ORIGINAL ARTICLE

Effect of cutting edge radius on surface roughness and tool wearin hard turning of AISI 52100 steel

T. Zhao1,2 & J. M. Zhou1& V. Bushlya1 & J. E. Ståhl1

Received: 26 August 2016 /Accepted: 16 January 2017# The Author(s) 2017. This article is published with open access at Springerlink.com

Abstract Performance of cutting tool in hard turning is sig-nificantly influenced by its microgeometry, such as edge radi-us. This study presents an experimental exploration to under-stand the effect of cutting edge radius on machining perfor-mance in terms of surface roughness and tool wear. The cut-ting tools (CBN) with three groups of nominal edge radius,20, 30, and 40 μm, were used in the study. The cutting edgeradii were characterized with an Alicona optical microscope,and variation of the edge radius was evaluated in this study.The machining tests were then conducted to experimentallyassess the effect of cutting edge radius on surface quality andtool wear under different machining conditions. Three-leveland two-factor experiments were designed in the test. Theresults in this study suggest that there is noticeable variationin the edge radius on a cutting tool with a certain nominalvalue of edge radius. The variations tend to be smaller withincrease of the nominal value of edge radius. Besides, theresults can be drawn that edge radii have a significant influ-ence on surface roughness and tool wear. Considering all fac-tors, the cutting tool with nominal edge radius of 30 μm dem-onstrate better machining performance among three groups ofcutting tool in hard turning of AISI52100 steel.

Keywords Hard turning .Microgeometry . Surfaceroughness . Tool wear

1 Introduction

As hard turning can offer attractive advantages in terms ofhigher material removal rate, shorter setup time, and re-duced production cost, it has become a potential substitutefor conventional grinding. In hard turning, workpiecehardness is usually higher than 45 hardness–Rockwell C(HRC) and a cutting tool is often subjected to extremelyhigh local mechanical and thermal stresses, which cancause chipping and wear on the edge of the cutting tooland thereby influence the cutting force, tool wear, chipformation, surface integrity, and accuracy of machining.Hence, cutting tool geometry, especially microgeometry,such as edge radius and chamfer (length and angle) playsan important role in the performance of the cutting toolduring the hard turning processes.

Over the years, many investigations have been con-ducted to explore the effect of cutting tool geometry onthe surface integrity, cutting force, and tool life in hardturning. Özel et al. [1] studied experimentally the effect ofcutting edge geometry and cutting speed, as well as work-piece hardness on surface roughness in finish hard turningof AISI H13 steel, and demonstrated the effect of twocutting parameters on the surface roughness. In the inves-tigation conducted by Chou et al. [2], the surface rough-ness was found to be strongly influenced by tool noseradius and tool wear, and the results manifested that largetool nose radius can obtain finer surface finish, but it alsoincreases tool wear. Fulemova et al. [3] studied the influ-ence of cutting edge preparation and cutting edge radiuson tool life and the roughness of machined surface. Zhouet al. [4] studied the effect of chamfer angle of the CBNtool on tool wear and tool life through FE simulation andexperimental validation. A large difference was found inthe tool life when the chamfer angle changes from 10° to

* J. M. Zhoujinming.zhou@iprod.lth.se

1 Division of Production and Materials Engineering, Lund University,22100 Lund, Sweden

2 Northwestern Polytechnical University, Xi’an 710072, China

Int J Adv Manuf TechnolDOI 10.1007/s00170-017-0065-z

30° in hard turning, and the best tool life was found at 15°of chamfer angle. However, effect of edge radius was notstudied in the paper. Attanasio et al. [5] studied the effecton tool wear and cutting parameters on white layer anddark layer formation in hard turning. The results revealedthat cutting parameters and tool wear affect noticeablywhite and dark layer formation. Yong et al. [6] proposeda prediction model by applying the modified Oxley’s ap-proach to explore the effect of tool thermal property oncutting force then employed the predicted results to com-pare with experiments. Huang et al. [7] presented a cut-ting force prediction algorithm which takes into accountthe effect of tool edge radius and verified the predictionalgorithm by comparing the experiment results and thepredicted value.

Although cutting tool geometry has an effect on sur-face quality, tool wear, and cutting force, few studies weremade on the variation of edge radius on surface qualityand tool performance in hard turning and variation of theedge radius on the cutting tool can sometimes be verysignificant. In this paper, an attempt has been made tocharacterize the edge radius of CBN cutting tools, analyzethe variation of the edge radius from their nominal valuescreated during the process of edge preparation, and exper-imentally assess the effect of the edge radius on surfacequality, cutting forces, and tool wear in hard turning ofAISI52100 steel under different process conditions.

2 Characterization of edge radius

The microgeometry of the cutting tool is often producedin the process called edge preparation, which includesdifferent methods, such as brushing, drag finishing,microblasting wet edge honing, laser treatment, etc. [8,9]. The tools with superior edge preparation often provide

the strength that is required to withstand the large stressesinduced during the machining. As a result, various typesof edge preparation such as honed edge, chamfered edge,and chamfered edge with honed radius are applied to theinsert as shown in Fig. 1. These various types of edgepreparation can be applied for different hard turning pro-cesses with consideration of factors as machining efficien-cy, surface quality, and tool life; for example, the cham-fered edge with honed edge radius can often be used forroughing due to its superior edge strength, while the edgewith honed edge radius can obtain better surface qualityand it is thus better for finishing. In addition, the CBNtools generally have lower toughness than other tool ma-terials; thus, edge chipping tends to be more likely duringhard turning. The proper edge preparation can improvethe strength of the cutting edge and attain favorable sur-face finishing.

For the CBN tools used in hard turning, the preparationof the edge radius on the cutting tool is critical for bothtool performance and quality of the machined component[12]. Variation of the edge radius may influence on chipformation, minimum chip thickness, cutting forces, toolwear, and tool life, as shown in Fig. 2, and it may alsoaffect the process stability and process quality. Therefore,

Fig. 1 Manufacturing process ofmicrogeometry and threeconditions of edge preparation[10, 11]

Fig. 2 Characterization of cutting tool microgeometry

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the edge radius needs to be evaluated before conductingthe experiment so as to ensure the consistence of the edgeradius and process stability. The required edge radius isoften created by the combination of speed and the dura-tion of abrasive movement element effect. The machiningerror exists in the process; thus, the real edge radius maydiffer from the nominal value. The present experimentalstudy will focus on the finishing hard turning process; theCBN tools employed in the present study were tools withhoned edge with a radius of 20∼40 μm.

A Gaussian fitted circle method was applied in thisstudy to characterize the edge radius of the CBN tools

[13]. The method includes the following steps: (1) Drawan appropriate least squares straight line on the fit flankface and the clearance face. (2) Make a fitted straight lineon the flank face and clearance face intersecting andcrossing the point of intersection. The angle with thefitted straight insert is β. (3) Draw a circle which inter-sects the tangent of the fitted straight and the point Pint.(4) Repeat the above steps to make sure the point Pint andthe fitted straight reach the optimal fit. (5) The radius ofthe fitted circle represents the cutting edge radius.

The inserts used in this study included three groups withdifferent nominal values of 20, 30, and 40 μm, respectively.

Fig. 3 Profile of cutting edge inthree inserts with different edgeradii

Fig. 4 Measurement of edgeradius

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Figure 3 represents a typical profile of the cutting edge withdifferent edge radii. Each group has four inserts. For eachinsert, three measurement points were placed on each side ofthe inserts and a total of six measurement points were mea-sured in order to study the variation of the edge radius on eachinsert. Meanwhile, 50 measurements were conducted fromeach measurement point to obtain statistically reliable values,as shown in Fig. 4. In total, 1200 measurement data wereobtained in each group of the edge radius. The distributionof the three groups’ edge radius and wedge angle is drawn,as shown in Fig. 5, which clearly demonstrates the variation ofthe edge radius from its nominal values. Additionally, themeans and variance of each group edge radius and wedgeangle is also calculated, as summarized in Table 1.

Figure 5 shows that most of the measurement pointsare in the range of nominal value ±5 μm, although withdifferent levels of variation in each group of inserts. Thevariation tends to be higher for the insert with smalleredge radius (20 μm) than the insert with larger edgeradius. Figure 6 demonstrates a clear trend of change inthe variation. With increase in nominal value, the toolwith larger edge radius is closer to the nominal valueand is more stable. The variation of the wedge angle,however, shows a different trend. For the group withan edge radius of 40 μm, the variation of the wedgeangle is higher than the group with an edge radius of20 μm. Nevertheless, the majority of measurements fromthe wedge angle are within the range of ±1°, which is

Fig. 5 Histogram of the edge radius in three groups of insert

Table 1 The means and variance of edge radius and wedge angle

Group Nominal edgeradius (μm)

Edge radius Wedge angle

Mean (μm) Variance (μm) Deviation ratio (%) Mean (μm) Variance (μm) Deviation ratio (%)

1 20 22.801 4.625 23.124 89.9 0.838 0.931

2 30 29.661 3.134 10.447 89.9 0.658 0.731

3 40 40.718 2.418 6.045 89.4 2.361 2.623

Fig. 6 Variance of edge radiusand wedge angles in three groupsof inserts with different nominalvalues

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close to their nominal value. Table 1 summarizes themean values and the variation of the edge radius andwedge angle from three groups of insert. It apparentlycan be seen that the variance decreases when the edgeradius increases, and the variance of the edge radius of40 μm is significantly less than the edge radius of20 μm. Additionally, the edge radius of 30 μm is thecloset nominal value. Therefore, to reduce the processingerrors and ensure the consistency of experiments, theedge radius with the nearest nominal value was chosenaccording to the measured results.

3 Experimental setup

3.1 Workpiece material

The workpiece material used in this study was AISI52100steel, which is widely employed for bearing and roller in aninternal combustion engine, drive shaft, etc. The workpiecewas in the bar shape with diameter of 50 mm and length of150 mm. The hardness of the workpiece is in the range of53∼58 HRC. The composition of the workpiece material isshown in Table 2 [14, 15].

3.2 Cutting tools

CBN cutting tools were used in the test. The tool materialcontains 50% CBN contents with an average grain size of2 μm. The binder material is the mixture of cobalt, tungsten,and aluminum ceramic. The cutting tool uses a round insertwith a diameter of 9.5 mm, and the tool holder is CRSNL3225which gives a tool geometry of −6° in rake angle −7° in clear-ance angle.

Before machining experiment, a pre-cut was conducted foreach workpiece to remove the rough outer layer remainingfrom the previous process and ensure the consistency of thesurface. Additionally, the workpiece was grooved with awidth of 10mm to avoid the interaction of different processingparameters. The experiment was performed on the three axialturning lathes, as shown in Fig. 7. During machining, cuttingforces were measured with a force dynamometer, Kistler9121. The process parameters are listed in Table 3.

3.3 Measurement tools

An Alicona InfiniteFocus optical microscope as a keymeasurement tool in this paper was used to measurethe edge radius and tool wear. In addition, the Th-1100 hardness tester from Innova Test Company wasused in the measurement of the hardness of theworkpiece.

4 Results and discussion

4.1 Surface roughness

The surface roughness measurement and analysis wereperformed by means of an InfiniteFocus Microscope,Alicona, which is an optical 3D measurement device.The microscope allows for the capture of images with alateral resolution down to 400 nm and a vertical resolu-tion down to 10 nm.

The surface produced by a hard turning process has thecharacters of anisotropic and periodical in the geometrical

Table 2 Chemical composition of workpiece material

AISI52100 C Si Mn P S Cr Mo Al Cu Fe

0.95∼1.05 0.15∼0.35 0.25∼0.45 0.025 0.015 1.40∼1.65 0.10 0.05 0.30 96.9

Table 3 Experimentalconditions Factors Description

Edge radius 20, 30, 40 μm

Cutting speed 120, 160, 200 m/min

Feed rate 0.08 mm/rev.

Depth of cut 0.1 mm

Coolant DryFig. 7 Setup of machining test

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structure, as shown in Fig. 8a. The anisotropic featuresinclude lays and grooves induced by edge chipping andbuilt-up edge, and periodic features include feed markscreated by the nose of the cutting tools. This means thatconventional 2D surface roughness Ra is not enough torepresent the surface character and 3D surface roughnessSa can provide better criteria for surface roughness, asshown in Fig.8b, c. 3D surface roughness Sa can be cal-culated by an average of the measurement points over acertain area, as follows:

Sa ¼ ∬a Z x; yð Þ dxdyjj ð1Þ

Influence of the edge radius on the roughness of the ma-chined surface in 2D (Ra) and 3D (Sa) can be seen in theFig. 9a, b, respectively. The 3D surface roughness values aregenerally higher than 2D surface roughness values, whichclearly indicate that some surface features are missed by the2D measurement. The lowest roughness of the machined sur-face is arrived with an edge radius of 30 μm in both 2D and3D surface roughness. The stability of the cutting processcould be the major reason for this. The roughness on the ma-chined surface produced by edge radii of 20 and 40 μm arehigh in all the tests. A microscope study observed the micro-grooves and chip flows on the machined surface, which couldattribute to the high roughness value of the surfaces. Cuttingspeed, however, shows little influence on the surface rough-ness except for the edge radius of 40 μm at the speed of200 m/min, in which a small vibration was observed duringthe test.

4.2 Cutting forces

Figure 10 shows the effect of edge radius and cutting speedon cutting force Ft, feed force Ff, and radial force Fr. Ascan be seen from the figure, all three force componentsincrease when increasing the cutting edge radius. Among

(a aS Z x= ∫∫ ),x y dxdy (1))

Fig. 8 a Typical surface topography. b, c Variation of 2D and 3D surface roughness

Fig. 9 Effect of edge radius on 2D and 3D surface roughness

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the three force components, radius force is the most sensi-tive to the change of the edge radius; as a result, theploughing effect is significantly affected by the size ofthe edge radius. Cutting speed has negatively affected thelevel of three force components. With increase in the cut-ting speed, the force magnitude is decreased primarily dueto increase in the cutting temperature which may soften thework material in the cutting area. Figure 10d reveals theinfluence of the feed rate and edge radius on the feed forcecomponent, which further demonstrates the increase of theploughing force with the increase in the edge radius as thefeed rate approaches zero value. A higher ploughing forcecomponent means higher friction force between cuttingedge and work material, which could significantly affectthe formation of machining surface quality and chip for-mation. This could be the explanation of higher roughnessvalues when the cutting tool with an edge radius of 40 μmwas used in the test.

4.3 Tool wear

The effect of the edge radius combined with cutting speed ontool flank wear was also evaluated during the study. The flankwear was measured by an Alicona infinite optical microscopewith resolution of ×10, as shown in Fig 11. The measurementwas conducted after every 300 mm of machining length. Fivetool wear measurements were made with a total 6000 mm of

cutting length or 85 cm3 of material removal volume (MRV).The progression of tool wear (VB) for the cutting tool withdifferent cutting edge radii under 6000mm of cutting length isdemonstrated in Fig. 12.

From Fig. 12, it can be seen that the cutting edge radi-us and cutting speed have a significant effect on flankwear. Flank wear decreases as the cutting edge radius isincreased. Especially when the tool with a cutting edgeradius 20 μm was used to process the workpiece, theflank wear rate is higher than the tool with a larger edgeradius. This is because the tool with a smaller edge radiusis sharper; flank wear is thus higher. With the increase inthe cutting speed, flank wear is increased significantly,and the increase in flank wear is almost linear with in-creasing material removing volume primarily, contributingto the increase in cutting speed which increases the

Fig. 10 Effect of cutting speed and edge radius on cutting force

Fig. 11 Topography of typical tool wear

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temperature of the contact zone. Therefore, flank wearwhen using the tool with edge radius of 20 μm at200 mm/min reaches the maximum value of 159 μm.

5 Conclusions

Variation of edge radius in CBN tools was characterized in thisstudy, and their effects on surface quality and tool wear wasalso experimentally evaluated in hard turning of AISI52100steel. The results show that there is a noticeable differencebetween the actual values of edge radius and the correspondentnominal edge radius. The variation of the edge radius andwedge angle is significant both for the cutting edge on the sameinsert and the cutting edge from a group of inserts. The devia-tion of most of measurement points is within the range of±5 μm, while the majority of measurement points are withinthe range of ±1° and close to the nominal. With the increase ofthe edge radius, the variation of the edge radius tends to besmaller and the distribution of the edge radius is closer to theirnominal values. Among the three groups of tool, the means ofthe second edge radius group with a nominal value of 30 μmshow the closest to its nominal value. The variation edge radiuscan significantly influence the cutting force, tool life, and sur-face quality. The edge radius with 20 μm nominal value dem-onstrates highest tool wear during the test. Among the threegroups of tool, the edge radius with 30 μm exhibits betterperformance in terms of surface quality and tool wear.

Acknowledgements This research is part of the strategic research pro-gram the Sustainable Production Initiative (SPI), cooperation betweenLund University and Chalmers University of Technology. Authors wouldacknowledge Henrik Sandqvist from SECO Tools AB for the supply ofcutting tools in this research. Authors would also like to thank the finan-cial support from the Chinese Scholarship Council (CSC).

Open Access This article is distributed under the terms of the CreativeCommons At t r ibut ion 4 .0 In te rna t ional License (h t tp : / /creativecommons.org/licenses/by/4.0/), which permits unrestricted use,distribution, and reproduction in any medium, provided you give appro-priate credit to the original author(s) and the source, provide a link to theCreative Commons license, and indicate if changes were made.

References

1. Özel T, Hsu TK, Zeren E (2005) Effects of cutting edge geometry,workpiece hardness, feed rate and cutting speed on surface rough-ness and forces in finish turning of hardened AISI H13 steel[J]. Int JAdv Manuf Technol 25(3–4):262–269

2. Chou YK, Song H (2004) Tool nose radius effects on finish hardturning[J]. J Mater Process Technol 148(2):259–268

3. Fulemova J, Janda Z (2014) Influence of the cutting edge radius andthe cutting edge preparation on tool life and cutting forces at insertswith wiper geometry[J]. Procedia Engineering 69:565–573

4. Zhou JM, Walter H, Andersson M, Stahl JE (2003) Effect of cham-fer angle on wear of PCBN cutting tool. Int J Mach Tools Manuf43(3):301–305

5. Attanasio A, Umbrello D, Cappellini C, Rotella G, M’Saoubi R(2012) Tool wear effects on white and dark layer formation in hardturning of AISI 52100 steel[J]. Wear 286:98–107

6. Huang Y, Liang SY (2005) Modeling of cutting forces under hardturning conditions considering tool wear effect[J]. J Manuf Sci Eng127(2):262–270

7. Huang P, Lee WB (2016) Cutting force prediction for ultra-precision diamond turning by considering the effect of tool edgeradius[J]. Int J Mach Tools Manuf 109:1–7

8. Denkena B, Lucas A, Bassett E (2011) Effects of the cutting edgemicrogeometry on tool wear and its thermo-mechanical load[J].CIRPAnnals-Manufacturing Technology 60(1):73–76

9. Bassett E, Köhler J, Denkena B (2012) On the honed cutting edgeand its side effects during orthogonal turning operations ofAISI1045 with coated WC-Co inserts[J]. CIRP J Manuf SciTechnol 5(2):108–126

10. Karpuschewski B, Schmidt K, Prilukova J et al (2013) Influence oftool edge preparation on performance of ceramic tool inserts whenhard turning[J]. J Mater Process Technol 213(11):1978–1988

11. Thiele JD, Melkote SN (1999) Effect of cutting edge geometry andworkpiece hardness on surface generation in the finish hard turningof AISI 52100 steel[J]. J Mater Process Technol 94(2):216–226

12. Bartarya G, Choudhury SK (2012) State of the art in hardturning[J]. Int J Mach Tools Manuf 53(1):1–14

13. Wyen CF, Wegener K (2010) Influence of cutting edge radius oncutting forces in machining titanium[J]. CIRP Annals-Manufacturing Technology 59(1):93–96

14. Yakimets I, Richard C, Béranger G et al (2004) Laser peeningprocessing effect on mechanical and tribological properties ofrolling steel 100Cr6[J]. Wear 256(3):311–320

15. de Siqueira GG, Stipkovic Filho M, Batalha GF (2006) Hard turn-ing of tempered DIN 100Cr6 steel with coated and no coated CBNinserts[J]. J Mater Process Technol 179(1):146–153

Fig. 12 a Influence of edge radius on tool wear. b Influence of cutting speed on tool wear

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