<p> One of the major industrial metalworking processes is extrusion
and it is of technological importance to be able to estimate the loads
and material flow characteristics within the deforming metal. Hot
metals and superplastic materials are particularly sensitive to the
speed of the operation al though it is difficult to col".sider this in an
analysis of the problem. </p> <p>
This thesis reviews the analytical techniques available to the
engineer to determine the loads in bulk forming processes and examines the way in which rate effects have been accommodated. The upper bound method, which is an approximate analytical technique, is reviewed in detail. The concept of a tangential shear zone of constant shear strain
rate is introduced and used to enable strain rate effects to be
considered within the upper bound technique. The work rate across each discontinuity is shown to be a function of the material strain rate
sensitivity, the shear zone width and the tangential veloc i ty change. </p>
A number of tangential velocity fields are proposed for the side
extrusion process. These are examined and compared by minimizing the
work rate using a computer optimization technique. The optimum solution
for a simple tangential velocity discontinuity field is shown to give
load estimates which are within 10% of those given by the more exact
slip-line field method. </p> <p>
Experiments, performed by the author on the side extrusion of two materials, which have very different strain rate sensitivities, are
reported in detail. A characteristic difference in the extrudate
geometry for the two materials is identified and shown to be a result of
the difference in the materials strain rate sensitivity index. The
experimental extrusion pressures for the two materials at different ram
velocities are compared with theoretical values derived using the theory
developed earlier in the thesis; the correlation is good. </p> <p>
The shape of the tangential discontinuity between a uniform
translational and uniform rotational field is examined and shown to be a circular arc. A number of new tangential velocity discontinuity fields
are presented for a variety of common metalworking processes. These fields comprise straight and circular discontinuities and represent a
new type of "mixed" field which predicts the rotation of the extrudate. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/17823 |
| Date | 12 1900 |
| Creators | Forster, James Allam |
| Contributors | Duncan, J. L., Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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