Potential of brazed cBN wheels to mill-grind hardened steels under near-dry environment

End mill cutters experience rapid tool wear and frequent replacement, when employed in machining of hardened steels (HRC 60 or above). The present investigation explores the feasibility of using brazed cBN tools with uniform grit distribution pattern for mill-grinding of such materials and explores whether it can be a potential alternative. Considering the high grinding temperatures in the process, minimum quantity lubrication (MQL) was also integrated for effective heat dissipation and lubrication at the grinding interface. Palm oil-based diamond and graphite nano-aerosols were used as MQL medium. The superior lubricating characteristics of the graphite nano-aerosol resulted in a 52% reduction in the coefficient of friction (CoF), whereas the diamond nano-aerosol produced the lowest tribo-track roughness of 7.9 µm by its polishing effect. A simple yet novel micro touch-dressing strategy was adopted to modify the wheel topography, thereby increasing the active grit density and promoting more uniform grit-workpiece engagement. The heat transfer coefficient of the nano-aerosols was investigated and found to increase by 27% and 10% for graphite and diamond nanofluids, respectively, compared with the base oil. The touch-dressed brazed cBN tool successfully performed mill-grinding under both dry and nano-MQL environments without noticeable wheel loading and with minimal tool wear, in contrast to the substantial tool wear commonly reported for carbide tools under comparable hard machining conditions. The novelty of this study lies in the evidential demonstration of the successful use of touch-dressed brazed cBN tools having uniform grit distribution, for thermally efficient mill-grinding of hardened steels with negligible wheel wear.