Use of nano-droplet-enriched cutting fluid (NDCF) in ultra-precision machining

Nano-droplet-enriched cutting fluid (NDCF) demonstrates a linear spreading rate when measured by a contact angle goniometer. The spreading continues beyond that a conventional goniometer can measure. Such thinness allows NDCF to penetrate deep into the tool-chip and tool-workpiece interfaces to affect the lubrication. In this paper, straight taper cutting was carried out using a single-point diamond tool. By examining the groove machined, the enhancement effect of NDCF on improving the surface roughness, reducing bouncing back, and suppressing form irregularities could be quantified. Without NDCF, form irregularities were found on the surface of the grooves in the nature of random localized upheavals. For shallow cuts, NDCF could stabilize the cutting with a depth of cut (DoC) below 1 μm and down to around 0.75 μm, so that the roundness of the machined groove could be maintained precisely. Whereas for deeper cuts, NDCF was found to be effective in preventing form irregularities and on reducing bounce back for a DoC larger than 1.5 μm. Regarding bounce back, the experimental work revealed that NDCF can prevent form irregularities from occurring when the DoC is beyond 1.5 μm. For those samples machined using a conventional oil lubricant, distorted rebounding with a magnitude as large as 200 nm was not uncommon.