**1. Introduction**

Nanofluids are suspensions of nanoparticles in fluids that show significant enhancement of their thermophysical properties with proper volumetric fraction of nanoparticles. Much of the research on nanofluids are about understanding their behavior, so that they can be utilized effectively as an alternative solutions in many industrial applications, nuclear reactors, transportation, electronics, machining, as well as biomedicine and food [1].

Environmental friendliness has become one of the biggest issues in modern industry worldwide, especially in machining industry. In addition, recent regulations on environmental problems,

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such as ISO 14000 and Green Round, have become much stricter for promoting green manufacturing approaches. The necessity of reducing environmental loads should be increasingly considered, and many green manufacturing processes have been developed and studied.

with the developments of suitable rigid machine tools, superhard cutting-tool materials and special tool (toolholders) designs, and complete set-ups, the machining of hardened parts has become more easily accessible and widely applied for the modern machining industry. However, the challenge of selecting a cutting-tool insert to ensure tool life and high-precision machining of the component is the main problem, which slows down the development and application of hard machining. Since its broader introduction in the mid-1980s in the form of hard turning, people have seen that the cutting inserts, such as coated carbides (PVD (Ti, Al)

Without cooling lubricating media, the enormous amount of heat generated from cutting zone remains a big question, which limits the cutting condition, reduces the tool life, and deteriorates the surface finish (i.e., the so-called "white layer" formation in hard machining). This problem has promoted the development of minimum quantity lubrication (MQL) using a special nozzle to form oil mist directly supplied to the machining interface with a tiny amount of fluid consumption (5–500 ml/hr). Because the cutting fluid mostly vaporizes and leaves dry chips, it brings out cost effective and green machining [4]. The very small amount of cutting fluids is utilized and delivered effectively to cutting zone, and the formation of oil films in contact faces plays an important role in lubrication [7]. Numerous publications have been reported on the effectiveness of the MQL technique for enhancing cutting performance [2, 4, 6, 7]. However, the main drawback of MQL technology is low cooling effect, and so it does not work so well in cutting difficult-to-machine materials with high strengths and hardness. To

diamond, and so forth) with at least one of their principal dimensions smaller than 100 nm [3] used in MQL technique recently reach a significant attention of worldwide researchers and

The applications of nanofluids for MQL machining have been proven to improve the interaction of friction in cutting zone due to the occurrence of nanoparticles. However, the direct evaluation of cutting performance faces many difficulties, and so numerous publications are focused on the indirect evaluation through machining outputs such as cutting forces, cutting temperature, tool wear, tool life, and surface integrity. In this section, the recent studies

From previous investigations, nanofluids have been found to possess enhanced thermophysical properties such as thermal conductivity, thermal diffusivity, viscosity, and convective heat transfer coefficients. The thermal conductivity of more than 50 various nanofluids based on

diamond was experimentally measured [8]. The obtained results had shown that the thermal


O3 , MoS<sup>2</sup>

Micro/Nanofluids in Sustainable Machining http://dx.doi.org/10.5772/intechopen.75091 163

, Al<sup>2</sup> O3 , TiO<sup>2</sup>

, ZrO<sup>2</sup>

, CuO, and

, SiO<sup>2</sup>

, CuO,

N–TiN and CVD Ti(C, N)–Al<sup>2</sup>

in various dry hard cutting processes.

**2.1. Thermal properties of nanofluids**

O3

improve the MQL technology, nanofluids containing nanoparticles (Al<sup>2</sup>

are up-to-date topics to increase the cutting performance and productivity.

related to the effects of nanofluids on machining performance will be discussed.

**2. The effects of nanofluids on machining processes**

water, ethylene glycol, and engine oil containing particles of SiO<sup>2</sup>

According to the statistics of cost distribution in manufacturing shown in **Figure 1**, the coolant expense for usage and disposal represents about 15% of total production costs, depending on the workpart and the types of cooling system, as well as machining location [3]. In contrast, tooling cost contributes only a small value of 4%. On the other hand, health and environmental issues associated with the airborne cutting fluid particles on factory shop floors motivate manufacturing enterprises to drastically reduce coolant consumption and, if possible, eliminate it altogether.

As a result, the conception of dry cutting has been first considered to achieve environmental friendliness. Eliminating the cutting fluids in machining processes means that there is no cooling lubricating media, which has three essential functions (i.e., reduction of friction, absorption of the generated heat, and chip evacuation). Hence, these following problems must be considered:


Especially in cases of machining difficult-to-machine materials like high-strength and highhardness steels, solving the mentioned problems has strong influence on leading industrial branches as automotive, roller bearing, hydraulic, and die and mold sectors. The term "hard machining" is a recent technology that can be defined as the machining operation of a workpiece that has a hardness value typically in the 45–70 HRC range, using directly tools with geometrically defined cutting edges [5]. Hard-cutting operations are capable of replacing, in some cases, grinding operations and produce comparable surface finish. Various machining operations in hard machining include milling, boring, broaching, hobbling, and others. Together

**Figure 1.** Distribution of manufacturing costs for wet machining [2].

with the developments of suitable rigid machine tools, superhard cutting-tool materials and special tool (toolholders) designs, and complete set-ups, the machining of hardened parts has become more easily accessible and widely applied for the modern machining industry. However, the challenge of selecting a cutting-tool insert to ensure tool life and high-precision machining of the component is the main problem, which slows down the development and application of hard machining. Since its broader introduction in the mid-1980s in the form of hard turning, people have seen that the cutting inserts, such as coated carbides (PVD (Ti, Al) N–TiN and CVD Ti(C, N)–Al<sup>2</sup> O3 -coated tools, etc.), ceramics, and (P)CBN, are widely utilized in various dry hard cutting processes.

Without cooling lubricating media, the enormous amount of heat generated from cutting zone remains a big question, which limits the cutting condition, reduces the tool life, and deteriorates the surface finish (i.e., the so-called "white layer" formation in hard machining). This problem has promoted the development of minimum quantity lubrication (MQL) using a special nozzle to form oil mist directly supplied to the machining interface with a tiny amount of fluid consumption (5–500 ml/hr). Because the cutting fluid mostly vaporizes and leaves dry chips, it brings out cost effective and green machining [4]. The very small amount of cutting fluids is utilized and delivered effectively to cutting zone, and the formation of oil films in contact faces plays an important role in lubrication [7]. Numerous publications have been reported on the effectiveness of the MQL technique for enhancing cutting performance [2, 4, 6, 7]. However, the main drawback of MQL technology is low cooling effect, and so it does not work so well in cutting difficult-to-machine materials with high strengths and hardness. To improve the MQL technology, nanofluids containing nanoparticles (Al<sup>2</sup> O3 , MoS<sup>2</sup> , SiO<sup>2</sup> , CuO, diamond, and so forth) with at least one of their principal dimensions smaller than 100 nm [3] used in MQL technique recently reach a significant attention of worldwide researchers and are up-to-date topics to increase the cutting performance and productivity.
