Tool wear and chip morphology in high-speed milling of hardened Inconel 718 under dry and cryogenic CO2 conditions

• Published in: Wear 2019-04, Vol.426-427, p.1683-1690
• Main Authors: Halim, N.H.A., Haron, C.H.C., Ghani, J.A., Azhar, M.F.
• Format: Article
• Language: English
• Subjects: Abrasion; Abrasive wear; Carbon dioxide; Chip morphology; Chipping; Cooling effects; Cooling systems; Cryogenic cooling; Cryogenic cutting; Cryogenic effects; Cutting parameters; Cutting speed; Cutting tools; Cutting wear; Dry cutting; Feed rate; Flaking; Hardening rate; High speed machining; Inconel 718; Inserts; Milling (machining); Morphology; Nickel base alloys; Production planning; Superalloys; Tool life; Tool wear; Tungsten carbide; Wear mechanisms
• ISSN: 0043-1648; 1873-2577
• DOI: 10.1016/j.wear.2019.01.095

This paper details an investigation into the performance of PVD tungsten carbide coated ball nose milling inserts when conducting high-speed cutting of Inconel 718 under eco-friendly machining methods of cryogenic carbon dioxide (CO2) and dry cutting conditions. The experiments were performed at varying cutting parameters of; cutting speed: 120–140 m/min, feed rate: 0.15–0.25 mm/tooth, and axial depth of cut: 0.3–0.7 mm. The radial depth of cut was kept constant at 0.4 mm. A new cryogenic CO2 cooling system was introduced for efficient and consistent cooling performance during cutting. The analysis includes the tool life, tool wear patterns and mechanisms as well as its relationship with the chips’ morphology. The experimental results showed that cryogenic and dry cutting conditions reported approximately similar tool wear patterns. The tool wear started with smooth abrasion and chipping around the depth of cut line, which then progressed into flank wear and finally notching and flaking via mechanisms of abrasive and adhesive wears. However, severe BUE was repeatedly observed under dry cutting, which widened the flaking and accelerated the notching. Hence, cryogenic CO2 showed significant improvement towards increasing the tool life to a maximum of 70.8% relative to dry cutting. The consistent cooling effect by the cryogenic CO2 managed to efficiently reduce the cutting temperature at the cutting point to 80% compared to dry cutting, which is believed to be the main factor causing the aforementioned improvement. The strong influence of cutting conditions and tool wear patterns upon the chip morphology was also evident. Compared to cryogenic cutting, the shape and colour of the chips were found to be severe, distorted, and darker in dry cutting, which confirmed that it was thermally affected by the high cutting temperature. •Effects of cryogenic CO2 in milling Inconel 718 on the wear performance of PVD carbide coated inserts and chips morphology using a cryogenic CO2 system were analyzed.•When compared to dry cutting, cryogenic cutting managed to prolong tool life by 152% due to the consistent cooling effect provided by the cryogenic CO2 regulation system.•Similar tool wear patterns were observed under cryogenic and dry cutting. A Smooth abrasion and pitting at cutting edge, flaking and notch wear at the flank and rake faces were noted.•FESEM and spectrum EDAX analyses conducted on the worn tools confirmed abrasive, adhesive, and oxidation wears as mechanis