Master of Science in Manufacturing
Institut für Umformtechnik und Leichtbau
Prof. Dr.-Ing. Dr.-Ing. E.h. A.
– Part 1
Anisotropy in hot extrusion
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Table of contents
Formula symbols and abbreviations
forming is not only a major industry, but also an important part of different
modern manufacturing industries, which in turn produce the final product. In those
processes the final shape of the product is achieved by plastic deformation of
the part. For that reason, the plastic flow properties of the materials are of
the main characteristics that have to be known in order to improve and optimize
the manufacturing process.
plastic metal forming materials tend to show anisotropic behavior. This phenomenon
is starting to get more attention with the evolution of the processing technologies
and the use of new lightweight materials. The understanding, prediction, and
analysis of anisotropic behavior are necessary considerations in all design
steps of the production process. This is of even greater importance in aluminum
hot extrusion processes, where the part in preheated to 375 – 500oC, and a very
severe plastic deformation can be observed. Because of the nature of aluminum
and the increased temperature, very intense anisotropic properties can be
observed when extruding aluminum profiles. Due to the big demand for new and
improved aluminum alloys from the automotive and aerospace industries,
different methods for predicting anisotropic behavior have been developed.
Example for that are the Taylor and Sachs analysis based on initial texture 1238.
several factors that influence the anisotropy of the material – grain shape,
dislocation structures, precipitates and most importantly texture of the
material. Different orientations of the grains can cause different anisotropic
properties. Accurate control of these parameters is needed to ensure an
improved, stable and profitable process.
is a forming process in which high pressure is applied to a block of material,
called a billet, in order to force it though a die opening with smaller
cross-sectional area. The process is usually used to produce rods or hollow
tubes. Extrusion can be hot (75% of material melting temperature) or cold (at
room temperature) and both processes can be used to produce a wide variety of
parts. Advantages of hot extrusion are that less pressure is needed to process
the material through the die and it takes less time to do it. On the other hand,
cold extruded parts have better mechanical properties, dimensional accuracy and
will not oxidize.
Additionally extrusion can be divided to two
basic types – direct (figure No) and indirect (figure No). The most commonly used
process is direct extrusion. There the material and the ram move in the same direction.
The billet slides on the surface of the container, generating a large amount
pressure, due to the occurring friction forces. These forces are reduced in indirect extrusion,
as the die moves to the billet and no motion between the material and the
surface of the container is present.
extrusion metal forming the material can withstand very large deformation without
fracture because of the high compressive stresses generated by the contact of
the billet with the container and the die. The pressure usually varies in the
range between 35 and 700MPa … . Where the extrusion force can be described
by the equation (…)
è Metal flow during extrusion
3.1. Types of anisotropy
3.1.3. ??? ????
3.2. Main factors influencing anisotropy
3.2.1. Extrusion ratio
3.2.2. Working temperature
3.3. Methods for predicting anisotropic
3.3.1. Sachs method
3.3.2. Tyler method