| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 107 === This research is to study the hot working process in a three rolls planetary high reduction mill (HRM) via a finite element method, where unsteady, three-dimensional model is adopted in the study under the assumption of a rigid-viscoplastic and constant-density workpiece. The commercial software, DEFORM 3D is employed for the numerical simulation of the plastic deformation of hot working process in HRM. Different process parameters, such as temperature, friction coefficient, diameter, are studied for S209 stainless steel in hot working process. Product characteristics and physical quantities, such as effective strain rate, effective strain, effective stress and temperature, are analyzed to identify the influence of processing parameter on the hot working process. The numerical result, indicates that the product characteristics are affected by processing parameters. A lower initial billet temperature results in products with shorter cavity at both ends. A billet with smaller initial diameter leads to products with less significant spiral marks along with shorter cavity at both ends. The effective stress and effective strain rate reach to peak values at the contact surface between the rolls and stay low in the middle part of workpiece. The effective strain grows through the rolling process and achieves the maximum at the end of the process. And a temperature peak is found at 5 mm below the surface of the workpiece, which the peak exceeds the melting point of working material. And it is deduced to be the outset of black zone as well as the material detachment inside the product.
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