Surface roughness is an important indicator of machining quality, particularly in the hard milling of hardened tool steels. This study experimentally compares the surface roughness of 9CrSi steel with a hardness of 50 HRC under three machining conditions: flood cooling with an emulsion, minimum quantity lubrication (MQL) using canola oil, and dry milling. The experiments were conducted on a MAZAK VCS-530C machining center using a 10 mm TiAlN-coated milling cutter. The cutting speed, feed per tooth, and depth of cut were maintained at 80 m/min, 0.02 mm/tooth, and 0.4 mm, respectively. The measured surface roughness values were 0.245 µm under flood cooling, 0.260 µm under MQL, and 0.310 µm under dry milling. Compared with dry milling, the surface roughness was reduced by approximately 21.0% with flood cooling and 16.1% with canola oil-based MQL. Flood cooling produced the lowest measured surface roughness, while MQL also improved the surface finish compared with dry milling. These findings provide an experimental comparison of three cooling and lubrication strategies for hard milling of 9CrSi steel under the investigated cutting conditions.

Hoang-Anh Truong,"TribalExperimental Comparison of Flood Cooling, Canola Oil-Based MQL, and Dry Hard Milling of 9CrSi Steel" International Journal of Advanced Multidisciplinary Research and Educational Development, V2(5): Page(978-980) September - October 2026. ISSN: 3107-6513. www.ijamred.com. Published by Scientific and Academic Research Publishing.