Adjustment of stochastic responses of typical cold forging systems

The stochastic nature of typical cold forging processes is assessed in this paper. Finite element computations have been applied to backward can extrusion, free upsetting, closed-die forging and forward rod extrusion in order to study the influence of scatter of the principal process input parameters on the dimensional accuracy of products and on the tool service life. Flow stress and mass of the workpiece have been varied in combination with tribological parameters to evaluate scatter of process responses for soft and stiff press. The results show that stochastic interactions differ radically for the four typical cold forging processes and that press stiffness has a significant influence on the stochastic relationships. For the closed-die upsetting it is demonstrated that statistical distributions of the input parameters can be adjusted in order to achieve reliable process. Here it is shown that bounds of operating windows defined by intersections between product tolerances and tool service life constraints are different for soft and stiff press. At the end of the paper an industrial example is provided to demonstrate how stochastic responses can be adjusted for production of the inner race.