The aim of this investigation is to study the performance of the new generation of the PVD coated grade and to map the influence of cutting conditions on the tool life in milling of ADI
The aim of this investigation is to study the performance of the new generation of the PVD coated grade and to map the influence of cutting conditions on the tool life in milling of ADI (Austempered Ductile Iron). The results show that chipping is the main wear mechanism which determines the tool life in dry condition and notch wear in wet condition for this application. This due to the different stress mechanisms and preexisting cracks in the coating. The wear development shows clearly that the new PVD coating (C20) has the best ability to delay the chipping growth. It was also found that a high content of Al in the new coating (C20) was especially favorable compared to a TiAlN multilayer with lower Al content (C30) or CVD coating. This is due to fine grains and low compressive stress level in the coating which increase the coating ability to withstand the mechanical and thermal impact. It was also found that the use of coolant decreases the tool life with 70-80% compare to dry milling. Keywords—Austempered Ductile Iron (ADI), coating, chipping, milling, tool performance.
Successfully Machining Austempered Ductile Iron (ADI)
Austempered Ductile Iron (ADI) is a relatively new material to the industrial marketplace. Many have tried to machine ADI as if it were steel, or as-cast Ductile Iron, and have been unsuccessful. Because of this, a myth has developed that ADI is not machinable. When the material properties and metal matrix of ADI are taken into consideration, ADI can be successfully machined.
Fracture Mechanics and Notch Sensitivity
A diagram valid for the analysis of the fatigue limit of cracks and notches centred in an infinite plate was recently proposed by the authors of the present work with the aim to make explicit the bridging at the fatigue limit between defect sensitivity (correlated to the length parameter a 0 , according to El Haddad-Topper-Smith's definition) and notch sensitivity (correlated to a*, where a* is a particular notch depth corresponding to the intersection between the ΔK th and Δσ 0 /K t curves). The expression a* = K 2 t .a 0 being valid, defect sensitivity and notch sensitivity were seen as two sides of the same medal. Such a diagram is now extended to finite size components by simply introducing the shape factor a commonly used in fracture mechanics. The obtained critical defect size is termed a D , which is a material and geometry dependent parameter, in order to distinguish it from a 0 , which is a material parameter. As a consequence the critical notch depth aN is introduced, such that. aN = K 2 t .a D This results in the proposal of a 'universal' diagram able to summarize experimental data related to different materials, geometry and loading conditions. The diagram, the validity of which is checked by means of several results available in the literature, is applied both to the interpretation of the scale effect and to the surface finishing effect.