It can also be seen (Figure 9) that the residual stresses have significantly lesser values of compressive stresses for coated PCBN tools than for uncoated ones, this being related to lower thermal conductivity of CCBN tools and higher thermally-related contribution. Additionally, stress profile for CCBN tools has bigger depth (~ 120 μm) than

UCBN tools (~ 100 μm), which, as for the case of subsurface deformation, is related to larger edge radius (rβ) of coated tools.

4. Conclusions

The article presents the results of experimental study of machinability of aged Inconel 718 during its high speed turning with coated and uncoated PCBN tools. The machinability was evaluated in terms of cutting forces, tool life, tool wear and generated surface integrity. The obtained results indicate that advantage of the coating on the PCBN tools has a cutting-speed-limited effect. With increase of speed to 300 m/min and above the coating provides no benefits in terms of tool life. Tool life was found to be highly sensitive to cutting speed, where it decreased by 250% with increase in speed from 250 m/min to 350 m/min. Findings of EDX analysis have shown that chemical wear mechanisms plays dominant role in this behavior. Atomic force microscopy has shown that abrasive wear also plays significant role in the wear

 of PCBN tools. Assessment of residual stress profiles for machined surface has shown generation of advantageous compressive surface stresses. Application of coated PCBN tools, as compared to uncoated ones, have shown a tendency of transition from compressive to tensile surface stresses.

Acknowledgements,源^自!吹冰/文-论/文*网[www.chuibin.com

This work has been done as a part of the research project ShortCut, SSF/Proviking as well as a part of the Sustainable Production Initiative (SPI). Support of SECO TOOLS AB and Siemens Industrial Turbomachinery AB is fully appreciated.

References

[1] Sharman, A.R.C., et al, 2006, An analysis of the residual stress generated in Inconel 718 when turning, Journal of Material Processing Technology, 173:359–367.

[2] Kramer, B.M., 1987, On tool materials in high speed machining, Journal of Engineering for Industry, 109:87-91.

[3] Gritsenko, E.I., Dalnik, P.E., Chapaluk, V.P., 1993, Turning Ni-based alloys with cubic boron nitride tools, Naukova Dumka, Kiev, (in Russian).

[4] Proskuriakov, S.L., 1989, Increase in efficiency of machining heat-resistant alloys with PCBN tools through optimization of cutting conditions, PhD thesis, Rybinsk Institute of Aviation Technology, (in Russian).

[5] Costes, J.P., et al, 2007, Tool-life and wear mechanisms of CBN tools in machining of Inconel 718, International Journal of Machine Tool and Manufacture, 47:1081-1087.

[6] M’Saoubi, R., et al., 2012, Surface integrity analysis of machined Inconel 718 over multiple length scales, Ann. CIRP, 61/1: 99–102.

[7] Sharman, A.R.C., et al, 2004, Workpiece surface integrity and tool life issues when turning Inconel 718 nickel based, Machining Science and Technology, 8/3:399–414.

[8] Arunachalam, R.M., et al., 2004, Residual stress and surface roughness when facing age hardened Inconel 718 with CBN and ceramic cutting tools, Int. J. of Machine Tools and Manufacture, 44/9:879-887

[9] Zhou, B.M., Chen, C., Huang, Q., An, Q., 2009, Study on surface damages caused by turning NiCr20TiAl nickel-based alloy, J. Mater. Process. Technol., 209:5802–5809

[10] Desmaison, J., Lefort, P., Billy, M., 1979, Oxidation of titanium nitride in oxygen: behavior of TiN0.83 and TiN0.79 plates, Oxid Met, 13/3:203–221.