Effect of liquid CO2 flow rate on TiAlN coated tools in hard turning of 42CrMo4 steel

With the growing demand for sustainable manufacturing solutions, liquid carbon dioxide (LCO₂) has emerged as a promising alternative to conventional cooling lubricating fluids due to its environmentally friendly properties, non-toxicity, and high cooling capacity. This study investigates the influence of LCO2 flow rate on the performance of TiAlN-coated cutting inserts during the turning of 42CrMo4 (AISI 4140) steel. Tool life, cutting forces, temperature, and surface roughness were evaluated at various LCO2 flow rates. The results demonstrate that LCO2 significantly affects machining performance. At optimal flow rates of 200–250 g/min, the tool life increases by up to 20% compared to dry cutting. Excessive LCO2 flow reduces cooling effectiveness, leading to reduced tool life. At LCO2 flow rates above 400 g/min, the tool life is even shorter compared to dry turning. Moreover, higher flow rates increase the machining costs without providing additional performance benefits. Although no changes in dominant wear mechanisms were observed when using LCO2, its cooling effect clearly influences wear progression. Optimized flow rates slow down wear development, whereas excessive cooling of the workpiece can accelerate tool wear. These findings highlight the importance of optimizing the LCO2 flow rate to achieve improved tool life, stable machining conditions, and cost-effective sustainable manufacturing.