Rake Angle Effect on a Machined Surface in Orthogonal Cutting of Graphite… · 2019. 7. 30. ·...

Research ArticleRake Angle Effect on a Machined Surface in OrthogonalCutting of GraphitePolymer Composites

Dayong Yang Zhenping Wan Peijie Xu and Longsheng Lu

School of Mechanical and Automotive Engineering South China University of Technology Guangzhou 510640 China

Correspondence should be addressed to Dayong Yang ydy425126com

Received 9 April 2018 Accepted 24 May 2018 Published 19 June 2018

Academic Editor Massimiliano Barletta

Copyright copy 2018 Dayong Yang et al )is is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Graphite and its composites have been widely used in various industrial fields It has been generally accepted that for positive rakeangles there is a significant increase in tension stress at the cutting zone during themachining of brittlematerials and cracks occur andspread easily degrading the quality of the machined surface quality However it is found in this study that positive rake angles canimprove the machined surface finish during the orthogonal cutting of graphitepolymer composites Better machined surface finish isobtained for a larger rake angle A finite element model is developed to reveal the mechanism of influence of the positive rake angle onthemachined surface Based on the effective stress field obtained from finite element analysis it can be predicted that the crack initiatesat the tool tip subsequently propagates downward and forward and later spreads gradually toward the free surface of the workpiece Alarger rake angle can promote crack propagation far from the machined surface )e crack initiation and propagation laws arevalidated by the edge-indentation experiments In addition the cutting force at various rake angles is investigated

1 Introduction

Graphite and its composites (GGCs) have been increasinglyused in the fabrication of various precision parts such asbiomedical implants [1] thermal sinks [2] bipolar plates offuel cells [3] electrical discharge machining (EDM) electrodes[4] semiconductor jigs pile cores and mechanical seals [5]GGCs have abrasive and brittle characters and the materialin cutting zone undergoes localized fractures rather than plasticdeformation during machining [6] Moreover the crack initi-ation and propagation laws of GGCs such as graphitepolymercomposites are unique and distinct from other brittle ma-terials [7] Hence the machining mechanism of GGCs isdifferent from that of the other brittle materials for examplestructural ceramics [8] and other types of composite materialssuch as carbonepoxy composites [9] and carbon fiber-reinforcedpolymerplastic [10] )erefore the machining of GGCs hasattracted considerable attention

To date the investigations on the machining of GGCsmainly focus on the tool wear and machined surface qualityGraphite is extremely abrasive due to the bond strength be-tween individual carbon molecules [11])erefore in graphitemachining randomly oriented graphite aggregates lead to

severe tool wear due to the abrasive character of graphite [12]and different process parameters will result in different toolwearmodesWhen the hot-filament chemical vapor-depositedand time-modulated chemical vapor-deposited diamond-coated tool inserts were used for the machining of graphitethe main wear modes were crater wear and notching resultingfrom the action of the graphite powder coming into contactwith and sliding against the tool surface during machining [6]During the high-speed milling of graphite using an AlTiN-coated carbide micro-end mill the flank wear is the dominantwear pattern in the steady wear stage [13] When the graphiteelectrodes were turned bymicrocrystalline and nanocrystallinediamond-coated Si3N4 ceramic inserts the main tool wearmode was abrasion-induced by the powdery graphite [12]According to the studies of Lei et al [14] and Hashimoto et al[15] the deposition of microcrystalline diamond films oncocemented tungsten carbide micro-drills and the in-troduction of nitrogen into the cutting area are effectivemethods for extending tool life On the other hand the in-vestigations conducted by Wan et al [7] indicated that therewere a huge number of tiny concavities on the machinedsurface of graphitepolymer composites Hence it is difficult toobtain a good surface finish because graphite is a brittle

HindawiAdvances in Materials Science and EngineeringVolume 2018 Article ID 3601918 8 pageshttpsdoiorg10115520183601918

material and brittle fracture is the main characteristic duringgraphite machining [16] To obtain a good surface nish greateorts have been conducted Wang et al [17] found thata smoother surface could be achieved with a small feed pertooth in the high-speed milling of a graphite electrode eexperimental results presented by Zhou et al [18] showed thatthe surface roughness of the machined surface increasedclearly with the depth of cut increasing in the orthogonalcutting of graphite Huo et al [11] found that the feed rate hasthe most signicant inshyuence on surface roughness and thesurface roughness is not sensitive to cutting speed on themicro-milling of ne-grained graphite e statistical analysisalso showed that the surface roughness decreased with a lowfeed rate [19] Experimental design methods [20] articialneural networks [21] and the gray relational analysis method[22] were used to optimize themachining parameters for high-purity graphite in the endmilling process Additionally Bajpaiand Singh investigated the orthogonal micro-grooving ofanisotropic pyrolytic carbon [23] and established a nite el-ementmodel to understand themechanics ofmaterial removalin the plane of transverse isotropy of pyrolytic carbon [24]

From the above literature survey little work has beenreported on the eect of the tool rake angle on the machinedsurface quality during graphitepolymer composite machiningis paper investigates the inshyuence of the tool rake angle onthe machined surface nish during the orthogonal cutting ofgraphitepolymer composites To reveal the mechanism ofinshyuence of a positive tool rake angle on the machined surfacenish the eective stress eld of the cutting zone was de-termined out by nite element analysis and then the crackinitiation and propagation path in the cutting zone werepredicted based on the eective stress eld e laws of crackinitiation and propagation were veried by edge-indentationexperiments which are eective methods for the study of thematerial removal mechanism during brittle material cutting[6 25 26] In addition the eect of the tool rake angle on thecutting force was investigated

2 Experimental Methodologies

21 Experimental Conditions of Orthogonal Cutting Dryorthogonal cutting experiments were conducted on planer

BC6063B e dimensions of the workpiece are 70mmtimes45mmtimes 5mm A superhard high-speed steel tool with theclearance angle of 10deg and dierent rake angles is used tomachine the workpiece at the cutting speed of 6mmin ecutting thicknesses are 02mm and 04mm A schematic dia-gramof the orthogonal cutting experiments is shown in Figure 1

e graphitepolymer composites used in this study area powder mixture of coke and natural graphite added toa bindere paste is rst homogenized and placed in a moldand then is suciently compacted e material is thenbaked slowly at high temperature e physical and me-chanical properties of the graphitepolymer composites areshown in Table 1

22 Edge-IndentationExperimental Setup e edge-indentationexperiments are conducted using a universal material test-ing machine (CMT5105) A schematic drawing of the edge-indentation experiments is shown in Figure 2 with theindenter positioned on the edge of the graphitepolymercomposite specimen e edge-indentation surface of the spec-imen is polished until no cracks can be observed in order toeliminate the inshyuence of tiny cracks on crack initiation andpropagatione indenter can rotate adaptively to ensure well-distributed pressure on the indentation surface e dimen-sions of the graphitepolymer composite specimen are 70mmtimes45mmtimes 5mm All specimens are indented at the constantspeed of 05mmmin

It can be seen from Figure 2 that the edge indentation issimilar to orthogonal cutting In Figure 2 cs is the rake angleof the indenter hD is the edge-indentation thickness and Pis the normal load imposed on the indenter e indenter issimilar to a cutting tool with the rake angle of cs and clearanceangle of 0deg and hD is the cutting thicknesserefore the lawsof crack initiation and propagation obtained from the edge-indentation experiments can be applied to validate the predictedcrack initiation and propagation rules for the graphitepolymercomposite orthogonal cutting process

3 Effect of Rake Angle on MachinedSurface Finish

Figure 3 shows the machined surface roughness Ra obtained atdierent rake angles for the cutting thicknesses of 02mm and04mm It can be seen from Figure 3 that the surface roughnessRa is largest when the rake angles are 0deg and 5deg and the surfaceroughness Ra decreases gradually with either an increase ordecrease in the rake angle e entire curve can be tted bya parabola e fact that a negative rake angle can reduce thesurface roughness conforms to the long-held notion that thecompressive stresses induced by a negative rake angle canweaken the breaking of the material resulting in improvedsurface qualities However the fact that a positive rake angle canalso reduce the surface roughness and improve the machinedsurface qualities conshyicts with the long-held notion that shyakingdue to tensile stresses induced by a positive rake angle damagesthe machined surface in the machining of brittle materials

Figure 4 shows the surface morphologies machined at dif-ferent rake angles for the cutting thickness of 02mm Due to the

Tool

10deg

5 mm

45 mm

WorkpieceCutting speed

70 mm

Cutting thickness

Figure 1 Schematic diagram of orthogonal cutting experiments

2 Advances in Materials Science and Engineering

breaking of the surface material many concavities are observedon themachined surface Furthermore the largest concavities areformed on the surface machined at the rake angle of 0deg Withincreased or decreased of rake angles the concavities grad-ually decrease It is suggested that with increasing rake anglethe machined surface qualities are improved for positive rakeangles during graphitepolymer composite orthogonal cutting

4 Mechanism of Influence of a Positive RakeAngle on a Machined Surface

e discussion in this section focuses only on the mechanismof inshyuence of a positive rake angle on the machined surfacenish because the mechanism of inshyuence of a negative rakeangle on machined surface qualities has been studied thor-oughly e crack initiation and propagation at the cutting

zone are the main processes during graphite machining thatresult in large amounts of crack and concavity formation onthe machined surface Hence the determination of the rulesthat govern crack initiation and propagation is highly im-portant for understanding the mechanism of inshyuence ofa positive rake angle on the machined surface

41 Eective Stress Field of the Cutting Zone During graphitepolymer cutting surface materials are removed through thebrittle fracture of the material e brittle fracture of material isdetermined by the eective stress eld of the cutting zoneHence the analysis of the eective stress eld of the cutting zoneis helpful for understanding the material removal mechanism

411 Fracture Criterion of Material According to Paul andMirandyrsquos theory [27] if σIIIσb lt (1minusN2) the fracturecriterion for the three-dimensional stress state is given by

Table 1 Mechanical properties of graphitepolymer composites

Properties Density(gcm3)

Hardness(shores)

Tensile strength(MPa)

Compressive strength(MPa)

Modulus of elasticity(GPa)

Porosity()

Parameter 19 75 173 1072 159 05

O

Projection A the indenter angleand indentation position

Projection A

hD

γs

Graphitepolymer specimen

P A

Indenter

Figure 2 Schematic drawing of edge-indentation experiment

1

2

3

4

5

6

7

Surfa

ce ro

ughn

ess R

a (microm

)

ac = 04 mmac = 02 mm

ndash30 ndash20 ndash10Tool rake angle (deg)

00 10 20 30

Figure 3 Machined surface roughness of graphitepolymercomposites at dierent rake angles

(I)

(II)

(III)

(IV)

(V)

5 mm

Figure 4 Surface morphologies machined at cutting thickness of02mm and dierent rake angles (I) minus20deg (II) minus10deg (III) 0deg (IV)10deg and (V) 20deg

Advances in Materials Science and Engineering 3

σeff N σI + σIII( 1113857 + 2

N2σIσIII + σI + σIII( 11138572

1113969

N 4minusN2( ) (1)

If σIIIσb ge (1minusN2) the fracture criterion for the three-dimensional stress state is

σeff σI (2)

where σeff is the effective stress σI and σIII are the maximalprincipal stress and minimum principal stress respectivelyand σb is the tension strength N is a constant determined bythe following equation

N

2 +σbcσbminus 2

1 +σbcσb

11139701113971

(3)

where σbc is the compressive strength

412 Finite Element Modeling ANSYS explicit dynamicsare used to calculate the effective stress field of the cuttingzone )e sketch of the graphitepolymer composite orthog-onal cutting is shown in Figure 1 In finite element modelingthe dimensions of the workpiece are 50mmtimes 25mmtimes 5mmand the properties of the workpiece material are described inTable 1 )e clearance angle of the tool is 10deg and the cuttingthickness is 2mm)e workpiece is fixed in all directions andthe cutting tool is modeled as a rigid body that moves forwardat the speed of 6mmin )e interaction between the chipand the tool can be modeled as sliding frictional behavior)e friction coefficient is defined as μ FtFn where Ft is thetangential force acting on the rake face and Fn is the normalforce acting on the rake face Based on the cutting forcemeasurements the friction coefficient is assumed to be 05 Inthe graphite cutting process high temperature is almost non-existent)e orthogonal cutting is simplified as two-dimensionalcutting and a total of 28300 quadrilateral meshes are used tomodel the workpiece as shown in Figure 5 A very fine meshdensity is defined at the contact zone of the tool tip and theworkpiece in order to obtain fine process output distributions

413 Effective Stress Field and Crack Initiation and Prop-agation Prediction )e effective stress contours of thecutting zone during the cutting process are shown in Figure 6when the rake angles of cutting tool are 0deg 10deg and 20degFigures 6(a)ndash6(c) show snapshots when the effective stressesin the vicinity of the tool tip just reach or approach thetension strength In the effective stress field the crack

initiates at the point where the stress reaches the tensionstrength and propagates along the direction of the minimumstress gradient In Figure 6 the curve c denotes the directionof the minimum stress gradient )us the curve c also in-dicates the crack propagation path in the cutting zone It canbe seen from Figure 6 that the crack initiates at the tool tipand then propagates downward and forward subsequentlyspreading gradually upward until it intersects the freesurface of the workpiece )erefore the block of theworkpiece material surrounded by the crack is removed bybrittle fracture and a concavity forms on the machinedsurface By comparing Figures 6(a) and 6(b) it can be easilyseen that when the rake angle of the tool is 10deg the crack cspreads toward the free surface of the workpiece soon after itsfirst appearance and a small concavity remains When therake angle is 0deg the crack propagation path is long and a largeconcavity forms As shown in Figure 6(c) the crack hardlypropagates downward and in this case a good surface finishcan be obtained )erefore a large positive rake angle canfacilitate crack spreading toward the free surface of theworkpiece and improves the machined surface qualities

42 Validation of Crack Initiation and Propagation Rules)e rules governing crack initiation and propagation predictedfrom the effective stress field of the cutting zone can elucidatethe mechanism of influence of the positive rake angle on themachined surface qualities However the predictions shouldbe verified by experiments)is section investigates the rulesgoverning crack initiation and propagation during graphitepolymer orthogonal cutting through edge-indentationexperiments

421 Crack Initiation and Propagation Path Figure 7 showsthe crack initiation and propagation path under the action ofan indenter with rake angles (cs) of 5deg 10deg and 20deg when hD is2mm With the increase in the normal load P no crackoccurs at the beginning of loading At this point a notchforms at the contact of the indenter and graphitepolymerspecimen as shown in Figure 7(a) )e crack initiatessuddenly and propagates rapidly when the normal loadincreases to a critical value In this case the propagation ofthe crack will terminate if the load can be removed quicklyHowever there is usually not enough time to remove thenormal load before the crack reaches the free surface)erefore a large block of graphite surrounded by the cracksheds as shown in Figure 7 where the crack spreadsdownward in the direction of the indentation in the initialstage and then propagates gradually toward the free surfaceof specimen )e propagation path of the crack is close to anarc shape )e crack spreads farther from the inside of thespecimen with the increase of rake angle of the indenter)at is a large rake angle can facilitate the crack spreadingfurther toward the free surface of the workpiece if the in-denter is considered as a cutting tool When cs is 20deg theformed crack hardly damages the machined surface asshown in Figure 7(c) )is outcome suggests that the ex-perimental results are in good agreement with the pre-dictions of crack initiation and propagation Furthermore

Figure 5 Mesh models of graphite composite orthogonal cutting


the crack propagation path in the graphitepolymer compositeis dierent from the glass crack propagation path which showsa rectilinear conguration in edge-indentation experimentsMore importantly a smaller rake angle leads to the glass crackpropagating farther away from the machined surface Hencethe rules governing the crack propagation of graphitepolymercomposites are in contrast to the laws of glass crack propa-gation us graphitepolymer composite machining has itsown unique laws that are unlike those of glass cutting

422 Relationship of the Rake Angle of the Indenter to CrackPropagation Path According to the above experimental

results the crack initiates at the contact of the indenter andspecimen and propagates in an arc-shaped path As a resulta concavity forms us the initial angle of crack propa-gation θ concavity depth cd and concavity width cw are usedto describe the crack propagation path as shown in Figure 8Figure 9 depicts the changing trend of the width and depth ofconcavities with the rake angle of the indenter at the edge-indentation thickness of 2mm e width and depth of theconcavities decrease as the rake angle of the indenter in-creases Larger rake angle of indentation leads to smaller sizeof the concavities Furthermore the concavity depth de-creases linearly as the rake angle of the indenter increases

C

C C

DD

D

D

D

DDD

D

D = 687E = 883

F = 1079 H = 1472C = 491 G = 1276 I = 1668

DD

C

C

C

C

B

B

EE

E

E

E

E

E

E

FF

F

F

F

G

GG

H

HHXI

I

Y

Z

Predictedcrack

c

MPa

1 mm

(a)

D

DD

D

D

D

DD

E = 920C = 511 G = 1329 I = 1737

CC

CC

CC

B

B

E

E

EEE

E

F

F

F

FF

G

G

G

H

H XZ

c

D = 715 F = 1124 H = 1533 MPa

1 mm

I

Y

(b)

D

DDD

DD

D

DDD

E = 927C = 515 G = 1339 I = 1751

CC

C C

CC

CCC

C

BBBB

B

B

C

B AA

BBB

BB B

B

E

EE E E E

E EF

F

F HI I

HH G

G

G

GG

F c

D = 721 F = 1133 H = 1545 MPa

1 mm

(c)

Figure 6 Eective stress contours in cutting zone and predicted crack propagation paths (the stresses in the vicinity of the tool tip just reachtension strength) at rakes angles of (a) 0deg (b) 10deg and (c) 20deg


while the largest width of the concavity formed by the actionof the indenter is obtained for the rake angle of 5deg isoutcome occurs because the indented specimen is vulnerableto collapse (as shown in Figure 10) when the rake angle ofthe indenter is 0deg and once the material of the indentationsurface is disintegrated the real edge-indentation thicknesswill be reduced us the concavity width produced atindenter rake angle of 0deg is even smaller than that producedat indenter rake angle of 5deg as shown in Figure 9 Conse-quently the surface roughness obtained at rake angle of 5deg islargest as shown in Figure 3

Figure 11 shows the dependence of the initial angle ofcrack propagation on the rake angle of the indenter It can beseen from Figure 11 that the initial angles of crack propa-gation decrease linearly with increasing rake angle of theindenter at is the larger the rake angle of the indenter isthe smaller the initial angle of crack propagation usa large rake angle of the indenter can make the crackpropagate farther away from the inside of the specimenisoutcome further conrms that a large rake angle of thecutting tool can improve the machined surface nish ofgraphitepolymer composites

500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)

Figure 7 Crack initiation and propagation paths at dierent rake angles of indenter (hD 2mm) (a) cs 5deg (b) cs 10deg and (c) cs 20deg

cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen

Figure 8 Parameters of crack initiation and propagation path

cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)

5 10 15 20 250Rake angle (deg)

Figure 9 Width and depth of concavities at dierent rake angles ofindenter (hD 2mm)

500 mm

Figure 10 Crack initiation and propagation path formed at in-denter rake angle of 0deg (hD 2mm)


5 Cutting Force at a Different Rake Angle

e cutting force was measured by a Kistler dynamometere horizontal cutting forces FH and vertical cutting forcesFV at dierent tool rake angles are shown in Figure 12 for thecutting speed v of 6mmin and the depth of cut ac of 04mmIt can be observed from Figure 12 that the cutting forcedecreases with increasing rake angle regardless of whetherthe rake angle is negative or positive Furthermore thecutting force decreases dramatically with increasing rakeangle when the rake angle is negative When the rake angle ispositive the horizontal cutting force decreases with a smallslope and the vertical cutting force is almost invariable whilethe rake angle is increasing us it can be observed thatthere is a turning point in the variation curve of cutting forcewhen the rake angle is 0deg Considering the inshyuence of therake angle on the machined surface nish and cutting forceit can be concluded that a positive rake angle that is higher

than 5deg should be selected and used for the machining ofgraphitepolymer composites

6 Conclusions

(1) When the rake angle during the graphitepolymercomposite orthogonal cutting is between 0deg and 5degthe machined surface nish is the poorest and themachined surface nish is improved with decreasingor increasing rake angle

(2) e crack initiates at the tool tip subsequentlypropagates downward and forward and then spreadsgradually toward the free surface of the workpieceresulting in the removal of a block of graphitesurrounded by the crack and the formation ofa concavity on the machined surface A large positiverake angle can facilitate crack propagation far awayfrom the machined surface erefore the concav-ities formed on the machined surface decrease usa large positive rake angle can improve the machinedsurface nish

(3) e cutting force decreases with increasing rakeangle Furthermore when the rake angle is negativethe cutting force decreases rapidly with increasingrake angle When the rake angle is positive thehorizontal cutting force decreases slowly while thevertical cutting force remains almost constant withincreasing rake angle

(4) Considering the machined surface nish and cuttingforce it is better to use a positive rake angle greaterthan 5deg to machine graphitepolymer composites

Notations

ac Cutting depth (mm)cd Concavity depth (mm)cw Concavity width (mm)FH Horizontal cutting force (N)Fn Normal force (N)Ft Tangential force (N)FV Vertical cutting force (N)hD Edge-indentation thickness (mm)N ConstantP Normal load imposed on indenter (N)cs Rake angle of indenter (degree)θ Initial angle of crack propagation (degree)μ Friction coecientv Cutting speed (mmin)σb Tension strength (MPa)σbc Compressive strength (MPa)σe Eective stress (MPa)σI Maximal principal stress (MPa)σIII Minimum principal stress (MPa)

Data Availability

e digital data used to support the ndings of this study areavailable from the corresponding author upon request

0

5

10

15

20

25

30

Initi

al an

gle (

deg)


Figure 11 Initial angle of crack propagation at dierent indenterrake angles

FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)

ndash20 ndash10 0 10 20 30ndash30Rake angle (deg)

Figure 12 Cutting forces at dierent rake angles (v 6mminac 04mm)


Conflicts of Interest

)e authors declare that there are no conflicts of interestregarding the publication of this paper

Acknowledgments

)is work is supported by the National Natural ScienceFoundation of China (no 51775198) and the Science andTechnology Project of Guangzhou China (201804010182)

References

[1] V Stary L Bacakova J Hornık and V Chmelık ldquoBio-compatibility of the surface layer of pyrolytic graphiterdquo5in Solid Films vol 433 no 1-2 pp 191ndash198 2003

[2] T C Chang S Lee Y K Fuh Y-C Peng and Z-Y LinldquoPCM based heat sinks of paraffinnanoplatelet graphitecomposite for thermal management of IGBTrdquo Applied5ermal Engineering vol 112 pp 1129ndash1136 2017

[3] K Kang S Park A Jo K Lee and H Ju ldquoDevelopment ofultralight and thin bipolar plates using epoxy-carbon fiberprepregs and graphite compositesrdquo International Journal ofHydrogen Energy International Journal of Hydrogen Energyvol 42 no 3 pp 1691ndash1697 2017

[4] M Zeis ldquoDeformation of thin graphite electrodes with highaspect ratio during sinking electrical discharge machiningrdquoCIRP Annals vol 66 no 1 pp 185ndash188 2017

[5] M Masuda Y Kuroshima and Y Chujo ldquo)e machinabilityof sintered carbons based on the correlation between toolwear rate and physical and mechanical propertiesrdquo Wearvol 195 pp 178ndash185 1996

[6] G Cabral P Reis R Polini et al ldquoCutting performance oftime-modulated chemical vapour deposited diamond coatedtool inserts during machining graphiterdquo Diamond and Re-lated Materials vol 15 no 10 pp 1753ndash1758 2006

[7] Z Wan D Yang L Lu J Wu and Y Tang ldquoMechanism ofmaterial removal during orthogonal cutting of graphitepolymer compositesrdquo International Journal of AdvancedManufacturing Technology vol 82 no 9ndash12 pp 1815ndash18212016

[8] C Nath G C Lim and H Y Zheng ldquoInfluence of thematerial removal mechanisms on hole integrity in ultrasonicmachining of structural ceramicsrdquo Ultrasonics vol 52 no 5pp 605ndash613 2012

[9] H Gao Y J Bao and Z M Feng ldquoA study of drilling uni-directional carbonepoxy compositesrdquo International Journalof Abrasive Technology vol 4 no 1 pp 1ndash13 2011

[10] X Wang X Shen G Yang and F Sun ldquoEvaluation of boron-doped-microcrystallinenanocrystal-line diamond compositecoatings in drilling of CFRPrdquo Surface and Coatings Tech-nology vol 330 pp 149ndash162 2017

[11] D Huo C Lin and K Dalgarno ldquoAn experimental in-vestigation on micro machining of fine-grained graphiterdquoInternational Journal of Advanced Manufacturing Technologyvol 72 no 5ndash8 pp 943ndash953 2014

[12] F A Almeida J Sacramento F J Oliveira and R F SilvaldquoMicro- and nano-crystalline CVD diamond coated tools inthe turning of EDM graphiterdquo Surface and Coatings Tech-nology vol 203 no 3-4 pp 271ndash276 2008

[13] L Zhou C Y Wang and Z Qin ldquoTool wear characteristics inhigh-speed milling of graphite using a coated carbide microendmillrdquo Proceedings of the Institution of Mechanical

Engineers Part B Journal of Engineering Manufacturevol 223 no 3 pp 267ndash277 2009

[14] X L Lei L Wang B Shen F Sun and Z Zhang ldquoEffect ofboron-doped diamond interlayer on cutting performance ofdiamond coated micro drills for graphite machiningrdquo Ma-terials vol 6 no 8 pp 3128ndash3138 2013

[15] M Hashimoto K Kanda and T Tsubokawa ldquoReduction ofdiamond-coated cutting tool wear during graphite cuttingrdquoPrecision Engineering vol 51 pp 186ndash189 2018

[16] R B Schroeter R Kratochvil and J D Gomes ldquoHigh-speedfinishing milling of industrial graphite electrodesrdquo Journal ofMaterials Processing Technology vol 179 no 1ndash3 pp 128ndash132 2006

[17] C Y Wang L Zhou H Fu et al ldquoHigh speed milling ofgraphite electrode with endmill of small diameterrdquo ChineseJournal of Mechanical Engineering vol 20 no 4 pp 27ndash312007

[18] L Zhou C Y Wang and Z Qin ldquoInvestigation of chipformation characteristics in orthogonal cutting of graphiterdquoMaterials and Manufacturing Processes vol 24 no 12pp 1365ndash1372 2009

[19] O S Lopez A R Gonzalez and I H Castillo ldquoStatisticalanalysis of surface roughness of machined graphite by meansof CNC millingrdquo Ingenierıa e Investigacion vol 36 no 3pp 89ndash94 2016

[20] Y K Yang M T Chuang and S S Lin ldquoOptimization of drymachining parameters for high-purity graphite in end millingprocess via design of experiments methodsrdquo Journal ofMaterials Processing Technology vol 209 no 9 pp 4395ndash4400 2009

[21] J R Shie ldquoOptimization of dry machining parameters forhigh-purity graphite in end-milling process by artificial neuralnetworks a case studyrdquo Materials and Manufacturing Pro-cesses vol 21 no 8 pp 838ndash845 2006

[22] Y K Yang J R Shie and C H Huang ldquoOptimization of drymachining parameters for high-purity graphite in end-millingprocessrdquo Materials and Manufacturing Processes vol 21no 8 pp 832ndash837 2006

[23] V Bajpai and R K Singh ldquoOrthogonal micro-grooving ofanisotropic pyrolytic carbonrdquo Materials and ManufacturingProcesses vol 26 no 12 pp 1481ndash1493 2011

[24] V Bajpai and R K Singh ldquoBrittle damage and interlaminardecohesion in orthogonal micromachining of pyrolytic car-bonrdquo International Journal of Machine Tools and Manufac-ture vol 64 pp 20ndash30 2013

[25] B Lawn and R Wilshaw ldquoReview indentation fractureprinciples and applicationsrdquo Journal of Materials Sciencevol 10 no 6 pp 1049ndash1081 1975

[26] Z P Wan and Y Tang ldquoBrittlendashductile mode cutting of glassbased on controlling cracks initiation and propagationrdquo In-ternational Journal of Advanced Manufacturing Technologyvol 43 no 11-12 pp 1051ndash1059 2009

[27] B Paul and L Mirandy ldquoImproved fracture criterion forthree-dimensional stress statesrdquo Journal of Engineering Ma-terials and Technology vol 98 no 2 pp 159ndash163 1976


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material and brittle fracture is the main characteristic duringgraphite machining [16] To obtain a good surface nish greateorts have been conducted Wang et al [17] found thata smoother surface could be achieved with a small feed pertooth in the high-speed milling of a graphite electrode eexperimental results presented by Zhou et al [18] showed thatthe surface roughness of the machined surface increasedclearly with the depth of cut increasing in the orthogonalcutting of graphite Huo et al [11] found that the feed rate hasthe most signicant inshyuence on surface roughness and thesurface roughness is not sensitive to cutting speed on themicro-milling of ne-grained graphite e statistical analysisalso showed that the surface roughness decreased with a lowfeed rate [19] Experimental design methods [20] articialneural networks [21] and the gray relational analysis method[22] were used to optimize themachining parameters for high-purity graphite in the endmilling process Additionally Bajpaiand Singh investigated the orthogonal micro-grooving ofanisotropic pyrolytic carbon [23] and established a nite el-ementmodel to understand themechanics ofmaterial removalin the plane of transverse isotropy of pyrolytic carbon [24]

From the above literature survey little work has beenreported on the eect of the tool rake angle on the machinedsurface quality during graphitepolymer composite machiningis paper investigates the inshyuence of the tool rake angle onthe machined surface nish during the orthogonal cutting ofgraphitepolymer composites To reveal the mechanism ofinshyuence of a positive tool rake angle on the machined surfacenish the eective stress eld of the cutting zone was de-termined out by nite element analysis and then the crackinitiation and propagation path in the cutting zone werepredicted based on the eective stress eld e laws of crackinitiation and propagation were veried by edge-indentationexperiments which are eective methods for the study of thematerial removal mechanism during brittle material cutting[6 25 26] In addition the eect of the tool rake angle on thecutting force was investigated

2 Experimental Methodologies

21 Experimental Conditions of Orthogonal Cutting Dryorthogonal cutting experiments were conducted on planer

BC6063B e dimensions of the workpiece are 70mmtimes45mmtimes 5mm A superhard high-speed steel tool with theclearance angle of 10deg and dierent rake angles is used tomachine the workpiece at the cutting speed of 6mmin ecutting thicknesses are 02mm and 04mm A schematic dia-gramof the orthogonal cutting experiments is shown in Figure 1

e graphitepolymer composites used in this study area powder mixture of coke and natural graphite added toa bindere paste is rst homogenized and placed in a moldand then is suciently compacted e material is thenbaked slowly at high temperature e physical and me-chanical properties of the graphitepolymer composites areshown in Table 1

22 Edge-IndentationExperimental Setup e edge-indentationexperiments are conducted using a universal material test-ing machine (CMT5105) A schematic drawing of the edge-indentation experiments is shown in Figure 2 with theindenter positioned on the edge of the graphitepolymercomposite specimen e edge-indentation surface of the spec-imen is polished until no cracks can be observed in order toeliminate the inshyuence of tiny cracks on crack initiation andpropagatione indenter can rotate adaptively to ensure well-distributed pressure on the indentation surface e dimen-sions of the graphitepolymer composite specimen are 70mmtimes45mmtimes 5mm All specimens are indented at the constantspeed of 05mmmin

It can be seen from Figure 2 that the edge indentation issimilar to orthogonal cutting In Figure 2 cs is the rake angleof the indenter hD is the edge-indentation thickness and Pis the normal load imposed on the indenter e indenter issimilar to a cutting tool with the rake angle of cs and clearanceangle of 0deg and hD is the cutting thicknesserefore the lawsof crack initiation and propagation obtained from the edge-indentation experiments can be applied to validate the predictedcrack initiation and propagation rules for the graphitepolymercomposite orthogonal cutting process

3 Effect of Rake Angle on MachinedSurface Finish

Figure 3 shows the machined surface roughness Ra obtained atdierent rake angles for the cutting thicknesses of 02mm and04mm It can be seen from Figure 3 that the surface roughnessRa is largest when the rake angles are 0deg and 5deg and the surfaceroughness Ra decreases gradually with either an increase ordecrease in the rake angle e entire curve can be tted bya parabola e fact that a negative rake angle can reduce thesurface roughness conforms to the long-held notion that thecompressive stresses induced by a negative rake angle canweaken the breaking of the material resulting in improvedsurface qualities However the fact that a positive rake angle canalso reduce the surface roughness and improve the machinedsurface qualities conshyicts with the long-held notion that shyakingdue to tensile stresses induced by a positive rake angle damagesthe machined surface in the machining of brittle materials

Figure 4 shows the surface morphologies machined at dif-ferent rake angles for the cutting thickness of 02mm Due to the

Tool

10deg

5 mm

45 mm

WorkpieceCutting speed

70 mm

Cutting thickness

Figure 1 Schematic diagram of orthogonal cutting experiments










Hardness(shores)




Porosity()

Parameter 19 75 173 1072 159 05

O


Projection A

hD

γs


P A

Indenter


1

2

3

4

5

6

7

Surfa

ce ro

ughn

ess R

a (microm

)



00 10 20 30


(I)

(II)

(III)

(IV)

(V)

5 mm



σeff N σI + σIII( 1113857 + 2


1113969

N 4minusN2( ) (1)


σeff σI (2)


N

2 +σbcσbminus 2

1 +σbcσb

11139701113971

(3)












C

C C

DD

D

D

D

DDD

D

D = 687E = 883

F = 1079 H = 1472C = 491 G = 1276 I = 1668

DD

C

C

C

C

B

B

EE

E

E

E

E

E

E

FF

F

F

F

G

GG

H

HHXI

I

Y

Z

Predictedcrack

c

MPa

1 mm

(a)

D

DD

D

D

D

DD

E = 920C = 511 G = 1329 I = 1737

CC

CC

CC

B

B

E

E

EEE

E

F

F

F

FF

G

G

G

H

H XZ

c

D = 715 F = 1124 H = 1533 MPa

1 mm

I

Y

(b)

D

DDD

DD

D

DDD

E = 927C = 515 G = 1339 I = 1751

CC

C C

CC

CCC

C

BBBB

B

B

C

B AA

BBB

BB B

B

E

EE E E E

E EF

F

F HI I

HH G

G

G

GG

F c

D = 721 F = 1133 H = 1545 MPa

1 mm

(c)





500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)


cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen


cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)



500 mm






6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls












Hardness(shores)




Porosity()

Parameter 19 75 173 1072 159 05

O


Projection A

hD

γs


P A

Indenter


1

2

3

4

5

6

7

Surfa

ce ro

ughn

ess R

a (microm

)



00 10 20 30


(I)

(II)

(III)

(IV)

(V)

5 mm



σeff N σI + σIII( 1113857 + 2


1113969

N 4minusN2( ) (1)


σeff σI (2)


N

2 +σbcσbminus 2

1 +σbcσb

11139701113971

(3)












C

C C

DD

D

D

D

DDD

D

D = 687E = 883

F = 1079 H = 1472C = 491 G = 1276 I = 1668

DD

C

C

C

C

B

B

EE

E

E

E

E

E

E

FF

F

F

F

G

GG

H

HHXI

I

Y

Z

Predictedcrack

c

MPa

1 mm

(a)

D

DD

D

D

D

DD

E = 920C = 511 G = 1329 I = 1737

CC

CC

CC

B

B

E

E

EEE

E

F

F

F

FF

G

G

G

H

H XZ

c

D = 715 F = 1124 H = 1533 MPa

1 mm

I

Y

(b)

D

DDD

DD

D

DDD

E = 927C = 515 G = 1339 I = 1751

CC

C C

CC

CCC

C

BBBB

B

B

C

B AA

BBB

BB B

B

E

EE E E E

E EF

F

F HI I

HH G

G

G

GG

F c

D = 721 F = 1133 H = 1545 MPa

1 mm

(c)





500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)


cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen


cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)



500 mm






6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




σeff N σI + σIII( 1113857 + 2


1113969

N 4minusN2( ) (1)


σeff σI (2)


N

2 +σbcσbminus 2

1 +σbcσb

11139701113971

(3)












C

C C

DD

D

D

D

DDD

D

D = 687E = 883

F = 1079 H = 1472C = 491 G = 1276 I = 1668

DD

C

C

C

C

B

B

EE

E

E

E

E

E

E

FF

F

F

F

G

GG

H

HHXI

I

Y

Z

Predictedcrack

c

MPa

1 mm

(a)

D

DD

D

D

D

DD

E = 920C = 511 G = 1329 I = 1737

CC

CC

CC

B

B

E

E

EEE

E

F

F

F

FF

G

G

G

H

H XZ

c

D = 715 F = 1124 H = 1533 MPa

1 mm

I

Y

(b)

D

DDD

DD

D

DDD

E = 927C = 515 G = 1339 I = 1751

CC

C C

CC

CCC

C

BBBB

B

B

C

B AA

BBB

BB B

B

E

EE E E E

E EF

F

F HI I

HH G

G

G

GG

F c

D = 721 F = 1133 H = 1545 MPa

1 mm

(c)





500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)


cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen


cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)



500 mm






6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







C

C C

DD

D

D

D

DDD

D

D = 687E = 883

F = 1079 H = 1472C = 491 G = 1276 I = 1668

DD

C

C

C

C

B

B

EE

E

E

E

E

E

E

FF

F

F

F

G

GG

H

HHXI

I

Y

Z

Predictedcrack

c

MPa

1 mm

(a)

D

DD

D

D

D

DD

E = 920C = 511 G = 1329 I = 1737

CC

CC

CC

B

B

E

E

EEE

E

F

F

F

FF

G

G

G

H

H XZ

c

D = 715 F = 1124 H = 1533 MPa

1 mm

I

Y

(b)

D

DDD

DD

D

DDD

E = 927C = 515 G = 1339 I = 1751

CC

C C

CC

CCC

C

BBBB

B

B

C

B AA

BBB

BB B

B

E

EE E E E

E EF

F

F HI I

HH G

G

G

GG

F c

D = 721 F = 1133 H = 1545 MPa

1 mm

(c)





500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)


cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen


cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)



500 mm






6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






500 mm

CrackNotch

(a)

500 mm

(b)

500 mm

(c)


cdθ

hDcw

Crack

Pγs

φ

Indenter

Specimen


cwcd

0

2

4

6

8

10

12

14

16

18

Con

cavi

ty w

idth

and

dept

h (m

m)



500 mm






6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls







6 Conclusions





Notations


Data Availability


0

5

10

15

20

25

30

Initi

al an

gle (

deg)



FHFV

0

20

40

60

80

100

120

140

160

180

Cutti

ng fo

rce (

N)






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Acknowledgments


References
































Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls






Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Rake Angle Effect on a Machined Surface in Orthogonal Cutting of Graphite… · 2019. 7. 30. ·...

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Transcript of Rake Angle Effect on a Machined Surface in Orthogonal Cutting of Graphite… · 2019. 7. 30. ·...