Extrusion processes are essentially influenced by friction between billet and extrusion tools. Not only process parameters but also the microstructure and mechanical properties of extrudates depend strongly on friction effects. A reliable determination of friction behavior is important for the construction of extrusion tools and optimization of whole extrusion processes. The problems for characterization of friction effects in extrusion processes are that common friction tests like pin-on-disk don't give relevant information about friction in extrusion situations due to lower hydrostatic stresses. There are few results about influence of normal stress, temperature, and velocity on friction. In this work, a two-step friction test was developed. In the first step an aluminum cylindrical specimen is placed in a ring-shaped steel die between two punches and compressed to a certain stress state chosen according to different extrusion situations. In the second step the force of one punch is kept constant while the other punch is moved by controlled displacement to shift the specimen. This experimental method enables a systematic change of normal stress, temperature, and velocity. Finite Element (FE) simulations were performed to analyze the loading situations, and a modified shear friction model was derived based on the experimental results.
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