coated sumiboron bnc2010/bnc2020 for hardened steel machining … · 2015. 4. 27. · the...

SEI TECHNICAL REVIEW · NUMBER 80 · APRIL 2015 · 85

INDUSTRIAL MATERIALS

1. Introduction

Cubic boron nitride (CBN)*1 has hardness and thermal conductivity second only to diamond, and has low reactivity with ferrous metals. Sumitomo Electric Hardmetal Corporation succeeded in developing the world’s first CBN tool for the machining of hardened steel parts by sintering a mixture of CBN particles and a special ceramic binder, and launched it on the market in 1977 under the trade name SUMIBORON. Since the release in 2000 of Coated SUMIBORON, which features higher wear resistance by ceramic coating on the CBN sintered body with PVD*2 technology, higher-precision and higher-efficiency machining have been realized. The shift from grinding to cutting, has contributed to productivity improvement and cost reduction, mainly in the automotive industry.

In the automotive industry, a trend is seen that, in line with the acceleration of automakers’ transferring production to developing countries, an increasing number of production lines are unmanned, or operated by a small number of people. For that reason, customers' demands for cutting tools have shifted from “high-efficiency cutting” to “long and stable tool life.” Furthermore, the requirement for high-precision cutting has become stronger against the background of an increase of high-functional automotive parts. To satisfy such demands, we have developed Coated SUMIBORON BNC2010 and BNC2020, which achieve considerably longer and more stable tool life than the conventional Coated SUMIBORON series. The advan-tages and cutting performance of BNC2010 and BNC2020 are described below.

2. Issues in Hard Turning

A coated CBN tool has a hard and tough CBN sintered body covered with a ceramic coating having excellent heat and oxidation resistance, as shown in Fig. 1. As the result, it can achieve longer tool life, even in hard turning where the cutting edge is subjected to high load and heat during the cutting. However, the hardness and toughness of a ceramic coating is lower than a CBN sintered body, abrasive wear and coating peelings occur in the case when the mechanical load is added at the cutting edge. On the other hand, desired shape and mechanical strength are given to the hardened steel workpieces by applying appropriate forming, forging and thermal treatments. However, surface integrity, such as hardness, microstructure and stress state, may vary among different lots and within the same lot, too. Moreover, an overall tooling system, composed of a lathe, a chuck and a holder, may not always has enough rigidity to cut hardened steel. As the result, above abra-sive wear or coating peeling may occur due to discon-tinuous load, and often cause shorter or more unstable tool life.

Coated SUMIBORON BNC2010/BNC2020 for Hardened Steel Machining Realizing Long and Stable Tool Life

Yusuke MATSUDA*, Hironari MOROGUCHI, Nozomi TSUKIHARA, Katsumi OKAMURA, Makoto SETOYAMA and Tomohiro FUKAYA

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------In the automotive industry, a trend is seen that in line with the acceleration of automakers’ transferring production to developing countries, an increasing number of production lines are unmanned, or operated by a small number of people. For that reason, there are strong demands for cutting tools having long and stable tool life. To satisfy such demands, we have developed Coated SUMIBORON BNC2010/BNC2020. Compared with conventional cutting tools, Coated SUMIBORON BNC2010 has improved in notch-wear resistance and achieves longer tool life, even in high-precision cutting of strict surface roughness criteria. BNC2020 has improved in breakage resistance and peeling resistance of the coating layer and achieves longer and more stable tool life in continuous and interrupted machining. This report describes the advantages and cutting performance of BNC2010/BNC2020.

----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Keywords: PCBN, hardened steel, high precision cutting, interrupted cutting, PVD coating

Coated CBN toolCross section of cutting edge

Ceramic coatingEdge preparation

CBN sintered bodyTool type： 2NC-CNGA120408

Fig. 1. Structure of Coated CBN tool

86 · Coated SUMIBORON BNC2010/BNC2020 for Hardened Steel Machining Realizing Long and Stable Tool Life

Figure 2 shows classification of the failure mode in hard turning. In the case of high-precision cutting with the required surface roughness of less than Rz 3.2*3, the feed rate is often set low for the superior theoretical surface roughness. As a result, the notch wear is increased by the focused mechanical load on the end-cutting edge of the notch where the thickness of the chip becomes thin. In such high-precision cutting, suppression of the notch wear is most important because it is transcribed on the machined surface and it becomes a deciding factor of the surface roughness, as shown in Fig. 3. In the case of general purpose, breakage from crater wear and chip-pings from coating peeling become the main failure mode because of the high feed rate, high depth of cut, or interruptions.

BNC2010 for high-precision cutting is able to main-tain superior surface finish by suppressing notch wear. BNC2020 has improved in breakage resistance and peeling resistance of the coating layer, achieving a longer and more stable tool life under various cutting condi-tions. As a result, BNC2010 and BNC2020 eliminate tool change at irregular intervals, making unmanned opera-tions possible over a longer time, and realizing signifi-cant progress in both productivity improvement and machining cost reduction.

3. Features of BNC2010 and BNC2020

3-1 Characteristics of BNC2010 and BNC2020Table 1 shows the specifications of BNC2010,

BNC2020 and conventional grades. Table 2 shows the

physical properties of these grades. The CBN content, particle size, and binding material are optimized and controlled, depending on the applications, to provide the CBN sintered body with the desired breakage and wear resistances.

Figure 4 shows the micro structure of the CBN sintered body of BNC2010 and BNC2020. Both have improved in wear and breakage resistances by extremely decreasing impurities which causes wear and cracks. Furthermore, BNC2010 shows high wear resistance in the cutting from high-speed to light interruption by applying a high-purity titanium carbonitride (TiCN) binder with excellent heat resistance. BNC2020 has improved in thermal conductivity and toughness by applying a larger size of CBN particles than conven-tional CBN grades and a high-purity titanium nitride (TiN) binder.

Ceramic coating can add various functions to the cutting tool by design of its composition, thickness and structure of coating layer. Figure 5 shows the cross section view of BNC2010 and BNC2020 coatings. BNC2010 has a trilaminar structure of a TiCN layer and unique multi-layer that shows excellent notch wear resistance. BNC2020 has a titanium aluminum nitride (TiAlN) layer and unique adhesion layer that shows

0

2

4

6

8

10

12

14

0 10 20 30Cri

teri

a o

f su

rfac

e ro

ug

hn

ess

Rz（

µm）

Efficiency Vc（m/min）・f（mm/rev.）

Notch wear

Crater → Breakage

General purpose

High-precision

Coating peeling

Previous edge

f

Notch wear Notch wearMachinedsurface

Surface roughnessRz

Edge

SEM image

Fig. 2. Failure mode for hard turning

Fig. 3. Relationship between notch wear and surface roughness

Table 1. Specifications of BNC2010 and BNC2020

Table 2. Physical properties of BNC2010 and BNC2020

Application GradeCBN sintered body Ceramic coating

CBN content（%）

CBN grainsize（µm）

Binder CompositionTickness（µm）

Highprecision

BNC2010 50-55 2 TiCN TiCN+Unique multi layer 1.5BNC100 40-45 1 TiN TiAlN+TiCN 2BNC160 60-65 3 TiN TiAlN+TiCN 2

GeneralBNC2020 70-75 5 TiN TiAlN+Unique adhesion layer 1.5BNC200 65-70 4 TiN TiAlN 2

Application GradeHardnessHV（GPa）

StrengthTRS（GPa）

ToughnessK1C（MPa・m1/2）

Thermal conductivity（W/m・K）

Highprecision

BNC2010 30-32 1.10-1.20 5.5-6.0 40-60BNC100 29-32 1.05-1.15 5.0-5.5 40-60BNC160 31-33 1.10-1.20 6.0-6.5 55-75

GeneralBNC2020 34-36 1.20-1.30 7.0-7.5 65-85BNC200 33-35 1.15-1.25 6.5-7.0 60-80

cBN

Conventional

Ceramics binder

Impurities

BNC2010/BNC2020

Issues of impurities

cBNHigh-purity binderHigh toughnessHigh heat resistance

Flank Wear

Less toughnessLess heat

resistance

Progress cracks → Breakage

Fig. 4. CBN sintered body of BNC2010 and BNC2020


excellent wear and coating peeling resistances, and real-ized stable coating during cutting.3-2 Edge preparation of BNC2010 and BNC2020

BNC2010 and BNC2020 have two types of edge preparations as shown in Fig. 6. “Standard” is for general purpose and “HS” is a stronger type. By using appro-priate edge preparation for each application, BNC2010 and BNC2020 can be used for various hard turning, which covers a wide range of machinability and shape of workpiece. “Standard”, with a good balance between sharpness and breakage resistance, is the first recom-mendation for general cutting. By using “HS”, the breakage in interrupted cutting could be suppressed by larger chamfer angle and width.

4. Cutting Performance of BNC2010 and BNC2020

4-1 High-precision cutting evaluation of BNC2010Figure 7 shows the results of a comparison of

BNC2010 with conventional BNC100 in continuous cutting of case hardened steel. BNC2010 achieved a twice longer tool life by maintaining a lower surface roughness than BNC100 in the case of the required surface roughness of Rz 3.2. Figure 8 shows the results of a comparison of the failure mode and machined surface after 8 km of cutting of these 2 grades. It seems that the notch wear of BNC2010 was smaller than that of BNC100 and the surface roughness became better.4-2 Interrupted cutting evaluation of BNC2020

Figure 9 shows the results of a comparison of BNC2020 with conventional BNC200 and a competi-

tor’s CBN in interrupted cutting by using a case hard-ened steel workpiece with 5 V-shaped grooves. The criteria of tool life was the breakage size of 0.2 mm. BNC2020 achieved 1.8 times longer tool life than BNC200 and 3 times more than the competitor’s CBN. It seems that BNC2020 achieved the longest tool life of the 3 grades because of its higher toughness.

TiN

TiCN

TiCN

TiCN

■BNC2010

Unique multi

Unique multi

Unique multi

1.5 µm

CBN sintered body

■BNC2020

TiAlN

TiN

Unique adhesion

1.5 µm

CBN sintered body

α W HoningStandard 25 0.12 Yes

HS 30 0.17 YesStandard 25 0.12 Yes

HS 35 0.27 Yes

BNC2010

BNC2020

Honing

Chamfer width W

Chamfer angle α

Breakage resistance better

Sha

rpne

ssbe

tter

Standard

HSIn case ofBreakage

Cross section of cutting edge

Fig. 5. Coating structure of BNC2010 and BNC2020

Fig. 6. Edge preparation of BNC2010 and BNC2020

0

1

2

3

4

5

6

7

0 2 4 6 8 10

Rz

(µm

)

Cutting length (km)

BNC2010

BNC100

SCM415 HRC 58-62 (Continuous cutting)4NC-DNGA150408 Vc = 160m/min, f = 0.08 mm/rev., ap = 0.1 mm, WET

BNC2010 BNC100

Failu

re m

ode

at 8

.0 k

mSu

rfac

ero

ughn

ess

Profi

le

Rz: 3.5 µm Rz: 6.4 µm

Small notch wear Large notch wear

0 1 2 3 4 5Tool life (km)

BNC2020 (5.0 km)

BNC200 (3.0 km)

Competitor’s CBN (2.5 km)SCM415 HRC 58-62 (Interrupted cutting)

4NC-CNGA120412Vc = 130 m/min, f = 0.1 mm/rev., ap = 0.6 mm, DRY8

Competitor’sCBN

BNC200

BNC2020

Fig. 7. High-precision cutting evaluation results of BNC2010

Fig. 8. Comparison of BNC2010 with conventional CBN

Fig. 9. Interrupted cutting evaluation results of BNC2020


4-3 Coating peeling evaluation of BNC2020Figure 10 shows the result of a coating peeling

evaluation of BNC2020, conventional BNC200 and a competitor’s CBN in accelerated cutting condition in which the cutting edge was repeatedly contacted to the case hardened steel workpiece. Comparing the average of the peeling areas after 1,000-time contacts repeated 3-time tests for each grade, the peeling area of BNC2020 is one-third of BNC200 and one-sixth of the competitor’s CBN. BNC2020 shows excellent coating peeling resistance due to the effect of its unique adhesion layer.

4-4 Continuous cutting evaluation of BNC2020Figure 11 shows the results of a comparison of

BNC2020 with conventional BNC200 in continuous cutting of case hardened steel. BNC2020 achieved 1.5 times longer tool life than BNC200 in the case of the required surface roughness of Rz 3.2. Comparing these failure modes after 3-km cutting, BNC2020 had smaller notch wear than BNC200 and showed better surface roughness. It seems that the coating of BNC2020 at the notch was maintained by the effect of unique adhesion layer and worked to suppressing notch wear.

5. Application Range of BNC2010 and BNC2020

Figure 12 shows the application range of Coated CBN grades in hard turning. BNC2020 is a general purpose grade which can use in a wide range from continuous to medium interrupted cutting. In the case of heavy interrupted cutting, conventional BNC300 is the first recommendation. BNC2010 can be applied from continuous to light interrupted cutting, and espe-cially shows excellent performance in high-precision cutting, such as a required surface roughness of less than Rz 3.2.

6. Cutting Example of BNC2010 and BNC2020

Figures 13–17 show the application example of BNC2010 and BNC2020.

Figure 13 is a high-precision cutting by BNC2010. It with WH-wiper achieved long and stable tool life, even in the case of a surface roughness requirement of Rz 1.6.

Competitor’s CBN

BNC200

Peeling area = 20293 µm2

Peeling area = 11340 µm2

0 10000 20000

SCM415 HRC 58-62 (Inching cutting)4NC-CNGA120412WHVc = 150 m/min, f = 0.2 mm/rev., ap = 0.2 mm, WET

BNC2020Peeling area = 639 µm2

Peeling area (µm2)

BNC200

BNC2020

Competitor’sCBN

0 1 2 3 4 5 6 7Tool life (km)

at 3 km

BNC2020

Notch wear

BNC2020

BNC200

Criteria: Rz = 3.2 µmSCM415 HRC58-62 (Continuous cutting)4NC-DNGA150408Vc = 130 m/min, f = 0.1 mm/rev., ap = 0.2 mm, WET

BNC200

Fig. 10. Coating peeling evaluation results of BNC2020

Fig. 11. Continuous cutting evaluation results of BNC2020

BNC2020

Cut

ting

spee

dV

c (m

/min

)

200

100

300

BNC300

25% 50% 100%

Load to cutting edge Large

Degree ofinterruption

Ratio ofinterruption

Light Medium Heavy

About severaloil holes

Bolt hole endface, etc.

Spline shaftoutside diameter

50

120

0%Continuous

Workpiece example

No interruption

BNC2010

CVJ outer race face turning

Criteria: Rz 1.6 μm Material: S53BC (HRC 58-63)Vc = 150 m/min, f = 0.2 mm/revap = 0.2 mm, DRY4NC-CNGA120412WH

0 200 400 600 800

BNC2010

BNC100

Rz: 0.9 µm

400 pcs

700 pcs(4.0 km)

Workpiece number (pcs)

Fig. 12. Application range of Coated CBN

Fig. 13. Application example 1 of BNC2010


Figure 14 is a high-precision cutting by BNC2010 with a surface roughness requirement of Ra0.6, nearly equal to Rz 3.2. It maintained a low surface roughness and achieved more than twice a longer tool life than the conventional CBN grade.

Figure 15 is interrupted cutting by BNC2020. It achieved 1.5 times longer tool life than conventional CBN grade. Furthermore, BNC2020 with HS-type edge preparation showed greater breakage resistance and could continue to cutting over 300 pcs.

Figure 16 is a carburized layer removal machining by BNC2020, which was a very hard application because of the tough cutting conditions like 0.5 mm of ap (depth of cut) for eliminating the hardened layer. BNC2020 achieved 1.5 times longer tool life than the conventional CBN grade, and 3 times longer tool life than the compet-itor’s CBN grade.

Figure 17 is a continuous cutting by BNC2020. In this application, coating peelings were the main issue

because of using a low rigidity lathe. BNC2020 achieved twice a longer tool life than the conventional CBN grade by suppressing coating peelings.

As described above, BNC2010 enables longer tool life in high-precision cutting by maintaining low surface roughness. BNC2020 realizes longer and more stable tool life with higher reliability against breakage and coating peeling in various cuttings, like interrupted or high-load cutting.

7. Conclusion

By using BNC2010 and BNC2020, longer and more stable tool life can be achieved in hard turning. It is expected that the use of BNC2010 and BNC2020 accelerates improvement in tool life making significant

Sun gear carburized layer removal machining Criteria: Dimension Material: SCR420 (HRC 60) Vc = 100 m/minf = 0.15 mm/revap = 0.5mm, WET4NC-CNGA120408

BNC2020: 300 pcs BNC200: 200 pcs

BNC2020


BNC200

100 200 300

Competitorʻs CBN

300 pcs

200 pcs

100 pcs

0

Hub outer diameter / face turningCriteria: Ra 1.6 μmDimensional accuracy 19 μmMaterial: S58C (HRC 58-60)Vc = 105 m/minf = 0.12 mm/revap = 0.2 mm, WET4NC-DNGA150412N-SV

0 Workpiece number (pcs)

BNC200

BNC2020

500250

240 pcs

490 pcs(18.7 km)

BNC200: 240 pcs

Coating peeling

BNC2020: 490 pcs

ø54

BNC2020 HS: 300 pcs BNC200: 200 pcs

CVJ cage outer finishingCriteria: Ra 0.8 μmMaterial: 21NiCrMo2 (HRC 60)Vc = 120 m/minf = 0.1 mm/revap = 0.15 mm, DRY4NC-TNGA160420


BNC2020 HS

0 100 200 300300 pcs

continuing

200 pcs

300 pcsBNC2020

BNC200

Main shaft outer diameter turning

Criteria: Ra 0.6 μm Material: 20NiCrMo2-2Vc = 200 m/min,f = 0.1 mm/revap = 0.35 mm, DRY4NC-DNGA150408

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 20 40 60 80 100

Ra（

µm）


Criteria

BNC2010: 80 pcs(5.7 km)

BNC100: 35 pcsCompetitorʼsCBN: 50 pcsBNC160

: 26 pcs






contributions to productivity improvement and cost reduction.

• SUMIBORON is a trademark or registered trademark of Sumitomo Electric Industries, Ltd.

Technical Terms＊ 1 CBN (cubic boron nitride): Has hardness and ther-

mal conductivity second only to diamond, and has low reactivity with ferrous metals.

＊2 PVD (physical vapor deposition): A coating method using physical reaction

＊3 Rz (ten point average roughness): A criterion of surface roughness. Micrometer order.

References(1) Harada et al., “Development of Coated cBN Sintered Tools,”

SEI Technical Review, No. 52, pp. 81–86 (2001)(2) Teramoto et al., “Development of SUMIBORON BNC100 for

High-Speed Cutting and SUMIBORON BNC160 for High-precision Cutting of Hardened Steel,” SEI Technical Review, No. 66, pp. 93–100 (2008)

(3) Okamura et al., “Development of SUMIBORON NEW BNC200 for High-Efficiency Machining of Hardened Steel Parts,” SEI Technical Review, No. 68, pp. 16–21 (2009)

(4) Harada et al., “Development of ‘SUMIBORON’ BN1000/BN2000 for Hard Turning” SEI Technical Review, No. 72, pp. 100–106 (2011)

Contributors (The lead author is indicated by an asterisk (*).)

Y. MATSUDA*• Super Hard Materials Development

Department, Sumitomo Electric Hardmetal Corp.

H. MOROGUCHI• Super Hard Materials Development


N. TSUKIHARA• Super Hard Materials Development


K. OKAMURA• Manager, Super Hard Materials

Development Department, Sumitomo Electric Hardmetal Corp.

M. SETOYAMA• Super Hard Materials Development


T. FUKAYA• General Manager, Super Hard Materials

Development Department, Sumitomo Electric Hardmetal Corp.

coated sumiboron bnc2010/bnc2020 for hardened steel machining … · 2015. 4. 27. · the...

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