key: cord-0294317-bjobq1x5 authors: Jamil, Muhammad; He, Ning; Li, Liang; Khan, Aqib Mashood title: Clean manufacturing of Ti-6Al-4V under CO2-snow and hybrid nanofluids date: 2020-12-31 journal: Procedia Manufacturing DOI: 10.1016/j.promfg.2020.05.029 sha: 4781928d6c3b0d839f5d43e1b56fb61654764d69 doc_id: 294317 cord_uid: bjobq1x5 Abstract During the machining of α+β intermetallic stable titanium alloy, their poor thermal conductivity and resistance at elevated temperature accumulates most of the shearing and friction heat. The resulting heat damage the cutting tool, causes in high power consumption, shorter tool life and poor surface quality. Therefore, it is important to choose a latest cooling technique with excellent capacity to remove heat, chips and frictional effects from the cutting zone. Therefore, Carbon dioxide snow (CO2-snow) and hybrid copper oxide (CuO)-multi-walled carbon nanotubes (MWCNTs) nanofluids based minimum quantity lubrication (MQL) are compared to achieve clean cooling/lubrication technique to machine biomedical/aerospace material Ti-6Al-4V. Taguchi L9 orthogonal array was applied to design the experiments. Critical machining parameters are cutting speed (m/min), feed (mm/rev), and cooling mode. The output responses are surface quality Ra (μm), cutting power Pc (W), cutting temperature T (oC), and tool life TL (min) were evaluated under CO2-snow and MQL-hybrid nanofluids. Findings have revealed less surface roughness and longer tool life under hybrid nanofluids. While CO2-snow has justified less temperature and power consumption at high cutting conditions. Global application of TiAl intermetallic titanium alloy family in the domain of aerospace, turbine blades and medical instruments is enormous owing to their superior mechanical properties such as; high stiffness, fatigue strength, strength to density ratio and resistant to creep and thermal softening. Among the TiAl alloy family, Ti-6Al-4V is considered as a standard alloy material. That is why, in recent decades, it is widely adopted and studied in the research field. Ti-6Al-4V has a specific characterization of α+β providing a stable structure. Here, Al is active α-stabilizer (close hexagonal pack) correlated with hardening, resistance to extrusion, and ductility. While V is a typical β-stabilizer (body-centered cubic), resistant to oxidation and strengthens the alloy [1] . Although Ti-6Al-4V contains remarkable properties; however, some bete-noire properties are also associated with it such as poor thermal conductivity, chip contact length and, high chemical affinity and high-temperature generation at the tool-chip joint interface. Therefore, machining of these difficult to cut materials is characterized in terms of surface quality (μm), cutting energy, cutting temperature and tool life [2, 3] . The application of conventional cutting fluids in machining is a common industrial practice to prolong the tool life, reduce machine power with better surface quality in hard to cut Global application of TiAl intermetallic titanium alloy family in the domain of aerospace, turbine blades and medical instruments is enormous owing to their superior mechanical properties such as; high stiffness, fatigue strength, strength to density ratio and resistant to creep and thermal softening. Among the TiAl alloy family, Ti-6Al-4V is considered as a standard alloy material. That is why, in recent decades, it is widely adopted and studied in the research field. Ti-6Al-4V has a specific characterization of α+β providing a stable structure. Here, Al is active α-stabilizer (close hexagonal pack) correlated with hardening, resistance to extrusion, and ductility. While V is a typical β-stabilizer (body-centered cubic), resistant to oxidation and strengthens the alloy [1] . Although Ti-6Al-4V contains remarkable properties; however, some bete-noire properties are also associated with it such as poor thermal conductivity, chip contact length and, high chemical affinity and high-temperature generation at the tool-chip joint interface. Therefore, machining of these difficult to cut materials is characterized in terms of surface quality (μm), cutting energy, cutting temperature and tool life [2, 3] . The application of conventional cutting fluids in machining is a common industrial practice to prolong the tool life, reduce machine power with better surface quality in hard to cut Global application of TiAl intermetallic titanium alloy family in the domain of aerospace, turbine blades and medical instruments is enormous owing to their superior mechanical properties such as; high stiffness, fatigue strength, strength to density ratio and resistant to creep and thermal softening. Among the TiAl alloy family, Ti-6Al-4V is considered as a standard alloy material. That is why, in recent decades, it is widely adopted and studied in the research field. Ti-6Al-4V has a specific characterization of α+β providing a stable structure. Here, Al is active α-stabilizer (close hexagonal pack) correlated with hardening, resistance to extrusion, and ductility. While V is a typical β-stabilizer (body-centered cubic), resistant to oxidation and strengthens the alloy [1] . Although Ti-6Al-4V contains remarkable properties; however, some bete-noire properties are also associated with it such as poor thermal conductivity, chip contact length and, high chemical affinity and high-temperature generation at the tool-chip joint interface. Therefore, machining of these difficult to cut materials is characterized in terms of surface quality (μm), cutting energy, cutting temperature and tool life [2, 3] . The application of conventional cutting fluids in machining is a common industrial practice to prolong the tool life, reduce machine power with better surface quality in hard to cut Global application of TiAl intermetallic titanium alloy family in the domain of aerospace, turbine blades and medical instruments is enormous owing to their superior mechanical properties such as; high stiffness, fatigue strength, strength to density ratio and resistant to creep and thermal softening. Among the TiAl alloy family, Ti-6Al-4V is considered as a standard alloy material. That is why, in recent decades, it is widely adopted and studied in the research field. Ti-6Al-4V has a specific characterization of α+β providing a stable structure. Here, Al is active α-stabilizer (close hexagonal pack) correlated with hardening, resistance to extrusion, and ductility. While V is a typical β-stabilizer (body-centered cubic), resistant to oxidation and strengthens the alloy [1] . Although Ti-6Al-4V contains remarkable properties; however, some bete-noire properties are also associated with it such as poor thermal conductivity, chip contact length and, high chemical affinity and high-temperature generation at the tool-chip joint interface. Therefore, machining of these difficult to cut materials is characterized in terms of surface quality (μm), cutting energy, cutting temperature and tool life [2, 3] . The application of conventional cutting fluids in machining is a common industrial practice to prolong the tool life, reduce machine power with better surface quality in hard to cut Global application of TiAl intermetallic titanium alloy family in the domain of aerospace, turbine blades and medical instruments is enormous owing to their superior mechanical properties such as; high stiffness, fatigue strength, strength to density ratio and resistant to creep and thermal softening. Among the TiAl alloy family, Ti-6Al-4V is considered as a standard alloy material. That is why, in recent decades, it is widely adopted and studied in the research field. Ti-6Al-4V has a specific characterization of α+β providing a stable structure. Here, Al is active α-stabilizer (close hexagonal pack) correlated with hardening, resistance to extrusion, and ductility. While V is a typical β-stabilizer (body-centered cubic), resistant to oxidation and strengthens the alloy [1] . Although Ti-6Al-4V contains remarkable properties; however, some bete-noire properties are also associated with it such as poor thermal conductivity, chip contact length and, high chemical affinity and high-temperature generation at the tool-chip joint interface. Therefore, machining of these difficult to cut materials is characterized in terms of surface quality (μm), cutting energy, cutting temperature and tool life [2, 3] . The application of conventional cutting fluids in machining is a common industrial practice to prolong the tool life, reduce machine power with better surface quality in hard to cut materials [4] . However, due to higher lubrication cost, 15~17% of total machining cost [5, 6] , health and ecological issues have forced the manufacturers to use an alternative cooling system with less cost and environmental benign cooling. In addition, the manufacturing sector is consuming 25~30% of the total energy produced. It is estimated that energy consumption demand will increase by 45% in 2030. Also, 99% environmental impact of manufacturing is associated with electrical energy utilization [7] . The carbon emission is evident in the generation of electricity through fossil fuels. Furthermore, the establishment of strict regulations from EPA (Environmental Protection Agency), EU goal of 20% reduction of CO2 emission, and a new concept of sustainability have unfolded some novel machining techniques to accommodate such types of challenges. With the goal of sustainable and cleaner production, dry, near to dry, minimum quantity lubrication (MQL), nanofluids assisted MQL, and cryogenic cooling technique ( Fig. 1 ) are applied for difficult to cut materials [8] . Lei and Liu [9] have machined Ti-6Al-4V at a high cutting speed of 250 m/min under dry machining to improve the material removal rate (MRR). Results have shown chip welding, galling, and smearing effects due to the elevation of temperature at the tool-chip interface. However, some researchers [10, 11] have mentioned the associated potentials of near-to-dry machining to enhance the machinability and life of the cutting tool compared to dry machining. The near-to-dry machining at a flow rate of 50~100 ml/h was applied at different levels of cutting speed (120, 135, and 150 m/min). Although the surface quality was not good, but longer tool life, better lubrication and fewer cutting forces were achieved in the machining of Ti-6Al-4V. The MQL assisted machining has also been highlighted to restrict the consumption of cutting fluids from gallons to milliliters. Fortunately, MQL has provided a fine mist of pure oil mixing at high pressure compressed air having superior penetration at the tool-chip joint interface [12] . It is pertinent to mention that experimental study mentioned the potential of MQL regarding the surface quality and normal forces under grinding of AISI-D2 steel. The final drop quality is strongly influenced by the distance between nozzle-workpiece surface and flow of air. Gurraj et al., [13] have tried to improve the performance of the MQL system by implementing the Ranque-Hilsch vortex tube (RHVT). Findings have suggested superior surface quality and less power consumption. Hegab et al. [3] have tried to improve the performance of MQL with the addition of multi-walled carbon nanotubes (MWCNTs) to machine difficult-to-cut Ti-6Al-4V alloy. The key objective was to enhance the thermal properties of MQL-solution for better heat transfer. Numerous types of nano-additives are mixed with the base fluid such as; alumina (Al2O3), zinc oxide (ZnO), multi-walled carbon nanotubes (MWCNTs), and copper oxide (CuO) nano-additives. Holistic literature has reported superior heat transfer and lubrication due to Brownian motion and a greater surface area [12] . Sidik et al. [14] have reviewed the potential of nanoparticles as well as the preparation method of nanoparticles. The findings have suggested that a mixture of different nanofluids dispersed in common base fluid with single or two-step preparation methods can provide superior thermal conductivity, limiting agglomeration, surface temperature, and surface roughness. Sharma et al. [15] have compared the mineral-based MQL and MWCNTs-MQL to ensure the effectiveness of nano-additives. The findings have shown the promising potential of nanofluids based MQL regarding the surface roughness, temperature, and heat transfer. Similarly, Al2O3 nanoparticles in different concentrations were prepared and evaluated the performance by comparing it with dry, mineral oil-based MQL. It was concluded that less cutting forces, surface roughness, and tool wear had been investigated under Al2O3based MQL [16] . Hegab and Kishway [17] have explored the hybrid nano-additives assisted MQL for the machining of Inconel 718. The superior thermophysical properties have provided better heat transfer, surface quality, and provision of the tribological film on the workpiece surface. Sharma et al. [18] have compared alumina/MWCNTs nano-additives based simulation and experimental results during the turning process to measure temperature. The findings have shown a low coefficient of friction and uniform temperature distribution at the tool rake face. Similarly, [19] have prepared water-based Al2O3-Cu and Al2O3 hybrid nanofluids with a two-phase approach. It was concluded that higher heat transfer and the higher Nusselt number was achieved. [20] have compared the performance of CuO, TiO2 and nano-diamond nano-additives mixed with base oil. The addition of CuO has significantly reduced the coefficient of friction under tribo-tester. Shabgard et al. [21] compared graphite and CuO nano-additives based MQL to get physical synergistic effect of nanoparticles morphology, structure, and physio-thermal properties. Authors have concluded that rolling action of CuO provided low partition energy, and superior surface quality compared to graphite nano-additives having a sliding mechanism of atomic planes throughout the process. Ecologically benign cryogenic cooling/lubrication technique has been reported in the literature with liquidcarbon dioxide (CO2-snow) and liquid-nitrogen (LN2) at high pressure. Carbon dioxide (CO2) is colorless, incombustible, and odorless. During impingement of CO2-snow on the surface, rapid expansion due to the Joule-Thomson effect leads to low-temperature dry ice. This dry ice touches the workpiece surface and sublimates directly to gas. The rapid spreading into air reduces the formalities of post-process cleaning and disposal complexities. The high-pressure CO2snow reaches the cutting zone and transfers the heat effectively from the primary cutting zone to the environment. Musfirah et al. [22] have investigated temperature, chip morphology, and surface roughness under cryogenic machining of Inconel-718 compared to dry machining. Results have revealed a 23% reduction in cutting forces and 88% improvement in surface finish. Similarly, Jerold and Kumar [23] experimented with comparing the effectiveness of CO2-snow with dry and flood cooling environment. Results have shown a 5~22% reduction in temperature, and 6~25% reduction in surface roughness compared to conventional wet machining. Jerold and Kumar [24] have compared the effectiveness of cryogenic LN2 and CO2-snow in the machining of Ti-6Al-4V regarding cutting temperature, cutting force, tool wear, and chip morphology. The observed reduction in cutting temperature was 36% and 47% under CO2-snow and LN2 respectively compared to conventional machining. Besides, CO2-snow provided 48% less surface roughness, 24% low cutting forces, and better chip evacuation compared to dry, flood and LN2 cooling techniques under machining. The extremely lowest temperature under LN2 leads to brittleness behavior in Ti-6Al-4V, results in high cutting forces that proven to be impractical in machining efficiency. Secondly, in LN2 cooling, consumption is very high due to its rapid evaporation as it touches the hightemperature primary cutting zone. Furthermore, LN2 rapid expansion depletes the oxygen in the close environment causing breathing difficulty. Pereira et al. [25] have compared the LN2 and CO2-snow revealed that the production process of both gases is different; however, CO2-snow is better in terms of global impact such as ozone layer depletion, 43% less spilled out than LN2. After a holistic review, it was concluded that hybrid nanofluids based MQL and cryogenic are clean and environmentally benign manufacturing techniques. On the one hand, hybrid nanofluids based MQL has superior thermal conductivity, lowers frictional coefficient, and Brownian motion. On the other hand, CO2-snow is also sustainable and clean cooling techniques. From the review mentioned above, various studies are preaching the advantages of using MQL technique in machining for superior workpiece surface, low machining power consumption, low cutting temperature, and tool wear and comparatively fewer effects on operator's health and our ecology. Similarly, numerous researchers have reported much potential of low-temperature CO2-snow (-78 o C) on product quality, power consumption, cutting temperature, tool wear of eco-benign cooling technique. However, there was a significant gap to identify which technique performs best regarding the machining of difficult-to-cut materials. Therefore, this study compares two sustainable lubrication/cooling techniques by exploring the machining characteristics under the turning of Ti-6Al-4V alloy. The hybrid nanofluids based MQL and CO2-snow have been used when turning Ti-6Al-4V at different cutting speed, feed. The constant depth of cut was 1.2mm, and the length of cutting workpiece was 80mm. The workpiece's original diameter was 50mm and 250mm length. The thermo-physical properties are provided [26] . The variable parameters levels, tool features, and tool-holder provided in Table. 1. The levels of each parameter were evaluated based on initial trial experiments and considering the tool manufacturer recommendations and machine tool's capabilities [7] . Table 1 . Cutting conditions and cutting insert specifications. For experimental design, Taguchi L9 array was used. For a detailed analysis of design and measured responses, Design Expert® 10.0.0 was used. For the cooling/lubrication, CO2snow at pressure (>5MPa), and flow rate of 0.46kg/min was used. For hybrid CuO-MWCNTs nanofluids preparation, 5vol% of Blaser oil is added into the distilled water. The 24% CuO colloidal suspension (spherical shaped 5~10nm in size and 50nm diameter) with the MWCNTs (10~30nm of size and 30nm diameter) were mixed in 90:10 in the blaser-distilled water base fluid. Also, sodium dodecyl (SDC), having a concentration of 0.1% was used to prevent agglomeration. The ultrasonication was carried out for 4hrs to get a homogenous solution. The prepared nanofluid was used within 1hr to prevent stability problems. The basic working setup consisted of CNC turning (BOOHI SK-509), with 7.5kW motor power. Ti-6Al-4V workpiece, CO2-snow tank, and MQL-based hybrid nanofluids system. The cubic boron nitride cutting tools were Feed rate fr (mm/rev) 0.08, 0.10, 0.12 CNGA-120408 T01020-WG Tool holder # DCLNR-2525M used. The CO2-snow having >5MPa pressure, and nozzle diameter of 0.5mm, hybrid nanofluids MQL having 4~5bar pressure, and 2.5ml/min flow rate. The spray nozzle was fixed 5cm way from the workpiece-tool joint interface. The surface roughness was measured using a portable Perthometer (Mahr: M1-Perthometer) having a stylus movement of 7mm with digital readout. The flank wear was measured using an optical microscope (ART-CAM: 130-MT-WOM) by following ISO-3685 standard. The average flank wear of 0.3mm was defined as tool life criterion according to ISO 8688-2. The machine cutting power was measured using a power monitoring system Raspberry Pi-3 (Model: B) and smart-Pi. Raspberry Pi-3 contains 64-bit CPU, Quad-Core 1.2GHz Broadcom, 1GB RAM, wireless and Bluetooth low energy system. Smart Pi is a customized board containing Raspberry-Pi with ADE7878 module converting analog current and voltages to digital signals. Current clamps were attached to the main power supply of the machine tool and sent signals to Raspberry-Pi. The machine power consumed by CNC turning for speed-feed (3×3) combinations by rotating workpiece and feed movement of the tool, total power consumption was collected during the cutting process. The power consumption was directly attained by data acquisition software compatible with smart-Pi. Each experiment was repeated three times to ensure the reliability of the data. A Ktype thermocouple (Ni-Cr) was used to measure the temperature between -200~1300 attached directly with a thermometer to determine the temperature. The thermocouple was fixed on the minor flank face to by drilling a hole and inserted thermocouple and fixed it with silicon paste. The adhesive sealant RTV silicone paste was applied at the thermocouple-workpiece interface to enhance the sensitivity and heat transfer capability. The thermocouple wire was connected with the 4th-channel TC41-thermocouple thermometer to get the temperature on the screen. Fig. 2 depicts the surface roughness (Ra) measurement under different levels of speed (m/min) and feed (mm/rev). Surface roughness decreases with a decrease in feed rate and increasing spindle speed from lower to a higher level. Similar trends of cutting speed and feed rate on surface roughness are reported [27] . However, overall lower surface roughness was observed under hybrid CuO-MWCNTs compared to CO2snow cooling mode. At spindle speed of 80 m/min, and feed of 0.08, 0.10, and 0.12 mm/rev, reduction in surface roughness was 18 The lower surface roughness can be associated with predominant Brownian motion of finely dispersed nanoadditives, higher surface area and superior thermophysical properties of two different nature of nanoparticles and superior tribological nature of hybrid nanoparticles [28] . The high percentage reduction in surface roughness is also due to the synergistic effect of CuO-MWCNTs hybrid nanofluids compared to single nano-additives based nanofluid. Fig. 3 gives a clear depiction of cryogenic and nanofluids comparison as per experiment. From experiments 1-3, feed rate increases, increasing the surface roughness and reduced by increasing the spindle speed. Throughout the experiments, hybrid nanofluids significantly reduced the surface roughness compared to CO2-snow. It is less probability of fluid to make a lubrication film on rake face having high surface tension. Instead of an excellent dispersion of nanofluid droplets, the phenomenon of bounce back has a high probability. Despite the higher surface tension of hybrid nanofluids, surface roughness was much lower under hybrid nanofluids compared to CO2-snow. It can be assumed that effective penetration of MQL and rolling effect of cylindrical MWCNTs at the toolworkpiece joint interface lessen the friction resulting in improved surface quality [29] . Regarding the sustainability viewpoint, the machine cutting power (Pc) is another key parameter that justifies the economic aspect of the process. It shows that power consumption increases with increasing spindle speed. At a high level of cutting speed, high power is required to rotate the spindle at high speed to remove the chip from the workpiece surface. Similarly, power consumption was lower at a lower level of feed and higher at a high level of feed [31] . At a low level of cutting speed, power consumption under CO2-snow was higher than under hybrid nanofluids. This is because CO2-snow having low temperature (-78 o C) reduced the workpiece temperature very low. That is why high-power consumption was required to cut the cold workpiece under cryogenic at low cutting speed. It is pertinent to mention that higher cutting speed led to high shearing ultimately generated high temperature led to the high temperature of the workpiece. So, at a high level of cutting speed, power consumption under CO2-snow and hybrid nanofluids were almost the same or little lower than hybrid nanofluids at a high feed. The low cutting power under cryogenic can be associated with less heat generation and friction even at high cutting speed. The CO2-snow impinges on the workpiece is an endothermic process. Carbon dioxide collects the water molecules from the air, and this behaves as a lubri-cooling phenomenon by providing excellent cooling and lubrication even at high speed-feed combinations. At high cutting speed, the minimum quantity of hybrid nanofluid may not be sustained to lower down the friction and temperature. So, less power consumption under cryogenic at high cutting speed. At low level of cutting speed (80m/min) and feed of 0.08, 0.10, and 0.12 (mm/rev), reduction in power consumption under hybrid nanofluids was 17.85%, 16.48%, and 13.65% respectively. However, at a high level of speed, CO2-snow lowered the power consumption of 4~5% compared to hybrid nanofluids. Overall, power consumption under CO2-snow was higher than under hybrid nanofluids due to the reduction in tool wear and provision of sufficient lubrication at tool-chip interface rather than cooling the workpiece which led to high hardness and less thermal softening [17] . Shokrani et al. [7] have reported relatively high machine power consumption at a low level of cutting speed under cryogenic compared to dry or near to dry turning of Ti-6Al-4V. Fig. 5 depicts the variation in cutting power per experimental run under CO2-snow and hybrid nanofluid. It shows that cutting power increases with an increase in cutting speed and feed. Also, the power consumption was lower under hybrid nanofluids compared to CO2-snow at a low level of cutting speed. However, at a high level of cutting speed and feed, power consumption higher under hybrid nanofluids. However, at a high level of cutting speed, a difference in power consumption was almost the same under hybrid nanofluids and CO2-snow. The less power consumption under hybrid nanofluids can be associated with smooth chip flow during machining of Ti-6Al-4V under adequate lubrication, because, hybrid nano-additives played as a variable size roller to ameliorate the frictional behavior and consequently decreased the energy consumption. The fine mist of MQL penetrated well into the tool-chip interface and generated a tribo-film on the tool and the workpiece surface reduced the frictional heat and coefficient of friction [32] . The effect of CO2-snow and hybrid nanofluids on the toolchip interface temperature in the turning process is portrayed in Fig. 6 . As mentioned above, CO2-snow impinged concurrently on the tool rake face. Presumably, CO2-snow exhibited superior cooling with snow mist lessening the temperature from the primary shearing zone (minimum temperature is 480 o C for Vc=80m/min, f=0.12mm/rev). On the other hand, the minimum temperature under hybrid nanofluids was 576 o C for Vc=80m/min, and f=0.12mm/rev. Based on the analysis, it can be concluded that the superior heat transfer capacity of dry ice impinged from the workpiece surface is credited responsible for superior cooling. Notably, an increase in cutting speed is affiliated with increasing temperature owing to high shearing at the tool-chip contact area produced elevated temperature. It can be endorsed to a high shear rate of chip converts mechanical energy to thermal energy. At the same time, high feed decreases the temperature. It can be associated with the fast tool movement at high feed reduces the contact time of the tool with a workpiece specific point. That is why heat transfer from the workpiece to cutting tool reduces. Fig. 7 depicts the temperature variation per experiment under CO2-snow and hybrid nanofluids. Findings have depicted dry machining generates tool-chip interface temperature above 1000 o C in turning of titanium owing to the poor thermal conductivity of Ti-6Al-4V, mentioned above. However, the maximum temperature of 660 o C and 465 o C generated under hybrid nanofluids and cryogenic, respectively. The overall less temperature generated under CO2-snow compared to hybrid CuO-MWCNTs. It can be associated with the excellent transfer of heat through convection. It can be stated that CO2snow expands through the Joule-Thomson effect to lower down the temperature. On the other hand, hybrid nanofluids have also reduced the temperature owing to favorable morphology, superior thermal conductivity, and sustainable nano-additives at the tool-chip interface that prevented direct contact of the tool on the workpiece surface. Also, weak Van der Waals forces of MWCNTs allowed better spreadability, high wetting per liquid volume in terms of heat transfer via convection or evaporation. CuO-MWCNTs in variable size reduced the coefficient of friction at the tribo-interface dissipated the heat under the lubrication function from the cutting zone. Moreover, spherical and cylindrical morphology of CuO and cylindrical MWCNTs respectively, are more susceptible to break under external pressure that significantly reduces the friction. The primarily low friction coefficient of MWCNTs behaves well as coolant owing to superior thermal conductivity; high wetting area reduces the heat generation. That is why enough lubrication has reduced the temperature based on superior lubrication and low cooling efficiency. In this way, CO2-snow performed well regarding the heat generation reduction compared to hybrid CuO-MWCNTs nanofluids. Tool wear is one of the important machining performance measures, that defines the quality and machinability of the process. Cutting tool wears highly depends upon cooling/lubrication, workpiece material, geometric tool features, and machining parameters. After machining experiments, flank wear of cutting insert was evaluated to find the correlation between tool wear and tool life from the viewpoint of machine cutting time. Experiments were performed under the highest cutting conditions to verify the variation in tool wear under CO2-snow and hybrid nanofluids. The criterion for tool life was defined as an average of 300μm on the leading cutting edge. The tool life under CO2snow was 4.6 minutes, while 5.3minutes under hybrid nanofluids, respectively. The longer tool life can be associated with superior lubrication under that reduced the coefficient of friction and dissipated the heat by enhancing the thermal conductivity, resulting in lower thermal softening of tool grains provided less wear even at high spindle speed. Scanning electron microscopy (SEM) images provided in Fig. 9(a, b) depicting the flank wear under CO2-snow and hybrid nanofluids, respectively. Flank wear under cooling/lubrication mode has shown attrition, adhesion and reactivity of Ti-6Al-4V led to tool failure and poor surface quality. For instance, adhesion due to diffusion adhered to the layers of tool grains at the tool-joint interface. Also, chip smearing on major flank face under hybrid nanofluids was more significant compared to CO2snow, which can be interpreted in terms of reduction of thermal softening under CO2-snow. Significant chipping and abrasion on flank face resulted in tool wear and failed in premature before reaching the expected tool life. In order to validate the performance of CO2-snow and CuO-MWCNTs hybrid nanofluids, the experiment was repeated three times at cutting speed of 120m/min, feed of 0.12mm/rev, depth-of-cut of 1mm under cooling modes. As a result, the average of the measured responses (Ra, Pc, TL, T) was taken to evaluate the performance provided in Table 2 . The values of measured responses depict the lower surface roughness (Ra) and higher tool life (TL) under hybrid nanofluids. However, cutting power and temperature were lower under CO2-snow. Several research studies have revealed the potential of hybrid nanofluids in the viewpoint of improved machining characteristics in conventional and highspeed machining. Higher cutting conditions are mainly associated with superior lubrication, thermal conductivity, and sustainability of nanoadditives. Biodegradable oil-based suspended nanofluids enhance the heat transfer coefficient, dissipate heat from the cutting zone and reduce adhesive tool wear. Extended tool wear can be associated with nano-additives spacers at toolchip interface limiting friction, surface roughness. Following key advantages are summarized; • Hybrid nanofluids, and pressured MQL fine mist provided a tribo-film with enhanced tribological properties. • Variable size and nature increased the performance of nanoadditives, because of their role as a spacer at close or a wide gap between the tool-workpiece surface. • Hybrid nanofluid penetrated inside narrow tool-chip interface prevented direct contact of Ti-6Al-4V with tool surface for any chemical reaction. The resulting complexities are also associated with the nanofluids: • Nanoparticles cannot be dissolved in liquid. • Nanoparticles such as MWCNTs, penetrate easily into operator skin, cause allergy, may disturb the immune system, coughing with no infection, a negative impact on DNA, and harms the seeds and plant growth. • Nanoparticles are hard to detect if discharged openly in the environment. Therefore, hazard appraisal should be carried out to lessen the danger during use because a little variation in the chemical structure converts into toxic compounds. Spray cooling system uses a phase change process to transfer a large amount of heat without forming a liquid film. Joule Thomson effect applies due to sudden pressure drop at the nozzle exit, converts liquid-gas mixture to solid dry ice particles. As the dry ice particles impinge on the workpiece surface, sublimation occurs in the phase change process that generates a cooling heat flux. The critical benefit of sublimation as the phase-change process having continuous spray mechanism has an absence of liquid film, providing isenthalpic expansion and isobaric process, transferring a large amount of heat by convection. The high heat transfer coefficient, rapid and short time cooling characteristics. The prominent cooling and thermal heat transfer increase the requirement of cutting power consumption at low cutting speed. However, high cutting speed is more suitable for cryogenic in the viewpoint of power consumption. Following essential application, advantages are highlighted for nextgeneration CO2-snow. • CO2-snow converts to dry ice abrasive particles sublimate at the tool-workpiece interface with no secondary contamination. • High-pressure mist penetrates well into the machining zone without any external motor power • Dry ice particles based on initial temperature, expansion, and nozzle diameter, agglomerates on the workpiece surface, a higher concentration of particles due to inertia, remove small chip particles. CO2-snow has been identified as a better alternative in the viewpoint of the global impact of carbon dioxide, ozone depletion, or operator respiratory problems with the application of traditional coolants are concerned. Specifically, CO2-snow winds-up the restriction of a confined environment by ensuring a sustainable working environment. A holistic research study revealed the application of CO2-snow nontoxic, easy to recycle, cheap alternative with limited environmental impact. Also, excellent dispersion of dry ice particles provides homogenous cooling, superior in rough machining. It can be concluded that CO2-snow is a potential alternative of emulsion/ ionic fluids. This manuscript summarizes an endeavor to enhance the machinability of Ti-6Al-4V. An experimental study has compared two sustainable lubri-cooling techniques, such as CuO-MWCNTs and CO2-snow. The machining characteristics are surface roughness (Ra), machine cutting power (Pc), temperature (Tc), and tool flank wear under lubri-cooling modes. Some of the key findings are as follow; • CuO-MWCNTs assisted minimum quantity lubrication has lessened the surface quality and extended tool life compared to CO2-snow cooling. Besides, hybrid nanofluids assisted MQL has provided less machining power consumption at a low level of cutting conditions. • At a low level of cutting parameters, such as cutting speed of 80m/min and feed of 0.08m/rev, the maximum reduction in surface roughness was 18.8% under hybrid nanofluids compared to CO2-snow. Similarly, at a high level of cutting speed (120m/min), and feed level of 0.08mm/rev, surface roughness was 36.9% lower than CO2-snow. • Besides, at a low level of speed (80m/min), and a high level of feed (0.12mm/rev), machine cutting power consumption was 13.65% lower under hybrid-nanofluids compared to CO2-snow. Similarly, at a high level of cutting speed (120m/min), and feed of 0.12mm/rev, CO2snow provided 5% less cutting power consumption. • At low cutting speed (80m/min), and a high level of feed of 0.12mm/rev reduction in temperature under CO2-snow was 22.36% than MQL-hybrid nanofluids. Also, at a lower level of speed (120mm/min) and feed (0.08mm/rev), 17.5% low temperature under CO2-snow was determined in comparison with hybrid nanofluids. • At a high level of cutting parameters such as cutting speed of 120m/min, feed of 0.12mm/rev, and cutting depth of 1mm, 14.5% increase in tool life under hybrid nanofluids was observed compared to CO2-snow. • Although, CuO-MWCNTs assisted MQL provided superior thermal conductivity, lubrication, and lower friction Thermophysical Properties of Solid and Liquid Ti-6Al-4V (TA6V) Alloy Machining β-titanium alloy under carbon dioxide snow and micro-lubrication: a study on tool deflection, energy consumption, and tool damage On machining of Ti-6Al-4V using multi-walled carbon nanotubes-based nano-fluid under minimum quantity lubrication Effects of duplex jets high-pressure coolant on machining temperature and machinability of Ti-6Al-4V superalloy Multiobjective optimization for grinding of AISI D2 steel with Al2O3 wheel under MQL Performance Evaluation of Jatropha and Pongamia Oil Based Environmentally Friendly Cutting Fluids for Turning AA6061 Energy conscious cryogenic machining of Ti-6Al-4V titanium alloy Performance Evaluation of Vegetable Oil-Based Nano-Cutting Fluids in Environmentally Friendly Machining of Inconel-800 High-speed machining of titanium alloys using the driven rotary tool Machinalibilty of Ti-6Al-4V under dry and near dry condition using carbide tools Ecological machining: Near-dry machining Multi-objective optimization of energy consumption and surface quality in nanofluid SQCL assisted face milling Energies Investigations of machining characteristics in the upgraded MQL-assisted turning of pure titanium alloys using evolutionary algorithms Recent progress on the application of nanofluids in minimum quantity lubrication machining: A review Investigation of effects of nanofluids on turning of AISI D2 steel using minimum quantity lubrication Effect of minimum quantity lubrication with Al2O3 nanoparticles on surface roughness, tool wear and temperature dissipation in machining Inconel 600 alloy Towards sustainable machining of Inconel 718 using nano-fluid minimum quantity lubrication Prediction of temperature distribution over cutting tool with alumina-MWCNT hybrid nanofluid using computational fluid dynamics (CFD) analysis A numerical study of water based Al2O3 and Al2O3-Cu hybrid nanofluid effect on forced convective heat transfer Experimental analysis of tribological properties of lubricating oils with nanoparticle additives Finite difference simulation and experimental investigation: effects of physical synergetic properties of nanoparticles on temperature distribution and surface integrity of workpiece in nanofluid MQL grinding process Tool wear and surface integrity of inconel 718 in dry and cryogenic coolant at high cutting speed Experimental comparison of carbon-dioxide and liquid nitrogen cryogenic coolants in turning of AISI 1045 steel The influence of cryogenic coolants in machining of Ti-6Al-4V Cryogenic and minimum quantity lubrication for an eco-efficiency turning of AISI 304 Effects of hybrid Al2O3-CNT nanofluids and cryogenic cooling on machining of Ti-6Al-4V Determining the effect of cutting parameters on surface roughness in hard turning using the Taguchi method Application of nanofluids during minimum quantity lubrication: A case study in turning process Study on convective heat transfer and pressure drop of MWCNTs/water nanofluid in mini-tube Investigations of Machining Characteristics in the Upgraded MQL-Assisted Turning of Pure Titanium Alloys Using Evolutionary Algorithms Investigations of Surface roughness, Power Consumption, MRR and Tool wear while turning hybrid composites Evaluation of machinability and economic performance in cryogenic-assisted hard turning of α-β titanium: a step towards sustainable manufacturing. Machining Science and Technology The authors are thankful to advance cutting technology (ACT) for providing all experimental facilities.