106,473 research outputs found
Analytical and experimental investigations on thread milling forces in titanium alloy
No full textThe authors would like to gratefully acknowledge the Walter Prototyp tool manufacturer who specially machined the requested tools. The first author would like to thank the support of BRAFITEC/CAPES and the research team in LABOMAP at Arts et Metiers ParisTech.This study deals with the thread milling process that is considered a complex machining technique due to its elaborated tool geometry and its tridimensional tool trajectory. It needed advanced research on the threading process which has not been much studied. Previous studies focused on geometrical modeling or mechanistic modeling of the thread milling process. There is a need for a better understanding of parameter effects to accomplish a model that tends to be more realistic and includes local parameters. This investigation does the analysis of thread milling parameters: thread geometry, cutting conditions and tool angles, which can be applied to the tool optimization. The cutting forces and torque were measured and representative values of its variation were calculated and analyzed as response of the experiments. A geometrical analysis and an analysis of variance were employed for determining the influence of the factors and based on the results, it is proposed a physical understanding of the process.Professeur invité ENSAM collaboration avec entreprise WALTER PROTOTY
Mechanical and physico-chemical study of sulphur additives effect in milling of high strength steel
No full textThe authors would like to express their appreciation to the TOTAL France Company for the technical and financial contribution to this study and to Béatrice Vacher for TEM images.Most machining operations require the presence of a cutting fluid in order to ensure their success due to the intensity of thermal and mechanical conditions generated on the cutting tools. In some cases of severe machining, the fluid contributes to lubrication in a physicochemical way thanks to the additives it contains. This study aims to analyze the tribochemical mechanisms of lubrication during milling operations and subsequently at optimizing the lubricant formulation. The objective of this study is also to identify and to compare, the performance of various Extreme Pressure (EP) sulfur-containing additives, and to understand their action mechanisms in metal cutting. Physico-chemical analyses are carried out by means of Auger Electron Spectroscopy (AES) and X-ray Photoelectron Spectroscopy (XPS) with the purpose of detecting the nature of additive reaction products on the surfaces involved in cutting and correlating them with the milling results. The polysulfide additive is found to exhibit the best efficiency (decrease of specific cutting energy and tool wear) in the tested milling conditions. A correlation is found between the additive chemical reactivity and the milling test results.Thèse CIFRE TOTA
Surface roughness prediction in milling based on tool displacements
No full textIn this paper, an experimental device using non-contact displacement sensors for the investigation of milling tool behaviour is presented. It enables the recording of high frequency tool vibrations during milling operations. The aim of this study is related to the surface topography prediction using tool displacements and based on tool center point methodology. From the recorded signals and the machining parameters, the tool deformation is modeled. Then, from the calculated deflection, the surface topography in 3D can be predicted. In recent studies, displacements in XY plane have been measured to predict the surface topography in flank milling. In this article, the angular deflection of the tool is also considered. This leads to the prediction of surfaces obtained in flank milling as well as in end milling operations. Validation tests were carried out: the predicted profiles were compared to the measured profile. The results show that the prediction corresponds well in shape and amplitude with the measurement
Surface roughness variation of thin wall milling, related to modal interactions
No full textHigh-speed milling operations of thin walls are often limited by the so-called regenerative effect that causes poor surface finish. The aim of this paper is to examine the link between chatter instability and surface roughness evolution for thin wall milling. Firstly, the linear stability lobes theory for the thin wall milling optimisation was used. Then, in order to consider the modal interactions, an explicit numerical model was developed. The resulting nonlinear system of delay differential equations is solved by numerical integration. The model takes into account the coupling mode, the modal shape, the fact that the tool may leave the cut and the ploughing effect. Dedicated experiments are carried out in order to confirm this modelling. This paper presents surface roughness and chatter frequency measurements. The stability lobes are validated by thin wall milling. Finally, the modal behaviour and the mode coupling give a new interpretation of the complex surface finish deterioration often observed during thin wall milling
Dynamic analysis of runout correction in milling
No full textTool runout and its effects is an important area of research within modelling, simulation, and control of milling forces. Tool runout causes tool cutting edges to experience uneven forces during milling. This fact also affects tool life and deteriorates workpiece surface quality. In this article a procedure, in order to diminish the effects of tool runout, is presented. The procedure is based on chip thickness modification by means of the fast correction of the tool feed rate. Dynamic feed rate modification is provided by superposing our own design of a fast feed system driven by a piezoelectric actuator to the conventional feed drive of the CNC machine tool. Previously, a model of the dynamic behaviour of the system was developed to analyze the influence of fast feed rate modification on cutting forces. The model incorporates the piezoelectric actuator response as well as the structural dynamics of the tool and the designed Fast Feed Drive System (FFDS). Simulated and experimental results presented in this paper show the effectiveness and benefits of this new tool runout correction procedure
Toolpath dependent stability lobes for the milling of thin-walled parts
No full textThe milling of thin-walled parts can become a seriously complex problem because the parts have variable dynamics. Firstly, the dynamics evolution of the part has been calculated through Finite Element Method (FEM) analysis. Then, the 3D stability lobes have been calculated for the thin walls and the thin floor. Finally, several milling tests have been performed in order to validate the predictions made by the model
Correlation between machining direction, cutter geometry and step-over distance in 3-axis milling: Application to milling by zones.
No full textComputer-Aided Manufacturing (CAM) occupies an increasingly important role in engineering with all it has to offer in terms of new possibilities and improving designer/manufacturer productivity. The present study addresses machining of free-form surfaces on a 3-axis NC machine tool. There have recently been a large number of studies devoted to planning tool paths on free-form surfaces with various strategies being adopted. These strategies are intended to increase efficiency by reducing the overall length of machining. Often, the choice of the cutter is arbitrary and the work focuses on planning. In order to boost productivity, the present work offers assistance in choosing the cutting tool, the machining direction and cutting by surface zones, adopting a milling strategy by parallel planes. To do so, a comparison is made between milling using a spherical end milling cutter and a torus end milling cutter with the same outer radius. This comparison relates to the radius of curvature of the trace left by the cutter at the point of contact between the tool and the workpiece in relation to the direction of feed motion
Experimental Analysis and Geometrical Modeling of Cutting Conditions Effect in 5 Axis Milling with Ti6Al4V Alloy
No full textThe 5 axis continuous milling is an advanced technique for free-form surfaces manufacturing. In finishing, this technique uses ball-end or hemispherical milling cutter. This type of operation for 5 axis milling allows the possibility to tilt the tool with two different angles. As a consequence, a mass of geometrical configurations exists and establishing accurate parameters is quite difficult to define. A geometrical model has been developed to find the effective cutting diameters and cutting speed on the cut and the finished surface. After an experimental validation, this study proposes an analysis of several 5 axis milling configurations in order to perform this technique
Some aspects about milling : expert system for cutting parameters selection and control designs
No full textMilling is a mechanical process which consist of the relative movement between feeding the work-piece and rotating the multitooth cutter, to remove material from the work-piece. Milling is used in industry for the manufacturing of mechanical components. During a operation static and dynamic effects can lead to undesared states, such as stick slip friction and forced and self-excited oscillations ). These oscillations, also called chatter oscillation, can culminate in non-smooth work-piece surface, inaccurate dimensions and excessive tool wear. The regenerative effect is the most widely recognized which causes chatter. Spindle speed selection or modulation and absorbers vibrations are the main solutions to supress chatter without reduce the productivity . But, the difficulties to introduce these techniques and the increasing competence lead to use intelligent techniques to evaluate process parameters, such as, time requeriments, programmed cutting parameters, machine tool selection and/or cuting tools selection . The present document covers some aspects of the mentioned. First, an analytical guidance for description, detection and suppresion of chatter in milling system is given. Then, an expert system is proposed to select an adequate tool, among the available set, and cutting paramaters according to productivity, power compsumsion or availavility, and robustly stability against posible perturbations in the cutting parameters requeriments. The expert system suply an informatic tool to obtain cutting conditions independently of the machine operator, and it is also intended to be programmed by them. Once the cutting parameters has been selected, a control strategy is required. Thus, control of milling operations, and especially the adaptive control, has an extensive research in manufacture literature, since they reduce costs, save time and in general, protect the machine. Model reference adaptive control strategy is developed to program at Computer Numerically Controlled (CNC). A fractional order hold is proposed to discretize the modelled continuous system of the milling machine. The extra degree of freedom, , allow the programmer tuned this parameter to a better system response behavior, in comparison with a zero order hold typically used in literature
Chatter Control by Spindle Speed Variation in High-Speed Milling
No full textHigh-speed milling operations are often limited by regenerative vibrations. The aim of this paper is to analyze the effect of spindle speed variation on machine tool chatter in high-speed milling. The stability analysis of triangular and sinusoidal shape variations is made numerically with the semi-discretization method. Parametric studies show also the influence of the frequency and amplitude variation parameters. This modeling is validated experimentally by variable spindle speed cutting tests with a triangular shape. Stable and unstable tests are analyzed in term of amplitude vibration and surface roughness degradation. This work reveals that stability must be considered at period variation scale. It is also shown that spindle speed variation can be efficiently used to suppress chatter in the flip lobe area
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