Experimental evaluation of cooling performance by friction coefficient and specific friction energy in nanofluid minimum quantity lubrication grinding with different types of vegetable oil

Accepted Manuscript Experimental evaluation of cooling performance by friction coefficient and specific friction energy in nanofluid minimum quantity lubrication grinding with different types of vegetable oil Yanbin Zhang, Changhe Li, Min Yang, Dongzhou Jia, Yaogang Wang, Benkai Li, Yali Hou, Naiqing Zhang, Qidong Wu PII:

S0959-6526(16)31221-5

DOI:

10.1016/j.jclepro.2016.08.073

Reference:

JCLP 7865

To appear in:

Journal of Cleaner Production

Received Date: 12 January 2016 Revised Date:

26 July 2016

Accepted Date: 16 August 2016

Please cite this article as: Zhang Y, Li C, Yang M, Jia D, Wang Y, Li B, Hou Y, Zhang N, Wu Q, Experimental evaluation of cooling performance by friction coefficient and specific friction energy in nanofluid minimum quantity lubrication grinding with different types of vegetable oil, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.08.073. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Experimental Evaluation of Cooling Performance by Friction Coefficient and Specific Friction Energy in Nanofluid Minimum Quantity Lubrication Grinding with Different Types

RI PT

of Vegetable Oil

Yanbin Zhang1, Changhe Li1*, Min Yang1, Dongzhou Jia1, Yaogang Wang1, Benkai Li 1, Yali Hou1, Naiqing Zhang2 and Qidong Wu2

SC

1. School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China 2. Shanghai Jinzhao Energy Saving Technology CO.LTD, 200436 Shanghai, China

M AN U

*Corresponding author. School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China，Tel: +86-532-68052760; Fax: +86-532-85071286; E-mail address: [email protected] (Changhe Li)

Aothorships: Yanbin Zhang, School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address:[email protected]

Changhe Li, School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address: [email protected]

TE D

Min Yang, School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address: [email protected]

Dongzhou Jia: School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address: [email protected] Yaogang Wang: School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China

EP

E-mail address: [email protected] Benkai Li: School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address: [email protected]

AC C

Yali Hou, School of Mechanical Engineering, Qingdao University of Technology, 266520 Qingdao, China E-mail address: [email protected]

Naiqing Zhang, Shanghai Jinzhao Energy Saving Technology CO.LTD, 200436 Shanghai, China E-mail address: [email protected]

Qidong Wu, Shanghai Jinzhao Energy Saving Technology CO.LTD, 200436 Shanghai, China E-mail address: [email protected]

-1-

Abstract:

ACCEPTED MANUSCRIPT

In accordance with the lubricating performance of nanofluid minimum quantity lubrication (N-MQL) grinding with different vegetable oils as the base oil in previous research, cooling performance was explored with a new method. Friction coefficient, specific friction energy, total heat flow density, and grinding peak

RI PT

temperature were used as evaluation parameters. The influence of the physical properties (viscosity, surface tension) of vegetable oils on the cooling effect was analyzed comprehensively. For the new method, a new ploughing force model and a friction force model were established, and cutting force and ploughing force

SC

were calculated theoretically. Afterward, friction force was obtained according to the theoretical model and experimental results and was used to calculate the evaluation parameters. The vegetable oil nanofluids

M AN U

showed better cooling performance than mineral oil because of their lubrication-favorable fatty acid molecules. Furthermore, the mechanism of the effect of nanofluid viscosity and surface tension on cooling performance was explored. Vegetable oil with a low viscosity and surface tension showed good cooling

TE D

performance and that with a high viscosity and surface tension showed good lubrication performance. As a result, palm oil nanofluid with a high viscosity and surface tension achieved the lowest friction coefficient (0.258), specific friction energy (27.09 J/mm3), and grinding peak temperature (123.8 °C) and exhibited

AC C

EP

better grinding performance than the others.

Keywords: minimum quantity lubrication (MQL) grinding, vegetable oil, friction coefficient, specific friction energy, cooling performance

Nomenclature and Abbreviation Ft Fn Ftc,total Ftp,total Fnc,total Fnp,total

tangential grinding force normal grinding force tangential cutting force tangential ploughing force normal cutting force normal ploughing force

MQL N-MQL MoS2 SDS Nanofluid SEM -2-

minimum quantity lubrication nanofluid minimum quantity lubrication molybdenum disulfide lauryl sodium sulfate fluid containing nanometer-sized particles scanning electron microscope

fS ftA fnA ftB fnB ιL ftS fnS Ns SB xcutmin xconmin S R

RI PT

fB

SC

fA

M AN U

Fnp

TE D

Ftp

EP

Fnc

grinding depth pressure in the lubrication oil film ap ACCEPTED MANUSCRIPT Vana micro-material removal rate total number of abrasive particles Vexp macro-material removal rate single abrasive particle tangential diameter difference hin cutting force Pcut cutting abrasive particle ratio single abrasive particle normal Pplow ploughing abrasive particle ratio cutting force Vs Peripheral speed of grinding wheel single abrasive particle tangential feed speed Vw ploughing force average abrasive particle diameter d single abrasive particle normal maximum abrasive particle diameter dmax ploughing force dmin minimum abrasive particle diameter friction force under direct contact w percentage of abrasive particles state friction coefficient µ friction force under boundary oil specific energy U film lubrication state total consumed grinding energy Pg friction force under furrow effect removal rate of materials per unit volume Qw state thermal flux qtotal tangential friction force under grinding power Q direct contact state energy transmitted into the workpiece qwb normal friction force under direct thermal diffusivity α contact state θmax grinding peak temperature tangential friction force under surface tension boundary oil film lubrication state σ γvl solid–liquid interface tension normal friction force under solid–gas interface tension boundary oil film lubrication state γsv γvl liquid–gas interface tension shear strength of lubrication oil θc contact angle film b grinding width tangential friction force under D diameter of the grinding wheel furrow effect state tangential friction force normal friction force under furrow ft fn normal friction force effect state Fp unit grinding force number of abrasive particles per ag average cutting depth unit area correlation coefficient of the material pressure in the lubrication oil film k Am mean grindings area area θ abrasive vertex angle x-coordinate value of the smallest δs yield strength cutting particle diameter af average ploughing depth x-coordinate value of the ιS shear strength ploughing particle diameter contact area of the grinding wheel PS plastic flowing pressure SA direct contact state area and workpiece β energy proportionality coefficient constant that depends on the shape of the transmitted into the workpiece heat source ds equivalent diameter of the grinding wheel (mm)

AC C

PL Ntotal Ftc

-3-

1. Introduction

ACCEPTED MANUSCRIPT

To address the current environmental and health problems in industrial production and sustainable development for energy, attempts have been made to replace traditional flood cooling lubrication with dry grinding and minimum quantity lubrication (MQL), which meet the environmental protection requirement as

RI PT

important grinding processing techniques in finish machining (Rabiei et al., 2015). Dry machining is the earliest proposed processing technology by researchers that considers environmental protection (Pusavec et al., 2014). Silva et al. (2013) reported that MQL technology originated from the mobile industry and is widely

SC

utilized at present in many machining forms. Dry machining does not use cutting fluid to guarantee cutter service life and part processing precision (Sharma and Sidhu, 2014). However, only a small proportion of heat

M AN U

generated in the grinding zone is removed through chips in the grinding process. The majority of the generated heat is transferred to the grinding wheel and workpieces (Li et al., 2013) and thus results in an overly high energy concentration on the workpiece surface; this overly high energy concentration could burn

TE D

and damage the surface of the workpiece (Malkin and Guo, 2007).

Tawakoli et al. (2010, 2011) reported that MQL grinding is another green processing technology, in which after mixing and atomizing, a small quantity of lubricants and gas with a certain pressure is jetted to the

EP

grinding zone as cooling lubrication. The flow of lubricants per unit wheel width in MQL and flood grinding

AC C

is 30–100 mL/h and 60 L/h, respectively. The cooling and chip removal effect is mainly achieved by high-pressure gas, as highlighted by Mao et al. (2013). However, Hadad et al. (2012a, 2012b) reported that MQL technology has not solved the technical bottleneck of grinding cooling performance; this inability to do so greatly limits the application of MQL technology. Sadeghi et al. (2009) conducted an MQL grinding experimental research on GB 20CrNiMo structural alloy steel. The results indicated that the high-pressure gas imported to the grinding zone does not have a good cooling effect and that the heat generated in the grinding process is partially removed through high-pressure gas. This result may lead to heat accumulation on the workpiece surface, which reduces the surface integrity of the grinding workpiece and shortens the service life -4-

of the grinding wheel or even destroys it according to Ding et al. (2013, 2015).

ACCEPTED MANUSCRIPT

The new nanofluid MQL (N-MQL) technology resolves heat transfer in the grinding zone effectively while enhancing the lubricating property in the zone. As previously reported (Alberts et al., 2009), nanoparticles can significantly improve the lubrication and heat transfer of a nanofluid. A nanofluid is a

RI PT

suspension formed by lubricating oil and 1–100 nm nanoparticles. Li et al. (2008) performed experiments to evaluate the performance of N-MQL technology and compared it with that of conventional flood cooling. Experimental data indicated that the proposed method does not negatively affect surface integrity and that

SC

process validity is verified. Choi et al. (2011) conducted a tribology performance research on nanofluids prepared with metal and carbon nanoparticles as the lubricating oil base. Hwang et al. (2011) conducted an

M AN U

experimental research on the thermal conductivity and lubricating property of nanofluids. Their results indicated that nanoparticles have excellent anti-wear and antifriction performance as well as high carrying capacity. Therefore, these particles are expected to further improve the lubrication effect in the grinding zone.

TE D

Lee et al. (2012) added nanodiamond (ND) and nano-Al2O3 particles into paraffin oil through nanofluid MQL micro-grinding. The experimental results showed that nanofluid MQL is effective in reducing grinding forces and enhancing surface quality. The authors also discovered that the type, size, and volumetric concentration of

EP

nanoparticles are critical parameters that influence the properties of the micro-grinding process. Mao et al.

AC C

(2012) utilized four different lubrication conditions (i.e., dry, flood, pure MQL, and water-based Al2O3 nanofluid MQL) for grinding experiments and analyzed the SEM photos of four types of workpiece surfaces. The results showed that the workpiece surface quality of water-based Al2O3 nanofluid MQL grinding is the best among the four.

MoS2 nanoparticles are usually spherical, and many molecular MoS2 layers overlap into thin layers. Shen and Shih (2008) performed a nanofluid grinding experiment with MoS2 nanoparticles. They concluded that the layers curl and pile up to form a pomegranate corrugation structure, which endows MoS2 with certain friability, flexibility, and ductility. Therefore, MoS2 nanoparticles can extend into thin physical films on the -5-

friction surface under external shear force. MoS2 nanoparticles have high surface activity and are easily

ACCEPTED MANUSCRIPT

adsorbed onto the friction surface. According to Hu et al. (2010), physical MoS2 nanoparticle films that fall off during friction can be quickly supplemented and renewed during follow-up adsorption, thereby retaining the lubrication effect. Kalita et al. (2012a) performed nanofluid plane grinding of cast iron and EN24 alloy

RI PT

steel by adding MoS2 nanoparticles to paroline and soybean oil. They confirmed the tribological properties of MoS2 nanoparticles by measuring and computing the grinding force, friction coefficient, specific grinding energy, and G ratio. The MoS2 film formation on the grains of the grinding wheel was observed through SEM.

SC

After content measurement of chemical elements in grains, Kalita et al. (2012b) analyzed the lubrication mechanism of MoS2 nanoparticles to a certain extent. The formation of tribo-chemical films of Mo-S-P

M AN U

chemistry complex on the workpiece surface was identified as the mechanism responsible for improvements. Zhang et al. (2015a) conducted an experimental evaluation of the lubrication performance of mixed nanofluid MQL grinding. Their results showed that MoS2-CNT hybrid nanoparticles achieve better lubrication effect

wt%, respectively.

TE D

than single nanoparticles. The optimal MoS2-CNT mixing ratio and nanofluid concentration are 2:1 and 6

The increasing attention devoted to the environmental and health effects of industrial activities by

EP

governmental regulations and the growing awareness level in the society are forcing industrialists to reduce

AC C

the use of mineral oil-based metalworking fluids as the cutting fluid. The applicability of vegetable oil-based metalworking fluids in machining of ferrous metals was investigated by Lawal et al. (2012) in their review paper. They reported in various papers that vegetable oil-based metalworking fluids could be an environmentally friendly mode of machining, with a performance similar to that when mineral oil-based metalworking fluids are used. Cetin et al. (2011) and Lawal et al. (2013) reported that degradable vegetable oil is typically utilized as the base oil in N-MQL grinding to reduce lubricant pollution to the environment and handling cost. Experimental research has been conducted on the use of vegetable oil as a metal machining liquid. Zhang et al. (2012) demonstrated that excellent lubricating property can be achieved with vegetable oil -6-

as the lubricant base oil and that the addition of nanoparticles can reduce the coefficient of friction and

ACCEPTED MANUSCRIPT

enhance the anti-wear capability of friction auxiliary materials. Jain and Bisht (2008), scholars from India, attempted to replace mineral oil with non-edible vegetable oil (i.e., rapeseed oil and Karanja oil), which has renewability, biodegradability, and lower price than synthetic ester oil and grease. In their experiment, 5%

RI PT

oil–water mixed liquors composed of many types of non-edible vegetable and mineral oil were compared with standard oil to measure their stability, load capacity, size distribution, and frictional wear. Rahim and Sasahara (2011a, 2011b, 2011c) conducted a series of experimental research. Palm oil and synthetic ester

SC

were used in a drilling experiment as MQL base oil, and various properties in the drilling process were compared. The researchers found better microhardness, surface roughness, surface defect, sub-surface

M AN U

deformation, and other properties of the workpiece after processing with palm oil as the MQL base oil than with synthetic ester. Zhang et al. (2014) investigated nanoparticle efflux MQL grinding by using soybean, rapeseed, and palm oils as the base oils. They found that the use of soybean oil in MQL grinding results in

TE D

better performance than when the two other vegetable oils are used.

As a part of this research, the lubrication performance of nanofluid MQL grinding with different vegetable oils as the base oil was explored (Zhang et al., 2014). In previous experimental research, the

EP

feasibility of using vegetable oils as the base oil of MQL was verified by evaluating their lubrication

AC C

performance. The effects of vegetable oil performance on the friction coefficient, specific grinding energy, and surface roughness were also studied. However, previous studies did not deal with the effect of vegetable oil performance on the cooling effect of the MQL grinding liquid and did not provide the substantial influence law. The current study conducted a comprehensive analysis of the lubrication and cooling performance of vegetable oils as the base oil of MQL. The mechanism or law of the influence of surface tension and viscosity of vegetable oils on cooling performance was established. A standard for selecting vegetable oils as the MQL base oil was provided. With regard to cooling performance evaluation parameters, a single parameter was used in previous research. In the current research, a comprehensive analysis was conducted on the effect of -7-

the physical properties of vegetable oil on cooling characterization parameters (e.g., energy proportionality

ACCEPTED MANUSCRIPT

coefficient, thermal flux, grinding peak temperature, and accumulative temperature rise). The corresponding influence law was obtained. With regard to lubrication performance evaluation parameters, the friction coefficient and specific

RI PT

grinding energy, which are calculated by measuring the grinding force through an experiment, were used in previous research. Morgan et al. (2012) reported that the friction coefficient reflects the lubrication effect on the grinding wheel–workpiece interface and grinding wheel–grinding interface. Typical µ values between 0.2

SC

and 0.7 in grinding were obtained by Rowe et al. (2012). Kalita et al. (2012a) used the friction coefficient as a measurand in determining process efficiency. Zhang et al. (2014) also used the friction coefficient as an

M AN U

evaluation parameter for grinding performance. The friction coefficient (µ) is defined as the tangential/normal force ratio in grinding; however, this definition is inaccurate. Grinding force can be divided into cutting, ploughing, and friction force. Friction force is affected by cooling and lubricating conditions, whereas the

TE D

others are not. Thus, friction force is related to lubrication and cooling performance. In this research, cutting and ploughing force under a fixed grinding condition were analyzed and calculated theoretically. With the theoretical model and experimental results, friction force was calculated and utilized as the basic evaluation

EP

parameter for lubrication and cooling performance. The friction coefficient was calculated from friction force,

AC C

and the specific cutting, ploughing, and friction energies were calculated from the three components of grinding force. Compared with the force ratio, the friction coefficient is more representative and accurate in characterizing lubrication and cooling performance. 2. Methods 2.1 Materials The experiments were conducted with a conventional white corundum abrasive grinding wheel (WA80H12V) on a 45 steel material. A K-P36 numerical control precision surface grinder was also utilized. Tables 1 and 2 present the composition and mechanical properties of the 45 steel (AISI/SAE 1045), -8-

respectively. The MQL base oils used were liquid paraffin, palm oil, rapeseed oil, and soybean oil. The basic

ACCEPTED MANUSCRIPT

properties of the four MQL base oils are listed in Table 3. Table 1. Chemical composition of 45 steel (AISI/SAE 1045) Element

C

Si

Mn

Cr

Ni

P

S

Component

0.16-0.25

≤ 1.0

≤ 1.0

12.0-14.0

≤ 0.6

≤ 0.035

≤ 0.03

RI PT

Table 2. Mechanical properties of 45 steel (AISI/SAE 1045) Density

Modulus of elasticity

Thermal conductivity

Specific heat

Yield strength

Tensile strength

Poisson's

(g/cm3)

(GPa)

(W/m K)

(J/Kg K)

(MPa)

(MPa)

ratio

7.85

210

50.2

480

355

600

0.269

Liquid

Oil type

Soybean oil

Property Total fatty acid

— content

94.96%

89.077%

Rapeseed oil

83.7%

Palmitic acid

Arachidic acid

7%-10%;

0.4%-1.0%;

Stearic acid

Palmitic acid

Oleic acid

2%-5%;

67.06%;

14%-19%;

n-alkanes

Arachidic acid

Oleic acid

Linoleic acid

(not fatty

3%;

17.15%;

12%-24%;

Oleic acid

Stearic acid

Erucic acid

22%-30%;

4.91%;

45%-55%;

C16-C20

TE D

Fatty acid type acid)

Proportion

Palm oil

M AN U

paraffin

SC

Table 3. Properties of the four base oils

EP

0.86-0.905

Linoleic acid

Linoleic acid

50%-60%;

1%-10%;

0.9150-0.9375

0.882

0.920

(20/4 °C )

AC C

MoS2 with a diameter of 50 nm was used as the nanoparticle. Many nanoparticles, such as carbon nanotubes (CNT), C60, TiO2, Al2O3, MoS2, and diamond, are added to fluids. Nanoparticles are generally excellent media to increase the thermal conductivity of the base fluid (Moghadassi et al., 2009). Nanoparticles also have a ball/roll bearing effect, and they significantly enhance tribological and wear characteristics according to Ginzburg et al. (2002). MoS2 is an important solid lubricant with excellent antifriction and anti-wear effect under high temperatures and high pressures. Shen and Shih (2008, 2009) investigated the forces and tool wear in N-MQL grinding by using MoS2, diamond, and Al2O3 nanoparticles and found that -9-

grinding force and tool wear are significantly reduced. Sridharan and Malkin (2009) studied N-MQL grinding

ACCEPTED MANUSCRIPT

processes by using MoS2 and CNT nanoparticles and showed that nanofluids can effectively improve surface finish and reduce specific grinding energy. Thus, in the present study, we experimented the with MoS2 nanoparticle.

RI PT

2.2 Nanofluid MoS2 was utilized as an additive to obtain nanofluid, with liquid paraffin, palm oil, rapeseed oil, and soybean oil as the base fluid. The mean size of the MoS2 nanoparticle was 50 nm. Lauryl sodium sulfate

SC

(SDS) with 1/10 volume of the nanoparticle volume was added as a surfactant to improve the stability of

M AN U

suspensions (O’Connell et al., 2002). The nanofluid was prepared by dispersing the nanoparticle in synthetic lipids via a two-step method (Liu, 2010). Sonication was performed for 1 h by using a numerical-control ultrasonic oscillator (version KQ3200DB). 2.3 Experimental scheme

TE D

Experiments were performed under three types of grinding conditions, namely, flood grinding, MQL grinding, and N-MQL grinding. Grinding performance was evaluated. Liquid paraffin, palm oil, rapeseed oil,

EP

and soybean oil were used as the base fluid in the MQL and N-MQL grinding. MoS2 was used as an additive to obtain nanofluid. Zhang D.K. et al. (2015) analyzed the role of MoS2 particles in grinding surface

AC C

lubrication at different nanoparticle volume concentrations. The volume concentration was set to 1%, 1.5%, 2%, 2.5%, and 3%. The grinding surface lubrication effects were satisfactory at a volume concentration of 2%. Moreover, the lubrication effects of nanoparticle jet MQL with 2% volume concentration in the grinding fluid cooling lubrication approach were optimal. Thus, in the current research, 2% volume concentration was set as the nanofluid concentration. The experimental plan is shown in Table 4.

- 10 -

Table 4. Experimental scheme

ACCEPTED MANUSCRIPT Experiment

Cooling and Grinding liquid

No.

lubricating condition Water-solute grinding liquid

1-1

Flood （5 vol.%）

2-1

Liquid paraffin

2-2

Soybean oil

2-3

Rapeseed oil

2-4

Palm oil

3-1

MoS2- liquid paraffin（2 vol.%）

3-2

MoS2- soybean oil（2 vol.%）

3-3

MoS2- rapeseed oil（2 vol.%）

3-4

MoS2- palm oil（2 vol.%）

RI PT

MQL

N-MQL

SC

2.4 Experimental condition

M AN U

The sizes of the workpiece and wheel were 40 mm×30 mm×30 mm and 300 mm×20 mm×76.2 mm, respectively. Table 6 shows the uniform grinding parameters of the experiment. Table 5 presents the unified grinding parameters of the experiment. To achieve a controllable grinding process and similar conditions for each grinding experiment, the grinding wheel was finished before each experiment. The dressing parameters

TE D

of the grinding wheel are listed in Table 6.

Table 5. Grinding parameters

Grinding parameters

Value

Grinding pattern

Surface grinding 30

Feed speed Vw（mm/min）

300

Cutting depth ap (µm)

10

MQL flow rate（ml/h）

50

Flood lubrication flow rate（L/h）

60

MQL nozzle distance（mm）

12

AC C

EP

Peripheral speed of grinding wheel Vs（m/s）

MQL nozzle angle（°）

15

MQL gas pressure（bar）

6.0

Working environment temperature（°C）

25

Table 6. Parameters of grinding wheel dressing Dresser type

Fixed PCD dresser of K-P36 grinder

Single stroke trimming amount (mm)

0.01

Transverse feed rate (mm/rev)

0.5

Number of strokes

20

- 11 -

2.5 Experimental setup

ACCEPTED MANUSCRIPT

In each group of experiments, grinding was conducted continuously for 50 times. Grinding forces and grinding peak temperatures were measured in each experiment. The contact angle between the MQL grinding liquid and the Ni-based alloy workpiece was measured with a contact angle meter. The

AC C

EP

TE D

M AN U

SC

RI PT

experimental setup is shown in Fig. 1.

Fig. 1. Experimental setup

2.5.1 Experimental equipment The experiment was conducted with a K-P36 numerical control precision surface grinder and a nanofluid transfer device (KINS KS-2106 minimum quantity oil supply system). The parameters of the K-P36 numerical control precision surface grinder are listed in Table 7. - 12 -

Table 7. Parameters of the K-P36 numerical control precision surface grinder

ACCEPTED MANUSCRIPT

Machine parameters

Value

Principal axis power

4.5 KW

Highest rotating speed

2,000 r/min

Grinding scope

600 mm × 300 mm × 240 mm

Corundum wheel size

300 mm × 20 mm × 76.2 mm

Wheel particle size

80 mess

47.32%

Highest Peripheral speed of grinding wheel

50 m/s

2.5.2 Grinding force measurement

RI PT

0.180

Grain size（mm） Grain percentage（%）

SC

Fig. 1 shows the experimental setup. For each experiment, a 3D grinding force dynamometer (YDM－ III99) was used to measure and record the normal, tangential, and axial forces. The measured sample

M AN U

frequency of grinding force was 1 kHz. The grinding force signal after sampling was in accordance with the Dynamic Grinding Force Test System software for filtering. The grinding force image and grinding force data documents were then obtained. A total of 100 data points were selected from the stable grinding force zone in each direction to evaluate the mean and obtain the single pass average force. Measurement was conducted 50

TE D

times with different nanofluids. The average value of grinding force was calculated by 50 “single pass average forces.” Statistical analysis of dates was performed through one-way analysis of variance followed by Tukey’s

EP

post-hoc test with confidence intervals (CI) of 95% in accordance with the study of Sullivan et al. (1998).

AC C

2.5.3 Grinding temperature measurement The temperature curve under different grinding conditions was determined through experiments. A clip-on MX100 thermocouple was utilized to measure the grinding temperature (Fig. 2). Each group of experiments was measured, and grinding temperature was recorded at a sampling frequency of 20 Hz. In addition, the temperature curve and peak temperature were obtained. Fig. 1 shows real-time images. The statistical analysis of dates was performed through one-way analysis of variance followed by Tukey’s post-hoc test with confidence intervals (CI) of 95% in accordance with the study of Sullivan et al. (1998).

- 13 -

SC

Fig. 2. Clip-type thermocouple

RI PT

ACCEPTED MANUSCRIPT

2.5.4 Contact angle measurement

M AN U

The contact angle between the MQL grinding liquid and the Ni-based alloy workpiece was measured with a DSA10 goniometer. Measurement was conducted 10 times with different nanofluids to calculate the average value. The average of three values was used for analysis. The measurement setup and the real-time

2.5.5 Viscosity measurement

TE D

image are shown in Fig. 1 and Fig. 12.

The dynamic viscosity of MQL and N-MQL grinding liquids was measured with a DV2T-LV digital

EP

viscometer. The testing fluids were heated to a certain temperature in a thermostatic water bath and then

AC C

cooled naturally. During this process, real-time measurements of the viscosity and temperature of the MQL grinding liquids were performed to obtain the viscosity–temperature curve of the different grinding liquids. 3. Results and discussion 3.1 Grinding force

Grinding force is an important evaluation parameter of grinding performance. Malkin (2008) reported that grinding force can significantly influence the wearing loss of grinding wheels, deformation of process systems, and the surface processing quality of the workpiece. In a previous research (Kalita et al., 2012), lubrication performances under different grinding conditions were analyzed by comparing measured - 14 -

tangential and normal grinding forces. The friction coefficient and specific grinding energy were calculated

ACCEPTED MANUSCRIPT

from the measured grinding force. Grinding force can be divided into cutting, ploughing, and friction forces (Eqs. 1 and 2). Cutting force is used to cut the workpiece into abrasive particles and generate grinding chips. Cutting force is related to the material properties of the workpiece and grinding wheel as well as to the

RI PT

grinding parameters. It is unrelated to the lubrication condition. Friction force is mainly produced by abrasive particles/workpiece friction and abrasive particle/grinding chip friction. Friction force is related to the material properties of the workpiece and grinding wheel as well as to the grinding parameters.

SC

Furthermore, this type of force influences the lubrication condition. Changing the lubrication condition will change the lubrication performance of the grinding zone and thus decrease the friction force while the cutting

M AN U

force remains unchanged. Therefore, friction force and the friction coefficient are calculated to characterize lubrication performance. The result will reflect the influence law of lubrication condition on friction force. Ft=Ftc,total +Ftp,total +ft ,

(2)

TE D

Fn=Fnc,total +Fnp,total +fn ,

(1)

where Ft is tangential grinding force, Fn is normal grinding force, Ftc,total is tangential cutting force, Ftp,total is tangential ploughing force, ft is tangential friction force, Fnc,total is normal cutting force, Fnp,total is

EP

normal ploughing force, and fn is normal friction force.

AC C

3.1.1 Measured grinding forces

Fig. 1 shows the experimental setup and typical grinding force measurement signal images. Fig. 3 shows the grinding force mean value and standard deviation of the different grinding conditions.

- 15 -

RI PT

ACCEPTED MANUSCRIPT

3.1.2 Theoretical model of grinding force (1) Cutting force model of single abrasive particle

SC

Fig. 3. Grinding force mean value and standard deviation of the different grinding conditions

M AN U

Cutting force is applied to cut the workpiece into abrasive particles and generate grinding chips. It is related to the material properties of the workpiece and grinding wheel as well as to the grinding parameters but is unrelated to the lubrication condition. Malkin and Guo (2008) established theoretical models and

TE D

calculations of cutting force under different grinding conditions. Zhang et al. (2007) viewed the single abrasive particle as a cone with 2θ vertex angle (Fig. 4) and obtained the calculation formula of cutting force of single abrasive particle as follows:

EP

Ftc=(π/4) Fp ag2 sinθ , Fnc=Fp ag2 sinθ tanθ .

(3)

AC C

(4)

Furthermore, Zhang et al. (2007) substituted the correlation coefficient k of the material and mean grinding area Am into Eqs. (3) and (4) and calculated the cutting force of the single abrasive particle as follows:

Ftc=(3/2cosθ) k Am-ε ag2 sinθ,

(5)

Fnc=(6/πcosθ) k Am-ε ag2 sinθtanθ,

(6)

where Ftc is single abrasive particle tangential cutting force, Fnc is single abrasive particle normal cutting force, Fp is unit grinding force, ag is the average cutting depth, k is the correlation coefficient of the - 16 -

material, Am is the mean grinding area, and θ is the abrasive particle vertex angle.

RI PT

ACCEPTED MANUSCRIPT

M AN U

(2) Ploughing force model of single abrasive particle

SC

Fig. 4. Single abrasive particle cutting model

Ploughing force causes abrasive particles to extrude on the workpiece, which in turn causes plastic deformation of the workpiece and development of furrows. Similar to cutting force, ploughing force is related to the material properties of the workpiece and grinding wheel as well as to the grinding parameters

TE D

but is unrelated to the lubrication condition. The material suffers from plastic deformation under ploughing force. The plastic deformation limit of materials is the yield limit. Given the isotropy of materials, the plastic deformation forces on different abrasive particle surfaces are all perpendicular to the surface and equal in

π

EP

value. The ploughing force of a single abrasive particle is

0

π

AC C

Ftp = ∫ 2 δ s ⋅ a f 2 ⋅ tan 2 θ ⋅ cos ϕ dϕ ,

Fnp = ∫ 2 δ s ⋅ a p 2 ⋅ tan θ ⋅ dϕ = 0

π 2

(7)

⋅ δ s ⋅ a f 2 ⋅ tan θ ,

(8)

where Ftp is single abrasive particle tangential ploughing force, Fnp is single abrasive particle normal ploughing force, δs is the yield strength, and af is the average ploughing depth.

- 17 -

RI PT

ACCEPTED MANUSCRIPT

Fig. 5. Single abrasive particle ploughing model

SC

(3) Friction force model

M AN U

Friction force is mainly produced by abrasive particle/workpiece friction and abrasive particle /grinding friction. Friction force is related to the material properties of the workpiece and grinding wheel as well as to the grinding parameters. Furthermore, it influences the lubrication condition. In MQL grinding, direct contact state (point A), boundary oil film lubrication state (point B), and furrow effect state (point S)

TE D

exist on the abrasive particles/workpiece interface upon their contact with each other. This behavior is related to the irregular continuous wave peaks and valleys on the workpiece surface. Given that the grinding force of

EP

all three states has the same lubrication mechanism, a model was established for the friction force of these three states. Friction force under the direct contact state originates from the plastic flowing pressure of metals

AC C

and is determined by the shear strength of the workpiece surface and the plastic flowing pressure of metals. Friction force under the boundary oil film lubrication state is produced by the flowing pressure of the lubrication oil film and is determined by the shear strength of the lubrication oil film and the pressure in the lubrication oil film. f= fA+fB+fS ,

(9)

where fA is friction force under the direct contact state, fB is friction force under the boundary oil film lubrication state, and fS is friction force under the furrow effect state. - 18 -

Friction force under the direct contact (point A) state originates from the plastic flowing pressure of

ACCEPTED MANUSCRIPT

metals and is determined by the shear strength of the workpiece surface plastic flowing pressure of metals as follows: (10)

fnA=PSSA ,

(11)

RI PT

ftA= ιSSA ,

where ftA is tangential friction force under the direct contact state, fnA is normal friction force under the direct contact state, ιS is shear strength, PS is workpiece surface plastic flowing pressure, and SA is the direct

SC

contact state area.

Friction force under the boundary oil film lubrication state (point B) is produced by the flowing

pressure in the lubrication oil film as follows: ftB= ιLSB ,

(12) (13)

TE D

fnB=PLSB ,

M AN U

pressure of the lubrication oil film and is determined by the shear strength of the lubrication oil film and the

where ftB is tangential friction force under the boundary oil film lubrication state, fnB is normal friction force under the boundary oil film lubrication state, ιL is the shear strength of the lubrication oil film, PL is

EP

pressure in the lubrication oil film, and SB is the boundary oil film lubrication state area.

AC C

Therefore, the friction force is

ft= ftA+ ftB+ ftS=ιSSA+ιLSB+ ftS ,

(14)

fn= fnA+ fnB+ fnS= PSSA + PLSB + fnS .

(15)

- 19 -

Fig. 6. Friction force model

RI PT

ACCEPTED MANUSCRIPT

(4) Probability statistical model of cutting and ploughing abrasive particle numbers

SC

Abrasive particles with different heights are distributed randomly and unevenly on the grinding wheel

M AN U

surface. Suppose that the protrusion height distribution of abrasive particles on the grinding wheel conforms to normal distribution. In the arc grinding zone, different protrusion heights of abrasive particles will lead to different cutting depths into the workpiece. Therefore, many statuses of abrasive particles are found in the arc grinding zone, namely, cutting, ploughing, scratching, contact, and non-contact. Only cutting, ploughing,

TE D

and scratching contribute to the grinding process. These three types of abrasive particles can be distinguished based on cutting depth. As a result, the probability function of different cutting depths can be obtained from

EP

the probability function of different abrasive particle heights. Hence, the proportions of these three types of

AC C

abrasive particles in the total abrasive particles can be calculated.

Fig. 7. Probability statistical model of abrasive particles size

- 20 -

The number of abrasive particles per unit area (Ns) was calculated from the maximum diameter (dmax),

ACCEPTED MANUSCRIPT

minimum diameter (dmin), and percentage of abrasive particles (w) on the grinding wheel Ns = (

2 8 3 w ) 3 π (d max − d min )

(16)

The total number of abrasive particles (Ntotal) in the arc grinding zone can be determined from the

Ntotal = N s ⋅ b ⋅ D ⋅ arccos（

RI PT

diameter of grinding wheel (D), grinding width (b), and grinding depth (ap).

D − ap ） D

(17)

SC

Zhang et al. (2007) established the calculation formula of micro-material removal rate (Vana) and determined the diameter difference (hin) between the largest abrasive particles and contact ones in the arc

micro-material removal rate (Vana).

Vana = l ⋅ Ntotal

1 2π

∫

+∞

xcut min

M AN U

grinding zone. The calculation was based on the principle of equal macro-material removal rate (Vexp) and

g x 2 ⋅ tan θ ⋅ e− x /2 dx , 2

(18)

TE D

where l is the grinding arc length and xcutmin is the x-coordinate value of the smallest cutting particle diameter.

The x-coordinate value of the ploughing particle diameter (xconmin) is

EP

d max − d min 10 − hin ) ⋅ . 2 d max − d min

(19)

AC C

xconmin = (

According to modern grinding theory (Li and Zhao, 2003), cutting occurs when the cutting depth of abrasive particles is 0.05 times the cutting particle radius. The x-coordinate value of the smallest cutting particle diameter is

xcut min = xcon min + 0.05

d cut min 10 ( ). 2 d max − d min

(20)

Therefore, the cutting abrasive particle ratio (Pcut) and the ploughing abrasive particle ratio (Pplow) are as follows: - 21 -

Pplow = Pcut =

1 2π 1 2π

∫

+∞

2

xcon min

∫

+∞

xcut min

ACCEPTED MANUSCRIPT

e− x /2 dx ,

(21)

e − x /2 dx . 2

(22)

(5) Calculation of cutting and ploughing forces

RI PT

The cutting and ploughing forces of the single abrasive particle as well as the proportions of ploughing and cutting particles can all be calculated from the theoretical equations shown above. Thus, the total cutting and ploughing forces at a fixed time are computed as

(23)

SC

Ftc, total= Ftc Pcut Ntotal Fnc, total= Fnc Pcut Ntotal

M AN U

Ftp, total= Ftp Pplow Ntotal Fnp, total= Fnp Pplow Ntotal .

In accordance with the above formula, cutting and ploughing forces were calculated with MATLAB software. Table 8 shows the input parameters, and Table 9 presents the calculation results.

TE D

Table 8. Input parameters Parameters

Value

diameter of the grinding wheel D (mm)

300

peripheral speed of grinding wheel Vs (m/s)

30

feed speed Vw (mm/s)

10

EP

grinding depth ap (mm) grinding width b (mm)

0.01 20 0.180

maximum abrasive particle diameter dmax (mm)

0.202

AC C

average abrasive particle diameter d (mm)

minimum abrasive particle diameter dmin (mm)

workpiece yield strength δs (Mpa) percentage of abrasive particles w (%)

0.158 355 47.32%

Table 9. Calculation results Parameters

number of abrasive particles per unit area (Ns)

Value 34.79

total number of abrasive particles Ntotal

1704.3621

diameter difference hin (mm)

0.0161382

cutting abrasive particle ratio Pcut (%)

0.7754

ploughing abrasive particle ratio Pplow (%)

12.96

cutting abrasive particle number Ncut

13.21

ploughing abrasive particle number Nplow

220.88

- 22 -

single abrasive particle tangential cutting force Ftc (N)

0.129

ACCEPTED MANUSCRIPT single abrasive particle normal cutting force F (N) 0.2179 nc

single abrasive particle tangential ploughing force Ftp(N)

2.6797×10-3

single abrasive particle normal ploughing force Fnp (N)

5.5859×10-3

tangential cutting force Ftc,total (N)

1.704

normal cutting force Fnc,total (N)

2.878

tangential ploughing force Ftp,total (N)

0.5919

normal ploughing force Fnp,total (N)

1.2334

RI PT

(6) Calculation of friction force

Although the theoretical calculation formula of friction force has been provided, friction force is difficult to calculate through a theoretical model because the lubrication mechanism under different

SC

lubrication conditions is highly complicated and lubrication force is influenced by many factors. In this part,

M AN U

friction force is the measured grinding force minus the theoretically calculated cutting and ploughing forces. The result was utilized to analyze lubrication performances under different working conditions. Friction

AC C

EP

TE D

forces under different grinding conditions are shown in Fig. 8.

Fig. 8. Friction force mean value in different grinding conditions

3.2 Lubricating property 3.2.1 Friction coefficient (µ) Fig. 9 shows the friction coefficient (µ) calculated in different grinding conditions of friction force.

- 23 -

RI PT

ACCEPTED MANUSCRIPT

Fig. 9. Friction coefficient in different grinding conditions

SC

Fig. 9 shows that flood grinding has the smallest friction coefficient (µflood=0.256). For the rest of the grinding conditions, MQL and N-MQL based on mineral oils (represented by liquid paraffin) show a high

M AN U

friction coefficient (µpara=0.335, µpara-nano= 0.312), whereas MQL based on vegetable oils has a small friction coefficient. N-MQL based on palm oil has the smallest µ among all vegetable oils (µpalm-nano= 0.258); its µ is almost equal to that of flood grinding. This result verifies that vegetable oils can replace mineral oils as the

TE D

base oil of MQL, and it’s lubricating property was closed to flood grinding. In both MQL and N-MQL grinding, different vegetable oils have different lubrication effects. The order in terms of the friction coefficient is palm oil < rapeseed oil < soybean oil. The palm oil nanofluid has the lowest friction coefficient

AC C

3.2.2 Specific energy (U)

EP

(µpalm-nano= 0.258). The soybean oil nanofluid has the lowest friction coefficient (µsoybean-nano= 0.283).

Specific grinding energy (U) refers to the energy consumption in removing a unit volume of material (Alonso et al., 2015). Despite the small amount of surface energy for developing a fresh surface, residual energy on the superficial layer, and deformation energy of grindings, most grinding energies are converted into grinding heats. Specific grinding energy can be divided into cutting, ploughing, and friction energies according to the usage. During the grinding process, specific cutting and ploughing energies are useful. However, specific friction energy is harmful to grinding and generates tremendous heat that will deteriorate grinding performance and workpiece surface quality. Therefore, calculating the specific energy of cutting, - 24 -

ploughing, and friction forces is necessary. Grinding performance under different grinding conditions can

ACCEPTED MANUSCRIPT

then be evaluated by specific friction energy. This method is important to control grinding quality and improve grinding performance. Eq. (24) is the calculation formula of specific energy. Specific energy under different grinding conditions is shown in Fig. 10. Pg Qw

=

Vs ⋅ Ft ⋅⋅⋅⋅⋅ ( J / mm3 ) , Vw ⋅ a p ⋅ b

(24)

RI PT

U=

where U is specific grinding energy (J/mm3), Pg is total consumed grinding energy (J), Qw is the

SC

removal rate of materials per unit volume, Ft is tangential grinding force (N), Vs is the peripheral speed of grinding wheel (m/s), Vw is the workpiece feed speed (mm/s), ap is the grinding depth (mm), and b is the

AC C

EP

TE D

M AN U

workpiece width (mm).

Fig. 10. Specific energy in different grinding conditions

Fig. 10 shows specific grinding energy with the same variation law of the friction coefficient under different grinding conditions: palm oil < rapeseed oil < soybean oil. Comparison of specific cutting, ploughing, and friction energies shows that the first two account for a small proportion of the total specific grinding energy. For example, N-MQL based on palm oil has the lowest specific grinding energy. Specific cutting and ploughing energies only account for 20.27% of the total specific grinding energy. Specific friction energy that accounts for 79.73% is converted into grinding heats. Therefore, studying the specific - 25 -

friction energy is important to reduce grinding heats and improve grinding performance.

ACCEPTED MANUSCRIPT

3.2.3 Discussion Grinding force can be divided into cutting, ploughing, and friction forces. Cutting and ploughing forces are calculated through a theoretical model, and friction force is the measured grinding force minus the

RI PT

theoretically calculated cutting and ploughing forces, which is used to analyze lubrication performances under different grinding conditions. This method does not involve cutting and ploughing forces, which are unaffected by lubrication conditions and are more scientific and accurate than the overall grinding force in

SC

evaluating grinding performance.

M AN U

(1) Under a certain grinding condition, the lubrication condition only influences friction force and does not affect cutting and ploughing forces. According to the above theoretical calculation and experimental research, the cutting and ploughing forces under this grinding condition are Ftc, total=1.70N, Fnc, total=2.89N and Ftp, total=0.59N, Fnp, total=1.23N, respectively. Then, the sum of tangential cutting and ploughing forces as

TE D

well as the sum of normal cutting and ploughing forces are calculated as 2.30 and 4.11 N, respectively. For example, soybean oil-based MQL has the highest experimental grinding force. Tangential and normal cutting and ploughing forces account for 9.29% and 5.84% of the total grinding force, respectively, and the rest are

EP

friction force. For the N-MQL based on palm oil, tangential and normal cutting and ploughing forces account

AC C

for 20.27% and 9.75% of the total grinding force, respectively, and the rest are friction force. The following text explains the significance of grinding heat generation through the calculation of friction force. (2) Previous research has proven that vegetable oils are feasible base oils of MQL. The factors that influence the lubrication performance of vegetable oils were analyzed through experiments. In these experiments, the friction coefficient and specific grinding energy were calculated from the measured grinding force, which cannot reflect the lubrication performance of the grinding zone fully because of the experimental error. This study only analyzed friction coefficient related to friction force. The following are the conclusions obtained from the experiments. - 26 -

MQL and N-MQL grinding obtained a low friction coefficient that is close to that of flood

ACCEPTED MANUSCRIPT

grinding. On one hand, given that a gas barrier layer existed on the wheel surface during the grinding process, a small proportion of flood grinding liquid can cross the layer, and the grinding liquid for lubrication only

RI PT

accounts for a small part. The increase in jet speed for MQL grinding liquid results in a large increase in the proportion of grinding liquid for lubrication (Zhang et al., 2015b). Therefore, although the flow rate of MQL and N-MQL is 50 mL/h, which is only 0.083% of flood lubrication, MQL and N-MQL still

SC

have a good lubrication effect. On the other hand, the lubricating oil forms absorption and reaction films on the friction pair surface because MQL base oil has polar groups (such as -OH, -COOH, and -COOR).

M AN U

MQL base oil presents higher viscosity than flood fluid, such that the lubricating oil forms present higher durability (Zhang et al., 2014). Furthermore, the nanoparticles in the nanofluid perform ball-bearing and anti-friction functions in the grinding process, which further reduce the sliding force of

TE D

the grains and the friction coefficient.

Compared with liquid paraffin MQL, vegetable oil MQL has a lower coefficient of friction. According to previous research (Zhang et al., 2014), vegetable oil fatty acid has a longer molecular

EP

carbon chain than liquid paraffin. This longer molecular carbon chain increases the durability of the

AC C

lubricating oil forms. Meanwhile, vegetable oil has higher viscosity than liquid paraffin, such that the lubricating oil forms present higher durability. Furthermore, in consideration of the difference in fatty acid type and content in the three types of vegetable oils, the order of the lubricating properties of the three types of vegetable oils is palm oil < rapeseed oil < soybean oil. (3) Specific grinding energy refers to the energy consumption in removing a unit volume of the material. Despite the small amount of surface energy for developing a fresh surface, residual energy on the superficial layer, and deformation energy of grindings, most grinding energies are converted into grinding heat. The specific cutting and ploughing energy ratio indicates that specific cutting and ploughing energies only account - 27 -

for a small proportion of the total grinding energy, and the rest is consumed by friction of the grinding zone.

ACCEPTED MANUSCRIPT

This situation causes a large loss of grinding energy, generation of excessive grinding heat, and deterioration of the processing surface quality and properties. Meanwhile, improving the lubrication condition effectively increases the proportions of specific cutting and ploughing energies. This condition can reduce the loss of

RI PT

grinding energy and improve the lubrication performance of the grinding zone and workpiece surface quality.

3.3 Cooling performance 3.3.1 Total heat flow density

SC

During the grinding process, the grinding wheel and workpiece produce grinding force. Energy is

M AN U

transformed into energy between the grinding power of the grinding wheel and workpiece through friction, shear, and other forces, as reported by Chinchanikar and Choudhury (2015). A small amount of grinding energy is consumed on the new surface formation, remains on the surface, and used in the degeneration of abrasive debris. Except for this amount of energy, most parts of the energy are transformed into grinding heat.

TE D

The grinding heat of the workpiece surface is produced by the rapid and continuous heat supply, such as the heat sources in the grinding zone. The continuously supplied heat sources are concentrated in the grinding

unit time is Q Ft ⋅ vs = , S lc ⋅ b

(25)

AC C

qtotal =

EP

zone and widely distributed in the entire grinding contact area. The thermal flux per unit of grinding width in

where qtotal is the thermal flux (J/(mm2·s)), Q is the grinding power (J/s), and S is the contact area of the grinding wheel and workpiece (mm2). The total heat flow density per unit of grinding width in unit time can be calculated according to the above formula. Hahn (1956) posited that friction force is the main source of grinding heat. Thus, the total heat flow density of different grinding conditions was calculated on the basis of friction force, as shown in Fig. 11. - 28 -

RI PT

ACCEPTED MANUSCRIPT

Fig. 11. Thermal flux of different grinding conditions

SC

Given fixed grinding parameters and because thermal flux variation is only related to tangential

M AN U

friction force, the variation trend of thermal flux under different lubrication conditions is consistent with the variation trend of tangential friction force. Fig. 11 reveals that thermal flux under flood grinding is small (8.42 J/(mm2s)), but that under MQL and N-MQL grinding based on palm oils is smaller, which are 23.99% and 34.32% lower than that of flood grinding, respectively. This result proves that MQL and N-MQL

TE D

generate less grinding heat than flood grinding. Compared with mineral oil, vegetable oil contributes a lower thermal flux during MQL grinding. MQL grindings using different vegetable oils as the base oil show

EP

different thermal fluxes: palm oil < rapeseed oil < soybean oil. The N-MQL grinding based on palm oil has the smallest thermal flux (5.53 J/(mm2s)), which is 52.97% lower than that of MQL grinding based on

AC C

soybean oil. This result is attributed to the different physical properties and lubrication performances of vegetable oils. Thermal flux presents the same variation trend in MQL and N-MQL grinding. However, N-MQL grinding has a lower thermal flux than MQL grinding because the involvement of the nanoparticle improves the lubrication of the lubrication zone.

3.3.2 Grinding peak temperature To sum up, different lubrication conditions lead to different thermal fluxes, that is, different grinding heat outputs. Given that different nanofluids have different heat exchange performances, the grinding heat - 29 -

transmitted to the workpiece surface differs. Therefore, the peak temperature of the grinding zone is

ACCEPTED MANUSCRIPT

determined by the thermal flux and heat exchange performances of nanofluids. The temperature curve under different grinding conditions can be determined through experiments. In this study, a clip-type thermocouple was used to determine the grinding temperature. Temperature measurement signal image under four grinding

EP

TE D

M AN U

SC

RI PT

conditions is shown in Fig. 12. The peak temperature under different grinding conditions is shown in Fig. 13.

AC C

Fig. 12. Temperature measurement signal image under four grinding conditions

Fig. 13. Peak temperature under different grinding conditions - 30 -

As shown in Fig. 13, flood grinding has the lower peak grinding temperature (129.0 °C)and dry

ACCEPTED MANUSCRIPT

grinding has the highest peak grinding temperature (325.9 °C). Workpiece surface peak temperature under MQL grinding is higher than that under flood grinding but is still lower than the burn temperature. Palm oil N-MQL has got the lowest peak grinding temperature (124.1 °C), which decreased by 61.92% compared

RI PT

with these for dry grinding. This result proved the feasibility of using vegetable oils in MQL. The sequence of the grinding peak temperatures of MQL and N-MQL based on three vegetable oils is as follows: palm oil < soybean oil < rapeseed oil. Palm oil has the lowest grinding peak temperature and rapeseed oil has the

SC

highest (235.6 °C). The sequence of the grinding peak temperatures of the three vegetable oils differs from that of thermal flux, indicating large differences in the heat exchange capability of the corresponding MQL

M AN U

grinding liquids.

3.3.3 Energy proportionality coefficient transmitted to the workpiece

The sequence of the grinding peak temperatures of the three vegetable oils differs from that of thermal

TE D

flux, indicating large differences in the heat exchange capability of the corresponding MQL grinding liquids. However, the heat exchange capability of MQL grinding liquids cannot be determined by analyzing the grinding peak temperature and thermal flux. Zhang D.K. et al. (2015) calculated the energy proportionality

EP

coefficient transmitted to the workpiece (R=qwb/qtotal) from the ratio between the energy transmitted to the

qwb =

AC C

workpiece (qwb) and the total energy (qtotal).

kvw1/2

βα w1/2α p1/ 4 d s1/ 4

θ max ,

(26)

where k is the correlation coefficient of the material (W/m2k), β is a constant that depends on the shape of the heat source (1.06), αw is thermal diffusivity (m2/s), and θmax is the grinding peak temperature (°C). Jin and Stephenson (2008) reported that the energy proportionality coefficient transmitted to the workpiece can reflect the heat exchange capability of MQL grinding liquids. The energy proportionality coefficient transmitted to the workpiece under different grinding conditions is displayed in Fig. 14. - 31 -

RI PT

ACCEPTED MANUSCRIPT

SC

Fig. 14. R under different grinding conditions

In Fig. 14, the minimum R is achieved by N-MQL based on soybean oil (44.81%), the maximum is

M AN U

achieved by dry grinding (82.70%). The R of N-MQL based on soybean oil has lower than that of flood grinding, and decreased by 45.82% compared with these for dry grinding. This result indicated that vegetable oil could get better cooling performance than flood grinding. The R sequence of the three vegetable oils is as

TE D

follows: soybean oil < rapeseed oil < palm oil. Soybean oil has the lowest (44.81%) and palm oil has the highest (73.08%).The R of the three vegetable oils integrates the grinding peak temperature and thermal flux

3.3.4 Discussion

EP

and can thus be the final evaluation index of the heat exchange capability of MQL grinding liquid.

AC C

The sequences of thermal flux, grinding peak temperature, and R are not completely the same. In practical processing, energy density represents lubrication performance and is the basis of analyzing the heat exchange capability of the workpiece. R is an important evaluation index of the heat exchange capability of the MQL grinding liquid. Grinding peak temperature is the collaborative consequence of the lubrication performance and heat exchange capability of the MQL grinding liquid. To study the relationship between grinding peak temperature and physical properties of MQL grinding liquids, the influence laws of physical properties on both R and energy density should be analyzed.

- 32 -

(1) Effect of the viscosity of nanofluid on cooling property

ACCEPTED MANUSCRIPT

In the past, researchers presented a conceptual effect of the viscosity of MQL grinding liquid on heat exchange capability. They analyzed the heat exchange capability of MQL grinding liquid through viscosity but did not explain the nature of heat convection. In this study, the viscosity of MQL and N-MQL grinding

RI PT

liquids was tested. Fig. 15 shows that with the increase in temperature, the viscosity of pure oils and different oil nanofluids decreases. The viscosity sequence of the different vegetable oils is as follows: soybean oil <

M AN U

SC

rapeseed oil < palm oil. Additionally, the viscosity of pure oil is lower than that of the same oil nanofluid.

TE D

Fig. 15 Viscosity of different nanofluids

Nanofluid for MQL grinding exists in turbulence flow in the grinding zone. The nanofluid absorbs

EP

grinding heat in the grinding zone through heat convection and cools the workpiece. The viscosity of MQL grinding liquid influences its heat convection intensity. The influence mechanism of viscosity on heat

AC C

exchange capability is mainly manifested from the following two aspects.

1) Effect of viscosity on the heat transfer coefficient of the nanofluid Fog drops of MQL grinding liquid jet into the grinding zone at a certain velocity and from a certain angle. They fall on the workpiece/grinding wheel interface and still flow forward at a certain velocity after contact with the workpiece. An oil film is formed on the contact surface between abrasive particles and the workpiece. Relative movements occur between liquid layers in the oil film because of the relative movement of the grinding wheel and workpiece. In these two cases, the heat exchange process of the grinding liquid - 33 -

drops conforms to the heat convection theory of flowing liquid. Therefore, the heat transfer coefficient of the

ACCEPTED MANUSCRIPT

MQL grinding liquid is related to viscosity. Given that the Reynolds number (Re) of MQL grinding is much higher than 2300, the MQL fog drops and MQL oil film cause heat convection through turbulent flows in the grinding zone (Fig. 16). In two states of fluids, Prandtl (2000) defined the thin layer (also called thermal

RI PT

boundary layer) as the area where the formation temperature of the workpiece/abrasive particle contact surface changes significantly. The turbulent thermal boundary layer can be further divided into viscous sublayer and turbulent layer. According to heat transfer theory, the temperature gradient of the thermal

SC

boundary layer reaches the peak at the viscous sublayer but is small in the turbulent layer. In other words, the heat exchange capability of the MQL grinding liquid is determined by the viscous sublayer. High viscosity of

M AN U

the MQL grinding liquid causes a thick viscous sublayer, that is, low temperature rise of the grinding liquid in unit time. This condition explains the effect of viscosity on the heat transfer coefficient from the nature of

AC C

EP

TE D

heat convection. The higher viscosity is, the lower the heat transfer coefficient of grinding liquid is.

Fig. 16. Convection heat transfer principle of the grinding zone

2) Effect of viscosity on the infiltration capacity of the nanofluid Fog drops of MQL grinding liquid enter into the grinding zone at a certain velocity and from a certain angle. The infiltration capacity of the MQL fog drops affects the heat exchange efficiency, thus influencing the heat exchange capability of the MQL grinding liquid. Viscosity is an influencing factor of infiltration capacity of the MQL grinding liquid. In Fig. 17, the MQL grinding liquid continues to flow forward after - 34 -

entering the grinding wheel–workpiece interface because of inertia. However, the viscosity force on the

ACCEPTED MANUSCRIPT

contact surface of the MQL grinding liquid and the workpiece hinders the flow trend of the fog drops. Therefore, a high-viscosity grinding liquid has poor fluid ability and short flowing distance and thus experiences difficulty infiltrating the gaps between the grinding wheel and the workpiece and the gaps

RI PT

between abrasive particles and grindings. On the contrary, a low-viscosity grinding liquid can infiltrate these

EP

TE D

M AN U

SC

gaps effectively. Hence, low viscosity results in high infiltration capacity of grinding liquids.

AC C

Fig. 17. Infiltration principle of MQL grinding liquids

(2) Effect of surface tension on cooling property Surface tension (σ) is an important physical property that influences the cooling and lubrication performances of MQL grinding liquids. This influence is manifested from many aspects. Previous research have thoroughly analyzed the influence of the surface tension of MQL grinding liquid on lubrication performance. The following text emphasizes the effect of surface tension of MQL grinding liquid on the cooling effect. Different vegetable oils have different types and contents of fatty acids, which result in - 35 -

different surface tensions. The contact angle between MQL fog drops and the workpiece surface (hereinafter

ACCEPTED MANUSCRIPT

referred as “contact angle”) is related to solid–liquid interface tension (γvl), solid–gas interface tension (γsv), and liquid–gas interface tension (γvl). Liquid–gas interface tension is surface tension. Derived from Young’s equation, contact angle is expressed as cosθc=(γsv-γsl)/γvl .

RI PT

(27)

Based on this equation, given the fixed workpiece material, the contact angle increases with the increase in γvl. In this experiment, the contact angles among the 3 vegetable oils and the 45 steel workpieces

SC

were measured (Fig. 18). The measured contact angles of the three nanofluids were θc(palm)=46.58°,

TE D

M AN U

θc(rapeseed)=37.26°, and θc(soybean)=31.74°, showing a sequence of palm oil > rapeseed oil > soybean oil.

EP

Fig. 18. Contact angle measured in theory and results

AC C

The surface tension sequence of the three vegetable oils is palm oil > rapeseed oil > soybean oil. Surface tension influences the cooling effect in two aspects. On one hand, surface tension affects the atomization effect of MQL grinding liquid at the nozzle and determines the size of MQL fog drops. On the other hand, surface tension influences the contact angle between MQL fog drops entering into the grinding zone and the workpiece. These two different influence mechanisms determine the cooling efficiency of MQL grinding liquid.

1) Effect of surface tension on atomization performance The atomization of the MQL grinding liquid at the nozzle is a complicated, multi-phase, transient - 36 -

process. The formed fog drops have a small size, large range, and large quantity. During atomization, the

ACCEPTED MANUSCRIPT

nozzle structure, jetting parameter, and the physicochemical properties of the MQL grinding liquid influence the atomization effect of the MQL grinding liquid. Surface tension is one of the important parameters that influence the atomization effect of the MQL grinding liquid. Specifically, different MQL grinding liquids

RI PT

have different surface tensions. Accordingly, the atomized fog drops will have different sizes, resulting in different cooling effects of the atomized MQL grinding liquids in the grinding zone. The surface tension of the MQL grinding liquid influences fog drop size as well. According to the theory of surface physicochemical

TE D

M AN U

SC

properties, fog drop size increases as surface tension increases (Fig. 19).

EP

Fig. 19. Effect of surface tension on fog drop size

To sum up, a proportional relationship exists between surface tension and fog drop size. An MQL

AC C

grinding liquid with low surface tension has high cooling efficiency for two reasons. First, MQL fog drops with low surface tension have a small size, large quantity, and high specific surface area. Hence, more fog drops enter the grinding zone per unit volume. Second, a high specific surface area increases the heat exchange area of the MQL grinding liquid. According to the experimental results, the surface tension sequence of the three vegetable oils is palm oil > rapeseed oil > soybean oil. The R sequence of MQL and N-MQL grindings based on different vegetable oils is palm oil > rapeseed oil > soybean oil. The experimental results verify the above analysis well. - 37 -

2) Effect of contact angle on cooling efficiency

ACCEPTED MANUSCRIPT

Regardless of the fog drop size, different MQL grinding liquids will form different contact angles between the fog drops and the workpiece, which further influences the infiltration area and cooling efficiency of the MQL grinding liquid. The contact angles between the 3 vegetable oils and the 45 steel workpieces

RI PT

were measured and showed a sequence of palm oil > rapeseed oil > soybean oil. The effect of contact angle on the cooling effect of the MQL grinding liquid is reflected from the following two aspects (Fig. 20). Theoretically, different fog drops have different infiltration capacities because of the different

SC

surface tensions. Fog drops with small surface tension have high infiltration capacity. In the experiment, a small contact angle results in a large infiltration area, which means the cooling area

M AN U

of the MQL grinding liquid is large. Meanwhile, fog drops with a small contact angle spread out more quickly than those with a large contact angle.

Grinding liquid fog drops enter the grinding zone at a certain velocity. The fog drops stay in the

TE D

grinding zone for a very short period and are then carried out by the grinding wheel. According to heat convection theory, fog drops can be divided into the thermal boundary layer and the main flow region during heat convection. The thickness of the thermal boundary layer remains unchanged.

EP

However, the grinding liquid in the main flow region is carried out from the grinding zone quickly

AC C

before absorbing enough heat. In other words, the grinding liquid in the main flow region will not provide a satisfactory heat exchange effect. When the contact angle decreases, the thermal boundary layer expands, and the proportion of grinding liquid in the main flow region declines. This result explains why MQL fog drops with a small contact angle have high cooling efficiency.

- 38 -

SC

RI PT

ACCEPTED MANUSCRIPT

(3) Continuous grinding temperature curve

M AN U

Fig. 20. Influence mechanism of contact angle

The influence law of the surface tension of the MQL grinding liquid on the atomization effect and contact angle has been disclosed in previous studies. On this basis, the influence law on cooling efficiency was determined. In single grinding, cooling efficiency is reflected by R. Given that practical grinding is a

TE D

continuous single grinding, temperature accumulation of continuous grindings is one of the evaluation parameters of cooling efficiency. The temperature variation in continuous grindings was explored, and the

EP

temperature curve of 10 successive grindings was measured. In the experiment, different vegetable oils were used as the base oil of the N-MQL grinding liquid. The temperature curves of the 8 successive grindings

AC C

under different grinding conditions are shown in Fig. 21.

- 39 -

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

EP

Fig. 21. Continuous grinding temperature curve under different grinding conditions

AC C

Soybean oil nanofluid with the smallest surface tension shows the lowest accumulative peak temperature rise, which is valued at 29.5 °C. This result is caused by the high cooling efficiency, intensive participation in heat exchange, and large heat exchange area. With these characteristics, soybean oil nanofluid can carry away more heat in each grinding, and the accumulative peak temperature rise after several grindings is relatively low. By contrast, the accumulative peak temperature increments of palm oil nanofluids is 75.9 °C, which is highest. The rapeseed oil nanofluid achieves the higher accumulative peak temperature rise (38.2 °C) than soybean oil, and its peak temperature curve fluctuates dramatically. This effect is due to the unsaturated fatty acid in rapeseed oils, which forms a less stable oil film in the grinding zone compared with saturated - 40 -

fatty acid. Consequently, the lubrication and cooling performances of rapeseed oil nanofluid are unstable.

ACCEPTED MANUSCRIPT

3.4 Conclusion on the influence law According to the above analysis, the following conclusions were obtained. First, the three vegetable oils provide better cooling and lubrication effects than mineral oils in MQL and N-MQL. Second, with

RI PT

different surface tensions and viscosities, these three vegetable oils also show different cooling and lubrication effects. The influence law of characteristics on cooling and lubricating performance was also analyzed. The conclusions are as follows.

SC

The friction coefficient (µ) and thermal flux (qtotal) are influenced by lubricating performance and

M AN U

are the decisive factors of grinding temperature. The energy proportionality coefficient (R), which is one of the decisive factors of grinding temperature, is influenced by cooling performance. Soybean oil with low viscosity and surface tension has a low energy proportionality coefficient (R) in the experiment, which indicates good cooling performance. Meanwhile, soybean oil nanofluid

TE D

has the lowest accumulative temperature rise (valuing at 29.5 °C), which confirms the previous conclusion. Palm oil with high viscosity and surface tension has a low thermal flux (qtotal) and friction coefficient (µ), which indicates good lubrication performance. This result reveals that the

EP

effects of viscosity and surface tension on the cooling effect and lubrication performance of the

AC C

grinding liquid are contrasting.

The sequence of grinding peak temperature (palm oil < rapeseed oil < soybean oil) indicates that viscosity and surface tension influence lubrication performance more than cooling performance. N-MQL based on palm oil has the poorest cooling effect because of its highest viscosity and surface tension but exhibits the best lubrication performance and the lowest grinding heat output, thus resulting in the lowest grinding peak temperature. Hence, palm oil has the best cooling effect and lubrication performance and is superior to the two other vegetable oils as the base oil of the MQL grinding liquid.

- 41 -

TE D

M AN U

SC

RI PT

ACCEPTED MANUSCRIPT

4. Conclusion

EP

Fig. 22. Conclusion on the influence law

AC C

The cooling performances of MQL grindings based on different vegetable oils were analyzed through experiments. Cutting and ploughing forces under experimental conditions were analyzed and calculated theoretically. The friction coefficient, specific friction energy, total heat flow density, and grinding peak temperature were utilized as evaluation parameters. The influence of the physical properties (viscosity and surface tension) of vegetable oils on the cooling effect was analyzed comprehensively. The conclusions are as follows. (1) Cutting force (Ftc, total=1.70 N, Fnc, total=2.89 N) and ploughing force (Ftp, total=0.59 N, Fnp, total=1.23 N) under a fixed grinding condition were calculated theoretically. Friction force was obtained according to - 42 -

the theoretical model. The experimental results were used to calculate the friction coefficient and thermal

ACCEPTED MANUSCRIPT

flux. Friction force can reflect lubrication and cooling performance more scientifically and accurately than the overall grinding force. (2) Comparison of specific cutting energy (5.11 J/mm3), specific ploughing energy (1.78 J/mm3), and

RI PT

specific friction energy shows that the first two factors account for a small portion of the total specific grinding energy. With N-MQL based on palm oil as an example, a small amount of surface energy (20.27%) was consumed for fresh surface formation. Residual strain energy in the superficial layer of grindings and

SC

kinetic energy were carried away by grindings. Most grinding energies (79.73%) were consumed for the heating workpiece, grinding wheel, and grindings as well as radiation stray.

M AN U

(3) For lubricating performance, vegetable oil with high viscosity and surface tension achieved low thermal flux (qtotal) and friction coefficient (µ), which indicates good lubrication performance. Lubrication performance showed a sequence of soybean oil < rapeseed oil < palm oil. This sequence is caused by

is, thermal flux.

TE D

different types of fatty acids and viscosity. Lubrication performance determines the grinding heat output, that

(4) For cooling performance, vegetable oil with low viscosity and surface tension showed low energy

EP

proportionality coefficient (R) in the experiment, which indicates good cooling performance. Cooling

AC C

performance showed a sequence of palm oil < rapeseed oil < soybean oil. Further research was carried out on the continuous grinding temperature curve, and the above conclusion was verified. Soybean oil nanofluid obtained the lowest accumulative temperature rise (29.5 °C). (5) The effects of grinding fluid viscosity and surface tension on cooling performance and lubrication performance are contrasting. The sequence of grinding peak temperature (palm oil < rapeseed oil < soybean oil) indicated that viscosity and surface tension influence lubrication performance more than the cooling effect. Although N-MQL based on palm oil had the poorest cooling effect because of its highest viscosity and surface tension, it exhibited the best lubrication performance and the lowest grinding heat output, thus - 43 -

resulting in the lowest grinding peak temperature. As a result, palm oil is the optimum base oil of MQL. The

ACCEPTED MANUSCRIPT

palm oil nanofluid obtained the lowest grinding temperature (123.8 °C) and the best lubrication performance (µ = 0.258, specific friction energy 27.09 J/mm3, and qtotal=5.53

J/(mm2s)).

RI PT

Acknowledgment This research was financially supported by the National Natural Science Foundation of China (51175276; 51575290), Qingdao Science and Technology Program of Basic Research Projects (14-2-4-18-jch), and

SC

Huangdao District Application Science and Technology Project (2014-1-55).

M AN U

Conflict of Interests

The authors hereby confirm that no conflict of interest exists for this article.

TE D

References

Alberts, M., Kalaitzidou, K., Melkote, S., 2009. An investigation of graphite nanoplatelets as lubricant in grinding. Int. J. Mach. Tools Manuf. 49 (12), 966-970.

EP

Alonso, U., Ortega, N., Sanchez, J.A., Pombo, I., Izquierdo, B., Plaza, S., 2015. Hardness control of grind-hardening and

AC C

finishing grinding by means of area-based specific energy. Int. J. Mach. Tools Manuf. 88, 24-33. Barczak, L.M., Batako, A.D.L., Morgan, M.N., 2010. A study of plane surface grinding under minimum quantity lubrication (MQL) conditions. Int. J. Mach. Tools Manuf. 50 (11), 977-985. Choi, C., Jung, M., Choi, Y., Lee, J., Oh, J., 2011. Tribological properties of lubricating oil-based nanofluids with metal/carbon nanoparticles. J. Nanosci. Nanotechnol. 11 (1), 368-371. Cetin, M.H., Ozcelik, B., Kuram, E., Demirbas, E., 2011. Evaluation of vegetable based cutting fluids with extreme pressure and cutting parameters in turning of AISI 304L by Taguchi method. J. Cleaner Prod. 19 (17), 2049-2056. Chinchanikar, S., Choudhury, S.K., 2015. Machining of hardened steel—Experimental investigations, performance modeling - 44 -

and cooling techniques: A review. Int. J. Mach. Tools Manuf. 89, 95-109.

ACCEPTED MANUSCRIPT

Ding, W.F., Xu, J.H., Chen, Z.Z., Yang, C.Y., Song, C.J. Fu, Y.C., 2013. Fabrication and performance of porous metal-bonded CBN grinding wheels using alumina bubble particles as pore-forming agents. Int. J. Adv. Manuf. Technol. 67: 1309-1315.

brazed CBN grains in monolayer grinding wheels. Wear, 332-333: 800-809

RI PT

Ding, W.F., Zhu, Y.J., Zhang, L.C., Xu, J.H., Fu, Y.C., Liu, W.D., Yang, C.Y., 2015. Stress characteristics and fracture wear of

Ginzburg, B.M., Hibaev, L.A., Kireenko, O.F., Shepelevskii, A.A., Baidakova, M.V., Sitnikova, A.A., 2002. Antiwear effect

SC

of fullerene C60 additives to lubricating oils, Russ. J. Appl. Chem. 75 (8), 1330–1335.

Hahn, R.S.,1956. The relation between grinding conditions and thermal damage in the workpiece, Trans. ASME 78,

M AN U

807-812.

Hwang, Y., Park, H.S., Lee, J.K., Jung, W.H., 2006. Thermal conductivity and lubrication characteristics of nanofluids. C. Appl. Phys. 6, 67-71.

TE D

Hu, K.H., Hu, X.G., Xu, Y.F., Hang, F., Liu, J., 2010. The effect of morphology on the tribological properties of MoS2 in liquid paraffin. Tribol. Lett. 40 (1), 155-165.

Hadad, M.J., Tawakoli, T., Sadeghi, M.H., Sadeghi, B., 2012a. Temperature and energy partition in minimum quantity

EP

lubrication-MQL grinding process. Int. J. Mach. Tools Manuf. 54, 10-17.

AC C

Hadad, M.J., Sadeghi, B., 2012b.Thermal analysis of minimum quantity lubrication-MQL grinding process. Int. J. Mach. Tools Manuf. 63, 1-15.

Jain, A., Bisht, R.P.S., 2008. Metalworking emulsions from industrial vegetable oils. J. Synth. Lubr. 25 (3), 87-94. Jin, T., Stephenson, D.J.,2008. A study of the convection heat transfer coefficients of grinding fluids. CIRP Ann. 57(1), 367-370. Kalita, P., Malshe, A.P., Arun, K.S., Yoganath, V.G., Gurumurthy, T., 2012a. Study of specific energy and friction coefficient in minimum quantity lubrication grinding using oil-based nano lubricants. Int. J. Manuf. Process. 14 (2), 160-166.

- 45 -

Kalita, P., Malshe, A.P., Rajurkar, K.P., 2012b. Study of tribo-chemical lubricant film formation during application of

ACCEPTED MANUSCRIPT

nanolubricants in minimum quantity lubrication (MQL) grinding. CIRP Ann. 61(1), 327-330. Morgan, M.N., Barczak, L., Batako. A., 2012. Temperatures in fine grinding with minimum quantity lubrication (MQL). Int. J Adv Manuf. Technol. 60(9-12), 951-958.

RI PT

Li, B.M., Zhao, B., 2003. Modern grinding technology. Beijing. China Machine Press. [Chinese]. Li, C.H., Hou, Y.L., Xiu, S.C., Cai, G.Q., 2008. Application of lubrication theory to near-dry-green grinding—feasibility analysis. Adv Mater Res. 135 (4), 44–46.

with Nano-particle Jet of MQL. Adv.in.Mech. Eng. 7 (2), 167-181.

SC

Li, C.H., Li, J.Y., Wang, S., Jia, D.Z., 2013. Modeling and Numerical Simulation of the Grinding temperature distribution

M AN U

Liu, Z.R., 2010. The research of heat transfer theory by nanofluids jet lubrication and the evaluation of the surface integrity in grinding. Master's thesis. Qingdao Technological University.

Lee, P.H., Nam, J.S., Li, C., Lee, S.W., 2012. An experimental study on micro-grinding process with nanofluid minimum

TE D

quantity lubrication (MQL). Int. J. Precis. Eng. Man. 13, 331-338.

Lawal, S.A., Choudhury, I.A., Nukman, Y., 2012. Application of vegetable oil-based metalworking fluids in machining ferrous metals—a review. Int. J. Mach. Tools Manuf. 52 (1), 1-12.

EP

Lawal, S.A., Choudhury, I.A., Nukman, Y., 2013. A critical assessment of lubrication techniques in machining processes: a

AC C

case for minimum quantity lubrication using vegetable oil-based lubricant. J. Cleaner Prod. 41, 210-221. Malkin, S., Guo, C., 2007. Thermal analysis of grinding.CIRP Ann. 56 (2), 760-782. Malkin, S., 2008. Grinding technology. Industrial Press. Malkin, S., Guo, C., 2008. Theory and application of machining with abrasives, in: S. Malkin, grinding technology. Industrial Press. pp, 107-245. Moghadassi, A.R., Hosseini, S.M., Henneke, D., Elkamel, A., 2009. A model of nanofluid effective thermal conductivity based on dimensionless groups. J. Therm. Anal. Calorim. 96 (1), 81–84. Mao, C., Tang, X., Zou, H., Huang, X., Zhou, Z., 2012. Investigation of grinding characteristic using nanofluid minimum - 46 -

quantity lubrication. Int. J. P.Eng. Manuf. 13 (10), 1745-1752.

ACCEPTED MANUSCRIPT

Mao, C., Zou, H., Huang, Y., Li, Y., Zhou, Z., 2013. Analysis of heat transfer coefficient on workpiece surface during minimum quantity lubricant grinding. Int. J. Adv. Manuf. Technol. 66 (1-4), 363-370. O'connell, M.J., Bachilo, S.M., Huffman, C.B., Moore, V.C., Strano, M.S., Haroz, E.H., Smalley, R.E., 2002. Band gap

RI PT

fluorescence from individual single-walled carbon nanotubes. Science 297 (5581), 593-596. Pusavec, F., Kenda, J., Kopac, J., 2014. The transition to a clean, dry, and energy efficient polishing process: an innovative upgrade of abrasive flow machining for simultaneous generation of micro-geometry and polishing in the tooling industry.

SC

J. Cleaner Prod. 76, 180-189.

Rowe, W.B., Dimitrov, B., Ohmori, H.,2012. Tribology of abrasive machining processes. William Andrew, 2012.

M AN U

Rahim, E.A., Sasahara, H., 2011a. An analysis of surface integrity when drilling inconel 718 using palm oil and synthetic ester under MQL condition.Mac.Sci.Technol. 15 (1), 76-90.

Rahim, E.A., Sasahara, H., 2011b. Investigation of tool wear and surface integrity on MQL machining of Ti-6AL-4V using

TE D

biodegradable oil. Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. 225 (9), 1505-1511 Rahim, E.A., Sasahara, H., 2011c. A study of the effect of palm oil as MQL lubricant on high speed drilling of titanium alloys. Tribol. Int. 44 (3), 309-317.

EP

Rabiei, F., Rahimi, A.R., Hadad, M.J., Ashrafijou, M., 2015. Performance improvement of minimum quantity lubrication

AC C

(MQL) technique in surface grinding by modeling and optimization. J. Cleaner Prod. 86, 447-460. Sullivan, P.A., Eisen, E.A., Woskie, S.R., Kriebel, D., Wegman, D.H., Hallock, M.F., Monson, R.R., 1998. Mortality studies of metalworking fluid exposure in the automobile industry: VI. A case‐control study of esophageal cancer. Am. J. Ind. Med. 34(1), 36-48.

Schlichting, H., Gersten, K., Gersten, K., 2000. Boundary-layer theory. Springer Science. Business Media. Sridharan, U., Malkin, S., 2009. Effect of minimum quantity lubrication (MQL) with nanofluids on grinding behavior and thermal distortion. Trans. NAMRI/SME 37, 629–636. Shen, B., Shih, A.J., 2008. Performance of Novel MoS2 nano-particles based grinding fluids in minimum quantity lubrication - 47 -

grinding. Trans. NAMRI/SME. 36, 357–364.

ACCEPTED MANUSCRIPT

Shen, B., Shih, A.J., 2009. Minimum quantity lubrication (MQL) grinding using vitrified CBN wheels, Trans. NAMRI/SME 37, 129-136. Sadeghi, M.H., Haddad, M.J., Tawakoli, T., Emami, M., 2009. Minimal quantity lubrication-MQL in grinding of Ti–6Al–4V

RI PT

titanium alloy. Int.J. Adv. Manuf. Technol. 44 (5-6), 487-500. Silva, L.R., Corrêa, E.C., Brandão, J.R., de Ávila, R.F., 2013. Environmentally friendly manufacturing: Behavior analysis of minimum quantity of lubricant-MQL in grinding process. J. Cleaner Prod. http://dx.doi.org/10.1016/j.jclepro.2013.

SC

01.033.

Sharma, J., Sidhu, B.S., 2014. Investigation of effects of dry and near dry machining on AISI D2 steel using vegetable oil. J.

M AN U

Cleaner Prod. 66, 619-623.

Tawakoli, T., Hadad, M., Sadeghi, M.H., 2010. Investigation on minimum quantity lubricant-MQL grinding of 100Cr6 hardened steel using different abrasive and coolant–lubricant types. Int. J. Mach. Tools Manuf. 50(8), 698-708.

TE D

Tawakoli, T., Hadad, M., Sadeghi, M.H., Daneshi, A., Sadeghi, B., 2011. Minimum quantity lubrication in grinding: effects of abrasive and coolant–lubricant types. J. Cleaner Prod. 19 (17), 2088-2099. Zhang, J.H., Ge, P.Q., Zhang, L., 2007. Research on the grinding force based on the probability statistics. China Mech. Eng.

EP

18 (20), 2399-2402．

AC C

Zhang, S., Li, J.F., Wang, Y.W., 2012. Tool life and cutting forces in end milling Inconel 718 under dry and minimum quantity cooling lubrication cutting conditions. J. Cleaner Prod. 32, 81-87. Zhang, Y.B., Li, C.H., Jia, D.Z., Zhang, D.K., Zhang, X.W., 2014. Experimental Evaluation of MoS2 Nano-particles in Jet MQL Grinding with Different Types of Vegetable Oil as Base Oil. J. Cleaner Prod. 87, 930-940. Zhang, Y.B., Li, C.H., Jia, D.Z., Zhang, D.K., Zhang, X.W., 2015a. Experimental evaluation of the lubrication performance of MoS2/CNT nanofluid for minimal quantity lubrication in Ni-based alloy grinding. Int. J. Mach. Tools Manuf. 99, 19-33. Zhang, Y.B., Li, C.H., Zhang, Q., Jia, D.Z., Wang, S., Zhang, D.K., Mao, C., 2015b. Improvement of useful flow rate of - 48 -

grinding fluid with simulation schemes. Int. J Adv Manuf. Technol. 1-14.

ACCEPTED MANUSCRIPT

Zhang, D.K., Li, C.H., Zhang, Y.B., Jia, D.Z., Zhang, X.W., 2015. Experimental research on the energy ratio coefficient and

AC C

EP

TE D

M AN U

SC

RI PT

specific grinding energy in nano-particle jet MQL grinding. Int. J Adv Manuf. Technol. 78 (5-8), 1275-1288.

- 49 -

ACCEPTED MANUSCRIPT Cooling performance of nanofluids MQL grinding with vegetable base-oil was explored.

2.

New ploughing force model and friction force model were established.

3.

Friction force was obtained according to theoretical model and experimental results.

4.

Friction force was used to calculate friction coefficient and specific friction energy.

5.

Palm oil with higher viscosity and surface tension showed better grinding performances.

AC C

EP

TE D

M AN U

SC

RI PT

1.