**1. Introduction**

Sustainability has become an important element to be considered in the manufacturing industry. Sustainable manufacturing has led machining industries to replace petroleum-based lubricants with bio-derived lubricants. Normally, the conventional lubricants consist of the combination of petroleum-based lubricant and additives that are toxic to the environment and difficult to be disposed of after the consumption [1]. The widespread use of petroleumbased lubricant may cause a negative effect to human such as dermatitis, acne, asthma, and a variety of cancers [2]. Hence, lubricants from vegetable oils are favorable as a sustainable alternative to the conventional petroleum-based oil. Vegetable-based lubricant offers significant environmental benefits with respect to resource renewability, biodegradability, as well as providing satisfactory performance in a wide array of applications [3].

lamellar powders that have low interlayer friction, ability to form protective boundary layers,

Zhang et al. [13] examined the effect of vegetable-based oils (soybean oil, palm oil, and rapeseed oil) as base lubricants containing nanometer-sized particles as additives and hence, the name nanofluids, during minimum quantity lubrication (MQL) grinding of 45 steel workpiece in comparison with liquid paraffin. The results indicated that palm oil-based nanoflu-

jet MQL condition due to the high saturated fatty acid and high film-forming property of the carboxyl groups in palm oil. They noted that high viscosity of nanofluids induced good lubricating effect but significantly reduced heat transfer performance. The combination of green solid particles in vegetable oil provided a strong absorption capability and high film strength which enhanced the lubricating property and heat transfer performance. Li et al. [14] performed an experiment on minimum-quantity lubricant cooling (MQLC) grinding of a Ni-based alloy. Palm-based oil was added with different volume fractions of carbon nanotube (CNT) nanoparticles in between 0.5 and 4%. The results found that the volume fraction of 2% of CNT nanoparticles in palm-based oil had achieved the optimal lubrication and heat transfer performance. They initiated that thermal conductivity and viscosity of nanofluids significantly influence the heat transfer properties. Nam et al. [15] conducted an experiment on MQL micro-drilling with the addition of nano-diamond particles in paraffin and vegetable-based oils. The experimental results show that 2 vol. % of nano-diamond particles in the vegetablebased oil significantly reduce the magnitudes of average drilling torques and thrust forces.

At present, the potential of hBN particle as an additive in MWF has been discovered. This solid additive acts as a viscosity, friction, and wear modifiers in many polar and nonpolar oils. Nguyen et al. [16] conducted an experiment on the 3-axis vertical milling center and the lubricant was supplied through MQL method. The results showed that 0.5 wt. % of hBN particles concentration in vegetable-based oil (Unist-Coolube 2210) reduced flank and central wear.

by mixing 0.5 vol. % of the solid particles in SAE 15 W40 with the particle size of 70 nm. The results showed that the viscosity index of nano-oil with hBN was improved by 3% compared

expansion coefficient of hBN (1 × 10−6/°C). The hBN particles were completely dispersed in the SAE 15 W40 oil and maintained the lubrication properties of the base oil. Furthermore, Talib et al. [18] conducted an experiment on four-ball tribology test of modified Jatropha oil with hBN particles as an application for MQL oil. The modified Jatropha oils were added with the various concentration of hBN particles between 0.05 and 0.5 wt. %. The results revealed that the addition of 0.05 wt. % of hBN particles in the modified Jatropha oil had exhibited excellent tribological performances of the four-ball tribology test in terms of low coefficient of friction, small wear scar diameter, smooth surface roughness, and low volume of wear rate. They indicated that the presence of 0.05 wt. % hBN particles tended to reduce the friction that occurred on the sliding surfaces. The lubrication effect of the MQL oil changed from sliding friction to rolling friction due to the presence of the small amount of hBN particles, which led to the

O3

A paper by Abdullah et al. [17] has studied the effect of hBN and Al<sup>2</sup>

to nano-oil without additive and nano-oil of Al<sup>2</sup>

reduction of friction and wear.

nanoparticles produce the best lubricating property in the nanoparticle

Tribological Interaction of Bio-Based Metalworking Fluids in Machining Process

http://dx.doi.org/10.5772/intechopen.72511

47

O3

. This finding was due the lower thermal

in diesel engine oil

and accommodate relative surface velocities [12].

ids mixed with MoS<sup>2</sup>

In the machining process, metalworking fluids (MWFs) are typically used to separate tool-workpiece interface. MWFs provide lubrication, reduce the friction and wear, cool, and protect metal surfaces against corrosion. Tribology process occurs at the contact area between tool and workpiece, which related to friction, lubrication, and wear of interacting surfaces in a relative motion. Tribology process can be classified as physical, physical-chemical (adsorption), or chemical in nature (tribochemistry) [4]. The absence of MWFs will result in acceleration of tool wear, residual stress, dimensional error, and poor surface finish [5]. Previous researchers have identified that MWFs made of canola/rapeseed, palm, and sunflower oils provided greater lubricating properties and showed comparable performance with currently used petroleum-based MWFs regarding cutting force, cutting temperature, surface finish, tool wear, and tribological behavior [6–8]. Vegetable-based MWFs have high viscosity and viscosity index that significantly influenced the machining performances that provide effective lubricating properties on the tool-chip contact surfaces [8]. Vegetable-based MWFs formed a thin film between tool and workpiece that offers good boundary lubrication condition with a low coefficient of friction [9].

Normally, MWFs contain a combination of base oil and additives. There are various functions of additives being used to enhance the MWFs performance such as antiwear, antifriction, extremepressure, antioxidant, and anticorrosion [10]. The addition of additives in base oil could give either beneficial or detrimental effect on the tribological behavior depending on the types of additive, particle size, and concentration. Hence, to have a better understanding on the lubrication and tribology, modified vegetable oils (modified Jatropha oil and modified RBD palm olein) were added with various types of additives (hexagonal boron nitride and phosphoniumbased ionic liquid). The effects of various formulations of modified vegetable oils were examined through rheological properties, tapping torque, and orthogonal cutting performances.

## **1.1. Green solid additive**

The green solid particles such as hexagonal boron nitride (hBN), aluminum oxide (Al<sup>2</sup> O3 ), molybdenum disulfide (MoS<sup>2</sup> ), carbon nanotube (CNT), and nano-diamond were added in various neat MWFs to increase thermophysical properties and generate a protective film on the contact surfaces [11]. These solid particle additives composed of environmentally benign lamellar powders that have low interlayer friction, ability to form protective boundary layers, and accommodate relative surface velocities [12].

**1. Introduction**

46 Lubrication - Tribology, Lubricants and Additives

**1.1. Green solid additive**

molybdenum disulfide (MoS<sup>2</sup>

Sustainability has become an important element to be considered in the manufacturing industry. Sustainable manufacturing has led machining industries to replace petroleum-based lubricants with bio-derived lubricants. Normally, the conventional lubricants consist of the combination of petroleum-based lubricant and additives that are toxic to the environment and difficult to be disposed of after the consumption [1]. The widespread use of petroleumbased lubricant may cause a negative effect to human such as dermatitis, acne, asthma, and a variety of cancers [2]. Hence, lubricants from vegetable oils are favorable as a sustainable alternative to the conventional petroleum-based oil. Vegetable-based lubricant offers significant environmental benefits with respect to resource renewability, biodegradability, as well

In the machining process, metalworking fluids (MWFs) are typically used to separate tool-workpiece interface. MWFs provide lubrication, reduce the friction and wear, cool, and protect metal surfaces against corrosion. Tribology process occurs at the contact area between tool and workpiece, which related to friction, lubrication, and wear of interacting surfaces in a relative motion. Tribology process can be classified as physical, physical-chemical (adsorption), or chemical in nature (tribochemistry) [4]. The absence of MWFs will result in acceleration of tool wear, residual stress, dimensional error, and poor surface finish [5]. Previous researchers have identified that MWFs made of canola/rapeseed, palm, and sunflower oils provided greater lubricating properties and showed comparable performance with currently used petroleum-based MWFs regarding cutting force, cutting temperature, surface finish, tool wear, and tribological behavior [6–8]. Vegetable-based MWFs have high viscosity and viscosity index that significantly influenced the machining performances that provide effective lubricating properties on the tool-chip contact surfaces [8]. Vegetable-based MWFs formed a thin film between tool and workpiece that

as providing satisfactory performance in a wide array of applications [3].

offers good boundary lubrication condition with a low coefficient of friction [9].

Normally, MWFs contain a combination of base oil and additives. There are various functions of additives being used to enhance the MWFs performance such as antiwear, antifriction, extremepressure, antioxidant, and anticorrosion [10]. The addition of additives in base oil could give either beneficial or detrimental effect on the tribological behavior depending on the types of additive, particle size, and concentration. Hence, to have a better understanding on the lubrication and tribology, modified vegetable oils (modified Jatropha oil and modified RBD palm olein) were added with various types of additives (hexagonal boron nitride and phosphoniumbased ionic liquid). The effects of various formulations of modified vegetable oils were examined through rheological properties, tapping torque, and orthogonal cutting performances.

The green solid particles such as hexagonal boron nitride (hBN), aluminum oxide (Al<sup>2</sup>

various neat MWFs to increase thermophysical properties and generate a protective film on the contact surfaces [11]. These solid particle additives composed of environmentally benign

), carbon nanotube (CNT), and nano-diamond were added in

O3 ), Zhang et al. [13] examined the effect of vegetable-based oils (soybean oil, palm oil, and rapeseed oil) as base lubricants containing nanometer-sized particles as additives and hence, the name nanofluids, during minimum quantity lubrication (MQL) grinding of 45 steel workpiece in comparison with liquid paraffin. The results indicated that palm oil-based nanofluids mixed with MoS<sup>2</sup> nanoparticles produce the best lubricating property in the nanoparticle jet MQL condition due to the high saturated fatty acid and high film-forming property of the carboxyl groups in palm oil. They noted that high viscosity of nanofluids induced good lubricating effect but significantly reduced heat transfer performance. The combination of green solid particles in vegetable oil provided a strong absorption capability and high film strength which enhanced the lubricating property and heat transfer performance. Li et al. [14] performed an experiment on minimum-quantity lubricant cooling (MQLC) grinding of a Ni-based alloy. Palm-based oil was added with different volume fractions of carbon nanotube (CNT) nanoparticles in between 0.5 and 4%. The results found that the volume fraction of 2% of CNT nanoparticles in palm-based oil had achieved the optimal lubrication and heat transfer performance. They initiated that thermal conductivity and viscosity of nanofluids significantly influence the heat transfer properties. Nam et al. [15] conducted an experiment on MQL micro-drilling with the addition of nano-diamond particles in paraffin and vegetable-based oils. The experimental results show that 2 vol. % of nano-diamond particles in the vegetablebased oil significantly reduce the magnitudes of average drilling torques and thrust forces.

At present, the potential of hBN particle as an additive in MWF has been discovered. This solid additive acts as a viscosity, friction, and wear modifiers in many polar and nonpolar oils. Nguyen et al. [16] conducted an experiment on the 3-axis vertical milling center and the lubricant was supplied through MQL method. The results showed that 0.5 wt. % of hBN particles concentration in vegetable-based oil (Unist-Coolube 2210) reduced flank and central wear. A paper by Abdullah et al. [17] has studied the effect of hBN and Al<sup>2</sup> O3 in diesel engine oil by mixing 0.5 vol. % of the solid particles in SAE 15 W40 with the particle size of 70 nm. The results showed that the viscosity index of nano-oil with hBN was improved by 3% compared to nano-oil without additive and nano-oil of Al<sup>2</sup> O3 . This finding was due the lower thermal expansion coefficient of hBN (1 × 10−6/°C). The hBN particles were completely dispersed in the SAE 15 W40 oil and maintained the lubrication properties of the base oil. Furthermore, Talib et al. [18] conducted an experiment on four-ball tribology test of modified Jatropha oil with hBN particles as an application for MQL oil. The modified Jatropha oils were added with the various concentration of hBN particles between 0.05 and 0.5 wt. %. The results revealed that the addition of 0.05 wt. % of hBN particles in the modified Jatropha oil had exhibited excellent tribological performances of the four-ball tribology test in terms of low coefficient of friction, small wear scar diameter, smooth surface roughness, and low volume of wear rate. They indicated that the presence of 0.05 wt. % hBN particles tended to reduce the friction that occurred on the sliding surfaces. The lubrication effect of the MQL oil changed from sliding friction to rolling friction due to the presence of the small amount of hBN particles, which led to the reduction of friction and wear.
