Laboratory tribological screening test methodologies to evaluate the performance of metalworking lubricants for punching stamping

Four different test methodologies simulating the punching stamping contact between a WC-Co tool and a sheet metal were applied using two tribological testing devices (a load scanner and a reciprocating slider) under dry and lubricated conditions, resulting in 17 different test environments. Using 19 different metalworking fluids (water, base oils, fully formulated vanishing oils and oil blends with specific additives), we screen the most suitable tribological laboratory test methodology that can differentiate the friction and wear performance of different metalworking fluids, including their physical, chemical and fully-formulated properties, and consider the metalworking specifics, and thus mimic the punching stamping process. The reciprocating sliding test with 10,000 cycles was found to be the best due to large difference in tribological performance between the different metalworking fluids and its ability to mimic the realistic mechanisms. Namely, it allowed the transfer of an Fe film from the metal sheet onto the WC-Co tool in the case of insufficient additives. In addition to the tribological laboratory test methodologies used, three sequential analyses of the punch tool from a real-scale industrial punching stamping process were made. The Fe transfer film that formed during the reciprocating-sliding tribological laboratory test was also found on the side surface of the cutting edge of the stamping punch, while critical wear occurred on the front surface, resulting in a rounder and less-sharp cutting edge.