Roger Serra

Influence of machining cycle of horizontal milling on the quality of cutting force measurement for the cutting tool wear monitoring

The cutting tools are today used a lot by industry and they are expensive, so it was interesting to optimize their use, by developing a predictive method of their wear, particularly, the flank wear Vb. For this task, the flank tool wear was measured in off-line using a binocular microscope, whereas, the cutting forces are recorded by means of a dynamometer (Kistler 9255B). The acquired signatures are analyzed during the milling operation throughout the tool life. In this paper, we are interested in the extraction of the appropriate indicators which characterize the tool wear by temporal and frequential analyses of the cutting force signals; and highlighting the influence of the clamp holes and the machining cycle to the quality of the measurements.

Machining carbon fibre reinforced plastics: lead angle effect

Surface milling of a multiaxial [(45/90/135/0)16]s carbon fibres reinforced plastic was investigated experimentally. A comparison between 19° and 60° lead angle tool are related in this study. The aim was to compare the cutting behaviour of a 19° and a 60° lead angle tool. Several points of comparison have been chosen such like cutting force, material temperature, milled surface roughness, delamination and tool wear. A wide range of cutting conditions was tested with a depth of cut equals to four plies in order to minimise the influence of plies orientation. This previous factor has been widely describe in the literature. Cutting results with 19° lead angle have shown reducing in cutting force, less wear and less delamination in comparison with 60° this results are partly explained by the insert geometry.

Tool design effect on microlubrication spray efficiency in milling using inner channels

This study consisted in investigating parameters that significantly influence the spray efficiency of minimum quantity lubrication in a milling tool with inner channels. An initial experimental approach was used to estimate the oil mist consumption and outlet particle velocities with different inlet pressures, for different shapes of inner channels, without rotation (static part). An experimental versus simulation comparison was undertaken between outlet velocities as a function of inlet pressure. The Reynolds-averaged Navier–Stokes model with the Lagrangian multiphase models was validated by comparing experimental and numerical outlet velocities for different inlet pressures. A numerical rotating tool with inner channels was used with the validated model in the second numerical simulation to analyze the influences of inlet conditions (inlet pressure) based on the tool shape and the rotation velocity, in a dynamic approach. The main objective of the oil mist is to reach the cutting edge (qualifying the minimum quantity lubrication spray efficiency) depending on the inlet conditions (inlet pressures) and the machining configurations (rotation velocities) by analyzing the streamlines of the oil mist particles. The study pointed out the tool design effect combined with its rotation velocity on the oil mist capability to reach the cutting edge. This study offered a trend of parameter sets to provide correct inlet parameters based on machining configurations. At high rotation speed, the inlet pressures needed to be high enough to counter the aerodynamic effects occurred by the tool design.

Genetic Algorithm Based Objective Functions Comparative Study for Damage Detection and Localization in Beam Structures

The detection techniques based on non-destructive testing (NDT) defects are preferable because of their low cost and operational aspects related to the use of the analyzed structure. In this study, we used the genetic algorithm (GA) for detecting and locating damage. The finite element was used for diagnostic beams. Different structures considered may incur damage to be modelled by a loss of rigidity supposed to represent a defect in the structure element. Identification of damage is formulated as an optimization problem using three objective functions (change of natural frequencies, Modal Assurance Criterion MAC and MAC natural frequency). The results show that the best objective function is based on the natural frequency and MAC while the method of the genetic algorithm present its efficiencies in indicating and quantifying multiple damage with great accuracy. Three defects have been created to enhance damage depending on the elements 2, 5 and 8 with a percentage allocation of 50% in the beam structure which has been discretized into 10 elements. Finally the defect with noise was introduced to test the stability of the method against uncertainty.

Dynamic characterization of the cutting conditions in dry turning

Machining instability in the form of violent vibrations or chatter is a physical process characterized by extreme cutting force at the cutting point. The process has very negative impact on machine integrity, tool life, surface quality and dimensional accuracy. Thus it could significantly compromise productivity and manufacturing quality. In the present paper, the importance of characterization and identification of dynamic instability in dry turning operation are shown. The stability behaviour of machine vibration or chatter has been examined and the various relevant parameters are studied and discuted. For chatter detection and identification of the transition between stable and unstable states, different methods are used. Results obtained proof the accuracy of these methods.

Roller Bearing Monitoring by New Subspace-Based Damage Indicator

A frequency-band subspace-based damage identification method for fault diagnosis in roller bearings is presented. Subspace-based damage indicators are obtained by filtering the vibration data in the frequency range where damage is likely to occur, that is, around the bearing characteristic frequencies. The proposed method is validated by considering simulated data of a damaged bearing. Also, an experimental case is considered which focuses on collecting the vibration data issued from a run-to-failure test. It is shown that the proposed method can detect bearing defects and, as such, it appears to be an efficient tool for diagnosis purpose.

Optimal milling conditions of aeronautical composite material under temperature, forces and vibration parameters

Optimal conditions for milling carbon/epoxy composite material were established by response surface methodology. The combination of cutting parameters such as cutting speed (Vc) and chip thickness (h) was set at various design points of a central composite design. Significant regression models describing the changes of vibration level, delamination of composite, cutting force, workpiece temperature were developed with the coefficient of determination greater than 0.90. Results suggested that beyond a threshold of vibration, the occurrence of delamination is regular. Vibration criterion was defined from the observations of the workpiece according to the delamination defect. The optimum milling conditions were graphically represented using design contour plots. The best combination of process variables was found, according to the cutting conditions. This new technique should help the operator to select the optimum cutting conditions such as cutting speed and feed rate (chip thickness) in order to avoid damage to the carbon/epoxy composite material T800S/M21 and increase machining productivity.

Experimental Shock and Vibration Analysis

The analysis of shock and vibration responses is the starting point to investigate the dynamic properties of a system, a structure, or a mechanism, as well as its expected response to a given excitation (harmonic, random, shock, etc.). By this approach it can be determined whether a particular system, structure, or mechanism will fulfill its intended function; in addition, the results of the dynamic loadings acting on a structure can be predicted, such as dynamic stresses, fatigue life, and noise levels, so that its usefulness can bemaintained andmaximized. Furthermore, the analysis allows seeking those structural parameters most affecting the dynamic response so that if any improvement or change in the response is required, the structure can be modified in the most economic and appropriate way. The methods also made important great strides. Indeed, the vibratory analysis is not one simple complementary tool. It is the basis of many powerful techniques which make it possible, for example, to probe the structures or the health monitoring of materials during their service, to detect the defects and the damage, and to follow their evolution in real-time.The shock and vibration analyses are massively present today in the various branches of industry, from aeronautics to car manufacturing and from machining and maintenance to civil engineering, to mention a few areas, which have made this special issue a true need. This scientific topic leading industrial and academic researchers’ communities concerned by experimental shock and vibration analysis has highly advanced taking positive steps in recent years to develop more comprehensive and rational procedures for dynamic assessment. Starting from forty-eight submitted papers, only seventeen papers on modal analysis, vibration-based condition monitoring, damage detection and localization, experimental/numerical combined approach, physical experiments with advanced computational methods investigations, and their various engineering/industrial applications have been selected and included in this special issue after completing a careful and rigorous peer review process by the international scientific committee. Although these papers do not make an exhaustive treatment of the entire experimental shock and vibration analysis topics, they reflect different interesting issues that have constituted important points of concern for researchers in this area. We trust that this document will contribute to disseminate the current trends and topics of interest in this fascinating and fast growing area and that it will be a valuable tool in research and professional activity.

Vibratory Analysis of Turning Process

The aim of the paper is to analyse the vibrations during a turning manufacturing process in terms of the Machine-Tool-Part unit having particularly complex dynamic characteristics. The vibratory phenomenon is influenced by many parameters like workpiece, tool overhang, cutting speed, depth of cut and feed rate. This phenomenon is not completely known yet, so the aim was to highlight its origins using two complementary approaches: numerical and experimental. Finite element calculations were carried out, in order to identify parameters which characterize vibrations in machining like structural parameters (lathe, tool holder, cutting tool, workpiece, tailstock, tool overhang ...). A design for an experiment of process parameters (depth of cut, feed and cutting speed) was used and one series of turning tests was performed. Results have shown a significant effect between these parameters on the resulting surface roughness, consumed power, cutting time and tool vibrations and a best comprehension of the process.