Faculty Publications
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Item Influence of die angle on containerless extrusion of CP titanium rods(2005) Srinivasan, K.; Venugopal, P.As the name implies containerless extrusion is done without container and the total force consists of three individual terms namely ideal force, shear force and die friction force. Container wall billet friction is absent. The shear force varies directly with die angle, die friction force varies inversely with Sine of twice the die angle and ideal force is independent of angle. At a particular angle the total force is minimum. This is termed as optimum die angle. This can be understood from slab analysis of the process. Theoretically the optimum die angle varies only with extrusion strain and friction factor. It is found to change from 25° at a strain of 0.15 to 30° at a strain of 0.42. Experimentally the optimum angle is found to be independent of strain and at all strains it is found to be 25° at a constant friction factor of 0.14. More over the experimental pressure is less than that-predicted by theory. This is attributed to the temperature rise in the deformation zone and a consequent decrease in flow stresses of titanium.Item This paper deals with an experimental investigation concerning the open die extrusion (ODE) of three materials of varying physical properties and mechanical properties. Two geometrical configurations (solid and tube) and two methods (by direct and indirect techniques) were considered to examine the influence of these variables in the generation and retention of heat in the deformation zone with the objective of ensuring a greater achievable strain. Studies reveal that solid configuration supports the retention of heat as against tubular configuration. Low thermal conductivity, density, specific heat and high flow stress which characterise 99Ti make this material an excellent candidate for ODE as opposed to AISI 1020 steel and aluminium, which fail to meet all the above physical and mechanical properties. The indirect technique reduces the friction factor and thus enables greater strains to be achieved. © 1997 Elsevier Science S.A.(Elsevier BV, Adiabatic and friction heating on the open die extrusion of solid and hollow bodies) Srinivasan, K.; Venugopal, P.1997Item A heterogeneous process such as open die extrusion has been done on CP titanium and the extent of heterogeneity has been determined. The pressure for carrying out the process has been calculated theoretically, measured experimentally and calculated indirectly from hardness measurement in the deformation zone. Hardness-stress-train correlation is very useful here. A nomogram has been given so that knowing, ?, ?, ? and hardness, the punch pressure can be read off. It is a steady-reckoner that is very relevant for the shop floor in industry or the laboratory.(Elsevier Science S.A., Hardness-stress-strain correlation in titanium open die extrusion: an alternative to visioplasticity) Srinivasan, K.; Venugopal, P.1999Item Open die extrusion (ODE) has been done on AISI 1020 steel, commercial purity aluminium and commercial purity titanium, in both direct and inverted modes. It was found that inverted extrusion requires lesser forces than direct extrusion. Limit strains are more for the former than for the later as measured experimentally and as calculated theoretically. Theoretical limit strains are lesser than experimental ones in both the case of rods and tubes. ODE is only for shorter components due to unsupported billet and interference from buckling. It is also only for smaller strains due to interference from upsetting of unsupported billet above the die rather than extrusion through the die. © 2004 Elsevier B.V. All rights reserved.(Direct and inverted open die extrusion (ODE) of rods and tubes) Srinivasan, K.; Venugopal, P.2004Item Influence of die angle on containerless extrusion of commercially pure titanium tubes(2007) Srinivasan, K.; Venugopal, P.Containerless tube extrusion has been investigated with commerically pure titanium at room temperature and a strain rate of 0.07 s-1 using 20 conical dies of five different strains and four different angles with MoS2 lubricant. Theoretical punch pressures have been calculated using appropriate equations from slab analysis of the process and compared with experimentally determined punch pressures. It is found that there exists an optimum angle at which the punch pressure is the least at a given strain.Item Formability limit in containerless (open die) extrusion of commercial purity titanium rods and tubes(2008) Srinivasan, K.; Venugopal, P.Containerless extrusion requires far less forces compared to conventional direct extrusion of rods and tubes due to the elimination of container wall-billet friction. But the strains that can be imparted are less in the former due to the unsupported billet which gets upset first if the axial stress exceeds yield stress of the billet material. If this stress is equal to yield stress, it corresponds to the limit of the process of pure containerless extrusion. It is found that this limit strain as predicted by theory is far less compared to what is observed experimentally. This discrepancy is explained on the basis of heating that takes place in the deformation zone due to ideal, frictional, and shear work done in carrying out the extrusion process.Item Compression testing of Ti-6Al-4V in the temperature range of 303-873 K(2008) Srinivasan, K.; Venugopal, P.Compression testing of Ti-6Al-4V alloy has been carried out at temperatures between 303 K to 873 K. To prevent embrittlement due to atmospheric oxygen and nitrogen, the samples were given a glass coating, which also acts as a lubricant simultaneously. Dynamic Strain Aging was observed to occur in the temperature range of 600 K to 800 K. Below 600 K stresses were high. Warm working has to be done above 800 K but below 1163 K (0.6 Tm where Tm = 1940 K) which is the recrystallization temperature. Based on these conclusions, warm extrusion has been successfully carried out in the Materials Forming Laboratory of I.I.T., Madras, Chennai, India.