CIRP Journal of Manufacturing Science and Technology 7 (2014) 264–273

Effect of cutting edge preparation of coated tools on their performancein milling various materials

K.D. Bouzakis a,b,*, E. Bouzakis a,b, S. Kombogiannis a,b, S. Makrimallakis a,b,G. Skordaris a,b, N. Michailidis a,b, P. Charalampous a,b, R. Paraskevopoulou a,R. M’Saoubi c, J.C. Aurich d, F. Barthelma e, D. Biermann f, B. Denkena g, D. Dimitrov h,S. Engin i, B. Karpuschewski j, F. Klocke k,b, T. Ozel l, G. Poulachon m, J. Rech n, V. Schulze o,L. Settineri p, A. Srivastava q, K. Wegener r, E. Uhlmann s, P. Zeman t

a Laboratory for Machine Tools and Manufacturing Engineering, Aristoteles University of Thessaloniki, Thessaloniki, Greeceb Fraunhofer Project Center Coatings in Manufacturing, Centre for Research and Technology Hellas, Thessaloniki, Greece, and Fraunhofer Institute for

Production Technology, Aachen, Germanyc R&D Materials and Technology Development, Seco Tools AB, Fagersta, Swedend Institute for Manufacturing Technology and Production Systems, University of Kaiserslautern, Kaiserslautern, Germanye GFE – Gesellschaft fur Fertigungstechnik und Entwicklung Schmalkalden e.V., Schmalkalden, Germanyf Institute of Machining Technology, Technical University Dortmund, Dortmund, Germanyg Institute of Production Engineering and Machine Tools, Leibniz Universitat Hannover, Hannover, Germanyh Rapid Product Development Laboratory, Stellenbosch University, Stellenbosch, South Africai Pratt & Whitney Canada Corp., Longueuil, Quebec, Canadaj Institute of Manufacturing Technology and Quality Management, University of Magdeburg, Magdeburg, Germanyk Laboratory for Machine Tools and Production Engineering (WZL), RWTH Aachen University, Aachen, Germanyl Rutgers State University of New Jersey, Piscataway, NJ, United Statesm Arts et Metiers ParisTech, LaBoMaP, Cluny, Francen Laboratory for Tribology and Systems Dynamics, ENISE, Saint-Etienne, Franceo wbk Institute of Production Science, Karlsruhe Institute of Technology, Karlsruhe, Germanyp Department of Management and Production Engineering, Politecnico di Torino, Turin, Italyq TechSolve, Inc., Cincinnati, OH, United Statesr inspire AG, Zurich, Switzerlands Institute for Machine Tools and Factory Management, Technische Universitat Berlin, Berlin, Germanyt Research Centre for Manufacturing Technology, Czech Technical University in Prague, Czech Republic

A R T I C L E I N F O

Article history:

Available online 2 June 2014

Keywords:

Cutting

Coatings

Cutting edge preparation

A B S T R A C T

The cutting edges of coated tools are commonly treated in separate production steps during tool

manufacturing. Various methods can be employed, focusing on the cutting edge strengthening by its

rounding or by more complicated geometries including chamfer and optimized tool wedge radius and

angles. The efficiency of diverse cutting edge preparations on the wear behaviour of coated tools, in

milling different materials, was investigated in the framework of a cooperative project of the Scientific

Committee ‘‘Cutting’’ of the International Academy for Production Engineering (CIRP). In this activity

twenty academic and industrial partners were involved according to a predefined project plan.

� 2014 CIRP.

Contents lists available at ScienceDirect

CIRP Journal of Manufacturing Science and Technology

jou r nal h o mep age: w ww.els evier . co m/lo c ate /c i rp j

Introduction

The positive effect of an appropriate cutting edge geometry onthe cutting performance of coated tools, has been recorded in

* Corresponding author at: Laboratory for Machine Tools and Manufacturing

Engineering, Aristoteles University of Thessaloniki, Thessaloniki, Greece.

Tel.: +30 2310996021; fax: +30 2310996059.

E-mail address: bouzakis@eng.auth.gr (K.D. Bouzakis).

http://dx.doi.org/10.1016/j.cirpj.2014.05.003

1755-5817/� 2014 CIRP.

several publications [1–5]. In this context, the tool wedgerounding affects significantly the developed mechanical andthermal loads during the material removal and thus, the cuttingperformance of the applied tools.

Related examples when milling Inconel 718 are demonstratedin Fig. 1a, whereas the developed stress fields in the cutting edgeregion of coated tools at different edge radii are demonstrated [6].The stress fields were calculated by the DEFORM and ANSYSsoftware packages, as described in [6,7]. Comparisons of the

Fig. 1. Stress distribution in the cutting wedge region at various: (a) cutting edge

radii (b) cutting edge radii, with chamfer on the rake.

Fig. 2. Comparison of the flank wear development at variously-treated cutting

edges.

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developed maximum stresses in the substrate and coating withtheir yield stresses respectively, are also shown in Fig. 1a. In theseexamples, simulating orthogonal cutting, no chamfer betweenthe tool wedge roundness and rake exists. The reduction of thesubstrate and coating loads using a larger cutting edge radius isobvious.

However, even at a cutting edge radius of 20 mm, which iscommonly used in commercial industrial applications, thedeveloped maximum stress, in both substrate and coating, exceedthe corresponding yield stresses respectively. To overcome thisproblem, the cutting wedge can be further strengthened byintroducing an inclined chamfer, as exhibited in Fig. 1b. Theapplication of this chamfer, along with increased edge radii, furtherdiminishes the developed stresses. In the case of the cutting edgeradius of 20 mm, combined with a chamfer inclined at 208, thedeveloped maximum stresses are comparably the lowest andthe yield stresses of the coating and substrate are not exceeded(see Fig. 1b).

Beside the cutting edge geometry, the tool wedge roundingmethods may affect significantly the wear behaviour of a coatedtool [1,8–10]. An example of improving the cutting performance ofcoated cemented carbide inserts, when their cutting edges arehoned and additionally micro-blasted, is illustrated in Fig. 2. Aspreviously described, the increase of the wedge radius diminishesthe developed stresses in the film during the material removalprocess. However, the tool life gain is significantly higher in thecase of the honed and additionally appropriately micro-blastedcutting edge, due to the enhanced coating adhesion, as explained in[8].

The aim of the conducted cooperative work was to study theefficiency of various cutting edge rounding methods as well as theeffects of these treatments on the wear behaviour of coated toolswhen milling characteristic metallic materials. Taking into account

the results presented in Fig. 1, concerning the effect of the wedgegeometry on the tool loads, chamfered cutting edges at aninclination angle of 208 were employed. The initial cutting edgeradius was chosen to be approximately 10 mm. This radius had tobe further increased by diverse tool wedge rounding methods fordetecting their potential effect on the coated tool cuttingperformance.

Layout of the investigations and experimental details

Cutting conditions adjustment when milling various materials

As test materials, hardened steel 42CrMo4, stainless steel 304Land, the difficult to cut Inconel 718 and Ti4Al6V were selected.These materials are commonly used in many industrial applica-tions. With respect to the effect of the developed thermal andmechanical cutting loads as well as of the material properties onthe tool wear evolution, the milling conditions had to beappropriately adjusted. In this way, it was intended to havecomparable mechanical and thermal loads during cutting and,moreover, moderate tool wear evolution for enabling its accuraterecoding.

The thermal loads of the cutting edge were approximated by theDEFORM software package, simulating orthogonal cutting. Inmilling hardened steel 42CrMo4 and Inconel 718 at the cuttingconditions shown at the bottom of Fig. 3, the developed cuttingtemperatures in the tool are lower than 350 8C (see Fig. 3a). Themaximum cutting temperature develops at the chamfer position 1.However, the highest mechanically-loaded transient region fromthe flank to the chamfer (position 2) is less thermally affected. Themaximum cutting temperature in this tool area is less than 250 8Cin both material cases. Moreover, the temperature fields moni-tored in Fig. 3b demonstrate the significantly higher temperatures

Fig. 3. (a) Cutting temperatures at characteristic positions of the cutting edge region during chip formation. (b) Temperature fields in the tool and workpiece.

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in the workpiece, compared to the developed ones in the coating.The latter issue will be further discussed in a next paragraph. Byconducting further FEM calculations in milling stainless steel 304Land Ti6Al4V, the cutting conditions were adapted appropriately forachieving similar cutting edge thermal loads, as in milling42CrMo4 and Inconel 718.

Since, even if the tool mechanical and thermal loads remainalmost on comparable levels, the tool wear in the test materialcases develops variously, due to the actual material propertiesduring the chip formation and flow. For example, according to the42CrMo4 steel properties, cutting temperatures shown in Fig. 3b ofca. 864 8C lead to crystalline structure transformations, which inturn improve the material machinability. In contrast, the badmachinability of Inconel 718 is not enhanced, since the propertiesof this heat resistant material remain almost unaffected at cuttingtemperatures of about 948 8C (see Fig. 3b). Additionally, hardeningeffects are released during the chip formation, which furtherdeteriorate the material machinability. In this way, it wasnecessary to conduct some preliminary milling investigations,for checking, whether at the milling conditions monitored in Fig. 4athe wear progress was sufficiently moderate and hence, itsaccurately recording was possible.

Applying the same finite elements analysis (FEA) methods forattaining the results presented in Fig. 1, the cutting conditionswere appropriately adjusted for achieving mechanical tool loadsat the same order of magnitude with these ones exhibited inFig. 1b. The cutting conditions, determined in this way, aredisplayed in Fig. 4a. The materials employed by the participants

who conducted milling tests at these conditions are monitored inFig. 4b.

Fig. 5 demonstrates the results of these preliminary tests. At thecutting speed of 250 m/min and the cutting temperature ofapproximately 864 8C (see Fig. 3b), the martensitic structure ofhardened steel 42CrMo4 transforms into a softer austenitic one,thus the abrasion between chip and rake diminishes. In the case ofthe austenitic stainless steel 304L, at the cutting speed of 300 m/min, the workpiece material deforms at higher strain rates, themartensitic transformation is decreased and the machinabilityimproved [11]. This happens because austenitic steels, whensubjected to very severe deformation at high strain rates result incopious amounts of dislocations that may hinder the motion of theglissade dislocations and thus the austenitic transformation [12–14]. Finally the heat resistant Ti6Al4V and Inconel 718 maintaintheir properties at the developed cutting temperatures in theworkpiece, as for example at the cutting temperature of 948 8C (seeFig. 3b). Additionally, hardening effects are released when thesematerials are deformed during the cutting process, furtherdeteriorating their machinability. In this way, abrasion mecha-nisms accelerate crucially the tool wear evolution compared to304L and 42CrMo4, practically at the same level of thermal andmechanical tool loads. This can be clearly observed in Fig. 5. Theobtained number of cuts, up to a flank wear land width of 0.15 mmin milling Inconel 718, amounts to approximately 12,000 cutswhereas in 42CrMo4 it is about 78,000. It is worth mentioning, thatat the applied cutting speeds when milling Inconel and Ti6Al4V, nomicroweldings with the coated tool surfaces were observed. Based

Fig. 4. (a) Applied milling conditions in the various material cases. (b) Employed

materials in the conducted cutting tests by the individual participants. Fig. 6. (a) Applied cutting edge treatment methods, (b) participants who conducted

cutting edge treatments.

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on these results, even in the Inconel 718 and Ti6Al4V difficult-to-cut material cases, the tool wear evolution is sufficiently moderateand thus it can be accurately recorded.

Experimental details

For the purposes of the described investigations, thousandcemented carbide inserts were supplied and coated by the

Fig. 5. Wear evolution on the coated tools.

participating company Seco Tools AB. Prior to the coatingdeposition diverse preparation methods were applied by thepartners. More specifically, portions of the cemented carbideinserts were treated by abrasive blasting AB, abrasive flowmachining AFM, abrasive magneto machining AMM, abrasiveslurry AS, brushing B, dragging D and laser machining LM. Essentialinformation concerning these methods is exhibited in Fig. 6a. Thecorresponding experimental arrangements will be further de-scribed in the next section. Fig. 6b displays which methods werecarried out by the individual participants.

The data of the cutting inserts and the cutting edge geometryare shown in Fig. 7a. For describing cutting edge geometry, whitelight scans along the cutting edges of variously treated cuttinginserts were conducted. In this way, successive cross sections ofthe cutting edges were monitored and with their aid, thecorresponding cutting edge radii as well as the average value rof the cutting edge roundness were estimated. By the appliedpreparation methods, the initial cutting edge radius of approxi-mately 10 mm was increased at about 10 mm. Fig. 7b demonstratesthe indicative workpiece geometry applied in the milling tests aswell as the corresponding tool path and the undeformed chipgeometry. The cutting conditions and the chip geometry wereappropriately selected depending on the employed test materialproperties, as described in the previous section.

The inserts were subsequently coated with a TiAlN coating anda thin superficial TiN layer. The film deposition was conducted bythe participating company Seco Tools AB, using a Sulzer MetaplasMZR323 industrial cathodic arc evaporation system at a back-ground pressure of about 10�3 Pa. Prior to the deposition theinserts were sputter etched in situ by Ar ions. The deposition wasthen conducted using 63 mm diameter composite TiAl cathodes ata N2 pressure of 4.5 Pa, temperature of about 450 8C, arc current of80 A and substrate bias voltage of �30 V. The roughness values of

Fig. 7. (a) Cutting edge geometry, (b) workpiece and chip geometries.

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the coated surfaces are slightly larger than the corresponding onesof the applied cemented carbide substrates.

Fig. 8a illustrates a cross section of the deposited coating on thecemented carbide substrate. The TiAlN coating has a compositionof Ti 34% and Al 66% (at) and a thickness of approximately 2.2 mm.

Fig. 8. (a) Applied TiAlN/TiN coating’s structure, (b) strength properties of the

deposited films and of the substrate.

The superficial thin TiN layer is about 0.4 mm thick. Themicrostructure is coarse-grained columnar and the crystalstructure is a purely NaCl solid solution. Fig. 8b exhibits theRockwell C imprint on the deposited TiN/TiAlN coating. Theperimeter of the displayed imprint is without cracks anddetachments, indicating an adequate adhesion. The adequateadhesion was further verified by inclined impact tests [15].

The mechanical properties of the applied cutting materials wereevaluated by nanoindentations and FEM supported calculations[16]. The chart of Fig. 8b shows the determined stress-strain curvesfor both layers and for the substrate. Taking into account of thecalculated data, the yield strength amounts to SY = 5.2 GPa for theTiAlN layer and to 5.1 GPa for the TiN superficial one. As expected,the cemented carbide substrate shows a lower yield strength(SY = 3.4 GPa). These data were considered in determining thestress fields introduced in Fig. 1.

The effect of the applied methods on the coated tools cuttingperformance was evaluated with the aid of milling investigationsemploying the mentioned materials. By the conducted cuttingedge treatments, the initial average cutting edge radius of ca.10 mm was increased. Almost in all treatment cases, a radius ofroughly 20 mm was attained. Thereby, a reduction of the developedstresses in the cutting edge region during the material removal wasachieved. As it will be further explained in Results and discussion,this reduction is variously intensive in the investigated workpiecematerial cases, due to their different mechanical strength thermaland crystalline properties, which strongly affect the chip formationmechanisms and the developed stresses and temperatures in thecoating and its substrate.

Applied cutting edge treatment’s methods

To check the effect of the cutting edge treatment for increasingits roundness, diverse methods were carried out by the individualparticipants prior to the coating deposition, as already described inFig. 6a and b.

Abrasive blasting is a commonly applied method for roundingcutting tool’s edges (see Fig. 9a [17]). Thus, abrasive particles, as forexample aluminium or zirconium oxides, are employed formodifying the surface roughness and roundness of the cuttingedges. The used particles are accelerated with the aid of asupporting medium against the cutting tools. For treating edges ofcomplex cutting tools and maintaining high process accuracy, theblasting nozzle is usually guided by a robot device. In the case ofabrasive flow machining, the tools are exposed to abrasion within acontrolled flow field, as exhibited in Fig. 9b. This arrangement issuitable for achieving high surface quality on inner, difficult-toaccess contours and complex geometrical details [18]. Moreover,during abrasive magneto machining, a magnetic field is exploitedto control the abrasive medium kinematic. The layout of thisprocess is illustrated in Fig. 9c. This method is also appropriate forreproducible cutting edge treatments [2,19].

Abrasive slurry and dragging are similar concerning theworkpiece kinematics and the manipulation of the loose particles(see Fig. 10a and b). The workpieces, i.e. the cutting tools to berounded, are rotated within an abrasive liquid or dragged througha mixture of diamond and organic particles respectively.

In the case of brushing, the cutting tools are processed byappropriate brushes. Fig. 11 illustrates a device for the brushing ofcutting inserts. The motion of the brushes is usually numericallycontrolled. The needles of the brushes could be of differentmaterials potentially with glued abrasive grains on their surfaces.

The described treatments induce compressive superficialresidual stresses in the cutting tool surfaces [20,21]. After thecoating deposition, due to annealing mechanisms activation in thevacuum chamber at the process temperature, all substrates

Fig. 10. Cutting edge preparation by: (a) abrasive slurry, (b) dragging.

Fig. 11. Cutting edge treatment by brushing.

Fig. 9. Cutting edge rounding by: (a) abrasive blasting, (b) abrasive flow machining,

(c) abrasive magneto machining.

Fig. 12. Cutting edge shaping by laser machining.

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possess lower residual stresses and consequently mechanicalproperties [20,21].

Finally, Fig. 12 exhibits the layout of laser machining forshaping the cutting tool’s edges. By laser machining, a reproduciblecutting edge micro-geometry can be achieved. However, the insertsurfaces may be thermally affected [3,21,22]. In this way, amongstother effects, due to the melting of the Co-binder in micro areas,WC grains can be covered by cobalt, thus deteriorating the filmadhesion. Moreover, according to the applied conditions during thelaser machining, WC carbides may be transformed, for instance toW3C ones which are comparably softer [20,22,23]. In this way, thecoated tool’s cutting performance may be reduced.

The attained cutting edge radii, after the conduct of theintroduced treatments, are displayed in Fig. 13. In the conductedprocesses, the employed abrasive grains had an average diameterless than 15 mm for achieving a uniform and low roughness on alltreated inserts. This target was also fulfilled by adjustingappropriate process conditions as well. The increase of theroughnesses Rt and Ra of the untreated inserts, shown in Fig. 7awas always less than 40%.

In this way, by the conducted wedge rounding methods, auniform carbide revelation from the cobalt binding phase wasreached. This ensures their sufficient holding on the substratesurfaces and a cutting edge free from microbreakages as well. Inaddition, it was attempted to hold the manufacturing time to a

reasonable level. The largest cutting edge radius was attained bybrushing followed by abrasive flow machining as well as by lasermachining. Lower cutting edge radius increases were achieved byabrasive blasting, abrasive magneto machining and abrasive

Fig. 13. Attained cutting edge radii by the various cutting edge treatments.

Fig. 15. Determination of the number of cuts NC associated with various levels of

flank wear land.

Fig. 14. Effect of the cutting edge radius on the maximum equivalent stress.

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slurry. The treatment by dragging led to a restricted tool wedgeradius growth. The achievement of larger radii in the cases ofabrasive slurry and dragging would have required unacceptablylong process times.

Results and discussion

The coated inserts were distributed to the participants, in thedescribed cooperative work, for carrying out the cutting tests. Forthe applied cutting conditions (see Fig. 4a), the tool temperaturesin milling all test materials were under 350 8C. These temperaturesare considered to be low for affecting the coated cemented carbideinserts’ wear. Hence, besides the test material properties, thedeveloped mechanical loads on the cutting wedge play animportant role for the tool wear evolution.

For determining the cutting edge mechanical loads, the finiteelements analysis (FEA) supported methods described in [6] wereemployed. Hereupon, the cutting forces and chip contact lengthsare calculated by the DEFORM software. Moreover, the stressesdeveloped in the cutting wedge are determined using a FEMsimulation of the material removal process by the ANSYS softwarepackage. According to the obtained results displayed in Fig. 14, inmilling hardened steel 42CrMo4 and stainless steel 304L, themaximum stresses at the same cutting edge radius are alwayslower compared to those when cutting Inconel 718 or Ti6Al4V. Inthe case of both steels, the developed stresses in the coating and

Fig. 16. Achieved number of cuts when using variously rounded cutting inserts in milling 42CrMo4 QT.

Fig. 17. Cutting performance of variously rounded cutting inserts in milling

42CrMo4 QT.

Fig. 19. Cutting performance of rounded cutting inserts by different methods in

milling AISI 304L.

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substrate are less than the corresponding yield stresses. Thus, thecutting edge radius enlargement may be more beneficial in millingInconel 718 and Ti6Al4V for increasing the coated tool cuttingperformance compared to the steel materials, because in the lattercases the coating and the substrate are comparably less loaded.

Since it was not possible that all participants have the samematerial supplier, reference cutting tests have been conducted. Inthese investigations coated tools with untreated edges wereemployed. Fig. 15 illustrates the wear evolution of suchinvestigations, when milling Ti6Al4V by a certain participant.Taking into account, the results of four tests, a mean wear curvewas calculated, associated with this material of this partner. Thiscurve was used as a reference when variously pre-treated coatedtools were employed in milling Ti6Al4V by this participant. Forfacilitating comparisons, the resultant number of cuts up to a flankwear land VB of 0.05 mm, 0.10 mm and 0.15 mm were determined,as explained in the diagram of Fig. 15. The flank wear land widthwas monitored by means of optical or scanning electronmicroscopy.

Results attained by the participants, when coated and variouslypre-treated cemented carbide inserts are used in milling hardenedsteel 42CrMo4, are demonstrated in Fig. 16. The chart shows theachieved number of cuts by the various partners up to the threepreviously mentioned flank wear land VB levels.

The first column indicates the number of cuts, achieved byuntreated tools in each partner case, followed by those obtained byrounded coated tools via different methods.

Fig. 18. Achieved number of cuts by the participants via va

Since the workpiece materials were provided by differentsuppliers and diverse machine tools were employed by theparticipants, large deviations in the conducted number of cutsup to various flank wear land levels occurred. More specifically, theresults of the participants (2), (3) and (5) converge sufficiently,whereas those of participant (1) are significantly worse and ofparticipants (4) and (12) better. In the case of the latter participant,it was necessary to increase the cutting speed up to 350 m/min forattaining comparable results, concerning the tool wear evolution.

For investigating the effect of the various cutting edge roundingmethods on the performance of the coated tools, the achievednumber of cuts NC by each partner, up to a flank wear land VB of0.15 mm was considered as reference and set to 100%. Theobtained results by each participant via variously pre-treated tools,were then calculated as a percentage of this reference value (seeFig. 17). It is obvious, in the material case of hardened steel42CrMo4, by all applied cutting edge preparation methods, onaverage negligible cutting performance improvement wasachieved.

A potential reason for this behaviour was already described inFig. 14. The cutting edges are not overloaded in the cutting edgeradii range between 10 mm and 20 mm. Thus, no significant cuttingperformance improvement is expected via the augmentation of thecutting edge roundness. Besides the treatment of the cutting edgesby laser machining can lead to a deterioration of the cuttingperformance, as already mentioned in Applied cutting edgetreatment’s methods, due to potential film adhesion deteriorationand WC carbides transformation to softer ones.

riously pre-treated cutting inserts in milling AISI 304L.

Fig. 20. Obtained number of cuts, when using variously treated cutting inserts in milling Inconel 718.

Fig. 21. Cutting performance in milling Inconel 718 of cutting inserts rounded by

diverse methods.

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In the case of milling stainless steel 304L, seven partners wereinvolved. The achieved numbers of cuts in the conductedinvestigations by the individual participants in this material casealso varied significantly, as shown in Figs. 18 and 19. In addition,the contribution of the various cutting edge treatments in

Fig. 22. Number of cuts achieved by the participants via d

enhancing the coated tool cutting performance can be judged asmarginal. The attained tool lives are generally similar, to those ofthe reference tools. The reasons for this behaviour may be similaras in the case of 42CrMo4. The tool mechanical loads are notaffected significantly by the cutting edge radius increase in therange of 10 mm to 20 mm, as already explained in Fig. 14. Lasermachining of the cutting edges accelerates the wear evolution, asalso found in the case of 42CrMo4.

On the contrary, when machining the difficult-to-cut materialsInconel 718 and Ti6Al4V, the pre-treated coated inserts showsuperior performance compared to the untreated ones. Fig. 20illustrates the performance of the variously pre-treated cuttingedges when milling Inconel 718. In most participants’ cases, theachieved numbers of cuts are systematically higher compared tothose in milling by untreated tools. Almost all cutting edgepreparation methods increase the cutting performance comparedto the untreated tools, as exhibited in Fig. 21.

Finally, Fig. 22 displays the determined numbers of cuts by thesix partners involved in milling Ti6Al4V investigations. Thepositive effect of the cutting edge radius augmentation is visible.In the majority of the conducted tests, the cutting performance ofthe pre-treated tools is comparable to the corresponding ones ofthe untreated inserts or significantly better, as demonstrated inFig. 23. The reasons for this behaviour are similar as in the case of

ifferently rounded cutting inserts in milling Ti6Al4V.

Fig. 23. Cutting performance in milling Ti6Al4V via cutting inserts rounded by

various methods.

Fig. 24. Efficiency of the applied preparation methods for increasing the cutting

performance.

K.D. Bouzakis et al. / CIRP Journal of Manufacturing Science and Technology 7 (2014) 264–273 273

Inconel 718, i.e. by increasing the cutting edge radius, the cuttingloads are drastically diminished.

Conclusions

An overview concerning the effect of the applied cutting edgerounding methods on the cutting performance of coated tools inmilling various materials is displayed in Fig. 24. The evaluated datacorrespond to the average of the attained tool performances perpre-treatment and workpiece material monitored in Figs. 17, 19, 21and 23. In milling Inconel 718 and Ti6Al4V a cutting performanceimprovement was obtained almost by all edge preparations, since asignificant cutting edge load reduction by increasing the wedgeradius develops. Hence, it is recommended to pay attention toappropriate tool wedge geometry in milling these materials, byapplying large cutting edge radii and chamfer on the rake.

In contrast, the contribution of the cutting edge preparations inmilling 42CrMo4, as well as, 304L was marginal. In the latter twomaterial cases, the loads in the cutting edge region of the untreatedtools were moderate. Thus, no crucial cutting performanceimprovement by increasing the cutting edge radius was achieved.The process conditions in the introduced rounding methods wereappropriately adjusted for achieving a restricted increase of theinserts’ roughness, thus ensuring sufficient carbide holding by thebinding phase and a cutting edge without micro breakages as well.It is worth mentioning, that the introduced tool rounding methodsattain a prescribed cutting edge radius for a different manufactur-ing cost.

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