The present paper proposes an empirical model describing friction behaviour
at the tool-chip interface in machining free-machining steels. Split tool
dynamometry is employed to measure stress distribution on the tool rake fac
e during machining various resulphurised steels. The role of free-machining
additives can be expressed as decreases in the shear flow stress of the ch
ip material at the tool-chip interface. The decreasing ratio compared to a
reference steel depends on the coverage and the shear stress of the additiv
es in the real area of contact. The empirical equation derived on the basis
of adhesion theory has a form similar to that for the reference steel, cov
ering the features observed in the experiment. Using the friction character
istics thus obtained, a finite element-based analysis differentiates the ro
le of free-machining additives in the cutting phenomena, which include chip
formation, cutting force and cutting temperature. The simulation results a
re found to be in reasonable agreement with experiments.