Complete Analytical Expression of the Stiffness Matrix of Angular Contact Ball Bearings

International audienceAngular contact ball bearings are predominantly used for guiding high speed rotors such as machining spindles. For an accurate modelling, dynamic effects have to be considered, most notably in the bearings model. The paper is based on a dynamic model of angular contact ball bearings. Different kinematic hypotheses are discussed. A new method is proposed for the computation of the stiffness matrix: a complete analytical expression including dynamic effects is presented in order to ensure accuracy at high shaft speed. It is demonstrated that the new method leads to the exact solution, contrary to the previous ones. Besides, the computational cost is similar. The new method is then used to investigate the consequence of the kinematic hypotheses on bearing stiffness values. Last, the relevance of this work is illustrated through the computation of the dynamic behavior of a high speed milling spindle. The impact of this new computation method on the accuracy of a finite element spindle model is quantified

L'histoire, un medium de didactique aux Nouvelles Technologies

National audienceL'enseignement de la Conception Assistée par Ordinateur en projet tutoré doit permettre d'appréhender d'une part les notions vues pendant les heures d'enseignement mais aussi les difficultés liées à une maquette numérique de taille industrielle (gestion de projet, des fichiers, travail collaboratif). La motivation et le suivi des étudiants sont les garants d'une étude intéressante et formative mais ils sont souvent délicats avec des projets industriels. Nous proposons ici un témoignage pédagogique d'une nouvelle thématique de recherche émergente: la conservation et la valorisation du patrimoine technique et industriel. La richesse technique des "vieilles" machines étudiées, du contexte de l'époque, et la qualité des différents intervenants dans le projet (conservateurs de ce patrimoine, historiens des techniques...) ont séduits les groupes d'étudiants réalisant ce type de projet et c'est pour nous, chercheurs et enseignants, un devoir de diffuser ce type de démarche afin de la rendre reproductible dans d'autres structures universitaires

Acceptation d'un gant d'assistance aux gestes de la main

International audienceAcceptation d'un gant d'assistance aux gestes de la mai

Foam additive manufacturing technology: main characteristics and experiments for hull mold manufacturing

International audiencePurpose The purpose of this paper is to present a novel methodology to produce a large boat hull with a foam additive manufacturing (FAM) process. To respond to shipping market needs, this new process is being developed. FAM technology is a conventional three-dimensional (3D) printing process whereby layers are deposited onto a high-pressure head mounted on a six-axis robotic arm. Traditionally, molds and masters are made with computer numerical control (CNC) machining or finished by hand. Handcrafting the molds is obviously time-consuming and labor-intensive, but even CNC machining can be challenging for parts with complex geometries and tight deadlines. Design/methodology/approach The proposed FAM technology focuses on the masters and molds, that are directly produced by 3D printing. This paper describes an additive manufacturing technology through which the operator can create a large part and its tools using the capacities of this new FAM technology. Findings The study shows a comparison carried out between the traditional manufacturing process and the additive manufacturing process, which is illustrated through an industrial case of application in the manufacturing industry. This work details the application of FAM technology to fabricate a 2.5 m boat hull mold and the results show the time and cost savings of FAM in the fabrication of large molds. Originality/value Finally, the advantages and drawbacks of the FAM technology are then discussed and novel features such as monitoring system and control to improve the accuracy of partly printed are highlighted

Investigation of the Evolution of Modal Behavior of HSM Spindle at High Speed

International audienceThe cutting stability and the lifetime of High Speed Machining spindles highly depend on its modal behavior. A specific electromagnetic excitation device is used to measure the Frequency Response Function of the spindle at high speeds. The evolution with speed of the eigenfrequencies and of the radial stiffness is analyzed. A numerical model is developed to obtain the associated modes shapes; since they cannot be measured experimentally. The simulations, which are in good agreement with the experiments, enable an understanding of the evolutions of the spindle dynamic, and notably of the evolution of modal coupling at high speed

Bearings Influence on the Dynamic Behavior of HSM Spindle

International audienceThe aeronautic industry requires high speed and high power spindles to obtain high material removal rates during long rough milling operations. The weakness of HSM spindle is the bearings, although high precision hybrid ball bearings have been developed to achieve this critical application. Inadequate use of spindles inevitably leads to shortened lifetimes. Choosing the operating conditions is a required step before machining applications. It can be achieved through either experimental tests or numerical modeling that leads to stability lobe diagrams. Stability of cuts relies on the dynamic behavior of the spindle, which is particularly due to the eigenfrequencies of the tool-shaft assembly. The frequencies depend on bearing stiffness that can change under operating conditions. That is why the impact of cutting conditions and bearing parameters on its stiffness are studied in the paper. A five degrees of freedom model of angular ball bearing is briefly presented. A complete bearing model is introduced. The originality of the approach is the complete technological modeling, notably of the radial expansions of inner and outer rings of bearing. A non-linear expression is established from continuum mechanics model. The influence of geometry of bearing, operating conditions and design parameters of spindle on the bearing stiffness are established and analysed. Then, modal analyses of the tool-spindle assembly are carried out in relation to the varying bearing stiffness. Finally, significance of the approach is demonstrated through the analyses of Frequency Response Function

Phenomenological model of preloaded spindle behavior at high speed

International audienceHigh-speed machining spindles are high-precision mechanisms with a complex and very sensitive behavior. Frequency response functions are required to avoid unstable cutting conditions that lead to premature failure of spindle and tool. However, FRFs are affected by stiffness loss of the bearings at high speed. Indeed, the rotor’s behavior is driven by its boundary conditions which are the preloaded bearings. In order to obtain an accurate model of the preloaded bearing system, this paper focuses on the axial spindle behavior. An analytical model that computes the equilibrium state of the shaft, rear sleeve, and bearing arrangement is presented. A model enrichment method is presented with several new physical phenomena: the macroscopic deformations of the shaft and bearing rings as well as the rear sleeve’s complex behavior. The significance of these phenomena is evaluated with a sensitivity analysis and used for the model updating to obtain a just accurate enough model. The contributions of these enrichments are presented for a case study performed on an industrial spindle. A good agreement between the simulation and the experimental results are achieved that validates the model updating strategy and the phenomenologically enriched model

Modeling and characterization of an electromagnetic system for the estimation of Frequency Response Function of spindle

International audienceAn electromagnetic system developped to measure the quasi-static and dynamic behavior of the machining spindles at different spindle speed is presented in this paper. This system consists in four Pulse Width Modulated amplifiers and four electromagnets to produce magnetic forces of ±190N for the static mode and ±80N for the dynamic mode at up to 5kHz. In order to measure the Frequency Response Function of the spindle at the tool tip, the precise prediction of the applied load is required. A dynamic force model is proposed in order to obtain the load from the measured current in the amplifiers. The model depends on the exciting frequency and on the magnetic characteristics of the system. The predicted force at high speed is validated with a specific experiment and the perfomance limits of the experimental device are investigated. The Frequency Response Functions obtained with the electromagnetic system are compared to a classical tap test measurement at 0 rpm

Experimental Investigation of the Dynamic Behavior of High Speed Machining Spindles with an Electromagnetic Excitation Device

International audienceFrequency Response Function measurements are carried out on two different industrial HSM Spindles rotating up to 24000rpm and powered from 40 to 70kW. An electromagnetic excitation device capable of applying a dynamic force to ±80N at 5kHz is used to perform the experiment. Measurements are made on four points by two displacement sensors and two accelerometers. A specific signal processing method that uses the cepstrum of the signal is applied to remove harmonics of the rotation in the signal. Variations of the dynamic behavior of the spindles with speed are observed and analyzed