Residual stresses in cold axisymmetric forging

In the present work, residual stresses in axisymmetric cold forging process are analysed. The updated Lagrangian formulation, which is convenient for handling the geometric and material non-linearities, is used. A new incremental objective stress measure [Dynamic large deformation elasto-plastic analysis of continua, M.Tech. Thesis, Mechanical Engineering Department, IIT Kanpur, 1997] and the logarithmic strain measure are employed as they allow the use of a larger increment size. The Newton–Raphson iterative technique is used to solve the non-linear incremental equations. The material is assumed to be elasto-plastic yielding according to the von Mises yield criterion and hardening according to a power law. A Coulomb friction law is used to model the interfacial friction. An axisymmetric large-deformation elasto-plastic finite element code, which incorporates unloading, has been developed for the analysis of the residual stresses. The code is validated by comparing the predicted finite element results with available experimental results. A detailed parametric study of the residual stresses is carried out to study the effects of four process parameters, namely the reduction, height-to-diameter ratio, friction coefficient and material properties. It is observed that the maximum value of the residual stress decreases with the height-to-diameter ratio. Further, as the friction coefficient is increased, the deformation becomes more inhomogeneous, because of which the residual stress levels go up. It is also observed that reduction and material properties do not have much effect on the pattern of residual stress distribution.