Effects of femtosecond laser surface modified WC and NbC based inserts during the face-milling of automotive Grey Cast Iron (a-GCI)

Abstract

Rapid pulsed electric current sintering (PECS), TiC, TiC₇N₃ and Mo additions, and femtosecond (fs) laser surface modification (LSM) were used to improve the machining of automotive grey cast iron (a-GCI) using WC and NbC based cemented carbides cutting inserts. Additions of Mo and TiC as well as the use of PECS refined the grain sizes of NbC-12Ni based cermet from ∼4.6 μm to ∼1 μm, increasing the hardness (by ∼3 GPa) and wear resistance. Shark skin (S-LSM) and pyramidal (P-LSM) patterns were introduced to improve the wear and mechanical impact resistance of the cutting inserts. Face milling of a-GCI was performed at 200 m/min cutting speed (V_c), 1.0 mm depth of cut (a_p), and 0.1 mm/tooth feed rate (f). The insert cutting-edge wear and damage were evaluated after every pass using optical microscopy and high angular annular dark field scanning transmission electron microscopy (HAADF-STEM). The machining performance of the cutting inserts was assessed by cutting forces, wear, and cutting insert tool life. The PECS produced NbC-10TiC-12[Ni/Mo] (wt%) P-LSM cutting insert had the lowest flank wear rate (FWR) (1.44 μm/min) after 20 min of machining. In addition, both the S-LSM and P-LSM patterns improved the cutting insert tool life of PECS produced NbC-12[Ni/Mo] (wt%) blank (B) cutting insert by ∼300 % and ∼ 900 %. Resulting in FWRs reductions of the respective insert from 21.04 μm/min after 2 min of machining to 5.97 μm/min and 1.94 μm/min after 8 min and 20 min. In general, LSM improved the NbC based cutting inserts' tool life and reduced the FWRs.