75 research outputs found
Cutting force model for machining of CFRP laminate with diamond abrasive cutter
No full textInternational audienceThe article presents a cutting force model for trimming operations of CFRP laminate with diamond abrasive cutters. Those tools are more and more encountered on industrial applications of CFRP trimming, due to their abrasion resistance and their low cost. Contrary to endmills, they consist of a large number of cutting grits, randomly distributed around the tool. To tackle the issue, a continuous model of tool engagement is proposed. Validity of the approach is verified. A mechanical model of cutting forces, adapted to CFRP laminate, is then presented. The evolution of specific cutting coefficient in relation to fibres orientation is investigated through a piecewise constant model. It leads to the proposal of a sine model for the specific cutting coefficients. The simulated forces are in good agreement with the experimental results of cutting tests, carried out in multidirectional CFRP laminate for different fibres orientation and widths of cut. Cutting mechanisms are finally discussed depending on fibres orientation. A. Boudelier, M. Ritou, S. Garnier, B. Furet, Cutting force model for machining of CFRP laminate with diamond abrasive cutter, Production Engineering, 2018. http://dx
Variant-specific patterns and humoral regulation of HP1 proteins in human cells and tissues
No full textWe have examined the occurrence and distribution of HP1alpha and HP1beta under in vivo, ex vivo and in vitro conditions. Consistent with a non-essential role in heterochromatin maintenance, both proteins are diminished or undetectable in several types of differentiated cells and are universally downregulated during erythropoiesis. Variant-specific patterns are observed in almost all human and mouse tissues examined. Yet, the most instructive example of HP1 plasticity is observed in the lymph nodes, where HP1alpha and HP1beta exhibit regional patterns that are exactly complementary to one another. Furthermore, whereas HP1alpha shows a dispersed sub-nuclear distribution in the majority of peripheral lymphocytes, it coalesces into large heterochromatic foci upon stimulation with various mitogens and IL-2. The effect of inductive signals on HP1alpha distribution is reproduced by coculture of immortalized T- and B-cells and can be confirmed using specific markers. These complex patterns reveal an unexpected plasticity in HP1 variant expression and strongly suggest that the sub-nuclear distribution of HP1 proteins is regulated by humoral signals and microenvironmental cues.J Cell Sc
Elasto-Dynamic Model of Robotic Milling Process Considering Interaction between Tool and Workpiece
No full textInternational audienceIn this paper, a reduced elasto-dynamic model of the robotic based milling process is presented. In contrast to previous works, it takes into account the interaction between the milling tool and the workpiece that depends on the end-effector position, process parameters and cutting conditions (spindle rotation, feed rate, geometry of the tool, etc.). To reduce the dimension of the problem, the robot dynamics is described as an equivalent mass-spring-damper system with six dimensions. This approach, based on the Rayleigh-Ritz approximation, aims at decreasing computational cost and at avoiding inaccuracy due to ill-conditioning in the full size model. To achieve a realistic modeling of the milling process, the machining efforts due to the interaction between robot, tool and working material are introduced into the robot model and calculated at each time instant. Using this global model that integrates the robot dynamics and the milling process particularities, it is possible to obtain the movement of the robot end-effector and corresponding quality of the final product (profile, macro geometry, etc.). In addition, this model allows selecting the best process parameters and avoiding the vibratory behavior of this machining system which can dramatically affect the milling quality. The developed model is applied to the behavior analysis of KUKA KR270 robot used for milling applications. This allows finding acceptable range for robot motion profile parameters
A Tool to Characterize the Electrical Influence of the Thermal and Mechanical Behaviors of Materials of Optics for CPV applications
No full textS.3123-3128Concentrating Photovoltaics (CPV) field aims to integrate expensive high efficiency multi-junction cells into modules with low cost concentrating optics. The choice of the optics depends on different factors: easiness of fabrication and integration process, added costs, optical efficiency and the profile of the spot uniformity reaching the cell. Indeed, previous work has shown a dependence between electrical performance and spectral and spatial uniformities of the light on the cell. To analyze it, a solar CPV test bench is developed at CEA-INES facilities. Lens and cell temperature can be applied separately, in order to evaluate independently different test conditions, while electrical or optical parameters are recorded. The present work shows how temperature and mechanical variations on first stage concentrating optic affects module performances. Several optics and materials are compared, in order to present the tool capabilities.2Nr.5
Contextual classification for smart machining based on unsupervised machine learning by Gaussian mixture model
No full textInternational audienceIntelligent machine-tools generate a large amount of digital data. Data mining can support decision-making for operational management. The first step in a data mining approach is the selection of relevant data. Raw data must, therefore, be classified into different groups of contexts. This paper proposes an original contextual classification of data for smart machining based on unsupervised machine learning by Gaussian mixture model. The optimal number of classes is determined by the silhouette method based on the Bayesian information criterion. This method is validated on real data from four different machine-tools in the aerospace industry. Manual data mining and k-fold cross-validation confirm that the proposed method provides good contextual classification results. Then, several key performance indicators are calculated using this contextual classification. They show the relevancy of the approach
Investigation of Aluminum Alloy Properties During Helical Roller Burnishing Through Finite Element Simulations and Experiments
No full textInternational audienceIndustry is always looking for ways to increase the lifetime of assemblies, especially the fatigue lifetime, from the production phase of fastening holes onwards. Helical roller burnishing is presented here as an innovative mechanical surface treatment. Applied directly after orbital drilling, this technique induces superficial plastic strains that reduce surface roughness and increase hardening and compressive residual stresses. Several studies on 3D finite element models of burnishing have been carried out but they are very time-consuming. In this review, a comparative numerical study of helical burnishing (in terms of calculation time and results on residual stress) between one 3D and two 2D plane strain finite element simulations is performed on 2024-T351 aluminum alloy drilled parts. The impact of the process operating parameters is also investigated. This comparison shows fairly similar results regarding the residual stress profiles but levels are rather different. This could be explained by the complex kinematics of helical roller burnishing, which is strongly three-dimensional. The numerical results of one of the cases studied reveal com-pressive residual stresses of around −100 and −490 MPa in the radial and circumferential directions of the hole, respectively. Burnishing depth and spindle rotation speed have a great impact on the final residual stress profiles. These simulations are then confronted with experimental results obtained during tests carried out using an orbital drilling unit (ORBIBOT). This demonstrates the interest of the modeling implemented and also points out ways to improve the developed models
Under urban mask: On rural landscapes with different logics
No full textAs a result of natural hazards, ecological disasters, lawlessness, wars and fluctuations in economy, numerous European landscapes slowly but surely lose their ‘raison d’être’. The consequence of this is a continuous process of degradation, both in respect to infrastructure as well as the social fabric. Effectively, the changes that occur create specific landscapes that encompass elements, which, at a first glance, could be considered both urban and rural. However, these are prone to mechanisms other than the progressive blurring of the rural-urban dichotomy brought on by urbanization; they are subject to a different kind of rationale. Are they just dissonant nests of desolation or merely slumbering resources for future creative uses? How do we view them? How should we handle them? To the fore of this special session we bring analyses of rural landscapes endowed with specific urban traits whose common denominator is their dysfunctional character. The main task of this special session is to unravel the logics of these particular landscapes by means of: (1) Cognition of the factors and mechanisms that contributed to their emergence; (2) Analyses of the processes that take place in them in order to: (a) determine their course and dynamics, (b) establish potential directions of change; (c) propose methodological solutions – how to do research; (3) Generalization of the research results in search of common problems and similarities in order to: (a) formulate universal methodological assumptions, (b) marshal solutions that are useful in decision-making on administrative and institutional levels. The session has attracted 10 presentations addressing any of these issues in the context of dysfunctional rural landscapes with interesting perspectives and innovative approaches. The spectrum of this double session included: post-war rural areas in Amsterdam (J.E. Abrahamse), Zagreb’s peri-urban fringe (A. Toskić, D. Njegač & D. Orešić), rural transformation from urban influences in Olsztyn (M. Wasilewicz-Pszczółkowska, A. Szczepańska & A. Senetra), degraded urban agglomerations in Poland (R. Krzysztofik, I. Kantor-Pietraga & T. Spórna), landscapes transcending rural-urban characteristics in Gothenburg (M. Dymitrow, R. Brauer, G. Holmertz, B. Apostolovska-Toševska, F. Holmberg & L. Johansson), landscape discriminants in valorization of rural areas in Poland (A. Bocheńska-Skałecka, Z. Kuriata, I. Niedźwiecka-Filipiak, A. Podolska & L. Serafin), degraded towns in Silesia (R. Szmytkie), agri-ghettos in central Poland (J. Biegańska, E. Grzelak-Kostulska & M. Dymitrow), Bucharest's Romani ghetto (D. Teodorescu) and urban agriculture in socially deprived areas of Thessaloniki (E. Gavriilidou, D. Dedousi, E. Oureilidou & M. Ritou)
Influence of bearing kinematics hypotheses on ball bearing heat generation
No full textSpindle dynamics is a key issue in machining. Thermo-mechanical models of spindle need to be developed to understand and predict the complex behavior of spindles at high speed. Accurate bearing stiffness model is required, since it is a boundary condition of the shaft. Besides, bearings also play an important role in heat generation in the spindle. Bearing models rely on kinematics hypotheses at the ball-race contacts. The aim of the paper is to study the influence of these kinematics hypotheses on bearing heat generation. The different kinematics hypotheses that can be found in literature are presented and implemented into the bearing friction model. Simulations of bearing dynamics are performed and contact force and torque at ball-race contacts are compared. Behavior of the bearing models with different kinematic models is studied using a coupled thermo-mechanical model of a specialized test bed. Loss torque and temperatures simulated are compared and validated by experiments
Modèle des interactions dynamiques
No full textIn robotic-based machining, an interaction between the workpiece and technological tool causes essential deflections that significantly decrease the manufacturing accuracy. Relevant compliance errors highly depend on the manipulator configuration and essentially differ throughout the workspace. Their influence is especially important for heavy serial robots. To overcome this difficulty this report presents a new technique for compensation of the compliance errors caused by technological process. In contrast to previous works, this technique is based on the non-linear stiffness model and the reduced elasto-dynamic model of the robotic based milling process. The advantages and practical significance of the proposed approach are illustrated by milling with of KUKA KR270. It is shown that after error compensation technique significantly increase the accuracy of milling.ANR COROUSS
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