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Surface generation in ultrasonic-assisted high-speed superabrasive grinding under minimum quantity cooling lubrication with various fluids
Tribology International 156 (2021) 106815
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Surface generation in ultrasonic-assisted high-speed superabrasive grinding under minimum quantity cooling lubrication with various fluids Anirban Naskar *, Amit Choudhary , S. Paul Machine Tool and Machining Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Ultrasonic assisted grinding Surface generation Residual stress Minimum quantity cooling lubrication
Ultrasonic assisted grinding (UAG), and minimum quantity cooling lubrication (MQCL) have individually improved grinding characteristics of difficult–to-cut super-alloys in terms of reduced forces and surface rough ness. In the present work, a hybrid grinding approach (UAG + MQCL) is utilized, and the effect of fluid’s lubricity on grit-workpiece interaction has been investigated during the grinding of Ti–6Al–4V. More lubricious fluid provided less resistance to vibration transfer to the grinding zone, and consequently, the effective amplitude of vibration increased with an increase in lubricity of the fluids. It has governed the mechanism of grinding scallop formation significantly. Additionally, more lubricious vegetable oil yielded the lowest grinding power and higher compressive residual stress. Further, 20–100% improvement in compressive residual stress was noted under UAG.
1. Introduction Properties like low coefficient of heat diffusion [1] and high chem ical reactivity with tool materials [2,3] distinguish titanium alloys from other super-alloys and put them on top in grinding difficulty index. Hence, improving grindability of titanium alloy has always been a key focus of the scientific community. Early research to improve the grind ability of titanium alloys was carried out at a relatively low grinding speed using a conventional grinding approach. In the 1990s Tang et al. [4] coated grinding wheel with solid lubricant (MoS2) and found a reduction in force and grinding temperature. Teicher et al. [5,6] used liquid nitrogen, neat cutting oil, alkaline soap, dry condition, and MoS2 coated grit (in dry mode) to investigate the grinding behavior of Ti–6Al–4V. They found significant improvement in grindability under neat oil and alkaline soap in terms of force, favorable chip formation, grit tip adhesion, and ground surface morphology. Shi and Attia [7] applied both grinding fluid (7% soluble oil emulsion) and wheel cleaning fluid at a very high pressure in shallow and creep-feed grinding to enhance the removal rate of titanium and avoid wheel loading. They [7] could achieve a removal rate of 8 mm2/s and 3 mm2/s for shallow and creep-feed grinding, respectively, without any visible wheel loading, burning, and smearing. Besides the aforementioned conventional grinding approaches, an
efficient and effective way of grinding fluid application is minimum quantity cooling lubrication (MQCL) [8,9]. The MQCL technique has been reported to provide a substantial improvement in the ductile cut ting of ceramics [10,11]. It has also been explored by various researchers to improve the grinding of titanium alloys [12–15]. Sadeghi et al. [12] noticed a better performance of MQCL than conventional wet grinding in terms of less plastic deformation, proper shearing, and less grinding forces in titanium grinding. The use of different grinding fluids in MQCL mode for titanium grinding has provided a reduction of 20% [13], 40–70% [14], and 22–35% [15] in grinding forces as compared to wet grinding. Additionally, improvement in chip formation, coefficient of friction, and ground surface morphology were also reported [13–15]. However, most of the studies were carried out at conventional grinding speed (limited to 30 m/s), and residual stress generated due to grinding was not investigated. Ultrasonic assisted grinding (UAG) is another grindability improve ment technique that has emerged in the 1950s [16]. Plenty of literature is available on the UAG of ceramic and brittle materials, where a reduction in grinding forces and other advantages have been reported [17–19]. However, the number of reports available on the UAG of metallic materials is limited. Tawakoli and Azarhoushang [20] observed a reduction in normal (60–70%) and tangential (30–50%) grinding forces with the application of UAG (on the workpiece) of soft 100Cr6 steel of hardness 82 HRB in dry mode. They [20] reported a reduction in
* Corresponding author. Machine Tool and Machining Laboratory, Department of Mechanical engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721 302, India. E-mail addresses: [email protected] (A. Naskar), [email protected] (A. Choudhary), [email protected] (S. Paul). https://doi.org/10.1016/j.triboint.2020.106815 Received 15 September 2020; Received in revised form 24 November 2020; Accepted 28 November 2020 Available online 4 December 2020 0301-679X/© 2020 Elsevier Ltd. All rights reserved.
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transfer to the grinding zone. However, reports dealing with the effect of UAG at different grinding speed could not be found. Moreover, most of the conducted work on UAG of metallic materials was focused on force, surface roughness, and ground surface morphology. The fatigue life of any ground surface would be greatly affected by the state and magnitude of surface residual stress present in it. But, reports on the effect of UAG on residual stress can be hardly found. In the present research work, an attempt has been made to address the gaps mentioned above in the reported literature. Fluids having different viscosity (lubricity) 0.65 to 48 cSt have been applied in mini mum quantity cooling lubrication (MQCL) mode in combination with ultrasonic-assisted grinding. The effect of fluid’s lubricity on the surface generation is discussed in detail. Both high (60 & 40 m/s) and low grinding speeds (20 m/s) were employed to study the influence of UAG at different grinding speeds. Residual stress for all the samples has been measured and analysed to study the effect of different fluid and UAG on surface residual stress. This study highlights the change in the gritworkpiece interaction.
Nomenclature ug Ft vs vw a bw ft c ds hm
α
L Sc Sh Xm f vw effective vw applied
specific grinding energy total tangential grinding force wheel speed workspeed downfeed width of the workpiece tangential force per grit grit density wheel diameter maximum uncut chip thickness semi apex angle of the square pyramidal grit intergrit distance pitch of scallop height of scallop effective amplitude of ultrasonic vibration frequency of ultrasonic vibration effective workspeed during ultrasonic grinding applied workspeed, same as vw
2. Experimental details 2.1. Ultrasonic vibration system and grinding details Ultrasonic assisted grinding was carried out in an indigenously developed set up shown in Fig. 1. The supplied electrical energy was first converted into mechanical vibration of 20 kHz through a piezoelectric transducer. In the later stage, booster and horn were used to amplify the vibration. The workpiece holder was kept on the block sonotrode. A frictionless table was provided underneath the sonotrode to minimize the loss of vibration. The vibration of 18 μm amplitude was recorded at no-load condition. The air supply was provided to control the temper ature of the system. The advantage of two directional UAG (2D-UAG) over one directional UAG (1-D UAG) is documented in the literature. However, due to the complexity and high set-up cost, 1-D UAG is preferred [26]. In 1-D UAG, vibration is applied in two directions, along the workpiece velocity and across the workpiece velocity (along the wheel axis). Both methods have demonstrated their benefits over con ventional grinding [26]. Thus, in the present study, the vibration has been applied in the direction of workpiece velocity to explore the effect of UAG. Ti–6Al–4V (25 mm × 8 mm × 8 mm in dimension) was ground in plunge surface grinding mode employing single-layer electroplated cBN grinding wheel of 25 mm diameter and 10 mm width. The grinding wheels contained ABN 900 grits of 151 μm size (mesh size #100). Fig. 2 shows a representative image of the wheel. Details of the grinding pa rameters are provided in Table .1. Three grinding fluids of widely different viscosity were applied through indigenously developed mini mum quantity cooling lubrication set-up [27]. Viscosities of the used fluids at 40 ◦ C are 0.65 cSt, 34 cSt [28] and 48 cSt [29] for soluble oil-water emulsion, neat oil (HP –Trimofin 23), and rice bran oil respectively. Soluble oil in water emulsion was prepared in 1:20 ratio, and thus the viscosity of the fluid was considered to be the same as the water. Grinding fluids with more viscosity have not been employed in the present work as they tend to loose effectiveness in grinding due to atomization and penetrability [14,30] issues.
thermal damage and surface roughness and an increase in G-ratio under UAG. Molaie et al. [21] also noticed a substantial decrease in normal grinding force in UAG of AISI52100 steel, but the effect of vibration on the tangential grinding force was found to be less. Bhaduri et al. applied ultrasonic vibration on the workpiece in creep feed grinding on γ-TiAl intermetallic alloy in flood cooling mode [22]. Similar to above-mentioned finish grinding [20,21], Bhaduri et al. [22] also observed a reduction in grinding forces along with lower wheel wear and marginal improvement in surface roughness. In addition, reduced effect of ultrasonic vibration on the grindability at higher depth of cut was realized and it was attributed to the hindrance of the vibration transfer to the grinding zone. Recently, Gao et al. [23] carried out a detailed analysis of ground surface characteristics in 1-D and 2-D UAG of nickel-based material and wider furrows were noticed on the finished surface in vibration assisted grinding. Few works on UAG of Ti–6Al–4V was also reported [24,25]. In addition to a reduction in force and surface roughness [24], improvement in residual stress was identified [25]. Nevertheless, most of the UAG research work utilized a single grinding fluid at conventional grinding speed, and very few works investigated the effect of UAG on residual stress. The effectivity of ultrasonic assistance on the grinding performance would largely depend on vibration transfer efficiency to the grinding zone. The amplitude of vibration at no-load and load conditions may differ. Bhaduri et al. [22] indicated that the effectiveness of ultrasonic assistance on the grinding performance reduces at a higher depth of cut. It seems that due to the increase in grinding load at higher depth of cut, effective vibration transfer could not take place and consequently, the effectivity of vibration on the grinding performance got reduced. The lubricity of the grinding fluids influences the grit-workpiece interaction and grinding load (forces) significantly. From the above discussion, it can be inferred that fluids having different lubricity may affect the grinding performance disproportionately under the application of UAG because of different degrees of vibration transfer to the grinding zone. Different degrees of transferred vibration would affect the finish surface generation. However, the influence of fluid’s lubricity on the performance of UAG has never been studied earlier, which is the subject of concern of the present work. Besides, most of the available reports on UAG of metallic materials dealt with a constant grinding speed (vs ) which was limited in the range 30–40 m/s. Rise in grinding speed yields lower forces (load) owing to less uncut chip thickness (hm ). Lower grinding forces reduce the grinding load, which may facilitate effective vibration
2.2. Measurement and analysis of grinding characteristics During grinding, spindle power was measured using Montronix PS200-NG power sensor. Both SEM (Zeiss Evo 18) and 3D contact type profilometer (Form Talysurf 50 Intra 2) were used to study the finished surface. An area of 4 × 4 mm2 was scanned using the profilometer, and later it was analysed using Talymap gold software. The residual stress of the samples was measured using XRD (PANalytical EMPYREAN). The stress measurement was performed at 141.7◦ of 213 crystallographic plane of the α phase of Ti–6Al–4V [31] employing Cu source of a 2
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Fig. 1. Schematic and actual experimental set-up of ultrasonic-assisted grinding.
Fig. 2. (a) SEM image of the wheel surface and (b) optical image of the wheel.
wavelength of 1.54 Å. Five inclination angles (0◦ , 18.43◦ , 26.57◦ , 33.21◦ , and 39.23◦ ) were provided both in a negative and positive di rection, which resulted in ten scans for each measurement. Each sample was repeated thrice, and the average value has been reported. During measurement, the Cu-tube was running at 45 kV and 40 mA. The raw data was fed to PANalytical stress plus software for stress analysis, after measurement. Poisson ratio and elastic modulus values of 0.32 and 114 MPa were used in the analysis, respectively [32].
2.3. Grit-workpiece interaction and scallop formation This section provides details of scallop formation in grinding, and the expressions of two scallop parameters namely, the pitch of scallop (Sc ) and the height of scallop (Sh ), have been derived. Fig. 3 shows cutting paths of three consecutive grits of the same radial height and equally spaced on the periphery of the wheel. The cutting path of individual grits is assumed to be identical to the wheel radius for simplicity. For ease of representation, the linear velocity of the workpiece (vw ) has been imposed on the wheel. The cutting arcs of the grains can be expressed as, 3
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Table 1 Grinding details.
Now, from triangle OP2
Grinding machine tool
Praga surface grinder, model 451
High-speed spindle
Precise Pr¨ azisionsspindeln GmbH, Model S60 Maximum power 1.1 kW, maximum RPM 66,000 Cutting speed 20 m/s, 40 m/s and 60 m/s Workpiece velocity 2 m/min Downfeed 6 μm Air delivery pressure 4.5 bar Air flow rate 34 Lpm Fluid flow rate 200 mL/h Nozzle to wheel distance 15 mm
Grinding parameters MQCL parameters
2
OP = O22 − P22
(
L vs
Sc =
vw L vs
(6)
)2 =
( )2 ( )2 ds Sc − 2 2
(7)
− ds Sh + Sh 2 = −
( )2 Sc 2
(8)
Neglecting the term Sh 2 , we get Sh =
Sc 2 4ds
Combining equations (3) and (9), the Sh is expressed as )2 ( 1 vw Sh = L 4ds vs
(1)
(9)
(10)
From equations (3) and (10), it can be realized that both the scallop parameters are depended on the vw and vs , if the wheel parameters (ds and L) remain unaltered. In the present work, the ultrasonic vibration has been imposed on the workpiece in the direction of the workpiece velocity. Therefore, it is most likely that the velocity of the workpiece (vw ) would change under application of UAG. Consequently, it would directly influence the scallop parameters as well.
Therefore, Sc can be represented as Sc = vw t
ds − Sh 2
(5)
( )2 ( )2 ds Sc − 2 2
(OX − PX)2 =
1X2K, 2Y3L and 3Z4M. However, due to the overlapping action of the preceding cutting path by the successor grit, the final cutting paths that remain on the finished surface are 1X2, 2Y3, and 3Z4 as illustrated in Fig. 4. The Sc and Sh are also shown in the diagram. If a grit takes time t to cover the inter-grit distance (L), then scallop pitch (Sc ) is the distance covered by the workpiece during this time. If the velocity of the grit is considered same as wheel velocity (vs ), t can be expressed as t=
(4)
Sh = Q2 = PX
(2) (3)
Fig. 5 presents an exaggerated view of scallop depicted in Fig. 4. The vertical distance between point 2 and Q is defined as scallop height (Sh ). The scallop pitch (Sc ) is equal to XY.
Fig. 3. Schematic diagram of different grit path and scallop formation.
Fig. 4. Final grinding scallop on finished surface. 4
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sectioning was done on the levelled profile. Peak to peak distance measurement was performed on the sectioned 2-D longitudinal profile to measure scallop pitch (Sc ) as illustrated in Fig. 6. Similarly, peak to valley distance was also measured to get the scallop height (Sh ). The measurements were undertaken using the graphical user-interface of the software with the help of a distance measurement tool in-built within the software. Thus, no specific cut-off value was required in this analysis. 3. Results and discussion 3.1. Grinding power under UAG Fig. 7 shows the effect of ultrasonic vibration on grinding power (Ft vs ) under different grinding fluids applied in MQCL mode with wide variation in grinding speed. It reveals that there is no beneficial effect of ultrasonic assistance on grinding power irrespective of the wide varia tion in grinding speed vs and choice of grinding fluid. The effect of ul trasonic vibration (applied on the workpiece) was noted to be more significant on normal grinding force than the tangential force due to effective grit penetration [21]. Present study reports grinding power (spindle power), which represents tangential force. Hence, the negli gible effect of UAG on the tangential force is in accordance with the literature. However, few studies have reported a reduction in both the forces [20,22]. Fig. 7 also depicts the increase in vs provided higher grinding power requirements. But, the increase is not linearly propor tional to the vs despite linear relation (power = Ft vs ). Equation (11) shows the interrelation between various grinding parameters and
Fig. 5. Exaggerated view of grinding scallop as depicted in Fig. 4.
2.4. Measurement of scallop As stated earlier, an area of 4 × 4 mm2 was scanned on the ground surface using a tactile profilometer and a typical scanned area is shown in Fig. 6. After scanning, the results were analysed using Talymap gold software. Fig. 6 also depicts the process sequence of scallop measure ment. Initially, the raw profile was levelled and after that longitudinal
Fig. 6. Process sequence of grinding scallop analysis. 5
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Fig. 7. Grinding power at different grinding speeds under different grinding environments.
maximum uncut chip thickness (hm ) [33]. The hm characterises the chip load per grit. As vs increases, the hm would decrease, yielding lower force per grit (ft ) (as shown in equation (12) - for details of equation (12), please refer to Annexure 1) and lower total grinding forces. This fact is also evident from Fig. 8, which shows a drop in tangential grinding force with the increase in vs . Consequently, lower grinding force (tangential force) at high speed would provide less than
proportional increase in grinding power with an increase in vs . √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ ( √̅̅̅̅ ) 3 vw a hm = ctanα vs ds ft =
tan α ug hm 2 3
Fig. 8. Tangential grinding force at different grinding speeds under different grinding environments, derived from Fig. 7. 6
(11) (12)
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The effect of viscosity of the grinding fluids on the power has also been captured in Fig. 7. More viscous fluids yielded lower grinding power throughout the experimental domain. It seems that fluid with higher viscosity acted as a better lubrication medium [34] at the grit-workpiece interface and provided less grinding power requirement. Such a substantial change in grinding power requirement would possibly affect the state of residual stress on the ground surface. This aspect has been discussed later in detail.
shown in Fig. 10. The extent of both pitch and height of scallop marks increased with an increase in viscosity of the grinding fluids under UAG. So it may be inferred that viscosity of the grinding fluid greatly affects grit workpiece interaction under ultrasonic assistance. During grinding with ultrasonic assistance, the workpiece vibrates along the direction of workspeed. Hence, depending upon the effective amplitude and fre quency of vibration, a particular grit may disengage because the vi bration could be in the opposite direction of work speed (as shown in equation (13) by the –ve sign). It can as well participate in chip for mation with higher workspeed due to the work speed and vibration being in the same direction (as shown in equation (13) by the +ve sign). If the effective amplitude of vibration imposed by the ultrasonic sono trode is Xm and frequency of vibration is f then effective workspeed (vw effective ) may change as per equation (13). This variation of workspeed affects the geometry of grit workpiece interaction and formation of scallop marks as characteristics in equations (3) and (10).
3.2. Effect of UAG on ground surface generation Fig. 9 reveals the ground surface topography under various grinding fluids with and without ultrasonic assistance. Repetitive grinding scallop marks are seen along the grinding direction when water-based soluble oil emulsion is employed as the grinding fluid with ultrasonic assistance (Fig. 9b) compared to conventional grinding with the same fluid without any ultrasonic assistance (Fig. 9a). The scallop marks though different in length, are apparent in Fig. 9c and d when grinding was performed with ultrasonic assistance under neat oil and rice bran oil, respectively. Ground surface topography of conventional grinding under neat oil and rice bran oil has not been shown as they appear similar to soluble oilwater emulsion (Fig. 9a), with no visible scallop. Fig. 10 visualises the longitudinal sectional view (along the grinding direction) of the ground surface topography, as shown in Fig. 9. It captures the two geometrical features of grinding scallop. Fig. 10 along with Fig. 9, is demonstrating a correlation between the pitch (Sc ) and height of scallop (Sh ) marks under various grinding fluids when ultra sonic assistance is employed. The pitch of the scallop marks has been
vw effective = vw applied ± 2Xm f
(13)
where Xm is the effective amplitude of vibration and f is the frequency of vibration. Earlier it has been observed that the viscosity of the fluid affects the formation of grinding scallops. More lubricious (high viscosity) fluids have consumed less grinding power, as shown in Fig. 7. It means lubricious fluids require less grinding force during grit-workpiece interaction (Fig. 8). Due to such less grinding force requirement at the grit level, for lubricious fluids (like rice bran oil under ultrasonic assis tance) the effective amplitude of vibration Xm is expected to be more as
Fig. 9. Tactile 3-D surface profilometry images of the ground surface at 40 m/s under various grinding environments. 7
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Fig. 10. Tactile profilometry image of longitudinal sectional view of the ground surface shown in Fig. 4.
compared to a situation when grinding force is relatively higher (like soluble oil-water emulsion under ultrasonic assistance). Lower grinding force reduces the hindrance of vibration transfer leading to higher Xm . Such a higher effective amplitude of vibration would promote higher effective workspeed (equation (13)), providing higher Sc and Sh , which is clearly visible in Fig. 10. The scallop marks have also been revealed in the SEM photo of the ground surface, as depicted in Fig. 11. The average pitch of the scallop increases from 254 μm to 505 μm and 800 μm when the grinding fluid environment is changed from soluble oil-water emulsion to neat oil and rice bran oil, respectively under ultrasonic assistance. The pitch of the scallop (observed under SEM – Fig. 11) correlates well with the scallops’ geometry as captured by tactile profilometry (Fig. 10) and the viscosity of the grinding fluids. Scallop marks would be formed in grinding, whether ultrasonic assistance is employed or not. However, Figs. 10 and 11 did not reveal scallop formation under soluble oil-water emulsion without ultrasonic assistance. The pitch and height of scallop are expected to be lower in the conventional grinding than UAG because of lower effective work speed (refer to equation (13)). The magnification of Fig. 11 probably
was not adequate to reveal the scallop of conventional grinding. Higher magnification image (Fig. 12) however, shows repetitive scallop marks under soluble oil-water emulsion under conventional grinding. The scallop pitch is much less (110 μm) compared to the UAG under various environments (Fig. 11), which follows the above discussion of scallop formation. The profile presented in Fig. 10 indicates that ultrasonic assisted grinding affected the sharpness of the surface profile. Kurtosis (Rku) value describes the sharpness of any profile [35]. Rku <3 indicates the profile is platykurtic and the profile is said to be leptokurtic when Rku >3. In the measurement of Kurtosis, selection of appropriate cut-off is very important. As depicted in Fig. 10, the scallop length is very high with UAG under high viscous fluids (500–800 μm). It is, thus, difficult to set an appropriate cut-off length in kurtosis measurement for high viscous fluids. Therefore, the kurtosis values are presented and compared only for soluble oil water emulsion. It is apparent from Fig. 13 that ultrasonic assisted grinding resulted in Rku <3 whereas conven tional grinding yielded Rku >3 at both the grinding speeds. It indicates, UAG altered the surface profile from peaky surface to plateau kind of surface. 8
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Fig. 11. SEM images of the ground surface showing grinding scallop at 40 m/s under different grinding environments.
Fig. 12. Grinding scallop at higher magnification for conventional grinding under soluble oil-water emulsion at 40 m/s.
produced higher compressive residual stress for most of the combina tions despite slightly higher grinding power requirement under UAG. It is attributed to intense peening effect under UAG. Higher workpiece velocity (or higher scallop height Sh ) under UAG promoted intense impact with the abrasive grit during the engagement, whereas lower workpiece velocity under conventional grinding resulted in mild or low intensity impact. This fact has also been schematically illustrated in Fig. 15. Higher is the intensity of the impact, more compressive the stress would be. However, it is to be mentioned that, higher workpiece velocity would increase the scallop pitch (Sc ) as well. A rise in scallop pitch would reduce the number of impact per unit length, which may have an opposite effect on residual stress. This counter-balancing effect has been discussed in the subsequent section. If the effect of different grinding fluids on the residual stress is observed under UAG, it can be realized that water-based soluble oil emulsion always produced higher percentage improvement in residual stress than other fluids (refer to Fig. 14). It could be due to different pitch (Sc ) and height of the scallop (Sh ) under different grinding fluids. It is specified in the earlier section that effect of Sc and Sh on residual stress is contrasting. The significant effect of different grinding fluids on the geometry of grinding scallop marks has already been discussed in sec tion 3.1. It was identified that in the case of water-based soluble oil emulsion both Sc and Sh are less (vide Figs. 10 and 11) whereas, for high lubricious fluids, e.g., rice bran oil, Sc and Sh are higher. As the pitch (Sc ) and height (Sh ) of grinding scallop marks have a counter-balancing
Fig. 13. Kurtosis of longitudinal surface profile of ground surface.
3.3. Residual stress under UAG Change in residual stress upon the application of ultrasonic assis tance is depicted in Fig. 14 at three different grinding speeds under various cooling-lubrication conditions. Ultrasonic assistance has 9
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Fig. 14. Effect of ultrasonic vibration on residual stress of ground surface at different speed-fluid conditions.
Fig. 15. Schematic representation of effect of workpiece velocity on impact intensity during engagement of the abrasive grit.
Fig. 16. The ratio of scallop height (Sh ) to scallop pitch (Sc ) at 40 m/s and 60 m/s under UAG. 10
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effect on residual stress, the resultant effect of Sc and Sh is a key factor that governs the final residual stress. This observation has been further enlightened with the help of Sh /Sc ratio. It is debated that, residual stress would become more compressive with the increase in Sh and decrease in Sc . Therefore, the higher ratio of Sh /Sc would provide more compressive stress. Fig. 16 reveals the Sh /Sc ratio for UAG at 40 m/s and 60 m/s. The highest Sh /Sc ratio could be noted for soluble oil water emulsion at both the speeds compared to other oils. It justifies the highest percentage improvement of residual stress upon application of UAG under soluble oil emulsion as observed from Fig. 14. However, the actual magnitude of residual stress cannot be directly correlated with this parameter. The variation in the residual stress with respect to Sh /Sc ratio under UAG is depicted in Fig. 17. No clear trend could be found. This is because the grinding temperature, which also governs the residual stress, would be different under various grinding environments and grinding speeds. Hence, along with Sh /Sc ratio, grinding temperature needs to be considered to get proper correlation with actual residual stress. Another interesting observation is that the effect of ultrasonic vi bration on residual stress became more at high grinding speed. Higher percentage improvement in compressive residual stress at higher grinding speed is prominent as can be seen in Fig. 14. It can be explained with the help of grinding force requirement. Earlier it has been identi fied that higher grinding force requirement hindered the transfer of ultrasonic vibration to the grinding zone. Therefore, it seems that lower tangential force requirement at higher grinding speed (Fig. 8) enhanced the effectivity of the UAG, which might have resulted in more percent age improvement in compressive residual stress at high speeds. Except for the ultrasonic vibration, effect grinding speed on residual stress is also noticed. Fig. 14 reveals that an increase in grinding speed has yielded less compressive residual stress irrespective of the choice of grinding fluid or imposition of ultrasonic assistance or otherwise. An increase in grinding speed leads to a reduction in maximum undeformed chip thickness providing more grit-workpiece interaction, rubbing and ploughing. It is expected to induce more compressive residual stress. But in the present work, just the opposite has been observed. The rise in grinding speeds provided a substantial increase in grinding power (refer to Fig. 7). It has provided a proportional increase in grinding heat flux leading to higher grinding zone temperature [33]. That has led to the predominance of thermal effect at high grinding speed, yielding less compressive residual stress. It is to note that more lubricious grinding fluid has resulted in more compressive residual stress, particularly at higher grinding speed (40 m/ s and 60 m/s) both in conventional and UAG. It is attributed to less grinding power requirement under more lubricious grinding fluids (refer to Fig. 7), which produced lower grinding heat flux and lower grinding temperature, enabling induction of higher compressive residual stress.
Fig. 17. Variation of residual stress with Sh/Sc ratio under UAG at 40 m/s and 60 m/s.
vibration more effectively, i.e., the effective amplitude of vibration in the grinding zone is more for high lubricious fluid. Consequently, grinding scallop or the surface generation depended largely on the grinding fluids under UAG. 3. Owing to the high effective amplitude of vibration, both the pitch and height of the scallop were higher in the case of high lubricious fluids than others. The grinding scallop measured from SEM and 3D profilometer matched very nicely. 4. Improvement in surface residual stress with ultrasonic-assisted grinding was observed for most of the grinding speed and fluid combinations. The effect of UAG on residual stress was found to be more significant at higher grinding speeds. 5. The resultant effect of pitch (Sc ) and height (Sh ) of grinding scallop governed the degree of improvement of residual stress under UAG. CRediT authorship contribution statement Anirban Naskar: Conceptualization, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing - original draft. Amit Choudhary: Conceptualization, Investigation, Methodology, Writing review & editing. S. Paul: Conceptualization, Funding acquisition, Re sources, Supervision, Methodology, Writing - review & editing. Declaration of competing interest
4. Conclusions
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The present work reports the grindability study of Ti–6Al–4V with ultrasonic-assisted grinding (UAG) under various cooling-lubrication conditions at different grinding speeds. Some major conclusions have been drawn based on the above-discussed results, which are as follows.
Acknowledgement The authors gratefully acknowledge the funding support received from ARDB, MoD, Government of India (Sanction No. ARDB/01/ 2031772/M/I, dated – August 10, 2015).
1. No clear effect of UAG on grinding power was observed at each of the grinding fluid and speed combinations. 2. A significant effect of the lubrication of grinding fluids on the effectivity of UAG was identified. Fluids of high lubricity transfer the
Annexure 1. Specific grinding energy in plunge surface grinding is expressed by equation (A1) as ug =
Ft vs abw vw
(A1) 11
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vw abw vs
(A2)
Ft = ug
Replacing total grinding force (Ft ) by the product of force per grit (ft ), grinding area and grit density yields (√̅̅̅̅̅̅̅ ) vw ft × c × ads bw = ug abw vs ft =
ug vw c vs
√̅̅̅̅ a ds
(A3) (A4)
Maximum uncut chip thickness is expressed as [33]. ( √̅̅̅̅ )0.5 3 vw a hm = c tan α vs ds
(A5)
Combining equation A4 and A5, the following expression for average tangential force per grit is obtained: ft =
tan α ug hm 2 3
(A6)
References
[18] Uhlmann E, Spur G. Surface formation in creep feed grinding of advanced ceramics with and without ultrasonic assistance. CIRP Annals 1998;47(no. 1):249–52. [19] Wang Yan, Lin Bin, Wang Shaolei, Cao Xiaoyan. Study on the system matching of ultrasonic vibration assisted grinding for hard and brittle materials processing. Int J Mach Tool Manufact 2014;77:66–73. [20] Tawakoli Taghi, Azarhoushang Bahman. Influence of ultrasonic vibrations on dry grinding of soft steel. Int J Mach Tool Manufact 2008;48(14):1585–91. [21] Molaie MM, Akbari J, Movahhedy MR. Ultrasonic assisted grinding process with minimum quantity lubrication using oil-based nanofluids. J Clean Prod 2016;129: 212–22. [22] Bhaduri Debajyoti, Leung Soo Sein, Aspinwall David K, Novovic Donka, Bohr Stefan, Harden Peter, Webster John A. Ultrasonic assisted creep feed grinding of gamma titanium aluminide using conventional and superabrasive wheels. CIRP Annals 2017;66(1):341–4. [23] Gao Teng, Zhang Xianpeng, Li Changhe, Zhang Yanbin, Yang Min, Jia Dongzhou, Ji Heju, et al. Surface morphology evaluation of multi-angle 2D ultrasonic vibration integrated with nanofluid minimum quantity lubrication grinding. J Manuf Process 2020;51:44–61. [24] Wang Yan, Lin Bin, Cao Xiaoyan, Wang Shaolei. An experimental investigation of system matching in ultrasonic vibration assisted grinding for titanium. J Mater Process Technol 2014;214(9):1871–8. [25] Kumar Maroju Naresh, Jin Xiaoliang. Effects of vibration assistance on surface residual stress in grinding of Ti6Al4V alloy. Procedia Manufacturing 2017;10: 171–82. [26] Dambatta Yusuf S, Sarhan Ahmed AD, Sayuti M, Hamdi M. Ultrasonic assisted grinding of advanced materials for biomedical and aerospace applications—a review. Int J Adv Manuf Technol 2017;92(9–12):3825–58. [27] Choudhary Amit, Naskar Anirban, Paul S. An investigation on application of nanofluids in high speed grinding of sintered alumina. J Manuf Process 2018;35: 624–33. [28] https://www.hplubricants.in/products/specialties/metal-cutting-fluids/trimof in-23-trimofin-25 (Accesed 21 July 2020). [29] Nagaraja AM, Prabhukumar GP. Characterization and optimization of rice bran oil methylester for CI engines at different injection pressures. No. 2004-28-0048. SAE Technical Paper; 2004. [30] de Moraes, Douglas Lyra, Garcia Mateus Vinicius, Jos´e Claudio Lopes, Fonteque Ribeiro Fernando Sabino, de Angelo Sanchez Luiz Eduardo, Foschini Cesar Renato, de Mello Hamilton Jos´ e, Aguiar Paulo Roberto, Bianchi Eduardo Carlos. Performance of SAE 52100 steel grinding using MQL technique with pure and diluted oil. Int J Adv Manuf Technol 2019;105(10):4211–23. [31] Prevey Paul S. X-ray diffraction residual stress techniques. ASM International, ASM Handbook 1986;10:380–92. [32] Wawra H. Die Kroner-Grenzen der Elastizitatsmoduln technisch wichtiger Werkstoffe: teil II. Zahlenwerte zur Temperaturabhangingkeit der Moduln der Elemente. Z Metallkd 1978;69(8):518–23. [33] Malkin Stephen, Guo Changsheng. Grinding technology: theory and application of machining with abrasives. Industrial Press Inc.; 2008. [34] Zhang Yanbin, Li Changhe, Jia Dongzhou, Zhang Dongkun, Zhang Xiaowei. Experimental evaluation of MoS2 nanoparticles in jet MQL grinding with different types of vegetable oil as base oil. J Clean Prod 2015;87:930–40. [35] Gadelmawla ES, Koura MM, Maksoud TMA, Elewa IM, Soliman HH. Roughness parameters. J Mater Process Technol 2002;123(1):133–45.
[1] Shaw, Milton Clayton. Principles of abrasive processing. No. 13. Oxford University Press on Demand; 1996. [2] Klocke Fritz, Leung Soo Sein, Karpuschewski Bernhard, Webster John A, Novovic Donka, Amr Elfizy, Axinte Dragos A, T¨ onissen Stefan. Abrasive machining of advanced aerospace alloys and composites. CIRP Annals 2015;64(no. 2): 581–604. [3] Soo Sein Leung, Hood Richard, Lannette Mathieu, Aspinwall David K, Voice Wayne E. Creep feed grinding of burn-resistant titanium (BuRTi) using superabrasive wheels. Int J Adv Manuf Technol 2011;53(9–12):1019–26. [4] Tang JS, Pu XF, Xu HJ, Zhang YZ. Studies on mechanisms and improvement of workpiece burn during grinding of titanium alloys. CIRP Annals 1990;39(1):353–6. [5] Teicher U, Ghosh A, Chattopadhyay AB, Künanz K. On the grindability of titanium alloy by brazed type monolayered superabrasive grinding wheels. Int J Mach Tool Manufact 2006;46(6):620–2. [6] Teicher U, Künanz K, Ghosh A, Chattopadhyay AB. Performance of diamond and CBN single-layered grinding wheels in grinding titanium. Mater Manuf Process 2008;23(3):224–7. [7] Shi Zhong De, Attia Helmi. Feasibility study on grinding of titanium alloys with electroplated CBN wheels. In: Advanced materials research. vol. 797. Trans Tech Publications Ltd; 2013. p. 73–8. [8] Virdi Roshan Lal, Singh Chatha Sukhpal, Singh Hazoor. Experimental investigations on the tribological and lubrication behaviour of minimum quantity lubrication technique in grinding of Inconel 718 alloy. Tribol Int 2020:106581. [9] Gao Teng, Li Changhe, Zhang Yanbin, Yang Min, Jia Dongzhou, Tan Jin, Hou Yali, Li Runze. Dispersing mechanism and tribological performance of vegetable oilbased CNT nanofluids with different surfactants. Tribol Int 2019;131:51–63. [10] Yang Min, Li Changhe, Zhang Yanbin, Jia Dongzhou, Li Runze, Hou Yali, Cao Huajun. Effect of friction coefficient on chip thickness models in ductileregime grinding of zirconia ceramics. Int J Adv Manuf Technol 2019;102(5–8): 2617–32. [11] Yang Min, Li Changhe, Zhang Yanbin, Jia Dongzhou, Li Runze, Hou Yali, Cao Huajun, Wang Jun. Predictive model for minimum chip thickness and size effect in single diamond grain grinding of zirconia ceramics under different lubricating conditions. Ceram Int 2019;45(12):14908–20. [12] Sadeghi MH, Haddad MJ, Tawakoli T, Emami M. Minimal quantity lubricationMQL in grinding of Ti–6Al–4V titanium alloy. Int J Adv Manuf Technol 2009;44(5): 487–500. [13] Setti Dinesh, Sinha Manoj Kumar, Ghosh Sudarsan, Venkateswara Rao P. Performance evaluation of Ti–6Al–4V grinding using chip formation and coefficient of friction under the influence of nanofluids. Int J Mach Tool Manufact 2015;88:237–48. [14] Ibrahim Ahmed Mohamed Mahmoud, Li Wei, Xiao Hang, Zeng Zhixiong, Ren Yinghui, Mohammad S, Alsoufi. Energy conservation and environmental sustainability during grinding operation of Ti–6Al–4V alloys via eco-friendly oil/ graphene nano additive and MQL lubrication. Tribol Int 2020:106387. [15] Singh Harpinder, Sharma Vishal S, Manu Dogra. Exploration of graphene assisted vegetables oil based minimum quantity lubrication for surface grinding of TI-6AL4V-ELI. Tribol Int 2020;144:106113. [16] Colwell LV. The effects of high-frequency vibrations in grinding. Trans. ASME 1956;78(no. 4):837. [17] Spur Günter, Holl S-E. Ultrasonic assisted grinding of ceramics. J Mater Process Technol 1996;62(4):287–93.
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Surface generation in ultrasonic-assisted high-speed superabrasive grinding under minimum quantity cooling lubrication with various fluids Anirban Naskar *, Amit Choudhary , S. Paul Machine Tool and Machining Laboratory, Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Ultrasonic assisted grinding Surface generation Residual stress Minimum quantity cooling lubrication
Ultrasonic assisted grinding (UAG), and minimum quantity cooling lubrication (MQCL) have individually improved grinding characteristics of difficult–to-cut super-alloys in terms of reduced forces and surface rough ness. In the present work, a hybrid grinding approach (UAG + MQCL) is utilized, and the effect of fluid’s lubricity on grit-workpiece interaction has been investigated during the grinding of Ti–6Al–4V. More lubricious fluid provided less resistance to vibration transfer to the grinding zone, and consequently, the effective amplitude of vibration increased with an increase in lubricity of the fluids. It has governed the mechanism of grinding scallop formation significantly. Additionally, more lubricious vegetable oil yielded the lowest grinding power and higher compressive residual stress. Further, 20–100% improvement in compressive residual stress was noted under UAG.
1. Introduction Properties like low coefficient of heat diffusion [1] and high chem ical reactivity with tool materials [2,3] distinguish titanium alloys from other super-alloys and put them on top in grinding difficulty index. Hence, improving grindability of titanium alloy has always been a key focus of the scientific community. Early research to improve the grind ability of titanium alloys was carried out at a relatively low grinding speed using a conventional grinding approach. In the 1990s Tang et al. [4] coated grinding wheel with solid lubricant (MoS2) and found a reduction in force and grinding temperature. Teicher et al. [5,6] used liquid nitrogen, neat cutting oil, alkaline soap, dry condition, and MoS2 coated grit (in dry mode) to investigate the grinding behavior of Ti–6Al–4V. They found significant improvement in grindability under neat oil and alkaline soap in terms of force, favorable chip formation, grit tip adhesion, and ground surface morphology. Shi and Attia [7] applied both grinding fluid (7% soluble oil emulsion) and wheel cleaning fluid at a very high pressure in shallow and creep-feed grinding to enhance the removal rate of titanium and avoid wheel loading. They [7] could achieve a removal rate of 8 mm2/s and 3 mm2/s for shallow and creep-feed grinding, respectively, without any visible wheel loading, burning, and smearing. Besides the aforementioned conventional grinding approaches, an
efficient and effective way of grinding fluid application is minimum quantity cooling lubrication (MQCL) [8,9]. The MQCL technique has been reported to provide a substantial improvement in the ductile cut ting of ceramics [10,11]. It has also been explored by various researchers to improve the grinding of titanium alloys [12–15]. Sadeghi et al. [12] noticed a better performance of MQCL than conventional wet grinding in terms of less plastic deformation, proper shearing, and less grinding forces in titanium grinding. The use of different grinding fluids in MQCL mode for titanium grinding has provided a reduction of 20% [13], 40–70% [14], and 22–35% [15] in grinding forces as compared to wet grinding. Additionally, improvement in chip formation, coefficient of friction, and ground surface morphology were also reported [13–15]. However, most of the studies were carried out at conventional grinding speed (limited to 30 m/s), and residual stress generated due to grinding was not investigated. Ultrasonic assisted grinding (UAG) is another grindability improve ment technique that has emerged in the 1950s [16]. Plenty of literature is available on the UAG of ceramic and brittle materials, where a reduction in grinding forces and other advantages have been reported [17–19]. However, the number of reports available on the UAG of metallic materials is limited. Tawakoli and Azarhoushang [20] observed a reduction in normal (60–70%) and tangential (30–50%) grinding forces with the application of UAG (on the workpiece) of soft 100Cr6 steel of hardness 82 HRB in dry mode. They [20] reported a reduction in
* Corresponding author. Machine Tool and Machining Laboratory, Department of Mechanical engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal, 721 302, India. E-mail addresses: [email protected] (A. Naskar), [email protected] (A. Choudhary), [email protected] (S. Paul). https://doi.org/10.1016/j.triboint.2020.106815 Received 15 September 2020; Received in revised form 24 November 2020; Accepted 28 November 2020 Available online 4 December 2020 0301-679X/© 2020 Elsevier Ltd. All rights reserved.
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transfer to the grinding zone. However, reports dealing with the effect of UAG at different grinding speed could not be found. Moreover, most of the conducted work on UAG of metallic materials was focused on force, surface roughness, and ground surface morphology. The fatigue life of any ground surface would be greatly affected by the state and magnitude of surface residual stress present in it. But, reports on the effect of UAG on residual stress can be hardly found. In the present research work, an attempt has been made to address the gaps mentioned above in the reported literature. Fluids having different viscosity (lubricity) 0.65 to 48 cSt have been applied in mini mum quantity cooling lubrication (MQCL) mode in combination with ultrasonic-assisted grinding. The effect of fluid’s lubricity on the surface generation is discussed in detail. Both high (60 & 40 m/s) and low grinding speeds (20 m/s) were employed to study the influence of UAG at different grinding speeds. Residual stress for all the samples has been measured and analysed to study the effect of different fluid and UAG on surface residual stress. This study highlights the change in the gritworkpiece interaction.
Nomenclature ug Ft vs vw a bw ft c ds hm
α
L Sc Sh Xm f vw effective vw applied
specific grinding energy total tangential grinding force wheel speed workspeed downfeed width of the workpiece tangential force per grit grit density wheel diameter maximum uncut chip thickness semi apex angle of the square pyramidal grit intergrit distance pitch of scallop height of scallop effective amplitude of ultrasonic vibration frequency of ultrasonic vibration effective workspeed during ultrasonic grinding applied workspeed, same as vw
2. Experimental details 2.1. Ultrasonic vibration system and grinding details Ultrasonic assisted grinding was carried out in an indigenously developed set up shown in Fig. 1. The supplied electrical energy was first converted into mechanical vibration of 20 kHz through a piezoelectric transducer. In the later stage, booster and horn were used to amplify the vibration. The workpiece holder was kept on the block sonotrode. A frictionless table was provided underneath the sonotrode to minimize the loss of vibration. The vibration of 18 μm amplitude was recorded at no-load condition. The air supply was provided to control the temper ature of the system. The advantage of two directional UAG (2D-UAG) over one directional UAG (1-D UAG) is documented in the literature. However, due to the complexity and high set-up cost, 1-D UAG is preferred [26]. In 1-D UAG, vibration is applied in two directions, along the workpiece velocity and across the workpiece velocity (along the wheel axis). Both methods have demonstrated their benefits over con ventional grinding [26]. Thus, in the present study, the vibration has been applied in the direction of workpiece velocity to explore the effect of UAG. Ti–6Al–4V (25 mm × 8 mm × 8 mm in dimension) was ground in plunge surface grinding mode employing single-layer electroplated cBN grinding wheel of 25 mm diameter and 10 mm width. The grinding wheels contained ABN 900 grits of 151 μm size (mesh size #100). Fig. 2 shows a representative image of the wheel. Details of the grinding pa rameters are provided in Table .1. Three grinding fluids of widely different viscosity were applied through indigenously developed mini mum quantity cooling lubrication set-up [27]. Viscosities of the used fluids at 40 ◦ C are 0.65 cSt, 34 cSt [28] and 48 cSt [29] for soluble oil-water emulsion, neat oil (HP –Trimofin 23), and rice bran oil respectively. Soluble oil in water emulsion was prepared in 1:20 ratio, and thus the viscosity of the fluid was considered to be the same as the water. Grinding fluids with more viscosity have not been employed in the present work as they tend to loose effectiveness in grinding due to atomization and penetrability [14,30] issues.
thermal damage and surface roughness and an increase in G-ratio under UAG. Molaie et al. [21] also noticed a substantial decrease in normal grinding force in UAG of AISI52100 steel, but the effect of vibration on the tangential grinding force was found to be less. Bhaduri et al. applied ultrasonic vibration on the workpiece in creep feed grinding on γ-TiAl intermetallic alloy in flood cooling mode [22]. Similar to above-mentioned finish grinding [20,21], Bhaduri et al. [22] also observed a reduction in grinding forces along with lower wheel wear and marginal improvement in surface roughness. In addition, reduced effect of ultrasonic vibration on the grindability at higher depth of cut was realized and it was attributed to the hindrance of the vibration transfer to the grinding zone. Recently, Gao et al. [23] carried out a detailed analysis of ground surface characteristics in 1-D and 2-D UAG of nickel-based material and wider furrows were noticed on the finished surface in vibration assisted grinding. Few works on UAG of Ti–6Al–4V was also reported [24,25]. In addition to a reduction in force and surface roughness [24], improvement in residual stress was identified [25]. Nevertheless, most of the UAG research work utilized a single grinding fluid at conventional grinding speed, and very few works investigated the effect of UAG on residual stress. The effectivity of ultrasonic assistance on the grinding performance would largely depend on vibration transfer efficiency to the grinding zone. The amplitude of vibration at no-load and load conditions may differ. Bhaduri et al. [22] indicated that the effectiveness of ultrasonic assistance on the grinding performance reduces at a higher depth of cut. It seems that due to the increase in grinding load at higher depth of cut, effective vibration transfer could not take place and consequently, the effectivity of vibration on the grinding performance got reduced. The lubricity of the grinding fluids influences the grit-workpiece interaction and grinding load (forces) significantly. From the above discussion, it can be inferred that fluids having different lubricity may affect the grinding performance disproportionately under the application of UAG because of different degrees of vibration transfer to the grinding zone. Different degrees of transferred vibration would affect the finish surface generation. However, the influence of fluid’s lubricity on the performance of UAG has never been studied earlier, which is the subject of concern of the present work. Besides, most of the available reports on UAG of metallic materials dealt with a constant grinding speed (vs ) which was limited in the range 30–40 m/s. Rise in grinding speed yields lower forces (load) owing to less uncut chip thickness (hm ). Lower grinding forces reduce the grinding load, which may facilitate effective vibration
2.2. Measurement and analysis of grinding characteristics During grinding, spindle power was measured using Montronix PS200-NG power sensor. Both SEM (Zeiss Evo 18) and 3D contact type profilometer (Form Talysurf 50 Intra 2) were used to study the finished surface. An area of 4 × 4 mm2 was scanned using the profilometer, and later it was analysed using Talymap gold software. The residual stress of the samples was measured using XRD (PANalytical EMPYREAN). The stress measurement was performed at 141.7◦ of 213 crystallographic plane of the α phase of Ti–6Al–4V [31] employing Cu source of a 2
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Fig. 1. Schematic and actual experimental set-up of ultrasonic-assisted grinding.
Fig. 2. (a) SEM image of the wheel surface and (b) optical image of the wheel.
wavelength of 1.54 Å. Five inclination angles (0◦ , 18.43◦ , 26.57◦ , 33.21◦ , and 39.23◦ ) were provided both in a negative and positive di rection, which resulted in ten scans for each measurement. Each sample was repeated thrice, and the average value has been reported. During measurement, the Cu-tube was running at 45 kV and 40 mA. The raw data was fed to PANalytical stress plus software for stress analysis, after measurement. Poisson ratio and elastic modulus values of 0.32 and 114 MPa were used in the analysis, respectively [32].
2.3. Grit-workpiece interaction and scallop formation This section provides details of scallop formation in grinding, and the expressions of two scallop parameters namely, the pitch of scallop (Sc ) and the height of scallop (Sh ), have been derived. Fig. 3 shows cutting paths of three consecutive grits of the same radial height and equally spaced on the periphery of the wheel. The cutting path of individual grits is assumed to be identical to the wheel radius for simplicity. For ease of representation, the linear velocity of the workpiece (vw ) has been imposed on the wheel. The cutting arcs of the grains can be expressed as, 3
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Table 1 Grinding details.
Now, from triangle OP2
Grinding machine tool
Praga surface grinder, model 451
High-speed spindle
Precise Pr¨ azisionsspindeln GmbH, Model S60 Maximum power 1.1 kW, maximum RPM 66,000 Cutting speed 20 m/s, 40 m/s and 60 m/s Workpiece velocity 2 m/min Downfeed 6 μm Air delivery pressure 4.5 bar Air flow rate 34 Lpm Fluid flow rate 200 mL/h Nozzle to wheel distance 15 mm
Grinding parameters MQCL parameters
2
OP = O22 − P22
(
L vs
Sc =
vw L vs
(6)
)2 =
( )2 ( )2 ds Sc − 2 2
(7)
− ds Sh + Sh 2 = −
( )2 Sc 2
(8)
Neglecting the term Sh 2 , we get Sh =
Sc 2 4ds
Combining equations (3) and (9), the Sh is expressed as )2 ( 1 vw Sh = L 4ds vs
(1)
(9)
(10)
From equations (3) and (10), it can be realized that both the scallop parameters are depended on the vw and vs , if the wheel parameters (ds and L) remain unaltered. In the present work, the ultrasonic vibration has been imposed on the workpiece in the direction of the workpiece velocity. Therefore, it is most likely that the velocity of the workpiece (vw ) would change under application of UAG. Consequently, it would directly influence the scallop parameters as well.
Therefore, Sc can be represented as Sc = vw t
ds − Sh 2
(5)
( )2 ( )2 ds Sc − 2 2
(OX − PX)2 =
1X2K, 2Y3L and 3Z4M. However, due to the overlapping action of the preceding cutting path by the successor grit, the final cutting paths that remain on the finished surface are 1X2, 2Y3, and 3Z4 as illustrated in Fig. 4. The Sc and Sh are also shown in the diagram. If a grit takes time t to cover the inter-grit distance (L), then scallop pitch (Sc ) is the distance covered by the workpiece during this time. If the velocity of the grit is considered same as wheel velocity (vs ), t can be expressed as t=
(4)
Sh = Q2 = PX
(2) (3)
Fig. 5 presents an exaggerated view of scallop depicted in Fig. 4. The vertical distance between point 2 and Q is defined as scallop height (Sh ). The scallop pitch (Sc ) is equal to XY.
Fig. 3. Schematic diagram of different grit path and scallop formation.
Fig. 4. Final grinding scallop on finished surface. 4
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sectioning was done on the levelled profile. Peak to peak distance measurement was performed on the sectioned 2-D longitudinal profile to measure scallop pitch (Sc ) as illustrated in Fig. 6. Similarly, peak to valley distance was also measured to get the scallop height (Sh ). The measurements were undertaken using the graphical user-interface of the software with the help of a distance measurement tool in-built within the software. Thus, no specific cut-off value was required in this analysis. 3. Results and discussion 3.1. Grinding power under UAG Fig. 7 shows the effect of ultrasonic vibration on grinding power (Ft vs ) under different grinding fluids applied in MQCL mode with wide variation in grinding speed. It reveals that there is no beneficial effect of ultrasonic assistance on grinding power irrespective of the wide varia tion in grinding speed vs and choice of grinding fluid. The effect of ul trasonic vibration (applied on the workpiece) was noted to be more significant on normal grinding force than the tangential force due to effective grit penetration [21]. Present study reports grinding power (spindle power), which represents tangential force. Hence, the negli gible effect of UAG on the tangential force is in accordance with the literature. However, few studies have reported a reduction in both the forces [20,22]. Fig. 7 also depicts the increase in vs provided higher grinding power requirements. But, the increase is not linearly propor tional to the vs despite linear relation (power = Ft vs ). Equation (11) shows the interrelation between various grinding parameters and
Fig. 5. Exaggerated view of grinding scallop as depicted in Fig. 4.
2.4. Measurement of scallop As stated earlier, an area of 4 × 4 mm2 was scanned on the ground surface using a tactile profilometer and a typical scanned area is shown in Fig. 6. After scanning, the results were analysed using Talymap gold software. Fig. 6 also depicts the process sequence of scallop measure ment. Initially, the raw profile was levelled and after that longitudinal
Fig. 6. Process sequence of grinding scallop analysis. 5
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Fig. 7. Grinding power at different grinding speeds under different grinding environments.
maximum uncut chip thickness (hm ) [33]. The hm characterises the chip load per grit. As vs increases, the hm would decrease, yielding lower force per grit (ft ) (as shown in equation (12) - for details of equation (12), please refer to Annexure 1) and lower total grinding forces. This fact is also evident from Fig. 8, which shows a drop in tangential grinding force with the increase in vs . Consequently, lower grinding force (tangential force) at high speed would provide less than
proportional increase in grinding power with an increase in vs . √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ ( √̅̅̅̅ ) 3 vw a hm = ctanα vs ds ft =
tan α ug hm 2 3
Fig. 8. Tangential grinding force at different grinding speeds under different grinding environments, derived from Fig. 7. 6
(11) (12)
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The effect of viscosity of the grinding fluids on the power has also been captured in Fig. 7. More viscous fluids yielded lower grinding power throughout the experimental domain. It seems that fluid with higher viscosity acted as a better lubrication medium [34] at the grit-workpiece interface and provided less grinding power requirement. Such a substantial change in grinding power requirement would possibly affect the state of residual stress on the ground surface. This aspect has been discussed later in detail.
shown in Fig. 10. The extent of both pitch and height of scallop marks increased with an increase in viscosity of the grinding fluids under UAG. So it may be inferred that viscosity of the grinding fluid greatly affects grit workpiece interaction under ultrasonic assistance. During grinding with ultrasonic assistance, the workpiece vibrates along the direction of workspeed. Hence, depending upon the effective amplitude and fre quency of vibration, a particular grit may disengage because the vi bration could be in the opposite direction of work speed (as shown in equation (13) by the –ve sign). It can as well participate in chip for mation with higher workspeed due to the work speed and vibration being in the same direction (as shown in equation (13) by the +ve sign). If the effective amplitude of vibration imposed by the ultrasonic sono trode is Xm and frequency of vibration is f then effective workspeed (vw effective ) may change as per equation (13). This variation of workspeed affects the geometry of grit workpiece interaction and formation of scallop marks as characteristics in equations (3) and (10).
3.2. Effect of UAG on ground surface generation Fig. 9 reveals the ground surface topography under various grinding fluids with and without ultrasonic assistance. Repetitive grinding scallop marks are seen along the grinding direction when water-based soluble oil emulsion is employed as the grinding fluid with ultrasonic assistance (Fig. 9b) compared to conventional grinding with the same fluid without any ultrasonic assistance (Fig. 9a). The scallop marks though different in length, are apparent in Fig. 9c and d when grinding was performed with ultrasonic assistance under neat oil and rice bran oil, respectively. Ground surface topography of conventional grinding under neat oil and rice bran oil has not been shown as they appear similar to soluble oilwater emulsion (Fig. 9a), with no visible scallop. Fig. 10 visualises the longitudinal sectional view (along the grinding direction) of the ground surface topography, as shown in Fig. 9. It captures the two geometrical features of grinding scallop. Fig. 10 along with Fig. 9, is demonstrating a correlation between the pitch (Sc ) and height of scallop (Sh ) marks under various grinding fluids when ultra sonic assistance is employed. The pitch of the scallop marks has been
vw effective = vw applied ± 2Xm f
(13)
where Xm is the effective amplitude of vibration and f is the frequency of vibration. Earlier it has been observed that the viscosity of the fluid affects the formation of grinding scallops. More lubricious (high viscosity) fluids have consumed less grinding power, as shown in Fig. 7. It means lubricious fluids require less grinding force during grit-workpiece interaction (Fig. 8). Due to such less grinding force requirement at the grit level, for lubricious fluids (like rice bran oil under ultrasonic assis tance) the effective amplitude of vibration Xm is expected to be more as
Fig. 9. Tactile 3-D surface profilometry images of the ground surface at 40 m/s under various grinding environments. 7
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Fig. 10. Tactile profilometry image of longitudinal sectional view of the ground surface shown in Fig. 4.
compared to a situation when grinding force is relatively higher (like soluble oil-water emulsion under ultrasonic assistance). Lower grinding force reduces the hindrance of vibration transfer leading to higher Xm . Such a higher effective amplitude of vibration would promote higher effective workspeed (equation (13)), providing higher Sc and Sh , which is clearly visible in Fig. 10. The scallop marks have also been revealed in the SEM photo of the ground surface, as depicted in Fig. 11. The average pitch of the scallop increases from 254 μm to 505 μm and 800 μm when the grinding fluid environment is changed from soluble oil-water emulsion to neat oil and rice bran oil, respectively under ultrasonic assistance. The pitch of the scallop (observed under SEM – Fig. 11) correlates well with the scallops’ geometry as captured by tactile profilometry (Fig. 10) and the viscosity of the grinding fluids. Scallop marks would be formed in grinding, whether ultrasonic assistance is employed or not. However, Figs. 10 and 11 did not reveal scallop formation under soluble oil-water emulsion without ultrasonic assistance. The pitch and height of scallop are expected to be lower in the conventional grinding than UAG because of lower effective work speed (refer to equation (13)). The magnification of Fig. 11 probably
was not adequate to reveal the scallop of conventional grinding. Higher magnification image (Fig. 12) however, shows repetitive scallop marks under soluble oil-water emulsion under conventional grinding. The scallop pitch is much less (110 μm) compared to the UAG under various environments (Fig. 11), which follows the above discussion of scallop formation. The profile presented in Fig. 10 indicates that ultrasonic assisted grinding affected the sharpness of the surface profile. Kurtosis (Rku) value describes the sharpness of any profile [35]. Rku <3 indicates the profile is platykurtic and the profile is said to be leptokurtic when Rku >3. In the measurement of Kurtosis, selection of appropriate cut-off is very important. As depicted in Fig. 10, the scallop length is very high with UAG under high viscous fluids (500–800 μm). It is, thus, difficult to set an appropriate cut-off length in kurtosis measurement for high viscous fluids. Therefore, the kurtosis values are presented and compared only for soluble oil water emulsion. It is apparent from Fig. 13 that ultrasonic assisted grinding resulted in Rku <3 whereas conven tional grinding yielded Rku >3 at both the grinding speeds. It indicates, UAG altered the surface profile from peaky surface to plateau kind of surface. 8
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Fig. 11. SEM images of the ground surface showing grinding scallop at 40 m/s under different grinding environments.
Fig. 12. Grinding scallop at higher magnification for conventional grinding under soluble oil-water emulsion at 40 m/s.
produced higher compressive residual stress for most of the combina tions despite slightly higher grinding power requirement under UAG. It is attributed to intense peening effect under UAG. Higher workpiece velocity (or higher scallop height Sh ) under UAG promoted intense impact with the abrasive grit during the engagement, whereas lower workpiece velocity under conventional grinding resulted in mild or low intensity impact. This fact has also been schematically illustrated in Fig. 15. Higher is the intensity of the impact, more compressive the stress would be. However, it is to be mentioned that, higher workpiece velocity would increase the scallop pitch (Sc ) as well. A rise in scallop pitch would reduce the number of impact per unit length, which may have an opposite effect on residual stress. This counter-balancing effect has been discussed in the subsequent section. If the effect of different grinding fluids on the residual stress is observed under UAG, it can be realized that water-based soluble oil emulsion always produced higher percentage improvement in residual stress than other fluids (refer to Fig. 14). It could be due to different pitch (Sc ) and height of the scallop (Sh ) under different grinding fluids. It is specified in the earlier section that effect of Sc and Sh on residual stress is contrasting. The significant effect of different grinding fluids on the geometry of grinding scallop marks has already been discussed in sec tion 3.1. It was identified that in the case of water-based soluble oil emulsion both Sc and Sh are less (vide Figs. 10 and 11) whereas, for high lubricious fluids, e.g., rice bran oil, Sc and Sh are higher. As the pitch (Sc ) and height (Sh ) of grinding scallop marks have a counter-balancing
Fig. 13. Kurtosis of longitudinal surface profile of ground surface.
3.3. Residual stress under UAG Change in residual stress upon the application of ultrasonic assis tance is depicted in Fig. 14 at three different grinding speeds under various cooling-lubrication conditions. Ultrasonic assistance has 9
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Fig. 14. Effect of ultrasonic vibration on residual stress of ground surface at different speed-fluid conditions.
Fig. 15. Schematic representation of effect of workpiece velocity on impact intensity during engagement of the abrasive grit.
Fig. 16. The ratio of scallop height (Sh ) to scallop pitch (Sc ) at 40 m/s and 60 m/s under UAG. 10
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effect on residual stress, the resultant effect of Sc and Sh is a key factor that governs the final residual stress. This observation has been further enlightened with the help of Sh /Sc ratio. It is debated that, residual stress would become more compressive with the increase in Sh and decrease in Sc . Therefore, the higher ratio of Sh /Sc would provide more compressive stress. Fig. 16 reveals the Sh /Sc ratio for UAG at 40 m/s and 60 m/s. The highest Sh /Sc ratio could be noted for soluble oil water emulsion at both the speeds compared to other oils. It justifies the highest percentage improvement of residual stress upon application of UAG under soluble oil emulsion as observed from Fig. 14. However, the actual magnitude of residual stress cannot be directly correlated with this parameter. The variation in the residual stress with respect to Sh /Sc ratio under UAG is depicted in Fig. 17. No clear trend could be found. This is because the grinding temperature, which also governs the residual stress, would be different under various grinding environments and grinding speeds. Hence, along with Sh /Sc ratio, grinding temperature needs to be considered to get proper correlation with actual residual stress. Another interesting observation is that the effect of ultrasonic vi bration on residual stress became more at high grinding speed. Higher percentage improvement in compressive residual stress at higher grinding speed is prominent as can be seen in Fig. 14. It can be explained with the help of grinding force requirement. Earlier it has been identi fied that higher grinding force requirement hindered the transfer of ultrasonic vibration to the grinding zone. Therefore, it seems that lower tangential force requirement at higher grinding speed (Fig. 8) enhanced the effectivity of the UAG, which might have resulted in more percent age improvement in compressive residual stress at high speeds. Except for the ultrasonic vibration, effect grinding speed on residual stress is also noticed. Fig. 14 reveals that an increase in grinding speed has yielded less compressive residual stress irrespective of the choice of grinding fluid or imposition of ultrasonic assistance or otherwise. An increase in grinding speed leads to a reduction in maximum undeformed chip thickness providing more grit-workpiece interaction, rubbing and ploughing. It is expected to induce more compressive residual stress. But in the present work, just the opposite has been observed. The rise in grinding speeds provided a substantial increase in grinding power (refer to Fig. 7). It has provided a proportional increase in grinding heat flux leading to higher grinding zone temperature [33]. That has led to the predominance of thermal effect at high grinding speed, yielding less compressive residual stress. It is to note that more lubricious grinding fluid has resulted in more compressive residual stress, particularly at higher grinding speed (40 m/ s and 60 m/s) both in conventional and UAG. It is attributed to less grinding power requirement under more lubricious grinding fluids (refer to Fig. 7), which produced lower grinding heat flux and lower grinding temperature, enabling induction of higher compressive residual stress.
Fig. 17. Variation of residual stress with Sh/Sc ratio under UAG at 40 m/s and 60 m/s.
vibration more effectively, i.e., the effective amplitude of vibration in the grinding zone is more for high lubricious fluid. Consequently, grinding scallop or the surface generation depended largely on the grinding fluids under UAG. 3. Owing to the high effective amplitude of vibration, both the pitch and height of the scallop were higher in the case of high lubricious fluids than others. The grinding scallop measured from SEM and 3D profilometer matched very nicely. 4. Improvement in surface residual stress with ultrasonic-assisted grinding was observed for most of the grinding speed and fluid combinations. The effect of UAG on residual stress was found to be more significant at higher grinding speeds. 5. The resultant effect of pitch (Sc ) and height (Sh ) of grinding scallop governed the degree of improvement of residual stress under UAG. CRediT authorship contribution statement Anirban Naskar: Conceptualization, Formal analysis, Investigation, Methodology, Validation, Visualization, Writing - original draft. Amit Choudhary: Conceptualization, Investigation, Methodology, Writing review & editing. S. Paul: Conceptualization, Funding acquisition, Re sources, Supervision, Methodology, Writing - review & editing. Declaration of competing interest
4. Conclusions
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
The present work reports the grindability study of Ti–6Al–4V with ultrasonic-assisted grinding (UAG) under various cooling-lubrication conditions at different grinding speeds. Some major conclusions have been drawn based on the above-discussed results, which are as follows.
Acknowledgement The authors gratefully acknowledge the funding support received from ARDB, MoD, Government of India (Sanction No. ARDB/01/ 2031772/M/I, dated – August 10, 2015).
1. No clear effect of UAG on grinding power was observed at each of the grinding fluid and speed combinations. 2. A significant effect of the lubrication of grinding fluids on the effectivity of UAG was identified. Fluids of high lubricity transfer the
Annexure 1. Specific grinding energy in plunge surface grinding is expressed by equation (A1) as ug =
Ft vs abw vw
(A1) 11
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vw abw vs
(A2)
Ft = ug
Replacing total grinding force (Ft ) by the product of force per grit (ft ), grinding area and grit density yields (√̅̅̅̅̅̅̅ ) vw ft × c × ads bw = ug abw vs ft =
ug vw c vs
√̅̅̅̅ a ds
(A3) (A4)
Maximum uncut chip thickness is expressed as [33]. ( √̅̅̅̅ )0.5 3 vw a hm = c tan α vs ds
(A5)
Combining equation A4 and A5, the following expression for average tangential force per grit is obtained: ft =
tan α ug hm 2 3
(A6)
References
[18] Uhlmann E, Spur G. Surface formation in creep feed grinding of advanced ceramics with and without ultrasonic assistance. CIRP Annals 1998;47(no. 1):249–52. [19] Wang Yan, Lin Bin, Wang Shaolei, Cao Xiaoyan. Study on the system matching of ultrasonic vibration assisted grinding for hard and brittle materials processing. Int J Mach Tool Manufact 2014;77:66–73. [20] Tawakoli Taghi, Azarhoushang Bahman. Influence of ultrasonic vibrations on dry grinding of soft steel. Int J Mach Tool Manufact 2008;48(14):1585–91. [21] Molaie MM, Akbari J, Movahhedy MR. Ultrasonic assisted grinding process with minimum quantity lubrication using oil-based nanofluids. J Clean Prod 2016;129: 212–22. [22] Bhaduri Debajyoti, Leung Soo Sein, Aspinwall David K, Novovic Donka, Bohr Stefan, Harden Peter, Webster John A. Ultrasonic assisted creep feed grinding of gamma titanium aluminide using conventional and superabrasive wheels. CIRP Annals 2017;66(1):341–4. [23] Gao Teng, Zhang Xianpeng, Li Changhe, Zhang Yanbin, Yang Min, Jia Dongzhou, Ji Heju, et al. Surface morphology evaluation of multi-angle 2D ultrasonic vibration integrated with nanofluid minimum quantity lubrication grinding. J Manuf Process 2020;51:44–61. [24] Wang Yan, Lin Bin, Cao Xiaoyan, Wang Shaolei. An experimental investigation of system matching in ultrasonic vibration assisted grinding for titanium. J Mater Process Technol 2014;214(9):1871–8. [25] Kumar Maroju Naresh, Jin Xiaoliang. Effects of vibration assistance on surface residual stress in grinding of Ti6Al4V alloy. Procedia Manufacturing 2017;10: 171–82. [26] Dambatta Yusuf S, Sarhan Ahmed AD, Sayuti M, Hamdi M. Ultrasonic assisted grinding of advanced materials for biomedical and aerospace applications—a review. Int J Adv Manuf Technol 2017;92(9–12):3825–58. [27] Choudhary Amit, Naskar Anirban, Paul S. An investigation on application of nanofluids in high speed grinding of sintered alumina. J Manuf Process 2018;35: 624–33. [28] https://www.hplubricants.in/products/specialties/metal-cutting-fluids/trimof in-23-trimofin-25 (Accesed 21 July 2020). [29] Nagaraja AM, Prabhukumar GP. Characterization and optimization of rice bran oil methylester for CI engines at different injection pressures. No. 2004-28-0048. SAE Technical Paper; 2004. [30] de Moraes, Douglas Lyra, Garcia Mateus Vinicius, Jos´e Claudio Lopes, Fonteque Ribeiro Fernando Sabino, de Angelo Sanchez Luiz Eduardo, Foschini Cesar Renato, de Mello Hamilton Jos´ e, Aguiar Paulo Roberto, Bianchi Eduardo Carlos. Performance of SAE 52100 steel grinding using MQL technique with pure and diluted oil. Int J Adv Manuf Technol 2019;105(10):4211–23. [31] Prevey Paul S. X-ray diffraction residual stress techniques. ASM International, ASM Handbook 1986;10:380–92. [32] Wawra H. Die Kroner-Grenzen der Elastizitatsmoduln technisch wichtiger Werkstoffe: teil II. Zahlenwerte zur Temperaturabhangingkeit der Moduln der Elemente. Z Metallkd 1978;69(8):518–23. [33] Malkin Stephen, Guo Changsheng. Grinding technology: theory and application of machining with abrasives. Industrial Press Inc.; 2008. [34] Zhang Yanbin, Li Changhe, Jia Dongzhou, Zhang Dongkun, Zhang Xiaowei. Experimental evaluation of MoS2 nanoparticles in jet MQL grinding with different types of vegetable oil as base oil. J Clean Prod 2015;87:930–40. [35] Gadelmawla ES, Koura MM, Maksoud TMA, Elewa IM, Soliman HH. Roughness parameters. J Mater Process Technol 2002;123(1):133–45.
[1] Shaw, Milton Clayton. Principles of abrasive processing. No. 13. Oxford University Press on Demand; 1996. [2] Klocke Fritz, Leung Soo Sein, Karpuschewski Bernhard, Webster John A, Novovic Donka, Amr Elfizy, Axinte Dragos A, T¨ onissen Stefan. Abrasive machining of advanced aerospace alloys and composites. CIRP Annals 2015;64(no. 2): 581–604. [3] Soo Sein Leung, Hood Richard, Lannette Mathieu, Aspinwall David K, Voice Wayne E. Creep feed grinding of burn-resistant titanium (BuRTi) using superabrasive wheels. Int J Adv Manuf Technol 2011;53(9–12):1019–26. [4] Tang JS, Pu XF, Xu HJ, Zhang YZ. Studies on mechanisms and improvement of workpiece burn during grinding of titanium alloys. CIRP Annals 1990;39(1):353–6. [5] Teicher U, Ghosh A, Chattopadhyay AB, Künanz K. On the grindability of titanium alloy by brazed type monolayered superabrasive grinding wheels. Int J Mach Tool Manufact 2006;46(6):620–2. [6] Teicher U, Künanz K, Ghosh A, Chattopadhyay AB. Performance of diamond and CBN single-layered grinding wheels in grinding titanium. Mater Manuf Process 2008;23(3):224–7. [7] Shi Zhong De, Attia Helmi. Feasibility study on grinding of titanium alloys with electroplated CBN wheels. In: Advanced materials research. vol. 797. Trans Tech Publications Ltd; 2013. p. 73–8. [8] Virdi Roshan Lal, Singh Chatha Sukhpal, Singh Hazoor. Experimental investigations on the tribological and lubrication behaviour of minimum quantity lubrication technique in grinding of Inconel 718 alloy. Tribol Int 2020:106581. [9] Gao Teng, Li Changhe, Zhang Yanbin, Yang Min, Jia Dongzhou, Tan Jin, Hou Yali, Li Runze. Dispersing mechanism and tribological performance of vegetable oilbased CNT nanofluids with different surfactants. Tribol Int 2019;131:51–63. [10] Yang Min, Li Changhe, Zhang Yanbin, Jia Dongzhou, Li Runze, Hou Yali, Cao Huajun. Effect of friction coefficient on chip thickness models in ductileregime grinding of zirconia ceramics. Int J Adv Manuf Technol 2019;102(5–8): 2617–32. [11] Yang Min, Li Changhe, Zhang Yanbin, Jia Dongzhou, Li Runze, Hou Yali, Cao Huajun, Wang Jun. Predictive model for minimum chip thickness and size effect in single diamond grain grinding of zirconia ceramics under different lubricating conditions. Ceram Int 2019;45(12):14908–20. [12] Sadeghi MH, Haddad MJ, Tawakoli T, Emami M. Minimal quantity lubricationMQL in grinding of Ti–6Al–4V titanium alloy. Int J Adv Manuf Technol 2009;44(5): 487–500. [13] Setti Dinesh, Sinha Manoj Kumar, Ghosh Sudarsan, Venkateswara Rao P. Performance evaluation of Ti–6Al–4V grinding using chip formation and coefficient of friction under the influence of nanofluids. Int J Mach Tool Manufact 2015;88:237–48. [14] Ibrahim Ahmed Mohamed Mahmoud, Li Wei, Xiao Hang, Zeng Zhixiong, Ren Yinghui, Mohammad S, Alsoufi. Energy conservation and environmental sustainability during grinding operation of Ti–6Al–4V alloys via eco-friendly oil/ graphene nano additive and MQL lubrication. Tribol Int 2020:106387. [15] Singh Harpinder, Sharma Vishal S, Manu Dogra. Exploration of graphene assisted vegetables oil based minimum quantity lubrication for surface grinding of TI-6AL4V-ELI. Tribol Int 2020;144:106113. [16] Colwell LV. The effects of high-frequency vibrations in grinding. Trans. ASME 1956;78(no. 4):837. [17] Spur Günter, Holl S-E. Ultrasonic assisted grinding of ceramics. J Mater Process Technol 1996;62(4):287–93.
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