Papers by Author: Karen Abrinia

Abstract: Die shape plays a key role in extrusion process through widely affects on the extrusion pressure and product quality. Therefore, prediction of the optimal die shape is the main objective for an effective extrusion process. In this study, the notion of Equi-Potential Lines (EPLs) was applied to 3D-die designing in extrusion process for the first time. To implement the analogy in the extrusion, the initial and final shapes were considered and two different potentials were assigned to them, and then EPLs were drawn between two shapes that show the minimum work path between the entry and exit cross sections. The drawn EPLs were connected to build up a 3D-die. The effectiveness of the proposed method was examined experimentally, by comparing the results between the designed die and the linear die (with the linear curve for the deformation zone). It was found that there was acceptable reduction in extrusion pressure for the designed die.

Abstract: Material flow pattern in extrusion is an important part of the forming process. Understanding and formulating the material flow helps to determine the optimum shape of the die and important details of the process. In this paper, physical modelling of forward extrusion of non-symmetric L-shape section has been carried out to obtain an experimental understanding of the material flow pattern. A theoretical formulation using the conformal mapping theory has also been presented to predict the material flow pattern. The conformal mapping function was set up to translate the non-circular cross-section region of special-shaped products into unit dish. The results for the material flow pattern for the forward extrusion of L shaped profile from circular billets are presented here. In the physical modelling tests plasticine was used as the model material and different coloured layers of plasticine were used to build up the billet. Experimental and theoretical results were compared and good agreements were observed.

Abstract: In this paper, based on the modified slab method theory, an analytical solution for ring rolling process is presented. The non-uniformity of the normal and shear stresses across the section of the deforming material are considered. The friction factor multiplied by the shear yield strength is used to present friction between the main roll and the ring. Complete expressions for the ring rolling pressure, force and torque are obtained and the position of neutral point is predicted. The influence of the process parameters such as friction factor, main roll rotational speed, feed speed, and others was investigated. Analytical results obtained from the present formulation were compared to previous experimental works and good agreement and improvements were observed.

Abstract: A generalized upper bound solution for the deformation of ring in the ring rolling process has been formulated. An admissible velocity field and strain rates are derived from the parametric definition of streamlines in the deformation zone. This new formulation was used to predict the upper bound on power. Minimizing the upper bound power with respect to neutral point position, the neutral point position and the rolling force were determined. Using the theory presented here, the variation of internal, shear, frictional and total powers with respect to ring revolution are discussed. Some of the results obtained from analysis were compared with experimental results.

Abstract: In this research, a new application of friction stir processing (FSP) in producing surface composite on circular billets was introduced. Al/Cu composite was fabricated by FSP on the surface of a 1050 aluminium cylinder with the diameter of 60 mm. Then this cylinder with surface composite was extruded with the extrusion ratio of 1.7. Finally, microstructure and microhardness were investigated before and after the extrusion. H13 hot work steel was used as the material of the tool whose pin diameter and length were 6 mm and shoulder diameter was 18 mm. The rotation and traverse speed of the tool were 1000 rpm and 25 mm/min respectively. The microstructural investigations show that the thickness of the composite layer decreases and a uniform layer of the composite remains on the surface after the extrusion. Also the microhardness measurements demonstrated that the hardness of the composite layer was higher than the base metal and the microhardness of all zones increased after the extrusion.