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Research activities in the Machining Group of Politecnico di Torino

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The research activities of the Machining Group at Politecnico di Torino will be presented. Research efforts are mainly concentrated in two directions: 1. Development and characterization of new coatings for cutting tools with high wear resistance properties at elevated temperatures. 2. Numerical simulation of cutting process, with the aim of forecasting cutting variables, such as forces, tool wear, residual stresses.

1) Development of coatings: This objective arises from the industrial need to reduce machining time and environmental impact of the machining operations, in order to cut costs and health risks for the operators. The use of coatings for cutting tools is nowadays widespread, however wear mechanisms are not always understood, and clear relationships between laboratory characterization tests and machining performance are seldom assessed. In particular, this point is of key importance, since the possibility of translating the results of laboratory characterization tests into functional performances allows to cut development costs. Nanocomposite coatings, consisting of nanocrystalline AlTiN and AlCrN dispersed in a matrix of amorphous Si3N4 were deposited onto hard metal substrates via Cathodic Arc PVD . The prepared materials were then used as cutting tools in milling operation with application to AISI M2 , a difficult to cut die steel. Their cutting performances were compared to those of a commercial nitride coating under dry conditions. Coating thickness, adhesion properties and hardness of the coatings were measured. Wear resistance was obtained via tribological tests, under different temperatures and the main wear phenomena were studied, using SEM -EDS. The results showed that such coatings are promising in milling operations and allowed to understand the main wear mechanisms.

2) Numerical simulation of cutting: Stringent control on the quality of machined surface and sub-surface during machining of mechanical components is necessary so as to achieve parts with greater reliability and longevity. In particular, residual stresses induced by machining processes play an important role on the lifetime of pieces. The characteristics that are influenced by residual stress include fatigue life, corrosion resistance, and part distortion, making such issue particularly delicate in the aeronautical industry. Several phenomena are responsible of these distributions: mechanical effects, thermal effects, microstructure modifications and/or a combination of the previous mechanisms. The research work performed at DISPEA is aimed at achieving a comprehensive investigation on the nature of deformation beneath the machined surface in 2D and 3D cutting. Preliminary simulations have been done on INCONEL 718 , a typical nickel alloy for aeronautical use, with the FE commercial code DEFORM -2D and its library data. Model validation has been carried out by comparison of numerical results with experimental ones in terms of cutting forces and surface and sub-surface residual stresses.

This talk is part of the Department of Engineering, Production Processes Group Seminars, Institute for Manufacturing series.

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