Étude de l'état de surface de trous percés dans des stratifiés carbone UD

Les exigences de qualité dimensionnelle, d’état de surface et de santé matière imposées sur les trous percés dans des stratifiés composites UD sont drastiques dans le domaine aéronautique, du fait parfois d’une mauvaise connaissance de l’impact des défauts générés pendant le perçage sur la tenue en service des assemblages. C’est le cas de l’exigence d’un critère de rugosité Ra. Nos travaux portent sur la caractérisation et la qualification des défauts de paroi rencontrés lors des opérations de perçage des stratifiés composites UD. Dans un premier temps, les endommagements caractéristiques d’une opération de perçage ont été identifiés et reliés à l’angle entre la vitesse de coupe et l’orientation des fibres d’un pli. Par la suite, la surface d’un perçage a été mesurée au rugosimètre à contact, sur toute sa circonférence, par pas de 5°. Il apparaît que la valeur de Ra obtenue dépend fortement de la position de la ligne de mesure. Cela s’explique par le fait que la position angulaire des endommagements varie et dépend de la séquence d’empilement du stratifié. Il apparaît également que le profil de rugosité R est en partie artificiel, du fait du filtrage de l’ondulation (ISO4287). Ces travaux démontrent donc qu’un critère Ra (ou autre critère de type R) n’est pas représentatif de l’état de surface des trous percés dans les stratifiés composites, et que d’autres critères doivent être envisagés. Par la suite, l’étude s’est attachée à identifier les critères de type P qui sont représentatifs des états de surface obtenus, et à étudier l’influence des conditions opératoires lors du perçage (conditions de coupe, usure outil) sur la dégradation du stratifié. Les résultats montrent qu’un seul critère ne suffit pas à caractériser l’état de surface. L’étude permet également d’identifier les relations entre l’endommagement de la surface percée et les conditions opératoires

Predicting the dynamic behaviour of torus milling tools when climb milling using the stability lobes theory

This paper investigates stability and dynamic behaviour of torus tool in climb milling on 5 positioned axes. The stability lobes theory is used to enable stable cutting conditions to be chosen. As the adaptation of such a theory to complex milling configurations is a difficult matter, new methods are presented to identify the dynamic parameters. Tool dynamic characteristics (stiffness and natural pulsation) are determined with an original coupled calculations-tests method. Start and exit angles are computed exactly using an original numerical model. A sensitivity analysis highlights the influence of machining parameters on stability of climb milling. This shows that a third region of “potential instability” must be taken into account in plotting stability lobes, due to the uncertainty of prediction due to modelling and identification of parameters. The results were validated experimentally with an innovative approach, especially through the use of high-speed cameras. Analysis of vibrations and the surface roughness allowed the analytical model to be verified so as to optimise the inclination of the tool on the surface

Comparative study of tools in drilling composites T700-M21 and T800-M21

The drilling of composite materials can produce, around the hole, defects and damages which decrease the mechanical resistance of the drilled workpiece. This study shows the influence of several tools (drill, mill and reamer) on the hole quality obtained, in the context of reference parts where surface integrity is a priority. An experimental study is suggested and the criteria used to assess the hole quality are defined. Results show the behavior of each type of cutting tool and their influence on the defects generated. Finally, this study helps creating a scale of recommended cutting conditions to reduce the tool wear and improve the hole quality

Topological surface integrity modification of AISI 1038 alloy after vibration-assisted ball burnishing

The objective of this paper is to analyze the effect of the vibration-assisted ball burnishing process on the topology of AISI 1038 flat surfaces, in order to evaluate its feasibility for surface enhancement towards wear prevention and fatigue enhancement in industrial components. With that aim, an experimental campaign based on a Taguchi orthogonal matrix has been deployed. Five factors were studied, namely: preload force, number of passes, feed, initial surface texture and strategy. The topologies of the resulting burnishing patches have been acquired with a non-contact optical device, and the 3D texture parameters have been calculated to quantify the effects of burnishing. In all cases, the bearing capacity of the burnished surfaces was improved, as the proportion of core material is increased due to the deformation of the surface peaks. The initial surface state proved to be the most influential parameter on amplitude, spatial, and volumetric parameters. In all cases, a set of optimal vibration-assisted ball burnishing parameters was found for the sake of reproducibility and systematization of the process. Finally, results have been compared to the conventional ball burnishing process, observing that it presents scratch damage on the surfaces that can be prevented through assistance through vibrations.Postprint (author's final draft

Etude du comportement dynamique des outils toriques en usinage 5 axes

Notre étude a pour but de mieux comprendre le comportement d'outils toriques de faibles diamètres lors de l'usinage de surfaces gauches. Des approches théorique et expérimentale ont été couplées. L'étude théorique s'attache à déterminer la relation entre la stratégie utilisée en terme de trajectoires outil (plans parallèles, Z constant, ...) et le comportement dynamique de l'outil en usinage. La partie expérimentale a permis d'analyser le comportement vibratoire de l'outil lors de la coupe pour différentes stratégies d'usinage. Pour cela, des analyses acoustiques, ainsi que des mesures dimensionnelles et d'états de surface ont été menées. Cela nous permet de définir des règles de construction de parcours d'usinage de surfaces complexes avec ce type d'outils. En effet, certaines stratégies s'avèrent préjudiciables à la qualité d'usinage et à la durée de vie d'outil alors que d'autres apportent une réelle amélioration sur la qualité de la pièce usinée

Effect of adding a woven glass ply at the exit of the hole of CFRP laminates on delamination during drilling

Composite materials are increasingly used in the aeronautical field. The assembly of structures requires usually drilling of composite parts. Drilling of composite materials generates defects, mainly delamination at the exit of the hole. This major defect diminishes the structure strength. Delamination is directly related to the drilling thrust force. Minimizing this force reduces the defects. Adding a woven glass ply at the exit of the hole is found to be another adequate solution to reduce the defects. In this paper, the drilling of carbon/epoxy thick composite structures with a woven glass ply at the exit of the hole is considered. An analytical model is developed to determine for a given tool geometry the critical delamination forces as function of the number of non-drilled plies remaining beneath the tool. The results are validated experimentally. These results show that adding a woven glass ply at the exit of the hole reduces delamination

Comprehensive analysis of surface integrity modification of ball-end milled Ti-6Al-4V surfaces through vibration-assisted ball burnishing

Peer ReviewedPostprint (author's final draft

Modelling kinematics and cutting forces in vibration assisted drilling

One of the main drawbacks of the traditional drilling process is the formation of long chips when cutting metallic parts. Usually, peck drilling cycles are used to break and evacuate the chips through the flutes of the drill. However, this solution increases the operation time and therefore decreases the productivity. To solve this problem, vibration assisted drilling has been developed to meet industrial needs in terms of productivity. Forced vibrations impose a variation of the chip thickness in order to obtain its fragmentation. This process has been recently developed and optimal cutting conditions have yet to be determined to improve it furthermore. This paper presents, on the first hand, an experimental study of the kinematics of vibration assisted drilling. It showed a strong reduction of the amplitude of vibration during drilling, in the configuration of the tests. In addition, tests were conducted to show the apparition of interference phenomena at the centre of the tool. Interferences are difficult to separate from the cutting phenomenon, making the modelling of cutting forces difficult. From the kinematic model, chip height can be simulated in order to model the cutting forces. A thrust force and a torque model applied to vibration assisted drilling are presented in this paper. The thrust force model is based on a representation of the tool by several zones corresponding to each cutting mechanism: indentation at the centre of the tool, cutting along the cutting edges and bad cutting conditions in an intermediary zone. The periodically variable feed speed modifies the size of each zone and the thrust force they generate. The model presented in this paper formulates the interaction of several zones of the tool with the material and explains the particular shape of the thrust force observed. The models are identified and validated through an application on aluminium alloy 7010

Kinematic modelling of a 3-axis NC machine tool in linear and circular interpolation

Machining time is a major performance criterion when it comes to high-speed machining. CAM software can help in estimating that time for a given strategy. But in practice, CAM-programmed feed rates are rarely achieved, especially where complex surface finishing is concerned. This means that machining time forecasts are often more than one step removed from reality. The reason behind this is that CAM routines do not take either the dynamic performances of the machines or their specific machining tolerances into account. The present article seeks to improve simulation of high-speed NC machine dynamic behaviour and machining time prediction, offering two models. The first contributes through enhanced simulation of three-axis paths in linear and circular interpolation, taking high-speed machine accelerations and jerks into account. The second model allows transition passages between blocks to be integrated in the simulation by adding in a polynomial transition path that caters for the true machining environment tolerances. Models are based on respect for path monitoring. Experimental validation shows the contribution of polynomial modelling of the transition passage due to the absence of a leap in acceleration. Simulation error on the machining time prediction remains below 1%

Effect of different cutting depths to the cutting forces and machining quality of CFRP parts in orthogonal cutting ─ a numerical and experimental comparison

The necessity of understanding the influence of cutting variables in orthogonal cutting of Carbon Fiber Reinforced Polymer (CFRP) is vital because of their significant influences to the quality of manufactured parts. In this present research work the influences of different cutting depths to the cutting and thrust forces have been analyzed and a comparison between an equivalent homogeneous material (EHM) macro-model and experimental results have been made. The reasons of the beginning high cutting and thrust forces have been studied and explained. The post analysis of the experimental machined surfaces has been done to analyze the generated surface roughness and fiber-matrix interface crack generation. Five different cutting depths and four individual fiber orientations have been tested both numerically and experimentally. Significant influence of cutting depths to the cutting force has been found and the surface quality of newly generated machined part is discovered as a function of cutting depth and fiber orientation