A friction model for free-machining steels and its applicability to machinability analysis

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.