A Study on lubrication and cooling performance and machining characteristics of magnetic field assisted minimum quantity lubrication used Fe3O4 nanofluid as cutting fluid

doi:10.21203/rs.3.rs-1621153/v1

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A Study on lubrication and cooling performance and machining characteristics of magnetic field assisted minimum quantity lubrication used Fe3O4 nanofluid as cutting fluid

https://doi.org/10.21203/rs.3.rs-1621153/v1

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As an effective alternative to traditional pouring lubrication method, minimum quantity lubrication (MQL) has been recognized by more and more scholars and applied in factories. However, there are still some technical shortcomings in the application of traditional oil-based MQL technology, such as poor cooling capacity and low lubrication efficiency. Aiming at the technical defects of oil-based MQL, a magnetic field assisted minimum quantity lubrication (mMQL) technology used Fe₃O₄ nanofluid as cutting fluid was proposed. Firstly, MQL equipment with controllable magnetic field was built, and the contact angle, surface tension and dynamic viscosity of Fe₃O₄ nanofluid droplets were measured under different magnetic induction intensity. Based on these variation parameters of physical properties of the magnetic nanofluid droplets, the influence of magnetic induction on the droplet penetrability was subsequently analyzed. Finally, the heat transfer performance and machining characteristics of the nanofluid droplets under different magnetic induction were compared and investigated. Results showed that the Fe₃O₄ nanofluid droplets exhibited lower contact angle and higher viscosity under the influence of magnetic field, thus showing better penetrability and heat transfer performance. Compared with traditional vegetable oil MQL, the cutting temperature, tool wear and cutting force under mMQL were reduced by ~ 35.5%, ~ 52.4% and ~ 43.2%, respectively. Under the influence of magnetic field, the contact angle of magnetic droplets was decreased, and the contact area between the droplets and heat transfer surface was larger, which led to the improvement of droplet evaporation heat transfer efficiency. In addition, the penetrability of Fe₃O₄ nanofluid assisted by magnetic field was improved, more nanofluid could penetrate into the tool-chip contact area, and finally improved its lubrication and cooling efficiency.

Magnetic field assisted minimum quantity lubrication

Penetrability

Heat transfer performance

Machining characteristic

To improve the cutting conditions and solve the environmental problems caused by the large use of cutting fluid in traditional cutting, minimum quantity lubrication (MQL) as an efficient and green cooling and lubrication method, by mixing compressed air with a very small amount of cutting fluid and atomizing, micron droplets are sprayed into the machining area to realize the cooling and lubrication between tools and workpieces. Compared with traditional lubrication methods, MQL presents the advantages of less cutting fluid consumption, effectively reducing cutting force, reducing tool wear and improving workpiece surface quality [1].

In recent years, scholars have presented a lot of research on MQL cutting performance, including turning, milling, drilling, grinding and other cutting methods, as well as titanium alloy, aluminum alloy, superalloy and other material types [2–4]. Tamang et al. [5] found through research that, compared with dry cutting, the tool wear of MQL when turning of superalloy was reduced by 16.57% and the surface quality was improved by 10.41%. Babu et al. [6] carried out milling tests of AISI 304 steel under different lubrication conditions. The mist particles generated by MQL atomization were conducive to improving lubrication conditions and reducing surface roughness. Benjamin et al. [7] proved that MQL cutting could reduce the friction coefficient between the material and the cutting tool, which thus reduced the surface roughness of the workpiece in the case of high-speed milling of titanium alloy.

However, the cooling capacity of traditional oil-based MQL is mainly realized by the evaporation heat transfer of micro cutting fluid and the convective heat transfer of compressed air, which leads to poor cooling effect and affects the machining performance [8, 9]. In addition, the oil drop penetrability under oil-based MQL is insufficient, and it is difficult for vegetable oil to effectively penetrate into the depth of the capillary between tool and chip, resulting in low lubrication efficiency and large tool wear [10, 11]. To alleviate the above technical limitations of traditional oil-based MQL, scholars from various countries have carried out relevant research. Jamil et al [12] combined low-temperature cooling and MQL technology to compare the tool wear using ethanol, Blaser oil and ethanol-Blaser oil hybrid lubricating coolant mixed with and without dry ice as cutting fluid to milling with Ti-6Al-4V titanium alloy. It was found that the tool wear of ethanol-Blaser oil hybrid lubricant mixed with dry ice could be reduced by 66% compared with the traditional MQL strategy, showing good lubrication and cooling effect. Khan et al [13] delivered vegetable oil, water and liquid nitrogen to the nozzle through MQL system and mixed in the nozzle to spray low-temperature water-oil mist to realize lubrication and cooling. When turning haynes-25 cobalt base alloy, this low-temperature MQL technology presented lower cutting temperature in comparison with the traditional flood lubrication method, and the maximum tool life could be prolonged by 111%. Xu et al. [14] developed an electrostatic minimum quantity lubrication (EMQL) system and used Al₂O₃ water-based nano-lubricant as cutting fluid. Compared with traditional vegetable oil MQL, water-based cutting fluid applied in this EMQL system showed better penetration effect and cooling capacity. Liu et al [15] reviewed the progress of cryogenic MQL (CMQL) processing in recent years, compared the machining performance of different CMQL technologies, and showed that the processing performance was significantly improved under the intervention of low-temperature fluid. To sum up, how to effectively improve the penetration and cooling capacity of oil mist under traditional oil-based MQL is a research hotspot today.

Magnetic nanofluid is composed of superparamagnetic nanoparticles uniformly dispersed in the base solution. Fe₃O₄ nanoparticles present the characteristic of high saturation magnetization, they are often made into magnetic nanofluid and applied to various rolling and sliding surfaces in relative contact for lubrication [16]. Compared with conventional lubrication, magnetic fluid lubrication could control the viscosity of magnetic fluid by changing the magnetic induction intensity under the action of external magnetic field, so as to improve the lubrication film-forming performance of magnetic fluid, improve the lubrication effect and reduce the temperature caused by friction. Huang et al. [17] investigated the tribological properties of Fe₃O₄ ferromagnetic fluid under different magnetic induction intensity, indicating that the magnetic field could significantly improve the anti-friction and anti-wear ability of this magnetic fluid and prolong the service life of friction materials. Wang et al. [18] explored the tribological properties of Mn–Zn–Fe magnetic nanofluid under the influence of magnetic field, and found that the magnetic nanoparticles under the influence of magnetic field were easier to adsorb on the friction interface, so as to fill and repair the friction pits and finally formed a lubrication film, and the tribological properties could be significantly improved. Ren et al. [19] designed a hydrodynamic lubrication mechanical seal structure using magnetic fluid as the lubricating medium based on the characteristic that the viscosity of magnetic fluid is controlled by the magnetic field strength, and used the external magnetic field to control the viscosity of magnetic fluid, so as to change the hydrodynamic characteristics of lubricating film. Moreover, the magnetic field also affects the surface energy of magnetic droplets, which could reduce the contact angle of the droplets and improve the evaporation heat transfer capacity on the heat transfer surface. In this research, magnetic nanofluid was applied in MQL, and apply a magnetic field by modified nozzle. Relying on the excellent performance of magnetic nanofluid in magnetic field is expected to improve the technical defects of traditional oil-based MQL.

In this paper, a MQL equipment which could generate magnetic field was firstly built, magnetic field assisted minimum quantity lubrication (mMQL), and Fe₃O₄ nanofluid was used as cutting fluid. The contact angle, surface tension and dynamic viscosity of Fe₃O₄ nanofluid under different magnetic induction were then investigated, and the capillary penetration depth of this nanofluid under different magnetic induction was simulated by using these three parameters to explore its penetrability. At the same time, a steady-state heat transfer experimental platform was built to investigate the heat transfer capacity of Fe₃O₄ nanofluid aerosol under different magnetic induction. Finally, the machining performance of Fe₃O₄ nanofluid mMQL applied to 430 stainless steel turning under different magnetic induction was compared, the preponderance of mMQL was compared with that of traditional vegetable oil MQL, and the wear mechanism of cutting tools was finally analysed.

2.1 Magnetic assisted MQL equipment and cutting fluid

The MQL equipment adopted Accu-Lube produced by ITW company of the United States. The plunger pump in Accu-Lube continuously delivered small amount of cutting fluid to the nozzle (continuously adjustable with 10–200 ml/h). A copper pipe was connected at the outlet of the liquid pipe in the nozzle. The copper pipe was wrapped with enamelled copper wire with 30 turns. The copper wire was connected with a steady current power supply. After being powered on, a magnetic field was generated, and the cutting fluid passed through the magnetic field. The magnetized cutting fluid was mixed with compressed air to form magnetized aerosol, which was sprayed into the machining area for lubrication and cooling. Different magnetic induction intensities were calibrated by Tesla meter. The technical schematic diagram of mMQL equipment is shown in Fig. 1.

The cutting fluid adopted LB-2000 vegetable oil produced by ITW company and Fe₃O₄ magnetic nanofluid. LB-2000 vegetable oil has been widely used in MQL machining industry, which presents the characteristics of good lubrication performance, green environmental protection, non-toxic and easy degradation. Preparation method of Fe₃O₄ nanofluid: the base solution was LB-2000 vegetable oil. Firstly, 1 wt.% Fe₃O₄ nanoparticles (nanoparticle average size of 50–80 nm, saturation magnetization of 18.3ka/m, purchased from Nanjing Xianfeng nano material technology Co., Ltd.) and 0.5 wt.% oleic acid (dispersant) were added to the base solution respectively, and fully stirred by magnetic stirrer. Then, the YPS17B-HB experimental ultrasonic treatment system (Hangzhou Chenggong ultrasonic equipment Co., Ltd.) was used to conduct constant temperature ultrasonic treatment (35 ± 1℃) with the prepared nanofluid for 1 h. The prepared nanofluid could be stably dispersed for 15 days without obvious stratification and sedimentation. The physical drawings of these two cutting fluids were shown in Fig. 2.

2.2 Physical property tests of cutting fluid

Contact angle, surface tension and dynamic viscosity characterize the wettability, spreading and lubrication film-forming characteristics of cutting fluid respectively. Therefore, these three physical properties of the nanofluid should be tested to reveal its lubrication and cooling mechanism.

The contact angle of cutting fluid was measured by angle measurement method [20]. The technical principle diagram of angle measurement method is shown in Fig. 3 (a). Firstly, the cutting fluid was placed in the burette, and the front end of the burette was sleeved with a copper tube wrapped with enamelled copper wire. The copper wire was connected with the steady current power supply to generate a magnetic field. After passing through the magnetic field, the cutting fluid formed droplets and fell into the surface of 430 stainless steel flat plate. Finally, the contact angle of cutting droplets was measured by VW-6000 microscope (Keyence, Japan).

The surface tension of cutting fluid was measured by the drop weight method [20]. The technical principle diagram of the drop weight method was shown in Fig. 3 (b). Firstly, poured the cutting fluid into the burette with enamelled copper pipe, control the glass stopcock, measure the weight of 10 drops falling into the beaker under different magnetic induction intensity, calculated the average value as the weight (m) of a single drop, and finally calculate the surface tension of the cutting fluid by using the following formula:

γ = F·mgR^− 1 (1)

here, γ is the surface tension, F is the correction coefficient (F = 1/2(πk)⁻¹) [21, 22], and R is the inner diameter of copper pipe (2 mm).

NDJ-5S rotary viscometer was used to measure the dynamic viscosity of cutting fluid. NdFeB permanent magnet was used to generate magnetic field, and the magnetic induction intensity was controlled by changing the number and distance of permanent magnets. Firstly, placed the beaker between the permanent magnets, and placed the Tesla probe in the beaker to determine the magnetic induction intensity, and then poured in the cutting fluid and measured its dynamic viscosity.

All the above tests were carried out in parallel for 5 times at room temperature, and the average value was taken as the final experimental result.

2.3 Steady state heat transfer experiment

The friction heat durning the turning process is generated continuously, so it is necessary to investigate and compare the steady-state heat transfer coefficient under different lubrication conditions. Figure 4 presents a physical diagram of the steady-state heat transfer experimental device. The device includes MQL system, Ni-Cr alloy heating element, K-type thermocouple (TT-K-30-36), ceramic terminal, high-power transformer, contact voltage regulator, ammeter and thermometer (RX4006D). Firstly, the thermocouple was welded on the back of the heating element, and ceramic terminals were sleeved on both ends of the heating element. Then connected the ammeter, voltage regulator and transformer in turn with high-voltage wires to form a loop. Finally, connected the positive and negative ends of the thermocouple into the thermometer. By adjusting the voltage regulator to control the temperature of the heating element. When the heating plate reached the specified temperature, the mMQL device was opened (spray parameters: air pressure 0.4 MPa, flow rate 20 ml/h, magnetic induction intensity 0–50 mT) to spray cooling on the heating element, the nozzle was 20 mm away from the heating element. When the temperature of the heating element was stable, recorded the voltage (U) and current (I) values in real time, and the formula q = UI / s was used to calculate the heat flux density of the heat transfer surface under different lubrication conditions, where s is the surface area of the heating element (0.3 cm²). Finally, the corresponding steady-state heat transfer coefficient was calculated by using the formula H = q / (T_W-T_F), where T_W is the surface temperature of the heating element and T_F is the oil mist temperature (25 ℃). The heat transfer experiments under all working conditions were carried out three times and the average value was taken.

2.4 Machining experiment

The machining experiment was carried out on CAK6150D CNC lathe. The workpiece material was 430 stainless steel with the size of Φ 80 mm × 400 mm. All workpieces were precut with a thickness of 1 mm before machining to ensure the consistency of the machined surface. The cutting tools adopted the cemented carbide coated tool produced by Sumitomo, Japan, and the model is CCMT09T304N-SU. Sawed off a fine groove (1 mm × 1 mm) 1.5 mm away below the cutting edge of the rake face, embedded the thermocouple in the groove, and pressed the groove with a 1.5 mm diameter copper wire to ensure that the thermal contact of the thermocouple was in full contact with the cutting tool. The positive and negative poles of the thermocouple were connected with the thermometer to monitor the temperature change druning the cutting process in real time. The cutting temperature reflected by the above temperature measurement method was not the real temperature of the machining area, but it could compare the cooling conditions under different lubrication methods to verify the improvement effect of mMQL. All processing experimental conditions are summarized in Table 1.

Table 1

Processing experimental conditions
Test contents	conditions
Machine tool	CAK6150D CNC lathe
Workpiece material	AISI 430 stainless steel Hardness 150 ~ 160 HB Dimension Φ 80 × 400 mm
Cutting tool	Cemented carbide coated inserts, PVD-TiAlN CCMT09T304N-SU, Sumitomo, Japan
Thermocouple	Standard K-type thermocouple TT-K-30-36
Turning parameters	Rotating speed: 77 m/min; Feed rate: 0.10 mm/rev; Cutting depth: 1 mm; Single cutting length: 350 mm
Cooling conditions	MQL and mMQL
Cutting fluids	LB-2000 vegetable oil Fe₃O₄ oil-based nanofluid
MQL/mMQL parameters	Magnetic induction / mT: 10, 20, 30, 40, 50; Flow rate: 20 ml/h; Air pressure: 0.4 MPa; Nozzle distance: 20 mm

The cutting tools used for measuring tool wear, cutting force and workpiece surface roughness were complete tools without cutting fine grooves. VW-6000 microscope was used to observe the tool wear. Kistler9129A three coordinate dynamometer was used to measure the main cutting force (F_y). All the above tests were recorded during the sixth round of machining (the single cutting length was 350 mm). After machining, the tool wear morphology under different lubrication conditions was analyzed by field emission scanning electron microscope (EVO18, Zeiss, Germany) and the tool wear mechanism was also explored.

3.1 Physical property

Figure 5 shows the variations of contact angle, surface tension and viscosity of Fe₃O₄ nanofluid under different magnetic induction intensities. As can be seen from Fig. 5 (a), the contact angle of Fe₃O₄ nanofluid droplets continued to decrease with the increase of magnetic induction intensity. Under the influence of magnetic field, the surface adsorption force and activity of magnetic fluid droplets were increased, so as to increase the surface energy, and the liquid surface molecules presented a significant directional arrangement, resulting in the decrease of contact angle, indicating that the wettability and penetrability of magnetic fluid droplets were improved after magnetic field intervention [23]. In addition, the droplet contact angle of magnetic nanofluid was also affected by the saturation magnetization of magnetic particles. As shown in Fig. 5 (a), when the magnetic induction was higher than 40 mT, the contact angle of Fe₃O₄ magnetic nanofluid did not change significantly. When the magnetic field was too large, the magnetization of the magnetic fluid was close to saturation, resulting in no obvious change in the contact angle.

As can be seen from Fig. 5 (b), the surface tension of Fe₃O₄ nanofluid increased slowly with the increase of magnetic induction intensity, and the increase range was not significant, indicating that within the given range of magnetic induction intensity, the influence of magnetic field presented little effect on the surface tension of this magnetic fluid.

As seen from Fig. 5 (c) that the dynamic viscosity of Fe₃O₄ nanofluid was gradually increased with the increase of magnetic induction intensity. When magnetic field was applied, the nanoparticles were magnetized and deflected in the direction of the external magnetic field. At the same time, the rotation of magnetic Fe₃O₄ was driven by the vortex of the base fluid, if the vortex vector direction of the base fluid was not parallel to the direction of the external magnetic field, the magnetic Fe₃O₄ would be affected by the magnetic torque, which hindered the flow of the base fluid and thus increased the viscosity of the base fluid [17, 24].

3.2 Penetrate property

The penetrability of cutting droplets under MQL presents great influence on droplet lubrication and cooling capacity. The cutting droplet with high penetrability is easier to penetrate into the capillary contact gap of tool-chip and tool-workpiece, so as to exhibit better lubrication and cooling effect. To explore the capillary penetrability of Fe₃O₄ nanofluid droplets under different magnetic induction intensity, a penetration model was established. Firstly, make two assumptions:

(1). A large number of capillaries were distributed in the tool-chip friction area, which were arranged along the direction of chip flowing out of the tool rake face.

(2). A single capillary was a cylindrical cavity with one end open and one end closed and was vacuum in the body. The length was about 1/3 ~ 2/3 of the tool-chip contact length, and the radius was set as 0.5 µm [25]. The model diagram was shown in Fig. 6:

The capillary penetration of cutting fluid was mainly affected by three forces: capillary driving pressure (F_cap) [26], viscous resistance (F_visco) [20] and atmospheric pressure (F_P).

$${F}_{cap}=\varDelta P\bullet \pi {r}^{2}=2\pi r\gamma cos\theta$$

$${F}_{visco}=8\pi \eta h\stackrel{-}{v}$$

$${F}_{P}=\pi {r}^{2}{P}_{atm}$$

Then the capillary penetrability equation of cutting fluid is:

$$2{\pi }\text{r}\gamma \text{c}\text{o}\text{s}\theta +{\pi }{\text{r}}^{2}·{P}_{\text{a}\text{t}\text{m}}-8{\pi }\eta h\stackrel{-}{\nu }=\frac{\text{d}\left(m\stackrel{-}{{\nu }}\right)}{\text{d}t}$$

Combined with the experimental data in Fig. 5, the capillary penetrability equation was calculated with MATLAB to obtain Fig. 7. It is seen that the capillary penetration depth of cutting fluid was increased first and then decreased with the increase of magnetic induction intensity. With the increase of magnetic induction intensity, the contact angle of magnetic nanofluid was decreased, resulting in the increase of capillary driving pressure, which presented a deeper penetration depth. However, when the magnetic induction was too large, the contact angle of this magnetic nanofluid did not decrease significantly due to the saturation magnetization, while the viscosity continued to increase and bore higher viscous resistance, resulting in the decrease of capillary penetration depth. When the magnetic induction was 40 mT, the penetration depth of Fe₃O₄ nanofluid was 19.8% greater than that of 0 mT, indicating that the magnetic nanofluid under the intervention of magnetic field could penetrate more into the capillary in the friction contact area, so as to present better lubrication and cooling performance.

3.3 Heat transfer performance

Figure 8 presents the steady-state heat transfer coefficient of Fe₃O₄ nanofluid aerosol under different magnetic induction intensity. It is seen that the steady-state heat transfer coefficient of this nanofluid aerosol was continuously increased with the rise of magnetic induction intensity under different heat transfer surface temperatures. When the heat transfer surface temperature was 190 ℃, the steady-state heat transfer coefficient of the aerosol at 50 mT was 26.2% higher than that at 0 mT, indicating that the Fe₃O₄ nanofluid aerosol under the influence of magnetic field presented better heat transfer performance. Under the influence of magnetic field, the contact angle of the magnetized droplet was decreased and exhibited larger spreading area, the evaporation heat transfer efficiency of the droplet was then improved, resulting in significant improvement of heat transfer performance. According to the research of Liu et al [27], the heat transfer capacity of droplets could be characterized by heat flow (Q), the greater the heat flow, the more heat transferred by the droplets. The heat flow is related to the droplet heat transfer coefficient (H), the heat transfer surface temperature T_W, the aerosol temperature T_f and the contact area (A) between the droplet and the heat transfer surface.

$$Q=H\times ({T}_{w}-{T}_{f})\times A$$

According to the steady-state heat transfer coefficient recorded in Fig. 8 (the heat transfer surface temperature was taken as 190 ℃) and the droplet contact angle recorded in Fig. 5 (a), the heat flow of droplet under different contact angles was calculated in Fig. 9. It can be seen that the droplet heat flow was increased significantly with the decrease of contact angle. The smaller the contact angle of droplet, the faster the spreading speed, and the droplet was easier to spread on the heat transfer surface to form a larger contact area, which improved the evaporation efficiency of droplet, thus showing a higher heat flow and evaporation heat transfer capacity.

3.4 Machining performance

Figure 10 shows the cutting temperature under different lubrication conditions. It is seen that the cutting temperature under mMQL using Fe₃O₄ nanofluid was significantly lower than that of traditional vegetable oil MQL, and the cutting temperature was gradually decreased with the increase of magnetic induction intensity. The cutting temperature under mMQL with 50 mT was 35.5% lower than that of traditional vegetable oil MQL, indicating that mMQL could effectively reduce the cutting temperature and improve the cooling effect. Under the influence of magnetic field, the contact angle of atomized Fe₃O₄ nanofluid droplet became smaller, which presented larger spreading area on the heat transfer surface of cutting tool and workpiece, and the droplet evaporation efficiency was higher, so as to exhibited better heat transfer performance and cooling effect. However, it is not difficult to see from Fig. 10 that when the magnetic induction was increased from 40 mT to 50 mT, the reduction range of cutting temperature was decreased significantly. The prepared Fe₃O₄ nanofluid basically reached the magnetization saturation intensity at 40mT. Further increasing the magnetic induction presented no significant effect on the droplet contact angle, and thus resulted in the insignificant reduction range of cutting temperature.

Figure 11 presents the optical micrograph of tool flank wear under different lubrication conditions. It is seen that different degrees of silver bright adhesion appeared on the blade under various lubrication conditions. These adhesion were caused by the adhesion residue of the workpiece material after the violent collision between the cutting tool and 430 stainless steel, indicating that the main wear form of the cutting tools was adhesive wear. It can be seen that the degree of tool adhesion residue and tool wear under Fe₃O₄ nanofluid mMQL were significantly less than that of vegetable oil MQL, indicating that this mMQL strategy could further inhibit tool wear and improve tool service life. The adhesion wear volume of the tool flank under mMQL with 50 mT was 52.4% lower than that of traditional vegetable oil MQL, which effectively inhibited the tool flank wear. The dynamic viscosity of magnetic Fe₃O₄ nanofluid droplets under mMQL was higher and the bearing capacity of the formed oil film was stronger, which could further inhibit the generation of friction heat and reduce the adhesion of workpiece materials to the cutting tools, thus reducing the tool wear degree. In addition, the contact angle of the Fe₃O₄ nanofluid droplets under the influence of magnetic field was reduced and the penetrability was improved. Droplets could penetrate more into the capillary on the tool chip contact surface, which improved the lubrication and cooling efficiency of this magnetic nanofluid. It can also be seen from Fig. 11 that with the increase of magnetic induction intensity, the adhesion degree and wear amount of the cutting tool were gradually decreased, which confirmed the effectiveness of mMQL.

Figure 12 shows the SEM micrograph and EDS elemental analysis of tool flank wear under Fe₃O₄ nanofluid mMQL (40 mT) and traditional vegetable oil MQL. It is seen that the adhesion degree of workpiece material on the tool flank of mMQL was evidently lower than that of traditional vegetable oil MQL. Table 2 presents the element content of tool wear area under these two lubrication conditions. It is seen that the contents of W, Ti and C with mMQL were 582.2%, 445.2% and 228.1% higher than those with traditional vegetable oil MQL, while the contents of Fe and Cr were 10.8% and 14.5% lower than those of MQL. Ti and W belong to the elements of tool coating, and mMQL presented higher elements of W and Ti, indicating that this lubrication condition could reduce the falling off of tool coating and effectively prolong the service life of the cutting tools. Element C belongs to the lubricating film formed by vegetable oil on the friction surface. More element C appeared under mMQL, which proved that this lubrication method could allow more cutting fluid to penetrate into the friction area to form lubricating film for lubrication and cooling, and thus further avoided tool wear. Fe and Cr elements belong to 430 stainless steel materials. Higher contents of Fe and Cr elements were detected under traditional vegetable oil MQL compared with mMQL, indicating that the tool flank was easier to adhere to the workpiece material and the adhesion wear was more seriously under this MQL lubrication model.

Table 2

Element content of tool flank wear area under vegetable oil MQL and Fe3O4 nanofluid mMQL (wt. %)
	W	Ti	C	Fe	Cr
Vegetable oil MQL	1.01	0.73	0.89	79.01	18.36
Fe₃O₄ nanofluid mMQL	6.89	3.98	2.92	70.51	15.7

Figure 13 presents the signal acquisition diagram of cutting force under different lubrication conditions. It can be seen that the cutting force under Fe₃O₄ nanofluid mMQL was significantly lower than that of traditional vegetable oil MQL, and the cutting force of mMQL was gradually decreased with the increase of magnetic induction intensity. The cutting force under mMQL with 50 mT was 43.2% lower than that of traditional vegetable oil MQL, presenting better lubrication effect. Under the influence of magnetic field, the contact angle of Fe₃O₄ nanofluid was decreased. More magnetic nanofluid could penetrate into the friction micro area to form lubricating film, further avoiding the contact of friction peak and reducing friction, thus showing lower cutting force. In addition, the excellent lubrication effect of this Fe₃O₄ nanofluid mMQL strategy ensured the sharpness of the cutting tool and avoided the tool wear, thus showing smaller cutting force. However, it can be seen from Fig. 13 that after the magnetic induction intensity was adjusted from 40 mT to 50 mT, the reduction range of cutting force was significantly reduced. indicating that the expected machining performance could be achieved by selecting 40 mT under this given spray parameters.

To improve the lubrication and cooling performance of traditional oil-based minimum quantity lubrication used in metal cutting process, a magnetic field assisted minimum quantity lubrication technology (mMQL) used Fe₃O₄ oil-based nanofluid as cutting fluid was proposed. The changes of contact angle, surface tension and dynamic viscosity of the prepared Fe₃O₄ nanofluid droplets under different magnetic induction were discussed, and the penetrability and heat transfer efficiency of this Fe₃O₄ nanofluid under the influence of magnetic induction were investigated. Finally, taking turning 430 stainless steel as the cutting condition, the machining performance of Fe₃O₄ nanofluid applied in mMQLwas comparatively analyzed. The results were summarized as follows:

(1) Under the influence of magnetic field, the contact angle of Fe₃O₄ nanofluid was decreased significantly, the surface tension was increased slightly, and the dynamic viscosity was increased, resulting in the significant improvement of the penetrability of Fe₃O₄ nanofluid.

(2) The contact angle of magnetized Fe₃O₄ nanofluid droplets was decreased, so as to increase the spreading area of droplets after reaching the heat transfer surface, and the evaporation heat transfer efficiency of these droplets was improved, which enhanced the heat transfer capacity of Fe₃O₄ nanofluid mMQL, and thus presented better cooling effect.

(3) Compared with traditional vegetable oil MQL, the cutting temperature of Fe₃O₄ nanofluid mMQL could be reduced by 35.5%, the tool wear was reduced by 52.4% and the cutting force was reduced by 43.2%, showing better machining performance. Magnetized Fe₃O₄ nanofluid droplets presented better penetration and heat transfer ability, effectively improved the friction condition in the tool-chip contact area and alleviated the generation of friction heat.

(4) When cutting 430 stainless steel with MQL, the main form of tool wear was adhesive wear. Compared with the traditional oil-based MQL, more W and Ti elements were detected on the tool flank wear area with the lubrication of Fe₃O₄ nanofluid mMQL, and the contents of Fe and Cr elements were significantly reduced, indicating that this novel lubrication and cooling method could effectively inhibit the adhesion of workpiece materials on the cutting tool, which alleviated the falling off of tool coating, and finally improved the service life of the cutting tool.

It is believed that this novel magnetic field assisted minimum quantity lubrication technology could provide a practical development strategy for the field of green lubrication machining.

Availability of data and material: All the experimental data and material are reflected in this article.

Code availability: Not applicable.

Author contribution: Conceptualization: Tao Lv, Xuefeng Xu; Methodology: Tao Lv, Haizhou Weng; WZOriginal draft writing: Tao Lv, Chengcheng Niu; Investigation: Tao Lv, Haizhou Weng; Review: Xuefeng Xu, Aibing Yu, Xiaodong Hu; Language editing: Tao Lv, Aibing Yu; Supervision: Tao Lv, Xuefeng Xu; Financial support: Tao Lv, Xuefeng Xu.

Funding: This study was financially supported by General scientific research projects of Zhejiang Provincial Department of Education with the project number of Y202043602, Ningbo Natural Science Foundation with the project number of 202003N4190, and National Natural Science Foundation of China with the project number of 51775507.

Ethics approval: Not applicable.

Consent to participate: Not applicable.

Consent for publication: All authors agree to publish.

Conflict of interest: The authors declare no competing interests.

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Editorial decision: Major Revisions Needed
30 Jul, 2022
Reviewers agreed at journal
21 May, 2022
Reviews received at journal
08 May, 2022
Reviewers invited by journal
07 May, 2022
Editor assigned by journal
06 May, 2022
First submitted to journal
03 May, 2022

You are reading this latest preprint version

A Study on lubrication and cooling performance and machining characteristics of magnetic field assisted minimum quantity lubrication used Fe3O4 nanofluid as cutting fluid

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Version 1

Abstract

Figures

1 Introduction

2. Experimental Details

2.1 Magnetic assisted MQL equipment and cutting fluid

2.2 Physical property tests of cutting fluid

2.3 Steady state heat transfer experiment

2.4 Machining experiment

3. Results And Discussion

3.1 Physical property

3.2 Penetrate property

3.3 Heat transfer performance

3.4 Machining performance

4. Conclusion

Declarations

References

Status:

Version 1