| Cutting fluids (CFs) are widely employed in machining operations to perform three major claimed functions: lubrication, cooling, and clearing of chips from the cutting zone. However, their use is now being questioned for environmental and economic reasons, leading to efforts directed at advancing dry, and minimal quantity of lubricant (MQL), machining. Several issues regarding CF application effects in modern machining---which is generally characterized by the use of relatively high cutting speeds, advanced tool-coating systems, and complex chip-breaking features---remain unresolved leading to inappropriate CF usage. This dissertation presents an experimental investigation of the overall influence of different CF application methods on machining performance under currently prevalent conditions.;An initial study involving drilling of A390.0 aluminum alloy revealed the incidence of higher concentrations of hazardous aerosol under MQL condition. The dominance of thermal effects over any possible lubrication was also established, and it was deduced that the fundamental mechanism underlying MQL action may be evaporative cooling rather than reduction in heat generated due to decreased friction, as is currently believed in the machining research community.;Subsequently, a more fundamental study involving orthogonal (two-dimensional) machining of AISI 1045 steel using uncoated and coated, flat-faced as well as grooved, carbide tools was conducted. It was found that during continuous cutting the effects of CF application were minor in comparison to those of tool coatings, and were almost entirely thermal in nature. When present, chip-breaking grooves on tools enabled applied CFs to have a slightly greater, though not necessarily beneficial, influence on the cutting process. CF application was able to significantly influence frictional conditions only during interrupted machining, where the cutting cycle was shorter than the time required to stabilize interfacial contact conditions under continuous cutting. Inverse estimation of tool-chip interface temperatures, and tool thermal properties, revealed some interesting trends regarding the nature of tool-chip contact in high-speed machining, with important ramifications for tool-coating development.;Finally, a tool wear progression study during turning of AISI 1045 revealed some important drawbacks associated with forcibly attempting to achieve CF-aided lubrication in high-speed machining. CFs with extreme-pressure additives, for enhanced lubricity in ferrous-alloy machining, were found to aggravate tool wear through chemical attack under conditions where the tool substrate was exposed, and accessible to the CF.;In summary, this dissertation presents information regarding the overall effects of CF application on machining performance under prevalent cutting conditions and tooling. Several avenues for future research are recommended based on this work. |
