Effect of cutting tool nose radius on surface roughness for Stellite 6 machining using coated carbide insert

Stellite 6 is cobalt based super alloy and is used extensively in applications requiring good wear, corrosion and heat resistance properties. Due to poor machinability and non-availability of machining processes design parameters Stellites are grouped as difficult-to-machine materials. Inadequate machined surfaces of stellite hard-faced components suffer immature fatigue failure. This paper concentrates on theoretical and experimental investigation of phenomena of reflection of cutting tool nose radius and effect of different nose radii of coated carbide inserts on surface roughness obtained in turning operations of Stellite 6. A possible theoretical model correlating nose radius and certain tool geometry to peak height (h) of surface texture has been discussed. The research finally reveals the carbide cutting tool with best suitable nose radius for the best possible output in machining Stellite 6 on the basis of surface roughness. A series of turning operations relevant to theoretical analysis have been carried out on a conventional lathe using each nose radius of coated carbide insert under various cutting conditions. Surface roughness (Ra) was evaluated for each sample by Stylus type Surtronic3+ instrument. The values of surface roughness were plotted against different cutting speeds, feed rates and depths of cut in graphical form and best values of surface roughness were recognized for each nose radius. The best values of surface roughness for feed rate, cutting speed and depth of cut were plotted against different nose radius to display the results in graphical forms. Optimal nose radius has been revealed using the optimum cutting regimes (previously published and some unpublished works of authors) which were recognized against the best values of surface roughness obtained. The final result representing a combination of optimal data has been created, which demonstrates a zone of optimal nose radii of carbide inserts that can be economically and effectively used for machining Stellite 6 with the best output.The output of this research may contribute for the machine manufacturing industries to achieve the best results in difficult-to-machine materials like Stellites.