Embossing

Technology suitable for both serial and small quantity production

Studies concerning coining aluminium sheet metal have been performed by Ike and Plancak [23]. Using dies with hole diameters from 0.05 to 1.6 mm, half hard commercially-pure aluminium of 2 mm in thickness and 30 mm in diameter, coining results were evaluated in terms of aspect ratio, the radial position of the hole and the die and the emerging forming load. As it has been shown, the beginning of plastic flow is independent from the radial position of the hole, but the height of the pins is clearly bound to the position of the holes and its diameter.

At LWP Saarbrücken, Germany [24], also coining of smallest cavities with a thickness of about 400 microns has been investigated. The results show, that in case of micro-coining the influence of the tool geometry and the tool deflection on the forming results must be considered. This is due to rather high nominal stresses (minimum three times the flow stress of the coined material) leading to a large impact on the tool system: tool deformation, tool deflection and tool damage.

The aim of the investigations on coining technologies at IWU Chemnitz was to establish this technology for the production of geometrically defined micro structures for applications in the fields of micro-fluidics, micro-optics and information technology [25, 26]. In a first set of experiments, tools were made out of single crystal silicon with an almost smooth surface. Thus, it was possible to create structures of 100 microns with radii of some 100 nm in aluminium, copper, brass and steel.

The analysis of the coined material shows that the shape of the rim strongly depends on the material. While aluminium shows a bulging of max. 30 % of the coining depth, steel shows only max. 5 %. Using fine grained ZnAl alloy in a superplastic state at 250 °C, high precision and surface quality are achieved at low compressive stresses of 25 MPa.

[23] Ike, H.; Plancak, M.: Controlling metal flow of surface microgeometry in coining process. In: Geiger, M. (Ed.): Advanced Technol. of Plasticity, Proc. Of the 6th Int. Conf. on Technology of Plasticity ICTP 1999, Nuremberg, Germany. Berlin, Springer, Vol. II, 907- 912

[24] Thome, M.; Hirt, G.; Ellert, J.: Metal Flow and Die Filling in Coining of Microstructures with and without Flash, In: Proc. of the International Conference on Sheet Metal 05, 2005, pp. 631 - 639

[25] Schubert, A.; Burkhardt, T.; Kadner, J.; Neugebauer, R.: High Precision Embossing of Metallic Parts with Microstructure. In; McKeown, P. et al (Eds.): Precision engineering – nanotechnology. Proceedings of the 1st International Euspen Conference, Aachen, Shaker, 1999, Vol. I, 530-533

[26] Schubert, A.; Böhm, J.; Burkhardt, T.: Mikroprägen - Herstellen metallischer Mikrostukturbauteile durch Kaltprägen. wt 90 (2000) H. 11/12, 479-483

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