal stiffness as well as the stiffness center. Through this step, it is observed that, at the time of an operation of turning, the movement of the point of the tool is carried out according to an ellipse located in a tilted average plan compared to the machine spindle. This movement is linked with the self-excited vibrations. This analysis could be exploited and transposed in the case of the High Speed Machining. It will make it possible to predict various aspects of machining related to the behavior of the tool in the process of cut.

physics.class-ph↗

arXiv2009

Experimental study of machining system: dynamic characterization

In the workspace model of machining an experimental procedure is implemented to determine the elastic behaviour of the machining system. In an other work we have proposed a static characterization of the machining system. In this paper a dynamic characterization and vibration analysis have long been used for the detection and identification of machine tool condition. The natural frequencies of the lathe machining system (Ernault HN400 - France) according with three different situations with no cutting process were acquired. The system modal analysis is used to identify the natural frequencies. These ones and these obtained on the spindle numerical model by finite element method are compared. This research is validated by experimental tests being based to measures of the lathe machine tool frequencies domain. Main focus is to identify a procedure to obtain natural frequencies values for machine tool components in order to establish better conditions in the cutting process on the machine tool.

physics.class-ph↗

arXiv2007

Nouvelle analyse des phénomènes vibratoires en tournage

In the cutting process, machine-tools vibrations are generally a real problem when the amplitude crosses the limits of dimensional or surface quality workpiece precision required. It is necessary to develop models taking into account the three-dimensional vibratory approach to control the vibrations phenomena. An experimental study has been realized to understand the behavior of the cutting system and to identify its vibrations properties. The displacement's localization of the tool in a spatial plan, showed by the experimental results, allows us to simplify the three-dimensional dynamical model. In this study, the experimental approach is completely presented and the first points of the three dimensional vibratory model are proposed according to the experimental results.

physics.class-ph↗