Studies on Flow Behavior of Aluminum Using Vision System during Cold Upsetting
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METAL forming is a widely used manufacturing process known for its minimum wastage, high-dimensional precision, and improved mechanical properties of the formed part. During metal forming, effective ductility depends on localized conditions of stress, strain, strain rate, and temperature. Material characteristics such as inclusion content and grain size control the ductility to a greater extent. Also, processing parameters such as die design, workpiece geometry, and lubrication contribute to effective ductility. Several investigators used the compression test on cylindrical specimens for the study of deformation behavior under combined stresses. Kudo and Aoi[1] in their investigation on the workability of upset specimens measured the axial and circumferential strains by means of indented marks at the equatorial free surface. Thomason[2] conducted a number of compression tests with various combinations of specimen geometry and platen friction conditions on the barreled surface to study the stress components and the strain increments at the equator. Friction and lubrication are of great importance in any metal forming operation. They affect the detailed material flow and the deformation characteristics of the workpiece, the wear and fatigue failure of the tool, and the mechanical properties of the formed parts. Good lubrication or low frictional constraint is always the key to a viable cold working process. Kobayashi[3] and Kuhn and Lee[4] measured the displacement distributions at the tool-work interface and SYED KAMALUDDIN, Assistant Professor, is with the GITAM College of Engineering, Visakhapatnam 530 045, India. J. BABU RAO, Assistant Professor, and M.M.M. SARCAR and N.R.M.R. BHARGAVA, Professors, are with Andhra University College of Engineering, Visakhapatnam 530 003, India. Contact e-mail: nrmrbhargava@rediffmail.com Manuscript submitted November 2, 2006. Article published online July 12, 2007. METALLURGICAL AND MATERIALS TRANSACTIONS B
on the development of barreling and strain variations at the free surface during the upsetting of solid cylinders. The ring test technique originated by Kunogi[5] and further developed by Male and Cockcroft[6] has the greatest capability for quantitatively measuring friction under normal processing conditions. Measurement of the final internal diameter of compressed rings provides a particularly sensitive means for studying interface friction, because the internal diameter increases when friction is small and decreases when friction is large. Correlation of changes in internal diameter with numerical values of friction can be obtained either by independent calibration or by the application of available theoretical analysis. Knowledge of material behavior requires the measurement of mechanical parameters. The noncontact and nondestructive methods can represent a real advancement for displacement, stress, strain, and interfacial friction measurements. Control of these parameters may thus be exercised to understand the conditions favorable for enhanced deformation. The process
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