R. Narayanasamy

Phenomenon of barrelling in aluminium solid cylinders during cold upset-forming

Abstract Experiments were carried out to generate data on the upset forging of solid cylinders of annealed aluminium. The curvatures of the barrelled aluminium cylinders measured physically were found to conform closely with the values calculated using the experimental data. The calculations were made on the assumption that the curvature of the barrel followed the geometry of a circular arc. It was further found that the measured radius of curvature of the barrel exhibited a straight-line relationship with the new geometrical shape-factor, irrespective of the aspect ratios of the cylinders. Further empirical relationships were found to exist between the measured radius of curvature of the barrel and other variables such as the hydrostatic stress and the stress-ratio parameter.

Generalised yield criteria of porous sintered powder metallurgy metals

Abstract A new form of yield criterion considering an anisotropic parameter for porous sintered powder metallurgy metals has been proposed in this technical paper. In addition to the above, the flow rule with anisotropic parameter for porous metal is introduced. The mathematical expression for the calculation of flow stress in the case of simple compression or tension test is deduced from the yield criteria for the P/M sintered preforms of the metals. Further, a new generalised form of yield criteria with five parameter constants for porous sintered powder metallurgy sheet metals has also been proposed in this technical paper.

Prediction of the barreling of solid cylinders under uniaxial compressive load

Abstract Axisymmetric compression tests on solid steel (AISI 5120) cylinders under various lubrication conditions and deformation speeds, suggest that the resulting curvatures of the barrels formed fit closely to circular arcs, the raddi of which follow a power law with respect to the true axial compressive stress. The true compressive stress-strain curve obtained from the experimental data shows that of all the lubricants tested the specific forming energy is minimum for a phosphate coat-soap type lubricant. An attempt is made to relate the surface-roughness value to the hoop strain.

Deformation Behavior of Cold Upset Forming of Sintered Al-Fe Composite Preforms

Cold upsetting experiments were carried out on sintered Al-Fe preforms in order to evaluate their deformation characteristics. The effects of iron content and initial fractional density of the preforms on deformation behavior have been investigated thoroughly by using graphite as a lubricant. Cylindrical preforms with different initial theoretical density and aspect ratio (0.75) were prepared using a suitable die, a punch and a die bottom insert on a 1.0 MN capacity Universal testing machine. The preforms were well covered with dry fine silica sand and sintered in an electric muffle furnace at 550 ±10°C for a period of 1 h and then furnace cooled. Cold deformation experiments were carried out in several steps. Dimensions such as height, contact, and bulged diameters and densities were measured for each test. In general, each compact was subjected to an incremental compressive loading in steps of 0.005 MN until fine cracks appeared on its free surface. Analysis of the experimental data has shown that the power law relationship between fractional theoretical density (ρ f /ρ th ) and e (e z -e θ) has been established. This remained valid for 0-8% iron content and all initial preform densities. Further it was found that the preforms of higher iron content shows higher values of deformation properties like the axial stress and the Poissons ratio than less/without iron preforms provided that the initial fractional density taken is kept constant.

Wrinkling of sheet metals when drawing through a conical die

Abstract This paper deals with the deep drawing of circular blanks into cylindrical cups through a conical die using flat-bottomed and hemispherical-ended punches. It is well established that the use of a conical die can enhance the limiting drawing ratio compared with that obtainable in a conventional drawing operation. When a conical die is employed, the need for a hold-down or clamping ring is eliminated. However, this enhances the propensity of the blank to fail by wrinkling or buckling, particularly in the early stages of a drawing process in which thin sheet blanks are used. An attempt is made to rank the properties that appear to suppress wrinkling. The wrinkling modes that develop during the different stages of drawing are identified. It is shown also that the onset of wrinkling takes place when the ratio of the plastic strain increment ( d ϵ r / d ϵ θ ) reaches a critical value. This value, which is determined experimentally, compares favourably with the results of theoretical analysis.

A study on the barrelling of sintered iron preforms during hot upset forging

Abstract Upset forging tests on iron preforms of cylindrical shape with different initial aspect ratios, forged at the temperature of 1150°C suggest that the experimentally determined theoretical density ratio has a straight-line relationship with the new strain parameter (eez−eθ) and the geometrical parameter ratio [(h0/hf)(3D02/(2Db2+Dc2))]. The barrel-radius curvature fits a circular arc. This shows that the bulged and contact diameters and height can be related to the theoretical density ratio. Also, an attempt has been made to establish the relationship between the measured barrel radius and the stress ratio parameters namely σ θ /σ z , σ z /σ m , and σ θ / σ , and Poisson’s ratio.

Wrinkling behaviour of cold-rolled sheet metals when drawing through a tractrix die

Abstract This paper deals with the deep drawing of circular blanks into cylindrical cups through a Tractrix die using flat-bottomed and hemispherically-ended punches. It is well established that the use of a Tractrix die can enhance the limiting draw ratio as compared with that obtainable in a conventional drawing operation. When the Tractrix die is employed, the need for a hold-down or clamping ring is eliminated. However, this enhances the propensity of the blank to fail by wrinkling or buckling, particularly in the early stage of a drawing process in which thin sheet blanks are employed. For the present work, cold rolled commercially-pure aluminium and copper blanks of different diameters are drawn through the Tractrix die under dry lubrication (with no lubricant) condition, until the appearance of a first-stage wrinkle. An attempt is here made to relate the amount of draw obtainable in the drawing process with the initial diameter of the blank. It is also shown that the onset of wrinkling takes place when the percentage change in thickness reaches a critical value, this value being found to be generally the same for both aluminium and copper sheets.

Strain-hardening behaviour in sintered aluminium–3.5% alumina composite preforms during axial compression with and without annealing

Abstract The present investigation has been undertaken to evaluate the strain-hardening phenomenon experienced in sintered aluminium–3.5% alumina composite preforms during axial compression tests. Powder preforms of three different initial density ratios, namely 0.75, 0.80 and 0.90, with three initial aspect ratios for each density level were prepared using a suitable die-set assembly on a 0.60 MN capacity hydraulic press. Sintering was carried out in an electric muffle furnace for a period of 90 min at 550°C in a nitrogen atmosphere. Each sintered compact was subjected to incremental compressive loading with and without annealing after each step of deformation. The annealing operation was carried out in a furnace at 200°C for 30 min in a nitrogen atmosphere. The strain-hardening exponent n and strength coefficient K were obtained for each initial preform and for each aspect ratio. Analysis of the experimental data shows the existence of empirical relationships between the material parameters namely, n values and K values and the ratio of the initial preform densities to the theoretical density. Further, it was found that n consists of two segments, one representing the work hardening of the matrix material and the other due to densification. It has been also established that a power-law relationship exists between K and the percent fractional theoretical density %( ρ d / ρ th ).

Sliding wear behaviour of AZ31B magnesium alloy and nano-composite

Abstract AZ31B magnesium alloy and nano-composite were manufactured by hybrid casting process and hot extruded at 350°C. The sliding wear behaviour of alloy and nano-composite was estimated at room temperature using the standard pin-on-disc wear test equipment. The tests were conducted under a normal load of 10 N at different sliding speeds ranging from 0.60 to 1.2 m/s for distance up to 2000 m. The wear mechanisms of the worn out surface were studied using SEM analysis. The influence of test parameters on wear rate of the pins was established using a linear regression model statistically. Compared with the AZ31B magnesium alloy, the nano-composite shows lower wear rates due to higher hardness improvement caused by the reinforcement. The wear mechanism appears to be a mix-up of ploughing, rows of furrows, delamination and oxidation.

Computer aided design and manufacture of streamlined extrusion dies

Abstract Extrusion is one of the widely used metal forming processes. The extrusion process is carried out conventionally using a shear faced die, but shear faced dies have many practical problems such as a dead metal zone, more redundant work, breaking of whiskers and above all the design of a shear die is done based on experience. To eliminate the above problems, a new approach of designing the die known as a streamlined die is tried here. The streamlined extrusion die is designed based on the principle of constant area reduction over the length of the die. In this, a uniform flow of metal is ensured from the surface to the core and this can be a more scientific approach of die design. Many methods are available in the literature to design the streamlined extrusion die such as cubic polynomial curves, the area mapping technique, the line-mapping technique and the use of a genetic algorithm. For solving the problem of die design Stokes’ theorem is suggested, but a new approach of transforming the peripheral point on the surface of a cylinder to the corresponding point on the extruded square is obtained by an analytical method. An attempt is made to identify an analytical solution for designing a streamlined extrusion die for a square cross-section.