Murudkar, Rahul R. (2009-08). Development of a Continuous Equal Channel Angular Extrusion (ECAE) Process. Master's Thesis.
Equal Channel Angular Extrusion (ECAE) has great potential for developing ultrafine grain structure consisting of homogeneous and equiaxed grains dominated by high angle grain boundaries. In addition, the ECAE-processed specimens retain their original cross-section, providing capabilities of multi-passing. However, the process is discontinuous as the length of the billet is limited due to potential buckling of the extruding ram. This problem provides an opportunity of making the process continuous. The objectives of this study were to examine the feasibility of a process obtained by combining ECAE and Equal Channel Angular Drawing (ECAD), evaluate the potential of the combined process for continuous processing of sheet metal, and to analyze the mechanical response of sheet metal subjected to the ECAE and ECAD techniques using numerical study. Numerical analyses of ECAE and ECAD were performed using the commercial FE analysis package ABAQUS/explicit. Experimental data and analytical models available in literature were used to validate the numerical results. Parametric studies on the effects of drawing angle, and sheet thickness to die radius ratio (t/r), on reduction in thickness, strain uniformity and resulting microstructure are presented. Numerical results indicate that ECAD through a closed channel should be preferred over conventional drawing (open channel) operation as reduction in thickness is decreased by 2-3% after a single pass. In the experimental study, it was observed that during ECAD, the reduction in thickness increases by 2.5-3.5% per pass. Also, a higher reduction is observed in route C compared to route A. Use of sharper die corners (higher t/r ratios) and smaller channel intersection angles tend to increase this thickness reduction, and results in an increase in hardness i.e., results in strengthening. ECAD most likely results in a non-uniform microstructure with low fraction of high angle grain boundaries. In addition, for a given pass, the average hardness of the ECADprocessed samples is approximately half that of ECAE-processed samples. This suggests that ECAD alone may not be commercially viable. However, a significant improvement in minimizing reduction in thickness is achieved by providing a little gap between the sheet metal and support plates. From the numerical analyses, the proposed continuous process appears to be effective in retaining continuity of the drawing operation, minimizing the percent reduction in thickness and imparting higher plastic strains. It is believed that an experimental study of the process will reveal some more promising information.