| Summary: | 碩士 === 逢甲大學 === 機械工程學系 === 89 === Among all the forming processes, cold extrusion is an extremely important and economical process, especially for producing round or nearly round parts in large quantities. It is a special kind of forging process in which a block of billet is reduced in cross-section by forcing it to flow through a die orifice under high extrusion pressure. It generates fine products both in shape and material properties, thus yields significant savings in material and machining.
An accurate evaluation of the effects of various parameters on metal flow and fracture is required for the proper design and control of extrusion process. Without the information of the influence of variables such as friction conditions, materials properties, and process geometry on the process mechanics, it would not be possible to control the change of the metallurgical structure of the deforming material, or to predict and prevent the occurrence of defects. The key issues concerned in extrusion are both how to increase its formability and how to lower the extrusion load. The reduction both in the number of perform or in extrusion pressure aids to lower the production capital.
The thesis aims to develop a finite element program based on an optimal upper bound formulation for the simulation and analysis of axisymmetric extrusion problem of metals. It analyzes the effects of parameters（such as material property, die shape, friction coefficient and area reduction ratio）on extrusion load in detail. Computational results were compared with available analytical data found in the literature in good agreement
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