Measurement of Friction Characteristics using a Three Pin System

Knowledge of tool/material contact stresses, especially in the tool design stage, is important in order to evaluate the dimensional accuracy of the part being produced and reduce the risk of tool damage. The intensity and distribution of contact stresses produce variable frictional resistance at the tool /material interface and hence influence the mode of plastic deformation. Using pressure pins, experimental techniques however enable the measurement of normal pressure and in some cases the friction resistance at the interface. This paper describes an experimental methodology suitable for the measurements of contact stresses and friction forces at the tool/material interface under hot working conditions. It employs a newly designed thermal pin which incorporates a column of zirconia that acts as a thermal break between the deforming material thermal conditions and the sensitive measuring device. The mechanism of forces at the interface is measured using three pins mounted at different orientation to the tool surface. Results from experiments are also compared with theoretical predictions in order to examine the progress of stress intensity along the tool/material interface.