Tool life and wear models were fitted for machining a martensitic stainless steel (JETHETE) with three ceramic-coated carbides [CVD-Ti(C,N)/Al2O3 (T1), CVD-Ti(C,N)/TiC/Al2O3 (T2) and PVD-TiN (T3)] using statistical regression analysis. The statistical analysis revealed the contribution of the cutting speed and feed rate to tool performance to be in excess of 80 per cent, with the cutting speed showing the greater degree of influence. Significant nose wear was the common failure mode observed at higher speed conditions. Plastic deformation and chipping/fracture at the cutting edge were additional failure modes observed when machining with the T2 and T3 tool grades respectively. The coarse grain size and high cobalt content contributed to the very poor performance of the multicoated T2 grade insert, while the improved microhardness of the PVD-TiN coating gave the single layer coated T3 grade a comparable performance with the multicoated T1 grade. Attrition wear was the principal wear mechanism at lower speed conditions, while dissolution/diffusion and abrasion were additional wear mechanisms when machining at higher speed conditions. A higher degree of diffusion wear occurred on the T3 grade insert owing to the relatively lower level of cubic carbides in the tool composition.

This paper presents results of a self-propelled rotary tool (SPRT) tipped with round uncoated carbide (WC-Co) inserts in the finish turning of titanium alloy IMI 318. SPRT inserts exhibited superior wear resistance to conventional round and rhomboid-shaped carbides as well as to the rhomboid-shaped physical vapour deposition (PVD) TiN-coated carbide inserts owing to the distribution of the cutting energy along the entire tool edge. The SPRT-tipped inserts suppressed thermally related wear mechanisms at higher speeds beyond the capability of conventional tools. Chipping was the dominant failure mode of the SPRT inserts, resulting from cyclically fluctuating thermal and mechanical shocks induced by the continuous shifting of the cutting edge during machining. A fitted exponential wear model revealed that about 97 per cent of the average flank wear rate of SPRT inserts can be attributed to the joint effect of speed, feed and inclination angle, ε. Tool performance was improved by increasing the inclination angle ε which resulted in a lower machining temperature on account of a higher rotary speed and a lower relative cutting speed during machining. Lower component forces were recorded with SPRT inserts because of the reduced amount of work done in chip formation and lower friction at the rake face.

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/ Al 2 O 3 (T1), Ti(C,N)/ Al 2 O 3 /TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al 2 O 3 /TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.

No abstract

No abstract

No abstract

No abstract

No abstract