Alain Barreau

Lifetime multiple response optimization of metal extrusion die

The aim of this paper is to optimize the lifetime of dies for the multiple response in metal extrusion process. The main objective of the multiple response optimization is to improve the quality of a product or process by minimizing the effects of variation without eliminating the causes. Numerical simulations with ABAQUS software obtain the results of the tests.

Density and temperature dependence of spectral moments in depolarized light scattering by rare gases

We present an extensive study of the first three even moments M 2n of depolarized light scattering (DLS) spectra of rare gases argon and xenon. Most of our results were obtained by molecular dynamics and Monte Carlo computer simulation methods, which were used to calculate the moments for pairwise-additive intermolecular pair potential and interaction-induced polarizability models over a wide density range and at two temperatures, one above and one below the critical point. Simulation was used to determine the dependence of the moments on the pair polarizability anisotropy β(r) by comparing the results for the first order dipole-induced dipole (DID) model with those obtained for a semiempirical model of β(r), recently proposed by Meinander, Tabisz and Zoppi (MTZ), which includes electron overlap, dispersion and second order DID interaction contributions. Comparison with experiment indicates that the MTZ model for β(r) is clearly superior. Moments of increasing order are found to be increasingly more sensi...

Robust Designs for Quality Improvement

Taguchis parameter design method allows one to make products or processes robust to uncontrollable noise factors. Recent research has focused on combining control and noise factors into a single array to model the response directly rather than relying on a performance measure such as the signal-to-noise ratio. Examination of control-by-noise interaction effects reveals control factor settings that dampen the effects of the noise factors. The objective of this paper is to propose modified cross-product designs for robustness improvement that enable one to reduce the experimentation costs while maximizing the amount of useful information.

Spectral Control Chart

In this article, we are proposing a new control chart, named the spectral control chart, whose construction is based on the spectral analysis. We are showing that it is possible to detect small mean shifts by using the information contained in the coefficients of the signal Fourier decomposition.

Designed fatigue experiments to improve the reliability of liquid crystal displays

The objective of this paper is to show how reliability improvement may be achieved using statistically designed experiments. Environmental stress testing has been performed on liquid crystal displays (LCDs) to identify the parameter settings that allow an increase in their lifetime. During their operating life, the LCDs are connected to electronic devices and are inserted into cases. They are used to display measurements to aircraft pilots during commercial flights. Typically the failure time was 4000 hours of flight which was considered not to be long enough. The design of experiments provided an opportunity to check whether the most likely hypothesis was correct. During the tests, degradation rates were used as a response. The effects of three factors were studied using two overlapped 2/sup 2/ orthogonal designs. A powerful spotlight located at 2.5 meters from the tested LCDs, was used to model the degradation rate. One of the factors was found to reduce dramatically the degradation rate, allowing a very substantial increase in the product lifetimes. More generally, we propose to use the slope of the degradation function as a response in designs of experiments for reliability. The advantages of doing this are that the responses are normally distributed and when the data are right censored, it does not cause as many problems as when failure times are recorded. The drawback is that the product degradation needs to be periodically monitored until an accurate estimate of the degradation rate is available, moreover the degradation function may not be linear so that a data transformation is required.

An application of the quality engineering approach reconsidered

Robust design methods allow one to make products or processes less sensitive to variations. The objective is to set the parameters of a system so that it functions well over a wide operative range while subjected to fluctuating uncontrollable factors. Conventional tightening of input tolerances is costly and it is not the only way to reduce variations in a process. Taguchis parameter design method consists in performing a design of experiment in which control and noise variables are set at fixed levels. Taguchi has developed cross product designs for experimentation that consist of two arrays, one for the noise factors and one for the control factors. Control factors are process or product variables that can be easily controlled. Noise factors can be controlled in the laboratory but cannot be controlled during production. The noise factor levels are varied according to an orthogonal outer array to simulate the variations of the process. The control array is used to select the design points where the process variance is to be estimated. The signal-to-noise (S/N) ratio proposed by Taguchi is designed to be used as a response to reduce dispersions. Cross-product arrays however, often require a very substantial number of runs. Moreover, fixing the level of the hard-to-control factors during the experimentation process is often costly. Robust design experiments are therefore frequently run in a split-plot way. That is, the levels of the hard-to-control factors are moved much less frequently than the levels of the control factors. In this paper, the cost-effectiveness of Taguchis direct cross-product arrays is compared to that of mixed resolution combined arrays.

Ductile damage variation analysis during metal extrusion process using design of experiment technique

In this work, the design of experiments method has been used for a better understanding of the influence of the deviation of the material parameters on the damage evolution within the workpiece. To predict the evolution of the material deterioration during the processes, a damage model accumulation has been implemented in a finite element code and applied with success to simulate damage and crack propagation, which can be generated by the plastic deformation during the operations. The simulation can predict forming defects such as crack initiation and propagation. The mechanical quality of a part is determined by the material property variation such as the hardening and damage states as a result of the increase in strain.

Statistical process control of wear phenomenon during metal extrusion process

The aim of this paper is the statistical process control (SPC) analysis of the tool wear evolution during metal extrusion process for better understanding the principal causes which generate the variability of such a complex phenomenon. The wear prediction is carried out using finite element simulation including Archard wear model. The tool wear modelling is presented briefly as well as the response surface methodology (RSM). The study is based on the application of the central composites designs and allows for the analysis of the response (wear) sensitivity of the tool. The statistical investigation of the process makes it possible to study the influence of each process parameters on the response sensitivity.

Minimal Design Augmentation Schemes to Resolve Complex Aliasing in Industrial Experiments

Highly fractionated designs are often used for screening purposes in order to reduce the number of runs. In fractionary-designed experiments, the factor effects are confounded with interactions that are potentially active. Estimating separately the confounded effects is sometimes difficult and the results may be inconclusive as to which effect is real. Foldover designs are usually used to resolve such ambiguities. In this article, a method based on overlapping designs that enables one to separate the confounded effects in a smaller amount of runs is proposed. We illustrate this with an application.

Tool Life Prediction in Metal Forming Processes Using Numerical Analysis

Abstract The aim of this paper is to provide a general finite element model allowing for the numerical prediction of the extrusion die wear which allows for the evaluation of the die life. A wear prediction model has been implemented in the finite element code Abaqus in which the tool wear is a function of the normal pressure and some material parameters. The tool wear profile is obtained and compared to industrial observations. The proposed approach is expected to the development of methodology for tool cost evaluation due to wear and to the determination the most economic extrusion conditions.