Estimation of frictional coefficient between tool and specimen in container-less tapered plug penetration test

Tribological developments including lubricant and die material etc. contribute to improvement of die life and product quality in forging. They have used several tribological tests in laboratories. A container-less tapered-plug penetration test was proposed to estimate tribological properties of lubricants with prevention galling and reducing friction. This simple test uses a thick and hollow specimen so that pressure can be higher even without the container. Not to use the container can limit the frictional interface between a tapered-plug and a specimen. Consequently, the friction directly affects the forming load, and it is more simply and precise to estimate the frictional coefficient. In this paper, the frictional coefficient between the tapered-plug and the specimen is estimated using a perturbation method with both FEM analytical and experimental data on the forming load. A change in the frictional coefficient is also indicated during the test.