Experimental evaluation of eco-friendly hybrid cooling methods in slot milling of titanium alloy

Official URL: http://dx.doi.org/10.1016/j.jclepro.2021.125817

The positive effects of cutting fluids on the machinability performance are well known in machining industry. However, it is also known that their use causes environmental and health problems. Moreover, manufacturers are faced with strict environmental regulations in order to employ dry machining, which is not efficient especially in machining of difficult-to-cut materials such as titanium alloys. Therefore, machining industry developed alternative green machining solutions such as minimum quantity of lubrication, vegetable based cutting fluids, cryogenics and hybrid cooling (combination of cryogenics and minimum quantity of lubrication). Up to now, no work has been documented in the literature on comparison of cryogenics and hybrid cooling with minimum quantity of lubrication. Furthermore, as no information regarding the effects of hybrid cooling on workpiece temperatures during milling of titanium alloy is available, this research aims to demonstrate the feasibility of implementing cryogenics and hybrid cooling method in slot milling of titanium alloy. Thus, the aim of this experimental study was to determine the machining performance of titanium alloy under various green lubricating/cooling methods. In order to do so, minimum quantity of lubrication, cryogenic cooling by spraying liquid nitrogen, cryogenic cooling by spraying carbon dioxide, simultaneous spraying of carbon dioxide and minimum quantity of lubrication, and simultaneous spraying of liquid nitrogen and minimum quantity of lubrication were applied during slot milling process under different cutting speeds. The performance of these methods was evaluated by measuring tool wear, temperature, cutting forces and surface roughness. The results showed that the efficiency of cryogenic cooling was based on the cutting speed where better results were obtained at higher speeds. It was also concluded that the simultaneous spray of cryogenic fluid and minimum quantity of lubrication improved the machinability of titanium alloy as compared to only spray of cryogenics because of both lubricating and cooling effects. In terms of environmental impact of machining operations, hybrid cryogenic methods offer an efficient solution to improve the process sustainability towards cleaner production since the coolant volume is reduced substantially compared to conventional cooling methods decreasing pollutants, and lung and skin diseases experienced by the workers in production facilities. Results showed that the combination of cryogenic and minimum quantity lubrication method provided a balance between productivity and environment. Hybrid method improved the productivity of milling process in terms of cutting speed, tool life, and cost while increasing environmental protection and operator health and reducing material waste.