Experimental Study on Surface Quality, Integrity and Tool Wear Mechanism under Cryogenic CO₂-Assisted Minimum Quantity Lubrication (MQL) Technology in Turning Hard Tool Steels

الملخص

This study investigates how minimum quantity lubrication (MQL) assisted by cooled carbon dioxide affects surface quality, substrate integrity, and tool wear when turning hard steel. Standard lubrication systems experience difficulty dissipating the heat and mechanical loads generated by machining these materials. By combining carbon dioxide cooling with minimum quantity lubrication, this study seeks to improve thermal stability, lubrication efficiency, tool durability, and the microstructure quality of the workpiece. Four environments, dry, MQL, CO₂ cooling, and CO₂ + MQL hybrid, are evaluated using metrics such as surface roughness (Ra), white layer depth, microhardness mapping, and flank wear progression.  All experiments and measurements were conducted at the Libyan Centre for Advanced Technology (ACT). The results reveal that MQL preparation with carbon dioxide results in finer surface finishes, longer tool life, and reduced thermal and mechanical damage, representing a practical and environmentally friendly approach to high-precision hard steel manufacturing.