# Sustainable Machining Using Eco-Friendly Cutting Fluids: A Review

Authors: Pankaj Kumar; Amit Kumar Jain; Prem Kumar Chaurasiya; Damodar Tiwari; Anitha Gopalan; Joshuva Arockia Dhanraj; Jenoris Muthiya Solomon; Aravinth Sivakumar; Karthikeyan Velmurugan; Johannex Fefeh Rushman
Journal: Advances in Materials Science and Engineering
 (2022)

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## Abstract

The base fluids of eco-friendly cutting fluids should contain some vegetable oil. Due to their eco-friendly, thermal, and tribological qualities, these types of machining fluids are becoming increasingly popular among researchers throughout the world. The authors summarized published research studies on the use of eco-friendly machining fluids (including nanofluids) in various metal removal processes such as turning, milling, grinding, and drilling in this review paper. The impact of several biodegradable oil-based machining fluids on performance metrics such as surface irregularity, machining force, tool wear, power demand, and temperature-induced during the machining process is also explored in this paper. According to the previous and current literature, using an eco-friendly nano machining fluid results in better surface features, less cutting tool wear, lower cutting force, less power required, and lower machining zone temperature during the machining operation due to superior cooling and lubrication properties.


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## Body

## 1. Introduction

Sustainability in the machining process is generally achieved by preserving the social, economic, environmental, and technological dimensions for a longer period of time. Sustainability is a new paradigm in manufacturing because of the fact that organizations face diverse challenges. Therefore, sustainability in manufacturing is the ability of the organization to fulfill the required demands without compromising the environment and destroying natural resources.Eco-friendly cutting fluids are nontoxic, environmentally friendly cutting fluids that are free of chemicals such as ammonium borohydride (amines), chlorine, and sulphur. It has superior properties in terms of corrosion resistance, effective lubrication, and reduced mist and sludge formation.Drivers of conventional manufacturing include cost, time, and quality whereas, modern manufacturing includes environmental-driven objectives in addition to cost, time, and quality. Major drivers of sustainability are market, technology, societal, and regulatory drivers as presented in Figure1.Figure 1
Major drivers of sustainability.Environment-driven objectives are attributed to low carbon emissions, minimizing utilization of natural resources and energy resources. These environment-driven objectives are added to the manufacturing system to minimize pollution and raw material usage, reduce energy intensity, and recycle or reuse waste. These attributes are put together to move towards sustainable manufacturing.Sustainable machining can be defined as a machining process that can be sustained for a longer duration of time with the same efficiency. It reduces waste and minimizes its environmental impact by conserving natural resources and energy. It is also known as a “green manufacturing process.” Sustainable or green manufacturing can be approached in terms of energy reduction, water reduction, emission reduction, the optimal supply pressure of the cutting fluids (at a pressure of 5.5 bar), cost minimization, safety maximization, and waste product reduction during a particular manufacturing practice [1–4]. Figure 2 demonstrates different elements of the sustainable manufacturing processes. The reduction of all these parameters should be implemented at the source for better effectiveness.Figure 2
Elements of sustainable manufacturing.Sustainable machining can be achieved by many approaches and techniques such as dry cutting, minimum quantity lubrication (MQL), use of vegetable oil-based cutting fluids, high-pressure coolants, cryogenic cooling, and hybrid cooling techniques as presented in Figure3.Figure 3
Sustainable machining approaches.Use of biodegradable cutting fluids in the machining is the approach for sustainable machining in a particular manufacturing organization. Application of biodegradable or eco-friendly cutting fluids leads to no release of harmful gases during the machining, and is harmless to the operator’s skin. Machine operator health is a big concern due to performing machining operations in the close vicinity of the machining zone which results in inhaling harmful gases released by the mineral-based cutting fluids. Therefore, many approaches have been implemented for the safe use of eco-friendly cutting fluids.Manufacturing environments face many challenges such as economic, social, environmental, and technological. Economic challenges comprise a shorter product life cycle, demand fluctuation, and product variety. Environment challenges mean climate change and the depletion of natural resources. It is another aspect that is enforced in manufacturing. Societal challenges include an aging workforce and the nonavailability of skilled manpower. Whereas, technological challenges attribute obsolesce to the technology used in a particular manufacturing organization. These different challenges put together result in different types of stresses, requirements, or needs in the manufacturing organization and these challenges in some sense force the organization to be more focused on sustainable development, where they would be looking at how to conserve the existing natural resources.Therefore, from this literature it can be concluded that manufacturing organizations face a wide range of sustainability-related challenges, necessitating the adoption of a new paradigm. In addition to cost, time, and quality, manufacturers in the modern era also have environmental goals in mind. Dry cutting, minimum quantity lubrication (MQL), vegetable oil-based cutting fluids, high-pressure coolants, cryogenic cooling, and hybrid cooling techniques are a few methods for achieving long-term sustainability in machining. Environmental, social, and technological issues all come into play in manufacturing.


## 2. Machining Fluids

The main objective of the application of machining fluids in different manufacturing processes is to remove the heat generated and to decrease the friction between the tool and workpiece [5, 6]. When the cutting fluid is sprayed into the clearance face, it cools more effectively, especially when the pressure is at least 300 kPa. Reduction in the heat produced in the metal removal processes will result in longer tools. The workpiece and tool have a longer life expectancy and are less distorted. In machining fluids, coolant and lubricant properties should be present [7]. Cooling properties of cutting fluids remove the heat created, while lubricating properties minimize friction between the tool and the workpiece. Performance, conditions, and maintainability are among the most important factors to consider while selecting a machining fluid [8]. Table 1 contains the information on these characteristics.Table 1
Basic parameters considered while selecting machining fluids.
Cutting fluidsPerformanceEnvironmentMaintainabilityProductivityHealthy safetyMix stabilityTool lifeWaste treatmentWater qualityEnergyRecyclabilityCorrosion sensitivityQualityReactivityCleanlinessCutting fluidsPerformanceEnvironmentMaintainabilityProductivityHealthy safetyMix stabilityTool lifeWaste treatmentWater qualityEnergyRecyclabilityCorrosion sensitivityQualityReactivityCleanliness


### 2.1. Preparation of Nano-Cutting Fluids

Preparation of eco-friendly cutting fluids requires base fluids, vegetable-based oil, surfactant, emulsifier, and additives. Generally, distilled water is used as the base fluid due to its highest specific heat capacity. Recently, some of the commonly used vegetable oils used for cutting fluids preparation include canola oil, cotton seed oil, ground nut oil, coconut oil, and sunflower oil [9]. The common types of surfactants used for cutting fluid are fatty acid, ester, alcohol, sorbitan, and phenol ethoxylate. An emulsifier is the most important component for the reparation of the cutting fluids. After blending with the base fluids, it ensures good lubricity, solubility, better thermal stability, and low foaming tendency. Commonly used emulsifiers include various fatty acid esters and ethers.Preparation of the vegetable oil-based cutting fluids starts with taking the required quantity of the base fluids, followed by mixing virgin vegetable oil in the required proportion with the base fluids. The emulsifier is added to this solution for proper mixing of the solute and solvent. Add the nanoparticles to the cutting fluid which enhances the properties of cutting fluids like thermal conductivity. The selected surfactant is added to the already prepared solution to lower the surface tension between the two liquids. At last, magnetic stirrer is used for the proper mixing of particles in the solution. The flowchart for the preparation of the vegetable oil-based cutting fluids is present in Figure4.Figure 4
Method for preparation of eco-friendly cutting fluids.


### 2.2. Testing and Characterization of Nano-Cutting Fluids

Testing and characterization of the cutting fluids include measurement of viscosity characteristics, activation energy, thermal gravimetric analysis, thermal conductivity, specific heat, bio-degradability test, corrosion test, wettability study, pH, density, flash point, and fire point of the cutting fluids.From these articles, it can be concluded that machining fluids reduce heat generated during operation by decreasing friction between tool and workpiece. The most important factors to consider are performance, conditions, and maintainability. For cutting fluid preparation, the emulsifier is one of the most critical components. Cutting fluids should possess a low foaming tendency, better thermal stability, and good lubricity. Cutting fluid properties such as thermal conductivity can be improved by adding nanoparticles.


## 2.1. Preparation of Nano-Cutting Fluids

Preparation of eco-friendly cutting fluids requires base fluids, vegetable-based oil, surfactant, emulsifier, and additives. Generally, distilled water is used as the base fluid due to its highest specific heat capacity. Recently, some of the commonly used vegetable oils used for cutting fluids preparation include canola oil, cotton seed oil, ground nut oil, coconut oil, and sunflower oil [9]. The common types of surfactants used for cutting fluid are fatty acid, ester, alcohol, sorbitan, and phenol ethoxylate. An emulsifier is the most important component for the reparation of the cutting fluids. After blending with the base fluids, it ensures good lubricity, solubility, better thermal stability, and low foaming tendency. Commonly used emulsifiers include various fatty acid esters and ethers.Preparation of the vegetable oil-based cutting fluids starts with taking the required quantity of the base fluids, followed by mixing virgin vegetable oil in the required proportion with the base fluids. The emulsifier is added to this solution for proper mixing of the solute and solvent. Add the nanoparticles to the cutting fluid which enhances the properties of cutting fluids like thermal conductivity. The selected surfactant is added to the already prepared solution to lower the surface tension between the two liquids. At last, magnetic stirrer is used for the proper mixing of particles in the solution. The flowchart for the preparation of the vegetable oil-based cutting fluids is present in Figure4.Figure 4
Method for preparation of eco-friendly cutting fluids.


## 2.2. Testing and Characterization of Nano-Cutting Fluids

Testing and characterization of the cutting fluids include measurement of viscosity characteristics, activation energy, thermal gravimetric analysis, thermal conductivity, specific heat, bio-degradability test, corrosion test, wettability study, pH, density, flash point, and fire point of the cutting fluids.From these articles, it can be concluded that machining fluids reduce heat generated during operation by decreasing friction between tool and workpiece. The most important factors to consider are performance, conditions, and maintainability. For cutting fluid preparation, the emulsifier is one of the most critical components. Cutting fluids should possess a low foaming tendency, better thermal stability, and good lubricity. Cutting fluid properties such as thermal conductivity can be improved by adding nanoparticles.


## 3. Application of Vegetable Oil-Based Cutting Fluids in Machining

Vegetable oil-based machining fluids are the cutting fluids that are prepared from plant oils, water, and air, or other raw ingredients [10, 11]. Biodegradable machining fluid is used for cooling and lubrication mechanisms, particularly for metal removal processes. The main aim of the utilization of these fluids is to decrease harmful gases released during machining operations and to increase biodegradability [12–14]. In addition, these machining fluids keep the works and tools at a stable temperature, increase tool life, and prevent rust formation. Eco-friendly cutting fluids are highly biodegradable and have no adverse environmental impact [15, 16]. Some of the common vegetable-based cutting oils are cottonseed, groundnut, coconut, sesame, canola, and soybean [17–21]. Table 2 lists the physical characteristics of cottonseed and groundnut oil.Table 2
Physical characteristics of cottonseed and groundnut oil [14].
ParametersGroundnut oilCottonseed oilFlash point320°C312°CFire point334°C360°CKinematic viscosity57.4 cSt31.347 cStCalorific value39.65 MJ/kg39.27 MJ/kgAuto-ignitionNonNonDensity923.33 kg/m3921.50 kg/m3


### 3.1. Turning

Sustainability and energy analysis during dry turning operations were investigated [22]. The author has reported that the exergy loss reduces with an increase in the machining speed until it attains the least value. The optimal values of machining conditions were achieved with minimum energy consumption and exergy loss. However, the author [23] presented optimal machining conditions to minimize the power required in the metal removal process. It is found that the cutting tool has to be carefully chosen based on the power required and the cutting velocity of the tool and the properties of the tool material so that the energy consumption can be reduced.Researcher [24] performed a machining operation in the turning of Haynes 25 super alloy and concluded how to decrease the amount of lubrication used in machining with good surface roughness and good machining capability at higher cutting speeds. Selection of appropriate machining fluids to diminish the influence of heat released during machining for better tool life, less surface irregularity, and improved accuracy is an important aspect in traditional machining processes [25, 26]. In addition, the author has presented that the metal removal rate is more at higher values of the machining parameters. Whereas, the effects of the cutting fluids on the environment and operators’ health are presented [27]. In this article, a model for the preparation of cutting fluids and their behavior along with how to decrease the flow of machining fluids during different cutting operations is discussed.Vegetable oil-based metal working fluids have been used to study performance in terms of cutting force, work piece surface polish, tool wear, and cutting zone temperature in the machining of various materials [28]. This article summarizes that eco-friendly cutting fluids have similar performance as metal working fluids. The use of different percentages of additives mixed with cutting fluids and dry cutting fluids was investigated. It is observed that the performance of canola oil-based machining fluid was superior to that of refined sunflower oil while turning AISI 304L [29].The use of coconut oil-based machining fluid while turning SS304 reported and estimated both the tool wear and surface irregularity. The comparison was made by using the coconut oil-based machining fluid as an emulsion and also as a neat machining oil. They observed that emulsion gives better results than straight cutting oil by reducing tool wear and increasing surface smoothness. The coconut oil-based machining fluid also outperformed the neat cutting oil and conventional soluble oil in terms of reduction of machining force and temperature [30].Eco-friendly cutting fluid is prepared using jatropha oil and modified in its chemical structure by the transesterification process using various concentrations of jatropha methyl esters [31]. The basic fluid properties were tested in terms of viscosity, density, and lubrication properties. These fluids were used during turning different steels and their performances were compared with synthetic fluids. They also found that modified oil reduces the cutting forces and temperature to a great extent. Whereas, researcher [32] performed investigation on jatropha and Pongamia oil machining fluids in the turning of AA 6061. This investigation reported that Pongamia oil-based machining fluid can be used for a better surface finish at lower cutting speeds, whereas jatropha oil-based cutting fluids at high speeds.Different sustainable machining fluids were prepared using oils such as coconut, sunflower, rapeseed, palm oil, and high Erucic rapeseed. The physical properties such as melting point, pour point, kinematic viscosity, oxidation stability, and lubricity were investigated and reported that low frictional values were obtained for naturally derived vegetable oils as compared to conventional fluids [33]. This article also reported that cutting fluids using vegetable oils have low cutting forces during machining.The researcher [34] conducted an experimental investigation of the influence of water-miscible vegetable oil-based machining fluid on the life of the cutting tool during machining of Ti6Al4V. This paper reported that the wear of the cutting tool can be decreased by maintaining a low machining speed, feed rate, depth of cut, and cutting fluid concentration of 10%. Many researchers [35–38] conducted a comparative study of mineral oil-based machining fluid with vegetable oil-based fluid and found that traditional machining fluid can be substituted by vegetable-based machining fluids because mineral cutting fluids are toxic and harmful to aquatic life during disposal of cutting fluid.An investigation into the machining of the AISI4340 using various machining fluids like canola oil, coconut oil, and soybean oil was carried out. It is observed that canola oil is a superior machining fluid in comparison to coconut and soybean oil due to reduced wear and increased life of the cutting tool used in the machining operation [39, 40]. Whereas the authors [41, 42] performed a study on turning operation of AISI4340 using Karanja oil-based machining fluids and reported that the chip thickness and tool wear decreased in comparison with the traditional machining fluids. Moreover, a comparative study using biodegradable and traditional machining fluids in the turning of AISI 1050 steel was performed. It is reported that the vegetable oil-based machining fluid accomplished superior cutting force during machining and wettability angle [43]. However, researchers [44, 45] investigated to estimate the influence of mixing of solid lubricant in vegetable-based machining fluid while machining Inconel 718. The author has observed that the mixing of MoS2 enhances tool life to a great extent and also enhances the machined surface features with a lower value of cutting forces during machining. Researchers [46, 47] discussed several aspects of the turning process, such as surface quality and tool life, that can be improved with the MQL system. These articles explain MQL techniques by implementing them. It could be beneficial to the industry in terms of cost, environmental impact, and safety, especially for metalworking companies.From this study, it can be concluded that sustainability and exergy analysis during dry turning operations show that the exergy loss reduces with an increase in the machining speed until it attains the least value. The wear of the cutting tool can be decreased by maintaining a low machining speed, feed rate, depth of cut, and cutting fluid concentration of 10%. Traditional machining fluids can be substituted by vegetable-based machining fluids because mineral cutting fluids are toxic and harmful to aquatic life.


### 3.2. Milling

The influence of various input parameters on the machining force and tool life in the milling of Inconel 718 under dry and MQL conditions was examined [48, 49]. It is observed that with the application of the MQL technique during the machining operation, a remarkable improvement in the cutting force is exerted and the tool life is extended. The author also presented that the MQL technique with biodegradable machining fluids can be a substitute for dry machining.Kuram et al. [50] investigated machinability during milling of AISI 304 in terms of specific energy, surface irregularity, and life of the cutting tool. The author has developed a mathematical model to optimize specific energy, surface irregularity, and life of the cutting tool and concluded that these prepared machining fluids can be utilized as a replacement to the traditional machining fluids in terms of performance and environmental impact. Burton et al. [51] investigated the performance of vegetable-based machining fluids and observed less surface irregularity, cutting force, and chip thickness as compared to traditional machining fluids. Whereas, the influence of various types of vegetable oil-based machining fluids such as sunflower, coconut, palm, and soybean oil in comparison with conventional cutting fluids in the milling of 7075–T6 hybrid aluminum metal matrix composite was explored [52]. It is reported that palm oil-based machining fluid results in lower cutting force and minimum vibration in comparison with other types of biodegradable machining fluids. Moreover, a comparative study on the use of different biodegradable oil-based machining fluids in the milling of AISI 1045 steel under the MQL technique was performed [53].Therefore, it is concluded that the MQL technique with biodegradable machining fluids can be a substitute for dry machining. Cottonseed and canola oil-based machining fluids have better cooling ability and higher tool life along with no environmental impact.


### 3.3. Grinding

Alves and Oliveira et al. [54] performed grinding operations on SAE 8640 with a vitrified CBN wheel. It was found that wheel wear and machined surface irregularity were less by using biodegradable machining fluid in comparison with conventional fluid. The chemical analysis of the formulated fluid shows that it is nontoxic and biodegradable with no corrosion inhibiting characteristics. The influence of various machining fluids during surface grinding of Ti-6Al-4V, WT-22, and TIGER 5 was performed [55]. Various machining oils include emulsion, oil, dry grinding, propylene glycol, micro-3000, eco cut Mikro 82, and bio cut 3000. The author has concluded that by using propylene glycol, cutting fluid is easily accessible, less harmful, environmentally friendly, and has a lower value of cutting force with less surface damage and deformation. Whereas, Wang et al. [56] investigated the surface grinding of nickel-based alloy GH4169 using several biodegradable machining fluids such as soybean, peanuts, maize, rapeseed, palm, castor, and sunflower oil. The author has reported that castor oil-based cutting fluid results in excellent surface morphology and the least surface irregularity (Ra = 0.366 and RSM = 0.324) with less friction and specific grinding energy.A comparative study of the surface grinding of Ti6Al4V using dry and biodegradable machining fluids was carried out and concluded that vegetable-based fluids result in superior surface quality than dry grinding with the least value of Ra at various grinding depths [57]. In addition, the author has also reported that surface irregularities such as side flow, plastic deformation, and redeposition exist in dry and fluid grinding.Using biodegradable machining fluids such as propylene glycol, the cutting fluid is less harmful and environmentally friendly. It has a lower value of cutting force with less surface damage and deformation. It can also be concluded that vegetable-based fluids result in superior surface quality, less friction, and specific grinding energy.


### 3.4. Drilling

From the previous investigations, it was observed that the chips removal from inside the drilled hole had difficulties. Moreover, the cutting fluids also extend the life of tools and improve the efficiency of manufacturing processes by cooling and lubricating the work surface. Previous research articles also reported that better dimensional precision and quality of the surface can be produced. A comparative study to estimate the performance of machining fluids in the drilling of AA1050 and turning of AA 6262-T6 aluminum alloy was carried out [58]. It is reported that during the machining of AA 1050-O aluminum, the increasing flow rate of the mist results in higher torque and lower feed force while surface finish remains unaffected. However, in the turning of AA 6162-T6 aluminum alloy, better machinability was seen such as lower surface irregularity and machining force at higher cutting speeds with lower values of feed rate and depth of cut. However, Bhowmick and Alpas [59] carried out a comparative study on the drilling of Al–6% Si (319 Al) alloy under MQL and conventional lubrication techniques. The experimental result shows that under the MQL technique, the drilling torque is reduced significantly as compared to conventional lubrication techniques. Whereas, Kuram et al. [60] performed a comparative experimental investigation using biodegradable and conventional machining fluids to estimate cutting force and surface irregularity in the drilling of stainless steel 304 (SS304) with an HSS tool. It is reported that the application of biodegradable cutting fluids results in lower values of thrust force, surface roughness, and negligible tool wear as compared to conventional cutting fluids. Sharma and Sidhu [61] investigated drilling operations on AISI D2 steel using biodegradable machining fluids under dry and near-dry machining techniques. The presented results indicate that near-dry machining has enhanced machinability than dry drilling in terms of surface irregularity and tool work interface temperature. In addition, we used neem and Mahua oil-based machining fluids in the drilling of AISI 304L and also performed statistical analysis to obtain the optimal values of surface irregularity, thrust force, and temperature in machining. These parameters were found to be optimum in Mahua-based cutting fluid [62]. Whereas, Kuram and Ozcelik [63] performed prediction of surface irregularity and machining force in the drilling of AISI 304 with biodegradable machining fluids using fuzzy logic and regression model. The results were compared with the established fuzzy logic model, regression model, and experimental values and reported that the fuzzy logic model is more accurate than the regression model. Therefore, the fuzzy logic model can be recommended for the prediction of the surface irregularity and thrust force. Whereas a comparison of palm oil and synthetic ester for drilling Ti6Al4V using the MQL technique revealed that palm oil outperformed synthetic ester in terms of specific cutting energy, power, and cutting force [64]. As a result, utilizing the MQL approach, palm oil can be employed as an alternative to a synthetic ester.The removal of chips from the drilled hole has been a problem in the past. In order to extend the life of the tools and increase the efficiency of manufacturing processes, cutting fluids must be chosen carefully. Aside from these advantages, cutting fluids with proper machinability have lower surface irregularity and machining force at higher cutting speeds with lower values of feeding rate, cutting speed, and depth of cut.


## 3.1. Turning

Sustainability and energy analysis during dry turning operations were investigated [22]. The author has reported that the exergy loss reduces with an increase in the machining speed until it attains the least value. The optimal values of machining conditions were achieved with minimum energy consumption and exergy loss. However, the author [23] presented optimal machining conditions to minimize the power required in the metal removal process. It is found that the cutting tool has to be carefully chosen based on the power required and the cutting velocity of the tool and the properties of the tool material so that the energy consumption can be reduced.Researcher [24] performed a machining operation in the turning of Haynes 25 super alloy and concluded how to decrease the amount of lubrication used in machining with good surface roughness and good machining capability at higher cutting speeds. Selection of appropriate machining fluids to diminish the influence of heat released during machining for better tool life, less surface irregularity, and improved accuracy is an important aspect in traditional machining processes [25, 26]. In addition, the author has presented that the metal removal rate is more at higher values of the machining parameters. Whereas, the effects of the cutting fluids on the environment and operators’ health are presented [27]. In this article, a model for the preparation of cutting fluids and their behavior along with how to decrease the flow of machining fluids during different cutting operations is discussed.Vegetable oil-based metal working fluids have been used to study performance in terms of cutting force, work piece surface polish, tool wear, and cutting zone temperature in the machining of various materials [28]. This article summarizes that eco-friendly cutting fluids have similar performance as metal working fluids. The use of different percentages of additives mixed with cutting fluids and dry cutting fluids was investigated. It is observed that the performance of canola oil-based machining fluid was superior to that of refined sunflower oil while turning AISI 304L [29].The use of coconut oil-based machining fluid while turning SS304 reported and estimated both the tool wear and surface irregularity. The comparison was made by using the coconut oil-based machining fluid as an emulsion and also as a neat machining oil. They observed that emulsion gives better results than straight cutting oil by reducing tool wear and increasing surface smoothness. The coconut oil-based machining fluid also outperformed the neat cutting oil and conventional soluble oil in terms of reduction of machining force and temperature [30].Eco-friendly cutting fluid is prepared using jatropha oil and modified in its chemical structure by the transesterification process using various concentrations of jatropha methyl esters [31]. The basic fluid properties were tested in terms of viscosity, density, and lubrication properties. These fluids were used during turning different steels and their performances were compared with synthetic fluids. They also found that modified oil reduces the cutting forces and temperature to a great extent. Whereas, researcher [32] performed investigation on jatropha and Pongamia oil machining fluids in the turning of AA 6061. This investigation reported that Pongamia oil-based machining fluid can be used for a better surface finish at lower cutting speeds, whereas jatropha oil-based cutting fluids at high speeds.Different sustainable machining fluids were prepared using oils such as coconut, sunflower, rapeseed, palm oil, and high Erucic rapeseed. The physical properties such as melting point, pour point, kinematic viscosity, oxidation stability, and lubricity were investigated and reported that low frictional values were obtained for naturally derived vegetable oils as compared to conventional fluids [33]. This article also reported that cutting fluids using vegetable oils have low cutting forces during machining.The researcher [34] conducted an experimental investigation of the influence of water-miscible vegetable oil-based machining fluid on the life of the cutting tool during machining of Ti6Al4V. This paper reported that the wear of the cutting tool can be decreased by maintaining a low machining speed, feed rate, depth of cut, and cutting fluid concentration of 10%. Many researchers [35–38] conducted a comparative study of mineral oil-based machining fluid with vegetable oil-based fluid and found that traditional machining fluid can be substituted by vegetable-based machining fluids because mineral cutting fluids are toxic and harmful to aquatic life during disposal of cutting fluid.An investigation into the machining of the AISI4340 using various machining fluids like canola oil, coconut oil, and soybean oil was carried out. It is observed that canola oil is a superior machining fluid in comparison to coconut and soybean oil due to reduced wear and increased life of the cutting tool used in the machining operation [39, 40]. Whereas the authors [41, 42] performed a study on turning operation of AISI4340 using Karanja oil-based machining fluids and reported that the chip thickness and tool wear decreased in comparison with the traditional machining fluids. Moreover, a comparative study using biodegradable and traditional machining fluids in the turning of AISI 1050 steel was performed. It is reported that the vegetable oil-based machining fluid accomplished superior cutting force during machining and wettability angle [43]. However, researchers [44, 45] investigated to estimate the influence of mixing of solid lubricant in vegetable-based machining fluid while machining Inconel 718. The author has observed that the mixing of MoS2 enhances tool life to a great extent and also enhances the machined surface features with a lower value of cutting forces during machining. Researchers [46, 47] discussed several aspects of the turning process, such as surface quality and tool life, that can be improved with the MQL system. These articles explain MQL techniques by implementing them. It could be beneficial to the industry in terms of cost, environmental impact, and safety, especially for metalworking companies.From this study, it can be concluded that sustainability and exergy analysis during dry turning operations show that the exergy loss reduces with an increase in the machining speed until it attains the least value. The wear of the cutting tool can be decreased by maintaining a low machining speed, feed rate, depth of cut, and cutting fluid concentration of 10%. Traditional machining fluids can be substituted by vegetable-based machining fluids because mineral cutting fluids are toxic and harmful to aquatic life.


## 3.2. Milling

The influence of various input parameters on the machining force and tool life in the milling of Inconel 718 under dry and MQL conditions was examined [48, 49]. It is observed that with the application of the MQL technique during the machining operation, a remarkable improvement in the cutting force is exerted and the tool life is extended. The author also presented that the MQL technique with biodegradable machining fluids can be a substitute for dry machining.Kuram et al. [50] investigated machinability during milling of AISI 304 in terms of specific energy, surface irregularity, and life of the cutting tool. The author has developed a mathematical model to optimize specific energy, surface irregularity, and life of the cutting tool and concluded that these prepared machining fluids can be utilized as a replacement to the traditional machining fluids in terms of performance and environmental impact. Burton et al. [51] investigated the performance of vegetable-based machining fluids and observed less surface irregularity, cutting force, and chip thickness as compared to traditional machining fluids. Whereas, the influence of various types of vegetable oil-based machining fluids such as sunflower, coconut, palm, and soybean oil in comparison with conventional cutting fluids in the milling of 7075–T6 hybrid aluminum metal matrix composite was explored [52]. It is reported that palm oil-based machining fluid results in lower cutting force and minimum vibration in comparison with other types of biodegradable machining fluids. Moreover, a comparative study on the use of different biodegradable oil-based machining fluids in the milling of AISI 1045 steel under the MQL technique was performed [53].Therefore, it is concluded that the MQL technique with biodegradable machining fluids can be a substitute for dry machining. Cottonseed and canola oil-based machining fluids have better cooling ability and higher tool life along with no environmental impact.


## 3.3. Grinding

Alves and Oliveira et al. [54] performed grinding operations on SAE 8640 with a vitrified CBN wheel. It was found that wheel wear and machined surface irregularity were less by using biodegradable machining fluid in comparison with conventional fluid. The chemical analysis of the formulated fluid shows that it is nontoxic and biodegradable with no corrosion inhibiting characteristics. The influence of various machining fluids during surface grinding of Ti-6Al-4V, WT-22, and TIGER 5 was performed [55]. Various machining oils include emulsion, oil, dry grinding, propylene glycol, micro-3000, eco cut Mikro 82, and bio cut 3000. The author has concluded that by using propylene glycol, cutting fluid is easily accessible, less harmful, environmentally friendly, and has a lower value of cutting force with less surface damage and deformation. Whereas, Wang et al. [56] investigated the surface grinding of nickel-based alloy GH4169 using several biodegradable machining fluids such as soybean, peanuts, maize, rapeseed, palm, castor, and sunflower oil. The author has reported that castor oil-based cutting fluid results in excellent surface morphology and the least surface irregularity (Ra = 0.366 and RSM = 0.324) with less friction and specific grinding energy.A comparative study of the surface grinding of Ti6Al4V using dry and biodegradable machining fluids was carried out and concluded that vegetable-based fluids result in superior surface quality than dry grinding with the least value of Ra at various grinding depths [57]. In addition, the author has also reported that surface irregularities such as side flow, plastic deformation, and redeposition exist in dry and fluid grinding.Using biodegradable machining fluids such as propylene glycol, the cutting fluid is less harmful and environmentally friendly. It has a lower value of cutting force with less surface damage and deformation. It can also be concluded that vegetable-based fluids result in superior surface quality, less friction, and specific grinding energy.


## 3.4. Drilling

From the previous investigations, it was observed that the chips removal from inside the drilled hole had difficulties. Moreover, the cutting fluids also extend the life of tools and improve the efficiency of manufacturing processes by cooling and lubricating the work surface. Previous research articles also reported that better dimensional precision and quality of the surface can be produced. A comparative study to estimate the performance of machining fluids in the drilling of AA1050 and turning of AA 6262-T6 aluminum alloy was carried out [58]. It is reported that during the machining of AA 1050-O aluminum, the increasing flow rate of the mist results in higher torque and lower feed force while surface finish remains unaffected. However, in the turning of AA 6162-T6 aluminum alloy, better machinability was seen such as lower surface irregularity and machining force at higher cutting speeds with lower values of feed rate and depth of cut. However, Bhowmick and Alpas [59] carried out a comparative study on the drilling of Al–6% Si (319 Al) alloy under MQL and conventional lubrication techniques. The experimental result shows that under the MQL technique, the drilling torque is reduced significantly as compared to conventional lubrication techniques. Whereas, Kuram et al. [60] performed a comparative experimental investigation using biodegradable and conventional machining fluids to estimate cutting force and surface irregularity in the drilling of stainless steel 304 (SS304) with an HSS tool. It is reported that the application of biodegradable cutting fluids results in lower values of thrust force, surface roughness, and negligible tool wear as compared to conventional cutting fluids. Sharma and Sidhu [61] investigated drilling operations on AISI D2 steel using biodegradable machining fluids under dry and near-dry machining techniques. The presented results indicate that near-dry machining has enhanced machinability than dry drilling in terms of surface irregularity and tool work interface temperature. In addition, we used neem and Mahua oil-based machining fluids in the drilling of AISI 304L and also performed statistical analysis to obtain the optimal values of surface irregularity, thrust force, and temperature in machining. These parameters were found to be optimum in Mahua-based cutting fluid [62]. Whereas, Kuram and Ozcelik [63] performed prediction of surface irregularity and machining force in the drilling of AISI 304 with biodegradable machining fluids using fuzzy logic and regression model. The results were compared with the established fuzzy logic model, regression model, and experimental values and reported that the fuzzy logic model is more accurate than the regression model. Therefore, the fuzzy logic model can be recommended for the prediction of the surface irregularity and thrust force. Whereas a comparison of palm oil and synthetic ester for drilling Ti6Al4V using the MQL technique revealed that palm oil outperformed synthetic ester in terms of specific cutting energy, power, and cutting force [64]. As a result, utilizing the MQL approach, palm oil can be employed as an alternative to a synthetic ester.The removal of chips from the drilled hole has been a problem in the past. In order to extend the life of the tools and increase the efficiency of manufacturing processes, cutting fluids must be chosen carefully. Aside from these advantages, cutting fluids with proper machinability have lower surface irregularity and machining force at higher cutting speeds with lower values of feeding rate, cutting speed, and depth of cut.


## 4. Application of Eco-Friendly Nanofluids

These cutting fluids are made up of nanoparticles and traditional cutting fluids. By incorporating nanoparticles into cutting fluids, features such as wettability, convective heat transfer coefficient, and lubricating qualities are improved. High thermal conductivity, a small thermal expansion coefficient, good heat carrying capacity, good wear resistance, and minimal friction are all characteristics of nano cutting fluids. Nanoparticle additions also increase load-carrying capacity, reduce wear, and reduce friction. Metal oxides, nitrides, ceramics, silicates, carbides, and nonoxide ceramics are some of the most frequent nanoparticles. Heat transfer is improved, wettability is improved, and tribiological characteristics are improved with nano-fluids.


### 4.1. Turning

[65] carried out an experimental study on the thermal behaviour of graphene oxide enhanced nano-fluids. The thermal conductivity of the graphene oxide nano machining fluid increased by 71 percent when compared to traditional machining fluids due to improved heat transfer capabilities, according to the author. Jamil et al. [66] employed a vegetable-based hybrid nano-fluid including Al2O3 and CNT nanoparticles that was combined with vegetable oil. In comparison to cryogenic cooling, average surface irregularity and cutting force were lowered by 8.72 percent and 11.8 percent, respectively, according to the stated data. Sahu et al. [67] employed a mixed nano-fluid of multiwalled carbon nanotubes (MWCNTs) to evaluate the performance of Ti6Al4V turning. In comparison to traditional cooling techniques, the performance of eco-friendly nano-cutting reveals reduced chip thickness as well as improved cooling and lubricating capabilities [68, 69]. Padmini et al. [70, 71] evaluated machining force, surface irregularity, temperature, and tool wear during machining of AISI 1045 steel using nano-molybdenum di-sulfide (nMoS2) in coconut (CC), sesame (SS), and canola (CAN) oil-based cutting fluids. In comparison to dry machining, the author claims that cutting force, surface irregularity, temperature, and tool wear are reduced by 37 percent, 39 percent, 21 percent, and 44 percent, respectively. Using a turning operation, the properties of different nano-cutting fluids, including aluminium oxide (Al2O3), molybdenum disulfide (MoS2), and graphite, were examined under minimal quantity lubrication (MQL) conditions on Inconel-800 alloy. Surface roughness, cutting forces, and tool wear were all used to evaluate the machining process’ performance. The addition of MoS2 to cutting fluids is said to improve the cooling and lubrication of the workpiece and tool during the machining process [72]. Under the MQL approach, the effect of biodegradable nano-machining fluids on machining force, surface irregularity, and tool wear in the turning of Inconel superalloy is investigated. In comparison to conventional machining fluids, MoS2 and graphite-based nano-fluids produce better outcomes at greater cutting rates, according to this study. Yildirim et al. [73] sought to investigate the impact of dry, MQL, and nano-MQL cooling and lubrication methods on surface irregularity, tool life, tool wear, and temperature in the turning of Inconel 625. The author claims that adding nanoparticles into cutting fluids significantly enhances the previously listed performance characteristics.However, the author [74, 75] discusses his research into the production of carbon nanotube-based nanofluids for improved machining efficiency over traditional cutting fluids. Different nanofluid samples were produced, and their appropriateness was assessed. The prepared carbon nanotube-based cutting fluids have higher thermal conductivity and reduced viscosity, according to the findings of this study. In addition, the author conducted comparison research by milling 42CrMo4 hardened steel utilizing a dry cutting, with conventional and nanofluid. Cutting performance was enhanced by a reduction of 29 percent in cutting temperature, 34 percent in surface roughness, 33 percent in cutting force, and 39 percent in tool wear when nano-cutting fluids were used. The impact of various vegetable-based nano machining fluids on tool wears is shown in Figure 5.Figure 5
Influence of different types of vegetable-based nano machining fluids on tool wear [75].


### 4.2. Milling

To assess tool wear and surface irregularity, Uysal et al. [76] milled AISI 420 steels with vegetable-based hybrid nanomachining fluids. It is reported that less good surface finish and less tool wear were observed upon application of the optimal supply of the cutting fluids during the machining operation. In contrast, Uysal [77] investigated tool failure in the milling of SS304 utilizing biodegradable nano machining fluid. It can be inferred that by using nano machining fluid, many forms of tool wear are greatly decreased. However, Prasad et al. [78] investigated the effects of nano-cutting fluids on surface irregularity and interface temperature to determine ideal values. The Taguchi technique was used to determine the ideal values for these parameters, and the reported optimal parameters are 510 rpm spindle speed, 16 mm/min feed rate, and 0.6 mm depth of cut for minimal surface irregularity. Figure 6 depicts the effects of various machining fluids on tool wear.Figure 6
Effects of various machining fluids on tool wear [78].Moreover, Settu and Nandagopal [79] noted that the current research investigates the machining of EN8 steel utilizing various cooling and lubrication techniques such as without using cutting fluids, with oil mixed in water, and eco-friendly nano-cutting fluids. The nanofluids were produced by the mixing of refined corn-oil and CuO nanoparticles in a mixing ratio of 0.3 percent by weight followed by ultrasonication. Furthermore, to find the optimal machining parameters, the Taguchi and ANOVA techniques were employed. The tool wear and surface finish during machining were evaluated using typical machining parameters. It was discovered that the eco-friendly nano-cutting fluids have better machining performance than dry and mineral oil-based cutting fluids.


### 4.3. Grinding

Using MQL techniques, Lee et al [80] investigated the microgrinding process with nano-fluid. The results reveal that when nanoparticles are added to the machining fluid, the grinding force is reduced greatly, and the surface quality is improved due to the greater lubricating qualities. In addition, the author concluded that nano-diamond particles outperformed nano Al2O3 in terms of reducing the magnitude of the grinding force. The major goal of the research was to find the best combination of nanoparticles and eco-friendly oil for grinding Ni-based alloys with the least amount of lubrication [81]. An experimental investigation was conducted on a variety of eco-friendly oils combined with castor oil. Grinding force, specific grinding energy, and surface roughness were used to evaluate the lubricating qualities of the prepared cutting fluids. According to reports, soybean oil-based cutting fluid outperforms castor oil and other mixed base oils when it comes to machining. Due to its exceptional lubricating capabilities, the lubricating capability of the oil was also examined by adding MoS2 nanoparticles. Whereas, Li et al. [82] used six different types of nanoparticles in palm oil-based cutting fluid to perform surface grinding on Ni-based alloys and reported that inclusion of carbon nanotube in the cutting fluid results in better cooling properties as compared to other nanoparticles. Important physical properties of nanofluids, such as viscosity, surface tension, and contact angle, are also being investigated to see how they affect cooling performance. The performance of grinding parameters such as coefficient of friction, machining forces, temperature, and power consumption was evaluated in an experiment on surface grinding and reported to have good surface finish and less friction coefficient using the MQL approach [83]. Chaudhari et al. [84] used an optimization technique to explore the impact of nano-fluids on surface grinding. In comparison to traditional approaches, the surface irregularity is reduced by 14% in this inquiry. However, Nandakumar et al. [85] used the MQL approach to experiment with surface grinding of Al Matrix Composites supplemented with nano-SiC. It is reported that the cutting force applied and induced temperature decrease as a result of the use of nano-machining fluids. Figure 7 shows the effect of various machining fluids on surface roughness.Figure 7
Effects of various cutting fluids on the surface roughness (a) nanodiamond enriched nanofluids (b) nano Al2O3 enriched nanofluids [80].


### 4.4. Drilling

Using various cooling and lubrication methods such as compressed air lubrication, pure MQL, and Nano-fluid MQL, Nam et al. [86] examined the performance of drilling parameters in terms of drilling force and torque, hole quality, and several holes. When compared to conventional cooling and lubricating methods, the use of nano-fluids under the MQL methodology significantly improves the surface quality of the fabricated holes [87]. The use of nano machining fluid resulted in considerable reductions in flank wear and surface roughness. In contrast, Liew et al. [88] published a study comparing the effects of carbon nanofiber-based nano cutting fluid and standard cooling on SS304 drilling. The burr formation, dimensional correctness, and surface polish of the produced hole were all used to evaluate the drilling’s performance. The findings show that a carbon nanofiber-based nano cutting fluid minimizes surface roughness and burr development while also improving hole precision. While Babu and Muthukrishnan [89] used copper nanoparticle mixed eco-friendly cutting fluids under MQL and traditional machining fluids for drilling of AA5052 alloy, it is reported that the application of eco-friendly cutting fluids results in less tool wear and good surface finish. Furthermore, Nam and Lee [90] used biodegradable nano machining fluids to microdrill Ti6Al4V under MQL. The results show that using a vegetable-based nano cutting fluid reduces thrust force and torque while also efficiently reducing burrs in produced holes at a lower feed rate. Figure 8 shows the influence of concentration of nanoparticles on average values of torque and thrust force with various biodegradable nano-fluids during hole drilling, whereas Figure 9 shows the influence of concentration of nanoparticles on surface roughness.Figure 8
Influence of concentration of nanoparticle on average values of torque and thrust force with various vegetable-based nano-fluids during hole drilling [90].Figure 9
Influence of concentration of nanoparticle on surface roughness [91].Lee et al. [91] reported an investigation on mesoscale grinding using the MQL technique for supply of cutting fluids and reported that the nano-fluid MQL technique can greatly reduce grinding forces and surface roughness. Furthermore, smaller nano-diamond particles may be more advantageous for creating superior grinding surfaces. A summary of the literature review on vegetable-based cutting fluids listed in Table 3 and a summary of the literature review on vegetable oil-based nano cutting fluids listed in Table 4.Table 3
Summary of the literature review on vegetable-based cutting fluids.
Sl. No.ReferencesMachining ProcessCutting FluidFindings1.Ghandehariun et. al. [22]TurningDryExergy loss reduces on increasing machining speed. A more environmental friendly set of cutting conditions can be provided by exergy analysis2.Rajemi et. al. [23]TurningDryThe cutting tool’s energy consumption has a significant impact on the machining cycle time and, as a result, the cutting velocity for minimum energy. For minimum energy required during machining, cutting speed should be relatively low3.Sarıkaya et. al. [24]TurningMQL, dry, and conventional coolingGood surface finish at higher machining speed and less wear on the cutting tool at lower machining speeds can be achieved4.Çakīr et. al. [26]TurningMQL, dry, chilled air, and cryogenic coolingOptimal machining such as longer tool life, lesser surface irregularity can be attained with a suitable selection of cutting fluids5.Adler et. al. [27]TurningMist cutting fluidsPresents a model for the cutting fluids preparation and its behavior along with how to decrease the flow of machining fluids during different machining processes6.Chowdary et. al. [28]TurningPalm kernel seed and cottonseed oil-based machining fluidsHigher MRR in comparison with the conventional machining fluid. Eco-friendly machining operation7.Ozcelik et. al. [29]TurningCanola and sunflower oil-based cutting fluidCanola oil-based machining fluid performed better than refined sunflower oil8.Xavior and adithan [30]TurningCoconut oil-based cutting fluidReduced surface irregularity, machining force using coconut-based cutting fluid as compared to conventional fluids9.Talib and Rahim [31]TurningJatropha oil-based cutting fluidReduced the cutting forces and temperature. The cutting force and maximum cutting temperature increased as the lubricant viscosity decreased10.Abdalla et. al. [33]TurningPalm olive, coconut, sunflower, rapeseed, and high Erucic rapeseedThe increased penetration and entrapment at the machining zone improves cooling and lubrication performance and helps to keep chips off the cutting tool11.Gariani et. al. [34]TurningWater miscible biodegradable fluidReduced tool flank wears at lower machining speed, feed rate, depth of cut, and machining fluid concentration of 10%12.Katna et. al. [35]TurningMineral and biodegradable fluidReduced values of cutting force, tool wear, surface irregularity, interface temperature using biodegradable machining fluids13.Gunjal and Patil [39]TurningCanola oil, coconut oil, and soybean oilReduced wear and increased life of the cutting tool. Traditional oil with MQL has a longer tool life at higher cutting speeds than vegetable-based cutting fluids14.Raj et. al. [40]TurningCoconut, canola oil, and soybean oilReduced wear and increased life of the cutting tool. In comparison to wet and dry turning, vegetable oil-based MCFA has improved cutting performance by reducing cutting force and contributing assured results, while reducing cutting fluid quantity to a greater extent15.Nizamuddin et. al. [41]TurningKaranja oil-based cutting fluidsThis study shows that using environmentally friendly Karanja oil in water-based cutting fluid significantly increases tool life by reducing chip thickness by 11%16.Carvalho et. al. [43]TurningVegetable and mineral oil-based machining fluidsLower cutting force and wettability angle using biodegradable machining fluid17.Marques Narala et. al. [44]TurningBiodegradable machining fluids mixed with solid lubricationsImproved tool life and cutting force on mixing MoS2.18.Zhang et al. [48]MillingDry and MQLUsing minimum quantity lubrication (MQL) in machining Inconel 718 is limited by the low cooling capacity of cryogenic air. Extending the life of the tool and reducing the cutting forces are just two benefits of MQCL cutting with biodegradable vegetable oil19.Kuram et al. [50]MillingVegetable-based cutting fluidsBetter machining performance and eco-friendly20.Burton goo et al. [51]MillingVegetable-based machining fluidsLower values of surface irregularity, cutting force, and chip thickness21.Shankar Mohanraj et al. [52]MillingSunflower, coconut, palm, and soyabean oil-based cutting fluidsPalm oil-based machining fluid results in lower cutting force and minimum vibration22.Junior et al. [53]MillingCottonseed and canola oil-based machining fluidsBetter cooling ability and higher tool life in comparison to conventional machining fluids23.Alves and de Oliveira [54]GrindingCastor oil-based machining fluidReduced wheel wear and surface irregularity using vegetable oil-based machining fluid24.Wojcik [55]GrindingEmulsion, oil, dry grinding, propylene glycol, micro 3000, eco cut Mikro 82, and bio cut 3000Propylene glycol cutting fluid easily accessible, less harmful, environment-friendly, lower value of cutting force with less surface damage and deformation.25.Wang et al. [56]GrindingSunflower oil soybean, peanut, maize, rapeseed, palm, and castorCastor oil-based cutting fluid results in superior surface morphology and lesser surface irregularity26.Guo et al. [57]GrindingDry and biodegradable machining fluidsBiodegradable machining fluids enhanced surface finish27.Mendes et al. [58]DrillingVegetable oil-based mistHigher torque and lower feed force while surface finish remains unaffected28.Bhowmick and alpas [59]DrillingMQL and conventional lubrication techniquesDue to their adhesion-mitigating properties, diamond-like carbon (DLC) coatings improve dry drilling performance. This method of H2O-MQL cutting was chosen over hydrogenated DLC because of the smaller built-up edge formation and reduced drill flute aluminium adhesion it produced29.Kuram et al. [60]DrillingVegetable oil and conventional oil-based machining fluidsLower values of the cutting force and surface irregularity at higher machining speed30.Sharma et al. [61]DrillingDry and near dryNear dry machining, it has been suggested, is more environmental friendly, cleaner to produce, and may even help improve desirable machinability characteristics to some degree31.Puttaswamy and Ramachandra [62]DrillingNeem and Mahua oil-based cutting fluidsOptimal values of irregularity, thrust force, and temperature developed during machining using Mahua based cutting fluid32.Kuram and Ozcelik [63]DrillingBiodegradable fluidsLesser surface irregularity and thrust force as compared to traditional machining fluids33.Rahim and sasahara [64]DrillingPalm oil and synthetic ester under MQLPerformance of palm oil is better than synthetic ester in terms of specific cutting energy, power, and machining forceTable 4
Summary of the literature review on vegetable Oils based nano cutting fluids.
Sl. No.ReferencesMachining ProcessNanoparticle/Base fluidMode of Nanofluid supplyFindings1.Ranjbarzadeh et al. [65]TurningWater/graphene oxide nanofluidDrop by drop using the dropperBetter surface quality and less surface damage due to the high heat transfer capability of graphene oxide2.Sahu et al. [67]TurningMultiwalled carbon nanotubes (MWCNTs) dispersed in distilled water and sodium dodecyl sulfate (SDS)Supplied through gravityCutting force was lowered by 28%, surface roughness was reduced by 7%, and tool wear was reduced by 34%3.Hegab et al. [68]TurningDispersed MWCNTs into the conventional fluid (vegetable oil)MQLSurface roughness was reduced by 38% at 4 wt. percent MWCNTs nano-fluids, while surface quality was improved by 50% at 2 wt. percent MWCNTs nano-fluids4.Su et al. [69]TurningPriEco6000 unsaturated polyol ester, LB2000 vegetable-based oil, graphite oil-based nanofluidMQLAt higher machining speed, cutting force and temperature reduced significantly with graphite based nanofluid5.Padmini et al. [70]TurningNano molybdenum disulfide (nMoS2) in coconut (CC), sesame (SS), and canola (CAN) oils at varying nanoparticle inclusions (npi)MQLCutting force, surface roughness, temperature, and tool wear all decrease by 37%, 39%, 21%, and 44%, respectively6.Padmini et al. [71]TurningNano-boric acid (nBA) and nano-molybdenum disulfide (nMoS2) individually in two vegetable oils which are, coconut oil (CC) and sesame oil (SS)MQLHigher heat reduction using nMoS2 suspensions in coconut oil-based cutting fluid7.Gupta et al. [72]TurningNano-cutting fluids using aluminum oxide (Al2O3), molybdenum disulfide (MoS2), and graphiteMQLAt high machining speeds, MoS2 and graphite-based nanofluids perform better8.Yıldırım et al. [73]TurningEster-based cutting oil as base-fluid for pure-MQLMQLSignificant improvement in cutting force and surface roughness with MoS2 and graphite-based nanofluids9.Sharmin et al. [75]TurningCNT-water based nano cutting fluidRemarkable improvement in the cutting force, specific cutting energy, and surface irregularity10.Uysal A. et. al. [76]MillingEraoil KT/2000 commercial vegetable cutting fluidMQLAt a flow rate of 40 ml/h, the surface irregularity and tool wear were at their lowest levels11.Uysal et al. [77]MillingEraoil KT/2000 commercial vegetable cutting fluid (12 cst at 40°C)MQLTool wear is significantly reduced12.Prasad et al. [78]MillingMWCNT and ZnO mixed in soluble oilMQLFor minimum surface roughness, the spindle speed should be 510 rpm, the feed rate should be 16 mm/min, and the depth of cut should be 0.6 mm13.Settu and Nandagopal [79]MillingRefined corn oil as a base fluid and the CuO nano particlesFlood type coolant supplyBetter machining performance using CuO14.Lee et al. [80]GrindingNanodiamond and nano-Al2O3 particles mixed in paraffin oilMQLDue to the excellent cooling and lubricating qualities, the grinding force is lowered while the surface quality is improved15.Jia et al. [81]GrindingSoybean/castor oil mixed with MoS2 nanoparticlesMQLThe machining fluid’s performance improves significantly. Excellent heat transfer performance is achieved by combining the lowest grinding temperature with the highest thermal conductivity16.Chakule et al. [83]GrindingDry, wet with soluble oilMQLThe surface roughness and coefficient of friction with the least amount of friction were 0.1236 m and 0.3906 m, respectively17.Chaudhari et al. [84]GrindingConventional flooded, MQL, and nanofluid MQLMQLSurface roughness reduced by 14%18.Nandakumar et al. [85]GrindingSiC nano Tio2 filled cashew nut shell oil as base oilsMQLReduced cutting force and temperature19.Nam et al. [86]DrillingNano-diamond particles mixed in the base fluids paraffin and vegetable oilsMQLReduced drilling force and torque with increased no. of holes as compared20.Muthuvel et al. [87]DrillingCoconut oil and copper nanofluidMQLSignificantly reduction of flank wear and surface roughness21.Babu and Muthukrishnan [89]DrillingCNF nanofluid with the base fluid (deionized water)MQLReduced surface irregularity, cutting temperature, and tool wear22.Nam and lee et al. [90]DrillingPalm oil as base fluid and nanodiamond particlesMQLReduced thrust force and torque at a slower feed rate


## 4.1. Turning

[65] carried out an experimental study on the thermal behaviour of graphene oxide enhanced nano-fluids. The thermal conductivity of the graphene oxide nano machining fluid increased by 71 percent when compared to traditional machining fluids due to improved heat transfer capabilities, according to the author. Jamil et al. [66] employed a vegetable-based hybrid nano-fluid including Al2O3 and CNT nanoparticles that was combined with vegetable oil. In comparison to cryogenic cooling, average surface irregularity and cutting force were lowered by 8.72 percent and 11.8 percent, respectively, according to the stated data. Sahu et al. [67] employed a mixed nano-fluid of multiwalled carbon nanotubes (MWCNTs) to evaluate the performance of Ti6Al4V turning. In comparison to traditional cooling techniques, the performance of eco-friendly nano-cutting reveals reduced chip thickness as well as improved cooling and lubricating capabilities [68, 69]. Padmini et al. [70, 71] evaluated machining force, surface irregularity, temperature, and tool wear during machining of AISI 1045 steel using nano-molybdenum di-sulfide (nMoS2) in coconut (CC), sesame (SS), and canola (CAN) oil-based cutting fluids. In comparison to dry machining, the author claims that cutting force, surface irregularity, temperature, and tool wear are reduced by 37 percent, 39 percent, 21 percent, and 44 percent, respectively. Using a turning operation, the properties of different nano-cutting fluids, including aluminium oxide (Al2O3), molybdenum disulfide (MoS2), and graphite, were examined under minimal quantity lubrication (MQL) conditions on Inconel-800 alloy. Surface roughness, cutting forces, and tool wear were all used to evaluate the machining process’ performance. The addition of MoS2 to cutting fluids is said to improve the cooling and lubrication of the workpiece and tool during the machining process [72]. Under the MQL approach, the effect of biodegradable nano-machining fluids on machining force, surface irregularity, and tool wear in the turning of Inconel superalloy is investigated. In comparison to conventional machining fluids, MoS2 and graphite-based nano-fluids produce better outcomes at greater cutting rates, according to this study. Yildirim et al. [73] sought to investigate the impact of dry, MQL, and nano-MQL cooling and lubrication methods on surface irregularity, tool life, tool wear, and temperature in the turning of Inconel 625. The author claims that adding nanoparticles into cutting fluids significantly enhances the previously listed performance characteristics.However, the author [74, 75] discusses his research into the production of carbon nanotube-based nanofluids for improved machining efficiency over traditional cutting fluids. Different nanofluid samples were produced, and their appropriateness was assessed. The prepared carbon nanotube-based cutting fluids have higher thermal conductivity and reduced viscosity, according to the findings of this study. In addition, the author conducted comparison research by milling 42CrMo4 hardened steel utilizing a dry cutting, with conventional and nanofluid. Cutting performance was enhanced by a reduction of 29 percent in cutting temperature, 34 percent in surface roughness, 33 percent in cutting force, and 39 percent in tool wear when nano-cutting fluids were used. The impact of various vegetable-based nano machining fluids on tool wears is shown in Figure 5.Figure 5
Influence of different types of vegetable-based nano machining fluids on tool wear [75].


## 4.2. Milling

To assess tool wear and surface irregularity, Uysal et al. [76] milled AISI 420 steels with vegetable-based hybrid nanomachining fluids. It is reported that less good surface finish and less tool wear were observed upon application of the optimal supply of the cutting fluids during the machining operation. In contrast, Uysal [77] investigated tool failure in the milling of SS304 utilizing biodegradable nano machining fluid. It can be inferred that by using nano machining fluid, many forms of tool wear are greatly decreased. However, Prasad et al. [78] investigated the effects of nano-cutting fluids on surface irregularity and interface temperature to determine ideal values. The Taguchi technique was used to determine the ideal values for these parameters, and the reported optimal parameters are 510 rpm spindle speed, 16 mm/min feed rate, and 0.6 mm depth of cut for minimal surface irregularity. Figure 6 depicts the effects of various machining fluids on tool wear.Figure 6
Effects of various machining fluids on tool wear [78].Moreover, Settu and Nandagopal [79] noted that the current research investigates the machining of EN8 steel utilizing various cooling and lubrication techniques such as without using cutting fluids, with oil mixed in water, and eco-friendly nano-cutting fluids. The nanofluids were produced by the mixing of refined corn-oil and CuO nanoparticles in a mixing ratio of 0.3 percent by weight followed by ultrasonication. Furthermore, to find the optimal machining parameters, the Taguchi and ANOVA techniques were employed. The tool wear and surface finish during machining were evaluated using typical machining parameters. It was discovered that the eco-friendly nano-cutting fluids have better machining performance than dry and mineral oil-based cutting fluids.


## 4.3. Grinding

Using MQL techniques, Lee et al [80] investigated the microgrinding process with nano-fluid. The results reveal that when nanoparticles are added to the machining fluid, the grinding force is reduced greatly, and the surface quality is improved due to the greater lubricating qualities. In addition, the author concluded that nano-diamond particles outperformed nano Al2O3 in terms of reducing the magnitude of the grinding force. The major goal of the research was to find the best combination of nanoparticles and eco-friendly oil for grinding Ni-based alloys with the least amount of lubrication [81]. An experimental investigation was conducted on a variety of eco-friendly oils combined with castor oil. Grinding force, specific grinding energy, and surface roughness were used to evaluate the lubricating qualities of the prepared cutting fluids. According to reports, soybean oil-based cutting fluid outperforms castor oil and other mixed base oils when it comes to machining. Due to its exceptional lubricating capabilities, the lubricating capability of the oil was also examined by adding MoS2 nanoparticles. Whereas, Li et al. [82] used six different types of nanoparticles in palm oil-based cutting fluid to perform surface grinding on Ni-based alloys and reported that inclusion of carbon nanotube in the cutting fluid results in better cooling properties as compared to other nanoparticles. Important physical properties of nanofluids, such as viscosity, surface tension, and contact angle, are also being investigated to see how they affect cooling performance. The performance of grinding parameters such as coefficient of friction, machining forces, temperature, and power consumption was evaluated in an experiment on surface grinding and reported to have good surface finish and less friction coefficient using the MQL approach [83]. Chaudhari et al. [84] used an optimization technique to explore the impact of nano-fluids on surface grinding. In comparison to traditional approaches, the surface irregularity is reduced by 14% in this inquiry. However, Nandakumar et al. [85] used the MQL approach to experiment with surface grinding of Al Matrix Composites supplemented with nano-SiC. It is reported that the cutting force applied and induced temperature decrease as a result of the use of nano-machining fluids. Figure 7 shows the effect of various machining fluids on surface roughness.Figure 7
Effects of various cutting fluids on the surface roughness (a) nanodiamond enriched nanofluids (b) nano Al2O3 enriched nanofluids [80].


## 4.4. Drilling

Using various cooling and lubrication methods such as compressed air lubrication, pure MQL, and Nano-fluid MQL, Nam et al. [86] examined the performance of drilling parameters in terms of drilling force and torque, hole quality, and several holes. When compared to conventional cooling and lubricating methods, the use of nano-fluids under the MQL methodology significantly improves the surface quality of the fabricated holes [87]. The use of nano machining fluid resulted in considerable reductions in flank wear and surface roughness. In contrast, Liew et al. [88] published a study comparing the effects of carbon nanofiber-based nano cutting fluid and standard cooling on SS304 drilling. The burr formation, dimensional correctness, and surface polish of the produced hole were all used to evaluate the drilling’s performance. The findings show that a carbon nanofiber-based nano cutting fluid minimizes surface roughness and burr development while also improving hole precision. While Babu and Muthukrishnan [89] used copper nanoparticle mixed eco-friendly cutting fluids under MQL and traditional machining fluids for drilling of AA5052 alloy, it is reported that the application of eco-friendly cutting fluids results in less tool wear and good surface finish. Furthermore, Nam and Lee [90] used biodegradable nano machining fluids to microdrill Ti6Al4V under MQL. The results show that using a vegetable-based nano cutting fluid reduces thrust force and torque while also efficiently reducing burrs in produced holes at a lower feed rate. Figure 8 shows the influence of concentration of nanoparticles on average values of torque and thrust force with various biodegradable nano-fluids during hole drilling, whereas Figure 9 shows the influence of concentration of nanoparticles on surface roughness.Figure 8
Influence of concentration of nanoparticle on average values of torque and thrust force with various vegetable-based nano-fluids during hole drilling [90].Figure 9
Influence of concentration of nanoparticle on surface roughness [91].Lee et al. [91] reported an investigation on mesoscale grinding using the MQL technique for supply of cutting fluids and reported that the nano-fluid MQL technique can greatly reduce grinding forces and surface roughness. Furthermore, smaller nano-diamond particles may be more advantageous for creating superior grinding surfaces. A summary of the literature review on vegetable-based cutting fluids listed in Table 3 and a summary of the literature review on vegetable oil-based nano cutting fluids listed in Table 4.Table 3
Summary of the literature review on vegetable-based cutting fluids.
Sl. No.ReferencesMachining ProcessCutting FluidFindings1.Ghandehariun et. al. [22]TurningDryExergy loss reduces on increasing machining speed. A more environmental friendly set of cutting conditions can be provided by exergy analysis2.Rajemi et. al. [23]TurningDryThe cutting tool’s energy consumption has a significant impact on the machining cycle time and, as a result, the cutting velocity for minimum energy. For minimum energy required during machining, cutting speed should be relatively low3.Sarıkaya et. al. [24]TurningMQL, dry, and conventional coolingGood surface finish at higher machining speed and less wear on the cutting tool at lower machining speeds can be achieved4.Çakīr et. al. [26]TurningMQL, dry, chilled air, and cryogenic coolingOptimal machining such as longer tool life, lesser surface irregularity can be attained with a suitable selection of cutting fluids5.Adler et. al. [27]TurningMist cutting fluidsPresents a model for the cutting fluids preparation and its behavior along with how to decrease the flow of machining fluids during different machining processes6.Chowdary et. al. [28]TurningPalm kernel seed and cottonseed oil-based machining fluidsHigher MRR in comparison with the conventional machining fluid. Eco-friendly machining operation7.Ozcelik et. al. [29]TurningCanola and sunflower oil-based cutting fluidCanola oil-based machining fluid performed better than refined sunflower oil8.Xavior and adithan [30]TurningCoconut oil-based cutting fluidReduced surface irregularity, machining force using coconut-based cutting fluid as compared to conventional fluids9.Talib and Rahim [31]TurningJatropha oil-based cutting fluidReduced the cutting forces and temperature. The cutting force and maximum cutting temperature increased as the lubricant viscosity decreased10.Abdalla et. al. [33]TurningPalm olive, coconut, sunflower, rapeseed, and high Erucic rapeseedThe increased penetration and entrapment at the machining zone improves cooling and lubrication performance and helps to keep chips off the cutting tool11.Gariani et. al. [34]TurningWater miscible biodegradable fluidReduced tool flank wears at lower machining speed, feed rate, depth of cut, and machining fluid concentration of 10%12.Katna et. al. [35]TurningMineral and biodegradable fluidReduced values of cutting force, tool wear, surface irregularity, interface temperature using biodegradable machining fluids13.Gunjal and Patil [39]TurningCanola oil, coconut oil, and soybean oilReduced wear and increased life of the cutting tool. Traditional oil with MQL has a longer tool life at higher cutting speeds than vegetable-based cutting fluids14.Raj et. al. [40]TurningCoconut, canola oil, and soybean oilReduced wear and increased life of the cutting tool. In comparison to wet and dry turning, vegetable oil-based MCFA has improved cutting performance by reducing cutting force and contributing assured results, while reducing cutting fluid quantity to a greater extent15.Nizamuddin et. al. [41]TurningKaranja oil-based cutting fluidsThis study shows that using environmentally friendly Karanja oil in water-based cutting fluid significantly increases tool life by reducing chip thickness by 11%16.Carvalho et. al. [43]TurningVegetable and mineral oil-based machining fluidsLower cutting force and wettability angle using biodegradable machining fluid17.Marques Narala et. al. [44]TurningBiodegradable machining fluids mixed with solid lubricationsImproved tool life and cutting force on mixing MoS2.18.Zhang et al. [48]MillingDry and MQLUsing minimum quantity lubrication (MQL) in machining Inconel 718 is limited by the low cooling capacity of cryogenic air. Extending the life of the tool and reducing the cutting forces are just two benefits of MQCL cutting with biodegradable vegetable oil19.Kuram et al. [50]MillingVegetable-based cutting fluidsBetter machining performance and eco-friendly20.Burton goo et al. [51]MillingVegetable-based machining fluidsLower values of surface irregularity, cutting force, and chip thickness21.Shankar Mohanraj et al. [52]MillingSunflower, coconut, palm, and soyabean oil-based cutting fluidsPalm oil-based machining fluid results in lower cutting force and minimum vibration22.Junior et al. [53]MillingCottonseed and canola oil-based machining fluidsBetter cooling ability and higher tool life in comparison to conventional machining fluids23.Alves and de Oliveira [54]GrindingCastor oil-based machining fluidReduced wheel wear and surface irregularity using vegetable oil-based machining fluid24.Wojcik [55]GrindingEmulsion, oil, dry grinding, propylene glycol, micro 3000, eco cut Mikro 82, and bio cut 3000Propylene glycol cutting fluid easily accessible, less harmful, environment-friendly, lower value of cutting force with less surface damage and deformation.25.Wang et al. [56]GrindingSunflower oil soybean, peanut, maize, rapeseed, palm, and castorCastor oil-based cutting fluid results in superior surface morphology and lesser surface irregularity26.Guo et al. [57]GrindingDry and biodegradable machining fluidsBiodegradable machining fluids enhanced surface finish27.Mendes et al. [58]DrillingVegetable oil-based mistHigher torque and lower feed force while surface finish remains unaffected28.Bhowmick and alpas [59]DrillingMQL and conventional lubrication techniquesDue to their adhesion-mitigating properties, diamond-like carbon (DLC) coatings improve dry drilling performance. This method of H2O-MQL cutting was chosen over hydrogenated DLC because of the smaller built-up edge formation and reduced drill flute aluminium adhesion it produced29.Kuram et al. [60]DrillingVegetable oil and conventional oil-based machining fluidsLower values of the cutting force and surface irregularity at higher machining speed30.Sharma et al. [61]DrillingDry and near dryNear dry machining, it has been suggested, is more environmental friendly, cleaner to produce, and may even help improve desirable machinability characteristics to some degree31.Puttaswamy and Ramachandra [62]DrillingNeem and Mahua oil-based cutting fluidsOptimal values of irregularity, thrust force, and temperature developed during machining using Mahua based cutting fluid32.Kuram and Ozcelik [63]DrillingBiodegradable fluidsLesser surface irregularity and thrust force as compared to traditional machining fluids33.Rahim and sasahara [64]DrillingPalm oil and synthetic ester under MQLPerformance of palm oil is better than synthetic ester in terms of specific cutting energy, power, and machining forceTable 4
Summary of the literature review on vegetable Oils based nano cutting fluids.
Sl. No.ReferencesMachining ProcessNanoparticle/Base fluidMode of Nanofluid supplyFindings1.Ranjbarzadeh et al. [65]TurningWater/graphene oxide nanofluidDrop by drop using the dropperBetter surface quality and less surface damage due to the high heat transfer capability of graphene oxide2.Sahu et al. [67]TurningMultiwalled carbon nanotubes (MWCNTs) dispersed in distilled water and sodium dodecyl sulfate (SDS)Supplied through gravityCutting force was lowered by 28%, surface roughness was reduced by 7%, and tool wear was reduced by 34%3.Hegab et al. [68]TurningDispersed MWCNTs into the conventional fluid (vegetable oil)MQLSurface roughness was reduced by 38% at 4 wt. percent MWCNTs nano-fluids, while surface quality was improved by 50% at 2 wt. percent MWCNTs nano-fluids4.Su et al. [69]TurningPriEco6000 unsaturated polyol ester, LB2000 vegetable-based oil, graphite oil-based nanofluidMQLAt higher machining speed, cutting force and temperature reduced significantly with graphite based nanofluid5.Padmini et al. [70]TurningNano molybdenum disulfide (nMoS2) in coconut (CC), sesame (SS), and canola (CAN) oils at varying nanoparticle inclusions (npi)MQLCutting force, surface roughness, temperature, and tool wear all decrease by 37%, 39%, 21%, and 44%, respectively6.Padmini et al. [71]TurningNano-boric acid (nBA) and nano-molybdenum disulfide (nMoS2) individually in two vegetable oils which are, coconut oil (CC) and sesame oil (SS)MQLHigher heat reduction using nMoS2 suspensions in coconut oil-based cutting fluid7.Gupta et al. [72]TurningNano-cutting fluids using aluminum oxide (Al2O3), molybdenum disulfide (MoS2), and graphiteMQLAt high machining speeds, MoS2 and graphite-based nanofluids perform better8.Yıldırım et al. [73]TurningEster-based cutting oil as base-fluid for pure-MQLMQLSignificant improvement in cutting force and surface roughness with MoS2 and graphite-based nanofluids9.Sharmin et al. [75]TurningCNT-water based nano cutting fluidRemarkable improvement in the cutting force, specific cutting energy, and surface irregularity10.Uysal A. et. al. [76]MillingEraoil KT/2000 commercial vegetable cutting fluidMQLAt a flow rate of 40 ml/h, the surface irregularity and tool wear were at their lowest levels11.Uysal et al. [77]MillingEraoil KT/2000 commercial vegetable cutting fluid (12 cst at 40°C)MQLTool wear is significantly reduced12.Prasad et al. [78]MillingMWCNT and ZnO mixed in soluble oilMQLFor minimum surface roughness, the spindle speed should be 510 rpm, the feed rate should be 16 mm/min, and the depth of cut should be 0.6 mm13.Settu and Nandagopal [79]MillingRefined corn oil as a base fluid and the CuO nano particlesFlood type coolant supplyBetter machining performance using CuO14.Lee et al. [80]GrindingNanodiamond and nano-Al2O3 particles mixed in paraffin oilMQLDue to the excellent cooling and lubricating qualities, the grinding force is lowered while the surface quality is improved15.Jia et al. [81]GrindingSoybean/castor oil mixed with MoS2 nanoparticlesMQLThe machining fluid’s performance improves significantly. Excellent heat transfer performance is achieved by combining the lowest grinding temperature with the highest thermal conductivity16.Chakule et al. [83]GrindingDry, wet with soluble oilMQLThe surface roughness and coefficient of friction with the least amount of friction were 0.1236 m and 0.3906 m, respectively17.Chaudhari et al. [84]GrindingConventional flooded, MQL, and nanofluid MQLMQLSurface roughness reduced by 14%18.Nandakumar et al. [85]GrindingSiC nano Tio2 filled cashew nut shell oil as base oilsMQLReduced cutting force and temperature19.Nam et al. [86]DrillingNano-diamond particles mixed in the base fluids paraffin and vegetable oilsMQLReduced drilling force and torque with increased no. of holes as compared20.Muthuvel et al. [87]DrillingCoconut oil and copper nanofluidMQLSignificantly reduction of flank wear and surface roughness21.Babu and Muthukrishnan [89]DrillingCNF nanofluid with the base fluid (deionized water)MQLReduced surface irregularity, cutting temperature, and tool wear22.Nam and lee et al. [90]DrillingPalm oil as base fluid and nanodiamond particlesMQLReduced thrust force and torque at a slower feed rate


## 5. Conclusions

The author offered a summary of previous and current research carried out in various machining processes using vegetable oil-based machining fluids (including vegetable-based nano machining fluids). Suitability and application of different eco-friendly cutting fluids with and without mixing of nanoparticles in the cutting fluids. Various dimensions of the sustainability of the eco-friendly cutting fluids were explored in terms of their social, economic, environmental, and technological dimensions. Different preparation steps and methods for the preparation of eco-friendly cutting fluids are introduced, along with testing and characterization. The article extensively discussed applications of eco-friendly cutting fluids for turning, milling, grinding, and drilling operations for different workpiece materials. Various cutting fluids prepared and used during machining include sunflower oil, coconut oil, palm oil, soybean oil, cottonseed, groundnut, jatropha, rapeseed, canola, and Karanja. Different nanoparticles mixed in cutting fluids include Al2O3, CNT, nMoS2, CuO, SiC, graphene, hBN, ZnO, and diamond particles. The cooling and lubrication techniques employed during machining include dry, near dry, flood, mist flow, chilled air, cryogenic, and MQL. The input parameters selected for the machinability analysis of the workpiece were explored in terms of cutting velocity, feed rate, depth of cut, the power required, amount of cooling, and lubricant supplied. Whereas, the output parameters were explored in terms of material removal rate, tool life, tool wear, cutting force, cutting zone temperature, chip thickness, and surface roughness of the machined workpiece.Compared to the standard vegetable-based machining fluids, nanoparticle enhanced in vegetable oil-based machining fluids greatly improves thermal and tribological properties, according to these literature. The following are some of the key takeaways from the literature review:(i)
Better surface finish and machining capability at higher cutting speeds as compared to conventional cutting fluids.(ii)
Enhanced tool life, less surface irregularity, and improved accuracy due to less heat generation using eco-friendly cutting fluids.(iii)
Application of vegetable oil-based cutting fluids results in low cutting forces during machining.(iv)
Low tool wear and less chip thickness can be achieved by maintaining a low machining speed, feed rate, depth of cut, and cutting fluid concentration of 10%.(v)
The use of eco-friendly cutting fluids results in less friction, specific grinding energy, surface damage, and deformation during the grinding process.(vi)
Reduced drilling torque, negligible tool wear, and less specific cutting energy are required during drilling operations using eco-friendly cutting fluids.(vii)
Eco-friendly nano machining fluids exhibit enhanced ability to dissipate heat and tribological properties.(viii)
Surface irregularity, tool wear, machining force, power consumption, and interface temperature are all reduced dramatically when nanoparticles are mixed in the base fluids (vegetable oil).


## 6. Future Work Recommendations

The focus of this review paper was to investigate the influence of eco-friendly cutting operations on the use of different machining operations. These investigations also explored used only one kind of nanoparticles mixed in an eco-friendly cutting fluid. Greater research can be performed into hybrid biodegradable nano-fluids in which more than one type of nanoparticles is present while preparing eco-friendly cutting fluids. Applications of the hybrid nano-cutting fluids in different machining operations can be performed and their influence can also be investigated. Furthermore, the effect of the shape and size of the nanoparticles in the base fluids on the machining fluids’ performance can be examined.



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