Tool Wear and Surface Evaluation in Drilling Fly Ash Geopolymer Using HSS, HSS-Co, and HSS-Tin Cutting Tools

materials

Article Tool Wear and Surface Evaluation in Drilling Fly Ash Geopolymer Using HSS, HSS-Co, and HSS-TiN Cutting Tools

Mohd Fathullah Ghazali 1,2,* , Mohd Mustafa Al Bakri Abdullah 2,3,*, Shayfull Zamree Abd Rahim 1,2, Joanna Gondro 4 , Paweł Pietrusiewicz 4 , Sebastian Garus 5 , Tomasz Stachowiak 5, Andrei Victor Sandu 2,6,7 , Muhammad Faheem Mohd Tahir 2,3, Mehmet Erdi Korkmaz 8 and Mohamed Syazwan Osman 9

1 Faculty of Mechanical Engineering Technology, Universiti Malaysia Perlis, Perlis 01000, Malaysia; [email protected] 2 Center of Excellence Geopolymer and Green Technology (CEGeoGTech), Universiti Malaysia Perlis, Perlis 01000, Malaysia; [email protected] (A.V.S.); [email protected] (M.F.M.T.) 3 Faculty of Chemical Engineering Technology, Universiti Malaysia Perlis, Perlis 01000, Malaysia 4 Department of Physics, Cz˛estochowaUniversity of Technology, 42-200 Cz˛estochowa,Poland; [email protected] (J.G.); [email protected] (P.P.) 5 Faculty of Mechanical Engineering and Computer Science, Cz˛estochowaUniversity of Technology, 42-200 Cz˛estochowa,Poland; [email protected] (S.G.); [email protected] (T.S.) 6 Faculty of Material Science and Engineering, Gheorghe Asachi Technical University of Iasi, 41 D. Mangeron St., 700050 Iasi, Romania 7 National Institute for Research and Development for Environmental Protection INCDPM, 294 Splaiul Inde-pendentei, 060031 Bucharest, Romania 8 Citation: Ghazali, M.F.; Abdullah, Machine Engineering Department, Faculty of Engineering, Karabuk University, 78050 Karabuk, Turkey; M.M.A.B.; Abd Rahim, S.Z.; Gondro, [email protected] 9 Faculty of Chemical Engineering, Universiti Teknologi MARA, Cawangan Pulau Pinang, J.; Pietrusiewicz, P.; Garus, S.; 13500 Permatang Pauh, Malaysia; [email protected] Stachowiak, T.; Sandu, A.V.; Mohd * Correspondence: [email protected] (M.F.G.); [email protected] (M.M.A.B.A.) Tahir, M.F.; Korkmaz, M.E.; et al. Tool Wear and Surface Evaluation in Abstract: This paper reports on the potential use of geopolymer in the drilling process, with respect Drilling Fly Ash Geopolymer Using to tool wear and surface roughness. The objectives of this research are to analyze the tool life of three HSS, HSS-Co, and HSS-TiN Cutting different economy-grade drill bit uncoated; high-speed steel (HSS), HSS coated with TiN (HSS-TiN), Tools. Materials 2021, 14, 1628. https://doi.org/10.3390/ma and HSS-cobalt (HSS-Co) in the drilling of geopolymer and to investigate the effect of spindle speed 14071628 towards the tool life and surface roughness. It was found that, based on the range of parameters set in this experiment, the spindle speed is directly proportional to the tool wear and inversely Academic Editor: Dolores proportional to surface roughness. It was also observed that HSS-Co produced the lowest value of Eliche Quesada surface roughness compared to HSS-TiN and uncoated HSS and therefore is the most favorable tool to be used for drilling the material. For HSS, HSS coated with TiN, and HSS-Co, only the drilling Received: 3 February 2021 with the spindle speed of 100 rpm was able to drill 15 holes without surpassing the maximum tool Accepted: 22 March 2021 wear of 0.10 mm. HSS-Co exhibits the greatest tool life by showing the lowest value of flank wear Published: 26 March 2021 and produce a better surface finish to the sample by a low value of surface roughness value (Ra). This finding explains that geopolymer is possible to be drilled, and therefore, ranges of cutting tools Publisher’s Note: MDPI stays neutral and parameters suggested can be a guideline for researchers and manufacturers to drill geopolymer with regard to jurisdictional claims in for further applications. published maps and institutional affil- iations. Keywords: geopolymer drilling; geopolymer machining; green materials

Copyright: © 2021 by the authors. 1. Introduction Licensee MDPI, Basel, Switzerland. This article is an open access article The use of environmentally friendly materials has been increasing across the globe be- distributed under the terms and cause it helps reduce waste, minimize pollution, and save energy. Geopolymer, for instance, conditions of the Creative Commons is one of the green materials and has been highly demanded in numerous applications, Attribution (CC BY) license (https:// particularly in construction materials, to replace ordinary cement [1]. The interest in these creativecommons.org/licenses/by/ materials has been increasing due to the manufacturing of this material that involves a 4.0/). very low rate of greenhouse gas emission [2,3]. Apart from that, geopolymer utilizes waste

Materials 2021, 14, 1628. https://doi.org/10.3390/ma14071628 https://www.mdpi.com/journal/materials Materials 2021, 14, 1628 2 of 14

materials such as recycled concrete and unwanted fly ash. This material has interesting properties because it is very durable and stable at high temperature; thus, this property has been one of the reasons why geopolymer materials are now widely used in many sectors, especially in the engineering sector such as civil construction, automotive industry, and aviation sector [2–5]. Geopolymer is a type of inorganic polymer with an amorphous structure that poly- merizes in a quick reaction of silica (Si)-alumina (Al) under alkaline conditions, creating a three-dimensional polymeric chain of Si-O-Al-O bonds [6,7]. Understanding that the existence of Si and Al can be used to easily produce geopolymer, this material is easily made by using a pre-shaped mold in which all required raw materials are mixed and left solidified at room temperature [6–8]. The final shape of the material highly depends on the mold’s shape and its final dimensional accuracy is still an issue. The need to manu- facture geopolymer in various forms and shapes with high accuracy is required so that its advantages can be widely benefited not just in construction applications. From the manufacturing point of view, one of the ways of producing materials in various forms and shapes can be achieved through machining processes [8]. Machining such as the drilling process is one of the important processes in shaping certain materials. Computer Numerical Control (CNC) milling machines, hole drilling apparatus, and milling cutters are used especially for drilling blind holes of certain depths that are not lengthwise and axial holes of certain precise dimensions. Basically, high-speed steel (HSS) drills are used in these processes. However, coated carbide and indexable drills have also been recently used [6–11]. Chip formation during the drilling process affects the cutting forces, cutting temperature, surface quality, and dimensional accuracy of the hole [6]. In addition, the disposability of the chip during the drilling operations directly affects the hole quality and changes according to the cutting parameters (spindle speed, feed). Amongst those parameters mentioned, spindle speed and feed are the most important parameters in drilling. These parameters directly affect cutting conditions that occur during the cutting process and are the factors that determine the performance of the cutting tool (drill) [11–15]. In the light of the studies in the literature, tool life (based on tool wear) and surface quality are therefore the main focus of this paper. Failure to control the flank wear occurring during the drilling process causes both the cutting tool and the workpiece to be significantly affected. It causes different types of wear on the cutting tool, eventually causing the tool to complete its life in a shorter time than expected. On the other hand, the surface quality of the workpiece is negatively affected, in addition to undesirable changes in the chemical structure of the workpiece. For these reasons, tool wear and surface roughness measurements in hole drilling have attracted the attention of many researchers. Previous reports showed that fly ash geopolymer can be machined using milling and turning processes but with very low spindle speeds and small depth of cuts [16–18] but have yet to provide evidence on drilling performance on geopolymer materials. Apart from the articles reported, literature related to geopolymer drilling is still lacking, and in order to fill in the gap in the literature, this paper assessed the relationship between spindle speeds and tool life of drilling fly ash geopolymer using three types of cutting tools—HSS, HSS coated with TiN, and HSS-cobalt (HSS-Co).

2. Methodology A set of class C ﬂy ash geopolymer blocks was prepared with a size of 100 mm × 100 mm × 100 mm. The methods of preparing the samples were as previously reported [16–18]. Table1 shows the list of apparatus used in producing the geopolymer samples. Materials 2021, 14, x FOR PEER REVIEW 3 of 14 Materials 2021, 14, 1628 3 of 14

Table 1. List of required tools in making geopolymer. Table 1. List of required tools in making geopolymer. Tools Description Raw MaterialTools Fly Ash class C Description ActivatorsRaw Material Sodium Fly hydroxide, Ash class C sodium silicate Apparatus/Equip-ActivatorsWellbeing Sodium glasses, hydroxide, clean sodiumpaper tiss silicateue, expendable nitrile gloves, la- ment boratory garment, and 100 mm × 100 mm × 100 mm cubic mould. Wellbeing glasses, clean paper tissue, expendable nitrile gloves, Apparatus/Equipment laboratory garment, and 100 mm × 100 mm × 100 mm cubic mould. The molarity of sodium hydroxide was controlled at 12 M whereby the ratio of sodium silicate (Na2SiO3) to sodium hydroxide (NaOH) was set at 2.5, and the solid-to- liquidThe ratio molarity was set of sodiumat 2.0, as hydroxide employed was in controlled a previous at 12report M whereby [19]. The the calculation ratio of sodium for silicatedetermining (Na2SiO the3 )weight to sodium of fly hydroxide ash and (NaOH)alkaline wasactivator set at based 2.5, and on the the solid-to-liquid cubic mold is ratio as wasfollows set at[18,19]: 2.0, as employed in a previous report [19]. The calculation for determining the weight of ﬂy ash and alkaline activator based on the cubic mold is as follows [18,19]: i. Sample size = 100 mm × 100 mm × 100 mm; ii.i. TotalSample weight size of = fly 100 ash mm used× 100= 1600 mm g;× 100 mm; iii.ii. Solid-to-liquidTotal weight ratio of ﬂy = ash2.0. used = 1600 g; iii. Solid-to-liquid ratio = 2.0. The weight of the alkaline activator was obtained as follows: The weight of the alkaline activator was obtained as follows: Weight of Fly ash 2.0 = (1) WeightWeight of Alkaline of Fly ashactivator 12.0.0 = (1) Weight of Alkaline activator 1.0 1600 g 2.0 = = 1600 g 2.0 = Weight of Alkaline Activator =1.0 Weight of Alkaline Activator 1.0 WeightWeight of o Alkalinef Alkaline Activator Activator = 800 g

Thus, the weight of NaOH + Na2SiO3 was 800 g. Since Na2SiO3/NaOH ratio was 2.5, Thus, the weight of NaOH + Na2SiO3 was 800 g. Since Na2SiO3/NaOH ratio was 2.5, the weight of Na SiO was calculated as shown below. the weight of Na2SiO33 was calculated as shown below. Weight of Na2SiO3 2.5 Weight of Na2SiO3 =2.5 (2) Weight of NaOH = 1.0 (2) Weight of NaOH 1.0

2.52.5 WeightWeight of o Naf NaSiO2SiO3== ××800 gg= 571.429 gg 2 3 2.52.5+ +1.0 1.0 WeightWeight of o NaOHf NaOH = 800 g− 571.429 gg = 228.571 gg Figure1 1 shows shows thethe geopolymergeopolymer blockblock samplesample after solidification solidiﬁcation and and ready ready for for the the drillingdrilling process.

Figure 1. (a) Preparation process of geopolymer samples and (b) workpiece of ﬂy ash geopolymer after solidiﬁed ready for drilling experiment.

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Three types of cutting tools—uncoated HSS, HSS-TiN, and HSS-Co—were selected Figure 1. (a) Preparation process of geopolymer samples and (b) workpiece of fly ash geopolymer for this experiment. HSS was chosen in this exploration study because this drill bit is after solidified ready for drilling experiment. affordable at a low price, and considering that it offers several advantages such as being easyThree to types maintain of cutting with a tools—uncoated seamless sharpening HSS, ofHSS-TiN, blunt tools and andHSS-Co—were having a high selected level of for compactnessthis experiment. and highHSS breakingwas chosen strength. in this HSS exploration coated with study TiN because and HSS-Co this drill were bit chosen is affordableas another at a set low of price, samples and because considering the coatings that it offers of TiN several and the advantages addition of such cobalt as elementsbeing in HSS were reported to offer more strength and increases durability [20]. The details of easy to maintain with a seamless sharpening of blunt tools and having a high level of the drilling parameters are shown in Table2, and the image of the cutting tools is shown in compactness and high breaking strength. HSS coated with TiN and HSS-Co were chosen Figure2. Six rows of 6.0-mm-hole diameter with 6.0-mm spaces in between each hole were as another set of samples because the coatings of TiN and the addition of cobalt elements set for drilling, as shown in Figure3. The maximum tool wear (Vbmax) of 0.10 mm was set in HSS were reported to offer more strength and increases durability [20]. The details of as the limit of the tool life as recommended by a previous report [21]. the drilling parameters are shown in Table 2, and the image of the cutting tools is shown in Figure 2. Six rows of 6.0-mm-hole diameter with 6.0-mm spaces in between each hole Table 2. Parameter details in drilling fly ash geopolymer. were set for drilling, as shown in Figure 3. The maximum tool wear (Vbmax) of 0.10 mm was set asParameter the limit of the tool life as recommended by a previous report Details [21]. Spindle speed (RPM) 250, 200, 150 and 100 RPM Table 2. Parameter details in drilling fly ash geopolymer. Feed rate (f) (mm/rev) 0.075 mm/rev Parameter Details Depth of cut (mm) 0.30 mm Spindle speed (RPM) 250, 200, 150 and 100 RPM FeedCutting rate (f) tool (mm/rev) types 0.075Coatings mm/rev Thickness Friction Coefficient HSSDepth (Danyang of cut (mm) Daming Tools, Ltd, Danyang, China) 0.30 mmN/A 0.1–0.23 HSSCutting Coated tool with types TiN (Jiangsu Industry Co. Ltd., Coatings Thickness Friction Coefficient 6 µm 0.050–0.065 HSS (DanyangYancheng, Daming China) Tools, Ltd, Danyang, China) N/A 0.1–0.23 HSS CoatedM35 HSS with Co TiN (5%) (Jiangsu (Jiangsu Industry Industry Co. Co. Ltd., Ltd., 6 µmN/A 0.050–0.065 0.030–0.045 Yancheng,Yancheng, China) China) M35 HSS Co (5%) (Jiangsu Industry Co. Ltd., No. of fluteN/A 2 0.030–0.045 Yancheng, China) No. of flute Flute length (mm) 2 50 Tool geometryFlute length (mm)Shank diameter (mm) 50 6 Shank diameter (mm) 6 Tool geometryspecifications Tool diameter (mm) 6 Tool diameter (mm) 6 specifications Overall length (mm) 102 Overall length (mm) 102 ◦ Point angle (°) Point angle ( ) 135 135 Helix angle (°) Helix angle (◦) 25 25

FigureFigure 2. Images 2. Images of high-speed of high-speed steel steel (HSS), (HSS), HSS HSScoated coated with withTiN (HSS-TiN), TiN (HSS-TiN), and M35 and M35HSS-cobalt HSS-cobalt (HSS-Co)(HSS-Co) with with new new conditions. conditions.

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(a)

(b)

Figure 3. (a) Diagram of designatedFigure 3. drilled(a) Diagram holes on of designatedthe workpiece drilled and holes(b) drilling on the operation workpiece on and (b) drilling operation on geopolymer samples. geopolymer samples.

Four different spindle speedsFour that different were spindle250 rpm, speeds 200 rpm, that 150 were rpm, 250 and rpm, 100 rpm 200 rpm,with 150 rpm, and 100 rpm a constant feed rate of 0.10with mm/rev a constant and feeddepth rate of ofcut 0.10 0.30 mm/rev mm were and set depth using of Akira cut 0.30 Seiki mm were set using Akira Performa SR3 CNC millingSeiki machine, Performa as SR3shown CNC in millingFigure 4. machine, Initially, as the shown parameter in Figure selec-4. Initially, the parameter tion was set in larger rangesselection based was on the set literature in larger ranges[22] with based respect on theto the literature nearest [similar22] with respect to the nearest samples; however, the samplessimilar samples; experienced however, major the cracks samples when experienced drilled at majorvarious cracks high when drilled at various spindle speed parameters,high and spindle therefore, speed the parameters, ranges had andto be therefore, lowered until the ranges the drilling had to be lowered until the process could be completeddrilling high processest at 250 could rpm. be The completed flank wear highest was at observed 250 rpm. in The the ﬂank se- wear was observed in quence of 5, 10, 15, 20, andthe sequence25 holes using of 5, 10,Xoptron 15, 20, Stereo and 25 Microscope holes using XST60 Xoptron digital Stereo mi- Microscope XST60 digital croscope and visualizedmicroscope using iSolution and Lite. visualized The surface using roughness iSolution Lite.was measured The surface using roughness was measured Accretech Handysurf E+using 35 Portable Accretech Surface Handysurf Tester on E+ each35 Portable sample. Surface The setup Tester of onthe each sur- sample. The setup of the face roughness measurementsurface is roughnessshown in Figure measurement 4a, while is the shown location in Figure of measurement4a, while the is location of measurement represented in Figure 4b.is represented in Figure4b.

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(a)

(b)

Figure 4. (a) The locationFigure of surface 4. (a) The roughness location measurement of surface roughness and (b) location measurement of measurement. and (b) location of measurement.

3. Results and Discussion3. Results and Discussion 3.1. Tool Wear Evaluation3.1. Tool Wear Evaluation Before discussing theBefore flank discussing wear, it is the interesting flank wear, to it note is interesting that the tochip note formed that the ob- chip formed observed served is powder-likeis chips. powder-like This type chips. of form Thised type chip of was formed due to chip the wasproperties due to of the the properties fly of the fly ash ash geopolymer, whichgeopolymer, is very hard which and isbrittle very [22]. hard Due and to brittle its brittleness, [22]. Due the to geopolymer its brittleness, the geopolymer experience brittle fractures,experience therefore brittle producing fractures, thereforediscontinuous producing chips discontinuous and most of the chips time and most of the time powder forms [23]. This powder-like chip also shows a sign of a potential reduction of the powder forms [23]. This powder-like chip also shows a sign of a potential reduction of the life of the bit, and even breaks the tool if high spindle speed is applied. Table3 shows tool life of the bit, and even breaks the tool if high spindle speed is applied. Table 3 shows tool wear (flank wear) as measured from the optical microscope on different spindle speeds wear (flank wear) as measured from the optical microscope on different spindle speeds using HSS, HSS-TiN, and HSS-Co. The data were then tabulated into graphs, as shown using HSS, HSS-TiN, and HSS-Co. The data were then tabulated into graphs, as shown in in Figure5. As expected, it can be observed that the flank wear increased as the drilling Figure 5. As expected, it can be observed that the flank wear increased as the drilling pro- processes went through until Hole-25. Continuous employment of the drilling process cesses went through until Hole-25. Continuous employment of the drilling process from from one hole to another is believed to have increased the cutting temperature, which one hole to another is believed to have increased the cutting temperature, which had a had a huge impact on wear, experiencing an increase in the flank wear, as mentioned by huge impact on wear, experiencing an increase in the flank wear, as mentioned by the the literature [24]. The images of the flank wear captured by the microscope for each cut literature [24]. The images of the flank wear captured by the microscope for each cut are are shown in Table4. From the table, there is an existence of growing tool wear occurred shown in Table 4. From the table, there is an existence of growing tool wear occurred due due to the friction between the underside of the tool (clearance face) and the geopolymer to the friction betweenworkpiece. the underside The wear of the happened tool (clearance at the face) drill and corner the due geopolymer to subjected work- horizontal and vertical piece. The wear happenedforces that at occurredthe drill andcorner from due the to spindle subjected speed horizontal and contact and length vertical at the maximum. This forces that occurred isand due from to thethe higherspindle friction speed and that contact happened length during at the the maximum. drilling process,This contributing to is due to the higher frictionthe removal that happened of small particles during the from drilling the sharp process, edges contributing of the cutting to the tools [25]. The cutting removal of small particlesedges from of the the flank sharp surface edges gradually of the cutting wore astools the [25]. drilling The process cutting progressededges with no sign of of the flank surface graduallyflaking or wore chipping. as the Anotherdrilling process interesting progressed finding with was thatno sign in the of flak- coating, the presence of ing or chipping. AnotherCo grain interesting started tofinding wear slowlywas that after in the a few coating, holes untilthe presence the end ofof holeCo 25, indicating that grain started to wearthe slowly coating after is nota few significant holes until in resistingthe end of flank hole wear. 25, indicating Previous researchthat the stated that HSS-Co coating is not significanthas poorin resisting heat and flank wear wear. resistance Previous [26 research,27], and stated the cornerthat HSS-Co edge startshas to wear after the poor heat and wear coatingresistance grains [26,27], are and lost inthe the corner worn edge zone. starts This to justifies wear after that the both coating HSS-Co and HSS-TiN are

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grains are lost in the worn zone. This justifies that both HSS-Co and HSS-TiN are the cheapest types of coated HSS in the market. However, both coated tools still manifest a the cheapest types of coated HSS in the market. However, both coated tools still manifest a betterbetter performance,performance, compared compared to to uncoated uncoated HSS. HSS.

Table 3. Tool wear effects on different spindle speeds using HSS, HSS-TiN, and HSS-Co. Table 3. Tool wear effects on different spindle speeds using HSS, HSS-TiN, and HSS-Co. Tool Wear (mm) Tool Wear (mm) Spindle Speed Spindle Speed: Spindle Speed: Spindle Speed: Spindle250 rpm Speed Spindle200 Speed:rpm Spindle150 Speed: rpm Spindle100 Speed:rpm 250 rpm 200 rpm 150 rpm 100 rpm No. of Holes No. of Holes No. of Holes HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN 55 0.08 0.08 0.060.06 0.050.05 0.040.04 0.030.03 0.020.02 0.040.04 0.020.02 0.010.01 0.020.02 0.020.02 0.010.01 1010 0.11 0.11 0.100.10 0.090.09 0.090.09 0.080.08 0.070.07 0.070.07 0.050.05 0.040.04 0.040.04 0.030.03 0.030.03 15 0.21 0.20 0.19 0.14 0.12 0.10 0.11 0.10 0.09 0.08 0.07 0.07 15 0.21 0.20 0.19 0.14 0.12 0.10 0.11 0.10 0.09 0.08 0.07 0.07 20 0.30 0.28 0.27 0.22 0.21 0.20 0.12 0.16 0.15 0.11 0.10 0.09 2520 0.35 0.30 0.340.28 0.320.27 0.330.22 0.310.21 0.300.20 0.220.12 0.200.16 0.180.15 0.120.11 0.110.10 0.110.09 25 0.35 0.34 0.32 0.33 0.31 0.30 0.22 0.20 0.18 0.12 0.11 0.11

FigureFigure 5. 5.Growth Growth of of ﬂank flank wear wear of of HSS, HSS, HSS-TiN, HSS-TiN, and and HSS-Co HSS-Co from from ( a(–ad–d).).

MaterialsMaterialsMaterialsMaterials 20212021 20212021,,, , ,14, 14 1414,,, , ,x,x x xx x FORFOR FOR FORFORFOR PEERPEER PEER PEERPEERPEER REVIEWREVIEW REVIEW REVIEWREVIEWREVIEW 888 8 of ofofof 15 151515

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TableTableTableTable 4. 4. 4.4. Images Images ImagesImages of of ofof flank flank flankflank wears wears wearswears gradually gradually graduallygradually emerge emerge emergeemerge on on onon HSS,HSS, HSS, HSS,HSS,HSS, HSS-TiN,HSS-TiN, HSS-TiN, HSS-TiN,HSS-TiN,HSS-TiN, andand and andandand HSS-CoHSS-Co HSS-Co HSS-CoHSS-CoHSS-Co underunder under underunderunder aa a aaa micro-micro- micro- micro-micro-micro- scopescopescopescope magnification magnification magnificationmagnification scale scale scalescale from from fromfrom 30× 30× 30×30× to150×. to150×. to150×.to150×. Table 4. Images of ﬂank wears gradually emerge on HSS, HSS-TiN, and HSS-Co under a microscope magniﬁcation scaleCuttingCuttingCuttingCutting from Speed Speed Speed 30Speed× to150 ×. ToolsToolsToolsTools InitialInitialInitialInitial Condition Condition ConditionCondition Final Final Final Final Condition Condition ConditionCondition (25th (25th (25th(25th Hole) Hole) Hole)Hole) (rpm)(rpm)(rpm)(rpm) Tools Cutting Speed (rpm) Initial Condition Final Condition (25th Hole)

250250250250250

HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS HSS

100100100100100

250250250250250

HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN HSS-TiN

100100100100100

250250250250250 HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co HSS-Co MaterialsMaterials 2021 2021, ,14 14, ,x x FOR FOR PEER PEER REVIEW REVIEW HSS-Co 99 ofof 1515

HSS-Co

100100100

FigureFigure 6 6 shows shows the the progression progression of of flank flank wear wear curves curves for for uncoated uncoated HSS, HSS, HSS-TiN, HSS-TiN, and and HSS-CoHSS-Co drill drill bits bits in in drilling drilling the the fly fly ash ash geopolymer geopolymer at at spindle spindle speeds speeds of of 100, 100, 150, 150, 200, 200, and and 250250 rpm rpm at at 25th 25th holes. holes. Although Although the the major major trends trends show show that that all all flank flank wears wears increase increase as as the the spindlespindle speed speed increases, increases, it it is is interesting interesting to to note note that that at at 100 100 rpm, rpm, the the flank flank wear wear does does not not showshow significant significant differences. differences. This This result result is is in in line line with with the the previous previous studies studies that that showed showed thethe increasing increasing value value of of tool tool wear wear as as spindl spindlee speed speed increases increases [22,26,28,29]. [22,26,28,29]. However, However, start- start- inging at at 150 150 rpm, rpm, the the flank flank wear wear differences differences sh showow noteworthy noteworthy differences. differences. The The presence presence of of aa layer layer of of coating coating increases increases the the hardness hardness and and wear wear resistance resistance of of the the HSS-TiN HSS-TiN and and HSS-Co HSS-Co drilldrill bits bits at at low low speed, speed, and and therefore, therefore, less less wear wear occurred, occurred, compared compared to to the the uncoated uncoated HSS HSS drilldrill bits bits [26], [26], but but yet yet the the coatings coatings could could not not sustain sustain the the friction friction at at 150 150 rpm. rpm. The The highest highest flankflank wear wear was was recorded recorded on on an an uncoated uncoated HSS HSS drill drill bit bit at at 250 250 rpm, rpm, with with a a value value of of 0.35 0.35 mm. mm. ThisThis highest highest is is in in line line with with the the literature literature [26–30] [26–30] due due to to the the fact fact that that HSS HSS is is less less superior, superior, comparedcompared to to HSS-TiN HSS-TiN coated coated and and HSS-Co. HSS-Co. The The lo lossss of of the the tool tool materi materialal can can be be observed observed onon the the tool tool flank, flank, due due to to abrasive abrasive wear wear of of the the cutting cutting edge edge against against the the machined machined surface. surface. AlthoughAlthough the the tool tool material material loss loss happened happened in in all all three three cutting cutting tools, tools, the the worst worst came came from from thethe uncoated uncoated HSS HSS due due to to its its direct direct engageme engagementnt between between the the HSS HSS materials materials and and the the work- work- piece.piece. Based Based on on the the range range of of parameters parameters used used in in this this experiment, experiment, it it demonstrates demonstrates that that spin- spin- dledle speed speed is is directly directly proportional proportional to to the the flan flankk wear wear value. value. Increases Increases in in spindle spindle speed speed re- re- duceduce the the tool-to-chip tool-to-chip contact contact area, area, therefore therefore reducing reducing friction, friction, which which allows allows better better surface surface qualityquality to to be be achieved. achieved.

HSSHSS HSS-TiNHSS-TiN HSS-CoHSS-Co 0.35 0.35 0.34 0.34 0.33 0.33 0.32 0.32 0.31 0.31 0.3 0.3 0.22 0.22 0.2 0.2 0.18 0.18 0.12 0.12 0.11 0.11 0.11 0.11 Flank wear, mm wear, Flank Flank wear, mm wear, Flank

100100 150 150 200 200 250 250 CuttingCutting speed, speed, rpm rpm FigureFigure 6. 6. Flank Flank wear wear value value of of cutting cutting tools tools 25 25thth hole hole at at different different spindle spindle speeds. speeds.

FigureFigure 7 7 shows shows the the comparison comparison of of flank flank wear wear at at various various spindle spindle speeds speeds under under the the samesame cutting cutting tool tool of of HSS, HSS, HSS-TiN, HSS-TiN, and and HSS-Co. HSS-Co. In In general, general, all all trends trends of of flank flank wear wear show show thatthat the the rate rate of of flank flank wear wear is is faster faster with with re respectspect to to the the speed speed of of the the drilling drilling processes. processes. For For thethe HSS HSS tool, tool, the the maximum maximum tool tool wear wear (Vb (Vbmaxmax) )is is already already seen seen to to exceed exceed 100 100 rpm rpm on on the the 20th20th hole, hole, suggesting suggesting that that the the maximum maximum of of 20 20 holes holes can can be be drilled drilled using using HSS HSS at at 100 100 rpm. rpm. HSSHSS can can be be used used at at faster faster spindle spindle speed; speed; somehow somehow the the Vb Vbmaxmax is is exceeded exceeded at at the the 15th 15th hole hole ifif 100 100 rpm rpm is is used. used. In In addition, addition, only only 10 10 holes holes can can be be drilled drilled on on the the materials materials if if 200 200 rpm rpm is is applied.applied. For For the the results results of of using using the the 250-rpm 250-rpm HSS HSS tool, tool, only only five five to to six six holes holes can can be be drilled drilled

Materials 2021, 14, x FOR PEER REVIEW 9 of 14

Materials 2021, 14, 1628 9 of 14

Figure 6 shows the progression of flank wear curves for uncoated HSS, HSS-TiN, and HSS-Co drill bitsFigure in 6drilling shows the the fly progression ash geopolymer of flank at wear spindle curves speeds for uncoated of 100, 150, HSS, 200, HSS-TiN, and and 250 rpm HSS-Coat 25th holes. drill bitsAlthough in drilling the major the fly trends ash geopolymer show that all at spindleflank wears speeds increase of 100, as 150, the 200, and spindle speed250 rpm increases, at 25th holes.it is interesting Although to the note major that trends at 100 show rpm, that the allflank flank wear wears does increase not as the show significantspindle speeddifferences. increases, This itresult is interesting is in lineto with note the that previous at 100 rpm,studies the that flank showed wear does not the increasingshow significantvalue of tool differences. wear as spindl This resulte speed is inincreases line with [22,26,28,29]. the previous However, studies that start- showed the ing at 150increasing rpm, the valueflank wear of tool differences wear as spindle show noteworthy speed increases differences. [22,26,28 The,29 ].presence However, of starting a layer ofat coating 150 rpm, increases the flank the wearhardness differences and wear show resistance noteworthy of the differences.HSS-TiN and The HSS-Co presence of a drill bits layerat low of speed, coating and increases therefore, the less hardness wear occurred, and wear compared resistance to of the the uncoated HSS-TiN HSS and HSS-Co drill bitsdrill [26], bitsbut atyet low the speed, coatings and could therefore, not sustain less wear theoccurred, friction at compared 150 rpm. toThe the highest uncoated HSS flank weardrill was bits recorded [26], but on yet an theuncoated coatings HSS could drill notbit at sustain 250 rpm, the with friction a value at 150 of rpm.0.35 mm. The highest This highestflank is wear in line was with recorded the literature on an uncoated [26–30] due HSS to drill the bit fact at that 250 rpm,HSS is with less a superior, value of 0.35 mm. comparedThis to HSS-TiN highest is coated in line and with HSS-Co. the literature The lo [ss26 –of30 the] due tool to materi the factal thatcan be HSS observed is less superior, on the toolcompared flank, due to HSS-TiNto abrasive coated wear andof the HSS-Co. cutting The edge loss against of the the tool machined material cansurface. be observed Althoughon the the tool tool material flank, due loss to happened abrasive wearin all ofthree the cutting tools, edge againstthe worst the came machined from surface. the uncoatedAlthough HSS due thetool to its material direct engageme loss happenednt between in all three the HSS cutting materials tools, the and worst the work- came from the piece. Baseduncoated on the HSS range due of toparameters its direct engagementused in this experiment, between the it HSS demonstrates materials and that the spin- workpiece. dle speedBased is directly on the proportional range of parameters to the flan usedk wear in thisvalue. experiment, Increases itin demonstratesspindle speed that re- spindle duce the speedtool-to-chip is directly contact proportional area, therefore to the flankreducing wear friction, value. Increaseswhich allows in spindle better speed surface reduce the quality totool-to-chip be achieved. contact area, therefore reducing friction, which allows better surface quality to be achieved.

HSS HSS-TiN HSS-Co 0.35 0.34 0.33 0.32 0.31 0.3 0.22 0.2 0.18 0.12 0.11 0.11 Flank wear, mm wear, Flank

100 150 200 250 Cutting speed, rpm Figure 6. FlankFigure wear 6. Flank value wear of cutting value oftools cutting 25thtools hole 25that different hole at spindle different speeds. spindle speeds.

Figure 7 Figureshows7 theshows comparison the comparison of flank ofwear flank at wearvarious at variousspindle spindlespeeds speedsunder the under the same cuttingsame tool cutting of HSS, tool HSS-TiN, of HSS, HSS-TiN, and HSS-Co. and HSS-Co.In general, In all general, trends all of trends flank wear of flank show wear show that the ratethat of the flank rate wear of flank is faster wear with is faster respect with to respect the speed to the of speedthe drilling of the processes. drilling processes. For For the HSS thetool, HSS the tool,maximum the maximum tool wear tool (Vb wearmax) is (Vb alreadymax) is seen already to exceed seen to 100 exceed rpm 100on the rpm on the 20th hole,20th suggesting hole, suggesting that the maximum that the maximum of 20 holes of 20can holes be drilled can be using drilled HSS using at 100 HSS rpm. at 100 rpm. HSS can HSSbe used can at be faster used atspindle faster speed; spindle somehow speed; somehow the Vbmax the is Vbexceededmax is exceeded at the 15th at thehole 15th hole if 100 rpmif 100is used. rpm In is used.addition, In addition, only 10 holes only 10can holes be drilled can be on drilled the materials on the materials if 200 rpm if 200is rpm is applied. applied.For the results For the of results using ofthe using 250-rpm the 250-rpmHSS tool, HSS only tool, five only to six five holes to sixcan holes be drilled can be drilled before it beforeexceeds it exceedsVbmax. Remarkably, Vbmax. Remarkably, the HSS-TiN the HSS-TiNtool also tooldoes also not doesshow not a significant show a significant improvementimprovement in drilling in fly drilling ash geopolymer fly ash geopolymer.. Similar to Similar what towas what experienced was experienced on HSS on HSS uncoateduncoated tool, the tool,use of the 100 use rpm of 100on HSS-Ti rpm onN HSS-TiN shows the shows same the number same numberof holes ofas holesHSS as HSS when it reacheswhen it Vb reachesmax, i.e., Vb 15max holes, i.e., and 15 holes 10 holes and were 10 holes recorded were recorded as the maximum as the maximum number number that can thatbe drilled can be with drilled 150 with and 150200 andrpm, 200 respectively. rpm, respectively. Interestingly, Interestingly, the coating the of coating TiN of TiN helps thehelps tool to the stay tool a tolittle stay bit a littlelonger bit in longer cutting in at cutting 250 rpm at 250 when rpm the when Vbmax the at Vb 250max rpmat 250 rpm was recordedwas recorded at the 10th at thehole. 10th hole.

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HSS 250 rpm 200 rpm 150 rpm 100 rpm 0.4 0.35 0.3 0.25 0.2 0.15

Flank Wear (vb) 0.1 0.05 0 0 5 10 15 20 25 Number of holes

HSS-TiN 250 rpm 200 rpm 150 rpm 100 rpm

0.4 0.35 0.3 0.25 0.2 0.15

Flank wear (vb) 0.1 0.05 0 0 5 10 15 20 25 Number of holes HSS-Co

250 rpm 200 rpm 150 rpm 100 rpm 0.4 0.35 0.3 0.25 0.2 0.15

Flank wear (Vb) wear Flank 0.1 0.05 0 0 5 10 15 20 25 Number of holes

FigureFigure 7.7. Comparison of ﬂankflank wearwear ofof HSS,HSS, HSS-TiN,HSS-TiN, andand HSS-CoHSS-Co atat variousvarious spindlespindle speeds.speeds.

ForFor the the HSS-Co HSS-Co cutting cutting tool, tool, it took it took the thesame same 25 holes 25 holes and and15 holes 15 holes to reach to reach Vbmax Vb at max100 atand 100 150 and rpm, 150 respectively. rpm, respectively. Nevertheless, Nevertheless, the performance the performance of HSS-Co of HSS-Cohelped the helped increase the increaseat 200 rpm. at 200 The rpm. Vbmax The was Vb recordedmax was at recorded the same at 15th the samehole when 15th hole 200 whenrpm was 200 applied rpm was to appliedthe drilling to the process. drilling Similarly, process. Similarly,only 10 holes only can 10 holesbe drilled can be using drilled HSS-Co using with HSS-Co 250 withrpm 250before rpm it beforereaches it Vb reachesmax. Vbmax.

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3.2. Surface Roughness Evaluation The surface roughness of the material is one of the most important aspects that need to be considered when carrying a drilling process. The result of the surface roughness help to determine whether the selected parameter of machining is sufficient enough to create a good finishing quality to the product. Thus, maintaining a low value of surface roughness will produce a good finishing to the product itself within the demand and thus will create an added value to the production. Figure 8 shows the comparison of surface roughness value for the cutting tools at a spindle speed of 250 rpm. The general trend shows gradual increases on Ra values indi- Materials 2021, 14, 1628 cating that the surface roughness quality is significantly affected by the engagement11 of of the 14 cutting tool with the workpiece. Another interesting point derived from the figure is that HSS-Co produces the lowest value of surface roughness, compared to HSS-TiN and uncoated HSS. When using uncoated drill tools, the thermal softening effects affected the 3.2.edge Surface of tools, Roughness resulting Evaluation in damage. This situation could contribute to the high surface roughnessThe surface of the roughness drilled surface of the [12]. material The HSS-Co is one of-coated the most drill important tool has a aspects superior that abrasive need toperformance, be considered which when helps carrying in shearing a drilling finer process. surface The finish, result compared of the surface to the roughness other counter- help toparts. determine During whether the drilling the selectedprocess, parameterthe cutting of tool machining can retain is hardness sufficient and enough stability to create at high a goodimpact finishing force and quality high to temperature, the product. Thus,hence maintainingproducing strong a low valuedrilling of surfaceaction to roughness slide and willproduce produce the aholes good consistently. finishing to It the should product be itselfnoted within that the the use demand of an uncoated and thus drilling will create tool angave added very value high tosurface the production. roughness, contributing to the major change in the percentage distribution.Figure Therefore,8 shows the for comparison the best drilling of surface performance, roughness HSS-Co value foris suggested the cutting to tools be used at aalong spindle with speed a spindle of 250 speed rpm. of The100 generalrpm. trend shows gradual increases on Ra values indicatingOn the that other the hand, surface Figure roughness 9 shows quality the comparison is significantly of surface affected roughness by the engagement value of the ofcutting the cutting tools toolafter withdrilling the geop workpiece.olymer Anotherat various interesting spindle speeds. point derived It can be from seen the from figure Fig- isures that that HSS-Co all the produces cutting tool thes lowestshowed value exact ofbehavior, surface in roughness, which the compared surface roughness to HSS-TiN val- andues uncoateddecrease HSS.with Whenthe increase using uncoatedin spindle drill speed tools, from the 100 thermal rpm up softening to 250 rpm. effects The affected effects theof spindle edge of tools,speed resultingon the surface in damage. roughness This situationobtained could in this contribute study are to in the agreement high surface with roughness of the drilled surface [12]. The HSS-Co-coated drill tool has a superior abrasive the results of previous studies [30–32]. Although increasing the spindle speed may in- performance, which helps in shearing finer surface finish, compared to the other coun- crease the quality of surface finish, higher spindle speed also comes with higher heat gen- terparts. During the drilling process, the cutting tool can retain hardness and stability at erated and therefore causes the tool to wear or blunt [32]. high impact force and high temperature, hence producing strong drilling action to slide The results shown in Figure 9 show that the performance of surface roughness is and produce the holes consistently. It should be noted that the use of an uncoated drilling closely related to the spindle speed. Increasing the spindle speed will lead to high friction, tool gave very high surface roughness, contributing to the major change in the percentage resulting in an increase in the temperature at the contact region. Hence, this will result in distribution. Therefore, for the best drilling performance, HSS-Co is suggested to be used thermal softening of the workpiece material and thus reduce the thrust force and enable along with a spindle speed of 100 rpm. the machine to feed the drill with less energy, resulting in a better surface finish [32].

HSS HSS-TiN HSS-Co 4 3.5 3 2.5 2 1.5 1

Surface Roughness, Ra Surface 0.5 0 0 5 10 15 20 25 Number of holes

FigureFigure 8.8. Surface roughnessroughness valuevalue ofof differentdifferent cuttingcutting toolstools atat aa spindlespindle speedspeed ofof 250250 rpm.rpm.

On the other hand, Figure9 shows the comparison of surface roughness value of the cutting tools after drilling geopolymer at various spindle speeds. It can be seen from Figures that all the cutting tools showed exact behavior, in which the surface roughness values decrease with the increase in spindle speed from 100 rpm up to 250 rpm. The effects of spindle speed on the surface roughness obtained in this study are in agreement with the results of previous studies [30–32]. Although increasing the spindle speed may increase the quality of surface ﬁnish, higher spindle speed also comes with higher heat generated and therefore causes the tool to wear or blunt [32]. Materials 2021, 14, 1628 12 of 14 Materials 2021, 14, x FOR PEER REVIEW 12 of 14

HSS 100rpm 150rpm 200rpm 250rpm 4 3.73 3.64 3.38 3.35 3.14 3.04 2.95 2.92 2.62 2.56 2.47 2.46 2.42 2.35 2.29 2.26 2.05 1.99 1.82 Surface roughness, Ra

5 10152025 Number of holes

HSS-TiN 100rpm 150rpm 200rpm 250rpm 3.85 3.73 3.64 3.21 3.18 2.94 2.87 2.79 2.7 2.42 2.37 2.29 2.28 2.25 2.1 2.1 2.07 1.88 1.75 1.65 Surface roughness, Ra

5 10152025 Number of holes

HSS-Co 100rpm 150rpm 200rpm 250rpm 3.59 3.33 3.24 2.97 2.91 2.73 2.62 2.56 2.53 2.38 2.2 2.08 2.06 1.98 1.98 1.89 1.86 1.65 1.58 1.42 Surface roughness, Ra

5 10152025 Number of holes

FigureFigure 9. Surface 9. Surface roughness roughness value value of the of thecutting cutting tools. tools.

4. ConclusionsThe results shown in Figure9 show that the performance of surface roughness is closelyThe first related conclusion to the spindle made speed.is that Increasingfly ash geopolymer the spindle is speed machinable will lead using to high drilling friction, processresulting either in HSS, an increase HSS-TiN, in theand temperature HSS-Co dril atl bits, the as contact indicated region. by Hence,the experiment. this will resultEven in so, thethermal experiment softening showed of the that workpiece almost all material tools surpass and thus the reduce 0.10-mm the targeted thrust force tool life and limit enable afterthe drilling machine 15 holes. to feed Furthermore, the drill with all less cutting energy, tools resulting show the in abehavior better surface as expected, ﬁnish which [32]. is to wear gradually with respect to the number of drilled holes. On the other hand, the

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4. Conclusions The first conclusion made is that fly ash geopolymer is machinable using drilling process either HSS, HSS-TiN, and HSS-Co drill bits, as indicated by the experiment. Even so, the experiment showed that almost all tools surpass the 0.10-mm targeted tool life limit after drilling 15 holes. Furthermore, all cutting tools show the behavior as expected, which is to wear gradually with respect to the number of drilled holes. On the other hand, the spindle speed is directly proportional with tool wear but inversely proportional with the surface roughness of the samples. The finding also shows HSS-TiN and HSS-Co increase the tool life at high spindle speed (200 rpm and above), compared to the HSS tool. HSS-Co exhibits the greatest tool life by showing the lowest value of flank wear and produces a better surface finish by exhibiting a low Ra value. Therefore, for the best drilling performance, Hss-Co is the most recommended tool to be used in drilling fly ash geopolymer material with a spindle speed of 100 rpm.

Author Contributions: Conceptualization, M.F.G., M.M.A.B.A., and S.Z.A.R.; data curation, M.F.G.; formal analysis, M.F.G. and M.M.A.B.A.; investigation, M.F.G. and M.M.A.B.A.; methodology, M.F.G., M.M.A.B.A., and S.Z.A.R.; project administration, M.F.G. and M.M.A.B.A.; visualization, M.E.K., M.S.O., T.S. and M.F.G.; writing—original draft preparation, M.F.G.; writing—review and editing, A.V.S., M.E.K., M.F.M.T., J.G., P.P., S.G., T.S. and M.S.O. All authors have read and agreed to the published version of the manuscript. Funding: The authors would like to acknowledge the support from the Fundamental Research Grant Scheme (FRGS) under a grant number of FRGS/1/2016/STG07/UNIMAP/02/1 from the Ministry of Higher Education Malaysia, Application ID 218885-247922 and code 9003-00572. Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: The data presented in this study are available on request from the corresponding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

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