Determination of Friction Behavior in Extrusion Processes with a New
Dong-Zhi Sun, Andreas Kailer, Florence Andrieux, and Andrea Ockewitz,
Fraunhofer Institute for Mechanics of Materials IWM, Freiburg, Germany
Track: EXTRUSION/DIE THEORETICAL - Friction and Pickup
ABSTRACT—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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