Computer Simulation of Orthogonal Cutting using a Tool with Multiple Coatings

Abstract

The development and evaluation of an orthogonal cutting simulation model for carbide tools with multiple coating layers (1 µm-TiN/3 µm-Al₂O₃/6 µm-TiC) is presented. The chip geometry, cutting forces, tool temperatures and stresses were predicted using the Finite Element Method (FEM). The results were analyzed with a focus on the understanding of the thermal influence of coating upon tool temperatures at the tool-chip interface and in the substrate. In the simulation model used, the thermal effect of tool coating was considered by using two different models: (a) use of individual coating layers defined with intrinsic thermal properties and (b) use of a composite coating layer defined with equivalent thermal properties. The proposed models were evaluated by comparing the predictions with the experimental data available in the literature under the same cutting conditions. The steady state tool temperature solution was obtained by adopting a three-step simulation scheme. It consisted of an initial Lagrangian-type simulation until a stable chip shape was formed and a subsequent Eulerian-type calculation with update of the free surface and plastic strain field of the workpiece. The predicted results indicated that for the coated tool considered the thin-film surface coatings with an Al₂O₃ intermediate layer did not significantly alter the steady state temperature gradients between the chip and the tool substrate and provided little thermal insulation effect to the tool substrate. However, the modified thermal response of the coated tool surface caused lower cutting temperatures at the tool-chip interface as compared to that for an uncoated tool under the same conditions. Although these results are consistent with similar experimental observations in the literature, further validation work needs to be conducted.

Acknowledgments

This study was partially based upon work supported by the National Science Foundation under Grant No. (DMI-9821020). The authors would like to express their appreciation to Dr. Chigurupati and Dr. Wu at Scientific Forming Technologies, Inc. (SFTC) for the technical support and valuable discussion. The authors would also like to acknowledge Dr. Grzesik's provision of the experimental cutting data for the coated tool investigated in this study.