K.S. Pandey

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.

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.

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 ).

Some aspects of workability studies in cold forging of pure aluminium powder metallurgy compacts

Abstract Powder metallurgy is a rapidly developing manufacturing process for the production of precision components in industries. This technique involves compaction, sintering and plastic deformation (forging). In this paper, a detailed discussion on a workability factor of aluminium powder metallurgy compacts with respect to the combined effect of the mean stress and the effective stress is described and compared for the cases of uniaxial upsetting, plane stress upsetting and triaxial stress state of upsetting.

Workability Behaviour of Fe-C-Mo Steel Preforms During Cold Forging

Asystematic method to construct the workability diagram for powder metalurgy (P/M) materials has been proposed. Preforms of Fe-0.8%C, Fe-0.8%C-1 %Mo and Fe-0.8%C-2% Mo were prepared to the relative density of 0.86 with two different geometries through primary operations of P/M processes. Each sintered preform was cold upset forged with incremental compressive loading of 0.04 MN under three different lubricant conditions til a visible crack appeared at the free surface. Oyane’s fracture criterion was used to develop a theory to study P/M products. The least squaremethod was used to determine the constants in fracture criteria and these equations were eventualy used to construct workability diagram. It is found that the proposed method was wel in agreement with the experimental results.