Li et al. - 2024 - Minimum Quantity Lubrication (MQL) Review PDF

The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 https://doi.org/10.1007/s00170-024-13902-3 ORIGINAL ARTICLE A comprehensive review of minimum quantity lubrication (MQL) machining technology and cutting performance Donghui Li1 · Tao Zhang1 · Tao Zheng1 · Nan...

The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 https://doi.org/10.1007/s00170-024-13902-3 ORIGINAL ARTICLE A comprehensive review of minimum quantity lubrication (MQL) machining technology and cutting performance Donghui Li1 · Tao Zhang1 · Tao Zheng1 · Nan Zhao2 · Zhen Li1 Received: 6 October 2023 / Accepted: 27 May 2024 / Published online: 11 June 2024 © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2024 Abstract The cutting fluid plays an important role in lubrication, cooling, chip removal, and rust protection in mechanical manufac- turing. The waste-cutting fluid can pose a threat to the water environment and even human health. The minimum quantity lubrication (MQL) technology can meet the requirements of clean manufacturing, and it has been widely recognized as a replacement for traditional flood-cutting technology. As an emerging green cutting technology, it has broad application pros- pects. The latest progress in MQL machining technology is reviewed, and the cutting performance of MQL is elaborated in this article. Firstly, the composition and implementation form of the MQL system were elaborated. The impact of the MQL system parameters on cutting performance was also illustrated in this part. Secondly, the combination of MQL technology, low-temperature technology synergistic effect of additives, and the atomization and hardware improvement of MQL was introduced. Thirdly, the cutting performance of MQL technology on cutting force, cutting temperature, residual stress, tool wear, and surface quality was analyzed. Finally, the limitations of MQL technology were discussed, and its development direction was prospected. It provides suggestions for the engineering application of MQL technology. Keywords Sustainable development · MQL · Lubrication · Cooling · Machinability 1 Introduction In high-temperature environments, the workpiece surface integrity is prone to deterioration, tool wear accelerates, Mechanical cutting is an important method in the manu- and tool life decreases. In order to reduce the cutting facturing process. The final purpose of cutting is to remove heat, the flood-cutting technology of pouring cutting fluid excess material from the workpiece with the relative motion into the cutting interface has been promoted and applied between the cutting tool and the workpiece, thereby get-. Flood cutting requires a large amount of synthetic cut- ting the desired shape and size of the part. In recent years, ting fluid, which can increase processing costs. Cutting improving productivity has been the most effective way fluid often contains organic solvents, heavy metals, ammo- to satisfy the rapid growth of product demand. Mechani- nia, and other harmful substances. Long-term inhalation or cal processing is increasingly inclined to be carried out at contact with these substances can lead to health problems high speeds. In the process of metal cutting, most of the such as poisoning. Harmful substances in cutting fluid enter energy consumed by material deformation and friction is the environment and cause pollution of water, soil, and air converted into heat and resulted in high-temperature contact. Dry cutting has been widely applied in many cutting between the tools-chips and the tools-workpiece interface. processes without cutting fluid costs and pollution [5, 6]. However, dry cutting lacks the cooling and lubrication of cutting fluid; the cutting speed is limited. The chips are easy * Tao Zhang to adhere to the tool in a high-temperature environment. The [email protected] high temperature leads to a decrease in workpiece surface 1 National‑Local Joint Engineering Laboratory of Intelligent quality and an increase in tool wear. With the increasing Manufacturing Oriented Automobile Die & Mould, Tianjin demand for cutting performance such as workpiece accuracy University of Technology and Education, Tianjin 300222, and smoothness, dry cutting can no longer meet the machin- China ing requirements. The appropriate lubrication process can 2 School of Mechanical Engineering, Tianjin University of Technology and Education, Tianjin 300222, China Vol.:(0123456789) 2682 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 improve machining efficiency, extend tool life, and have an stress, tool wear, and improving surface quality is illustrated. impact on the surface quality of the workpiece. The conclusions are drawn, and the development trend of Therefore, under the premise of ensuring machining effi- MQL is prospected. ciency and quality, minimum quantity lubrication (MQL) cutting technology has become the best solution with low- cost and micro pollution, even zero pollution cutting. MQL 2 Minimum quantity lubrication can exhibit superior cutting performance compared with dry cutting in different machining methods such as turning, The MQL technology was proposed by Klock in 1997. milling, and grinding [9, 10]. MQL belongs to the category Due to the use of degradable vegetable oil, MQL can effec- of sustainable manufacturing technology. The fundamental tively reduce pollution in the environment and the health purpose of sustainable manufacturing is to produce goods in threat to the operator. MQL is the most mature processing an efficient and cost-effective manner while avoiding energy technology among green cutting technologies besides dry waste and minimizing environmental damage. MQL uses a cutting and is widely used in turning, milling, drilling, and small amount of cutting fluid mixed with high-pressure gas, grinding. As an alternative to traditional cutting, clean man- and the entire cutting zone is covered with oil mist. ufacturing methods have been recognized by many research- The small amount of cutting fluid can take away part of the ers [16–18]. cutting heat and reduce the cutting temperature. And at the Researcher has pointed out that in the processing opera- same time, it forms a layer of oil film at the tool-workpiece tions of the automobile industry, the cost of lubrication/ interface for lubrication. Therefore, MQL can reduce tool cooling accounts for 16 to 18%, and the cost of cutting tools wear, increase tool life, and improve workpiece surface qual- only accounts for 7 to 8%. The application of MQL can ity [12, 13]. reduce the cost of machine tools by at least 15%. Ben- The lubrication medium flow rate range of MQL is edicto et al. summarized the costs of various cooling/ 20 ~ 200 ml/h. The flow rate of traditional flood cutting is lubrication systems based on the research results of previ- about 60 L/h and is much greater than that of MQL. The low ous researchers and conducted a qualitative analysis of the flow rate makes the chips under MQL nearly dry and easy to costs combined with raw material costs, fluid consumption, collect and recover. The oil mist sprayed by MQL can and equipment costs (Table 1). From Table 1, it can be seen penetrate into the tool-chip interface to form an oil film. As that MQL has the lowest cost among all lubrication methods a result, the oil film changes the friction conditions between except for dry cutting, and all costs are relatively uniform. the tool-workpiece and affects cutting performance. With the advancement of technology, MQL has been 2.1 MQL system widely used in machining, especially in the cutting process of difficult-to-cut materials. The research progress of MQL The MQL system mainly consists of an air compressor, technology is reviewed, and the application forms of MQL oil cup, oil pump, mixing chamber, nozzle, pipeline, and devices in different machining methods are summarized in various regulating valves. This integrated system is sim- this article. The lubrication mechanism of MQL is analyzed, ple in structure, small in size, light in weight, and easy and the influence of MQL system parameters on cutting to install on various mechanical equipment. The MQL performance is also elaborated. Finally, the effectiveness of device is composed as shown in Fig. 1. The oil is driven MQL in reducing cutting force, cutting temperature, residual by the oil pump in the oil cup and flows into the mixing Table 1  Qualitative estimation of lubricant/lubrication system costs Raw material cost Fluid con- Equipment costs Tools cost Cleaning costs Disposal costs sumption Cutting fluids ** ***** **** *** ***** ***** Dry machining * * * ***** * * MQL ** ** *** ** ** ** Solid lubricant **** *** *** *** *** **** Cryogenic cooling *** *** ***** *** * * Gaseous cooling *** *** **** **** * * Sustainable cutting fluids *** **** **** ** **** *** Nanofluids ***** **** **** *** **** ***** (*) Very low; (**) low; (***) medium; (****) high; (*****) very high. The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2683 MQL 2.2.1 External jet MQL Nozzle The oil mist of external jet MQL is sprayed onto the cut- Tool Work piece ting zone through external pipeline equipment. External jet Tool holder is currently the most widely used implementation form of MQL. This spraying method is not affected by the machine MQL Pump tool, and it is convenient to adjust the angle and number of Fluid chamber nozzles. External jet MQL can get the best injection angle and injection effect. Cetindağ et al. built an external jet MQL and sprayed Compressed air the cutting fluid and liquid nitrogen through the external Mixing chamber pipe, respectively, to realize the external jet liquid nitrogen Pressure gauge composite MQL. ul Haq et al. fixed the MQL nozzle on Valve the side of the machine tool spindle and adjusted the incli- nation angle between the nozzle and the workpiece surface to 45° and the distance of 25 mm. The milling process is Compressor shown in Fig. 2. The high-pressure gas disperses the nano- fluids into the nozzle to form the mist flow. The spray speed Fig. 1  Schematic view of MQL device of the mist flow is higher than the cutting speed. When the nozzle angle is 45°, the nozzle is directly opposite the chip fracture site, so that the fog is filled between the tool-chip fracture channel at all times. It causes the oil mist to form a chamber. At the same time, the compressed gas enters the lubrication film at the cutting zoneand enhances the lubrica- mixing chamber to disperse the lubricating oil and forms tion effect in the cutting zone, thereby frictional shear stress a certain concentration of micrometer-level oil mist. By and tangential cutting force are reduced. Pusavec et al. adjusting the oil control valve and air pressure valve, the usedMQL with multiple nozzles, which has the advantage air and lubricating oil are fully mixed to form oil in the of adjusting the number and position of nozzles according mixing chamber mist. Finally, the oil mist is sprayed into to experimental requirements (Fig. 3). the cutting zone through the nozzle to achieve lubrication External jet MQL separates the lubrication system from and cooling effects. the machine tool. The spray angle and distance can be set The MQL device also has certain defects in actual use. arbitrarily according to different cutting methods. But there After the gas is compressed, it enters the mixing chamber are also certain limitations. The distance between the drill- through a pneumatic pulse generator. The periodic output ing hole and the drill bit is too narrow to allow oil mist to of the pneumatic pulse generator can lead to insufficient enter effectively in the drilling process, so it is impossible gas–liquid mixing. The controls of gas pressure and lubri- to achieve lubrication and cooling effects. For milling, the cating oil flow rate are also difficult to ensure matching. MQL effect is relatively stable when the jet speed is higher Excessive gas pressure will cause lubricating oil to flow than the tool speed. However, when the jet speed is lower back into the oil cup, while too low pressure will lead to than the tool speed, the high-speed rotation of the milling insufficient mist formation. In the future, researchers need cutter generates a rotating airflow field around it, and it seri- to continue to upgrade MQL equipment. Digital control ously affects the injection of oil mist. Therefore, external and equipment stability are the key research and develop- jet MQL is often used for turning, grinding, and medium to ment directions. low-speed milling. 2.2.2 Internal supply MQL 2.2 Application form of MQL device Internal supply MQL requires a special machining tool and When the MQL system is working, different forms of oil modification of the cutting tool, tool handle, and even the mist supply will also have different effects on the lubrica- machine tool spindle. The oil mist is sprayed onto the cut- tion and cooling effects. According to the oil mist reaching ting zone through the machine tool or its accessories. In the cutting interface through the internal components of order to ensure the rigidity of the cutting tool and shank the machine tool, the implementation methods of the MQL and strong cutting fluid pressure, the internal supply channel supply system can be divided into an external jet and an is usually designed in a smaller dimension. Duchosal et al. internal supply. studied the spray efficiency of the milling cutter with 2684 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Fig. 2  Schematic illustration of the MQL milling process Fig. 3  Multi nozzle MQL Nozzle supplying LN or MQL on the rack face Nozzle supplying LN ahead of the cutting tool Cutting insert for cooling the workpiece Dynamometer for Workpiece measuring cutting (Inconel 718) forces Nozzle supplying LN or MQL on the flank face an internal channel. They found it very important to avoid With the advancement of internal supply MQL, some oil mist droplets colliding with each other in the milling researchers have begun to develop tool shank transfer cutter channel. At the same time, it is necessary to consider devices to achieve the internal supply effect. Zaman et al. a higher pressure to overcome aerodynamic phenomena designed an embedded dual nozzle (Fig. 5), which was caused by high-speed rotation. Zhang et al. divided the made up of a tool shank with an inlet connector and two internal supply MQL milling cutter into three types of dou- specially designed nozzles. The above three holes intersect ble helical channel (DHC), single straight channel (SSC), at a common intersection point inside the shank and are per- and double straight channel (DSC) according to the num- pendicular to each other. This nozzle reduces the additional ber and arrangement of pipelines (Fig. 4). The experiment installation time of the nozzle, and its compactness is ben- results showed oil mist droplets collide with each other and eficial to improve the lubrication and cooling effects of the adhere to the wall in DHC, so the lubrication and cooling MQL. effects of DHC are not as good as those of DSC. The cutting Internal supply MQL can achieve accurate injection of oil tool life of the double straight channel was 1.59 times that of mist. But internal supply MQL requires a conveying pipe- the double-helical channel. line inside the tool, which reduces the strength of the tool. The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2685 Fig. 4  Internal channel struc- tures of three milling cutters: a DHC, b SSC, c DSC Fig. 5  Schematic view of the double jet nozzle According to the characteristics of various cutting processes, the nozzle distance resulted in fewer and smaller droplets internal supply MQL is commonly used in milling or drill- being deposited. Emami et al. believed that the droplet ing. The high-speed rotation of the cutting tool can easily size of MQL atomization was related to the flow rate of the cause oil mist droplets to adhere to the tool tube wall due lubricant, the gas flow rate, and the physical properties of to centrifugal force, thereby reducing the spraying effect. the lubricant itself. In the future, it is necessary to study and optimize the more Increasing the gas pressure can reduce the droplet size stable injection structure according to different processing and increase the droplet velocity. However, with the increase methods, so that the lubricating medium can obtain the best in pressure, the droplet size in the same plane is not uniform, permeability. and the particle size near the center line of the nozzle is larger and sparser. The droplet size outside the cone-shaped 2.3 Atomization characteristics of MQL liquid beam is smaller, but it is easy to drift into the air. In the future, it is necessary to realize the controllability of the The appropriate droplet size can affect the coverage and particle size of the MQL droplets and minimize the harm of permeability of the lubricant on the friction surface. The the dispersed particles to the environment and the health of smaller the droplet size, the more effective it is to form a the workpiece. lubricating film. The droplet with a smaller particle size has less kinetic energy, and it is easier to diffuse out- 2.4 Lubrication mechanism of MQL ward from the center line of the nozzle. Park et al. studied the particle size distribution of MQL. They found Cutting fluid can effectively reduce the friction between that the higher the nozzle pressure, the higher the droplet tools-chips and tools-workpiece, cutting temperature and flow rate, and the easier it is for the lubricant to atomize cutting force. The basic lubrication principle of MQL into small droplets. The higher the nozzle pressure, the more is to form a lubricant film between the rubbing pairs at the droplets reach the cutting interface. In addition, increasing cutting interface. Virdi et al. used MQL in grinding 2686 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Inconel 718 alloy.They found that appropriate droplet size angle between the spraying direction and the feed direction helps to form an oil film in the grinding zone. The oil mist (β), nozzle elevation angle (α), and distance between the reduces the contact area between friction pairs and supports nozzle and the cutting zone (d). The nozzle had the best the load on the grinding wheel. In addition, the nanoparti- spraying effect by sending oil mist into thecutting zone cles added to the lubricating oil can act as ball bearings at when β, α, and dwere 120°, 60°, and 20 mm, respectively. the cutting zone. Sliding friction is made towards rolling Huang et al. conducted surface grinding experiments friction. The penetration ability of cutting fluid also has a on AISI 5140 steel and studied the parameters of the MQL significant impact on lubrication and cooling effects. Cur- system (flow rate, air pressure, nozzle position, and noz- rently, the capillary phenomenon is the most widely recog- zle distance). They found that the spraying direction of nized research on the penetration mechanism of the cutting the nozzle was the most important factor affecting the fluid. The rack face of the cutting tool has micro-surface MQL grinding performance. The surface roughness and roughness. The sliding friction and plowing between the depth of the hardened layer decrease with the increase of tool-chip cause the tool to form micro-cracks. These micro- flow rate and air pressure and increase with the increase cracks are a large number of capillaries, and the cutting fluid of nozzle distance. They concluded the balance of MQL infiltrates the cutting zone through siphonage. parameters in order to ensure a certain number of hardened Although the flow rate of MQL cutting fluid is only layers and better surface quality. Yao et al. compared 1 ~ 10% of that of flood cutting, the lubrication effect of the cutting performance of four different nozzles (Fig. 7). MQL can reach or even exceed that of traditional flood cut- The experiment found that the droplet diameter of nozzle ting. Under the condition of MQL, the oil mist particles II was the smallest, and the atomization effect was the are small in size and fast in speed, and the nozzle can be best. Therefore, the penetration ability of nozzle II oil mist adjusted, which makes it easier to penetrate into the cutting interface. In addition, the tool-workpiece generates high- energy electrons during severe friction during the cutting process. It is easier to separate oxygen atoms from the oil mist mixture at high temperatures, and the oxide film is gen- erated at the metal interface through chemical reactions. 3 The influence of MQL system parameters Nozzle ĉ Nozzle Ċ on cutting performance In the actual cutting process, there is a certain matching rela- tionship between the parameters of the MQL system and the cutting technology due to differences in workpiece materials and processing techniques. The shape and position of the nozzle directly affect the spray effect of the oil mist. The design and installa- tion position of the nozzle can affect the oil mist spraying Nozzle ċ Nozzle Č onto the rubbing pair zone. Yan et al. provided three parameters for determining the nozzle orientation (Fig. 6): Fig. 7  Atomization structure and outlet shape of four nozzles Fig. 6  Schematic view of nozzle position The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2687 droplets was the highest, and the cutting force and cutting S x temperature were the lowest. In addition, compared with Nominal is the best characteristic, N = 10log 2 Sx (1) nozzles I, III, and IV, the surface roughness with nozzle II was reduced by 20%, 27%, and 24%, respectively, and the S 1 ∑ 2 ( ) tool wear width was reduced by 2.7%, 13.6%, and 1.4%, Smaller is the better characteristic, = 10log x N n respectively. (2) The optimal combination of MQL parameters should S 1 1 ( ) be selected according to the cutting characteristics to Larger is the better characteristic, = log (3) N n x2 achieve the optimal cutting effect. Liu et al. con- ducted experimental studies on the effects of different where x is the measurement response; x is the average value MQL parameters (including flow rate, air pressure, and of x; Sx2 is the variation of response x; n is the number of nozzle position) on titanium alloy milling. The study experimental data. found that the air pressure and nozzle distance too large Different lubricating oils have different lubrication and or too small were not conducive to oil mist infiltration cooling effects on MQL. Liao et al. studied the effect into the cutting zone. The quality of MQL oil mist drop- of different oil–water ratios on MQL cutting. They found lets has a significant impact on milling force and milling that adding a certain proportion of water to the lubricat- temperature. Huang et al. conducted electrostatic ing oil will affect the viscosity of the fluid, which in turn MQL turning experiments on AISI 304 stainless steel. affects the ability of the lubricating fluid to enter the cut- With the increase of the cutting fluid flow rate, the depo- ting interface. They concluded through experiments that sition rate of droplets on the cutting zone increased, lead- the best oil–water ratio in high-speed cutting was 60:40. ing to a decrease in the friction force and a reductionof Wang et al. studied the effects of seven typical vegetable the surface roughness. The experiment found that the oils (soybean, peanut, maize, rapeseed, palm, castor, and electrostatic MQL had optimal air pressure and nozzle sunflower oil) on grinding performance. Castor oil showed position. Appropriate selection of these parameters can the best lubrication performance in grinding experiments. effectively promote the entry of oil mist into the cut- Compared with water grinding, the friction coefficient and ting zone, reducing friction and wear between the tool specific wear energy of castor oil were reduced by 50.1% and and the workpiece. Abd Rahim et al. studied the 49.4%, respectively. By comparing the comprehensive per- performance of MQL under different combinations of formance of different oils, they sorted the lubricity of these spraying and processing parameters. The results show seven oils: maize oil < rapeseed oil < soybean oil < sunflower that the spray cone angle formed by the nozzle was the oil < peanut oil < palm oil < castor oil. best when the input air pressure was 0.4 MPa. In addi- However, most optimal results are limited to a certain tion, when the distance between the nozzle and the cut- level range of selected cutting parameters in the experiment. ting zonewas 6 ~ 9 mm, the inlet pressure was 0.4 MPa, In the actual cutting process, the optimal cutting parameters and the nozzle diameter was 3.0 mm; it was the most may not be included in the selected cutting parameters. favorable parameter combination to reduce cutting force Therefore, how to select a group of optimal MQL parameters and cutting temperature. is an urgent problem through a large number of experiments Due to the lack of mechanism research, there is a cer- to provide support for MQL parameters. tain blindness in selecting MQL parameters. Andit is difficult to determine the optimal match between cutting parameters and MQL system parameters. Some researchers believe that optimizing MQL parameters is the prerequisite 4 Improvement of MQL for achieving effective grinding and the key to achieving sustainable grinding processes. At present, there are As the main technology of green cutting, MQL has various some mature mathematical models for optimizing cutting advantages in mechanical cutting. But MQL also faces many parameters based on roughness [45, 46]. But there are few challenges, especially in extreme environments such as high methods for optimizing the parameters of MQL, and the speed, high pressure, and high temperature. Researchers most widely recognized method is the Taguchi method have begun to improve MQL technology. The improvement. Mia et al. [48–50] used the Taguchi method based of MQL is summarized in this section, and the impact of the on grey correlation to optimize some important parameters improved technology on cutting performance is analyzed of tool-workpiece interaction. The optimization process based on the previous summary. Overall, the improvement was completed by signal-to-noise ratio (S/N). According of MQL is mainly divided into four parts: cryogenic MQL, to the optimal principle, the continuous response function MQL atomization improvement, MQL and additive combi- has three different characteristics: nation, and MQL equipment improvement (Fig. 8). 2688 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Fig. 8  Improvement of MQL Cryogenic air MQL(CA+MQL) Cryogenic MQL Supercritical CO2 Cryogenic nanofluids MQL (CMQL) MQL(scCO2+MQL) Liquid nitrogen MQL atomization MQL(LN2+MQL) Nanofluids ultrasonic improvement atomizing MQL Improvement of Nanofluids MQL MQL(NMQL) MQL+additive Ionic liquid MQL New Potential MQL MQL equipment Technology MQL hardware restructuring improvement MQL nozzle design 4.1 Cryogenic minimum quantity lubrication (CMQL) The cryogenic cutting technology rapidly reduces the tem- perature of the cutting zone through the cooling media. At present, cryogenic cutting is mainly achieved through cryo- genic air (CA), liquid nitrogen (­ LN2), and supercritical car- bon dioxide media ­(scCO2). CMQL under the dual action of cutting fluid and cryogenic air, can effectively reduce the cutting temperature. CMQL is an advanced manufacturing technology suitable for cutting difficult-to-cut materials. 4.1.1 CA + MQL The cryogenic air minimum quantity lubrication (CA + MQL) uses the cryogenic air below − 10 °C syner- gistic MQL to reduce the temperature of the cutting zone. The CA + MQL device adds a refrigeration system on the basis of the MQL device. At present, cryogenic air is mainly obtained through the following aspects: adding low boiling point medium refrigeration, air adiabatic expansion direct refrigeration, cycle compression indirect refrigeration, and vortex tube compression refrigeration. Zhang et al. found oil mist on the tool or workpiece at low temperatures which canbe easier to form micro-droplets and penetrate into the cutting zone. Saberi et al. formed Fig. 9  MQL processing device assisted by vortex tube cryogenic air through vortex tube compression and mixed it with lubricating oil in the nozzle to form cryogenic drop- lets (the experimental device shown in Fig. 9). The grinding of the workpiece. Even in high-speed cutting, CMQLcan force and friction coefficient under CMQLwere lower than exhibit a lower friction coefficient. These characteristics those of flood cutting and dry cutting. They concluded that provide support for the study of the cutting mechanism of the use of vortex tube-assisted MQL was expected to break metal under MQL. the cooling limit of conventional MQL. The CMQL is an Zhang et al. established a convective heat transfer effective alternative to conventional cooling lubrication. coefficient model based on boiling heat transfer and ther- Benjamin et al. reached the same conclusion in addition mal conductivity theory and numerically simulated the tem- to the CMQL cutting performance research. The cryogenic perature field of the grinding zone under different vortex air provided by the vortex tube increases the viscosity of the tube cryogenic air flow rates. The simulation results were lubricating oil and promotes the formation of the lubricating only 5.1% different from the experimental data, and it indi- oil film between the tool-chip and the tool-workpiece. At the cated that the theoretical model has a high accuracy. The same time, low temperatures reduce the thermal softening establishment of a theoretical model makes the heat transfer The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2689 performance of the CMQL be predicted in advance, which A large number of studies have shown that ­LN2 has good helps to accurately select parameters during machining. advantages in MQL as a cooling medium, especially for dif- ficult-to-cut materials. At present, there are some unsolved problems in the use of ­LN2 + MQL. The low-temperature 4.1.2  LN2 + MQL environment hardens the cemented carbide tool. Some materials undergo changes in crytal structure at ultra-low The lowest temperature can reach − 196 °C when ­LN2 is temperature environments, and the processing conditions used as the cooling medium. When ­LN2 is mixed with cut- decrease with the temperature decreasing. In addition, the ting fluid and injected into the cutting zone, the cutting tem- cost of L­ N2 is relatively high and requires additional costs perature can be greatly reduced. In addition, the nitrogen for preservation. It results in the ­LN2 which can only be medium layer formed can isolate oxygen and reduce tool applied in a certain specific material processing or specific oxidation wear. Ghosh et al. found that ­LN2 + MQL fields as a cooling medium for MQL. reduced the flank face wear by 38% compared withNMQL in the experiment of turning Nimonic 90 alloy. Wu et al. 4.1.3  scCO2 + MQL carried out experiments on ­LN2 + MQL in high-speed milling hardened steel and compared them with experiments Liquid ­CO2, especially supercritical ­CO2, is currently recog- on single MQL and ­LN2. At the cutting speed of 350 m/ nized as a “green solvent.” It can be used as a solvent to dis- min, the tool life under L ­ N2 + MQL increased 64% and 61%, solve cutting fluids, as well as a cooling medium to achieve respectively, compared with the single use of MQL and L ­ N2. strong cooling. The s­ cCO2 plays the role of oxygen insula- At the cutting speed of 450 m/min, the tool life under the tion and protection in the cutting zone and has great devel- ­LN2 + MQL increased by 50% and 14%, respectively. The opment potential. Research has shown that adding soluble experiment results showed that ­LN2 + MQL can reduce the vegetable oil to ­scCO2 can greatly improve the lubrication surface roughness of the workpiece and tool wear. Gajrani performance of the cutting zone [61, 62]. The combination et al. machined Ti-6Al-4V alloy in dry cutting, MQL, of ­scCO2 and MQL combines the characteristics of liquid and ­LN2 + MQL environments. The experimental results are and gas states. shown in Fig. 10. ­LN2 + MQL not only shows good cutting Arafat et al. pointed out that C ­ O 2 expands rap- performance but also has a quenching effect. The quenching idly through a smaller diameter nozzle in a supercriti- effect increases the hardness of the cutting tool. cal state. At the same time as energy conservation, the Fig. 10  Comparison of cutting performance under dry, MQL, and ­LN2 + MQL 2690 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 rapid expansion of oil mist droplets leads to an increase The CMQL combines the advantages of CA and MQL in kinetic energy and a loss of heat energy. Therefore, the and makes up for the defects of two different cutting tech- diameter of the nozzle is the key improvement in the appli- nologies. Hydrogen, neon, helium, carbon dioxide, oxygen, cation of ­scCO2 + MQL. liquid nitrogen, and other compressed gases can be applied An et al. milled Ti6Al4V alloy under four condi- as cooling mediums in CMQL. Although CMQL has great tions: dry, s­ cCO2, ­scCO2 + antifreeze water-based MQL advantages, there are also shortcomings in its application. ­( scCO 2 + WMQL), and ­s cCO 2 + water oil-based MQL Low temperature results in the viscosity of lubricating oil ­(scCO2 + OoWMQL). The experiment results showed that increasing, which leads to a decrease in its fluidity and wet- theflank face wear width VB was the largest (286.7 µm) tability. In addition, the surface tension of lubricating oil when ­scCO2 was used alone. But under the synergistic effect droplets increases in the low-temperature environment. The of ­scCO2 and MQL, the cutting performance was greatly oil mist does not easily infiltrate the capillary channels on improved. The flank face wear of ­scCO2 + WMQL and the surface of the material between the tool-workpiece. ­scCO2 + OoWMQL was 121.5 µm and 94.0 µm. Tu et al. Therefore, the equilibrium adaptation state of viscosity- cut compacted graphite cast iron (CGI), flake graphite temperature characteristics and the wettability of lubricat- cast iron (FGI), and nodular graphite cast iron (NGI) under ing oil under different processing conditions will be a key various conditions. The oil film reduces the friction between research direction in the future. the tool and the workpiece by S ­ cCO2 + MQL in the cutting zone. In addition, cryogenic ­CO2 retains good thermal con- 4.2 Combination of MQL and additives vection and heat transfer and has excellent heat dissipation performance. Therefore, the S ­ cCO2 + MQL reduces the cut- Some researchers have added heat transfer media with good ting temperature by 30 to 40% compared with dry cutting thermal stability and high thermal conductivity to the lubri- (Fig. 11). cating oil. Fig. 11  Evolution of temperature of FGI, CGI, and NGI depends on the various conditions under dry, ­ScCO2, and ­ScCO2 + MQL conditions The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2691 4.2.1 Nanofluid minimum quantity lubrication (NMQL) et al. found the nanofluids had better lubrication and cooling effects than flood cutting during the grinding Nanofluid is a fluid containing nanoscale solid particles, usu- of Inconel 718 alloy. Due to the high pressure of MQL, ally generated by adding metal or non-metallic nanoparticles nanoparticles can better penetrate the cutting interface to with a diameter of less than 100 nm into the cutting liquid improve grinding performance.. As additives for MQL, commonly used nanoparticles Although NMQL has many advantages, it should be include ­Al2O3 , ­MoS2 , ­SiO2 , CNTs , and noted that production cost and stability are the main factors SiC. hindering its wide use. At the same time, nanofluids also Researchers have done a lot of research on the NMQL face huge challenges in different applications. In addition, cutting performance. Bai et al. added ­Al2O3 nanoparti- the synergistic effect of NMQL and cryogenic cutting tech- cles into cottonseed oil. The molecular structure of ­Al2O3has nology is also the direction of future development. a strong adsorption capacity, which can adsorb cottonseed oil extra. The A­ l2O3 nanoparticles are mainly spherical in shape with a small diameter (≤ 70 nm). And it can quickly 4.2.2 MQL of ionic liquid enter the cutting zone to form a thin lubricating oil film (Fig. 12a). Nanoparticles can fill the surface cavity of the Ionic liquids (ILs) are liquids at room temperature or near workpiece and repair the pits caused by friction on the work- room temperature and are completely composed of positive piece surface (Fig. 12b). Therefore, nanoparticles can reduce and negative ions. ILs have good thermal conductivity and friction wear and improve the surface smoothness of the are highly promising thermal conductivity medium. workpiece. Günan et al. studied the cutting performance Goindi et al. added a small amount of ILs to the veg- of ­Al2O3 nanofluids at 0.5 vol%, 1 vol%, and 1.5 vol%. No etable oil for cutting experiments. Although the content of adhesion wear was found when the concentration of A ­ l 2O 3 ILs is relatively low in vegetable oil, it significantly affects was 1 and 1.5 vol% in the milling process, and the higher the tribological performance of metal cutting in ordinary the concentration, the lighter the crater wear of the tooltip. carbon steel cutting experiments. Babu et al. turned Zhang et al. studied the effect of SiC nanofluid on Inconel 825 alloy inan ILs + MQL environment.The ILs the cutting performance of A ­ l2O3/TiC ceramic tools based exhibited excellent cutting performance under MQL condi- on NMQL. They found that theNMQL during high-speed tions. The surface roughness of the workpiece was reduced cutting reduced tool wear by 55.1%, cutting temperature by 88% and 75% compared with dry cutting and flood cut- by 41.5%, and surface roughness by 19.2%. Naresh Babu ting, respectively, and the cutting temperature was reduced et al. added graphene particles to oil to form nanoflu- by 49% and 74%, respectively. And the tool wear was the ids. Compared with dry turning and flood cutting, it was smallest under the condition of ILs + MQL. found that surface roughness was reduced by 85% and Due to the special physical and chemical properties, ILs 44%, respectively in NMQL turning of D3 steel, and the can form a thicker lubricating film. The lubricating film cutting temperature was reduced by 53% and 32%. Virdi withstandssliding friction at the tool-workpiece interface. At present, research on the performance of ILs as lubricating additives in MQL processing is still limited. As an advanced and green lubricant, ILs are the focus of future work to study the anti-friction mechanism from itsown microscopic level and to apply ILs in different fields. With the development of MQL, its improvement mainly focuses on the MQL synergistic technology. As shown in Table 2, various MQL synergistic technologies have their own excellent performance. However, the application of MQL under specified operating conditions still requires sys- tematic research. It is necessary to study the mechanism of lubrication and cooling of various synergistic technologies and form a database for the types of lubricating oils and the exploration rules of MQL parameters. At present, the technical research of CMQL and NMQL is more in-depth and has relatively wide application in engi- neering. In addition, researchers have conducted research on potential MQL technologies such as nanofluids ultrasonic Fig. 12  Schematic of lubrication at the milling interface atomization MQL and cryogenic nanofluids MQL. 2692 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Table 2  Application characteristics of MQL synergistic technology MQL synergistic technology Technical feature Application problem CA + MQL The CA is used as the transmission medium to further Requires high power and is accompanied by problems reduce the temperature of the cutting zone such as serious noise and difficulty in heat removal ScCO2 + MQL Can reduce the temperature of the cutting zone and The medium needs additional preparation, and there will control the concentration of lubricating oil be insufficient supply during the processing for a long time LN2 + MQL The lowest temperature medium that can be reached at The ­LN2 cost is high, and additional consumption costs present are required for storage, and the temperature of the transmission process is easy to be lost NMQL and ILs + MQL The formation of lubricating film provides better lubri- The preparation cost of additives is high and the stability cation performance is low 4.3 MQL atomization improvement adsorption in the machine tool and penetrates into the cut- ting zone. EMQL reduces the oil mist content in the external The traditional pneumatic atomization involves a large environment and exhibits alternative cutting performance. amount of energy exchange when the gas disperses the lubri- EMQL technology provides ideas for clean-cutting in the cating oil. The droplet size is different, which affects the new era. Due to the presence of charged droplets, EMQL penetration ability of the mist. In order to solve the above enhances the lubrication performance of the lubricating problems, researchers have developed electrostatic minimum medium and makes up for the limitations of poor film forma- quantity lubrication (EMQL) and ultrasonic atomization tion stability of ordinary cutting fluids. In the future, on the minimum quantity lubrication (UAMQL). basis of EMQL, nanofluids and low-temperature media will be added to integrate the advantages of various technologies. 4.3.1 EMQL The nozzle of the MQL equipment was improved to a 4.3.2 UAMQL charged nozzle, and corona discharge electrodes were placed at the nozzle. There is a corona discharge near the nozzle, The ultrasonic-enabled atomization method has also been which makes the droplets charged after gas atomization. developed. High-frequency vibration will cause the sur- Huang et al. studied the effect of the strength and polar- face of the cutting fluid medium to bulge and break to form ity of electrostatic voltage on the processing performance of micro-droplets. Hadad et al. designed a new type of EMQL. Researchers have found that voltage intensity and MQL nozzle based on ultrasonic vibration (Fig. 13). The polarity significantly affect machining performance. Com- new nozzle enhances the lubrication performance of MQL pared with traditional MQL, EMQL reduces surface rough- and improves the surface roughness of the workpiece in the ness by 6%. At the negative electrode, EMQL achieves better turning test of AISI 304L stainless steel. Gao et al. stud- performance at low voltage. But at positive polarity, EMQL ied the coupling effect of multi-angle two-dimensional ultra- achieves better performance at high voltage. During the sonic vibration of NMQL.The wettability of MQLoil mist friction process, EMQL makes the lubricating oil to more is greatly improved under the action of ultrasonic vibration, effectively penetrate the cutting interface. A mixed lubrica- and it leads to the improvement of the cutting performance tion layer is composed of a metal soap film and an oxide of MQL. Meng et al. compared the cutting performance film, and it prevents direct contact of rough peaks on the of Ti-6Al-4V in dry turning and ultrasonic vibrationMQL surface of the tool and workpiece. Liu et al. proposed a turning. Compared with dry cutting, the tool life by 1.6 times new machining method for Ti-6Al-4V alloy called “Cold Air and the surface roughness reduced by 47.6% under ultra- Electrostatic Minimum Quantity Lubrication (CAEMQL).” sonic vibration MQL conditions increased. Madarkar et al. CAEMQL has higher heat flux density and heat transfer carried out grinding experiments on Ti-6Al-4V alloy to coefficient. More cutting fluid penetrates into the cutting verify the performance of ultrasonic atomization of cutting zone due to the smaller particle size of charged droplets. fluid. They found through experiments that ultrasonic atomi- The cutting temperature of CAEMQL was the lowest, and zation can produce a large number of ultrafine droplets and it was 50.33%, 44.29%, and 13.23% lower than that of MQL, form a lubricating film at the grinding interface. Compared EMQL, and CAMQL, respectively. Lv et al. found that with dry grinding, the grinding force and normal grinding the adsorption capacity of S ­ iO2 droplets was greater than force under ultrasonic atomization conditions were reduced charged vegetable oil droplets. ­SiO2 is prone to electrostatic by 38% and 32%, respectively. The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2693 Fig. 13  Ultrasonic nozzle- MQL(UN-MQL) system. a, b Schematic and detailed design. c, d Manufactured, assembled, and sealed nozzle 2694 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 In summary, MQL synergistic technology can replace the designed an improved nozzle, as shown in Fig. 14. The traditional MQL processing method to a certain extent by improved nozzle can ensure the delivery of cutting fluid to virtue of its unique energy-increasing mechanism and excel- the entire grinding zone. Therefore, the improved nozzle lent heat transfer performance. EMQL is becoming more reduces the grinding temperature more than the traditional and more mature in theory, but atomization devices are only nozzle, with the maximum reduction of 6.5%. limited to the design and modification of nozzles. Different atomization devices have different atomization effects, and the complete atomization system should be designed accord- 5 MQL cutting performance analysis ing to actual processing needs. In the future, electrostatic atomization, pneumatic atomization, and ultrasonic atomi- Mechanical cutting performance can reflect the quality of zation will be integrated into a set of MQL devices, so the metal cutting. The cutting force and cutting temperature are processing performance of MQL will be greatly improved. generated by the relative motion between the cutting tool and the workpiece. Electric energy is converted into cutting 4.4 MQL hardware improvements energy, and the workpiece is removed. This process leads to cutting tool wear, workpiece residual stress, and workpiece Research on MQL mainly focuses on performance, and there surface roughness change. Especially for difficult-to-cut are relatively little research on MQL equipment. At present, materials, the particularity of their physical and chemical the improvement of MQL equipment is mainly focused on properties leads to the use of special cutting processes and the nozzle. Choosing a suitable nozzle can improve the lubrication systems to carry out cutting processing. As the quality of the cutting fluid sprayed into the cutting zone most widely used green energy-saving cutting technology,. In order to improve the injection pressure, the MQL MQL is widely used in the cutting of difficult-to-cut materi- nozzle is often designed as a tapered nozzle. This nozzle als. With the continuous progress of science and technol- has limitations such as high noise and reduced atomiza- ogy, research on the cutting performance under MQL is tion quality. Therefore, researchers have begun to conduct constantly deepening. This section summarizes the cutting research on the structural design of MQL nozzles. Pereira performance of difficult-to-cut materials under MQL. et al. developed two nozzle adapters. The first adapter has a gas convergence outlet, and the second adapter has 5.1 Cutting force a convergence-divergence outlet. The experiment showed the convergence-divergence adapter nozzle has a higher cut- The cutting force mainly comes from overcoming the elas- ting fluid flow rate than the convergent nozzle. This design tic–plastic deformation of the workpiece material and the is more suitable for mechanical machining. Sharmin et al. friction between the tool and the workpiece. Cutting force Fig. 14  a Conventional nozzle. b Modified nozzle The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2695 is an important indicator for measuring cutting performance When the feed rate is 10 mm/min, the radial cutting force. MQL will seriously reduce the cutting force due to the is reducedby 72% by the MQL, and the axial cutting force effect of lubricating oil on the cutting zone. is 35% compared with dry cutting. Sun et al. focused Research has shown that the feed rate has the greatest on the effects of MQL and MQL + water on cutting force. impact on cutting force, reaching 86.8%. Elbah et al. The cutting force under MQL and MQL + water conditions evaluated the performance of different machining decreased by 12.8% and 28.2% compared with dry cutting. environments (dry cutting, flood cutting, and MQL) with Naturally degradable oil molecules have hydrophilic groups experiments. The cutting force increases with the increase (anions) under the MQL + water. Oil molecules will adsorb of feed rate and cutting depth. On the other hand, the cut- side by side on the water surface and form a thin oil film. ting force decreases with the increase of cutting speed. The Under the forced action of compressed air, the oil mist is force decreases due to the increase in the temperature and sprayed into the cutting zone at a certain speed to achieve softness of the shear strength of the material in the cutting the purpose of cooling and removing chips. In order to pre- zone. Niu et al. milled Ti-6Al-4V alloy under ultrasonic dict the cutting force better, Shetty develops a system vibration MQL. As shown in Fig. 15, the increase in cutting with the response surface second-order model and JAVA speed intensifies the hardening of the workpiece at lower programming. For different process parameters in the cut- cutting speeds, and it results in an increase in cutting force. ting process, the cutting force for Ti-6Al-4V alloy is auto- As the cutting speed continues to increase, the cutting heat matically generated under MQL conditions. The predicted generated is higher. The hardness of the workpiece decreases cutting force values were relatively close to the predicted under the action of thermal softening, and it results in a values. Therefore, the developed cutting force prediction decrease in cutting force. Under the action of high-frequency system can analyze cutting force in a shorter time and at a tool vibration, the cutting fluid accelerates to penetrate into lower cost. the tool-workpiece contact interface and improves the anti- The MQL can significantly reduce cutting force during friction performance. the cutting process. It is because the oil mist forms a physi- Li et al. carried out milling experiments on Ti-6Al- cal film at the cutting interface, and it plays a role in lubricat- 4V alloy. The friction between the tool and the chip is ing and reducing friction. Especially the added nanoparticles reduced in the MQL, especially at low-speed cutting. to lubricating oil reduce cutting force obviously. The various Fig. 15  The main cutting force variation 2696 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 nanoparticles act as “rolling balls” at the cutting interface applied it to MQL. The inclusion of graphite in the cutting and make friction tend towards rolling friction. In addition, fluid increases the thermal conductivity of the cutting fluid, MQL can effectively reduce the adhesion of the tool. The especially in medium- to low-speed cutting. In addition, even large amount of cutting heat generated during the cutting if the cutting fluid evaporates rapidly at the cutting interface, process can cause changes in material hardness. Therefore, the graphite deposited on the tool can provide solid lubricant exploring the characteristic and removal mechanisms of and reduce the friction at the cutting interface. Makhesana different materials and establishing corresponding mapping et al. cut Inconel 690 and found the NMQL reduce the databases to provide data support for future material pro- cutting temperature by 36%, 7%, and 14% compared with cessing are two difficult work under MQL. dry cutting, flood cutting, and MQL. The addition of nano- particles increased thermal conductivity and improved the 5.2 Cutting temperature tribological conditions between the tool-workpiece and the tool-chip. The cutting heat mainly comes from the plastic deforma- Gupta et al. researchedthe high temperatures tion of the cutting layer material of the workpiece and the machining can lead to the evaporation of cutting fluid in the friction between the tool-chip and the tool-workpiece. The cutting zone during superalloy. The cooling degree of MQL research methods for cutting temperature mainly include the is not as good as that of ­LN2. Using ­LN2 to assist MQL is experimental method and numerical simulation method the best strategy to reduce cutting temperature. Liu et al. under MQL. Studying the cutting temperature is sig- also stated the cooling mechanism of CMQL. Low nificant for optimizing the cutting process and improving the temperature avoids rapid evaporation of cutting fluid and processing efficiency and quality under MQL. maintains the lubricating film for a longer time (as shown in Qin et al. turned TC11 alloy using various mate- Fig. 17a). Low-temperature media can maintain the cutting rial cutting tools under dry and MQL and analyzed the cut- zone temperature at a relatively low level and avoid oil film ting performance. The experimental results are shown in oxidation failure caused by high temperature (as shown in Fig. 16. No matter what kind of tool was used, the cutting Fig. 17b). temperature can be significantly reduced under MQL, andthe In recent years, researchers have conducted a large num- maximum reduction is 28.7%. ber of comparative experiments on the cutting temperature The proper use of nanoparticle concentration to enhanced under MQL. The cutting temperatures are all better than dry heat transfer is crucial. Amrita et al. added 0.3 wt% cutting, but their advantages are not significant compared nano-graphite to the cutting fluid to form nanofluids and with CMQL. Adding nanoparticles to MQL cutting fluid can Fig. 16  Cutting temperature comparison under dry and MQL conditions The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2697 Fig. 17  A representation of the effect of CMQL on the cutting zone. a The effect on viscosity. b The effect on the working of oil film significantly reduce cutting temperature and improve cutting efficiency of cutting tools is improved, and economic ben- performance. Currently, research on cutting temperature has efits are increased under MQL. shown that CMQL is most beneficial for reducing cutting Wika et al. studied the effect of ­scCO2 + MQL on temperature. tool wear in milling AISI 304L stainless steel. The experi- ment results show that the tool life under s­ cCO2 + MQL 5.3 Tool wear significantly improves cutting time. Liu et al. studied the effect of cutting parameters on tool wear under CMQL Tool wear is a major issue in the machining process. It and conducted turning experiments on AISI 304 stainless decreases tool life, results in poor machining quality, and steel. The experimental results show that the influences decreases productivity. Studies have shown tool failure of cutting speed, feed rate, and cutting depth on tool wear accounts for 20% of the downtime of the machining center, were 46.725%, 28.120%, and 6.810%. At low cutting speeds, which greatly increases the processing cost. There- adhesive wear was the main wear mechanism of cutting fore, studying tool wear is significant for improving machin- tools. When the cutting speed increases to 400 m/min, the ing quality and efficiency. By budgeting tool wear, the tool main mechanisms of tool wear are diffusion wear and abra- releases the maximum value and avoids the waste caused by sive wear. Ha et al. conducted milling experiments replacing the tool in advance. on Ti-6Al-4V alloy, and the experimental results are shown Silva et al. milled of UNS S32205 stainless steel in Fig. 18. The use of MQL and ­CO2 alone can effectively and pointed out that the MQL could reduce tool wear by 80 reduce tool wear, which was mainly caused by built-up edge to 90%. Khaliq et al. used a tungsten carbide-coated on the rack face of the tool. As shown in Fig. 18d, using cutting tool to mill Ti-6Al-4V alloy under dry cutting and ­CO2-assisted MQL cutting was the most effective method MQL. When the cutting speed was constant at 30 mm/min, to reduce tool wear. the wear of the flank face under MQL improved by 26.2% Nguyen et al. conducted dry cutting, MQL, and compared with dry cutting. When the tool speed is constant NMQL turning experiments of Ti-6Al-4V titanium alloy. at 35,000 RPM, the wear of the flank face is improved by They found the tool crescent pit wear in various machining 27.79% under MQL compared with dry cutting. Experiments environments. The use of NMQL can significantly reduce have shown that the MQL exhibits superior performance in tool wear and increase tool life by two times compared with tool wear compared with dry cutting. Szczotkarz et al. dry cutting. They found that the effectiveness of MQLwas studied the effect of cutting on tool wear under dry cutting decisively related to the nozzle orientation. Gupta et al. and MQL. Experiments showed that theMQL reduced tool analyzed the tool wear mechanism in MQL. Cutting wear by 21% compared with dry cutting. Da Silva et al. fluid with compressed air penetrates into the cutting zone milled AISI 1047 steel under three cooling meth- through the action of a capillary tube for heat transfer and ods: flood cutting, low flow rate cooling, and MQL. They friction reduction together. The pits and chipping were found found that higher machining length and material removal on the flank face of the tool under MQL. It is the result of rate can be achieved in MQL, and it reduces tool break- the combined action of abrasive wear, adhesive wear, and age and wear. Experiments have shown that the production diffusion wear. Sampaio et al. think the main reason 2698 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Fig. 18  Wear images of the cutting tool flank face accord- ing to the cutting fluid injection methods for tool wear is abrasive wear caused by particles released depends on the thermal stress generated during the cutting from the tool and workpiece. MQL can reduce the pres- process and decreases with the increase of cutting fluid ence of cutting interface particles. At the same time, MQL flow rate in the experiment. The depth and size of the maxi- changes the microstructure of the chip through cooling and mum residual compressive stress are greatly affected by the slows down tool wear. mechanical stress during processing. The penetration depth MQL not only reduces tool wear by affecting cutting heat of residual stress not only depends on the cutting force but but also removes particles and chips at the cutting interface also on the geometric shape of the tool. Sadeghifar et al. with high-pressure airflow reducing tool abrasive wear. The found that the residual stress decreased with the cut- analysis of cutting experiments can explain the mechanism ting speed, feed rate, and cutting depth decrease. of some tool wear. The tool wear is analyzed from the ther- Rajaguru et al. cut stainless steel in different envi- mal and mechanical coupling, and the explanation of tool ronments. In dry cutting, the severe friction of the cutting wear at the micro level is the focus of future research. zone resulted in high temperatures and significant tensile residual stress on the surface of the workpiece. In the lubri- 5.4 Residual stress cating environment, the residual tensile stress is reduced, and the decrease in temperature reduces the tensile stress Residual stress is an important factor to determine the fatigue generated on the surface of the workpiece due to the cool- life and surface integrity of the machined workpieces. ing and lubrication effects of the cutting zone. The differ- Machined workpieces with compressive residual stress have ence in residual stress between flood cutting and MQL can a longer lifespan than original workpieces without mechani- be attributed to the differences in mechanical and thermal cal processing. The occurrence of tensile residual stress con- loads generated in different machining directions. As shown tributes to the propagation of fatigue cracks and shortens in Fig. 19, the residual stress generated by dry cutting is the the fatigue life of the workpiece. This section mainly largest and the MQL is the smallest. summarizes the causes and influencing factors of cutting The different workpiece materials, processing environ- residual stress in MQL. ment, and cutting parameters make the experimental results Ji et al. conducted orthogonal turning experiments different. Khaliq et al. conducted milling experiments on AISI 4130 alloy steel in MQL. The residual stress mainly on Ti-6Al-4V titanium alloy in different environments. They The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2699 Fig. 19  Effect of coolant approaches on surface residual stress found that dry milling performed better than MQL in terms to introduce phase transition mechanisms to improve the of residual stress. de Paula Oliveira et al. found that residual stress model and further improve the accuracy of the cutting fluid provided by flood cutting can penetrate residual stress prediction. more into the cutting zone. A large amount of cutting fluid is beneficial to reduce harmful tensile residual stress. Com- 5.5 Surface quality pared with MQL, flood cutting improves the residual stress and provides longer cutting lengths. The good surface quality not only improves the appearance Some researchers have started to predict residual stresses and texture of the workpiece but also prolongs the lifes- of difficult-to-cut material under MQL with analytical meth- pan and performance of the workpiece. Cagan et al. ods. Ji et al. [125, 126] conducted a series of studies on the pointed out that MQL machining is currently the most relia- analytical model of cutting residual stress under MQL. The ble machining method in cutting Al7050-T6 alloy. It is envi- cutting force and cutting temperature were coupled into a ronmentally friendly and can provide better surface quality thermo-mechanical model to predict residual stress gener- for the workpiece. Tomaz et al. studied the relationship ated under lubrication conditions. The prediction model between cutting parameters and machined surface quality process is shown in Fig. 20. The residual stress in the model during flood cutting and MQL milling of maraging steel is a function of cutting parameters, tool geometry, material 300. Research has shown the feed rate was the most impor- properties, and MQL system parameters. Shao et al. tant milling parameter affecting the surface roughness. MQL proposed a physical model to predict grinding residual stress reduces the roughness by about 10% compared with flood under MQL. The mechanical and thermal stresses gener- cutting. They believed the MQL technology had certain ated by grinding were calculated using grinding force and advantages in milling martensitic steel. Praveen et al. temperature distribution inside the workpiece. Finally, the turned EN47 steel under MQL to study the effect of MQL stresses were coupled to the elastic–plastic sliding friction on the surface quality of the workpiece. Compared with dry calculation method to solve the residual stress. cutting, the surface quality of EN47 steel has been improved According to comprehensive literature, cutting force and by about 48.35% in MQL. Şahinoğlu cut AISI 52100 cutting temperature are the main factors affecting residual steel in different machining environments. They found that stress. The participation of MQL can affect the cutting MQL can reduce the roughness by reducing the vibration of force and cutting temperature during the cutting process. the cutting interface. At present, research on residual stress in MQL is limited Abbas et al. used dry cutting, MQL, and NMQL to mechanical and thermal effects. It is not considered that to mill AISI 316 alloy. The surface roughness under MQL the high temperature generated in the cutting zone may lead and ­Al2Q3 + MQL increased by 40% and 44%, respectively to a phase change of the workpiece material, resulting in compared with dry cutting. The MQL can reduce the adhe- additional residual stress. Therefore, future research needs sion effect of cutting tools and inhibit the growth of built-up 2700 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 Fig. 20  Flowchart of residual stress prediction model in MQL machining edges. The addition of A ­ l2Q3 particles increases the viscos- In addition to affecting the surface quality of the work- ity of the cutting fluid. The high-viscosity oil film further piece through cutting force and cutting heat, micro-lubrica- reduces the surface wear of the workpiece. Spherical nano- tion can also improve the surface finish of the workpiece by particles act as ball bearings at the cutting interface and have filling the micro-pits and cracks of the workpiece material a positive effect on surface roughness. Stachurski et al. with a lubricating film. Difficult-to-cut materials are often ground 20MnCr5 steel under conditions of flood cutting and prone to tool vibration and cutting oscillation during the MQL. They found that the surface roughness after MQL cutting process, which affect the surface quality of the work- was 20 ~ 47% lower than that of flood cutting (Fig. 21). The piece. MQL can improve the surface quality of the work- grinding fluid is sprayed into the grinding zone at high speed piece by reducing the vibration and resonance of the tool. in using MQL. The oil mist particles effectively enter the MQL is widely recognized as an environmentally friendly grinding interface and reduce the friction conditions in the and feasible cutting method. But there are different opinions grinding zone. on its machining performance. Some researchers have found Kadi et al. used the Taguchi method and response that the MQL can provide very good processing performance surface methodology for multi-response optimization. The. But some people also believe the MQL still has many effects of MQL and cutting parameters on the surface rough- shortcomings, especially in difficult-to-cut materials. ness of AISI 316 stainless steel turning were studied. The In general, there is a consensus that the machining perfor- highest flow rate (90 ml/h) was the most important factor mance of workpieces under MQL is better than dry cut- to reduce surface roughness, accounting for 81.88% of the ting. Residual stress, cutting temperature, cutting force, tool impact. wear, and surface roughness affect each other in the cutting The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 2701 Fig. 21  Value determining the roughness of ground surface with WET and MQL methods process. High cutting temperature and high cutting force will be a healthier and more environmentally friendly often accelerate tool wear and result in poor surface quality development trend for MQL. of the workpiece material. This is a direct reflection of the (2) External jet MQL is mostly used in turning, grinding, cutting process. MQL has been widely used in mechanical and low-speed milling. While internal supply MQL processing. Explaining the processing mechanism of MQL is more effective in drilling and high-speed milling. from the micro level and finding a breakthrough from the Parameters such as air pressure, flow rate, nozzle struc- principle are the key directions for the development of MQL. ture, nozzle distance, and angle have significant effects In practical applications, accurately selecting MQL param- on machining performance. Among the parameters, eters and cutting parameters to match them is the foundation air pressure has the greatest influence on MQL per- to apply MQL correctly. formance and directly affects the droplet size distribu- tion. There is a certain degree of matching between the parameters of the MQL system and the cutting param- 6 Conclusions and prospects eters. Each parameter has an optimal interval, and an optimal combination is between each parameter. Over the past decade, MQL has been proven as an effec- (3) The combination of MQL and other technologies sig- tive method to reduce cutting force and cutting temperature, nificantly improves the processing performance of improve workpiece surface quality, and extend tool life by a MQL. EMQL and UAMQL can effectively reduce the large number of literatures. In this paper, the development size of oil mist particles in the processing environment and improvement of MQL and the cutting performance of and enhance the stability of the lubricating film at the MQL are reviewed and summarized. The following conclu- cutting interface. NMQL changes the composition of sions can be drawn: the lubricating film so that the sliding friction becomes rolling friction, which significantly reduces the friction. (1) The popularization of MQL reduces the pollution to The use of CMQL greatly reduces the cutting tempera- the environment and the harm to human health. MQL ture and increases the viscosity of the lubricating oil. saves at least 15% of production costs compared with CMQL effectively combines the performance of low flood cutting. The usage amount of MQL cutting fluid temperature and MQL in processing, showing excellent is 20 ~ 200 ml/h, which is only one-thousandth of that overall performance. The improvement and develop- of flood cutting. The use of biodegradable lubricants ment of MQL have their own advantages and appli- 2702 The International Journal of Advanced Manufacturing Technology (2024) 133:2681–2707 cation problems. It is necessary to comprehensively base is established to realize the regulation of intelli- consider the cutting environment and select the appro- gent MQL technology under multiple parameters. priate MQL scheme to achieve the most cost-effective lubrication cutting scheme. (4) The cutting fluid sprayed with MQL is filled into the cutting interface by a capillary siphon to form a lubri- Author contribution All authors contributed to the study conception cating oil film. The use of vegetable oil can further and design. Material preparation, data collection, and analysis were reduce cutting force, cutting temperature, and tool performed by Donghui Li, Tao Zhang, Tao Zheng, Nan Zhao, and Zhen wear. The polar groups in the degradable vegetable oil Li. The first draft of the manuscript was written by Donghui Li and Tao molecules help to form a stable lubricating film. Exper- Zhang. All authors read and approved the final manuscript. iments show that castor oil has the best performance in Funding The authors would like to appreciate the support of the Tian- vegetable oil. jin City High School Science & Technology Fund Planning Project (5) Compared with dry cutting, MQL can reduce cut- (2017KJ111). ting force by 15 ~ 70%, reduce cutting temperature by Data availability All data generated or analyzed during this study are 5 ~ 30%, and reduce tool wear by 20 ~ 50%. MQL can included in this published article. improve the surface quality by 10 ~ 40%. The applica- tion of MQL improves the limitations of traditional cut- Declarations ting and effectively improves processing efficiency. Ethical approval The authors confirm that this work does not contain any studies with human participants performed by any of the authors. In recent years, MQL has achieved significant results in engineering manufacturing. But there are still certain limi- Conflict of interest The authors declare no competing interests. tations. Future research on MQL will mainly focus on the following aspects: (1) The incomplete theoretical system makes it difficult to References define various process parameters in the application 1. Singh R, Dureja JS, Dogra M (2019) Performance evaluation of MQL. In future research, the lubrication and cool- of textured carbide tools under environment-friendly minimum ing mechanism of MQL are expounded from the micro quantity lubrication turning strategies. J Braz Soc Mech Sci level. Exploring the essence of interface phenomena, 41:87. https://​doi.​org/​10.​1007/​s40430-​019-​1586-1 2. Carou D, Rubio EM, Davim JP (2015) A note on the use of including friction, wear, and lubricants is the method the minimum quantity lubrication (MQL) system in turn- to improve the performance and stability of MQL. ing. 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