Theoretical and experimental evaluation of no-slip feeding condition in ECAP-Conform of a square-section metallic rod
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ORIGINAL ARTICLE
Theoretical and experimental evaluation of no-slip feeding condition in ECAP-Conform of a square-section metallic rod Hasan Ghaforian Nosrati 1 & Khalil Khalili 1 & Mahdi Gerdooei 2 Received: 23 June 2020 / Accepted: 16 November 2020 # Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract This study addresses the applicability of the equal channel angular pressing–Conform (ECAP-Conform) process, which is recently used to obtain the fine-grained structure via severe plastic deformation (SPD). A novel theoretical method based on preventing the deformed rod from slipping on the feeder roll called slip threshold criterion (STC) was presented. Firstly, the total required torque was calculated by combining the energy balance and the upper bound methods. The amount of the minimum rollcontact angle was specified so that no slip happened between the rod and the roll. The STC was achieved in terms of the roll radius, roll-contact angle, raw material strength, and frictional condition between the rod and the tooling. To validate the analytical model, the ECAP-Conform process for a square cross-section rod of grade 2 commercially pure titanium was performed, and the reactive torque was measured empirically then compared with the analytically calculated value. It was found that there is a reasonable agreement between the theoretical model and the experimental outcome (an error of less than 11%). The results revealed that the performance of the process improves by increasing the roll-contact angle, roll friction, and roll radius, as well as decreasing the friction of the segment and die surfaces. Keywords ECAP-Conform . Roll-contact angle . Required torque . Slip threshold . Upper bound analysis
1 Introduction Nowadays, the ultrafine-grained structure materials can be produced by the severe plastic deformation (SPD) method with desirable mechanical properties. Equal channel angular pressing–Conform (ECAP-Conform) technique as a continuous SPD process has attracted the most attention of researchers due to the elimination of two major defects of the traditional ECAP process. The first defect of ECAP is the length of the specimen, which must be smaller than a critical value so that the specimen does not bend during the process [1] and the second disadvantage is the discontinuity of this process resulting in increased cost and less efficiency in the industry.
* Khalil Khalili [email protected] 1
Department of Mechanical Engineering, University of Birjand, Birjand, Iran
2
Faculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran
In 1974, Etherington developed a novel process for the continuous extrusion of metals called Conform. The feedstock in the Conform process, in the form of round wires or powders, is pushed into the groove on a rotating wheel. The objective of the Conform process is to change the geometry of the raw material or amalgamate the powders, so the specimen that passing through the orifice usually has a different crosssection from
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