Study of the wear behaviour of TiAlSiN and TiAlN PVD coated tools on milling operations of pre-hardened tool steel

Coatings usually play an important role in terms of machining tool behaviour and lifespan. TiAlN is a well-known PVD coating but, the permanent need for improved performance is inducing new compositions around this coating. In this work, the wear behaviour of different PVD coated tools with different geometries was analysed, in the milling of pre-hardened tool steel. The selected tools had two different geometries, namely ball nose end mill and end mill tools. Additionally, these were coated with two different PVD coatings, TiAlSiN and TiAlN. These tools were employed in milling operations of W 1.2711 pre-hardened tool steel. The cutting parameters were defined in a way to enable a valid comparison between the milling tools, varying only feed and cutting length, to analyse the influence of these parameters on the tool's wear mechanisms. Cutting force data was collected during the milling tests using a dynamometer in order to identify the different wear stages of the tool, and surface roughness was measured after each test. Furthermore, after the milling tests the tools were submitted to a SEM analysis, in order to analyse the wear mechanisms of each coated tool. The main wear mechanisms that were identified in both coatings are adhesion and abrasion, followed by coating delamination. Moreover, the analysed wear was less significant in the TiAlSiN PVD coated tools used, mainly in the ball-nose tools, providing as well very good surface roughness of the machined surface. The surface morphology of the tool and the direction of the grooves left on the tool surface after grinding operations of the uncoated tool showed a significant influence on the coating wear mode. The best machining conditions have been established, taking into account the lowest surface roughness obtained on the machined surface and the lowest wear rate of the tool.