Most mechanical work supplied during cutting becomes heat. Important heat sources are plastic deformation in the shear zone and friction where the chip contacts the tool.

High temperature can accelerate tool wear, soften the cutting edge, change friction and contribute to dimensional error through thermal expansion.

A cutting fluid can serve several different functions:

• cooling by carrying heat away;
• lubrication by reducing friction at accessible interfaces;
• flushing chips away from the cutting zone;
• protecting surfaces and machine components from corrosion.

Cooling and lubrication are not the same objective. At very high cutting speeds, much of the heat can leave with the chip, while fluid may have difficulty penetrating the hottest contact region. In other processes, lubrication dominates because friction strongly affects force and surface quality.

Cutting fluids also create costs and constraints: purchase, filtration, mist exposure, disposal, contamination and compatibility with downstream operations.

Dry machining, minimum-quantity lubrication and flood cooling are therefore alternatives chosen according to the tool-workpiece pair and process conditions rather than a simple hierarchy.

The key connection is:

cutting conditions -> deformation + friction -> heat generation
                                      ↓
                         tool wear, dimensions, surface

Thermal management is consequently part of process design, not an afterthought.