Evaluation of Tribological Characteristics of Mineral Oils for Copper Product by Cold Extrusion Test

Abstract

This study aims to evaluate lubricant which is useful for metal forming processes restricted by thin oil film formation. Tribological characteristics of lubricants for copper products were evaluated by carrying out a series of plane strain cold extrusion experiments. An extrusion apparatus with a combination of a taper die and plane plate tool with a small extrusion ratio of 1.1 was used to measure the amount of plastic deformation that resulted from using different lubricants. The variation in degree of plastic deformation, extrusion load, and surface condition of the billet due to sliding friction, were investigated depending on lubricant type and initial mass of oil film on the test surface of the taper die. The billet was made of OFC：Oxygen–Free Copper, C1020 (JIS) and the extrusion apparatus was made of SKD11 (JIS). Two types of different mineral oils；paraffinic mineral oil and naphthenic mineral oil, were used as test lubricants in the experiments and five different viscosity grade oils were prepared from each mineral oil. The amount of plastic deformation in the deformation zone of the billet when paraffinic mineral oils were used was found to be larger than that of naphthenic mineral oils, and the difference of ratio of plastic deformation to extrusion load affects plastic deformation near the surface of the billet.