Mechanism of lubrication enhancement in drilling with MWCNTs nanocapsules cutting fluid

Insufficient micro-lubricant supply during drilling operations results in inadequate heat dissipation and ineffective friction reduction at elevated temperatures, thereby limiting machining efficiency. This study addresses the issue by preparing nanocapsules via a wet chemical method. Chlorinated paraffin (T301), a lubricating agent, was encapsulated within carbon nanotubes (CNTs) to form nanocapsules, which were subsequently used as additives in nanofluids. During drilling, these nanocapsules release T301, enabling a self-lubricating effect that enhances penetration and retention in the cutting zone, thereby improving both cooling and lubrication performance. The mechanical and thermodynamic properties of the nanofluids were characterized, and a series of drilling tests were conducted using these enhanced fluids. The study also analyzed heat transfer in the drilling area and the formation of a lubrication layer influenced by the nanofluids. The nanocapsules demonstrated excellent thermal conductivity and dispersion stability. When drilling 45 steel, the inclusion of nanocapsules resulted in significant improvements: torque was reduced by 35.6%, drilling temperature by 19.3%, surface roughness of the inner hole by 22.7%, and tool wear by 25.5%, compared to the use of commercial emulsions. Surface composition analysis of the drill bit revealed that the self-lubricating effect was due to the rupture of multi-walled carbon nanotubes (MWCNTs) during metal cutting and drilling, which released the T301 lubricant directly into the drilling zone.