The influence of the coating thickness on its strength properties and on the milling performance of PVD coated inserts

The evolution of the physical vapour deposition (PVD) process has contributed to the wide application of thin hard coatings on cutting tools. The film thickness can significantly affect the tool cutting performance. In the present paper, PVD (Ti46Al54)N coatings with thickness from 2 to 10 mum were deposited on cemented carbide inserts. The coating material properties and especially their stress-strain relationship for the various coating thicknesses were determined by means of a FEM-based evaluation procedure on nanohardness measurement results. An increasing of the coating thickness deteriorates the coating mechanical strength, however it can lead to higher effective cutting edge radii, thus inducing lower stresses on the cutting edge, as the related FEM simulation results of the cutting edge region during the material removal show. Moreover, the substrate is better protected against abrasive wear and thermal loads occurring during the cutting process. The tool wear investigations conducted in milling are depicted by the numerically extracted dependencies, explaining the increased cutting performance of thicker coatings which, on the other hand, cause higher PVD costs. (C) 2003 Elsevier Science B.V All rights reserved.