Size effects in manufacturing of metallic components

Micro and Nano Machining by Electro-Physical and Chemical Processes

Product miniaturization is an emerging trend for facilitating product usage, enabling unique product functions to be implemented in micro-scaled geometries and features, and further reducing product weight and volume. Recently, a demand for microparts increased significantly in many industry clusters. Development of the advanced micromanufacturing technologies for fabrication of such microparts has thus become a critical issue. Microforming, which offers attractive characteristics including high productivity, low cost and good quality of the formed parts, provides a promising approach to fabricating metallic microparts. In the last two decades, a lot of effort has been made to the researches on size effect related deformation behaviors in microforming process and the development of the process. Having a panorama of these researches is necessary to support micropart design and development via microforming, and further advance this micromanufacturing process. In this paper, an intensive review on the latest development of microforming technologies is presented. First of all, the paper is focused on the review of the size effect-affected deformation behaviors and the mechanisms of the changes of flow stress, flow behavior, fracture behavior, elastic recovery, tooling–workpiece interfacial friction and the surface finish of the formed parts. The state-of-the-art microforming processes, including micro deep drawing, microembossing, micropunching, microcoining, microextrusion, microheading, and micro progressive forming are then presented. Finally, some research issues from the implementation of mass production perspective are also discussed.

A review on the state-of-the-art microforming technologies

Cette derniere Newsletter avant les Grandes Vacances est, pur concours de circonstances, entierement consacree a l’Education. Mais l’Education sous l’angle de son importance pour la consecration dans l’excellence. La consecration, c’est ce qu’a obtenu Gisele Mophou-Massengo, quand son jury de soutenance l’a declaree Habilitee a Diriger des Recherches. C’est egalement la reconnaissance qui est accordee a Elina Marie Devoue par le jury du prix « Religions et Developpement » pour son article consacre aux Religions et a leurs impacts sur la societe dans la Caraibe.La reconnaissance du savoir et du savoir-faire ne passe pas forcement par sa consecration. Elle passe egalement par sa diffusion la plus large. C’est ce que tente de faire le Ceregmia en organisant depuis 2009 ses « seminaires intra Ceregmia » qui permettent l’expression de la transversalite du laboratoire sur des chantiers en cours ou deja finalises autour de thematiques que nous vous invitons a decouvrir en page 2. De meme, le Ceregmia a lance une nouvelle publication en 2010, ses « Documents de Travail ». Ces Documents d’audience plus confidentielle sont reellement reserves a un public de scientifiques. Diffuser le savoir en l’adaptant aux evolutions de l’environnement et aux exigences du marche. C’est ce qu’a fait le Ceregmia grâce a sa nouvelle offre de formation en Masters qui a ete habilitee par le Ministere et qui ouvrira des la rentree 2010 (p. 4). Par ailleurs, nous avions eu l’occasion de vous entretenir des changements intervenus a l’IFGCar suite au seisme du 12 janvier 2010 en Haiti. Nous sommes heureux aujourd’hui, de vous annoncer que l’IFGCar qui est desormais l’IAC retourne s’installer en Haiti. Les formations en Master reprendront des le 1 er . Octobre. Enfin, Nous vous signalons la parution de deux ouvrages aux Editions Ibis Rouge ils vous invitent a decouvrir la Guyane sous un angle moins connu, celui de l’anthropologie. Charley Granvorka

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Habilitation a diriger des recherches

Material behavior modelling in micro/meso-scale forming process with considering size/scale effects

Microforming using a small machine (or so-called desktop machine) is an alternative new approach to those using full-size heavy equipment for manufacturing microparts. Microparts are commonly defined as parts or structures with at least two dimensions in the submillimeter range, which are used extensively in electronics and micromechanical products. However when scaling down a conventional forming process to microscale, the influence of the so-called size effect needs to be considered. The individual microstructure (size, shape, and orientation of grains) and the interfacial conditions show a significant effect on the process characteristics. In this paper, the process of extrusion is investigated to establish it as a viable process for microforming. A forming assembly is fabricated and used in conjunction with a loading substage to extrude micropins with a final diameter of I mm. The effect of grain size is investigated by using workpieces heat treated to produce grain sizes varying from 32 μm up to 211 μm. Two extrusion dies with different roughness are used to study the effect of surface finish. While experiments lead to interesting questions and new discoveries, theoretical or numerical solutions are necessary tools for process optimization. Here, knowing the limits of the current widely used numerical simulation tools [i.e., the Finite Element Method (FEM)], a new method, the Reproducing Kernel Element Method (RKEM), has recently been developed to address the limitations of the FEM (for example, remeshing issue), while maintaining FEM's advantages, e.g., the polynomial reproducing property and function interpolation property. The new RKEM method is used to simulate the microextrusion problem. Its results are compared with that obtained from the FEM and the experiment result. Satisfactory results were obtained. Future directions on the experimental and simulation work are addressed.

Microforming: Experimental Investigation of the Extrusion Process for Micropins and its Numerical Simulation Using RKEM

Method of forming depressions (e.g. dimples) in a sheet material to form a textured surface thereon involves pressing one or more tool tips into a metallic or non-metallic sheet material while the sheet material is supported by a support layer that is relatively softer (e.g. having a lower Young's modulus) than the sheet material so as to allow plastic deformation and reduce pile-up of raised displaced material of the sheet material at the edges of the depressions.

Anthony Swanson

Papers

Microforming: Experimental Investigation of the Extrusion Process for Micropins and its Numerical Simulation Using RKEM

Microforming method and apparatus