Friction shear stress on the tapered surface of the punch has been directly detected using friction sensors during the taper cup test. An aluminum alloy circular cylinder block was used for the test piece with various lubricants. Punch load increased with the frictional stress on the tapered punch surface. The increase in frictional stress with the stroke was estimated to be due to the increase in surface expansion ratio on the tapered punch surface during punch insertion. The relationship between the frictional stress on the punch and the punch load was compared by FEM analysis using friction shear and friction factors. By this study, it was confirmed that the friction sensor can detect frictional stress directly under lubrication, and it will be applicable to the detection of the local friction change during forging under high pressure and under an increasing surface expansion ratio.
