Determining Friction and Flow Stress of Material during Forging

Abstract

Determination of flow stress and friction in cold forging is of paramount importance. In this work, an inverse procedure is developed for predicting the Coulomb’s coefficient of friction and strain-dependent flow stress simultaneously based on the measurement of bulge and forging load. It is also established that in cold forging Coulomb’s coefficient of friction can be approximated as half the friction factor in Tresca (or constant friction) model. In the inverse procedure, forging load is estimated analytically but bulging is estimated by developing an empirical relation. The efficacy of the inverse procedure is ascertained by the data obtained from finite element method simulations. Finite element method was implemented in ABAQUS and validated with the results available in literature. In most of the cases, inverse procedure provides less than 5% error in the estimates of friction and flow stress. A sensitivity analysis is also carried out to study the effect of measurement error. It is observed that error in the estimation of friction is proportional to error in the measurement of bulge. The novelty of the method lies in the quickness and simplicity of the method.

Derivation of the Coefficients in the Coulomb Constant Shear Friction Law from Experimental Data on the Extrusion of a Material into V-Shaped Channels with Different Convergence Angles: New Method and Algorithm

“…The comparable results of [2,16,[44][45][46] in experiments for the analytical calculation of friction law parameters for extruding metal into narrow V-shaped channels are presented in Table 3, with dependence (32). This analysis showed that it possible to extend the relationship between m and its equivalent µ to the process of filling narrow channels with a large contact area, which, for example, allows one to calculate the forging flash formation when designing finishing dies.…”

“…Dixit and Narayanan [45] obtained the die-pressure distributions in the plane-strain upsetting of a specimen of height h and width w for Coulomb and constant friction models. Based on this study, Dixit et al [46] after several simplifications, obtained the following result:…”

“…Recent studies tried to establish an approximate relationship between μ and m [15,16,[43][44][45][46]. Molaei et al [44], proposed the following relation based on FEM simulations of double cup extrusion and barrel compression tests, which provided better accuracy than some other relationships: The experimental data clearly indicated that the extrusion of the material into radial channels with small convergence angles was dominated by the constant shear law because the relative length of the Coulomb friction law zone was negligible (see Table 3).…”

“…Recent studies tried to establish an approximate relationship between µ and m [15,16,[43][44][45][46]. Molaei et al [44], proposed the following relation based on FEM simulations of double cup extrusion and barrel compression tests, which provided better accuracy than some other relationships:…”

“…for (µw/h) 1, m ≈ 2µ [46]. Zhou et al [39], in FE simulation of sideways extrusion, adopted the Levanov friction model.…”