The effect of coating thickness, mechanical strength and hardness properties on the milling performance of PVD coated cemented carbides inserts

The film deposition conditions on individual specimens in the vacuum chamber during a physical vapour deposition coating procedure cannot be considered as constant. Depending among others on the magnetic field distribution in the vacuum chamber as well as on the specimen fixture geometry and kinematics, the coating hardness and mechanical properties may vary. In order to investigate the effect of coating hardness and strength on the cutting performance in milling, (Ti46Al54)N films having thickness from 3 to 10 μm and varying hardness were deposited on cemented carbides inserts. The coating material properties and especially their stress–strain laws were determined from the nanoindentation measurement results using a finite elements method (FEM) based evaluation procedure. The initiation and progress of the coating and tool wear in milling were studied using scanning electron microscopy and energy dispersive X-ray spectroscopy. The investigations revealed that as the coating grows thicker, its superficial hardness and strength decreases. For the thick coatings, however, this does not affect the cutting performance as much as for the thin coatings. In the case of thin coatings, a corresponding decrease of the film hardness and strength, diminishes significantly the cutting performance. A FEM simulation of the cutting process, whereas the coating mechanical properties vs. the film thickness are considered, elucidates the aforementioned results.