ARTICLE

J. Cent. South Univ. (2019) 26: 1042-1049

DOI: https://doi.org/10.1007/s11771-019-4069-8

Lubrication performance of rapeseed oil-based nano-lubricants in parallel tubular channel angular pressing process

Mehdi KASAEIAN-NAEINI, Ramin HASHEMI, Ali HOSSEINI

School of Mechanical Engineering, Iran University of Science and Technology, Tehran, Iran

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: Due to the biological risks of using the conventional lubricants, the vegetable oils have been considered nowadays. Besides, to improve the tribological properties of the vegetable oils in various applications like metal forming processes, nanoparticles have been used as additives. This research evaluated the lubrication performance of the Al₂O₃ and TiO₂ nanoparticles dispersed in rapeseed oil during the parallel tubular channel angular pressing (PTCAP) process. The experimental PTCAP tests have been fulfilled under three lubrication conditions and the comparison between the PTCAP processed tubes has been performed in terms of the maximum forming force, surface roughness, and microhardness. The experimental results indicate that adding the mentioned nanoparticles has caused at least a 50% reduction in the maximum deformation load. Moreover, a remarkable decrement in the surface roughness of the formed tubes has been obtained.

Key words: parallel tubular channel angular pressing; nano lubricant; nano-particle additives; vegetable oil; aluminum alloy

Cite this article as: Mehdi KASAEIAN-NAEINI, Ramin HASHEMI, Ali HOSSEINI. Lubrication performance of rapeseed oil-based nano-lubricants in parallel tubular channel angular pressing process [J]. Journal of Central South University, 2019, 26(5): 1042–1049. DOI: https://doi.org/10.1007/s11771-019-4069-8.

1 Introduction

It is well-known that there are significant physical and mechanical properties in ultrafine grain (UFG) materials by severe plastic deformation (SPD) techniques such as equal channel angular pressing (ECAP) [1, 2], accumula- tive roll bonding (ARB) [3–5], high pressure torsion (HPT) [6, 7] and tubular channel angular pressing (TCAP) [8, 9]. In SPD processes, with imposing a considerable strain, high strength nano-grained material is achieved. The nanostructured materials via SPD are developed rapidly due to many advantages of the SPD methods, such as constant cross-section of the specimen before and after the process, producing UFG materials with high-angle grain boundaries, appropriate mechanical and microstructural properties, and good superplastic forming capability at high temperature [10, 11]. In spite of the numerous requirement for the tubes with superior mechanical properties in the industry, the tube SPD processes have been less considered [12]. TAVAKKOLI et al [13] introduced parallel tubular channel angular pressing (PTCAP) in which a metallic tube is hugely deformed and a UFG tube is obtained. The two half cycles of the PTCAP are shown in Figure 1. As can be seen, the tube is pressed into the deformation zone by a first punch in the first half-cycle and the diameter of the tube increases. Then, the second punch pushes back the tube in the second half-cycle [14].

Despite the lower forming force of the PTCAP than similar SPD processes like TCAP, the extreme force is being applied to the tube [15]. This is because of the applied large strains and high friction force due to the large contact surface between die and tube. Hence, the need for appropriate lubrication in the PTCAP process is felt. The proper lubrication condition leads to a significant improvement in surface quality, a reduction in the erosion of the die components, and a decrease in forming force [16].

Figure 1 Schematic of PTCAP process [13]

Several types of research have been performed to evaluate the effects of different lubrication condition on the metal forming and machining processes. LAZZAROTTO et al [17] used the upsetting-sliding test to choose the suitable lubricating oil according to the cold forward extrusion conditions. The performance of boric acid in the different metal forming processes was investigated by RAO et al [18]. They concluded that boric acid has the best performance among other lubricants such as Teflon, grease, graphite in oil, and oleic acid in the sliding condition of workpiece surfaces. KIM et al [19] compared the different stamping lubricants by utilizing the deep drawing and ironing tests and predicted temperature and pressure at the interface of the workpiece and die with the aid of FE simulation. TOMALA et al [20] reported a marked reduction in wear at the elevated temperature by using three types of solid lubricants. The effect of solid lubricants on the performance of machining was investigated by KRISHNA et al [21]. The results showed the favorable effect of solid lubricants on the tool wear and surface roughness in comparison with dry and wet machining. Besides, with the advent of nanotechnology and the need for improving the efficiency in the metal forming processes, the nano-lubricants are generated as a new type of the lubricants [22]. Nanoparticles improve the tribological properties of the various lubricants and reduce the forming load and friction [22]. Due to the explained features, many researchers have been encouraged to investigate more on nano-lubricants in recent years. The effects of liquid paraffin with the SiO₂ nanoparticles on wear and friction were examined by PENG et al [23]. They demonstrated that the combination of SiO₂ nanoparticles and liquid paraffin has a better load-carrying capacity and more friction reduction than pure liquid paraffin. HERNANDEZ et al [24] compared the potential of CuO, ZnO, and ZrO₂ nanoparticles as an antiwear additive in the polyalphaolefin. The results showed that the friction coefficient and wear reduction values are depending on nanoparticle concentration. Due to decreased surface roughness of the workpiece and crater wear on the tool rake face, KHALILPOURAZARI et al [25] used suspension of the Al₂O₃ nanoparticle and mineral- based oil in the hobbing process. Besides, the use of different nano-lubricants in the rolling process has shown a decrease of the friction coefficient, rolling force and remarkable improvement in surface topography of workpieces [26–29]. ABE et al [30] added SiO₂, ZrO₂ and Al₂O₃ into the oil to decrease surface roughness and to enhance the hardness of the extruded aluminum alloy billets. Their results showed that the extruded billet with large particle diameter and a high percentage of particles has better surface roughness and larger hardness. ZAREH-DESARI et al [31] studied the lubrication performance of oil-based Al₂O₃ nanofluid in the deep-drawing process and proposed the optimum range of nanoparticles concentration to achieve the lowest average surface roughness.

Due to the hazardous effects of the utilizing traditional lubricants in the different applications, researchers have focused on the potential of bio-based lubricant because of its environmental benefits [32]. SYAHRULLAIL et al [33] utilized palm oil as a vegetable lubricant in the plane strain extrusion process. The results indicated that palm oil could effectively reduce extrusion load and surface roughness value. Besides, the lubrication performance of two difference vegetable oil-based nano-lubricants was compared with two conventional metal forming lubricants in the standard ring compression test by ZAREH- DESARI et al [34]. Their results showed that the nanoparticles could increase the friction reduction of vegetable lubricants. DIABB et al [35] scrutinized the effects of vegetable oil nano- lubricant on single point incremental sheet forming (SPIF) process.

In this research, nano-Al₂O₃ and nano-TiO₂ with many environmental applications have been chosen as an additive to disperse in vegetable oil (rapeseed). The PTCAP process has been selected as an SPD process to study the effects of nanoparticles added in vegetable oil on the deformation load, surface roughness, and hardness of the tubes after a single-pass PTCAP. The experimental results designate that adding the mentioned nanoparticles has caused at least a 50% reduction in the maximum deformation load. Moreover, a remarkable decrement in the surface roughness of the formed tubes has been obtained.

2 Materials and methods

2.1 Lubricants

To have excellent lubricating properties in metal forming processes and machining operations, the rapeseed oil has been chosen as base oil [34, 36, 37]. Its physicochemical properties are given in Table 1.

Table 1 Physicochemical properties of rapeseed oil

Nano-alumina is one of utilized nanoparticle. It is used in various engineering applications such as cutting tools industry, polishing material, and metal matrix composite reinforcement. Besides, nano-titania is another employed nanoparticle which has many industrial applications like photovoltaic, fuel cells, and self-cleaning surfaces [38]. Along with mentioned applications, the tribological properties of Al₂O₃ and TiO₂ nanoparticles have been proved by former studies [39]. TiO₂ and Al₂O₃ nanoparticles with a diameter of 50 nm have been added to the rapeseed oil at a concentration of 1 wt%. Figure 2 shows the scanning electron microscope (SEM) images of alumina and titanium dioxide. As observed, nanoparticles have a spherical shape and appropriate to utilize as an additive in lubricants. To produce a homogeneous nanolubricant, an ultrasonic mixer has been used for mixing the rapeseed oil and the additives for 1.5 h (Figure 3). Furthermore, the prepared nano-lubricants have been employed in the PTCAP tests immediately after dispersing nanoparticles into the rapeseed oil to prevent agglomeration and sedimentation [40].

Figure 2 SEM images of Al₂O₃ (a) and TiO₂ (b) nanoparticles

Figure 3 Ultrasonic shaker apparatus

2.2 PTCAP experiments

The PTCAP specimens have been made from Al 5083 tube which is usually used in automotive and marine industries. The tubes have been prepared with 15 mm in inner diameter, 2.5 mm in thickness and 30 mm in length. Besides, they have been annealed at 345 °C for 2 h to get a homogeneous microstructure. The composition and mechanical properties of the Al 5083 tube are given in Tables 2 and 3, respectively.

Table 2 Chemical composition of aluminum 5083 alloy

Table 3 Mechanical properties of Al 5083 alloy

The geometrical parameters of PTCAP die demonstrated in Figure 1. The experiments have been performed on a servo-electric testing machine (SANTAM, STM-150) with a capacity of 150 kN. Figure 4 depicts the experimental setup for PTCAP tests. The experiments have been done under three lubrication conditions of rapeseed oil, rapeseed oil with 1 wt% TiO₂ and rapeseed oil with 1 wt% Al₂O₃ nanoparticles. Furthermore, all experiments have been performed for one pass PTCAP and each test has been repeated three times to ensure the correctness of the results. As it mentioned, each pass of PTCAP process has two steps and they are called one half cycle. After PTCAP tests, the roughness of samples has been measured by a Mahr PS1 surface roughness tester. Furthermore, the microhardness tests have been carried out on a KOOPA KM3 microhardness tester with an indentation load of 0.2 kg for a loading time of 10 s. The microhardness measurements have been repeated three times and the mean amounts have been reported.

3 Results and discussion

3.1 Effect of Al₂O₃ and TiO₂ nanoparticles on forming load

The PTCAP tests have been fulfilled with the explained experimental setup to investigate the process performance. Figure 5 depicts the maximum deformation load under different lubricant conditions for one pass PTCAP. As can be seen, the nanolubricants present lower deformation load than PTCAP process with bio-base oil for the first half cycle. It occurs mainly due to the friction reducing capability of the nanoparticles which were dispersed into rapeseed oil. Each of these nanoparticles can operate like nano-ball bearing and decrease the metal to metal contact [34]. Hence, the maximum forming forces for first half-cycle under the nanolubrication condition with Al₂O₃ and TiO₂ nanoparticles are reduced by 50.34% and 56.33%, respectively. The TiO₂ nano-lubricat has better friction reducing ability than the Al₂O₃ nano-lubricant, so it is more effective in decreasing the deformation load [40]. On the other hand, the forming force augmentation in the second half-cycle causes to crush the nanoparticles and nano-lubricants have no significant effect on the maximum deformation load. Besides, the oxidation and changes in chemical properties of the vegetable oils cause their poor performance under high pressure condition [41]. Nevertheless, the forming forces of the rapeseed oils containing nano TiO₂ and Al₂O₃ particles are 3% and 1.6%, respectively, lower than used vegetable oil base lubricant for the second half-cycle.

Figure 4 Experimental setup (a) and PTCAP die (b)

Figure 5 Maximum deformation load for rapeseed oil, Al₂O₃ and TiO₂ nano-lubricants

3.2 Effect of Al₂O₃ and TiO₂ nanoparticles on surface roughness

The average surface roughness of the formed tube under various lubrication conditions is shown in Figure 6. As can be noted, the nano-lubricants have a non-negligible effect on surface roughness and the base oil with no additive condition has a poor level of surface quality. The Ra for the rapeseed oil is 2.48 μm and its amount is decreased to 0.797 and 0.92 μm for Al₂O₃ and TiO₂ nano-lubricants, respectively. It is because the nanoparticles prevent the metal-to-metal contact, and also have a rolling performance between surfaces. Furthermore, the forming load of the PTCAP process for the second half-cycle is high. Thus, it can be concluded that the formed tubes surface are polished by the nanoparticles. The best surface roughness is obtained by using the Al₂O₃ nanolubricating condition. It occurs mainly due to the formation of a protective film through a chemical reaction between the Al₂O₃ nanoparticles and the tube surface. This film makes a proper contact between tube and PTCAP die so that the surface quality will be better. The generation of a protective film was also reported by many researchers previously [22, 40, 42–44].

Figure 6 Average surface roughness of PTCAPed tubes under different lubrication conditions

3.3 Effect of Al₂O₃ and TiO₂ nanoparticles on microhardness

The Vickers microhardness of the formed tube along the thickness direction is detailed in Figure 7. As predicted, the hardness of the tubes increases significantly due to the single pass PTCAP process. The hardness before the PTCAP process is 75 Vickers and at least 27% enhanced after the forming. Besides, under the bio-based lubrication condition, the microhardness is expanded at the inner and outer surfaces. This is concluded because of the existence of high strain hardening in the result of the poor lubrication. Nonetheless, the uniform distribution of the hardness is observed by embedded nanoparticles to the rapeseed oil. As seen, the addition of nanoparticles in rapeseed oil is caused to the hardness enhancement. This improvement was also reported on the studies carried out by BAO et al [29], ABE et al [30], and GAO et al [45].

Figure 7 PTCAPed tube hardness along thickness

4 Conclusions

1) Adding nanoparticles like Al₂O₃ and TiO₂ to the rapeseed oil had a considerable effect on the reduction of the maximum deformation load for first half-cycle. It is because of the rolling effect of nanoparticles dispersed in vegetable oil. Furthermore, due to the better anti-friction capability, the TiO₂ nano-lubricant showed better performance in reduction of the forming force.

2) Based on the results, the average surface roughness has been also decreased by 63% and 68% for the use of titania and alumina nano-lubricants, respectively, as compared with the rapeseed oil without nanoparticles. As is evident, the Al₂O₃ nano-lubricant is more efficient in improving the surface quality because of the form of a solid protective film on the surface.

3) According to the results of the microhardness test, due to a single-pass PTCAP test, the hardness of the PTCAPed tubes has grown up at least 27%. Besides, despite at the inner and outer surface of tubes, the hardness has been augmented with the scattering nanoparticles to the vegetable oil.

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(Edited by YANG Hua)

中文导读

菜籽油纳米润滑剂在平行通道转角挤压过程中的润滑性能

摘要：由于使用传统润滑剂存在生物风险，植物油已成为人们关注的焦点。此外，为了提高植物油在金属成型工艺等各种应用中的摩擦性能，纳米颗粒被用作添加剂。本文研究了平行通道转角挤压(PTCAP)过程中分散在菜籽油中的Al₂O₃和 TiO₂纳米颗粒的润滑性能。在三种润滑条件下进行了PTCAP实验，并在最大成形力、表面粗糙度和显微硬度方面对PTCAP加工通道进行了比较。实验结果表明，加入上述纳米颗粒可使最大变形力至少降低50%。此外，成型通道的表面粗糙度明显降低。

关键词：平行通道转角挤压过程；纳米润滑剂；纳米颗粒添加剂；植物油；铝合金

Received date: 2018-11-16; Accepted date: 2018-12-24

Corresponding author: Ramin HASHEMI, Associate Professor; Tel: +98-21-77240540; E-mail: rhashemi@iust.ac.ir; ORCID: 0000- 0001-8369-0390