Microforming of a low carbon steel.

In recent years the use of micro products has been strongly increased. Microforming can be considered the most suitable technology to manufacture very small metallic parts for mass production. Performances are strongly coupled with material properties, determining forming forces, interface pressures and tooling life. However research activities on this topic show that the interactions between material, lubricant and forming tools substantially differ from those of macro-forming. Models developed in the macro world can not be directly transferred to the micro world. The models should be modified and tuned, or new models should be developed and adopted. In order to allow the optimization of a microforming process, the authors start a research project aimed at investigating the following metal microforming features: i) workmaterial rheology, and ii) friction between workpiece and tooling. Research activities are splitted in three steps. The first is devoted to the development of rheological and tribological models by investigating micro wires drawing. The second step is aimed at building and setting-up a FE-numerical model which integrates the models developed in the previous step. The third one concerns the design and development of a sort of a microforming benchmark to be used for an extended validation of developed models: a laboratory tests operating on a 3D geometry simplified, but representative of a non-stationary bulk forming operation. The chosen microforming process is the hydrostatic microextrusion. The paper presents in the first part the main results of the experimental and numerical campaign on 300 μm wires aimed at: i) performing small reduction (few tens of μm) by fine wires drawing, ii) investigating different material models for surface and bulk layers by the measurement of UTS, as well as grain structure analysis, and iii) developing a friction model. These models have been integrated in a FE-numerical model tuned and validated by experimental results. In the second part of the paper is detailed the test configuration design adopted for microextrusion tests.