A Review of Friction and Lubricant in Metal Forming

Friction conditions, along with the flow behaviors of materials, significantly impact plastic deformation during metal forming. Extensive practical research on friction has thus been conducted, and industrial development has been remarkable. However, it has been continuously pointed out in academia that an in-depth analysis of friction laws and phenomena linked to the metal forming simulation (MFS) has not yet reached a sufficient state from an engineering perspective. Despite the significant impact of friction on the MFSs, its importance has been underestimated, and the related studies have been relatively limited. A few researchers on metal forming emphasized the inadequacy of the constant shear friction law (CSFL) and the constant friction coefficient for the Coulomb friction law (CFL). Yet, most researchers still use the CFL with a constant friction coefficient or the CSFL. Many researchers have related the friction coefficient to the yield criterion, and they believe that the friction coefficient cannot exceed a certain value (for example, 0.577). It has also been believed that the sticking condition is the same as the friction factor of unity, even though displacement and traction cannot be prescribed simultaneously in natural phenomena. Despite many researchers’ innovative academic and industrial contributions, friction phenomena in metal forming remain in an incomplete state of confusion. This study reviewed and synthesized research on friction phenomena during metal forming. The main review topics include friction phenomena, friction modeling and friction laws, friction-related issues, lubrication regime change (LRC), lubricants, and tribometers, with their application spaces limited to metal forming. This review synthesizes existing research related to friction in metal forming, proceeding in a problem-identifying and solution-oriented manner.