FEM simulation of friction testing method based on combined forward rod-backward can extrusion

A new friction testing method by combined forward rod-backward can extrusion is proposed in order to evaluate frictional characteristics of lubricants in forging processes. By this method the friction coefficient mu and the friction factor m can be estimated along the container wall and the conical die surface in the forward rod extrusion using theoretical calibration diagrams representing the relationship between the punch travel, the forward rod extrusion length and mu or m without requirements of measuring the forming forces and the paw stress of the workpiece.

The theoretical calibration curves are obtained by rigid-plastic FEM simulations in a combined forward rod-backward can extrusion process for a reduction in area R-b = 25, 50 and 70 percent in the backward can extrusion. It is confirmed that the friction factor m(p) on the punch nose in the backward cart extrusion has almost no influence on the calibration curves.

The optimum initial height/diameter ratio of the workpiece is 1.0-1.1. The influence of the workhardening index on the calibration curves is insignificant in the range 0.1 less than or equal to n less than or equal to 0.5. Experimental friction tests are carried out in a mechanical press with aluminium alloy A6061 as the workpiece material and different kinds of lubricants.

They confirm the analysis resulting in reasonable values for the friction coefficient and the friction factor.