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https://hdl.handle.net/2142/21416
Description
Title
Modeling methods and die design in extrusion
Author(s)
Ulysse, Patrick
Issue Date
1996
Doctoral Committee Chair(s)
Johnson, Robert E.
Department of Study
Mechanical Science and Engineering
Discipline
Theoretical and Applied Mechanics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Applied Mechanics
Engineering, Mechanical
Language
eng
Abstract
The process of extrusion consists of placing a cylindrical billet in the cylinder of an extrusion press and forcing the metal through an orifice or die opening having the shape of the desired product. In this work topics in extrusion of industrial interest are considered.
In the first part of this work, the stress distributions during the extrusion of metals at high temperatures (hot extrusion) are investigated. Axisymmetric extrusion processes are considered. The metalworking operation is assumed to be adiabatic. To simplify the analysis, flow fields derived from the Stokes flow equations, valid for very viscous fluids, have been used as kinematically admissible fields to determine the strainrate and the adiabatic temperature which are needed to determine the stress distributions in the flowing material. Tensile axial stresses which are known to be responsible for the formation of internal cracks in the extruded product are analyzed.
In the second part of this work, a plane-strain upper-bound analysis of eccentric single-hole extrusion and unsymmetrical multi-hole extrusion is presented by using analytical and semi-analytical expressions. The given relations may be applied to an extrusion die with any number of aligned orifices. The analytical and numerical optimizations of the upper-bound expression for the power allowed a study of the deadzone angles of the assumed pattern of deformation. To verify the accuracy of the results, quantitative and qualitative comparisons are made with published works from the literature.
Finally, in the third part of this work, the subject of extrusion die design is considered. In this study, a model is proposed which should guide the preliminary design of extrusion dies. The model is focused on the distortions of the extruded product due to exit velocity variations. It is assumed that the metal flow can be modeled as a linearly viscous or Newtonian fluid. The die design model is limited to the extrusion of thin sections through solid dies (used for non-hollow shapes). Since the die opening is assumed to be long and slender, asymptotic approximations have been used in the analysis. In addition, for more intricate sections, a numerical approach has been adopted. Some die design examples are discussed.
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