Influence of friction on the prediction of forces, pressure distributions and properties in upset forging

Abstract

The axial compression of solid cylinders with initially equal height and diameter between flat parallel platens is examined. A finite-element method is used to predict the platen forces, the pressure distribution, and the strain and hardness distributions within the billet, for various levels of interface shear stress. The theoretical predictions of pressure distribution indicate that a simple friction-hill does not occur for this billet shape; a number of different distributions are found, dependent on the boundary conditions. Two distinct modes of flow are identified, again dependent on the boundary conditions. Experiments with commercially pure aluminium cylinders show good correlation with the predictions for unlubricated aluminium and for aluminium lubricated by a thin film of lead.