Multiscale Roughness Analysis in Injection-Molding Process

The roughness of polymer surfaces is often investigated to guarantee both the surface integrity and the surface functionality. One of the major problems in roughness measurement analyses consists in determining both the evaluation length and the reference line (i.e., the degree of the polynomial equation) from which roughness parameters are computed. This article outlines an original generic method based on the generalized analysis of variance and experimental design methodology for estimating the most relevant roughness parameter p, the most pertinent scale, s, and finally, the degree of the polynomial fitting, d. This methodology is then applied to characterize the influence of four process parameters on the final roughness of poly(polypropylene) samples obtained by injection molding. This method allows us to determine the most efficient triplet (p, s, d) that best discriminates the effect of a process parameter q. It is shown that different (p, s, d) values are affected to each process parameter giving finally the scale on which each process parameter modifies the roughness of a polymeric surface obtained by injection molding. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineer

A multi-scale approach of roughness measurements: Evaluation of the relevant scale

This paper proposes a new multi-scale measurement approach performed to compare the surface roughness and the visual aspect of polished surfaces. In this investigation, five specimens of glass moulds presenting different visual aspects are considered. All roughness profiles assessed by tactile profilometry were rectified by a first degree polynomial fitting, and current roughness parameters were calculated with respect to the evaluation length among which they are estimated. A variance analysis was then performed to discriminate each roughness parameter and each evaluation length with regard to a correlation with the visual aspect. Although the average roughness amplitude is about 100 nm, the results show that the optimal correlation with the visual aspect is obtained for a 400 μm evaluation length. Moreover, the multi-scale method allows to confirm results already found in the bibliography about the high wavelengths origin of “orange peel” aspect. This application allowed us to conclude on the advantages and the limits of the implemented method

Analyse multi-échelle de la rugosité des surfaces

L’analyse de la rugosité des surfaces consiste à séparer les défauts à différents ordres ou types correspondant à la forme, l’ondulation et la rugosité. La norme appliquée aux cas courants utilise un filtrage gaussien pour réaliser cette séparation. Il s’agit alors de fixer la longueur d’onde de coupure, appelée cut-off, pour calculer les paramètres afin de caractériser la rugosité. Cette valeur est choisie parmi les suivantes : 0,08, 0,25, 0,8, 2,5 et 8mm, en fonction du type de la rugosité étudiée. Chaque paramètre est ensuite calculé sur une longueur dite "de base" dont la valeur correspond à celle du cutoff. De plus, même si la plupart des mesures de rugosité visent à valider la qualité de la surface, certaines études cherchent à mettre en évidence : - soit l’influence d’un processus d’obtention de la surface sur la rugosité, - soit la corrélation entre la rugosité et une propriété de la surface étudiée. Dans chacun de ces cas, on recherche à mettre en évidence un ou plusieurs phénomènes physiques mis en jeu dans la création ou la fonctionnalité de la surface. Dés lors, une question se pose : « Les valeurs normalisées de longueur de base sont-elles les plus pertinentes pour mettre en évidence les phénomènes physiques recherchés ? ». La réponse peut être apportée par l’approche multi-échelle qui consiste à ne faire aucune hypothèse sur la longueur de base à utiliser, et à appliquer le filtrage sur une gamme de longueurs de base. Il s’agit ensuite de discriminer la longueur de base qui permet de mettre au mieux en évidence l’effet du process d’obtention de la surface ou la corrélation avec la propriété recherchée par analyse de variance

Multiscale Roughness Analysis in Injection-Molding Process

The roughness of polymer surfaces is often investigated to guarantee both the surface integrity and the surface functionality. One of the major problems in roughness measurement analyses consists in determining both the evaluation length and the reference line (i.e., the degree of the polynomial equation) from which roughness parameters are computed. This article outlines an original generic method based on the generalized analysis of variance and experimental design methodology for estimating the most relevant roughness parameter p, the most pertinent scale, s, and finally, the degree of the polynomial fitting, d. This methodology is then applied to characterize the influence of four process parameters on the final roughness of poly(polypropylene) samples obtained by injection molding. This method allows us to determine the most efficient triplet (p, s, d) that best discriminates the effect of a process parameter q. It is shown that different (p, s, d) values are affected to each process parameter giving finally the scale on which each process parameter modifies the roughness of a polymeric surface obtained by injection molding. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineer

Sliding wear of a-C:H coatings against alumina in corrosive media

This paper reports the results obtained from the study of friction and sliding wear in two corrosive solutions of an a-C:H coating deposited on 316L stainless against an alumina ball, employed as static counter part. Calculations of the values of the von Mises stresses developed at the coating–substrate interface, as soon as the ball touches the coated sample, and how this state of stress influences the response of the coated system under the corrosion environment, are presented and discussed. The results obtained from these calculations, as well as from the experiments conducted in the present research, are compared with other experiments published in the literature, where a-C:H coatings deposited on different substrates and with different coating architectures were tested in similar corrosive media. It has been determined that in those systems, where the von Mises stress in the coating, found in the vicinity of the interface, exceeds the threshold value of approximately 370MPa, coating failure with spallation will take place, regardless of the substrate nature on which this coating has been deposited. From this analysis it has been concluded that the coating yield strength is of utmost importance in conferring the a-C:H coated system there quired stability in a corrosive solution

Characterization of innovative steels by dual mechanical tests

Les auteurs remercient MM. Gaëtan Starzyk, Florian Baratto et Nicolas Charoy pour le travail effectué lors de leur projet de fin d’étude ingénieur Arts et Métiers au centre de Lille, travail qui a permis la mise en place du dispositifd’essai et la réalisation des essais mécaniques de caractérisation des échantillons. De même, nous remercions ArcelorMittal Maizières (Maizières-lès-Metz) pour les échantillons d’acier dual-phase transmis pour la réalisation de ce travail de rechercheDans le domaine du développement des aciers innovants, en recherche et développement, les volumes réduits de matière disponibles ne permettent pas une caractérisation fiable et rapide du comportement des matériaux élaborés. Un essai de caractérisation mécanique « Small Punch Test » est proposé comme essai de caractérisation adapté à l’étude de faibles volumes de matière. Cet essai se réalise par la déformation progressive d’une pastille d’épaisseur réduite, pour atteindre la rupture. Une méthode inverse, basée sur l’algorithme du simplexe, a été développée pour exploiter la courbe effort/enfoncement et déterminer les propriétés mécaniques. Cette approche a été appliquée à une nuance d’acier dual-phase développé pour cette étude. Nous montrons néanmoins que cet essai n’est pas satisfaisant pour estimer précisément les paramètres de la loi de comportement mécanique, et nous proposons de croiser les résultats obtenus avec un essai de macrodureté Vickers instrumentée pour obtenir un résultat pertinent. L’amélioration dans la prévision du comportement est montrée et permet de valider la démarche proposée.In the research and development field on innovative steels, the available amounts of materials do not allow a quick and reliable characterization of their mechanical properties. An easy test called “Small Punch Test” is proposed as a differential characterization test adapted to a small amount of material. This test consists in the slow deformation of a small and thin disc of the steel. The test is conducted till the breaking of the sample. An inverse method based on the simplex algorithm is proposed in order to estimate the mechanical properties from the load/displacement curve. This approach has been applied to a dual-phase steel grade elaborated for this study. We show that this single test is not sufficient in order to precisely estimate the parameters of the constitutive law for the mechanical behaviour of the steel. We propose to compare the previous results with the ones of a macro-hardness instrumented Vickers test. This enables to obtain a reliable couple of parameters. The improvement in the constitutive law parameter estimation is shown. These dual tests show the advantage of this approach in order to estimate the mechanical properties of innovative steels

Estimation of the constitutive law by dual Small Punch Test and Instrumented Indentation

The authors thank Mrs. G. Starzyk, F. Baratto, N. Charoy and M. Moura for the projects they realised to develop the SPT equipment and to realize the tests presented here. Moreover we thank Drs. S. Allain and J.-Ph. Masse (ArcelorMittal, Maizières-lès-Metz) for the DP steel sheets supplied and discussions on the DP characterization. We also thank J.C. Vervisch for its valuable help in experimental activities.In this paper an inverse finite element procedure was developed to assess the true- stress strain relationship of a DP dual phase. Experiments were performed both by means of instrumented indentation and small punch tests on small samples cut in the same steel sheet. Tests are developed on a Zwick macro-hardness tester. Single test are first proposed in order to estimate the parameters of the constitutive law (K,n). We propose to conduct SPT tests using PTFE lubricant and hard (WC / Co) ball. An inverse method based on the Nelder and Mead algorithm has been developed in order to found experimental curves. Nevertheless we show that this method lead to poor estimation of the parameter of the constitutive law. We propose to improve these estimations by cross-mechanical tests. Indeed we show that the estimation of the low-error (K,n) domains deduced from each single test can be crossed. This method leads to a better estimation of the constitutive law. Moreover both load/displacement curves of SPT and macrohardness can be found again.contrat ARTS avec ArcelorMitta

Characterization of innovative steels by dual mechanical tests

Les auteurs remercient MM. Gaëtan Starzyk, Florian Baratto et Nicolas Charoy pour le travail effectué lors de leur projet de fin d’étude ingénieur Arts et Métiers au centre de Lille, travail qui a permis la mise en place du dispositifd’essai et la réalisation des essais mécaniques de caractérisation des échantillons. De même, nous remercions ArcelorMittal Maizières (Maizières-lès-Metz) pour les échantillons d’acier dual-phase transmis pour la réalisation de ce travail de rechercheDans le domaine du développement des aciers innovants, en recherche et développement, les volumes réduits de matière disponibles ne permettent pas une caractérisation fiable et rapide du comportement des matériaux élaborés. Un essai de caractérisation mécanique « Small Punch Test » est proposé comme essai de caractérisation adapté à l’étude de faibles volumes de matière. Cet essai se réalise par la déformation progressive d’une pastille d’épaisseur réduite, pour atteindre la rupture. Une méthode inverse, basée sur l’algorithme du simplexe, a été développée pour exploiter la courbe effort/enfoncement et déterminer les propriétés mécaniques. Cette approche a été appliquée à une nuance d’acier dual-phase développé pour cette étude. Nous montrons néanmoins que cet essai n’est pas satisfaisant pour estimer précisément les paramètres de la loi de comportement mécanique, et nous proposons de croiser les résultats obtenus avec un essai de macrodureté Vickers instrumentée pour obtenir un résultat pertinent. L’amélioration dans la prévision du comportement est montrée et permet de valider la démarche proposée.In the research and development field on innovative steels, the available amounts of materials do not allow a quick and reliable characterization of their mechanical properties. An easy test called “Small Punch Test” is proposed as a differential characterization test adapted to a small amount of material. This test consists in the slow deformation of a small and thin disc of the steel. The test is conducted till the breaking of the sample. An inverse method based on the simplex algorithm is proposed in order to estimate the mechanical properties from the load/displacement curve. This approach has been applied to a dual-phase steel grade elaborated for this study. We show that this single test is not sufficient in order to precisely estimate the parameters of the constitutive law for the mechanical behaviour of the steel. We propose to compare the previous results with the ones of a macro-hardness instrumented Vickers test. This enables to obtain a reliable couple of parameters. The improvement in the constitutive law parameter estimation is shown. These dual tests show the advantage of this approach in order to estimate the mechanical properties of innovative steels

A multi-scale approach of roughness measurements: Evaluation of the relevant scale

This paper proposes a new multi-scale measurement approach performed to compare the surface roughness and the visual aspect of polished surfaces. In this investigation, five specimens of glass moulds presenting different visual aspects are considered. All roughness profiles assessed by tactile profilometry were rectified by a first degree polynomial fitting, and current roughness parameters were calculated with respect to the evaluation length among which they are estimated. A variance analysis was then performed to discriminate each roughness parameter and each evaluation length with regard to a correlation with the visual aspect. Although the average roughness amplitude is about 100 nm, the results show that the optimal correlation with the visual aspect is obtained for a 400 μm evaluation length. Moreover, the multi-scale method allows to confirm results already found in the bibliography about the high wavelengths origin of “orange peel” aspect. This application allowed us to conclude on the advantages and the limits of the implemented method

Effects of working parameters on the surface roughness in belt grinding process: the size-scale estimation influence

This paper outlines a new method to evaluate roughness parameters considering the scale used for their evaluation. Application is performed for grinding hardened steel with abrasive belts. Seven working variables are considered through a two-level experimental design. For all configurations, 30 surface profiles were recorded by tactile profilometry and rectified by a first degree B-spline fitting before calculating a set of current roughness parameters. The relevancy of each roughness parameter, to highlight process parameters influence, is then estimated for each scale by variance analysis. The results show that each influent input parameter is characterised by a related relevant evaluation length