Résumé: Quality of products is a major concern for hard machining industry aspects. However, the prediction of surface roughness in the function of the machining parameters is a targeted objective by the majority of researchers due to important industrial interest. This work is a contribution for developing comprehensive analyses of surface roughness models during dry hard turning of cold work steel AISI D2. It is focused on the treatment of predicted surface roughness values in correlation with cutting conditions such as cutting parameters (cutting speed, feed rate, and depth of cut), tools material, tool geometry, workpieces hardness, and machining times in order to establish of orientations for use which applied successfully in the industry from optimal selection of process variables. The approach consists in first conducting a literature survey through collecting and validating surface roughness models together with the corresponding material and also the cutting conditions. Then, results have been tabulated as to permit data mining treatment under data processing software which was developed. As a significant result, a strategic dashboard generating roughness data mining was made available to researchers and industrials. The optimums of parameters which condition the achievement of best machined surface qualities have been selected.

Résumé: Tool wear and surface roughness as performance indexes are considered to be the most important in terms of hardened materials’ machinability. The best combination of cutting parameters which enhances the compromise between tool life, productivity and machined surface quality contribute to benefice on production cost, which makes manufacturing industry interested in it. The aim of this research is to investigate the life of ceramic cutting tool and machining productivity together with surface roughness during turning of hardened steel C45, with focus on the selection of the optimal cutting parameter combination. The experiments are carried out based on uni-factorial planning methodology of cutting speeds and feed rates. The results show that the mixed ceramic tool is suitable for turning hardened steel C45 (40 HRC) and the conclusion is that it performed well in terms of tool life, productivity and surface quality at a combination of cutting speed (200 m/min), feed (0.08 mm/rev) and depth of cut (0.3 mm). Additionally, a tool life model has been proposed which is presented very high coefficient of determination.

Résumé: Hard machining is a process that has become highly recommended for replacing grinding in the manufacturing industry. This is due to its ability to machine complex shapes with reduced production costs by reducing the machining time and being an ecological process. Three technological parameters determine the quality and productivity generated from this process: cutting vibration, surface roughness and tool wear. Therefore, the analysis of the correlation between them is very important. In the present investigation, the analysis of the correlation between cutting vibration, surface roughness and tool wear during a dry machining of hardened steel with a mixed ceramic tool is conducted in order to control these parameters online. This analysis is validated by developing predictive mathematical models. To neutralize the effect of cutting parameters, a combination of parameters such as cutting speed, feed rate and depth of cut to be used in the experimental tests is selected from the literature based on a quality-productivity optimum performance. In the early stage, the effect of machining time on the three technological parameters is studied, then assessed by developing predictive mathematical models. In the second stage, an experimental and statistical analyses such as the Pearson and Spearman correlation methods are employed to determine correlations between tool wear, surface roughness and cutting vibration. Each parameter is compared with the other two. The models and their validations are developed using the Minitab 16 tool, and the predictions are obtained with desirable deviations. The examination of the outcomes from the first stage reveals that the machining time has a significant effect on the three parameters. The regression models are found to be satisfactory in predicting each technological parameter. In the second stage, the results show a strong cor-relation between tool wear and cutting vibration, confirmed by the high Pearson and Spearman coefficients. The correlations between surface roughness and tool wear or the cutting vibration are strong only when the flank wear Vb is inferior 0.3 mm (which is required by the ISO standard). The regression models are developed with a desirable coefficient of regression (R2). The novelty of this work lies in the fact that we consider the cutting vibration as a response generated the during cutting process and not as a variable affecting the other technological parameters. This was rarely studied in previous researches.

Résumé: The objective of this experimental study is to evaluate the performance of three tool materials (mixed ceramic (CC650), PVD-coated carbide tool (GC1025) and CVD-coated carbide tool (GC4015)) during hard turning process of bearing steel 100Cr6 (66HRC) under dry environment. To do this, long-term tests used out to determine the tools life, productivity and machined surface quality in relationship with variation of the cutting speed and feed. The admissible parametric of cutting conditions has been obtained in order to reach a compromise tool life, its productivity and machined surface quality of part. Results showed that cutting speed is the most important factor affecting tool life but surface roughness was mainly influenced by feed. Second order regression models was developed to find out the relationships between cutting speed and tools life time in the one hand and the correlation between tools life time and feed rate on the other hand. The results were compared to the literature. For comparative study, the results showed that ceramic tool has been characterized by a good productivity and better surface quality compared to PVD-coated carbide tool. The latter was in turn more efficient than CVD coated carbide tool, which beyond the cutting speed 75 m/min was unproductive

Résumé: Hard machining is a process which has become highly recommended in manufacturing industry to replace grinding and perform production. The important technological parameters that determine this process are tool wear, machined surface roughness, cutting force and morphology of the removed chip. In this work, an attempt has been made to analyse the morphology and form of chip removed during turning of hardened steel AISI 1045 (40HRC) with mixed ceramic tool type CC650. Using a Taguchi plan L9, whose factors are cutting speed and feed rate with three levels for each. Macroscopic and microscopic results of chip morphology were correlated with these two cutting parameters additional to surface roughness. Sufficient experimental results were obtained using the mixed ceramic tool when turning of hardened steel AISI 1045 (40HRC) at high cutting speeds. Roughness of machined surface confirmed that it is influenced by feed rate. Chips show a sawtooth shape for all combinations of the experimental plan used. The chip form changed with cutting parameters variation and given an important indicator of surface quality for industrial. Having the indicators on the surface quality from simple control of chip without stopping machining give an important advantage in order to maximize production and reduce costs.

Résumé: Wear investigation has been conducted on mixed ceramic cutting tool (70% Al2O3 + 30% TiC) when machining hardened AISI 52100 steel (66 HRC). Experimental planning method has been used to assess the relationship between radial cutting vibrations and surface roughness as a function of the machining conditions. First, wear results show that when the cutting speed is increased 3.78 times, tool life drops of 8.75 times. When increasing the feed rate by a factor of 2.75 tool life decreases by a factor of 1.4. Then, the effect of cutting parameters (speed, feed and depth) on one hand surface roughness (Ra) and in the other hand radial tool vibrations has been determined using the multiple regression models with a coefficient of determination R² equal to respectively 95.5% and 89.3%. With regards to surface roughness, ANOVA analyses reveal that feed rate contributes of about 84% in the surface roughness. Meanwhile, looking at the vibration phenomena, the cutting speed has the most significant effect on the values of radial tool vibrations comparing to depth and feed rate effect. Finally the correlation between surface roughness and tool radial vibrations has been analyzed through the linear and nonlinear correlation coefficients. The values of Pearson and Spearman coefficient were respectively low 0.465 and 0.554 showing that above 1000 rpm of cutting speed, the machining system is no more stable generating a great effect of cutting vibrations.

Résumé: Ce travail est une étude d’investigation de l’effet des paramètres d’usinage (vitesse de coupe, avance et profondeur) sur la rugosité de surface et sur les vibrations radiales de la coupe durant le tournage dur à sec de trois nuances d’aciers trempés: AISI 52100 (66HRC), AISI 4140 (61HRC) et AISI 1045 (39HRC) avec la céramique mixte CC650 (70%Al2O3+30%TiC). Une analyse ANOVA d’un plan expérimental orthogonal Taguchi L27 est appliquée afin de déterminer la contribution de chaque paramètre ainsi que les interactions sur la rugosité de surface et les vibrations radiales. Les résultats ont montré que l’avance est le paramètre le plus significatif pour déterminer la rugosité de surface des trois aciers suivis par la profondeur de passe, alors que pour les vibrations de coupe radiales, c’est la vitesse de coupe qui a un effet primordial. Les corrélations entre les deux réponses étudiées : rugosité de surface (Ra) et Amplitude des vélocités de vibration de coupe, sont faibles. Ceci est dû aux vibrations excessives du système usinant lors de l'usinage avec des vitesses de rotation élevées. Les deux réponses rugosité de surface et vibration de coupe sont modélisées par des équations de régression multiple de second ordre avec des coefficients de corrélation (R2) très acceptables.

Résumé: Gaseous carburizing effects on improvement of performance of a new grade hot working tool steel close to as either chromium AISI H11/H13 are investigated. Such treatments are performed at 930 °C for various processing times. Formed layers that are characterized by their basic properties (i.e. thickness, depth, formed phases, hardness distributions, carbon/carbides distributions and redistribution of alloys in the carburized layers) show a close dependence of both time-temperature process and chemical composition of material. Test results indicate that retained austenite amount act to improve significantly the wear resistance of components despite their relatively lower hardness. In addition, it is addressed that performance and productivity of the as-new material could be extensively enhanced when the above treatment is used. Metallurgical evaluations are carried out using metallographic techniques, optical, scanning electron microscopy equipped with an energy-dispersive X-Ray spectrometer and X-ray diffraction techniques. Mechanical properties are achieved mainly by standard hardness and wear tests.

Résumé: Le but de cet article est d’identifier la nécessité de la structuration de la stratégie d'entreprise durant le changement organisationnel de l’entreprise lors de migration d’un statut stratégie d'entreprise (corporate) à une stratégie indépendante d'unité. Ce travail est le feedback d’analyse d’une situation concrète, des difficultés qui sont rencontrés par l’entreprise étatique nationale de la sidérurgie, Sider el Hadjar (Ex- ArcelorMittal Algérie) après son indépendance du groupe international ArcelorMittal. La méthodologie de l’étude a été basée sur l’analyse des paramètres de performance de l’entreprise en vue des changements organisationnels entre les deux statuts. Une importance particulière a été mise sur le positionnement de la stratégie par rapport au groupe d’une part et par rapport à l’unité indépendante d’une autre part. L’analyse a montré que durant ce niveau de changement structurel, les parties sont plus intéressées au transfert financier sans prise en compte du transfert du savoir et du savoir-faire. Cette investigation présente une solution organisationnelle couvrant les lacunes générées depuis la migration d’une stratégie corporate à une stratégie d’unité indépendante. Ce travail est opérationnel quand peut le généraliser avec adaptation à l’ensemble des entreprises étatiques de ce segment.