2004 Volume 45 Issue 9 Pages 2832-2837
The behavior of the interface of a cold forging tool coated with a hard film is analyzed by the finite element method (FEM). The mechanical properties of the interface between a hard film and a tool material are modeled under the framework of the irreversible thermodynamic constitutive equation theory with continuum damage mechanics. The interface damage variable and its evolution law are introduced, which express the degradation of the interface. The hemispherical tool of SUJ2 in JIS coated with an electroplated coating of chromium indents into a cylindrical workpiece of S25C in JIS, which is performed to examine the validity of the proposed model. In FE analysis, the proposed constitutive equations are implemented by the nonlinear springs between opposite nodes of the interface. Calculated results show that the maximum interfacial normal displacement is observed close to the front of the lip of indentation, whereas maximum interfacial tangential displacement is observed close to the back of the lip of indentation. The region where debonding will first occur as indicated by the calculation results, is similar to the region of the behavior during an actual forging operation. Finally, a method of evaluating the interfacial debonding life of coated tools is proposed.