Database Development for Comparative Analysis of the Performance of Metalworking Fluids Based on Drilling Operations

Metalworking fluids (MWFs) play a significant role in machining operations. Despite their importance, the manufacturing industry lacks tools to make functionally sound and economical decisions about them. In this research project, a second generation drilling testbed was developed to evaluate the performance of MWFs with respect to lubricity and cooling capacity. A desktop drilling machine was used to make the testbed with a load cell sensor and a thermocouple located in the oil-hole of the drill. The testbed characterized MWFs based on torque, thrust, and temperature measurements. A standardized test procedure was developed to ensure that comparisons of fluids were accurate, repeatable, and representative of the actual differences in the fluids. System repeatability was found to be very good with a coefficient of variation well under 0.1. The system was found to determine differences within 1-2.9% for torque, 1.4-2.5% for thrust, and 2.7-8.2% for temperature based on five replicates per experimental condition and an α = 0.05 statistical analysis. Ten MWFs were chosen, representing a cross-section of soluble oils, semi-synthetics, and synthetic products from a variety of manufacturers. The performance of these fluids at a 10% concentration was analyzed based on a set of four separate comparative experiments designed to compare various drilling conditions and reveal how the MWFs performed based on changes of workpiece material, feedrate, and dilutent. The results were evaluated within each experiment by comparing how individual fluids performed within their type and how fluid types performed with respect to each other. Comparative analysis was also conducted among separate experiments to determine how changes in feedrate, workpiece material, and dilutent affect MWF performance. Conclusions based on the data analysis are presented. Additional MWF evaluation tests were used to further characterize the fluids. Tests for viscosity, surface tension, emulsion stability, and corrosion inhibition were conducted. These results were compared with the lubricity and cooling results to check for correlation. General trends indicated a correlation between fluid performance in lubrication and viscosity and surface tension results. Surface tension was found to be more a function of the emulsifiers and additives used in a fluid than the concentration of oil, while viscosity showed a definite correlation with oil content. It was also found that the synthetic fluids showed the most resistance to fluid breakdown due to hard water as measured by emulsion stability titration testing. There was no correlation found between type of fluid (soluble oil, semi-synthetic, and synthetic) and corrosion inhibition or surface tension.