Hardware-in-the-loop simulator for stability study in orthogonal cutting

International audienceThe self-excited vibrations due to the regenerative effect, commonly known as chatter, are one of the major problems in machining processes. They cause a reduction in the surface quality and in the lifetime of mechanical elements including cutting tools. Furthermore, the experimental investigations of chatter suppression techniques are difficult in a real machining environment, due to repeatability problems of hard to control parameters like tool wear or position dependent dynamic flexibility. In this work, a mechatronic hardware-in-the-loop (HIL) simulator based on a flexible structure is proposed for dimensionless study of chatter in orthogonal cutting. Such system reproduces experimentally, on a simple linear mechanical structure in the laboratory, any stability situation which can be used to test and optimize active control devices. For this purpose, a dimensionless formulation is adopted and the delay related to the phase lag of the actuator and the controller employed on the HIL is compensated

Framework for coupled digital twins in digital machining

This paper presents a further elaboration of the use of the digital twin concept in digital machining. The main goal of the research is an attempt to combine digital representations of different objects involved in the machining process in a holistic manner. Digital twins of the in-process workpiece, cutting tool, clamping, and machine tool along with the process twin are connected in a framework in which all these elements can influence each other. The framework shows different levels of integration of different digital twins and practical recommendation on the implementation. Besides, the framework supports a simulation layer that provides data for the intensity of the interaction. Such interactions can result in, for instance, cascading calculations of cutter workpiece engagement, cutting forces, tool wear, tool deflection, chatter, and so on. Eventually, a design for a software mockup was elaborated to present the developed framework. The entire workflow to simulate part machining in such a digital representation can be used as an ultimate tool for CAM simulation and NC verification within the Zero Defect Manufacturing paradigm

Commande numérique ouverte : interpolation optimisée pour l'usinage 5 axes grande vitesse des surfaces complexes

The manufacturing process reaches maturity concerning Computer Aided Manufacturing and cutting process performances. Nowadays, major improvements are linked to the optimization of the Computer Numerical Control and its interactions with the rest of the manufacturing process. The aim of this thesis is to control the basic components of a CNC in order to optimize the 5-axis high speed machining process of complex surfaces. The realization of an open CNC requires the development of algorithms which transform the machining program into command setpoints for the machine drives. The first part of this thesis allows to round the 5-axis discontinuities caused by the linear tool path interpolation commonly used. Then, a feedrate interpolation algorithm computes the trajectory while respecting the kinematical constraints of the machine and especially the jerk of each axis. The implementation of this work allows to control a 5-axis high speed machine with an open CNC. Hence, the technological barriers that prevent CNC optimizations are removed and the manufacturing process is under control from CAD/CAM to axis displacement. The complete control over the CNC offers the possibility to define the tool path exactly from Computer Aided Design entities without introducing any geometrical deviation generally induced by standard NC code. The direct interpolation of the trajectory on the machined surface significantly improves the quality and the productivity of complex surface machining. The PREMIUM-OpenCNC allows to prove experimentally the efficiency of this work and opens new ways for future manufacturing process improvements.Le processus de fabrication des pièces usinées arrive à maturité concernant la fabrication assistée par ordinateur et la maîtrise du procédé d’usinage. Aujourd’hui, les perspectives d’améliorations importantes sont liées à l’optimisation de la commande numérique et de ses interactions avec le reste du processus de fabrication. L’objectif de cette thèse est donc de maîtriser les briques de base de la commande numérique pour optimiser le processus d’usinage 5 axes grande vitesse des surfaces complexes. La création d’une commande numérique ouverte nécessite le développement des algorithmes qui transforment le programme d’usinage en consignes échantillonnées pour les axes de la machine. La première partie des travaux consiste à rendre la géométrie suffisamment continue notamment pour les trajets interpolés linéairement en 5 axes qui présentent des discontinuités en tangence. Ensuite, l’interpolation temporelle du trajet crée la trajectoire d’usinage respectant les contraintes cinématiques et en particulier le jerk de chacun des 5 axes de la machine. L’implémentation matérielle de ces algorithmes permet de piloter une machine d’usinage grande vitesse 5 axes avec une commande numérique ouverte. Ainsi, les verrous technologiques associés aux commandes numériques industrielles sont levés et la chaîne numérique est entièrement contrôlée de la CFAO jusqu’au déplacement des axes. La maîtrise complète de la commande numérique offre la possibilité de définir exactement le trajet d’usinage à partir de la CAO sans introduire les écarts géométriques inhérents aux formats de description standards. L’interpolation de la trajectoire d’usinage directement sur la surface à usiner améliore de manière significative la qualité et la productivité de l’usinage des surfaces complexes. La commande numérique PREMIUM-OpenCNC permet la validation expérimentale de ces travaux et ouvre de nombreuses autres voies d’amélioration du processus de fabrication

Open CNC : optimized interpolation for 5-axis high speed machining of complex surfaces

Le processus de fabrication des pièces usinées arrive à maturité concernant la fabrication assistée par ordinateur et la maîtrise du procédé d’usinage. Aujourd’hui, les perspectives d’améliorations importantes sont liées à l’optimisation de la commande numérique et de ses interactions avec le reste du processus de fabrication. L’objectif de cette thèse est donc de maîtriser les briques de base de la commande numérique pour optimiser le processus d’usinage 5 axes grande vitesse des surfaces complexes. La création d’une commande numérique ouverte nécessite le développement des algorithmes qui transforment le programme d’usinage en consignes échantillonnées pour les axes de la machine. La première partie des travaux consiste à rendre la géométrie suffisamment continue notamment pour les trajets interpolés linéairement en 5 axes qui présentent des discontinuités en tangence. Ensuite, l’interpolation temporelle du trajet crée la trajectoire d’usinage respectant les contraintes cinématiques et en particulier le jerk de chacun des 5 axes de la machine. L’implémentation matérielle de ces algorithmes permet de piloter une machine d’usinage grande vitesse 5 axes avec une commande numérique ouverte. Ainsi, les verrous technologiques associés aux commandes numériques industrielles sont levés et la chaîne numérique est entièrement contrôlée de la CFAO jusqu’au déplacement des axes. La maîtrise complète de la commande numérique offre la possibilité de définir exactement le trajet d’usinage à partir de la CAO sans introduire les écarts géométriques inhérents aux formats de description standards. L’interpolation de la trajectoire d’usinage directement sur la surface à usiner améliore de manière significative la qualité et la productivité de l’usinage des surfaces complexes. La commande numérique PREMIUM-OpenCNC permet la validation expérimentale de ces travaux et ouvre de nombreuses autres voies d’amélioration du processus de fabrication.The manufacturing process reaches maturity concerning Computer Aided Manufacturing and cutting process performances. Nowadays, major improvements are linked to the optimization of the Computer Numerical Control and its interactions with the rest of the manufacturing process. The aim of this thesis is to control the basic components of a CNC in order to optimize the 5-axis high speed machining process of complex surfaces. The realization of an open CNC requires the development of algorithms which transform the machining program into command setpoints for the machine drives. The first part of this thesis allows to round the 5-axis discontinuities caused by the linear tool path interpolation commonly used. Then, a feedrate interpolation algorithm computes the trajectory while respecting the kinematical constraints of the machine and especially the jerk of each axis. The implementation of this work allows to control a 5-axis high speed machine with an open CNC. Hence, the technological barriers that prevent CNC optimizations are removed and the manufacturing process is under control from CAD/CAM to axis displacement. The complete control over the CNC offers the possibility to define the tool path exactly from Computer Aided Design entities without introducing any geometrical deviation generally induced by standard NC code. The direct interpolation of the trajectory on the machined surface significantly improves the quality and the productivity of complex surface machining. The PREMIUM-OpenCNC allows to prove experimentally the efficiency of this work and opens new ways for future manufacturing process improvements

Kinematical analysis of 5-axis corner smoothing for transitions between linear (G1) blocks

5-axis high speed machine tools are widely used in industry. The axis movements are generated by the Computer Numerical Controller (CNC) which has to transform the part program into a sequence of axis setpoints. Most of the time, the tool path is described with linear segments (G1) which lead to tangency discontinuities between blocks. With acceleration and jerk limitations, these discontinuities will induce a zero feedrate and thus surface marks and an increase in machining time. The aim of this paper is to study a 5-axis corner smoothing method required to obtain a C2 continuous tool path geometry. Several methods have been developed in 3-axis but the 5-axis corner smoothing is still a challenge. To smooth the tool tip position and the tool orientation, the 5-axis tool path is represented by two B-Spline curves. The proposed corner smoothing model allows to control the contour and orientation tolerances in the workpiece coordinate system. The main difficulty is to obtain a C2 continuous connection between the initial tool path and the newly inserted smoothing portion. This connection is linked to the parametrization of the bottom and top B-Splines. This algorithm can be integrated to a feedrate interpolator to control a 5-axis milling machine equipped with an Open CNC

Direct Trajectory Interpolation on the Surface using an Open CNC

International audienceFree-form surfaces are used for many industrial applications from aeronautical parts, to molds or biomedical implants. In the common machining process, computer-aided manufacturing (CAM) software generates approximated tool paths because of the limitation induced by the input tool path format of the industrial CNC. Then, during the tool path interpolation, marks on finished surfaces can appear induced by non smooth feedrate planning. Managing the geometry of the tool path, as well as the kinematical parameters of the machine tool, are two key factors for quality and productivity improvements. The aim of this paper is to present a unified method to compute the trajectory directly on the surface to be machined avoiding CAM approximations and producing a smoother trajectory. This paper proposes an interpolation of the trajectory based on the free-form surface mathematical model while considering the kinematical limitations of a high-speed milling machine (velocity, acceleration, and jerk). The amelioration of the data exchange between computer-aided design (CAD)/CAM and CNC opens new ways to optimize the manufacturing process. The direct trajectory interpolation on the surface (DTIS) method allows to obtain both a higher productivity and a better surface quality. Machining experiments carried out with an Open CNC on a 5-axis high-speed milling machine show the benefits of the proposed method compared to the classical strategies available with an industrial CNC

Amélioration de la qualité des pièces usinées par interpolation directe du trajet sur surface

National audienceDespite recent advances in technology and software, the High Speed Machining process of complex surfaces still has challenges to achieve simultaneously productivity and high surface quality. Two of them are the tool path generation and its treatment by the numerical controller during real-time interpolation. To date, the classical solution "CAM-CNC" imposes breaks in the digital chain, limiting the final results that are really reached. This paper proposes a unified method, named DTIS (Direct Trajectory Interpolation on the Surface), for multi-axis tool paths generation and interpolation within a HSM context. It avoids the geometrical deviations related to the description format of the tool path and to their jerk limited interpolation. Thanks to the development of an open CNC on the LURPA's 5-axis high speed machining center, it is possible to evaluate the improvements provided by such an approach compared to the usual process.Malgré les avancées technologiques et logicielles, le processus de réalisation par UGVdes pièces de formes complexes comporte des points durs pour atteindre simultanément productivité et qualité de surface élevées. Un des verrous scientifiques concerne les phases de calcul des trajectoires puis leur traitement par la Commande Numérique lors de l'interpolation temporelle.A ce jour, la solution FAO logicielle-CN impose une « fracture dans la chaîne numérique, limitant les performances finales atteintes. Cet article propose une méthode unifiée, nommée DTIS (Direct Trajectory Interpolation on the Surface), pour la génération et l'interpolation des trajectoires dans un contexte UGV multi-axes. Ellepermet d'annuler les écarts géométriques liés à la description et à l'interpolation à jerk contrôlé des trajectoires. Grâce au développement d'une CN ouverte sur le centre UGV 5 axes industriel du LURPA, il est possible d'évaluer le gain apporté par une telle démarche vis-à-vis du processus classique. Mots clés : écart géométrique, erreur de corde, trajectoire, UGV, interpolation à jerk contrôlé

Maximum Feedrate Interpolator for Multi-axis CNC Machining with Jerk Constraints

A key role of the CNC is to perform the feedrate interpolation which means to generate the setpoints for each machine tool axis. The aim of the VPOp algorithm is to make maximum use of the machine tool respecting both tangential and axis jerk on rotary and linear axes. The developed algorithm uses an iterative constraints intersection approach. At each sampling period, all the constraints given by each axis are expressed and by intersecting all of them the allowable interval for the next point along the path is computed. Examples and comparisons with an industrial CNC demonstrate the performances of the algorithm

Feedrate interpolation with axis jerk constraints on 5-axis NURBS and G1 tool path

International audienceA key role of the CNC is to perform the feedrate interpolation which consists in generating the setpoints sent to each axis of a machine tool based on a NC program. In high speed machining, the feedrate is limited by the velocity, acceleration and jerk of each axis of the machine tool. The algorithm presented in this paper aims to obtain an optimized feedrate profile which makes best use of the kinematical characteristics of the machine. This minimum time feedrate profile is computed by intersecting all the constraints due to the drives in an iterative algorithm. It is worth noting that both tangential jerk and axis jerk are taken into consideration. The proposed VPOp (Velocity Profile Optimization) method is universal and can be applied to any articulated mechanical structure as it is demonstrated in the examples. Moreover the algorithm has been implemented for various formats: linear interpolation (G1) and NURBS interpolation in 3 and 5-axis. The effectiveness of the algorithm is demonstrated thanks to a comparison with an industrial CNC and can be freely tested using the VPOp software which is available on the internet http://webserv.lurpa.ens-cachan.fr/geo3d/premium/vpo