Near Ductile Regime Machining of Tungsten Carbide insert through Control of Cutting Speed Parameter While Using a Poly-Crystalline Diamond Tool

Available online at www.sciencedirect.com

ScienceDirect Procedia Manufacturing 8 (2017) 549 – 556

14th Global Conference on Sustainable Manufacturing, GCSM 3-5 October 2016, Stellenbosch, South Africa

Near ductile regime machining of Tungsten Carbide insert through control of cutting speed parameter while using a Poly-Crystalline Diamond Tool Ramesh Kuppuswamya and Nomvelo Mkhizeb a,b

Department of Mechanical Engineering, The University of Cape Town, South Africa.

Abstract Grinding is an acceptable manufacturing process for processing tungsten carbide components but grinding a pocket for manufacture of a die & mold still remains as a daunting task despite of the developments on the cutting tools and machining systems. A study was attempted to understand the high speed machining behavior for tungsten carbide materials while using the Poly-crystalline diamond tools. An experimental set up with a comprehensive data acquisition system was developed to conduct the machining experiments. The literature review enabled to select the cutting conditions: depth of cut, feed rate and cutting speed. Bifano’s equation was used to find the critical depth of cut for configuring the near-ductile regime machining conditions. The machining performance characteristics in terms of: cutting force, tangential force, friction ratio, shear angle, cutting ratio and shear strain are unveiled. 2016The TheAuthors. Authors. Published by Elsevier ©2017 © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of the 14th Global Conference on Sustainable Manufacturing. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 14th Global Conference on Sustainable Manufacturing Keywords: Tungsten carbide (WC); high speed micromachining; polycrystalline diamond (PCD) tool; ductile mode cutting; brittle fracture;

1.

Introduction Powder metallurgy technology and grinding processes are being used for processing tungsten carbide components. However, the grinding process cannot be applied for processing pockets and cavities which are the essential features for dies and molds [1]. The process of high speed machining has been successfully applied to a wide range of metallic and non-metallic materials having a hardness value 30 HRC and above. The majority of applications were centered on steel components of hardness 32-42 HRC used for specific parts of dies or molds [2, 3]. The wear behavior during wire drawing of steel cords was found to be better for dies made of Tungsten carbide (WC-6%Co) than hardened steel and the results suggest more and more applications of carbide dies and molds [4]. However, machining of a die cavity on tungsten carbide (WC) material still remains a daunting challenge and hence the application of tungsten carbide dies remains limited. Efforts were applied to process a pocket on tungsten carbide Corresponding author. Tel.: +27 21 650 4872 ; fax: +27 21 650 3240.E-mail address: [email protected]

2351-9789 © 2017 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the 14th Global Conference on Sustainable Manufacturing doi:10.1016/j.promfg.2017.02.070

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dies using electrode discharge machining (EDM) with different operating parameters and electrode materials. Past studies identify detrimental effects when using electrodes with lower thermal and electrical conductivity [5]. Electrodischarge machining enabled the production of pockets on tungsten carbide materials but the machined surface requires extensive polishing. A recent attempt on an ultrasonic vibration assisted polishing method on an aspheric mould on tungsten carbide material has produced a surface roughness (R Z) of 8 nm. However, the associated cost of polishing was found to be extremely higher [6]. Prior studies on micro-machining of super-micro grain tungsten carbide (WC) by a poly-crystalline diamond (PCD) micro end mill suggests the feasibility of achieving high quality surfaces of surface roughness of value < 40 nm. However, if the depths of cut and feed rates go beyond 1Pm and 0.5 Pm/tooth respectively, a severe deterioration on the surface quality was observed [7]. Another study to evaluate the cutting performance of tungsten carbide under ductile mode using a Makino V55 machine with CBN cutters has revealed the domination of tool wear mechanisms by abrasion, adhesion, and diffusion [8]. Research conducted on generating high quality surface on tungsten carbide by polycrystalline diamond (PCD) milling tool has achieved mirror quality surfaces, with surface roughness(Ra) around 40 nm [9]. Conclusively, the past research clearly indicates very limited archive of past research work on machining of tungsten carbide work material. Therefore, this study was aimed to understand the machining characteristics of tungsten carbide (WC) with applications of speed parameter while using a poly-crystalline diamond (PCD) tool. 2.

Tool Design & Experimental Set Up Shown in Fig.1 is the developed Poly-Crystalline Diamond (PCD) tool to perform the machining experiments. Table 1 enumerates the cutting conditions for the machining experiments and the machining experiments were done using a Roeders RFM 600 machining centre. Throughout the experiments the force signatures were captured, amplified and further analysis was done using the data acquisition software Dewesoft-7 to understand the tool-work interface behavior. Every cutting experiment was repeated five times and the average cutting forces of at least three tests with the clearest values were taken. Prior to machining experiments, the tungsten carbide workpieces were ground on a surface grinder to make the sides of the rods flat and ready for testing. The tool geometry details are listed in Table 2. The machined workpiece surface texture was examined using a scanning electron microscope (SEM) and the surface roughness was examined using a Surtronic profilometer. The flank wear was measured using a tool maker’s microscope and the surface hardness of the machined tungsten carbide workpiece was measured using the Zwick Macro-hardness tester that uses a 30 kg load and a diamond indenter. Three points were selected for the hardness measurement for each surface and the average hardness was taken. Table 1: Experimental Conditions for Machining the Tungsten Carbide Cutting Conditions Cutting speed (m/min) Feed/tooth (Pm/tooth) Radial Depth of Cut (Pm) Axial Depth of cut (Pm) Machine Tool

Value 50 a 400 0.5 a 4 0.5 a 4 0.5 a 8 Roeder’s RFM 600 Corner radius PCD end mill Size: D6 x60 mm

Table 2: Tool Geometry Details

Figure 1: Sketch of the developed PCD end mill tool

Details of Tool Geometry Tool Type No of inserts Grain size of PCD (Pm) Type (SYNDITE) Rake angle (q) Primary Clearance angle Secondary Clearance Cutting Edge radius Helix angle (q) Core Diameter (mm)

Value PCD end mill (D6x60) 2 10 CTB-R70.0-360-005PL 0q 6q 12q 0.3 a 0.5 0q 1.74

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3. Results and Discussion 3.1 Cutting forces The experimental findings of the cutting forces were obtained for different cutting conditions and they are shown in Fig. 2 and Fig.3. The chief influencing factors for the cutting force were found to be the cutting speed, depth of cut and the feed rate. In order to accommodate the effect of the PCD tool cutting edge surface integrity, the cutting force evaluation was centered on the cutting force/mm3 instead of the specific cutting pressure [10]. The experimental results suggest that an increase of the cutting speed from 79 to 376 m/min reduces the cutting force/MRR which is similar to many other materials. However, while the cutting speed was increased from 56 m/min to 79 m/min the cutting force/MRR (N/ (mm3/s)) was found to increase from 519 to 3706 N/ (mm3/s), 2673 to 3675 N/ (mm3/s) and 2900 to 7195 N/ (mm3/s) for depths of cut of 2, 3 and 4 Pm respectively. When the cutting speed was increased from 79 m/min to 376 m/min the cutting force/MRR (N/(mm3/s)) was found to decrease from 3706 to 321 N/(mm3/s), 3675 to 1109 N/(mm3/s) and 7195 to 814 N/(mm3/s) for depths of cut of 2, 3 and 4 Pm respectively. A similar trend was observed for the tangential force/MRR (N/ (mm3/s)). The Fig.2 & Fig. 3 shows the influence of the depth of cut on the cutting forces against the cutting speed factor. The results suggest an increasing trend of the cutting forces/MRR (FN/ (mm3/s)) when the depth of cut was increased from 2 to 4 Pm. The results were analyzed. The Bifano equation [11] is widely used to establish the critical depth of cut (ac) at which the transition from brittle fracture to the ductile fracture would occur. The Bifano equation is given below: ௄

ଶ

ா

ܽ஼ ൌ ܾ ቀ ೎ቁ ቀ ቁ ………………………………………………………………………………… (1) ு

ு

Where KC = Fracture toughness (1.43 MPa.m1/2 ); H = Hardness (15990 MPa); E = Young’s Modulus (421800 MPa) & b= brittle-ductile transition factor (0.15) Applying the material properties ac for Tungsten carbide was computed to be 3.16 Pm. The Bifano equation is centred on dislocation along the primary plane and doesn’t account for the secondary plastic deformation. Therefore, computation of Peierl’s shear stress and the applied stress was done to better establish the brittle ductile transition. The applied shear stress (Wc-A) to move a dislocation through a crystal lattice in the direction of applied force is given by Peierl’s Stress in equation 2 below, as; ଶீ

߬௖ି஺ ൌ  ቂሺଵିଶఊሻቃ ݁ ቀ

షమഏഘ ቁ ್

………………………………………………………………………… (2)

where G = elastic shear modulus for Tungsten carbide (WC) (263 GPa); J = Poisson’s ratio (0.21); b= is magnitude of the dislocation direction (equated to contact length of the tool-work interface); Z = width of the effective dislocation region (measured from the machined surface texture) The theoretical shear stress (߬௖ି் ሻ was computed using equation 3 which is given as [12]; ߬௖ି் ൌ 

ீ

ଶగ

…………………………………………………………………………………........ (3)

Applying the shear modulus values for the workpiece (WC) the ߬௖ି் value was computed to be 41.87 GPA. The tool-work interface conditions were evaluated in terms of the un-deformed chip thickness and correlated against the applied shear stress (Wc-A) for various cutting speeds. The results are given in Fig. 4. When the cutting speed was increased from 79 to 376 m/min and when the depth of cut was 4 Pm and below the applied shear stress ((Wc-A) was found to be higher than the theoretical shear stress (߬௖ି் ሻ. It was also noted that between 79 to 211 m/min of cutting speed the applied stress was found to be higher when the axial depth of cut was maintained at 2 and 4 Pm then at 3 Pm. The reasons were analysed. The study of cutting force signatures (see Figure 2 & 3) along with the surface texture examinations (See Figures 5, 6 & 7) reveal the different amounts of brittle-ductile transition for a depth of cut of 2 and 4 Pm then for 3 Pm. The findings further strengthen the close correlation between the computed value of the critical depth of cut and the experimental values. 3.2 Surface texture The surface texture examinations of the machined tungsten carbide work-pieces were done using a scanning electron microscope. Fig. 5, Fig. 6 and Fig.7 are the images of the surfaces machined at varying cutting speeds, with depths of cut of 2, 3 and 4 µm respectively. The machined surface texture observations indicate the presence of largely ductile fractured surfaces at all cutting speeds except at 56 m/min. Also, the machined surfaces show a varying level of ductile-brittle fractures. The area of ductile fractures covered at a cutting speed of 376 m/min was found to be larger than the area at cutting speeds from 79 to 211 m/min. Furthermore, at a 376 m/min cutting speed, when the depth of cut was increased from 2 to 4 Pm less micro-chip adhesion on the machined surface texture was

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Cutting Force(F )/Material removal rate (N/(mm /s))

3

14000 12000 10000 Depth of Cut

8000

2Pm 3 Pm 4Pm

T

6000 4000 2000 0 0

50

100

150

200

250

300

350

400

12000

10000

8000

6000

Depth of Cut

4000

4Pm 3 Pm 2Pm

2000

0 0

50

. Figure 2: Influence of cutting speed on normal cutting forces (FN/(mm3/s))

150

200

250

300

350

400

Figure 3: Influence of cutting speed on tangential cutting forces (FT/(mm3/s))

Undeformed chip thickness when Depth of cut 2 Pm

0.1

3 Pm 4 Pm

m

Undeformed chip thickness, g (Pm)

100

Cutting Speed , V (m/min)

Cutting Speed , V (m/min)

0.08

Applied shear stress when depth of cut 2 Pm

350

3 Pm 4Pm

300

Theortical shear stress

250

0.06

200 150

0.04

100

Shear Stess, W GPa

N

3

Cutting Force (F ) / Material removal rate (N/(mm /s))

noted. Such results suggest a reduction in ductile fractures for the WC material at higher depths of cut. It was also noted that at a cutting speed of 56 m/min, large amounts of brittle fractures were visibly seen. The computed undeformed chip thickness at a cutting speed 56 m/min and depth of cut 2, 3 and 4 Pm was found to be 0.061, 0.075 and 0.086 Pm respectively. The increase of the cutting speed from 56 to 376 m/min resulted in a decrease of the undeformed chip thickness from 61 to 9 nm, 75 to 11 nm and 86 to 12.9 nm for 2, 3 and 4 Pm depth of cut and facilitated the apparent increase of ductile fractures. (See Fig. 5, Fig. 6 and Fig.7). 3.3 Surface finish Shown in Fig. 8 is the surface finish behaviour of Tungsten carbide (WC) while machining at various cutting speeds. The surface finish measured was in the perpendicular direction to the feed. The results suggest an improvement in the surface finish with an increase in the cutting speed from 56 to 376 m/min. The improvement of the surface finish was found to be higher for surfaces machined at a 2 Pm depth of cut than the 4 Pm depth of cut. While increasing the cutting speed from 56 to 376 m/min the surface finish (R a) was reduced from 1.6 to 0.36 Pm, 1.2 to 0.13 Pm and 0.95 to 0.4 Pm for depths of cut of 2, 3 and 4 Pm respectively. Chipping and scratches were observed on surfaces machined as a speed of 56 m/min. More micro-pits, micro-voids and craters were seen on surfaces machined at high speeds, such as at 376 m/min. 3.4 Surface hardness Fig. 9 shows the effect of the cutting speed on the surface hardness of the machined surface for depths of cut 2 to 4 Pm. When the cutting speed was increased from 56 to 376 m/min the surface hardness of the machined surface was found to increase from 1185 to 1711; 1192 to 1710; 1245 to 1669 for the depths of cut of 2, 3 and 4 Pm respectively. The results coincide with the experimental observations of the cutting forces and surface textures. The surface hardness results, along with the surface texture observations depict a large presence of brittle fracture at lower cutting speeds. However, while the cutting speed was increased from 79 to 376 m/min the material fracture transformed into ductile fracture which was observed in the form of dislocation and plastic deformation regions.

0.02 50 0 0

50

100

150 200 250 300

0 350 400

Cutting Speed, V (m/min)

Figure 4: Influence of cutting speed on applied shear stress (Wc-A) and un-deformed chip thickness

Ramesh Kuppuswamy and Nomvelo Mkhize / Procedia Manufacturing 8 (2017) 549 – 556

Particle pull out and microfractures

Particle pull out and microfractures

Elastic and plastic dislocation (plowing grooves and steaks)

Elastic and plastic dislocation (plowing grooves and steaks)

Figure 5: Surface texture behaviour for WC at different cutting speeds at a constant depth of cut = 2 Pm

Figure 6: Surface texture behaviour for WC at different cutting speeds at a constant depth of cut = 3 Pm

Particle pull out and microfractures

Elastic and plastic dislocation (plowing grooves and steaks)

Surface Finish , Ra (Pm)

Depth of cut 2 Pm 1.5

3 Pm 4 Pm

1

0.5

0

2000

Depth of cut 2 Pm 3 Pm 4 Pm

2

2

Surface Hardness (HV30) (Kg/mm )

Figure 7: Surface texture behaviour for WC at different cutting speeds at a depth of cut = 4 Pm

1500

1000

500

0 56

79 131 211 Cutting Speed , V (m/min)

376

Figure 8: Influence of cutting speed on surface finish (Ra) for the WC material

56

79 131 211 Cutting Speed , V (m/min)

376

Figure 9: Influence of cutting speed on surface hardness for the WC material

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3.5

Friction ratio Shown in Fig. 10 is the machining behaviour of tungsten carbide at various cutting speeds, characterized in terms of the tool-work interface friction. The friction was computed as a ratio of Tangential Cutting Force (F T) and Normal Cutting Force (FN). Within the performed experiments the friction factor at a cutting speed 56 m/min was found to be higher than the other experimented cutting speeds. The friction factor was reduced from 0.71 to 0.12 when the cutting speed was increased from 79 to 376 m/min for a depth of cut 2 µm. A similar trend was observed while machining tungsten carbide (WC) for depths of cut of 3 and 4 µm. 3.5

50

2

1

3 Pm 4 Pm

0

30 Shear angle, I

4 Pm

1.5

20 10 0 -10

0.5

-20

0

-30

56

`

40

3 Pm

2.5

Depth of cut 2 Pm

2 Pm

T

N

Friction Factor (F /F ratio)

Depth of cut 3

79 131 211 Cutting Speed , V (m/min)

376

Figure 10: Influence of cutting speed on friction ratio for the WC material

56

79 131 211 Cutting Speed , V (m/min)

376

Figure 11: Influence of the cutting speed on the shear angle for the WC material

3.6

Shear angle The past research on metal cutting has emphasized the role of the shear angle to optimize the cutting tool geometry with minimum power consumption. The fracture of solids is different for brittle and ductile materials. Often brittle materials undergo fragmentation failure so that the solids break into two or more separated parts but ductile materials exhibit elastic and plastic dislocations and eventual fractures. The computation of the shear angle indirectly helps to quantify the fractures and in this analysis the Lee and Shaffer shear angle equation was used. The Lee and Shaffer equation is given as [13]; ‫ ׎‬ൌ Ͷͷ଴ ൅ ߙ െ ߚ …………………………………………………………................................. (4) Where “α” is the tool’s rake angle = 0o and “β” is the friction angle = Tan – (FT/FN) The computed results suggest that a negative value of shear angle was seen while machining tungsten carbide at a cutting speed of magnitude 56 m/min. The negative value suggests the occurrence of brittle fracture and the values further confirm the findings shown in the surface texture. While the cutting speed was increased from 79 to 376 m/min the shear angle was increased from 13.7q to 38.4q, 14.9q to 40q and 25.7q to 37q for depth of cut 2, 3 and 4 Pm respectively (see Fig. 11). The increasing shear angle at higher cutting speeds implies a changing trend of fractures from brittle to elastic-plastic dislocation type failures. 3.7 Shear strain Further attempts were made to understand the influence of the compression ratio and shear strain against the cutting speed while machining the Tungsten carbide. The magnitude of the shear strain would vary depending upon the material properties such as hardness and toughness. To compute the shear strain, the PCD tool and the Tungsten carbide work interface conditions were equated to an orthogonal cutting process. A typical tool- work interface and shear strain is shown in Fig. 12. (b)

5

5 Depth of cut (compression ratio) 4

2 Pm 3 Pm 4 Pm

3

3 Depth of cut (Shear Strain) 2

2

4 Pm 3 Pm

1

Compression ratio

Shear Strain , H

4

1

2 Pm

Figure 12: (a) A typical tool-work interface and (b) shear displacement sketch

0 0

50 100 150 200 Cutting Speed, V (m/min)

0 250

Figure 13: Influence of cutting speed on shear strain & compression ratio for the WC material

Ramesh Kuppuswamy and Nomvelo Mkhize / Procedia Manufacturing 8 (2017) 549 – 556

The shear strain was computed using equation 5, given below [13];

H

's 'y

NP MK

NK  KP MK

ach ac

cos(I  J o ) sin I ………………………………………………………………………... (6)

…………………………………………………………... (5) Applying the shear angles and rake angles based on the PCD tool geometry the shear strain equation 5 is given as ߝ ൌ ܿ‫ ׎ݐ݋‬൅ –ƒሺ‫ ׎‬െ ߛ଴ ሻ The compression ratio was computed using equation 6 given below [13];

[

where, ach= chip thickness and ac = depth of cut Shown in Fig. 13 are the experimental results which suggest an increasing trend of the shear strain and compression ratio with an increase in the cutting speed during the machining of the Tungsten carbide material. While increasing the cutting speed from 56 to 211 m/min, the shear strain was found to increase from 2.36 to 4.08; 1.9 to 3.79; and 2.25 to 3.99 for a depth of cut 2, 3 and 4 Pm respectively. Similarly, while increasing the cutting speed from 211 to 376 m/min the compression ratio was found to increase 2.37 to 4.22; 2.2 to 3.92 and 2.24 to 4.13 for a depth of cut 2, 3 and 4 Pm respectively. The results further confirm the increasing trend of elastic-plastic dislocation type failures for the WC materials. 3.8 Tool wear A tool maker’s microscope was used to examine the tool wear after machining WC at varying speeds and depths of cut. It appears that there is chipping on the tool insert at both the rake and the flank face, as can be seen on the top view of Figure 14. The front view displays the rake face of the tool insert in Figure 14 where it can be seen that the insert is heavily damaged and the tool’s cutting edge radius is completely damaged especially at low cutting speeds. The chipping of the tools PCD insert could be a form of abrasive wear generated as a result of the hardness of the WC workpiece. On an overall note an improved tool life was observed between 56 to 211 m/min of cutting speed for the tungsten carbide (WC) material. (See Figure 15)

DOC= 2 Pm W/P= WC Tool = PCD Cutting distance = 30meter

Chipping of cutting edge at cutting speeds

Figure 14: PCD tool wear generated during machining 4.

10.5

15

Flank Wear (Pm)

Chipping at cutting distance beyond 80 meters

13.15

15.78

16.5

20

10

5

0

56

79 131 Cutting Speed (m/min)

211

Figure 15: Flank wear behaviour at different cutting speeds for WC at a depth of cut = 2 µm for a cutting distance of 30 metres

Conclusions The following are the main conclusions drawn: x The experimental results suggest that increasing the cutting speed reduces the cutting force for both the normal and the tangential force. x The computed value for the critical depth of cut was found to be 3.16 µm for WC and the experimental findings were seen to have a close matched value of 3 µm for speeds above 56 m/min. Surfaces with a lower depth of cut were seen to have a higher quality surface finish when compared to surfaces with higher depths of cut of value 3 µm and above.

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x

Increasing the cutting speed decreases the un-deformed chip thickness which facilitated an increase in ductile fractures. The friction factor, computed through the tangential and the normal cutting force, was seen to be marginally higher for surfaces machined in brittle fracture than those machined in ductile mode A negative shear angle in the experiment was an indication of an occurrence of brittle fracture whereas a positive and increasing shear angle, with speed, implied the changing trend of fractures from brittle to elastic-plastic dislocation type failures. Machining under cutting speeds of value 56 m/min and below produces a surface with brittle fractures. Increasing the cutting speed improves the surface finish but machining at high cutting speeds of value 376 m/min and above does not produce ductile fractured surfaces as it contains several craters.

Acknowledgement The authors wish to thank Mr. Jonathan Ho & Ms. Jess Foo (Alignment Tools, Singapore) for the support rendered towards manufacturing the PCD tools and SOMTA Tools SA Pty Ltd for donating the Tungsten Carbide workpieces. This project was supported by fund NRF GRANT: INCENTIVE FUNDING FOR RATED RESEARCHERS (IPRR) –South Africa through Reference: IFR150204113619 and Grant No: 96066 References [1.] K, Liu., and X, P. Li., 2001. Ductile Cutting of Tungsten Carbide. Journal of Materials Processing Technology, 113, pp. 348-354. [2.] Sandvik., High Speed Machining and Conventional Die and Mould Machining. Available from: http://www2.coromant.sandvik.com/coromant/pdf/dm_articles/hsm1_5.pdf. [3.] Aramcharoen, A., and Mativenga, P. T., 2009. Size Effect and Tool Geometry in Micro-milling of Tool Steel. Precision Engineering, 33(4), pp. 402–407. [4.] Masayuki, Takada1., Hideaki, Matsubara., and Yoshihiro, Kawagishi., 2013. Wear of Cemented Carbide Dies for Steel Cord Wire Drawing. Japan Materials Transactions, 54(10), pp. 2011 to 2017. [5.] M,P. Jahan., Y,S. Wong., M, Rahman., 2009. A Study on the Fine-Finish Die-Sinking Micro-EDM of Tungsten Carbide Using Different Electrode Materials. Journal of Materials Processing Technology, 209, pp. 3956–3967. [6.] H, Suzuki., S, Hamada., T, Okino., M, Kondo., Y, Yamagata., T, Higuchi.,2010. Ultraprecision Finishing of Micro-Aspheric Surface by Ultrasonic Two-axis Vibration Assisted Polishing. CIRP Annals - Manufacturing Technology, 59, pp. 347–350. [7.] Kazuo, Nakamoto., Kazutoshi, Katahira., Hitoshi, Ohmori., Kazuo, Yamazaki., Tojiro, Aoyama., 2012. A Study on the Quality of Micro-Machined Surfaces on Tungsten Carbide Generated by PCD Micro EndMilling. CIRP Annals - Manufacturing Technology, 61, pp. 567–570. [8.] Kui, Liu., Xiaoping, Li., 2004. Nanometer-Scale Ductile Cutting of Tungsten Carbide. Journal of Manufacturing Processes, 6(2), pp.187-195. [9.] Zhongbo, Zhan., Ning, He., Liang, Li., Rabin, Shrestha., Jingyu, Liu., and Shulong, Wang., 2015. Precision Milling of Tungsten Carbide with Micro PCD Milling Tool. International Journal of Advanced Manufacturing Technology, 77(9), pp. 2095-2103. [10.] Joseph, McGeough., 2002, Micromachining of Engineering Materials , Marcel Dekker, USA. [11.] T,G. Bifano., T,A. Dow., R,O. Scattergood., 1991. Ductile-Regime Grinding: A New Technology for Machining Brittle Materials. ASME Journal of Engineering Industry, 113, pp. 184-189. [12.] Norio, Taniguchi., 1996. Nano-technology – Integrated Processing Systems for ultra –precision and UltraFine Products, Oxford University Press, USA. [13.] S, Kalpakjian., and S, R. Schmid., 2009. Manufacturing, Engineering and Technology, 6th Edition in SI Units, Pearson, pp. 957-959.