Drilling Burr Minimization by Changing Drill Geometry

materials

Article Drilling Burr Minimization by Changing Drill Geometry

Emilia Franczyk * , Łukasz Slusarczyk´ and Wojciech Z˛ebala Production Engineering Institute, Mechanical Faculty, Cracow University of Technology, Al. Jana Pawła II 37, 31-864 Kraków, Poland; [email protected] (Ł.S.);´ [email protected] (W.Z.) * Correspondence: [email protected]; Tel.: +48-12-374-32-45

Received: 6 May 2020; Accepted: 16 July 2020; Published: 18 July 2020

Abstract: This article presents an attempt to solve the problem of the formation of burrs and drilling caps in the process of drilling in difficult-to-cut materials, specifically in the titanium alloy Ti-6Al-4V. In order to eliminate these phenomena, a chamfer of specific length and angle was made on FANAR drill’s margin. Taguchi and ANOVA methods were used to plan and analyze the experiment aimed at determining the optimal geometry of the modified drill. Chamfer with a length of 2 mm and an angle of 10◦ was selected. In the next stage of research, the values of cutting forces and burr heights obtained during drilling with the original and modified drill were compared for three different feed rate values. It turned out that the introduced changes significantly reduced both the axial cutting force (22–23%) and the height of burrs (10–22%) and caused the complete elimination of the presence of drilling caps. Additionally, a positive correlation between the cutting force and the burr size was found.

Keywords: burrs; deburring; titanium alloy; drilling; cutting forces

1. Introduction Rapid development of industry entails the need to use new types of materials and to improve the methods of their processing. Due to their specific properties, titanium alloys, especially Ti-6Al-4V alloy, are becoming more and more popular. Their most important features are good corrosion resistance, biocompatibility and great strength to weight ratio. Due to these properties, they are used, for example, in aviation, chemical, automotive, military and space industries, as well as in medicine (implantology) [1,2]. On the other hand, such materials have a significant disadvantage—their processing causes many difficulties. This is due to their very good mechanical properties, low thermal conductivity and strong chemical reactivity. During cutting, high temperatures, vibrations, friction and high mechanical loads appear on both the workpiece and the tool [1]. Due to the occurrence of high temperatures and friction forces in the machining process, tools wear quickly [3]. Saketi et al. demonstrated that complex physical and chemical mechanisms of tool wear exist while drilling in Ti-6Al-4V, and that they may vary depending on the cutting parameters [4]. In order to ensure the desired quality of items manufactured from such materials, proper selection of process parameters and the use of appropriate tools are required. This also applies to drilling processes. One of the problems that arise during such processes, also related to titanium alloys, is the phenomenon of burr formation on workpiece surfaces. The ISO-13715 standard defines a burr as the deviation outside the ideal geometrical shape of an edge. Their formation is associated with the occurrence of plastic deformations present in the area where the tool enters or leaves the workpiece [5,6]. There are a number of studies on phenomena related to burr formation. Abdelhafeez et al. [7] showed that parameters such as feed and cutting speed have a significant impact on the size of burrs in the drilling process. Patil et al. [5] also demonstrated the influence of feed and cutting speed, as well as the

Materials 2020, 13, 3207; doi:10.3390/ma13143207 www.mdpi.com/journal/materials Materials 2020, 13, 3207 2 of 12 tool geometry, and exposed the interactions between these factors. Dornfeld et al. [6] indicated that drill geometry (helix angle, split point vs. helical point, lip relief angle, point angle) has a significant impact on height and thickness of burrs generated during drilling. Bahce et al. [8] showed that the burr height is influenced by the shape of the workpiece output surface. Nithin et al. [9] highlighted the impact of cooling conditions (dry/wet drilling) and drilling aspect ratio. The impact of the type of cooling was also demonstrated by Biermann et al. [10]. Based on the research done in CFRP/titanium/aluminum stacks, Rimpault et al. [11] showed that the size of burrs also depends on the level of tool wear. Joy et al. [3] proved that, depending on the configuration of cutting parameters (cutting speed, feed, temperature), different values of cutting forces are obtained in the process. As noted by Rimpault et al. [11], there is a correlation between the values of these forces and the size of burrs formed. Analytical model of burr formation in Ti-6Al-4V alloy and its experimental verification was already presented in great detail by Rana et al. [12]. Another model (specific for high-speed microdrilling) was developed by Mittal et al. [13]. The presence of burrs on the edges of objects is a very unfavorable phenomenon. It may hinder or completely prevent the subsequent assembly of manufactured elements, cause damage to neighboring parts or lead to personal injury. Abdelhafeez et al. [14] also proved that the presence of burrs on the edges of drilled holes affects the fatigue strength of components made of Ti-6Al-4V alloy. Thus, problems caused by the presence of burrs force manufacturers to take appropriate action. One of the common solutions is the use of additional deburring operations. This is inseparably connected with the extended cycle time, the use of additional tools and the increased amount of labor. As a result, production efficiency decreases while its costs increase. Therefore, it seems that the method of minimizing the phenomenon of burr formation during the drilling process would be a better solution. Although it is not possible to completely avoid burrs, their size can be minimalized by process optimization. Various methods have been developed in order to control the size of burrs and to remove them without the use of additional operations. The most common method is to optimize the process by appropriate selection of the drilling parameters, the correct choice of the tool material and geometry and the control of its wear. Drilling burr control charts (DBCCs), used to predict and control the size of burrs depending on various factors, presented for example by Min et al. [15] and Kim et al. [16], may also be useful in this context. The possibility of reducing the size of burrs by implementing ultrasonic vibrations in the drilling process was proved by Chang et al. [17]. Mondal et al. [18] also showed that the size of burrs can be reduced by using support element under the workpiece, and by making pre-drilled holes on the tool’s exit side of the processed material. According to Mahdy [19], making preliminary, chamfered holes (pre-drilling and pre-chamfering) may also be a good solution. Rimpault et al. [11] suggested controlling the size of burrs by monitoring the value of the drilling force and torque. The drilling process is inseparably associated with occurrence of burrs, and in some cases also with the formation of drilling caps. This phenomenon has been described by several researchers [5,6,20]. It has been shown that the formation of drilling caps is related to the plastic deformations present at the exit edge of the drilled hole. Depending on the degree of ductility of the workpiece, feed and geometry of the tool (especially the point angle), the material may remain unbroken even if some part of the drill has already crossed the exit plane. As the drill advances, stress in the material increases until the occurrence of a fracture. If the loss of material integrity occurs around the tip of the drill, a large, irregular burr appears. However, if the material is torn around the edge of the resulting hole, the burr is smaller, but the drilling cap is formed [5]. The diagram of this process is presented in Figure1. Materials 2020, 13, 3207 3 of 12

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FigureFigure 1. 1. BurrBurr and and drilling drilling cap cap formation formation scheme. scheme.

NotNot only only the the shape shape and and size size of of the the drilling drilling cap cap depends depends on on the the factors factors mentioned mentioned above, above, but but also also thethe burr. burr. As As shown shown in in [20], [20 ],burr burr width width is isrelated related to tothe the thickness thickness of the of the cap. cap. If drilling If drilling cap capdoes does not fallnot off fall during off during the drilling the drilling process, process, it must itbe mustremoved be removed in an additional in an additional operation. operation.This is particularly This is problematicparticularly in problematic case of intersecting in case of holes intersecting or interior holes cavities or interior [6]. The cavities optimal [6]. solution The optimal to this solution problem to wouldthis problem be to develop would be a drilling to develop method a drilling that allows method making that allows holes making with a holesrelatively with small a relatively burr, while small eliminatingburr, while eliminatingthe phenomenon the phenomenon of drilling caps of drilling formation. caps formation. VariousVarious authors have attempted to develop or modi modifyfy tools tools to to minimalize minimalize burrs burrs or or remove remove them them asas a a part part of of drilling drilling operations. operations. Kim Kim et al. et [21] al. [designed21] designed a drill a with drill an with additional an additional movable movable plate which plate removeswhich removes burrs on burrs both onsides both of the sides drilled of the element. drilled A element. similar solution A similar was solution presented was by presented Yamada byet al.Yamada [22] and et al.Waschek [22] and [23]. Waschek Kubota [23 et]. al. Kubota [24] developed et al. [24] a developed drill with atwo drill additional with two cutting additional edges, cutting that enablesedges, that the enablesdeburring the process deburring in a process single inmachining a single machining operation operationby using contouring by using contouring control (circular control interpolation)(circular interpolation) in a CNC in machining a CNC machining center. Patil center. et Patilal. [5] et obtained al. [5] obtained smaller smaller burrs burrswhen when they theyhad chamferedhad chamfered the drill thedrill corner corner and and the thecutting cutting edge. edge. Ko Koet al. et al.[20] [20 prop] proposedosed a anew new concept concept of of the the drill, drill, consistingconsisting of of changing changing point angle, flute flute geometry and length of the chisel edge. FromFrom the the above above analysis analysis of of the the literature, literature, it it can can be be concluded concluded that that the the problem problem of of burr burr formation formation isis still still relevant, relevant, and and the the methods methods of of its its minimalization minimalization require require further further development. development. However However various various authorsauthors have have already already presented presented research research and simulations related to the formation formation of of burrs burrs in in titanium titanium alloys,alloys, as as well well as as similar solutions solutions for for tool tool construc constructiontion [5], [5], this this article article attempts attempts to to optimize optimize the the geometrygeometry of a specificspecific tool toto workwork withwith Ti-6Al-4VTi-6Al-4V alloy. alloy. Therefore, Therefore, in in order order to to improve improve the the process process of ofdrilling drilling holes holes in thein the titanium titanium alloy, alloy, modifications modifications were were made made to the to geometrythe geometry of the of Fanar the Fanar coated coated solid solidcarbide carbide drill. Conducteddrill. Conducted research research proved proved that thanks that tothanks the introduced to the introduced modification modification it was possible it was to possibleeliminate to the eliminate formation the of formation drilling caps, of drilling and to caps, significantly and to significantly reduce the size reduce of burrs. the size The of results burrs. of The this resultsstudy canof this provide study valuable can provide guidance valuable for cuttingguidance tool for manufacturers. cutting tool manufacturers.

2.2. Materials Materials and and Methods Methods

2.1.2.1. Workpiece Workpiece Material Material A 600 mm 100 mm ﬂat bar, 10 mm thick, made of Ti-6Al-4V titanium alloy, which composition A 600 mm ×× 100 mm flat bar, 10 mm thick, made of Ti-6Al-4V titanium alloy, which composition isis shown shown in in Table Table 11,, waswas usedused toto carrycarry outout thethe research.research. Physical properties of the alloy are presented inin Table Table 22.. Table 1. Chemical composition of Ti-6Al-4V titanium alloy. Table 1. Chemical composition of Ti-6Al-4V titanium alloy. Element Al V O Fe N C H Ti Element Al V O Fe N C H Ti WeightWeight (%) (%) 6.10 6.104.13 4.13 0.10 0.10 0.05 0.05 0.01 <<0.010.01 0.0030.003 BalanceBalance

TableTable 2. 2. PhysicalPhysical properties properties of of Ti Ti-6Al-4V-6Al-4V titanium titanium alloy. alloy.

TensileTensile Strength Strength (MPa) Yield Yield Strength Strength 0.2% 0.2% (MPa) ElongationElongation (%) ReductionReduction of Area of Area (%) HardnessHardness (HRC) (MPa)1000 (MPa) 900 (%) 15 41(%) 30(HRC) 1000 900 15 41 30

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MaterialsMaterials 2020 2020, 13, ,13 x, FORx FOR PEER PEER REVIEW REVIEW 4 of4 of12 12 2.2. Experimental Setup 2.2.2.2. Experimental Experimental Setup Setup The test stand consisted of three basic elements: The Haas Minimill CNC machining center, TheThe test test stand stand consisted consisted of of three three basic basic elements: elements: The The Haas Haas Minimill Minimill CNC CNC machining machining center, center, a a a dynamometer capable of measuring cutting forces and a high-speed camera. A piezoelectric dynamometerdynamometer capable capable of of measuring measuring cutting cutting forc forceses and and a ahigh-speed high-speed camera. camera. A Apiezoelectric piezoelectric dynamometer Kistler 9257B (Kistler Group, Winterthur, Switzerland) was installed in the working area dynamometerdynamometer Kistler Kistler 9257B 9257B (Kistler (Kistler Group, Group, Winter Winterthur,thur, Switzerland) Switzerland) was was installed installed in in the the working working of the machine, and connected to a PC via Kistler 5070B charge ampliﬁer (Kistler Group, Winterthur, areaarea of of the the machine, machine, and and connected connected to to a aPC PC via via Kistler Kistler 5070B 5070B charge charge amplifier amplifier (Kistler (Kistler Group, Group, Switzerland). DynoWare software (Version 2825A, Kistler Group, Winterthur, Switzerland) was used to Winterthur,Winterthur, Switzerland). Switzerland). DynoWare DynoWare software software (Version (Version 2825A, 2825A, Kistler Kistler Group, Group, Winterthur, Winterthur, acquire and display data. The test stand conﬁgured in this way enabled cutting forces to be measured Switzerland)Switzerland) was was used used to to acquire acquire and and display display data. data. The The test test stand stand configured configured in in this this way way enabled enabled during the drilling process. The burr formation phenomena were recorded using a Vision Research cuttingcutting forces forces to to be be measured measured during during the the dril drillingling process. process. The The burr burr formation formation phenomena phenomena were were Phantom v5.2 high-speed camera (Vision Research, Wayne, PA, USA), equipped with a Nikon AF recordedrecorded using using a aVision Vision Research Research Phantom Phantom v5.2 v5.2 high-speed high-speed camera camera (Vision (Vision Research, Research, Wayne, Wayne, PA, PA, Micro-Nikkor 200 lens (Nikon, Tokyo, Japan) and a Dedocool Cool Light Kit (Mengel Engineering, USA),USA), equipped equipped with with a Nikona Nikon AF AF Micro-Nikkor Micro-Nikkor 200 200 lens lens (Nikon, (Nikon, Tokyo, Tokyo, Japan) Japan) and and a Dedocoola Dedocool Cool Cool Virum, Denmark). The scheme of the measuring path and a photograph of the research stand is shown LightLight Kit Kit (Mengel (Mengel Engineering, Engineering, Virum, Virum, Denmar Denmark).k). The The scheme scheme of of the the measuring measuring path path and and a a in Figure2. photographphotograph of of the the research research stand stand is isshown shown in in Figure Figure 2. 2.

FigureFigureFigure 2. 2.Measuring Measuring path path scheme scheme (left (left). ).Research Research Research stand stand (right (right). ).1—dynamometer, 1—dynamometer, 2—high-speed 2—high-speed camera,camera,camera, 3—PC 3—PC 3—PC for for for data data acquisition, acquisition, 4—charge 4—charge amplifier. amplifier. ampliﬁer. The dynamometer was attached between the workpiece and the mill table as shown in Figure3. TheThe dynamometer dynamometer was was attached attached between between the the workpiec workpiece ande and the the mill mill table table as as shown shown in in Figure Figure 3. 3.

FigureFigure 3. 3.Method Method of ofmounting mounting the the dynamometer dynamometer in ina amachine machine tool. tool. 1—drill, 1—drill, 2—workpiece, 2—workpiece, 3— 3— Figure 3. Methodofmountingthedynamometerinamachinetool. 1—drill, 2—workpiece,3—dynamometer. dynamometer.dynamometer. 2.3. Characteristics of Standard and New Concept Drills 2.3.2.3. Characteristics Characteristics of ofStan Standarddard and and New New Concept Concept Drills Drills Initiatory tool for the experiment was the FANAR W9-604013-1000/WK DIN-6537 3xD 10.00 VHM twistInitiatoryInitiatory drill (Figure tool tool for4 for) (Fanar,the the experiment experiment Ciechan wasó wasw, the Poland), the FANAR FANAR with W9-604013-1000/WK W9-604013-1000/WK a diameter of 10 mmDIN-6537 DIN-6537 and a 3xD point 3xD 10.00 angle10.00 VHM twist drill (Figure 4) (Fanar, Ciechanów, Poland), with a diameter of 10 mm and a point angle VHMof 140 twist◦. The drill tool (Figure was made 4) (Fanar, of ﬁne-grained Ciechanów, carbide Poland), and with covered a diameter with a of titanium 10 mm aluminumand a point nitride angle ofof(TiAlN) 140°. 140°. The The coating. tool tool was was made made of of fi ne-grainedfine-grained carbide carbide and and covered covered wi withth a atitanium titanium aluminum aluminum nitride nitride (TiAlN)(TiAlN) coating. coating.

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FigureFigure 4.4. FANARFANAR W9-604013-1000 W9-604013-1000/WKW9-604013-1000/WK/WK DIN-6537 DIN-6537DIN-6537 3xD 3xD3xD 10.00 10.0010.00 VHM VHMVHM solid solidsolid carbide carbidecarbide twist twisttwist drill drill (drilld1 = ((10dd11 = mm,= 1010 mm,dmm,2 = 10 dd22 = mm,= 1010 mm,mm,l1 = 89ll11 == mm, 8989 mm,mm,l2 = ll4722 == mm).4747 mm).mm).

TheThe modificationmodificationmodification consisted consistedconsisted of ofof making makingmaking a chamfer aa chamferchamfer of a ofof specific aa specificspecific length lengthlength and angle andand onangleangle the drillonon thethe margin. drilldrill margin.Suchmargin. modified SuchSuch modifiedmodified tool is shown tooltool inisis Figureshownshown5 .inin Selected FigureFigure geometrical5.5. SelectedSelected geometricalgeometrical parameters ofparametersparameters the drills areofof the presentedthe drillsdrills areare in Tablepresentedpresented3. inin TableTable 3.3.

FigureFigure 5.5. ModifiedModiﬁedModified drill. drill.

Table 3. Geometrical parameters of the drills. TableTable 3.3. GeometricalGeometrical parametersparameters ofof thethe drills.drills. Chisel Edge Chisel Edge Clearance Clearance Angle of the PointPoint Angle (Chisel◦) Edge Chisel Edge RakeRake Angle (◦) Clearance Clearance Angle of the Point ChiselLength Edge (mm) ChiselAngle Edge (◦) Rake ClearanceAngle (◦ ) ClearanceChamfered Angle Part (◦ )of the AngleAngle (°)(°)0.01 LengthLength (mm)(mm) 0.2 AngleAngle 130 (°)(°) AngleAngle 30(°)(°) AngleAngle (°) 8(°) ChamferedChamfered 14 PartPart (°)(°) 0.010.01 0.20.2 130 130 3030 8 8 14 14 Implementation of the chamfer shortened the main cutting edge from the corner of the drill and ImplementationImplementation ofof thethe chamferchamfer shortenedshortened thethe mainmain cuttingcutting edgeedge fromfrom thethe cornercorner ofof thethe drilldrill andand simultaneously created an additional cutting edge. This type of modification affected the distribution simultaneouslysimultaneously createdcreated anan additionaladditional cuttingcutting edge.edge. ThThisis typetype ofof modificationmodification affectedaffected thethe distributiondistribution of cutting forces in the drilling process. ofof cuttingcutting forcesforces inin thethe drillingdrilling process.process. It is assumed that, with a symmetrically loaded drill, the cutting resistance, represented by the ItIt isis assumedassumed that,that, withwith aa symmetricallysymmetrically loadedloaded drill,drill, thethe cuttingcutting resistance,resistance, representedrepresented byby thethe resultant cutting force F, is divided into two components, located on the cutting edges: Horizontal resultantresultant cuttingcutting forceforce F,F, isis dividividedded intointo twotwo components,components, locatedlocated onon thethe cuttingcutting edges:edges: HorizontalHorizontal force Fc and perpendicular to the cutting edge in the vertical plane force Fa. Next, the force Fa can be forceforce FFcc andand perpendicularperpendicular toto thethe cuttingcutting ededgege inin thethe verticalvertical planeplane forceforce FFaa.. Next,Next, thethe forceforce FFaa cancan bebe divided into two components: Ff and Fp. If the force value for one blade is Ff, it will be 2Ff for both divideddivided intointo twotwo components:components: FFff andand FFpp.. IfIf thethe forceforce valuevalue forfor oneone bladeblade isis FFff,, itit willwill bebe 2F2Fff forfor bothboth blades. Since Ff = Fasinκ1, the axial force increases with the increase in the drill point angle (2κ). blades.blades. SinceSince FFff == FFaasinsinκκ11,, thethe axialaxial forceforce increasesincreases withwith thethe increaseincrease inin thethe drilldrill pointpoint angleangle (2(2κκ).). Creating an additional cutting edge caused a change in the distribution of forces. In this case, CreatingCreating anan additionaladditional cuttingcutting edgeedge causedcaused aa changechange inin thethe distributiondistribution ofof forces.forces. InIn thisthis case,case, the value of the total cutting force F is the sum of the resistances arising on the primary and on the thethe valuevalue ofof thethe totaltotal cuttingcutting forceforce FF isis thethe sumsum ofof thethe resistancesresistances arisingarising onon thethe primaryprimary andand onon thethe additional cutting edge. Due to great value of the point angle of the additional cutting edge, the axial additionaladditional cuttingcutting edge.edge. DueDue toto greatgreat valuevalue ofof thethe pointpoint angleangle ofof thethe additionaladditional cuttingcutting edge,edge, thethe axialaxial force Ff2 is significantly smaller than the axial force Ff1 that occurs on the original cutting edge. Near the forceforce FFf2f2 isis significantlysignificantly smallersmaller thanthan thethe axialaxial forceforce FFf1f1 thatthat occursoccurs onon thethe originaloriginal cuttingcutting edge.edge. NearNear edge of the hole drilled, the amount of force acting in the radial direction is much greater than in thethe edgeedge ofof thethe holehole drilled,drilled, thethe amountamount ofof forceforce actiactingng inin thethe radialradial directiondirection isis muchmuch greatergreater thanthan inin the axial direction. The local reduction in the value of the axial force caused that the ejection of the thethe axialaxial direction.direction. TheThe locallocal reductionreduction inin thethe valuevalue ofof thethe axialaxial forceforce causedcaused thatthat thethe ejectionejection ofof thethe workpiece material, provoked by the tool movement, takes place with less intensity around the edge of workpieceworkpiece material,material, provokedprovoked byby thethe tooltool movement,movement, takestakes placeplace withwith lessless intensityintensity aroundaround thethe edgeedge the hole than in its center. Thus, a significant reduction in material stress values around the perimeter ofof thethe holehole thanthan inin itsits center.center. Thus,Thus, aa significantsignificant reductionreduction inin materialmaterial stressstress valuesvalues aroundaround thethe of the drilled hole was achieved. Distributions of cutting force components for original and modified perimeterperimeter ofof thethe drilleddrilled holehole waswas achieved.achieved. DistribuDistributionstions ofof cuttingcutting forceforce compcomponentsonents forfor originaloriginal andand drills are presented in Figure6. modifiedmodified drillsdrills areare presentedpresented inin FigureFigure 6.6.

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Figure 6. Components of cutting force for a factory (a) and modified (b) drills. Figure 6. Components of cutting force for a factory (a) and modifiedmodified ((b)) drills.drills. 2.4. Experiment Setup 2.4. Experiment Setup 2.4. ExperimentIn order to Setupverify the impact of the described modification on the phenomenon of cap formation, and onIn orderthe size to (height) verify the of impact burrs arising,of the described described a number mo modification ofdification drilling testson the were phenomenon performed. of The cap studyformation, formation, was conductedand on thethe in sizesize a stabilized (height)(height) ofof phase burrsburrs of arising,arising, the process. aa numbernumb Noer ofincreasedof drillingdrilling cutting teststests werewere edge performed.performed. wear was Theobserved, study wasand theconducted modified inin angles aa stabilizedstabilized remained phase phase stable. of of the the The process. process. experiment No No increased increased plan, presented cutting cutting edge in edge Table wear wear 4, was was was observed, developed observed, and using and the themodifiedthe Taguchimodified angles method. angles remained remained Preliminary stable. stable. Thetests The experiment allowed experiment to plan,spec plan,ify presented the presented research in Table in scope, Table4, was 4,i.e., was developed cutting developed data using (feed) using the Taguchi method. Preliminary tests allowed to specify the research scope, i.e., cutting data (feed) and andthe Taguchidrill geometry. method. Three Preliminary factors testswere allowedtested: feed to spec f, lengthify the l research3 and chamfer scope, angle i.e., cutting κ2, each data on (feed)three drill geometry. Three factors were tested: feed f, length l3 and chamfer angle κ2, each on three levels. levels.and drill The geometry. measured Three dependent factors value were was tested: the feedburr fhe, lengthight (Figure l3 and 7)chamfer and the angle obtained κ2, each results on werethree developedThelevels. measured The usingmeasured dependent the ANOVA dependent value analysis was value the method.burrwas heightthe burrThree (Figure he hoightles7) (Figure andwere the drilled 7) obtained and for the each results obtained of werethe resultstests. developed In were the furtherusingdeveloped the part ANOVA using of the the analysiswork, ANOVA burr method. heightsanalysis Three resulting method. holes were fromThree drilledthe ho lesuse forwere of each the drilled factory of the for tests. and each Inmodified of the the further tests. drillpart Inwere the of comparedthefurther work, part burrfor of heightsthethree work, resultingdifferent burr heights fromfeeds. the resultingThe use ofheights the from factory theof anduseburrs of modified theformed factory drill were and were measuredmodified compared drillusing for threewere a profilographometer.dicomparedfferent feeds. for Thethree heights different of burrs feeds. formed The wereheights measured of burrs using formed a profilographometer. were measured using a profilographometer.Table 4. Experiment plan developed according to Taguchi method. Table 4. Experiment plan developed according to Taguchi method.

TestTest No. No. Table1 14. Experiment2 2 plan3 3 developed4 4 according 5 to Taguchi 66 method. 77 88 9 9 f [mm/rev]Testf [mm No./rev] 0.0810.08 0.082 0.08 0.08 0.083 0.14 0.144 0.14 5 0.140.146 0.200.207 0.200.208 0.200.209 l3 [mm] 1.0 1.5 2.0 1.0 1.5 2.0 1.0 1.5 2.0 f [mm/rev]l3 [mm] 0.081.0 0.081.5 0.082.0 0.141.0 0.141.5 0.142.0 0.201.0 0.201.5 0.202.0 κ2 [◦] 10 15 20 15 20 10 20 10 15 l3κ [mm]2 [°] 101.0 151.5 202.0 151.0 201.5 102.0 201.0 101.5 152.0 κ2 [°] 10 15 20 15 20 10 20 10 15

Figure 7. BurrBurr height height hh—value—value measured measured during during the experiment. Figure 7. Burr height h—value measured during the experiment. 3. Results Results and and Analysis Analysis 3. Results and Analysis The results obtained—burr height h depending onon thethe shapeshape ofof thethe tooltool usedused ((ll33, κ2)) and and the the feed feed f—aref—areThe summarized results obtained—burr in Table 5 5,, and and height presented presented h depending in in Figure Figure on8 . 8.the shape of the tool used (l3, κ2) and the feed f—are summarized in Table 5, and presented in Figure 8. Table 5. Burr height depending on the shape of the tool used and on the feed.

Test No. f [mm/rev] l3 [mm] κ2 [◦] Mean h [µm] σh [µm] 1 0.08 1.0 10 142 8.7 2 0.08 1.5 15 120 6.0 3 0.08 2.0 20 120 6.5 4 0.14 1.0 15 160 9.5 5 0.14 1.5 20 132 11.1 6 0.14 2.0 10 98 12.0 7 0.20 1.0 20 232 10.0 8 0.20 1.5 10 110 8.5 9 0.20 2.0 15 105 5.5

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Table 5. Burr height depending on the shape of the tool used and on the feed.

Test No. f [mm/rev] l3 [mm] κ2 [°] Mean h [µm] σh [µm] 1 0.08 1.0 10 142 8.7 2 0.08 1.5 15 120 6.0 3 0.08 2.0 20 120 6.5 4 0.14 1.0 15 160 9.5 5 0.14 1.5 20 132 11.1 6 0.14 2.0 10 98 12.0 7 0.20 1.0 20 232 10.0 Materials 2020, 13, 32078 0.20 1.5 10 110 8.5 7 of 12 9 0.20 2.0 15 105 5.5

Figure 8. Burr height h depending on the shape of the tool used and on the feed. Figure 8. Burr height h depending on the shape of the tool used and on the feed.

The ANOVA methodmethod waswas usedused to to process process the the results. results. The The analysis analysis of of variance variance is is shown shown in in Table Table6, 6, while the dependence of the burr height h on the feed f, length l3 and chamfer angle κ2 is shown in while the dependence of the burr height h on the feed f, length l3 and chamfer angle κ2 is shown in Figure9 9..

TableTable 6. Analysis of ANOVA variance for burr height h..

SourceSource DF DF Adj SS Adj SS Adj Adj MS MS F-Value F-Value p-Valuep-Value f [mm/rev] 2 837.6 418.8 0.86 0.538 f[mm/rev] 2 837.6 418.8 0.86 0.538 3 l [mm]l3 [mm] 2 28402.9 8402.9 4201.4 4201.4 8.63 8.63 0.104 0.104 κ2 [°] κ2 [◦] 2 23220.2 3220.2 1610.1 1610.1 3.31 3.31 0.232 0.232 Error Error 2 2973.6 973.6 486.8 486.8 Total Total 8 813,434.2 13,434.2 Materials 2020, 13, x FOR PEER REVIEW 8 of 12

Figure 9. Graphs representing the relation between burr height h and the feed f, chamfer length l3 and Figure 9. Graphs representing the relation between burr height h and the feed f, chamfer length l3 and chamfer angle κ2. chamfer angle κ2.

Interactions between the tested factors were also determined. As can be seen in Figure 10, the effect of chamfer length l3 and angle κ2 on burr height is greatest for high feed rates. It can also be seen that the effect of the chamfer angle κ2 is strongest for the shortest chamfer.

Figure 10. Interaction plot for burr height h.

As a part of the analysis, the regression equation correlating burr height h and the feed f, chamfer length l3 and chamfer angle κ2 was determined:

ℎ = 461 + 2269 ∙ 𝑓 + 88.7∙𝑙 + 0.427 ∙ 𝜅 − 455 ∙ 𝑓 − 336 ∙ 𝑙 − 8.3∙𝜅 (1)

Among the tested drill geometries, the version with a chamfer length of l3 = 2 mm and an angle of κ2 = 10° proved to be optimal. In the further part of the work, the average values of the burr height for the factory drill and the drill modified in the above manner were compared. Additionally, the axial cutting force (Ff) values for various feeds were compared between those two drill geometries. The results of these measurements are presented in Table 7. Studies have shown that the change allowed for a significant reduction in the size of burrs (Figure 11). The results obtained are in line with the models presented by Rana et al. [12] and Mittal et al. [13].

Materials 2020, 13, x FOR PEER REVIEW 8 of 12

Materials 2020, 13, 3207 8 of 12 Figure 9. Graphs representing the relation between burr height h and the feed f, chamfer length l3 and

chamfer angle κ2. Interactions between the tested factors were also determined. As can be seen in Figure 10, the eﬀect Interactions between the tested factors were also determined. As can be seen in Figure 10, the of chamfer length l3 and angle κ2 on burr height is greatest for high feed rates. It can also be seen that effect of chamfer length l3 and angle κ2 on burr height is greatest for high feed rates. It can also be the eﬀect of the chamfer angle κ2 is strongest for the shortest chamfer. seen that the effect of the chamfer angle κ2 is strongest for the shortest chamfer.

Figure 10. Interaction plot for burr height h.

As a a part part of of the the analysis, analysis, the theregression regression equation equation correlating correlating burr height burr heighth and theh and feed thef, chamfer feed f, chamferlength l3 lengthand chamferl3 and angle chamfer κ2 was angle determined:κ2 was determined:

2 2 2 ℎ = 461h = + 4612269+ ∙2269𝑓 +f 88.7∙𝑙+ 88.7l ++ 0.4270.427 ∙κ 𝜅 −455 455f ∙ 𝑓336 −l 3368.3 ∙ 𝑙κ − 8.3∙𝜅 (1)(1) · · 3 · 2 − · − · 3 − · 2

Among the tested drill geometries, thethe versionversion withwith aa chamferchamfer lengthlength ofof ll33 = 2 mm and an angle of κκ22 == 10°10 ◦provedproved to tobe beoptimal. optimal. In the In further the further part partof the of work, the work, the average the average values values of the burr of the height burr heightfor the forfactory the factory drill and drill the and drill the modified drill modiﬁed in the in above the above manner manner were were compared. compared. Additionally, Additionally, the theaxial axial cutting cutting force force (Ff) (F valuesf) values for forvarious various feeds feeds were were compared compared between between those those two two drill drill geometries. geometries. The results of thesethese measurementsmeasurements are presentedpresented inin TableTable7 .7. StudiesStudies havehave shownshown thatthat thethe changechange allowed forfor aa signiﬁcantsignificant reduction reduction in in the the size size of of burrs burrs (Figure (Figure 11). 11). The The results results obtained obtained are inare line in withline thewith models the models presented presented by Rana by Rana et al. [et12 al.] and [12] Mittal and Mittal et al. [et13 al.]. [13].

Table 7. Burr height and axial force value depending on the type of drill used.

Drill Type f [mm/rev] h [mm] Ff [N] 0.08 114 559 Original drill 0.14 117 696 0.20 125 820 0.08 89 430 Modiﬁed drill 0.14 98 540 0.20 112 632

It can be seen that the higher the feed, the smaller the relative effect. After applying the drill modification, for f = 0.20 mm/rev the burr height was lower by 10%, and for f = 0.08 mm/rev by 22%. The relative change in burr size depending on the feed, for extreme values of this parameter (f = 0.08–0.20 mm/rev) was 9% for the factory drill, and 20% for the modified drill. Materials 2020, 13, x FOR PEER REVIEW 9 of 12

Table 7. Burr height and axial force value depending on the type of drill used

Materials 2020, 13, x FOR PEER REVIEW 9 of 12 Drill Type f [mm/rev] h [mm] Ff [N] 0.08 114 559 Table 7. Burr height and axial force value depending on the type of drill used Original drill 0.14 117 696 Drill Type f [mm/rev]0.20 h [mm]125 Ff820 [N] 0.08 11489 559430 ModifiedOriginal drill drill 0.14 11798 696540 0.20 125112 820632 0.08 89 430 Materials 2020, 13, 3207 Modified drill 0.14 98 540 9 of 12 0.20 112 632

Figure 11. Burr height h as a function of feed f for factory and modified drills.

It can be seen that the higher the feed, the smaller the relative effect. After applying the drill modification, forFigure f = 0.20 11. Burrmm/rev height the h asburr a function height ofwas feed lower f for factoryby 10%, and and modified for f = 0.08drills. mm/rev by 22%. Figure 11. Burr height h as a function of feed f for factory and modified drills. The relative change in burr size depending on the feed, for extreme values of this parameter (f = 0.08– 0.20 mm/rev)AsIt can can be be wasseen seen 9% that in Figurefor the the higher 12factory, for the all drill, feedfeed, and rate the 20% values smaller for the the cuttingmodified relative force drill. effect. was significantlyAfter applying lower the when drill drillingmodification,As withcan be afor seen modified f = in0.20 Figure drillmm/rev 12, (approx. for the all burr feed 22–23%). height rate va Thewaslues datalower the presentedcutting by 10%, force and in Figureswas for significantly f = 0.0811 and mm/rev 12 lower prove by when 22%. that, asThedrilling the relative feed with increases, change a modified in both burr drill the size cutting(approx. depending force 22–23%). andon the the The feed, burr data for height presented extreme increase values in also.Figures of For this 11 both parameter and drill 12 geometriesprove (f = 0.08– that, 0.20as the mm/rev) feed increases, was 9% both for the the factory cutting drill, force and and 20% the burr for the height modified increase drill. also. For both drill geometries a positive correlation can be noticed between axial drilling force Ff and burr height h (Figure 13). a positiveAs can correlation be seen in canFigure be noticed12, for all between feed rate axial values drilling the cutting force F forcef and wasburr significantly height h (Figure lower 13). when drilling with a modified drill (approx. 22–23%). The data presented in Figures 11 and 12 prove that, as the feed increases, both the cutting force and the burr height increase also. For both drill geometries a positive correlation can be noticed between axial drilling force Ff and burr height h (Figure 13).

Figure 12. Axial drilling force Ff as a function of feed f for factory and modified drills. Figure 12. Axial drilling force Ff as a function of feed f for factory and modiﬁed drills.

In each case, the drilling process was recorded using a high-speed camera. When using the factory drill, regardlessFigure of 12. the Axial feed drilling used, drilling force Ff capsas a function were formed of feed and f for later factory they and had modified to be removed drills. from the edge of the hole mechanically. In the case of a modiﬁed drill, regardless of the feed value, drilling caps did not appear. Figures 14 and 15 present camera frames from the drilling process with a factory and modiﬁed drill, respectively. Materials 2020, 13, x FOR PEER REVIEW 10 of 12 Materials 2020, 13, x FOR PEER REVIEW 10 of 12

Materials 2020, 13, 3207 10 of 12

Materials 2020, 13, x FOR PEER REVIEW 10 of 12

Figure 13. Burr height h as a function of axial drilling force Ff. Figure 13. Burr height h as a function of axial drilling force Ff. In each case, the drilling process was recorded using a high-speed camera. When using the In each case, the drilling process was recorded using a high-speed camera. When using the factory drill, regardless of the feed used, drilling caps were formed and later they had to be removed factory drill, regardless of the feed used, drilling caps were formed and later they had to be removed from the edge of the hole mechanically. In the case of a modified drill, regardless of the feed value, from the edge of the hole mechanically. In the case of a modified drill, regardless of the feed value, drilling caps did not appear. Figures 14 and 15 present camera frames from the drilling process with drilling caps did not Figureappear. 13. Figures Burr height 14 and h as15 a present function camera of axial frames drilling from force the Ff. drilling process with a factory and modifiedFigure drill, 13. respectively.Burr height h as a function of axial drilling force Ff. a factory and modified drill, respectively. In each case, the drilling process was recorded using a high-speed camera. When using the factory drill, regardless of the feed used, drilling caps were formed and later they had to be removed from the edge of the hole mechanically. In the case of a modified drill, regardless of the feed value, drilling caps did not appear. Figures 14 and 15 present camera frames from the drilling process with a factory and modified drill, respectively.

Figure 14. Camera frames showing subsequent stages of drilling with a factory drill. FigureFigure 14. 14.Camera Camera frames frames showingshowing subsequent stag stageses of of drilling drilling with with a afactory factory drill. drill.

Figure 14. Camera frames showing subsequent stages of drilling with a factory drill. Figure 15. Camera frames showing subsequent stages of drilling with a modified drill. FigureFigure 15. 15.Camera Camera frames frames showingshowing subsequent stag stageses of of drilling drilling with with a amodified modified drill. drill. 4. Conclusions 4.4. Conclusions Conclusions A novelty presented in the paper is the proposed method of burr minimizing by modifying the A novelty presented in the paper is the proposed method of burr minimizing by modifying the geometryA novelty of the presented cemented in carbide the paper drill is working the proposed in a titanium method alloy. of burr Implemented minimizing modifications by modifying geometry of the cemented carbide drill working in a titanium alloy. Implemented modifications the(chamfer geometry length of the 2 mm, cemented chamfer carbide angle drill10°) resulted working in in relatively a titanium large alloy. reduction Implemented in the size modifications of burrs, (chamfer length 2 mm, chamfer angle 10°) resulted in relatively large reduction in the size of burrs, (chamferand complete length elimination 2 mm, chamfer of the anglephenomenon 10◦) resulted of drilling in relatively cap formation. large Depending reduction inon thethe feed size ofvalue, burrs, and completeFigure elimination 15. Camera of frames the phenomenon showing subsequent of drilling stag capes formation.of drilling withDepending a modified on the drill. feed value, andburr complete height decreased elimination in ofa range the phenomenon from 10 to 22%. of drilling Thus, the cap necessity formation. of mechanical Depending removal on the feed of caps value, burr height decreased in a range from 10 to 22%. Thus, the necessity of mechanical removal of caps burrand height the need decreased for additional in a range operations from 10 to aimed 22%. Thus,at reducing the necessity the size of of mechanical burrs were removal eliminated. of caps The and 4. Conclusionsand the need for additional operations aimed at reducing the size of burrs were eliminated. The thechange need forintroduced additional in operationsthe drill geometry, aimed atwhich reducing is a technologically the size of burrs simple were and eliminated. low-cost Thesolution, change change introduced in the drill geometry, which is a technologically simple and low-cost solution, introducedprovedA novelty to in be the presentedeffective. drill geometry, Used in the in paper whichindustry, is is the a by technologically proposed reducing method the simplenumber of burr and of low-costtools,minimizing operations solution, by modifying and proved energy to the be proved to be effective. Used in industry, by reducing the number of tools, operations and energy geometryeffective.consumed, Usedof theit incould cemented industry, have a by positivecarbide reducing effectdrill the workingin number terms of ofin reduction tools,a titanium operations of costalloy. and and Implemented environmental energy consumed, modifications impact. it could consumed, it could have a positive effect in terms of reduction of cost and environmental impact. (chamferStudies length have 2 mm, shown chamfer that the angle size 10°)of burrs resulted depend in srelatively on the feed large value. reduction The drilling in the process size of with burrs, have aStudies positive have effect shown in terms that of the reduction size of burrs of cost depend and environmentals on the feed value. impact. The drilling process with anda modifiedcomplete drillelimination seems to of be the more phenomenon sensitive to of changes drilling in cap this formation. parameter. Depending For the original on the drill, feed there value, a modifiedStudies havedrill seems shown to that be more the size sensitive of burrs to dependschanges in on this the parameter. feed value. For The the drilling original process drill, there with a burrwas height a 9% changedecreased in the in burra range height from between 10 to 22%.the extr Thus,eme valuesthe necessity of the tested of mechanical feed (0.08–0.20 removal mm/rev). of caps modifiedwas a 9% drill change seems in tothe be burr more height sensitive between to changes the extreme in this values parameter. of the tested For the feed original (0.08–0.20 drill, mm/rev). there was and the need for additional operations aimed at reducing the size of burrs were eliminated. The a 9% change in the burr height between the extreme values of the tested feed (0.08–0.20 mm/rev). changeFor the modifiedintroduced drill in itthe was drill 22%, geometry, respectively. which Based is a on technologically these results, itsimple can be and expected low-cost that solution, at higher provedfeeds the to e ffbeect effective. will decrease, Used andin industry, it even may by re becomeducing negative. the number It is thenof tools, possible operations to further and optimize energy consumed,the shape of it the could drill have to increase a positive the effect effect ofin minimalizingterms of reduction the size of ofcost burrs. and Theenvironmental desirable solution impact. is to Studies have shown that the size of burrs depends on the feed value. The drilling process with a modified drill seems to be more sensitive to changes in this parameter. For the original drill, there was a 9% change in the burr height between the extreme values of the tested feed (0.08–0.20 mm/rev).

Materials 2020, 13, 3207 11 of 12 obtain the greatest effect possible for relatively high feed rates so as to ensure, apart from satisfactory hole edge quality, high machining efficiency. The cutting forces decreased with a use of modified drill (22–23% depending on the feed value), which can have a positive effect on the tool life. The existence of a correlation between the cutting force and the size of burrs allows, by measuring this force during the drilling process, to estimate the size of burrs in real time. After proper validation, consisting of determining the relationship between burr height and cutting force for a given material, tool and cutting parameters, such solution could become a common method of manufacturing process control. In the next stage of work it is also advisable to make wear curves for both tools. Comparison of their endurance will allow to estimate the production potential of the modified drill. Given that the cutting forces have decreased after the drill has been modified, one can hope that its service life will be satisfactory, or even better than the original drill. The limitation for the experiment was the type of tool and material used. The further course of this research should include examining the impact of proposed modification on other types of drills (geometry, material, coating), so as to derive more general conclusions about the effect brought by implementation of a chamfer. Similar tests should also be carried out for other difficult-to-cut materials to check the effect of hardness, adhesion, etc. on the phenomenon of burr formation and on the effectiveness of chamfering operation. Information obtained from such experiments would, in practice, allow for a wider choice of material depending on the application and the acceptable size of burr.

Author Contributions: Conceptualization, E.F. and W.Z.; methodology, E.F.; software, Ł.S.;´ formal analysis, W.Z. and Ł.S.;´ data curation, E.F. and Ł.S.;´ investigation, E.F. and W.Z.; resources, E.F., W.Z. and Ł.S.;´ writing—original draft preparation, E.F.; writing—review and editing E.F., Ł.S.´ and W.Z.; project administration, E.F. and W.Z.; funding acquisition, E.F. and W.Z.; supervision, W.Z. All authors have read and agreed to the published version of the manuscript. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Machado, A.R.; Wallbank, J. Machining of titanium and its alloys—A review. Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. 1990, 204, 53–60. [CrossRef] 2. Słodki, B.; Z˛ebala,W.; Struzikiewicz, G. Turning Titanium Alloy, Grade 5 ELI, With the Implementation of High Pressure Coolant. Materials 2019, 12, 768. [CrossRef][PubMed] 3. Joy, N.; Prakash, S.; Krishnamoorthy, A.; Antony, A. Experimental Investigation and Analysis of Drilling in Grade 5 Titanium Alloy (Ti-6Al-4V). Mater. Today Proc. 2020, 21, 335–339. [CrossRef] 4. Saketi, S.; Odelros, S.; Östby, J.; Olsson, M. Experimental Study of Wear Mechanisms of Cemented Carbide in the Turning of Ti6Al4V. Materials 2019, 12, 2822. [CrossRef] 5. Patil, R.; Shinde, S.; Joshi, S.S.; Marla, D. Experimental analysis of burr formation in drilling of TI-6AL-4V alloy. Int. J. Mechatron. Manuf. Syst. 2016, 9, 237. [CrossRef] 6. Dornfeld, D.; Kim, J.; Dechow, H.; Hewson, J.; Chen, L. Drilling Burr Formation in Titanium Alloy, Ti-6AI-4V. CIRP Ann. 1999, 48, 73–76. [CrossRef] 7. Abdelhafeez, A.; Soo, S.L.; Aspinwall, D.; Dowson, A.; Arnold, D. Burr formation and hole quality when drilling titanium and aluminium alloys. Procedia CIRP 2015, 37, 230–235. [CrossRef] 8. Bahçe, E.; Özdemir, B. Investigation of the burr formation during the drilling of free-form surfaces in Al 7075 alloy. J. Mater. Res. Technol. 2019, 8, 4198–4208. [CrossRef] 9. Mathew, N.T.; Vijayaraghavan, L. Drilling of titanium aluminide at diﬀerent aspect ratio under dry and wet conditions. J. Manuf. Process. 2016, 24, 256–269. [CrossRef] 10. Biermann, D.; Hartmann, H. Reduction of Burr Formation in Drilling Using Cryogenic Process Cooling. Procedia CIRP 2012, 3, 85–90. [CrossRef] 11. Rimpault, X.; Chatelain, J.-F.; Klemberg-Sapieha, J.E.; Balazinski, M. Burr height monitoring while drilling CFRP/titanium/aluminium stacks. Mech. Ind. 2017, 18, 114. [CrossRef] Materials 2020, 13, 3207 12 of 12

12. Rana, A.; Dongre, G.; Joshi, S.S. Analytical modeling of exit Burr in drilling of Ti6Al4V alloy. Sadhana 2019, 44, 133. [CrossRef] 13. Mittal, R.K.; Yadav, S.; Singh, R. Mechanistic Force and Burr Modeling in High-speed Microdrilling of Ti6Al4V. Procedia CIRP 2017, 58, 329–334. [CrossRef] 14. Abdelhafeez, A.M.; Soo, S.L.; Aspinwall, D.K.; Dowson, A.; Arnold, D. The inﬂuence of burr formation and feed rate on the fatigue life of drilled titanium and aluminium alloys used in aircraft manufacture. CIRP Ann. 2018, 67, 103–108. [CrossRef] 15. Min, S.; Kim, J.; A Dornfeld, D. Development of a drilling burr control chart for low alloy steel, AISI. J. Mater. Process. Technol. 2001, 113, 4–9. [CrossRef] 16. Kim, J.; Min, S.; Dornfeld, D.A. Optimization and control of drilling burr formation of AISI 304L and AISI 4118 based on drilling burr control charts. Int. J. Mach. Tools Manuf. 2001, 41, 923–936. [CrossRef] 17. Chang, S.S.; Bone, G. Burr size reduction in drilling by ultrasonic assistance. Robot. Comput. Manuf. 2005, 21, 442–450. [CrossRef] 18. Mondal, N.; Sardar, B.S.; Halder, R.N.; Das, S. Observation of Drilling Burr and Finding out the Condition for Minimum Burr Formation. Int. J. Manuf. Eng. 2014, 2014, 1–12. [CrossRef] 19. Mahdy, M. Economic drilling conditions for a given deburring radius. J. Mater. Process. Technol. 2001, 110, 197–205. [CrossRef] 20. Ko, S.-L.; Lee, J.-K. Analysis of burr formation in drilling with a new-concept drill. J. Mater. Process. Technol. 2001, 113, 392–398. [CrossRef] 21. Kim, K.H.; Cho, C.H.; Jeon, S.Y.; Lee, K.; A Dornfeld, D. Drilling and deburring in a single process. Proc. Inst. Mech. Eng. Part B J. Eng. Manuf. 2003, 217, 1327–1331. [CrossRef] 22. Yamada, J.; Miura, K. Drilling Tool. U.S. Patent No. US 6,238,150 B1, 29 May 2001. 23. Waschek, D.E. Drill Bit with Deburring Device. U.S. Patent No. 3,940,214, 24 February 1976. 24. Kubota, H.; Tabei, H.; Sawairi, Y. Development of a Drilling Tool with a Function of Deburring. J. Jpn. Soc. Precis. Eng. 1992, 58, 655–660. [CrossRef]

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