Tribological properties of sheet metal forming fluids modified with dispersed nanoparticles.

摘要

Sheet metal forming fluids are quite important in reducing friction, prolonging the life of tools by reducing wear, and improving the overall quality of workpieces. Improving the quality of these fluids helps in reducing wear of sheet metals and dies, and lowering friction at the interface between the die and workpiece materials. The tribological properties of forming fluids can be improved by using nanoparticle additives. In this research, nanoparticles of different materials that have been previously used for solid lubrication were used to modify the tribological properties of commercial sheet metal forming fluids. Specifically, Molybdenum disulfide (MoS2), Tungsten disulfide (WS2) and Hexagonal boron nitride (hBN) nanoparticles with varying particle sizes were dispersed in the forming oil by the use of an ultrasonic disruptor, and their effects on friction and wear were evaluated using a pin-on-disc tester. The tribological properties of the modified fluid were studied by varying the concentration of the nanoparticles in oils. The size effects of these nanoparticles on the tribological properties were also studied for each material. The tribological properties were studied by using a pin-on-disc tester wherein a 440C steel ball was used as the pin and titanium and steel sheets were used as the disc materials. Experimental results indicated that for a 440C ball sliding against a steel sheet in the presence of the modified oil using nanoparticles, the wear of the ball was reduced by as much as 90-95% for MoS2 particles of 10 nm average size. For the ball sliding against a titanium sheet, the amount of wear of titanium sheet was reduced by as much as 35-43% using the modified fluid.;The quality of dispersion of nanoparticles was also studied in this research. Different physical and chemical methods were used to disperse nanoparticles in oils. The physical techniques that were used in this study are the Ultrasonic Disruptor and the High Pressure Homogenizer, and the chemical method was the addition of a surfactant. The quality of dispersion was examined using a light-scattering machine. Light scattering results indicated that the high pressure homogenizer markedly enhanced the dispersion of nanoparticles.;Finally, the mechanism by which nanoparticles contributed to the tribological improvement of the forming fluid was studied by using a Scanning Electron Microscope (SEM) and an Electron Dispersive Spectroscopy (EDS). After each tribotesting, the structure of the worn out surface of the ball was studied by SEM, and elements involved inside the wear scar were detected by EDS. The results confirmed that the nanoparticles entered between the entrapped wear particle agglomerates, and created weak shear lines. Hence, the collapse of wear agglomerates occurred faster along the nanoparticles' lines, and reduced plowing of the softer surface. Therefore, friction and wear were reduced.