The tribological properties of metal working differ from equipment lubrication. Metal working frequently operates under extreme-pressure boundary lubrication conditions, characterized by high temperature, heavy load, and continuously renewed surfaces of friction pairs within an extremely short time. The lubricity, cooling performance, rapid penetration capacity and surface adsorption property of base oil directly affect processing efficiency and machining quality.

 For metal forming processes, in addition to extreme-pressure boundary lubrication, mixed lubrication regimes also exist. The viscosity of base oil affects oil film formation and must be taken into consideration. Furthermore, neither excessively good nor poor lubricity is desirable. Overly good lubricity causes slipping and wrinkling, while insufficient lubricity increases wear and fails to meet the surface finish requirements of workpieces.

For cutting operations, large volumes of chips are generated. If the base oil has excessively high viscosity and strong adhesion, a large amount of cutting fluid will be carried away by chips and workpieces, and workpiece cleaning will become difficult.

Some newly developed multi-axis machine tools adopt a working mode where the cutting tool remains stationary while the workpiece rotates at high speed. When selecting cutting fluids, apart from meeting machining requirements, the lubrication of workpiece supporting spindles also needs to be considered. Base oil with appropriate viscosity shall be selected, which is similar to equipment lubrication; otherwise, accidents are likely to occur.

At present, research on the tribological characteristics of metal working is insufficient. Most studies focus on mechanical mechanics, while investigations into lubrication mechanisms are limited. Moreover, continuous emergence of new processes and new materials deserves more attention.