Experimental Investigation of Material Removal and

Materials and Manufacturing Processes

ISSN: 1042-6914 (Print) 1532-2475 (Online) Journal homepage: http://www.tandfonline.com/loi/lmmp20

Experimental Investigation of Material Removal and Surface Roughness during Optical Glass Polishing Raj Kumar Pal, Harry Garg, RamaGopal V. Sarepaka & Vinod Karar To cite this article: Raj Kumar Pal, Harry Garg, RamaGopal V. Sarepaka & Vinod Karar (2015): Experimental Investigation of Material Removal and Surface Roughness during Optical Glass Polishing, Materials and Manufacturing Processes, DOI: 10.1080/10426914.2015.1103867 To link to this article: http://dx.doi.org/10.1080/10426914.2015.1103867

Accepted author version posted online: 21 Oct 2015. Published online: 21 Oct 2015. Submit your article to this journal

Article views: 80

View related articles

View Crossmark data

Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=lmmp20 Download by: [CSIO Central Scientific Instruments Organisation]

Date: 31 May 2016, At: 03:55

Materials and Manufacturing Processes, 0: 1–8, 2016 Copyright # Taylor & Francis Group, LLC ISSN: 1042-6914 print=1532-2475 online DOI: 10.1080/10426914.2015.1103867

Experimental Investigation of Material Removal and Surface Roughness during Optical Glass Polishing Raj Kumar Pal1,2, Harry Garg2, RamaGopal V. Sarepaka3, and Vinod Karar2 1

Downloaded by [CSIO Central Scientific Instruments Organisation] at 03:55 31 May 2016

Advanced Instrumentation Engineering, Academy of Scientific & Innovative Research, Chennai, Tamil Nadu, India 2 Optical Devices and Systems, CSIR-Central Scientific Instruments Organisation, Chandigarh, Punjab, India 3 Formerly with Optical Devices and Systems, CSIR-Central Scientific Instruments Organisation, Chandigarh, Punjab, India It has been a challenge to finish optical glass surfaces due to their hard and brittle nature. Moreover, tight tolerances of surface figure and finish make polishing a more critical operation. This work reports the results of an experimental study performed for full aperture polishing of BK7 optical glass. Flat samples of borosilicate (BK7) glass are polished using an optical pitch polisher and cerium oxide (CeO2) slurry. Taguchi’s L9 orthogonal array is used for the design of experiments. Abrasive concentration, pressure and overarm speed are considered as variable process parameters. Polishing is performed for duration of 120 minutes for each combination of parameters. Material removal is measured using the precision weighing balance. Surface roughness was measured using a Form Talysurf PGI 120 profiler. Abrasive slurry concentration is observed to be one of the most significant parameters in the optical polishing process. It affects both the material removal rate (MRR) and the surface roughness. Pressure applied at the workpiece–polisher interface affects the MRR, but the variation of pressure is not found to affect the surface roughness significantly. Relative motion at the workpiece–polisher interface is also observed to be significant in defining the final polishing outputs. Keywords Abrasive; Finish; Glass; Lapping; Optical; Pitch; Polishing; Roughness; Surface; Taguchi.

fabrication generally includes a number of operations such as rough shaping, curve generation or grinding, lapping, and polishing. The final step, i.e., polishing, is a very critical step during which the surface is smoothed in order to remove surface and subsurface defects induced during grinding and lapping processes [6–11]. In a conventional setup (Fig. 1), it has been a skill-based process for long. It may take a number of hours to days depending on the targeted surface quality, dimensions of the workpiece and the level of surface roughness from previous operations. Polishing involves chemical and mechanical actions taking place at the workpiece–polisher interface, which leads to material removal [12]. It is a very precise and highly demanding operation, yet there is not much research done in this area considering it as an art more than a science [13–15]. The underlying mechanism of the polishing process is still not clear [16–21]. Preston [22] proposed the first fundamental model for macro-level material removal during glass polishing. However, it is a very basic model for material removal rate (MRR) during polishing considering the influence of pressure and relative velocity only. The major limitation of Preston’s equation and its modified versions is that the parameters related to consumables (abrasive slurry and polisher) and workpiece are not explicitly defined in the equations. Thus, there is no information regarding the control of these parameters. Cook [23] proposed the involvement of chemical actions in polishing. He suggested that at the molecular level, material is removed mainly through chemical actions. In abrasive slurry, cerium oxide (CeO2) is

INTRODUCTION Borosilicate (BK7) glass is used in a number of applications because of its high strength, chemical inertness, low thermal expansion coefficient (3 106= C at 20 C) and excellent transmission characteristics in the whole visible range and near-infrared spectra and till 350 nm in the ultraviolet. Astronomical reflecting telescope glass mirrors, folding mirrors of head-up display, reflectors, etc. are made of BK7 glass because of its low coefficient of expansion with heat [1]. Owing to its high chemical resistance, it is used as the mirror and polarizer for high-power solid-state lasers, which are used as energy sources for the generation of nuclear fusion energy [2]. It is also used to make guides for the transmission of hot and cold neutron beams used in most of the neutron exploration setups [3]. It is used in electronic substrates, display covers and substrates for biomedical imaging and sensing [4, 5]. For laser and other optical applications, there is a need of ultra-low surface roughness and surface figure errors to avoid scattering of light and distortion of wave-fronts. However, the fabrication of high-precision optical lens and mirrors is a challenge due to the demand of high surface accuracies and ultra-precision finish. Optical Received August 4, 2015; Accepted September 29, 2015 Address correspondence to Raj Kumar Pal, Optical Devices and Systems, CSIR-Central Scientific Instruments Organisation, Sector-30 C, Chandigarh 160030, India; E-mail: [email protected], [email protected] Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/lmmp.

1

2

R. K. PAL ET AL.


BK7 glass using CeO2 particles, chemical actions have less role to play, and material removal mainly occurred through plastic removal mechanism. A number of studies have been performed by various researchers to understand the effects of polishing process parameters on final surface quality and to understand how material removal takes place during the polishing process, but still these aspects need to be understood more in depth [33–35]. In the present study, the three process parameters, i.e., abrasive concentration, pressure and overarm speed, have been investigated upon to evaluate their individual and interaction effects on MRR and surface quality during the polishing of BK7 optical glass.

FIGURE 1.—Schematic of polishing setup.

present in the form of cerium hydroxide, which condenses with the glass surface to form a Ce-O-Si bond whose bond strength is higher than that of Si-O-Si bond (glass). Thus, material removal takes place as the slurry particles (e.g., CeO2) react with glass surface and take out the silica molecules. Different chemical parameters such as pH, slurry concentration, temperature, etc. affect MRR. Much research has been carried out on the chemical mechanical polishing of materials, which are of interest to semiconductor and opto-electronic industry [24–28]. However, research on optical glass polishing is still lacking. As the material properties of optical glass are quite different from metals and semiconductors, the mechanism of material removal for optical glass polishing cannot be similar to those of metals and semiconductors. Therefore, researchers have started working to explore the material removal behavior of polishing process for optical glass. Suratwala et al. [29, 30] investigated the polishing of fused silica glass and reported that the pressure distribution is not uniform over the workpiece and is a function of load distribution over the workpiece–polisher interface, elastic properties and viscoelastic relaxation of polisher, moments due to overarm and frictional forces at interface. It is also reported that load per particle defines the material removal mechanism during optical glass polishing. Belkhir et al. [31] conducted a study to understand the relationship among the parameters, viz. polishing pressure, contact surface and friction coefficient, during optical polishing, which was based on the direct measurement of the mentioned parameters. It was reported that contact surface and pressure distribution affect the glass surface shape and frictional behavior, which influences the material removal mode during the process. Yu et al. [32] explored quantitative wear behavior and friction at nanoscale for BK7 glass using atomic force microscopy and reported that low frictional mechanical energy was not sufficient enough to break the Si-O-Si bonds; thus during polishing of

MATERIALS AND METHODS Schott BK7 optical glass is used as the workpiece material for the polishing experiments. Taguchi’s method has been used for the design of experiment, which is being widely used for optimizing the process parameters [36, 37]. In this study, Taguchi’s L9 orthogonal array is used to explore the relationship of MRR and Ra with the polishing parameters. The control parameters are abrasive concentration, pressure and overarm speed, each having three levels (Table 1). Table 2 presents Taguchi’s standard L9 orthogonal array used for the polishing experiments. A known weight of CeO2 powder (abrasive particle size: 1.7–2.4 mm) is mixed with a known quantity of deionized water and used as slurry for the polishing process. Eight samples (diameter 30 mm, height 6 mm) of workpieces are blocked together on an iron tool using wax. The blocked workpieces are lapped over the iron lap tool using three different grades of emery (mainly Al2O3) in the following order: 302 (M2), 303 (M3) and 303.5 (M3.5), having mean particle sizes of 28 mm, 14.5 mm and 10 mm, respectively, to make the workpieces ready for polishing. Each workpiece is polished using a Full Aperture Polishing machine (LOHTRONIC, shown in Fig. 2). Pitch Polisher with annular grooves is used for the polishing of BK7 optical glass samples. Abrasive slurry is fed manually at constant intervals of time. Each polishing experiment is run for 120 minutes at room temperature (22 C), after which the workpiece surface is cleaned. The polished workpiece is shown in Fig. 3. Ra is measured using a Taylor Hobson PGI Mechanical Profiler. After every polishing experiment, the amount of material removed is measured using a Mettler Toledo TABLE 1.—Control parameters and their levels for the experiment. Levels Parameters

1

Abrasive Conc. (%wt)-(A) Pressure (g=cm2)-(B) Overarm speed (rpm)-(C)

5 30 15

2

3

6.25 32.5 20

8.25 35 25

MATERIAL REMOVAL & SURFACE ROUGHNESS IN OPTICAL POLISHING

3

TABLE 2.—Taguchi’s L9 design of experiments summary table. Run Order


1. 2. 3. 4. 5. 6. 7. 8. 9.

Abrasive Concentration

Normal Force

Overarm speed

1 1 1 2 2 2 3 3 3

1 2 3 1 2 3 1 2 3

1 2 3 2 3 1 3 1 2

weighing balance (max. capacity 220 g, resolution of 0.01 mg). MRR is calculated using Eq. (1):

MRR ¼

4 Dm 109 Dt q p d 2

FIGURE 3.—Workpiece surface after two hours of polishing.

ð1Þ

where Dm is the change in mass of workpiece, Dt is the polishing time (min), q is the density of the BK7 glass workpiece (2.51 g=cm3) and d is the diameter of the workpiece in mm. Material removal during polishing is affected by the relative velocity of the workpiece surface with respect to the polisher surface. The greater the relative velocity of abrasive particles, the more the number of abrasive particles will take part in the polishing process and will thus remove more material. The angular motion (N1, h) of overarm gives the workpiece to-and-fro motion (v1) over the polisher (Fig. 4).

The stroke velocity of the workpiece (v1) is determined as v1 ¼

2LhN1 60

ð2Þ

where h is the angle of rotation in radians, L is the length of overarm in meters and N1 is the rpm of the overarm. The polisher is attached to a motor spindle rotating at N2 rpm (45 rpm). The rotational motion of the polisher is transferred to the workpiece when they both come in frictional contact. After repeated trials, it is observed that the workpiece rotates with an rpm of N3, where N3 ¼ ð0:8 N2 Þ

ð3Þ

Thus, the average relative velocity (vrel) of the workpiece surface with respect to the polisher surface can be estimated using the equation reported by Suratwala et al. [29]: 2pN3 2pN2 vrel ¼ v1 þ r: ðr dÞ 60 60

ð4Þ

where r is the average distance of a point on the workpiece surface from its center, which has been taken in this case as 30 mm, and d is the gap between the centers

FIGURE 2.—Full aperture optical polishing machine.

FIGURE 4.—Kinematic model of polishing setup.

4

R. K. PAL ET AL.


of the workpiece and the polisher surfaces, which is kept zero in this case. RESULTS AND DISCUSSION MRR and Ra values obtained for the polishing experiments conducted are shown in Table 3. Figure 5 shows the main effects and interaction plots for MRR. The highest value of MRR is observed at the combinations A2B2, A2C3 and B2C3, i.e., A2B2C3. Change of abrasive concentration from 5% to 6.25% increases the value of MRR by approximately 56%. Abrasive concentration determines the relative number of abrasive particles that take part in the polishing process. As the concentration of abrasive particles in the slurry increases, more particles come in direct contact with the workpiece surface and abrade the material. Apart from abrasion, ceria particles react with the hydrated glass surface and remove silica molecules as described by Cook [23, 38]. Thus, it can be assumed that the material removal is directly proportional to the number of particles coming in contact with the workpiece surface. This result is on similar lines of the result reported by Zhang et al. [39] and Chen et al. [40]. Change of pressure from 30 g=cm2 to 32.5 g=cm2 increases the value of MRR by approximately 29%. Further changes in abrasive concentration and pressure from level 2 to level 3 do not make a significant difference in the value of MRR. Further increase in abrasive concentration may not increase the number of active abrasive particles; more particles are lying between asperities of the polisher. In this case, little increase in MRR is observed because of material removal taking place through the chemical phenomenon. Material removed by abrasive actions may redeposit on the workpiece surface because of the elasto-plastic nature of the hydrated glass surface layer. However, it gets removed chemically in terms of single or multiple silica tetrahedral molecules through the dissolution process [23, 38]. Increase in pressure definitely increases the number of particles making contact with the workpiece, which should increase the MRR. But it also restricts the movement of abrasive particles as they experience increased frictional force because of increase in applied pressure, which leads to reduced momentum of abrasive particles. This resulted in a small change in MRR due to increase TABLE 3.—Experimental results. Experiment No.

1 2 3 4 5 6 7 8 9

(A1B1C1) (A1B2C2) (A1B3C3) (A2B1C2) (A2B2C3) (A2B3C1) (A3B1C3) (A3B2C1) (A3B3C2)

MRR (nm=min)

Ra (nm)

SNR for Ra

4.40 6.02 7.86 6.70 11.14 10.46 9.86 9.63 9.41

29.5 20.5 27.2 23.7 25.6 30.9 13.4 18.3 14.7

29.4 26.2 28.7 27.5 28.2 29.8 22.5 25.2 23.3

FIGURE 5.—Main effects and interaction plots for MRR.

in pressure. However, change in overarm speed from 20 rpm to 25 rpm increases the value of MRR by approximately 30%. This may be due to the increase in momentum of abrasive particles, which also increases their material removal action. The least value of Ra is observed at the combinations A3B1, A3C3 and B1C3, i.e., A3B1C3 (Fig. 6). It can be observed that initial change in abrasive concentration does not change Ra significantly, but further change in abrasive concentration from 6.25% to 8.25% reduces the value of Ra by approximately 44%. Initial change in overarm speed from 15 rpm to 20 rpm reduces Ra by approximately 30%, but further increase in overarm speed does not affect Ra significantly. Variation in pressure is observed to affect Ra very little. The two response parameters (MRR and surface roughness) behave differently to the variation in polishing parameters. Therefore, these output parameters cannot be optimized at the same time. There is a need of trade-off to achieve the process optimization. To achieve higher MRR or machining efficiency, the combination A2B2C3 should be selected. In the same way to achieve better Ra, the combination A3B1C3 should be selected. Therefore, the optimal combination of the three variables investigated is A3B1C3, which means the combination of 8.25% abrasive concentration, 30 g=cm2 pressure and 25 rpm overarm speed. At this optimized combination, MRR of 9.86 nm=min and Ra of 13.4 nm are achieved (Fig. 7). Surface texture for BK7 glass is observed through Taylor Hobson CCI Optics before and after polishing (shown in Fig. 8).

5


MATERIAL REMOVAL & SURFACE ROUGHNESS IN OPTICAL POLISHING

FIGURE 6.—Main effects and interaction plots for Ra.

Further ANOVA is used to verify the effect of each parameter on MRR and Ra obtained after polishing the optical glass. Signal to noise ratio (SNR) values are used to evaluate the level of system performance. The values of SNR corresponding to Ra are listed in

FIGURE 8.—Surface texture observed through Taylor Hobson CCI Optics before and after polishing.

Table 3. The highest value of SNR corresponding to Ra is obtained for the parametric combination A3B1C3 and minimum surface roughness has been achieved for the same. Table 4 shows the ANOVA results for MRR. It is observed that abrasive concentration, pressure and overarm speed are significant in decreasing order for MRR. The effect of uncontrolled and unknown parameters on the variation is negligible. Table 5 shows the ANOVA results for Ra. The least F-value for pressure depicts its little impact on Ra. Similar results were reported by Lien and Guu [41] during the polishing of glass substrate of Super-Twisted Nematic-Liquid Crystal display (STN-LCD).

TABLE 4.—Analysis of variance of means for MRR. Source

FIGURE 7.—Average surface roughness (Ra) of BK7 glass measured using Taylor Hobson PGI Mechanical Profiler (a) before polishing (344 nm) and (b) after two hours of polishing using A3B1C3 combination of parameters: 13.4 nm.

Abrasive Concentration Pressure Overarm speed Residual Error Total

DF

Seq SS

Adj SS

Adj MS

F

2 2 2 2 8

0.085427 0.032303 0.027960 0.002861 0.148551

0.085427 0.032303 0.027960 0.002861

0.042713 0.016152 0.013980 0.001430

29.86 11.29 9.77

6

R. K. PAL ET AL. TABLE 5.—Analysis of variance of means for Ra.

Source

Abrasive Concentration Pressure Overarm speed Residual Error Total

DF

Seq SS

Adj SS

Adj MS

F

2 2 2 2 8

233.342 12.649 66.842 4.969 317.802

233.342 12.649 66.842 4.969

116.671 6.324 33.421 2.484

46.96 2.55 13.45


The regression equations obtained for MRR and Ra are as follows: MRR ¼ 12:5 þ 99:8c þ 0:00361P þ 104vrel

ð5Þ

Ra ¼ 42:5 339c þ 0:00331P 298vrel

ð6Þ

generally very little when compared to mechanical abrasion; however, they play a significant role in avoiding the redeposition of the removed material over the glass surface through the dissolution process. It is also observed that both MRR (the larger the better) and Ra (the smaller the better) cannot be optimized simultaneously for the polishing process. Thus, there is a need of trade-off between the two. Hence, the optimized parameters reported are A3B1C3, i.e., 8.25% abrasive concentration, 30 g=cm2 pressure and 25 rpm overarm speed. At these optimized parameters, MRR of 9.86 nm=min and Ra of 13.4 nm are achieved. REFERENCES

where MRR is in nm=min, Ra is in nm, c is abrasive concentration (ratio), P is pressure in N=m2 and vrel is relative velocity in m=s. It can be inferred that abrasive concentration directly affects MRR by controlling the number of abrasive particles taking part in the polishing process. This parameter has not largely been considered in other reported models. Different combinations of parameters may give the same MRR, but the mode of contact (solid–solid contact, hydroplaning contact or mixed contact) across the workpiece–polisher interface may change [42]. The different modes of contact may lead to different surface roughness levels even for the same MRR. CONCLUSIONS This article reports the results of polishing experiments carried out using full aperture polishing process for a substrate of Schott BK7 optical glass. The experiment is designed using Taguchi’s method taking three levels for the three process parameters, i.e., abrasive concentration, pressure and overarm speed. The workpiece is initially lapped using alumina slurry and then it is polished using an optical pitch polisher with CeO2 slurry. Polishing is performed for duration of 120 minutes for each sample using Taguchi’s L9 orthogonal array configuration and then material removal and surface roughness are measured. It is observed that abrasive concentration plays a significant role in determining MRR as well as Ra, and the same is reflected through ANOVA results. Pressure applied at the workpiece–polisher interface affects MRR, but the variation of pressure is not found to affect Ra significantly (least F-value obtained for ANOVA results). MRR is affected by the process parameters in the following decreasing order of significance: abrasive concentration, pressure and relative velocity. Similarly, surface roughness is affected by the process parameters in the following order of decreasing significance: abrasive concentration, relative velocity and pressure. The kinematics of the polishing setup has a key role in defining the material removal behavior and surface quality of the polished surface. Material removal due to chemical phenomenon during glass polishing is

1. Tsegaw, A.A.; Shiou, F.-J.; Lin, S.-P. Ultra-precision polishing of N-Bk7 using an innovative self-propelled abrasive fluid multi-jet polishing tool. Machining Science and Technology 2015, 19 (2), 262–285. DOI:10.1080=10910344.2015.1018532. 2. Moses, E.I. Advances in inertial confinement fusion at the National Ignition Facility (NIF). Fusion Engineering and Design 2010, 85 (7–9), 983–986. DOI:10.1016=j.fusengdes. 2009.11.006. 3. Boffy, R.; Kreuz, M.; Beaucour, J.; Ko¨ster, U.; Bermejo, F.J. Why neutron guides may end up breaking down? Some results on the macroscopic behaviour of alkali-borosilicate glass support plates under neutron irradiation. Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 2015, 358, 179–187. DOI:10.1016=j.nimb.2015.06.017. 4. Limbach, R.; Winterstein-Beckmann, A.; Dellith, J.; Mo¨ncke, D.; Wondraczek, L. Plasticity, crack initiation and defect resistance in alkali-borosilicate glasses: From normal to anomalous behavior. Journal of Non-Crystalline Solids 2015, 417–418, 15–27. DOI:10.1016=j.jnoncrysol.2015.02.019. 5. Preedy, E.; Perni, S.; Nipicˆ, D.; Bohinc, K.; Prokopovich, P. Surface roughness mediated adhesion forces between borosilicate glass and gram-positive bacteria. Langmuir 2014, 30 (31), 9466–9476. DOI:10.1021=la501711t. 6. Jain, V.K.; Sidpara, A.; Sankar, M.R.; Das, M. Nano-finishing techniques: A review. Journal of Mechanical Engineering Science 2012, 226 (2), 327–346. DOI:10.1177= 0954406211426948. 7. Lee, Y. Evaluating subsurface damage in optical glasses. Journal of the European Optical Society – Rapid publications 2011, 6, 1–16. DOI:10.2971=jeos.2011.11001. 8. Li, Y.; Huang, H.; Xie, R.; Li, H.; Deng, Y.; Chen, X.; Wang, J.; Xu, Q.; Yang, W.; Guo, Y. A method for evaluating subsurface damage in optical glass. Optics Express 2010, 18 (16), 17180–17186. DOI:10.1364=oe.18.017180. 9. Agarwal, S.; Venkateswara Rao, P. Grinding characteristics, material removal and damage formation mechanisms in high removal rate grinding of silicon carbide. International Journal of Machine Tools and Manufacture 2010, 50 (12), 1077–1087. DOI:10.1016=j.ijmachtools.2010.08.008. 10. Blaineau, P.; Andre´, D.; Laheurte, R.; Darnis, P.; Darbois, N.; Cahuc, O.; Neauport, J. Subsurface mechanical damage during bound abrasive grinding of fused silica glass. Applied Surface Science 2015, 353, 764–773. DOI:10.1016= j.apsusc.2015.07.047.


MATERIAL REMOVAL & SURFACE ROUGHNESS IN OPTICAL POLISHING 11. Yu, T.; Li, H.; Wang, W. Experimental investigation on grinding characteristics of optical glass BK7: With special emphasis on the effects of machining parameters. The International Journal of Advanced Manufacturing Technology 2015, 1–15. DOI:10.1007=s00170-015-7495-2. 12. Suratwala, T.; Steele, W.; Wong, L.; Feit, M.D.; Miller, P.E.; Dylla-Spears, R.; Shen, N.; Desjardin, R. Chemistry and formation of the Beilby layer during polishing of fused silica glass. Journal of the American Ceramic Society 2015, 98 (8), 2395–2402. DOI:10.1111=jace.13659. 13. Marinescu, I.D.; Uhlmann, E.; Doi, T.K. Handbook of Lapping and Polishing; CRC Press=Taylor & Francis Group: London, 2007; 491pp. 14. Lo, V.H.Y.; Huang, G.Q.; Cheng, K.C.; Tsang, Y.M. The use of Taguchi methods in polishing for quality optimization. International Journal of Reliability, Quality and Safety Engineering 2007, 14 (03), 297–309. DOI:10.1142=s0218539 307002660. 15. Landis, A.C. Factors influencing material removal and surface finish of the polishing of silica glasses. M.Sc. Thesis, Charlotte University of North Carolina, 2006; p.106. 16. Savio, G.; Meneghello, R.; Concheri, G.; D’Angelo, L. Process optimization in glass polishing based on a material removal model. Advanced Science Letters 2013, 19 (2), 539–542. DOI:10.1166=asl.2013.4723. 17. Tian, Y.B.; Ang, Y.J.; Zhong, Z.W.; Xu, H.; Tan, R. Chemical mechanical polishing of glass disk substrates: Preliminary experimental investigation. Materials and Manufacturing Processes 2013, 28 (4), 488–494. DOI:10.1080=10426914. 2011.654161. 18. Savio, G.; Meneghello, R.; Concheri, G. A surface roughness predictive model in deterministic polishing of ground glass moulds. International Journal of Machine Tools and Manufacture 2009, 49 (1), 1–7. DOI:10.1016=j.ijmachtools. 2008.09.001. 19. Klocke, F.; Dambon, O.; Schneider, U.; Zunke, R.; Waechter, D. Computer-based monitoring of the polishing processes using labview. Journal of Materials Processing Technology 2009, 209 (20), 6039–6047. DOI:10.1016=j.jmatprotec. 2009.08.014. 20. Yeruva, S.B.; Park, C.-W.; Rabinovich, Y.I.; Moudgil, B.M. Impact of pad–wafer contact area in chemical mechanical polishing. Journal of the Electrochemical Society 2009, 156 (10), D408–D412. DOI:10.1149=1.3186032. 21. Zhong, Z.W. Recent advances in polishing of advanced materials. Materials and Manufacturing Processes 2008, 23 (5), 449–456. DOI:10.1080=10426910802103486. 22. Preston, F.W. The theory and design of plate glass polishing machine. J Soc Glass Technol 1927, 11 (44), 214–256. 23. Cook, L.M. Chemical processes in glass polishing. Journal of Non-Crystalline Solids 1990, 120 (1–3), 152–171. DOI:10. 1016=0022-3093(90)90200-6. 24. Kwon, T.-Y.; Ramachandran, M.; Park, J.-G. Scratch formation and its mechanism in chemical mechanical planarization (CMP). Friction 2013, 1 (4), 279–305. DOI:10.1007= s40544-013-0026-y. 25. Mpagazehe, J.N.; Higgs, C.F. A Comparison of active particle models for chemical mechanical polishing. ECS Journal of Solid State Science and Technology 2013, 2 (3), P87–P96. DOI:10.1149=2.019303jss.

7

26. Xie, Y.; Bhushan, B. Effects of particle size, polishing pad and contact pressure in free abrasive polishing. Wear 1996, 200 (1–2), 281–295. DOI:10.1016=S0043-1648(96)07275-4. 27. Aida, H.; Takeda, H.; Kim, S.-W.; Aota, N.; Koyama, K.; Yamazaki, T.; Doi, T. Evaluation of subsurface damage in GaN substrate induced by mechanical polishing with diamond abrasives. Applied Surface Science 2014, 292, 531–536. DOI:10.1016=j.apsusc.2013.12.005. 28. Guoshun, P.; Ning, W.; Hua, G.; Yan, L. An empirical approach to explain the material removal rate for copper chemical mechanical polishing. Tribology International 2012, 47 (0), 142–144. DOI:10.1016=j.triboint.2011.10.010. 29. Suratwala, T.I.; Feit, M.D.; Steele, W.A. Toward deterministic material removal and surface figure during fused silica pad polishing. Journal of the American Ceramic Society 2010, 93 (5), 1326–1340. DOI:10.1111=j.1551-2916.2010.03607.x. 30. Suratwala, T.; Feit, M.; Steele, W.; Wong, L.; Shen, N.; Dylla-Spears, R.; Desjardin, R.; Mason, D.; Geraghty, P.; Miller, P.; Baxamusa, S. Microscopic removal function and the relationship between slurry particle size distribution and workpiece roughness during pad polishing. Journal of the American Ceramic Society 2014, 97 (1), 81–91. DOI:10.1111= jace.12631. 31. Belkhir, N.; Aliouane, T.; Bouzid, D. Correlation between contact surface and friction during the optical glass polishing. Applied Surface Science 2014, 288 (0), 208–214. DOI:10.1016= j.apsusc.2013.10.008. 32. Yu, J.; Yuan, W.; Hu, H.; Zang, H.; Cai, Y.; Ji, F. Nanoscale friction and wear of phosphate laser glass and BK7 glass against single CeO2 particle by AFM. Journal of the American Ceramic Society 2015, 98 (4), 1111–1120. DOI:10.1111=jace. 13356. 33. Hooper, A.R.; Boffa, C.C.; Sarkas, H.W.; Cureton, K. Improving profitability through slurry management: A look at the impact of slurry pH on various glass types. In Proceedings of the Optical Manufacturing and Testing XI, August 27, 2015; Fa¨hnle O.W., Williamson R., Kim D.W., Eds.; SPIE: San Diego, California, United States, 2015. 34. Jin, X.L.; Zhang, L.C. Predicting the material removal in polishing: The applicability of two types of statistical models. Machining Science and Technology 2014, 18 (2), 199–220. DOI:10.1080=10910344.2014.897838. 35. Pashmforoush, F.; Rahimi, A. Nano-finishing of BK7 optical glass using magnetic abrasive finishing process. Applied Optics 2015, 54 (9), 2199–2207. DOI:10.1364=ao.54.002199. 36. Garg, H.; Karar, V.; Kumar, R.; Lall, A.K. Optimization design of microchannel heat sink based on taguchi method and simulation. In Proceedings of the Science and Information Conference (SAI), London, Oct 7–9, 2013; IEEE: London, 2013. 37. Sun, Y.; Zuo, D.; Zhu, Y.; Li, J. Using Taguchi method to optimize polishing parameters in ice fixed abrasive polishing. Materials and Manufacturing Processes 2013, 28 (8), 923–927. DOI:10.1080=10426914.2013.792419. 38. Krishnan, M.; Nalaskowski, J.W.; Cook, L.M. Chemical mechanical planarization: Slurry chemistry, materials, and mechanisms. Chemical Reviews 2010, 110, 178–204. DOI:10.1021=cr900170z. 39. Zhang, Z.; Liu, W.; Song, Z. Effect of abrasive particle concentration on preliminary chemical mechanical polishing of

8


glass substrate. Microelectronic Engineering 2010, 87 (11), 2168–2172. DOI:10.1016=j.mee.2010.01.020. 40. Chen, G.; Yi, K.; Yang, M.; Liu, W.; Xu, X. Factor effect on material removal rate during phosphate laser glass polishing. Materials and Manufacturing Processes 2014, 29 (6), 721–725. DOI:10.1080=10426914.2014. 893061.

R. K. PAL ET AL. 41. Lien, C.H.; Guu, Y.H. Optimization of the polishing parameters for the glass substrate of STN-LCD. Materials and Manufacturing Processes 2008, 23 (8), 838–843. DOI:10.1080=10426910802384839. 42. Lai, J.Y. Mechanics, mechanisms, and modeling of the chemical mechanical polishing process. PhD Thesis. Massachusetts Institute of Technology, 2001; p.308.