Machining Duplex Stainless Steel: Comparative Study ...

coatings Article

Machining Duplex Stainless Steel: Comparative Study Regarding End Mill Coated Tools Ronny M. Gouveia 1 , F. J. G. Silva 1, *, Pedro Reis 1 and A. P. M. Baptista 2 1 2

*

ISEP (School of Engineering, Polytechnic of Porto), Porto 4200-072, Portugal; [email protected] (R.M.G.); [email protected] (P.R.) INEGI (Instituto de Ciência e Inovação em Engenharia Mecânica e Engenharia Industrial), Porto 4200-465, Portugal; [email protected] Correspondence: [email protected]; Tel.: +351-228-340-500

Academic Editor: James Krzanowski Received: 31 August 2016; Accepted: 12 October 2016; Published: 26 October 2016

Abstract: The difficulties in the machining of duplex stainless steel are well known. However, research on this matter is rather limited. Suppliers offer quite different cutting tools for the same raw material, with end mills of two, three or even four knives and a huge number of distinct coatings, some of them under commercial brands, making it difficult to assess the advantages they offer. Furthermore, there is a remarkable difference among the several types of duplex stainless steel available nowadays on the market. The present work intends to assess the machining performance of different tools, analyzing the behavior and wear mechanisms with two different cutting lengths, keeping constant the machining trajectory. Some other parameters were also kept constant, such as cutting speed, depth of cut and cutting width, as well as feed per tooth. The machining process was carried out under lubricated conditions, using an emulsion of 5% oil in water. Tools provided with a different number of teeth and surface coatings were tested, analyzing the wear behavior of each cutting length using scanning electron microscopy, trying to identify wear performance and how each coating contributes to increased tool life. The surfaces produced were also analyzed by means of profilometry measurements, correlating tool wear and part surface roughness. This comparative study allows determining the advantages of different tools relative to others, based on coatings and tool geometry. Keywords: wear; machining processes; cutting tool wear; end milling machining; duplex stainless steel; surface quality; roughness; coated tools

1. Introduction Machining remains one of the most employed processes in the world’s metalworking context. The aeronautics, naval and automobile industries are, probably, the economic sectors that most demand this kind of process through the engineering of parts included directly and indirectly in aircrafts, ships, trucks, buses and cars. Machining processes are necessary when surface quality is one of the main requirements demanded by customers or designers. However, competitiveness is a key factor in such industries, requiring accurate and extremely efficient equipment. Indeed, the available equipment on the market has continued to grow, becoming increasingly sophisticated and allowing an improved accuracy [1], answering to the need of the market for complex organic shapes and high surface quality. Researchers have contributed significantly to this development, devoting their efforts to explaining many of the machining related phenomena, anticipating market needs and studying the best ways to increase production and improve products through tooling improvements, more accurate machining parameters, optimized machining trajectories, and so on.

Coatings 2016, 6, 51; doi:10.3390/coatings6040051

www.mdpi.com/journal/coatings

Coatings 2016, 6, 51

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With regards to the cutting process, mechanical work developed is converted into plastic deformation, creating friction between the tool and workpiece, resulting in heat generation [2]. Increasing the tool temperature causes materials to become softer and wear increases rapidly, reducing the tool life and decreasing the machining efficiency and the accuracy attained. Some experiments suggest that tool temperature rises as speed machining increases [3,4] in continuous cutting processes. However, Palmai [5], studying the interrupted cutting characteristics of the milling machining process, though not directly supported by experimental work, suggested that temperature can diminish as speed machining increases. Many studies have been carried out trying to optimize the parameters set for each material [6–8]. Rawangwong et al. [7], studying the main factors that affect the surface roughness of a semi-solid AA7075 alloy in face milling, suggested that feed rate ratio and cutting speed are the principal factors, whereas the depth of cut does not influence the surface quality. Furthermore, the same authors stated in the same work that higher cutting speed and lower feed rate tend to decrease the surface roughness. Zhang et al. [8] concluded as well that cutting speed and feed rate are the main factors influencing the surface roughness, rather than the depth of cut, in the milling process. A similar study has been carried out by Sai et al. [9] using as sample materials carbon steel and duplex stainless steel, concluding that a very slow cutting speed leads to build-up edge (BUE) formation, resulting in poor surface quality. They showed that a cutting speed of between 220 and 440 m/min achieved the best roughness surface values for small feed rate. An increase in the surface micro hardness and tensile residual stresses was also registered with higher values of cutting speed and feed rate. The correlation among the parameters of surface integrity and fatigue life of machined components has also been studied. Li et al. [10] focused on the Inconel 718 milling process, studying the relationship between tool wear, fatigue life and surface integrity, concluding that more tool wear generates low surface roughness, and, with tool wear up to VB = 0.2 mm (VB, width of the flank wear land), no fatigue took place in up to four million cycles on the machined samples. Furthermore, considering end mill tools provided with PVD coated inserts, the roughness in the step-over direction was more pronounced than in the feed direction. Stability during a machining process is a key factor in obtaining lower surface roughness and accurate products. Regarding the milling process, Stepan et al. [11] have studied the milling process stability using three different milling tools (conventional, variable helix and serrated milling tools). By means of semi-discretization and multi-frequency solution, the authors concluded that serrated milling tools provided the best contribution to cutting stability, despite this type of tool being used essentially in roughing operations, whereas the optimized variable helix end mill tools are more adequate for finishing operations, providing a better result in terms of stability than conventional ones. The cost, quality and lead-time of the plastic products are directly influenced by the mould industry, which is based essentially on machining processes. When creating large mould cavities, milling operations are one of the most necessary means utilized [12,13], however, the surface roughness usually required by this industry cannot be achieved solely by this process [14]. The need to involve hand polishing operations is required, despite the use of High Speed Machining (HSM) and sophisticated tool path trajectories created through Computer Aided Manufacturing (CAM) software. Souza et al. [12] have stated that a correct selection of tool paths can save 88% of machining time and cut 40% of mould machining costs, when compared with a poor strategy option. Denkena et al. [15] recently studied the influence of cutting edge geometry in tough milling operations on hardened steel moulds, trying to overcome the thermo-mechanical stresses developed on tools. The main goal of these authors was to decrease tool friction and wear by changing the flank face geometry. Simulations were made, which allows the provision of tools with undercut geometries, whereby an increase in tool life and a decrease in induced residual stress on machined parts can be observed. Coatings have proven to be an attractive way to extend tool life by increasing surface hardness, acting in addition to other crucial parameters concerning tool work such as: decreasing the friction between tool and part; creating a thermal barrier between the surface and the hard metal substrate

Coatings 2016, 6, 51 Coatings 2016, 6, 51

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Coatings have proven be an attractive way to extend tool life bythe increasing surface hardness, and allowing a better surfacetotemperature distribution by dissipating heat generated during tool actingwith in addition to other crucialpart parameters concerning tool work such as: decreasing friction contact chips and machined [16,17]. Thus, tool coating requirements are largethe and of high between tool and part; creating a thermal barrier between the surface and the hard metal substrate importance. Tool manufacturers started using the conventional TiN, however, this coating was not and allowing a better temperature distribution by dissipating the heat generated sufficient to solve all thesurface previously mentioned problems, hence, multilayered coatingsduring startedtool to be contact with chips and machined part [16,17]. Thus, tool coating requirements are large and of high developed in order to improve tool performance. Nowadays, tools recently introduced on the market importance. Tool manufacturers started using the conventional TiN, however, this coating was not present three or more layers, each one with specific functions, in order to satisfy all the requirements. sufficient to solve all the previously mentioned problems, hence, multilayered coatings started to be order to improve tool performance. Nowadays, tools recently introduced on the market 2. developed Materials in and Methods present three or more layers, each one with specific functions, in order to satisfy all the requirements. The raw material chosen to be machined for this study was a CD4MCuN duplex stainless steel (material specification: ASTM A890, Werkstoff-Nr. 1.4517 or EN 10283, ARSOPI, Vale de Cambra, 2. Materials and Methods Portugal). It is composed of a dual phase microstructure of both austenite and ferrite in similar The raw material chosen to be machined for this study was a CD4MCuN duplex stainless steel amounts. The chemical composition given by the supplier for this batch of steel was (wt %) C 0.03%, (material specification: ASTM A890, Werkstoff-Nr. 1.4517 or EN 10283, ARSOPI, Vale de Cambra, Si 0.41%, Mn It1.48%, P 0.02%,ofCra25.41%, Ni 6.08%, Mo 2.91%,ofCu 3.30%, Nb 0.01%, V 0.02%, W 0.04%, Portugal). is composed dual phase microstructure both austenite and ferrite in similar ◦ C and N amounts. 0.19%, CoThe 0.08% and Fe 60.02% [18]. It is sold in a heat treated state (quenched at 1135 chemical composition given by the supplier for this batch of steel was (wt %) C 0.03%, water cooled) according toCr the25.41%, supplier a yield strength ultimate tensile strength Si 0.41%, Mnand 1.48%, P 0.02%, Nihas 6.08%, Mo 2.91%, Cu(0.2%) 3.30%,and Nb an 0.01%, V 0.02%, W 0.04%, of N 489 MPa and 797 MPa, respectively (in accordance with ISO 6892-1 [19]), as well as hardness 0.19%, Co 0.08% and Fe 60.02% [18]. It is sold in a heat treated state (quenched at 1135 °C and water of 267cooled) HB (ISO [20]).toAmong several material properties, of the most important and6506-1 according the supplier hasdifferent a yield strength (0.2%) and an some ultimate tensile strength of are489 its MPa high and mechanical (approximately twice asISO much as the more common ASTM of 304 and 797 MPa,strength respectively (in accordance with 6892-1 [19]), as well as hardness 267 316HB stainless steels), good corrosion pitting resistance, goodsome toughness, good weldability and (ISO 6506-1 [20]). Among severaland different material properties, of the most important are its high twice much as theofmore common ASTM 304 316 ease of mechanical fabrication.strength Typical(approximately applications are the as construction chemical equipment andand tubbing, stainless steels), goodvessels, corrosion and pitting resistance, good good weldability and ease of pressurized tanks and heat exchangers, cellulose andtoughness, paper fabrication, sea water processing, Typical applications the construction of chemical andnumerous tubbing, pressurized etc.fabrication. This duplex stainless steel is are thought to be of interest due toequipment the fact that flanges and tanks and vessels, heat exchangers, cellulose and paper fabrication, sea water processing, etc. This accessories, which require machining, are made from this material and information surrounding duplex stainless steel is thought to be of interest due to the fact that numerous flanges and accessories, this topic is scarce. A round bar with a diameter of 60 and 300 mm in length was sufficient for all which require machining, are made from this material and information surrounding this topic is testing trials. scarce. A round baroperations with a diameter of 60 and 300 in length was sufficient for all testing Haas trials. VF2 The machining were performed onmm a 3-axis CNC machine (brand/model: The machining operations were performed on a 3-axis CNC machine (brand/model: Haas VF2 vertical machining center, Hass Automation, Inc., Oxnard, CA, USA). A 3-jaw self-centering chuck vertical machining center, Hass Automation, Inc., Oxnard, CA, USA). A 3-jaw self-centering chuck (brand/model: Bison 3575, BISON-BIAL, S.A., Bielsk Podiaski, Poland) was mounted to the machine’s (brand/model: Bison 3575, BISON-BIAL, S.A., Bielsk Podiaski, Poland) was mounted to the machine’s work table (in accordance with standard DIN 6350 [21]), guaranteeing the exact same positioning work table (in accordance with standard DIN 6350 [21]), guaranteeing the exact same positioning of of the round bar between each trial. The use of a hydraulic tool holder (brand/model: WTE DIN the round bar between each trial. The use of a hydraulic tool holder (brand/model: WTE DIN 6987169871-AD/B [22], Präzisionstechnik WTE Präzisionstechnik Kempten, was as necessary this type AD/B [22], WTE GmbH, GmbH, Kempten, Germany)Germany) was necessary this type as of system of minimized system minimized unwanted vibrations during testing. Figure 1 illustrates several components unwanted vibrations during testing. Figure 1 illustrates several components utilized utilized duringduring testing.testing.

(a)

(b)

(c)

Figure 3-jawself-centering self-centeringchuck chuckattached attached to to the (b)(b) Hydraulic Figure 1. 1. (a)(a) 3-jaw the work worktable tablesecuring securingthe thesteel steelbar; bar; Hydraulic tool holder; (c) Complete assembly during a machining run. tool holder; (c) Complete assembly during a machining run.

The comparative study is based on the wear analysis of four different milling tools advertised comparative is based on stainless the wearsteels. analysis four different advertised as The being appropriate study for milling duplex Theof milling tools usedmilling all havetools in common a as cutting being appropriate milling duplex stainless steels. milling tools used all haveMilling in common diameter of for 4 mm, a 6 mm shank diameter and The a coated hard metal substrate. tools a cutting diameter of 4 mm, a 6 mm shank diameter and a coated hard metal substrate. Milling tools


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with a 4 mm shank diameter were initially tested, however, they proved to be too fragile, suffering Coatings 2016, 6, 51 premature breakage. Table 1 lists the characteristics of all four different selected end mills. 4 of 30 with a 4 mm diameter tested, study: however, to be (D too=fragile, Tableshank 1. Milling toolswere used initially in comparative Endthey mill proved cutting tools 4 mm). suffering premature breakage. Table 1 lists the characteristics of all four different selected end mills. Brand Model Substrate Material Coating Z1 Table 1. Milling tools used in comparative study: End mill cutting tools (D = 4 mm). 2 Walter Protostar N45 Compact H30140418-4 Hard metal 4 TiAlN 3 HPMT SE30 Brand Plunge-Mill G10040005006 Hard metal Model Substrate Material AlCrN Coating Z 13 3 HPMT SE45 NovianoN45 Standard Hard AlCrN Walter Protostar Compact V47BXZ024GX040001 H30140418-4 Hardmetal metal TiAlN 2 44 3 DORMER Spectrum S812HA Hard metal 2 AlCrN 3 HPMT SE30 Plunge-Mill G10040005006 Hard metal AlCrN 3 1 Number of cutting flutes; 2 Titanium aluminium nitride; 3 Aluminium chromium nitride. Notes: 3 HPMT SE45 Noviano Standard V47BXZ024GX040001 Hard metal AlCrN 4 DORMER Spectrum S812HA Hard metal AlCrN 3 2 2 Titanium 3 Aluminium For easier reading and referencing, willaluminium be referred to by their manufacturer’s Note: 1 Number of cutting flutes;tools nitride; chromium nitride.name, followed by the number of cutting and composition of coating (e.g.,to Dormer Z2manufacturer’s AlCrN) instead of their For easier readingflutes and referencing, tools will be referred by their name, complete designation. followed by the number of cutting flutes and composition of coating (e.g., Dormer Z2 AlCrN) instead Besides analyzing the influence of coatings on wear behavior, the number of cutting flutes was of their complete designation. also changed to investigate itsinfluence effect onoftool longevity. Usually, the amount of cutting flutes influences Besides analyzing the coatings on wear behavior, the number of cutting flutes was also of changed to investigate its effectsense on tool longevity. Usually, the amount cuttingoperations flutes the ease chip removal, so it is common to use tools with less cutting flutes inofslotting ease of chip removal, so it is commonWhen sense chip to use tools with less cutting flutes inedge and influences tools withthe more flutes in side milling operations. removal is difficult, a buildup slotting operations and tools with more flutes in side milling operations. When chip removal is may appear on the tool. difficult, a buildup edge may appear on the tool. In order to evaluate the wear of each tool, a simple roughing machining strategy was created order to evaluate the wear of each tool, a simple roughing machining strategy was created to to ensureInrepeatability of test conditions. Based on the round format of the bar, a spiral path was ensure repeatability of test conditions. Based on the round format of the bar, a spiral path was created created to optimize cutting length, as can be seen in Figure 2. The tool begins side milling on the to optimize cutting length, as can be seen in Figure 2. The tool begins side milling on the outer side outer side of the stainless steel bar making its way to the center. A ramp plunge movement is used in of the stainless steel bar making its way to the center. A ramp plunge movement is used in the initial the initial of the machining stage to create atool gradual tooltoapproach to the material, avoiding portionportion of the machining stage to create a gradual approach the material, avoiding potential potential collisions. collisions.

Figure 2. Tool path strategy.

Figure 2. Tool path strategy.

All machining parameters remain the same throughout testing with the exception of the feed All machining parameters remain the same throughout with are theadjusted exception of thetofeed speed. As the number of cutting flutes changes from tool to tool,testing feed speeds in order speed. As the cutting flutes fromallows tool to tool, cutting feed speeds are adjusted order to ensure thatnumber feed perof tooth speeds are changes similar. This similar conditions on each in cutting tooth, promoting equal working and wearing conditions. Spindle speed was established based on ensure that feed per tooth speeds are similar. This allows similar cutting conditions on each cutting tool manufacturers’ and initial testing, ensuring surfacewas finish capable of based being on tooth, promoting equalrecommendations working and wearing conditions. Spindlea speed established by the profilometer. Depth ofand cut initial and working engagement were determined tool analyzed manufacturers’ recommendations testing, ensuring avalues surface finish capablebased of being on trial and error. Initial trials using 1 mm depth of cut were tested, however, this depth proved to analyzed by the profilometer. Depth of cut and working engagement values were determined based be excessive for the combination of small tool diameter and high hardness steel, needing to be on trial and error. Initial trials using 1 mm depth of cut were tested, however, this depth proved to be reduced to 0.5 mm. Recommended working engagement values are usually 60%–70% of tool excessive for the combination of small tool diameter and high hardness steel, needing to be reduced to diameter, so 3 mm was chosen for this parameter as smaller values may promote rougher surface 0.5 mm. Recommended working engagement values are usually 60%–70% of tool diameter, so 3 mm finishing and decrease tool life span. was chosen this parameter as tool smaller mayusing promote rougher surface finishing and Thefor surface wear of each wasvalues evaluated a SEM microscope provided with an decrease EDS tool (Energy-Dispersive life span. X-ray Spectroscopy) system (EDAX X-ray micro-analysis). For this study, the The surface wear of aeach tool was using a SEM OR, microscope provided equipment chosen was FEI Quanta 400 evaluated FED SEM (FEI, Hillsboro, USA). Several globalwith and an EDSclose (Energy-Dispersive X-ray Spectroscopy) system (EDAX X-ray micro-analysis). For this study, up images of the worn edges were registered. Per tool, two global images are shown, one taken with secondary electron and the400 other with retro diffused electron imaging. areas and the equipment chosen wasimaging a FEI Quanta FED SEM (FEI, Hillsboro, OR, USA). Whenever Several global


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close up images of the worn edges were registered. Per tool, two global images are shown, one taken with secondary electron imaging and the other with retro diffused electron imaging. Whenever areas of discontinuities (promoted either by loss of coating or adhesion of external materials) were detected, an EDS analysis was made to determine the chemical composition of that unknown area. Close up images of each cutting flute were taken to evaluate and measure flank wear present on the cutting edges. These measurements are designated by the abbreviation VB. Table 2 sums up all the machining parameters used with each tool. Cutting fluid emulsion was used during all machining operations, being composed of a mix of 5% oil in water. Table 2. Machining parameters for each tool. Tool

Z1

N 2 (rpm)

vc 3 (mm/min)

vf 4 (mm/min)

f z 5 (mm/tooth)

Walter 4Z TiAlN HPMT 3Z AlCrN HPMT 4Z AlCrN DORMER 2Z AlCrN

4 3 4 2

4000 4000 4000 4000

50.27 50.27 50.27 50.27

250 190 180 125

0.0156 0.0158 0.0113 8 0.0156

ae

6

(mm) 3 3 3 3

ap 7 (mm) 0.5 0.5 0.5 0.5

Notes: 1 Number of cutting flutes; 2 Spindle speed; 3 Cutting speed; 4 Feed speed or tables speed; 5 Feed per tooth speed; 6 Working engagement; 7 Depth of cut; 8 f z value lower than expected due to geometrical conditions of tool (higher cutting area).

The analysis of post-machined surface roughness was achieved using a surface profilometer (brand/model: Mahr Perthometer M2, MAHR, GmbH., Gottingen, Germany) provided with a diamond stylus tip with a 2 µm radius (ISO 4288:1996) [23]. Two different roughness readings were taken, one in a radial orientation and the other in a tangential orientation, utilizing a cutoff value of 0.8 mm. Arithmetic mean surface roughness (Ra ), surface roughness depth (Rz(DIN) ) and maximum height of the roughness profile (Rmax ) were registered for each machined surface after each experimental run. Ra is an arithmetical mean average and may not truly represent the roughness of the surface. Rz is the sum of the height of the largest peak plus the depth of the deepest valley, inside the measured length. Rmax is the height of the largest peak or the depth of the deepest valley encountered in the measured length. With radial readings it is possible to evaluate the surface roughness left by the tool feed marks (boundary lines between tool passes) while with tangential readings it is possible to verify the surface roughness in between these lines. For each tool trial, six measurements were taken (three in a radial direction and three in a tangential direction), allowing to determine a mean-value that better represents the overall roughness of the machined surface. 3. Results Having concluded all experimental trials, the wear suffered by each tool was evaluated by measuring the surface roughness on each machined part and by a microscopically analyzing the cutting edges of each tool. Average roughness values were calculated to represent the overall level of roughness present on each surface. These results allow evaluating the specific performance of each tool. 3.1. Machining Strategy The adopted machining strategy was based on the premises discussed previously. For every trial, each end milling tool will repeatedly machine a pre-determined quantity of metal (cycle). One cycle corresponds to a completion of a machining pass, with a depth of cut of 0.5 mm, starting on the outer side of the stainless steel bar and making its way to the center. Each tool will be evaluated after completing one run of eight machining cycles, which equals to a total machining distance of 7.5 m. Another set of tools will be tested during 16 cycles, totalizing a machining distance of 15 m.


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3.2. Map of Experiments In order to pursuit the main goals of this work, a map of experiments was drawn, which can be seen in Table 3, showing the different tools used in the comparative study as weel as the selected machining parameters. Table 3. Experimental parameters for each trial. Cycles/ Machining Distance

Trial

Tool

Coating

Z1

N2 (rpm)

vc 3 (mm/min)

vf 4 (mm/min)

fz 5 (mm/tooth)

ae 6 (mm)

ap 7 (mm)

8/7.5 m

1 2 3 4

WALTER 4Z HPMT 3Z HPMT 4Z DORMER 2Z

TiAlN AlCrN AlCrN AlCrN

4 3 4 2

4000 4000 4000 4000

50.27 50.27 50.27 50.27

250 190 180 125

0.0156 0.0158 0.0113 0.0156

3 3 3 3

0.5 0.5 0.5 0.5

16/15 m

5 6 7 8

WALTER 4Z HPMT 3Z HPMT 4Z DORMER 2Z

TiAlN AlCrN AlCrN AlCrN

4 3 4 2

4000 4000 4000 4000

50.27 50.27 50.27 50.27

250 190 180 125

0.0156 0.0158 0.0113 0.0156

3 3 3 3

0.5 0.5 0.5 0.5

Notes: 1 Number of cutting flutes; 2 Spindle peed; 3 Cutting speed; 4 Feed speed or tables speed; 5 Feed per tooth speed; 6 Working engagement; 7 Depth of cut.

3.3. Experimental Results 3.3.1. Walter 4Z TiAlN—Roughness and SEM Results The 8 cycles run trial for the Walter 4Z TiAlN end mill produced unexpected surface roughness results. When compared to the values obtained by the 16 cycles run, the shorter trial returned higher roughness values. There seems to be no significant explanation for these results (values can be seen in Table 4). Table 4. Part surface roughness obtained after 8 and 16 cycles of machining with Walter 4Z TiAlN end mill. Measurements

Radial

Tangential

Ra (µm)

Rz (µm)

Rmax (µm)

8 Cycles

16 Cycles

8 Cycles

16 Cycles

8 Cycles

16 Cycles

1 2 3

0.443 0.472 0.442

0.531 0.545 0.504

2.562 2.644 2.687

3.509 3.262 2.784

5.220 5.420 5.390

6.460 7.690 6.670

Average

0.452

0.527

2.631

3.185

5.343

6.940

1 2 3

0.259 0.253 0.268

0.247 0.261 0.244

1.681 1.552 1.568

1.515 1.574 1.553

2.360 2.040 1.760

1.740 1.780 1.720

Average

0.260

0.251

1.600

1.547

2.053

1.747

The obtained radial Rz roughness values for the 8 cycles trial are lower when compared to the 16 cycles run, meaning that the machined surface has a smaller profile height between surface peaks and valleys. This translates in to a smoother and stronger machined surface with better dimensional and mechanical properties. Due to its configuration (4 cutting flutes), coating and toughness, it is an ideal tool for machining harder materials, as the one used in this experiment. Although radial roughness values increased from 8 to 16 cycles (as expected), the difference between both is of low significance. This leads to the assumption that wear evolution is slow, when compared to other tools, translating into a longer tool life. The SEM analysis of the tool surfaces reveals that, for the shorter machining cycle (shown in Table 5), tool wear is very low with a small VB value (flank wear), showing edge chipping as the only type of wear present. Its influence is of low importance as shown by the small roughness values discussed earlier. The images shown in Table 5 demonstrate the existence of several surface impurities.


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Coatings 2016, Coatings 2016, 6, 51 6, 51 Table 5. Walter 4Z TiAlN SEM analysis after 8 cycles of machining. Coatings 2016, 6, 51 7 of 30 Coatings 2016, 6, 51 6, 51 Coatings 2016, Coatings Coatings 2016, 6, 2016, 51 6, 51TableTable 5. Walter 4Z TiAlN analysis 8 cycles of machining. 5. Walter 4Z TiAlN SEM SEM analysis after after 8 cycles of machining.

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Top View End Mill Table 5. Walter 4Z TiAlN SEM analysis afterof 8 cycles of machining. Table 5. 4Z SEM analysis after of Table 5. Walter Walter 4Z TiAlN TiAlN SEM analysis after cycles of machining. machining. TableTable 5. Walter Walter 5. 4Z TiAlN TiAlN 4Z SEM SEM analysis analysis after 8after 8 cycles cycles 88 cycles of machining. machining. of

(a)

(a) (a)

(a) (a) (a) Issues (a) Observed Observed Issues Observed Issues Observed Issues Observed Observed Issues Edge chipping [24] Issues Observed Observed IssuesIssues

• •

(b) (b) (b)

(b) (b) Observable Issues Analysis (b) Possible (b) Probable Causes Solutions Probable Causes Possible Solutions Probable Possible Solutions Probable Causes Possible Solutions Causes Unstable  Probable Unstable Causes Possible Solutions Probable Causes Possible Solutions Probable Probable Causes Causes Possible Possible Solutions Solutions  Unstable machining machining  Unstable  Unstable  Stabilize machining conditions  Stabilize machining conditions Unstable  Unstable machining conditions conditions Unstable machining conditions Stabilize machining conditions  Stabilize machining conditions machining machining • Select tools tougher geometry  Select tools with with tougher geometry machining machining conditions  Stabilize machining conditions Stabilize machining conditions toolHard/fragile  Hard/fragile Hard/fragile class Select tools with tougher geometry Stabilize •with Stabilize machining machining conditions conditions conditions  Select tools tougher geometry conditions conditions conditions  Hard/fragile  Select tools with tougher geometry  Select tools with tougher geometry tool class tool class Select  Select tools tools with tougher with tougher geometry geometry  Hard/fragile Hard/fragile Hard/fragile  Hard/fragile tool class tool tool class class tool class class tool

Cutting Edges Close Up

(c)

(c)

(c)

(c) (c)

(c) (c)

(e)

(e)

(d) (d) (d)

(d) (d) (d) (d)

(f)

(f)

(f) (a)(e) Secondary electron 50×); (b) Retro diffused electron imaging (mag. 50×); (c) Cutting Note: Note: (a) Secondary electron imaging (mag.(mag. 50×); (b) Retro diffused electron imaging (mag. 50×); Cutting edge edge (e) (f) (e) imaging (f) (c) (e) (mag. (e) (f) (f) Note: (a) Secondary electron imaging 50×); (b) Retro diffused electron imaging (mag. 50×);500×); (c) Cutting Cutting edge 3edge with VB = µ 45.50 µ m 500×);500×); (d) Cutting with VB = µ 34.00 µ m (mag. (e) Cutting with VB 1 with1VB = 45.50 m (mag. (d) Cutting edge 2edge with2 VB = 34.00 m (mag. 500×); (e) edge with3VB Note: Note: (a) Secondary electron imaging (mag. (mag. 50×); (b) Retro diffused electron imaging (mag. (mag. 50×); (c) Cutting edge edge (a) Secondary Secondary electron imaging 50×); (b) Retro Retro diffused electron imaging 50×); (c) Cutting Cutting Note: (a) Secondary (a) electron imaging imaging (mag. (mag. 50×);VB (b) 50×); Retro (b) diffused diffused electron electron imaging imaging (mag. (mag. 50×); (c) 50×); Cutting (c) edge edge 1 with VB =Note: = 28.00 45.50 µm m (mag. 500×); (d)electron Cutting edge 2with with 34.00 µ (mag. 500×); (e) Cutting edge 3 with VB =µ 28.00 µ m (mag. 500×); (f) Cutting 4VB with =µ 31.50 µ mdiffused (mag. 500×). (mag. 500×); (f) Cutting edge 4edge ==31.50 mm(mag. 500×). Notes: Secondary electron imaging (mag. 50 × );VB (b) Retro electron (mag. 503× ); (c)VBCutting 1 (a) with VB = 45.50 µ45.50 m (mag. 500×); (d) Cutting edge 2edge with VB = 34.00 µ34.00 m (mag. 500×);500×); (e)imaging Cutting edge 3edge with VB 1 with VB = µ m (mag. 500×); (d) Cutting 2 with VB = µ m (mag. (e) Cutting with with1VB with = 45.50 =Cutting µ45.50 m (mag. m (mag. 500×); 500×); (d)VB Cutting Cutting edge edge with2500×). VB with = 34.00 VB = µ34.00 m (mag. (mag. 500×);500×); (e) Cutting (e) Cutting edge 3edge VB with VB = 28.00 (mag. 500×); (f) edge 4 with = (d) 31.50 µ m 2(mag. edgeµ m 1=1with VB =VB 45.50 µmµ(f) (mag. 500 × );(d) Cutting edge 2 µwith VB =µ m 34.00 µm (mag. 500 ×); with (e) 3Cutting edge 3 28.00= µ28.00 m (mag. 500×);500×); Cutting edge 4edge with4VB = 31.50 µ31.50 m (mag. 500×).500×). µ m (mag. (f) Cutting with VB = m (mag. = 28.00= µ28.00 m (mag. µ m (mag. 500×);500×); (f) Cutting (f) Cutting edge 4edge with4VB with = 31.50 VB = µ31.50 m (mag. µ m (mag. 500×).500×).

with VB = 28.00 µm (mag. ); (f) Cutting 4 with VB 31.50 µm (mag. 500 ×to ). Table When analyzing the×results ofSEM the edge SEM analysis after 16 cycles (referring it is possible When analyzing the 500 results of the analysis after 16= cycles (referring to Table 6), it 6), is possible When analyzing the results ofhave the SEM analysis afterfurther 16 cycles (referring to Table 6), it is possible to observe VB values increased, indicating further tool wear. to observe VB values have increased, indicating tool wear. When analyzing the of analysis after 16 (referring to 6), is When analyzing the results results ofSEM the SEM SEM analysis after 16 cycles cycles (referring to Table Table 6), it is is possible possible When analyzing analyzing the results results the of the theof SEM the analysis analysis afterafter 16 cycles cycles 16 (referring (referring to Table Table to 6), it it 6), is possible possible it to observe VBWhen values have increased, indicating further tool wear. to VB have increased, further tool to observe VBthe values have increased, indicating further tool wear. to observe observe to observe VB values values VB values have have increased, increased, indicating indicating further further tool wear. wear. tool When analyzing results of theindicating SEM analysis after 16 wear. cycles (referring to Table 6), it is possible

to observe VB values have increased, indicating further tool wear.


Coatings 2016, 2016, 6, 6, 51 51 Coatings

of 30 30 88 of

Coatings 2016, Coatings 6, 51 2016, 6, 51 Table 6.

Walter 4Z 4Z TiAlN TiAlN SEM SEM analysis analysis after after 16 16 cycles cycles of of machining. machining. Table 6. Walter

8 of 30

8 of 30

88 of of 30 30

8 of 30 8 of 30

8 of 30

Table 6. Walter 4Z TiAlN SEM analysis after 16 cycles of machining. Table 6. Walter Table4Z 6. Walter TiAlN SEM 4Z TiAlN analysis SEM after analysis 16 cycles afterof16machining. cycles of machining.

Coatings Coatings 6, Coatings 2016, 2016, 6, 51 51 2016, 6, 51 Coatings 2016, 6, 51

Top View of End Mill

Table Table4Z 6. Walter TiAlN 4Z TiAlN analysis SEM after analysis 16 afterof cycles of machining. Table 6. 6. Walter Walter 4Z TiAlN SEM SEM analysis after 16 cycles cycles of16machining. machining. Table 6. Walter 4Z TiAlN SEM analysis after 16 cycles of machining.

(a)(a) (a)

(b) (b) (b) (b) Observable Issues Analysis Damage Issues Damage Issues Probable Causes Causes Probable Causes Possible Solutions Possible Solutions Damage Issues Probable Causes Possible Solutions Probable Possible Solutions Damage Issues Possible Solutions (a) (a) (b)   Increase (b) rake Increase angle rake to improve angle to improve (a) (b) Increase rake angle to improve improve  Increase rake(b) angle to Notch Wear [24] (a)  Friction Friction  Friction sharpness • sharpness Increase rake angle to improve sharpness sharpness • Friction sharpness Damage Damage Issues Causes Probable Causes  • Change Possible Solutions Solutions  Oxidation Probable Oxidation  depth Change ofPossible cut depth of cut Change depth of cut cut Damage Issues Issues Probable Causes Possible Solutions Oxidation  Change Change depth of •  Oxidation Damage Issues Probable Causes Possible Solutions depth of cut Hardened  Hardened or doughy or material doughy material CVD coating CVD to coating improve to wear improve wear  • Increase  rake Increase angle rake to improve angle towear improve CVD coating to improve Increase rake angle to improve Hardened or or doughy doughy material material  CVD CVD coating torake improve wear •  Hardened Increase angle to improve to improve wear Negative Negative geometry  • sharpness PVD coating  coating PVD to coating improve to BUE improve and BUE  geometry Friction sharpness  Friction Friction sharpness PVD coating to improve BUE andand scaling Negative geometry PVD coating to improve BUE and and Friction sharpness •  Negative PVD coating to improve scaling of tool scaling of tool  geometry Oxidation   Change depth Change of depth of cutBUE  Oxidation Oxidation Change depth of cut cut oftool Oxidation Change depthtowear ofimprove cut scaling ofto tool  Hardened  Hardened or doughyor material doughy material  CVD coating  CVD coating improve wear scaling of tool (a)

  

Edge Chipping [24]

 • •

 

Hardened or doughy material  CVD coating to improve wear Hardenedgeometry or doughy material CVD coating to improve wearand Negative  geometry Negative  PVD  machining PVD to improve to BUE improve and BUE Stabilize Stabilize machining conditions conditions Negative geometry PVD coating coating to coating improve BUE and Unstable  machining Unstable machining conditions conditions Negative geometry  PVD coating to improve BUE and scaling of tool scaling of tool   Select tools Select with tools tougher with tougher Stabilize machining conditions scaling of tool Stabilize machining conditions Hard/fragile  machining Hard/fragile tool classconditions tool class Unstable scaling of tool conditions Unstable Unstable machining machining conditions conditions • geometry Stabilize machining geometry Select tools with tougher  Select tools with tougher Hard/fragile tool class Hard/fragile  • Stabilize  machining Stabilize machining conditions Hard/fragiletool toolclass class Select tools with tougherconditions geometry geometry Stabilize machining conditions geometry Unstable  machining Unstable machining conditions toolsSelect Stabilize machining conditions Unstable machining conditionsconditions  Select  with tools tougher with  Hard/fragile Unstable machining conditions  Select tools with tougher tougher Hard/fragile  tool class tool class  Select tools with tougher Hard/fragile tool class geometry  Hard/fragile tool class geometry geometry geometry


(c)

(c)

(d)

(d)

(c)(c) (c)

(c) (c)

(d) (d) (d) (d)

(d) (d)

(e)

(e)

(f)

(f)

(e) (e)

(e) (e)

(f)

(f) (f)

(f) (e) Notes: (a) Secondary (e) electron imaging (mag. 50×); (b) Retro diffused electron (f) imaging (mag. 50×); (c) Cutting edge 1 with VB = 69.50 µm (mag. 500×); (d) Cutting edge 2 with VB = 78.50 µm (mag. 500×); (e) Cutting edge 3 with VB = 63.50 µm (mag. 500×); (f) Cutting edge 4 with VB = 42.50 µm (mag. 500×).


9 of 30

Note: (a) Secondary electron imaging (mag. 50×); (b) Retro diffused electron imaging (mag. 50×); (c) Cutting edge Coatings 2016, 6, 51 9 of 30 1 with VB = 69.50 µ m (mag. 500×); (d) Cutting edge 2 with VB = 78.50 µ m (mag. 500×); (e) Cutting edge 3 with VB = 63.50 µ m (mag. 500×); (f) Cutting edge 4 with VB = 42.50 µ m (mag. 500×).

In Figure 3 it is possible to observe distinct areas, such as regions where the tool has lost its coating. In Figure 3 it is possible to observe distinct areas, such as regions where the tool has lost its This phenomenon is due to the natural occurring wear caused by friction and abrasion between the coating. This phenomenon is due to the natural occurring wear caused by friction and abrasion tool and the material being machined. It is also possible to observe white specs which are caused by between the tool and the material being machined. It is also possible to observe white specs which the collision of metal shavings with the tool surface during machining operations. The area marked as are caused by the collision of metal shavings with the tool surface during machining operations. The Z1 shows a section with intact coating composed of titanium aluminium nitride. The marked Z2 area area marked as Z1 shows a section with intact coating composed of titanium aluminium nitride. The contains adhered material from the machined andsubstrate several other impurities, marked Z2 area contains adhered materialpart, fromtool thesubstrate machinedmaterial part, tool material and being composed mainly of carbon, titanium, chromium, iron and manganese. The adhesion these several other impurities, being composed mainly of carbon, titanium, chromium, ironofand impurities mayThe be adhesion related toofthe geometry of this end as 4tocutting flutes hinder manganese. these impurities may be mill, related the geometry of this the end ease mill,of aschip 4 removal, promoting collisions between the tool and the built up material. The area marked as cutting flutes hinder the ease of chip removal, promoting collisions between the tool and the built upZ3 represents as Z3 therepresents EDS analysis displays elements withdisplays the composition material.the Thetool areasubstrate marked as the tool substrate as thecoherent EDS analysis elements of hard metal.with the composition of hard metal. coherent

(b)

(a)

(c) Figure 3. Cont.


10 of 30 10 of 30

(d)

(e) Figure 3. Chemical composition of encountered surface areas on Walter 4Z TiAlN mill after 16 cycles Figure 3. Chemical composition of encountered surface areas on Walter 4Z TiAlN mill after 16 cycles of machining. (a) Discontinuous areas and impurities detected on the tool (mag. 500×); (b) Close up of machining. (a) Discontinuous areas and impurities detected on the tool (mag. 500×); (b) Close up of of adhered foreign material (mag. 4000×); (c) Chemical composition of area marked as Z1; adhered foreign material (mag. 4000×); (c) Chemical composition of area marked as Z1; (d) Chemical (d) Chemical composition of area marked as Z2; (e) Chemical composition of area marked as Z3. composition of area marked as Z2; (e) Chemical composition of area marked as Z3.

3.3.2. HPMT 3Z AlCrN—Roughness and SEM Results 3.3.2. HPMT 3Z AlCrN—Roughness and SEM Results Roughness results shown in Table 7 demonstrate no significant variation in terms of Ra Roughness results shown in Table no significant variation in terms low, of Raalthough roughness roughness from one trial to the other.7Rdemonstrate z roughness values for 8 cycles are relatively from one trial to the other. R roughness values for 8 cycles are relatively low, although worse than z worse than when compared to the previous Walter 4Z TiAlN end mill. The evolution of roughness when compared to the previous Walter 4Z TiAlN end mill. The evolution of roughness values from values from 8 to 16 machining cycles clearly demonstrates an increase of surface roughness and loss 8 to 16 machining demonstrates increase offact surface roughness and loss of tool cutting of tool cutting cycles quality.clearly Tangential Ra and Rzan values are in the highest values obtained across all tested Tangential tools, creating coarser surfaceare finish which lead tovalues loss ofobtained dimensional tolerance. Radial quality. Ra aand Rz values in fact thecan highest across all tested tools, valuesaposition this toolfinish in third place, translates to a machined surface with noticeable feed creating coarser surface which canwhich lead to loss of dimensional tolerance. Radial values position thismarks. tool in third place, which translates to a machined surface with noticeable feed marks.


11 of 30


11 of 11 30 of 30

Table 7. Part surface roughness obtained after 8 and 16 cycles of machining with HPMT 3Z AlCrN end7.mill. Table Part surface roughness obtained after 8 and 16 16 cycles of of machining with HPMT 3Z3Z AlCrN Table 7. Part surface roughness obtained after 8 and cycles machining with HPMT AlCrN end mill. end mill.

11 of 30 11 of 30 Ra (µm) Rz (µm) Rmax (µm) Measurements Ra R (µm) Rz R (µm) Rmax (µm) a (µm) z (µm) R max (µm) 8 Cycles Cycles Cycles 16ofCycles 8with Cycles 16AlCrN Cycles Measurements Measurements 7. Part roughness surface roughness obtained after and 16ofcycles machining HPMT 3Z Table 7.Table Part surface obtained16 after 8 and 1688cycles machining with HPMT 3Z AlCrN 8 Cycles Cycles Cycles Cycles 8 Cycles 16 16 Cycles 8 Cycles 8 Cycles 16 16 Cycles 8 Cycles 8 Cycles 16 16 Cycles 0.526 0.633 2.960 3.194 5.400 5.050 end mill.end mill.1 1 1 2 0.526 2.960 3.194 5.400 5.050 0.5260.4930.633 0.633 0.612 2.960 2.779 3.194 5.400 5.050 3.077 4.420 4.060 Ra (µm) Rz (µm) 3.445 R4.570 max (µm) Ra0.612 (µm) (µm) Rmax (µm) Radial 2 2 Measurements 2.779 3.077 4.420 4.060 0.4930.463 0.612 2.779Rz 2.556 3.077 4.420 4.060 3 0.493 0.663 5.160 Measurements Cycles 162.556 Cycles 16 Cycles 8 Cycles 16 Cycles 8 Cycles80.663 16 Cycles 82.556 Cycles8 Cycles 16 3.445 Cycles 84.570 Cycles 16 5.160 Cycles 3 Average 0.463 3.445 3 0.463 0.663 4.570 5.160 0.494 0.636 2.765 3.239 4.979 4.757 0.633 1 0.49410.526 0.636 0.633 2.765 2.960 2.960 3.194 3.194 5.400 5.400 5.050 Average 3.239 4.979 4.757 Average 0.4940.274 0.526 0.636 2.765 3.239 4.979 4.7575.050 2.410 12 0.386 1.953 2.280 2.570 20.493 0.493 0.612 0.612 2.779 2.779 3.077 3.077 4.420 4.420 4.060 4.060 1 1 2 0.274 1.953 2.280 2.570 2.410 0.2740.3130.386 0.386 0.370 1.953 1.914 2.280 2.570 2.410 2.233 2.290 2.500 30.463 0.463 3 0.663 0.663 2.556 2.556 3.445 3.445 4.570 4.570 5.160 5.160 Tangentia 2 3 0.330 0.350 2.107 2.099 2.340 2.460 0.313 0.370 1.914 2.233 2.290 2.500 2 0.313 0.370 1.914 2.233 2.290 2.500 AverageAverage 0.494 0.494 0.636 0.636 2.765 2.765 3.239 3.239 4.979 4.979 4.757 4.757 3 Average 0.330 0.350 2.107 2.099 2.340 2.460 0.306 0.274 2.204 2.400 3 1 0.330 0.350 2.107 2.099 2.280 2.340 2.570 2.4602.410 2.457 10.274 0.386 1.953 0.3860.369 1.953 1.991 2.280 2.570 2.410 Average 2.204 2.400 2.457 Average2 0.306 0.306 0.369 1.991 2.204 2.233 2.400 2.290 2.4572.500 20.313 0.369 0.313 0.370 0.370 1.991 1.914 1.914 2.233 2.290 2.500 30.330 0.330 3 0.350 0.350 2.107 2.107 2.099 2.099 2.340 2.340 2.460 2.460 Looking at the SEM analysis for 8 cycles, shown in Table 8, it is possible to observe foreign material Looking at at thethe SEM analysis forfor 8 0.306 cycles, in in Table 8, 8, it 2.204 is possible to observe Average 0.369 1.991 2.400 2.457 foreign Average 0.306 0.369 shown 1.991 2.204 2.400 2.457 Looking SEM analysis 8 cycles, shown Table it is possible to observe foreign

Radial Tangentia

Radial Tangentia

Tangentia Tangentia

Radial Radial

Coatings Coatings 2016, 6, 512016, 6, 51

adhered to the tool surface. As shown in Figure 4, the analysis of the adhered material shows that it material adhered to to thethe tool surface. AsAs shown in in Figure 4, the analysis of of thethe adhered material shows material adhered tool surface. shown Figure 4, the analysis adhered material shows is mainlyLooking composed ofSEM iron, nickel and8 chromium, consistent with the composition of stainless steel, Looking at the SEM analysis for 8 cycles, shown in Table 8, it is possible to observe foreign at the analysis for cycles, shown in Table 8, it is possible to observe foreign that it is mainly composed of iron, nickel and chromium, consistent with the composition of stainless that it is mainly composed of iron, nickel and chromium, consistent with the composition of stainless confirming that the origin of this material is the machined part. This type of phenomena may lead to a material adhered to the tool surface. As shown in Figure 4, the analysis of the adhered material shows material adhered to origin the toolof As shownisinthe 4, the analysis of thetype material shows steel, confirming that the this material machined part. This of of phenomena may steel, confirming that the originsurface. of this material isFigure the machined part. Thisadhered type phenomena may that it is mainly composed of iron, nickel and chromium, consistent with the composition of stainless that it is mainly composed of iron, nickel and chromium, consistent with the composition of stainless large upbuild onup the surface and and consequently coating detachment. lead to to a build large build ontool thethe tool surface consequently coating detachment. lead a large up on tool surface and consequently coating detachment. steel,4,confirming the origin ofview this material isdistinct the machined part. This ofwear phenomena may steel, confirming that thethat origin of this material is the machined part. This type of type phenomena may In Figure it is possible to closely several areas representing and material In In Figure 4, it is possible to closely view several distinct areas representing wear and material Figure 4, it is possible to closely view several distinct areas representing wear and material to build a largeupbuild uptool on the tool surface and consequently detachment. lead to alead large on the surface and consequently coating coating detachment. adhesion, aswell well asthe the EDS analysis for those areas. adhesion, as as well as as the EDS analysis forfor those areas. adhesion, EDS analysis those areas. In 4, Figure 4, it is possible to closely view several areas representing wear and material In Figure it is possible to closely view several distinct distinct areas representing wear and material adhesion, wellEDS as the EDS analysis forareas. those areas. adhesion, as well as the analysis for those Table HPMT 3Z AlCrN SEM analysis 8 of cycles of machining. Table 8. HPMT 3Z3Z AlCrN SEM analysis after 8 after cycles machining. Table 8. 8. HPMT AlCrN SEM analysis after 8 cycles of machining. HPMT 3ZSEM AlCrN SEM analysis after of 8 cycles of machining. Table 8. Table HPMT8.3Z AlCrN analysis after 8 cycles machining.


(a)(a)

(a)

(a)

(b)

(b)(b)

Observable Issues Analysis Probable Causes Probable Causes Probable Causes Probable Causes Probable Causes

Issues 

 Unstable machining Unstable machining



(b)

Possible Possible SolutionsSolutions

Possible Solutions Possible Solutions Possible Solutions  Stabilize machining conditions Stabilize machining conditions

conditions conditions Select tools with tougher Select with tougher machining conditions •  Unstable machining Stabilize machining conditions Unstable machining Unstable machining conditions   Stabilize • tools Stabilize machining conditions  Hard/fragile  conditions Hard/fragile tool classtool class   Select geometry geometry conditions tools with tougher Select tools with • Hard/fragile tool class • Select toolstougher with tougher geometry   Hard/fragile tool class Hard/fragile tool class geometry geometry

Edge chipping [24] Flank wear [24]

 Excessive cutting speed   cutting Lowerspeed cutting speed Excessive cutting speed Lower Low wear resistance/tool  tools Select tools withtoughness higher toughness Low wear resistance/tool Select with higher   Excessive cutting speed   Lower cutting speed Excessive cutting speed Lower cutting speed grade too soft grade grade too soft grade • Excessive cutting speed • Lower cutting speed   Low wear resistance/tool  Select tools with higher toughness Low wear resistance/tool Select tools with higher toughness  rate Feed rate too lowgrade  Increase Increase feed rate higher Low Feed too low feed rate • wear resistance/tool • Select tools with grade too soft grade grade too soft grade  angle Flank  toughness Increase flank angle too soft Flank tooangle smalltoo small  Increase flank angle grade  

•  Feed rate too low Feed rate too low Feed rate too low •  Flank angle too small Flank angle too small Flank angle too small

  Increase feed rate Increase feed rate • Increase feed rate   Increase flank angle Increase flank • Increaseangle flank angle


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Table 8. Cont. Cutting Edges Close Up

Coatings 2016,Coatings 6, 51 6, 51 2016, 6, 51 Coatings 2016,

12 of 30 12 of 30 12 of 30


(c)(c) (c)

(d) (d) (d) (d)

(c)

(e) (e) (e) Note:Note: (a) Secondary Note: (a) electron Secondary imaging electron (mag. imaging 50×); 50×); (mag. (b)(e)Retro 50×); diffused (b) diffused Retro electron diffused imaging electron (mag. imaging 50×); 50×); (mag. 50×); (a) Secondary electron imaging (mag. (b) Retro electron imaging (mag. Notes: (a) Secondary electron imaging (mag. 50× ); (b) Retro diffused electron imaging (mag. 50×);µ(c) Cutting (c) Cutting edge (c) Cutting 1 with VB = VB 1105.00 with VB µ m=(mag. 300×); µ m300×); (mag. (d) Cutting 300×); edge (d) Cutting 2 with VB =VB 2117.50 with VB µ m=(mag. m (mag. (c) Cutting edge 1 edge with = 105.00 µ105.00 m (mag. (d) Cutting edge 2 edge with = 117.50 µ117.50 m (mag. edge 1 with = 105.00 µm (mag.imaging 300×); (d) Cutting 2 withdiffused VB = 117.50 µm (mag. 300(mag. ×); (e)50×); Cutting Note: (a)VB Secondary electron (mag. 50×);edge (b) Retro electron imaging 300×);300×); (e) Cutting 300×); edge (e) Cutting 3 with edge VB = VB 377.50 with µVB m (mag. =µ m 77.50 300×). µ m300×). (mag. 300×). (e) Cutting edge 3 with = 77.50 (mag.

edge with VB edge = 77.50 µm (mag. 300×). µ m (mag. 300×); (d) Cutting edge 2 with VB = 117.50 µ m (mag. (c)3 Cutting 1 with VB = 105.00 300×); (e) Cutting edge 3flank with VB = 77.50 µbetween m both (mag. 300×). When comparing When comparing flank wearwear flank between wearboth trials, both an increase trials, anofincrease values isofnoticeable values is noticeable afterafter 16 16 after 16 When comparing between trials, an increase of values is noticeable cycles of machining. cycles of machining. For instance, For the instance, highest the VBhighest value for VB the value 8the cycles for the run cycles 117.50 run µnoticeable m,117.50 the µ m, while cycles of machining. For instance, the highest VB value for 8 cycles run was 117.50 µwhile m, while the When comparing flank wear between both trials, an increase of8 was values iswas after 16the cycles When comparing flank between both increase of is after 16 16 cycles run 16 cycles present run a value present ofwear 380.00 a of value µof m.380.00 Nevertheless, µ m.trials, Nevertheless, thean performance the performance of values this tool of is noticeable this acceptable tool is acceptable 16 cycles run present a value 380.00 µ m. Nevertheless, the performance of this tool is acceptable of machining. For instance, the highest VB value for the 8 cycles run was 117.50 µm, while the 16 cycles bearing mind bearing itsin low mind acquisition its low acquisition price. These price. values These can values be seen can in8Tables be 8run in and Tables 9. 9. 8 and 9.µ m, while the cycles ofin machining. For instance, theprice. highest VBvalues value for the cycles 117.50 bearing in mind its low acquisition These can be seen inseen Tables 8 was and

run present a value of 380.00 µm. Nevertheless, the performance of this tool is acceptable bearing in 16 cycles run present a value of 380.00 µ m. Nevertheless, the performance of this tool is acceptable mindbearing its lowinacquisition price. These price. values can values be seencan inbe Tables 8 and 9. 8 and 9. mind its low acquisition These seen in Tables

(a) (a)

(a)

(b) (b)

(a)

(b) Figure 4. Cont.

(b)


13 of 30 13 of 30

Coatings 2016, 6, 51 Coatings 2016, 6, 51 Coatings 2016, 6, 51 Coatings 2016, 6, 51

1330 of 30 13 of 13 of 30 13 of 30

(c) Figure 4. 4. SEM of cutting cutting tool tool HPMT HPMT 3Z 3Z after after 88 cycles. cycles. (a) (a) Build Build up up edge edgeon onflank flank(mag. (mag.300 300×); Figure SEM analysis analysis of ×); (c)(c) (b) Build Build up up edge edge on on flank flank (mag. (mag. 750 750×) area (Z1) for EDS analysis; (c) EDS analysis of (b) ×) with with marked marked area (Z1) for EDS analysis; (c) EDS analysis of (c) Figure 4. SEM analysis of cutting HPMT after 8 cycles. Build edge flank (mag. 300×); Figure 4. Z1. SEM analysis of cutting tooltool HPMT 3Z 3Z after 8 cycles. (a) (a) Build up up edge on on flank (mag. 300×); (c) marked area marked area Z1. Figure 4. SEM analysis of flank cutting tool HPMT 3Z after 8area cycles. (a) Build upanalysis; edge on(c) flank (mag. 300×); Build edge (mag. 750×) with marked area (Z1) for EDS analysis; (c) EDS analysis (b)(b) Build up up edge on on flank (mag. 750×) with marked (Z1) for EDS EDS analysis of of Figure 4. SEM analysis of cutting HPMT after 8area cycles. Build edge on(c) flank 300×); (b) Build uparea edge on flank (mag.tool 750×) with 3Z marked (Z1)(a)for EDSup analysis; EDS(mag. analysis of marked marked area Z1.Z1. Table 9.flank HPMT 3Z750×) AlCrN SEM analysis after 16 cycles of machining. machining. (b) Buildarea up edge (mag. withSEM marked area (Z1) for16 EDS analysis; (c) EDS analysis of Tableon9. HPMT 3Z AlCrN analysis after cycles of marked Z1. marked area Z1. Table 9. HPMT 3Z AlCrN SEM analysis after 16 cycles of machining. Table 9. HPMT 3Z AlCrNTop SEMView analysis cycles of machining. of after End16 Mill Table 9. HPMT 3Z AlCrNTop SEM analysis afterMill 16 cycles of machining. View of End Table 9. HPMT 3Z AlCrN SEM analysis after 16 cycles of machining.

(a) (a) Damage Issues Damage Issues

Damage Issues Damage Issues

Damage Issues Damage Issues

Notch wear [24]

Notch wear [24]

Edge Chipping [24]

Edge Chipping [24]

(b)(b) (b) (b) (b) Observable Issues Analysis Probable Causes Possible Solutions Probable Causes Possible Solutions Observable Issues Analysis Probable Causes Possible Probable Causes Possible Solutions Increase rake angle toSolutions improve   Increase rake angle to improve Probable Causes Possible Solutions Probable Causes Possible Solutions  Increase rake angle to improve sharpness sharpness  Friction  Friction • Increase rake angle to  Increase rake angle to improve  Increase rake angle to improve • Friction Change depth of sharpness cut  sharpness Change depth of cut Oxidation Oxidation improve Friction sharpness  Friction  Change depth of cut sharpness  Oxidation  CVD coating to improve wear  • Friction CVD• coating to improve Hardened or doughy material  Hardened or doughy material Change depthwear of cut Oxidation  Change depthtoofimprove cut  Oxidation coating Hardened or geometry doughy material coating to improve BUE Negative  CVD PVD coating todepth improve BUE andand wear Negative geometry  PVD Change ofwear cut • Oxidation • CVD coating to improve Hardened or doughy material  CVD coating to to improve improve BUE wear  Hardened or doughy material PVD coating and wear Negative geometry scaling of tool scaling of tool  CVD coating to improve  • Hardened orgeometry doughy material PVD•coating PVD coating to improve BUE Negative Negative geometry scaling of toolto improve BUE and and scaling tool  PVD coating toofimprove BUE and  Negative geometry scaling of tool Unstable machining   Unstable machining  Stabilize machining conditions  Stabilize machining conditions scaling of tool  Unstable machining conditions conditions  Stabilize machining conditions Select tools with tougher geometry Select with tougher geometry  Unstable machining • tools Stabilize machining conditions Hard/fragile classconditions • conditions Hard/fragile tooltool class  Stabilize machining conditions Unstable machining Select tools with tougher geometry conditions Hard/fragile tool class • Select tools with  • Unstable machining  Select tools with machining tougher geometry Hard/fragile tool class  Stabilize  Hard/fragile tool class tougher geometryconditions

(a) (a) (a)



conditions Hard/fragile tool class



Select tools with tougher geometry


14 of 30

Table 9. Cont. Coatings 2016, 6, 51 Coatings 2016, 6,6,51 Coatings 2016, 6, Coatings 2016, 5151

Flank wear [24]

14 of 30 14 14 of 14of of30 3030

Observable Issues Analysis

Excessive cutting speed  • Excessive cutting speed • Lower cutting speed  Lower cutting speed Excessive cutting speed Excessive cutting speed Excessive cutting speed Low wear resistance/tool grade •  Low wear resistance/tool • cutting Select tools higher  Lower  Lower speedwith  Lower cutting speed  Select toolscutting withspeed higher toughness grade   grade Low wear resistance/tool Low wear resistance/tool Low wear resistance/tool too soft too soft toughness grade  Select tools with higher toughness grade  Select tools with higher toughness grade  Select tools with higher toughness grade  Increase feed rate grade too soft grade too soft grade too soft Feed rate too  • Feed rate too low low • feed Increase   Increase Increase rate Increase feed ratefeed rate Increase feed rate  flank angle Feed rate too low Feed rate too lowsmall Feed rate too low Flank angle too •  Flank angle too small • flank Increase flank angle   Increase angle Increase flank angle Increase flank angle   Flank angle too small Flank angle too small Flank angle too small Cutting Edges Close Up

(c) (c) (c)(c)

(d) (d) (d)(d)

(e) (e) (e)(e)

Notes: (a) Top view of end mill by secondary electron imaging (mag. 50×); (b) Top view of end mill by retro diffused electron imaging (mag. 50×); (c) Cutting edge 1 with VB = 380.00 µm (mag. 300×); (d) Cutting edge 2 with VB = 229.20 µm (mag. 300×); (e) Cutting edge 3 with VB = 115.00 µm (mag. 300×).

3.3.3. HPMT 4Z AlCrN—Roughness and SEM Results

3.3.3. 3.3.3. HPMT 4Z AlCrN—Roughness and SEM Results HPMT 4Z AlCrN—Roughness and SEM Results 3.3.3. HPMT AlCrN—Roughness and SEM Results 3.3.3. HPMT 4Z4Z AlCrN—Roughness and SEM Results

Even though all machining and testing parameters where kept equal for all trials, the results

Even though all machining and testing parameters where equal for allthe trials, the results Even all machining and testing parameters where kept equal for all trials, results Even though machining and testing parameters where kept equal for trials, the results Even though allall machining and testing parameters where kept equal for allall trials, the results obtained bythough this tool are somewhat unexpected. Seen in Table 10, thekept surface roughness produced obtained by this tool are somewhat unexpected. Seen in Table 10, the surface roughness produced obtained by this tool are somewhat unexpected. Seen in Table 10, the surface roughness produced obtained by this somewhat unexpected. Seen in in Table 10,the the roughness produced obtained by this tool are somewhat unexpected. Seen Table 10,16surface the surface after 8 cycles wastool the are worst of all measured results. Regarding cycles run, roughness the Ra radialproduced after 88 cycles was the worst all measured Regarding the 16 cycles run, the Ra radial after 8cycles cycles was the worst of all measured Regarding the 16 run, the radial was the worst allof measured results. Regarding the 16 cycles run, the RaRa radial is, as well, the highest the batchresults. ofresults. experiments, delivering acycles surface ofRa radial after roughness 8after cycles was the worst ofofofall measured results. Regarding the 16machined cycles run, the roughness is, as well, the highest of the batch of experiments, delivering a machined surface of roughness is, as well, the highest of the batch of experiments, delivering a machined surface roughness is, as well, the highest of the batch of experiments, delivering a machined surface ofof inferioris, quality. However, in termsof the tangential this tool delivering delivered a surprisingly low roughness as well, the highest batch Ra of values, experiments, a machined surface of inferior quality. However, in terms of tangential Ra values, this tool delivered a surprisingly low inferior quality. However, in terms of tangential Ra values, this tool delivered a surprisingly low inferior quality. However, in terms of tangential Ra values, this tool delivered a surprisingly low surface roughness, being tied with the WALTER 4Z TiAlN end mill (best values measured across all inferior quality. However, intied terms of tangential RaTiAlN values, this tool values delivered a across surprisingly low surface roughness, tied the WALTER 4Z TiAlN mill (best measured all surface roughness, being with the WALTER mill (best measured across surface roughness, being tiedwith with the WALTER 4Z4Z TiAlNend end mill (best values measured across allall experiments). Whenbeing comparing these two tools, the HPMT 4Zend AlCrN hasvalues a major price advantage, surface roughness, being tied with the WALTER 4Z TiAlN end mill (best values measured across all experiments). When these two tools, the HPMT 4Z AlCrN has aamajor price advantage, experiments). When comparing these two tools, the HPMT AlCrN has amajor major price advantage, experiments). When comparing these two tools, the HPMT 4Z4Z AlCrN has price advantage, with the downside ofcomparing having a shorter working life. experiments). When comparing two tools, the HPMT 4Z AlCrN has a major price advantage, with the downside of having aashorter working life. with the downside having athese shorter working life. with the downside ofof having shorter working life. with the downside of having a shorter working life.


15 of 30

Table 10. Part surface roughness obtained after 8 and 16 cycles of machining with HPMT 4Z AlCrN end mill. Ra (µm)

CoatingsCoatings 2016, 6,2016, 51 6, 51 Measurements Coatings 2016, 6, 51

Rz (µm)

Rmax (µm) 15 of 3015 of 30

Radial Tangential

Radial Tangential

Tangential

Radial

30 8 Cycles 16 Cycles 8 Cycles 16 Cycles 8 Cycles 15 of16 Cycles 10.surface Part surface roughness obtained 8 and 16 cycles of machining with HPMT 4Z AlCrN Table Table 10. Part roughness obtained after 8after and 16 cycles of machining with HPMT 4Z AlCrN 1 roughness1.771 9.590 15.010 Table Part mill. surface obtained after1.184 8 and 16 cycles of machining6.528 with HPMT 27.650 4Z AlCrN end end10. mill. 2 1.594 1.117 9.432 6.105 23.530 15.440 end mill. Radial 3 1.714 1.079 22.190 14.860 Ra (µm) Rz (µm) 6.393Rmax (µm) Rmax (µm) Ra (µm) Rz10.513 (µm) MeasurementsRa (µm) Measurements R z (µm) R max (µm) Average 1.693 1.127 9.845 24.457 8 Cycles 16 Cycles 8 Cycles 16 Cycles 8 Cycles 16 Cycles 15.103 8 Cycles 16 Cycles 8 Cycles 16 Cycles 86.342 Cycles 16 Cycles Measurements 8 Cycles 16 Cycles 1.184 8 Cycles Cycles 8 Cycles 16 Cycles 1 1.771 9.590 9.590 16 27.650 27.650 15.010 11 1.1911.771 1.1840.259 6.2626.528 6.5281.849 7.95015.010 2.500 1 2 1.771 1.184 9.590 6.528 27.650 15.010 2 1.594 1.117 1.1170.255 9.432 9.432 6.105 6.105 23.530 23.530 15.440 2 1.2801.594 6.679 1.758 7.07015.440 2.100 2 33 1.594 1.117 9.432 6.105 23.530 15.440 Tangential 3 1.714 1.079 1.3601.714 6.917 1.671 8.87014.860 1.960 1.0790.246 10.513 10.513 6.393 6.393 22.190 22.190 14.860 3 1.714 1.079 10.513 6.393 22.190 14.860 Average 1.693 1.127 9.845 6.342 24.457 15.103 Average 1.693 1.127 9.845 6.342 24.457 15.103 Average 1.277 0.253 6.619 1.759 7.963 2.187 Average 1.693 1.127 9.845 6.342 24.457 15.103 1 1.191 1.191 1 0.259 0.259 6.262 6.262 1.849 1.849 7.950 7.950 2.500 2.500 1 2 1.191 0.259 6.262 1.849 7.950 2.500 2 1.280 1.280 0.255 0.255 6.679 6.679 1.758 1.758 7.070 7.070 2.100 2.100 1.280 0.255 6.679 1.758 2.100 As referred to2 previously, results obtained after 87.070 cycles indicate poor performance. 3 1.360 the 1.360 3 0.246 0.246 6.917 6.917 1.671 1.671 8.870 8.870 1.960 1.960 3 1.360 0.246 6.917 1.671 8.870 1.960 Average 1,277 0.253 6.619 1.759 7.963 2.187 Average 1,277 0.253 6.619 1.759 7.963 2.187 When observing Table 11, it is possible to see that most cutting flanks suffered severe damage. Average 1,277 0.253 6.619 1.759 7.963 2.187

The registered VB wear values after 8 machining cycles are the highest of all tools (exceeding in some As referred to previously, the results obtained 8 cycles indicate poor performance. As referred to previously, the results obtained after 8after cycles indicate poor performance. WhenWhen cases 1As mm in length). The most plausible hypothesis for this phenomenon is the factWhen that the material referred to previously, obtained after most 8cutting cycles indicate poorsuffered performance. observing Table itthe is results possible tothat see most that cutting flanks damage. observing Table 11, it 11, is possible to see flanks suffered severesevere damage. The The being machined not containing localized areas higher values. observing Table is possible see8 that most cutting flanks suffered severe damage. The registered VBitcompletely wear values after machining cycles are the highest of allwith tools (exceeding in some registered VBis11, wear values after to 8homogenous, machining cycles are the highest of all tools (exceeding inhardness some registered VB wear values after 8 machining cycles are the highest of all tools (exceeding in some These areas are essentially microstructures with different metallurgical phases. The existence of in length). The plausible most plausible hypothesis forphenomenon this phenomenon is the factthe that the materialthese cases 1cases mm 1inmm length). The most hypothesis for this is the fact that material cases 1 mm in length). The most plausible hypothesis for this phenomenon is the fact that the material being machined is not completely homogenous, containing localized areas with higher hardness being machined is not completely homogenous, containing localized areas with higher hardness heterogeneities can be seen, in Figure 5, being also possible to observe a dragging pattern on the being machined is notareas completely homogenous, containing localized areas withphases. higher hardness values. These are essentially microstructures with different metallurgical phases. The existence values. These areas are essentially microstructures with different metallurgical The existence surface of the machined part. This pattern was formed by the impact between the tool and the higher values. These areas are essentially microstructures metallurgical The existence of heterogeneities these heterogeneities be in seen, in Figure 5,different being also possible to phases. observe a dragging pattern of these can becan Figure 5,with being also possible to observe a dragging pattern on on hardness areas and seems to seen, be seen, the main reason of wear in tools, being particularly noticeable during of these heterogeneities can be in Figure 5, being also possible to observe a dragging pattern onthe the surface the machined part.pattern This pattern was formed the impact between theand tool and the the surface of theof machined part. This was formed by theby impact between the tool this thetrial. surface of the machined part. pattern was formed the impact between theparticularly tool and the higher hardness areas andThis seems to be the reason main reason of in wear in tools, being noticeable higher hardness areas and seems to be the main ofby wear tools, being particularly noticeable higher hardness areas and seems to be the main reason of wear in tools, being particularly noticeable When viewing the SEM images for the 16 cycles run (Table 12), it is possible to observe the loss of during this trial. during this trial. trial. theduring flankthis edges. This type of wear caused higher radial R roughness values and led to more noticeable viewing the images SEM images 16 cycles it is possible to observe the loss WhenWhen viewing the SEM for thefor 16the cycles run (Table 12), it 12), is possible to observe the loss arun (Table When viewing the SEMtype images forofthe 16 cycles runhigher (Tableradial 12),roughness itRa is possible to observe thetoloss the flank edges. This type wear caused roughness values and led to more theofembossments. flank edges. This of wear caused higher radial Ra values and led more feed of mark of the flank edges. This mark type embossments. of wear caused higher radial Ra roughness values and led to more noticeable feed noticeable feed mark embossments. noticeable feed markTable embossments. 11. HPMT 4Z AlCrN SEM analysis after 8 cycles of machining. 11. HPMT 4Z AlCrN SEM analysis 8 cycles of machining. Table Table 11. HPMT 4Z AlCrN SEM analysis after 8 after cycles of machining. Table 11. HPMT 4Z AlCrN SEM analysis after 8 cycles of machining.


(a)

(a) (a) Damage Damage Issues Issues Damage Issues Damage Issues

Notch Wear [24]

•  • 

• • 

(b)

Observable Issues Analysis Probable Causes Probable Causes Probable Causes

(b)

(b)

Possible Solutions Possible Solutions Possible Solutions Probable Causes  Possible Increase rake to angle to improve  Increase rakeSolutions angle improve  Friction  Friction  Increase rake angle torake improve • Increase angle to sharpness sharpness  Oxidation Friction Oxidation Friction improve sharpness  Change depth of cut sharpness Change depth of cut  Hardened or doughy Oxidation Hardened or doughy Oxidation Change depth of cutimprove • Change depth of cut wear  CVD coating to improve  CVD coating to wear Hardened or doughy material material  CVD tocoating improve Hardened or doughy material coating PVD towear improve BUE wear and PVD coating tocoating improve BUE and • CVD to improve material  Negative geometry   Negative geometry PVD coating to improve and Negative geometry of tool BUE scaling ofPVD tool • scaling coating to improve BUE and Negative geometry scaling of tool scaling of tool


16 of 30

Table 11. Cont. Coatings 2016, 6, 51 Coatings 2016, 6, 51 CoatingsCoatings 2016, 6,2016, 51 6, 51 EdgeCoatings Chipping 6, 51 Coatings 2016, 6,2016, 51 [24]

 • •    •  • 

Breakage/Fracture [24]

•

• 

Unstable machining Unstable machining  Stabilize • machining Stabilizeconditions machining conditions Unstable machining conditions conditions Stabilize machining conditions conditions Unstable  Unstable machining machining  Select tools with tougher geometry Select tools with tougher geometry  Unstable machining Hard/fragile class Hard/fragile Unstable machining Stabilize • Stabilize machining machining conditions conditions tooltool class  Select tools with tougher geometry  Stabilize machining conditions conditions conditions  Stabilize machining conditions Hard/fragile tool class conditions conditions  Select  Select tools with toolstougher with tougher geometry geometry  Select toolstougher with tougher geometry  Hard/fragile  Hard/fragile tool class tool class  Select tools with geometry wear tool class  Hard/fragile tool class Excessive Hard/fragile Excessive wear Tool grade too hard Excessive wear  Reduce vibrations Tool Excessive  Excessive wear grade toowear hardwear  Reduce • vibrations Reduce vibrations ofgrade Excessive Lack Excessive wear cutting edge  Lower feed rate Tool hard Lack Tool of cutting grade Tooltoo grade too hard too hard edge  Reduce  Reduce vibrations vibrations  Lower rate •feed Lower feedtoughness rate  grade Tool grade too hard  ToolReduce strength Tool too hard  Reduce vibrations vibrations grade with higher Lack cutting edge strength Lack  ofofLack cutting of cutting edge strength edge  ToolLower • Lower feed rate feed rate grade with higher toughness of holder of cutting edge Lack Lack ofLack cutting edge Tool grade with higher toughness rigidity  Lower feed rate  Lower feed rate Lack holder rigidity strength strength Lack ofof holder rigidity  Tool  grade Tool grade with higher with higher toughness toughness strength strength  Tool grade with higher toughness  Tool grade with higher toughness Close Up  Lack  Cutting ofLack holder ofEdges holder rigidity rigidity Edges Close Up  Cutting of holder rigidity  Lack ofLack holder rigidity Cutting Edges Close Up Cutting Cutting Edges Edges Close Close Up Up Cutting Cutting Edges Edges Close Close Up Up

Cutting edge 1; VB = 1137 mm

(c) (c)

Cutting edge 2; VB = 866.7 µm

(d) (d) (c) (c)

(c) (c)


(e) (e)

16 of 30 16 of 30 16 of 3016 of 30 16 of 3016 of 30

Observable Issues Analysis

(d) (d)

(d) (d)


(f) (f)

(e) (e) (f) Note: (a) Top view of end(e) mill by electron imaging (mag. 50×); (b) Top(f) view (f) of end mill by (e)secondary Note: (a) Top view of end mill by secondary electron imaging (mag. 50×); (b) Top(f) view of end mill by retro diffused electron imaging (mag. 50×); (c) Cutting edge 1 with VB = 1137 mm (mag. 150×); Note: (a) Note: Top (a) view Topof view endof mill end bymill secondary by secondary electron imaging imaging (mag. 50×); (mag. (b) 50×); Top (b) view Top of view end of mill end bymill by retro diffused electron imaging (mag. 50×); (c)electron Cutting edgeimaging 1 (mag. with VB =×(b) 1137 mm (mag. Note: (a) Top view of end by secondary electron (mag. 50×); (b) Top view of end Note: Top view end=mill mill bymill secondary electron imaging 50×); Top view of end mill bymill Notes: (a)(a) Top view ofof end by secondary electron imaging (mag. 50 ); (b) Top view of150×); end mill byby retro (d) Cutting edge 2 with VB 866.70 µ m (mag. 150×); (e) Cutting edge 3 with VB = 1013 mm (mag. retro diffused retro diffused electron electron imaging imaging (mag. (mag. 50×); (c) 50×); Cutting (c) Cutting edge 1 edge with 1 VB with = 1137 VB = mm 1137 (mag. mm (mag. 150×); 150×); (d) Cutting edge 2 with VB = 866.70 µ m (mag. 150×); (e) Cutting edge 3 with VB = 1013 mm (mag. diffused electron imaging (mag. 50× ); (c) (mag. Cutting edge 1 Cutting with VB1edge =with 1137 mm= (mag. 150 × ); (d)(mag. Cutting edge 2 retro diffused electron imaging 50×); (c) 1 with VB = 1137 mm 150×); retro diffused electron imaging (mag. 50×); (c) Cutting edge VB 1137 mm (mag. 150×); 150×); cutting edge2edge 4with with VB = 866.70 1107 mm (d)(f) Cutting (d) Cutting edge 2VB with =× VB 866.70 µ m(mag. (mag. µ m150×). (mag. 150×); 150×); (e) Cutting (e) Cutting edge edge with3VB with = 1013 VB mm 1013(mag. mm (mag. 150×); (f) cutting edge 4with with VB 1107 with = 866.70 µm2edge (mag. 150 ); (e)==mm Cutting 3 with = 1013 mm33edge (mag. 150 );VB (f)==mm cutting edge 4 with (d) Cutting 2VB with VB 866.70 µedge m150×). (mag. 150×); (e) Cutting with 1013(mag. mm (mag. (d)VB Cutting edge ==866.70 µ m(mag. (mag. 150×); (e)VB Cutting edge with3VB =×1013 (f) cutting (f) cutting edge with with = 1107 VB =mm 1107 (mag. mm 150×). (mag. 150×). VB 150×); = 1107150×); mm (mag. 1504×edge ). 4VB (f) cutting with VB =mm 1107 mm (mag. 150×); 150×); (f) cutting edge 4edge with4VB = 1107 (mag. 150×). 150×).


17 of 30


17 of 30

CoatingsCoatings 2016, 6,2016, 51 6, 51 Coatings 2016, 6, 51 Coatings 2016, 6, 51 Coatings 2016, 6, 51

17 of 3017 of 30 17 of 30 17 of 30 17 of 30

(a)

(b)

Figure 5. 5. Heterogeneous Heterogeneous inclusions inclusions found found in in post-trial post-trial machined machinedmaterial materialchip/shavings: chip/shavings; (a) Global Figure (a) Global (a) (a) (b) (b) view of heterogeneous inclusion (mag. 1000×); (b) Close up of inclusion (mag. 4000×). view of heterogeneous(a) inclusion (mag. 1000×); (b) Close up of inclusion (mag. 4000×). (b) (a) inclusions (b) 5. Heterogeneous inclusions in post-trial machined material chip/shavings; (a) Global FigureFigure 5. Heterogeneous found found in post-trial machined material chip/shavings; (a) Global (a) (b) Figure 5.of Heterogeneous inclusions found(mag. in post-trial machined material chip/shavings; (a) Global view of heterogeneous inclusion 1000×); (b) Close up of inclusion (mag. 4000×). view heterogeneous inclusion (mag. 1000×); (b) Close up of inclusion (mag. 4000×). Table 12. HPMT 4Z AlCrN SEM analysis after 16 cycles of machining. Figure 5. Heterogeneous found in post-trial machined material chip/shavings; (a) Global Table 12.inclusions HPMT 4Z AlCrN SEM analysis after 16 cycles of machining. Figure Heterogeneous inclusions found in post-trial material chip/shavings; (a) Global view of5.heterogeneous inclusion (mag. 1000×); (b) Closemachined up of inclusion (mag. 4000×). view of heterogeneous inclusion (mag. 1000×); (b) Close up of inclusion (mag. 4000×). view of heterogeneous 1000×); (b) Close up of inclusion (mag. 4000×). Table 12.(mag. HPMT 4Z AlCrN SEM analysis after 16 cycles of machining. Tableinclusion 12. HPMT 4Z AlCrN SEM analysis after 16 cycles of machining. Top View of End Mill Table 12. HPMT 4Z AlCrN SEM cycles of machining. Top analysis View ofafter End16Mill Table 12. HPMT 4Z AlCrN SEM analysis after 16 cycles of machining. Table 12. HPMT 4Z AlCrN SEM analysis after 16 cycles of machining.

(a) (a) (b) (b) (a) (b) (a) (b) (a) (b) Observable Issues Analysis (a) (b) Damage Probable Possible Solutions Damage Issues Issues Probable CausesCauses Possible Solutions Observable Issues Analysis Damage Issues Probable Causes Possible Solutions Damage Issues Probable Causes Possible Solutions  Increase rake angle to improve  Increase rake angle to improve Damage Issues Issues Probable Causes Possible Solutions Damage Probable Causes Possible Solutions  Friction  Friction Damage Issues Probable Causes Possible Solutions •sharpness Increase rake angle to  Increase rake angle to improve sharpness  Increase rake angle to improve Notch wear [24]  Friction  Oxidation Oxidation  improve Increase rake angle to improve sharpness Friction   Increase rake angle to •  Friction sharpness Change depth of cut Change depth of cutimprove Friction Notch wear [24]   Friction sharpness Oxidation  Hardened or doughy Hardened or doughy sharpness • Change depth of cut sharpness Oxidation • Oxidation  Change depth oftocut  depth CVD of coating to improve CVD coating improve wear wear   Oxidation   Change cut Oxidation Hardened or doughy material material   Change depth of cut • CVD coating to improve wear Hardened or doughy material • Hardened or doughy CVD coating tocoating improve wear  Change depth of cut BUE  PVD to improve and PVD coating to improve BUE   Hardened orgeometry doughy  CVD coating to improve wear and material  Negative geometry Hardened or doughy Negative  CVD wear •scaling PVD coating to improve BUE and • material Negative geometry PVD coating to improve BUE and scaling of tool of tool  CVD coating to improve wear material  PVD coating to improve BUE and  Negative geometry material scaling of tool BUE and  PVD coating  Negative geometry scaling of toolto improve  ofPVD  Negative geometry scaling tool coating to improve BUE and  Unstable machining scaling of tool Unstable machining  Negative geometry Edge chipping [24]  Stabilize machining conditions  Stabilize machining conditions scaling of tool  Unstable machining conditions conditions  Unstable machining   Stabilize machining conditions  Select tools with tougher geometry Select tools with tougher geometry •  Unstable machining Stabilize machining conditionsconditions Unstable machining conditions • Stabilize machining Edge chipping [24] conditions  Hard/fragile tool class  Hard/fragile tool class Stabilize machining conditions conditions Select tools with tougher geometry  Unstable machining conditions  Select tools with tougher geometry Hard/fragile • Select tools with tougher geometry • Hard/fragile tooltool classclass  Select with tougher geometry  Hard/fragile tool class  tools Stabilize machining conditions  Excessive wear   Hard/fragile tool Excessive wearclass conditions  Select tools with tougher geometry  Reduce vibrations  Excessive weartoo hard  Reduce vibrations  grade Tool tooclass hard Tool Hard/fragile tool   Excessive weargrade Breakage/Fracture [24]   Excessive wear  Reduce vibrations  Lower feed rate Tool grade too hard  Lower feed rate grade of cutting edge strength Lack ofLack cutting edge strength  Reduce vibrations • Tool too hard Excessive wear vibrations •Tool Reduce vibrations   Tool too hard Lower feed rate  feed Tool grade with higher toughness Lack of cutting edge strength grade with higher toughness grade of holder rigidity   Reduce Lack ofLack holder rigidity Lower rate •  Lack of cutting edge strength Breakage/Fracture [24] Excessive wear Toolofgrade too hard  Lower feed rate feed • grade Lower rate  Lack cutting edge strength Tool with higher toughness holder rigidity  Toolgrade with higher toughness •  Lack of of holder rigidity Reduce vibrations Lack cutting Tool grade tooedge hardstrength  Tool with higher toughness • grade Tool grade with higher toughness  Lack of holder rigidity

•



Lack rigidity Lackofofholder cutting edge strength

Lack of holder rigidity

 

Lower feed rate Tool grade with higher toughness


18 of 30

Table 12. Cont. Coatings 2016, 6,2016, 51 6, 51 Coatings

18 of 3018 of 30

Cutting Edges Close Up Coatings 2016, 6, 51

18 of 30


(c)

(d)

(c)

(c)

(e)

(d)

(d)

(f)

(e)

(f)

Notes: (a) Top view of end (e) mill by secondary electron imaging (mag. 52×); (b) (f)Top view of end mill by retro diffused electron imaging (mag. 52 × ); (c) Cutting edge 1 with VB = 760.00 µm (mag. 250of ×end ); (d)mill Cutting Note: (a) Top view of end mill by secondary electron imaging (mag. 52×); (b) Top view by edge 2 with VB = 85.50 µm (mag. 500×); (e) Cutting edge 3 with VB = 86.50 µm (mag. 500×); (f) Cutting edge 4 with retro diffused electron imaging (mag. 52×); (c) Cutting edge 1 with VB = 760.00 µ m (mag. 250×); VB = 636.00 µm (mag. 250×). (d) Cutting edge 2 with VB = 85.50 µ m (mag. 500×); (e) Cutting edge 3 with VB = 86.50 µ m (mag. 500×); In 6a, which isVB a close upµof cutting edge 1, it is1,possible to observe several whitewhite specs specs In Figure which a close of 250×). cutting edge it is possible to observe several (f)Figure Cutting edge 46a, with = is 636.00 m up (mag.

In Figure 6a, which is of a close of cutting edgeoccurs 1, it is possible to observe several white which indicate lack oflack coating. Thisup phenomenon occurs when machined chips collidecollide with the end which indicate coating. This phenomenon when machined chips with the endspecs mill and chisel away at the surface coating. EDS analysis 6bmachined shows the composition area mill and chisel away surface EDSoccurs analysis in Figure shows the composition of area In Figure 6a,of which isat a the close up of coating. cutting edge 1, itinisFigure possible to 6b observe several whiteofspecs which indicate lack coating. This phenomenon when chips collide with the end Z1 as being perfectly coherent with the composition of the tool substrate (hard metal), indicating loss which indicate lack of coating. This phenomenon occurs when machined chips collide with the end Z1 as being perfectly coherent with the composition of the tool substrate (hard metal), indicating loss mill and chisel away at the surface coating. EDS analysis in Figure 6b shows the composition of area Z1 of coating. In theaway same manner, the coating. Z2the area composed mainly of aluminum and chromium, which mill and chisel the surface EDS analysis Figure 6b of shows the composition of areawhich of coating. In theatsame manner, Z2is area is composed mainly aluminum and chromium, as being perfectly coherent with the composition of theintool substrate (hard metal), indicating loss of are elements that form AlCrN coating. Z1 the asare being coherent with composition theperfectly elements that the form the the AlCrN coating. of the tool substrate (hard metal), indicating loss coating. In the same manner, the Z2 area is composed mainly of aluminum and chromium, which are of coating. In the same manner, the Z2 area is composed mainly of aluminum and chromium, which the elements that form AlCrN coating. are the elements thatthe form the AlCrN coating.

(a)

(a)

(a)

Figure 6. Cont.


19 of 30


19 of 30

(b)

(c) Figure 6. SEM analysis for cutting tool HPMT 4Z after 16 cycles; (a) Marked areas of detected

Figure 6. SEM analysis for cutting tool HPMT 4Z after 16 cycles: (a) Marked areas of detected discontinuities (mag. 500×); (b) EDS analysis for marked area Z1; (c) EDS analysis of marked area Z2. discontinuities (mag. 500×); (b) EDS analysis for marked area Z1; (c) EDS analysis of marked area Z2.

3.3.4. DORMER Spectrum S812HA—Roughness and SEM Results

3.3.4. DORMER Spectrum S812HA—Roughness and SEM Results

This tool returned low surface roughness values for the 8 cycles run (Table 13). Radial and

tangential a and Rz values for this test were the lowest all tested factors and This tool R returned low surface roughness valuesoffor the 8 tools. cyclesThis runcombination (Table 13).of Radial leads to feedtest marks onthe the lowest surface of machined part. On combination the other hand,ofthe tangential Raalmost and Rimperceptible were of the all tested tools. This factors z values for this roughness values from 8 to on 16 cycles indicates a rapid tool degradation, which mayhand, leadsevolution to almostinimperceptible feed marks the surface of the machined part. On the other translate into low tool life/durability. the evolution in roughness values from 8 to 16 cycles indicates a rapid tool degradation, which may Bearing in mind that this mill just presents two cutting edges, the roughness values obtained translate into low tool life/durability. after 16 cycles of machining can be considered reasonable. Lesser cutting knives signify higher Bearing in mind that this mill just presents two cutting edges, the roughness values obtained after working loads per knife (twice as much when compared to a 4-edge cutting mill), so the observed 16 cycles ofshould machining canaccount be considered reasonable. Lesser cutting knives signify higher working values take into this factor. loads per knife (twice as much when compared to a 4-edge cutting mill), so the observed values should take into account this factor.


20 of 30

When taking an overall look at Table 13, it is possible to say that this tool creates good machined surface quality, especially for shorter machining paths. However, due to its high degradation rate, its longevity may be reduced. Table 13. Part surface roughness obtained after 8 and 16 cycles of machining with DORMER 2Z AlCrN 20 of 3020 of 30 end mill. an overall look at Table 13,possible it is possible saythis thattool thiscreates tool creates good machined WhenWhen takingtaking an overall look at Table 13, it is to sayto that good machined Rmachining Rz due (µm)todue Rmax rate, (µm)its surface quality, especially for shorter machining However, to itsdegradation high degradation rate, its surface quality, especially for shorter paths.paths. However, its high a (µm) Measurements longevity may be reduced. longevity may be reduced. 8 Cycles 16 Cycles 8 Cycles 16 Cycles 8 Cycles 16 Cycles CoatingsCoatings 2016, 6,2016, 51 6, 51

1 0.315 0.572 1.818 3.449 2.360 6.470 13.surface Part surface roughness obtained 16 cycles of machining with DORMER 2Z Table Table 13. Part roughness obtained after 8after and 816and cycles of machining with DORMER 2Z 2 0.248 0.553 1.574 4.192 2.230 6.240 AlCrN end mill. AlCrN end mill. Radial 3 0.289 0.579 1.961 3.400 3.200 6.640

Radial

Tangentia l Tangentia l

Radial

Ra (µm) Rz (µm) Rmax2.597 (µm) Ra (µm) Rz (µm) Average 0.284 0.568 1.784 3.680Rmax (µm) 6.450 Measurements Measurements 8 Cycles 160.330 Cycles 8 Cycles 16 Cycles 8 Cycles 16 Cycles 2.320 8 Cycles 16 Cycles 8 Cycles 16 Cycles 82.110 Cycles 16 Cycles 1 0.188 1.255 1.610 1 0.315 0.315 0.572 0.352 0.572 1.818 1.818 6.470 3.449 3.4492.311 2.360 2.360 6.470 21 0.167 1.076 1.270 2.590 Tangential 2 0.248 0.248 0.553 0.363 0.553 1.574 1.574 6.240 4.192 4.1922.133 2.230 2.230 6.240 32 0.185 1.329 1.600 3.180 3 0.289 0.289 0.579 0.579 1.961 1.961 3.400 3.400 3.200 3.200 6.640 6.640 3 Average 0.180 0.348 1.220 2.185 1.493 2.697 Average Average 0.284 0.284 0.568 0.568 1.784 1.784 3.680 3.680 2.597 2.597 6.450 6.450 1 0.188 0.188 0.330 0.330 1.255 1.255 2.110 2.110 1.610 1.610 2.320 2.320 1 0.352 1.076 1.076 2.311 results, 2.311 1.270 1.270 2.590 2 the2 previously 0.167 0.167 0.352 2.590 In accordance with discussed roughness the SEM analysis for an 8 cycles 3 0.185 0.363 1.329 2.133 1.600 3.180 3 0.185 0.363 1.329 2.133 1.600 3.180 (Table 14) illustrates that this tool does not present any major damage to its cutting edges. It is Average Average 0.180 0.180 0.348 0.348 1.220 1.220 2.185 2.185 1.493 1.493 2.697 2.697

run also noticeable that one cutting edge returns a higher VB value than the other edge. This situation is mainly caused thewith factthe that onepreviously of the cutting flanks executes an initial roughing cut, a larger In by accordance with the discussed roughness results, the analysis SEM analysis anwith 8 cycles In accordance previously discussed roughness results, the SEM for anfor 8 cycles material removal rate, while the other edge executes a type of finishing pass, rectifying the previous run (Table 14) illustrates thattool thisdoes tool not doespresent not present any major damage its cutting run (Table 14) illustrates that this any major damage to its to cutting edges.edges. It is It is cut. also Thenoticeable loads applied to cutting the area smaller consequently also noticeable that onesecondary cutting edgeedge returns higher VBand value than the other edge. This situation is that one edge returns a higher VB value than the other edge.less Thissevere. situation is mainly caused by the fact that one of the cutting flanks executes an initial roughing cut, with a larger mainly caused by the fact that one of the cutting flanks executes an initial roughing cut, with a larger As stated previously, in spite of this having a superior wear after 16 cycles, the work load material removal rate, while the other edgeany executes type of finishing pass,experiment. rectifying the Regardless previous material removal rate, while theis other edgethan executes aother typeaof finishing pass, the previous completed by each cutting edge higher tool present in rectifying this of cut.loads The loads applied the secondary edge are smaller and consequently less severe. cut. The applied to theto secondary edge are smaller and consequently less severe. this fact, the tool generated a fairly satisfactory machined surface quality. As stated previously, in spite this having a superior after 16 cycles, the work As stated previously, in spite of thisofhaving a superior wear wear after 16 cycles, the work load load No EDS analysis was cutting made this did not show differences from theRegardless previous ones completed by cutting each edge is tool higher than any other toolmajor present inexperiment. this experiment. completed by each edge as is higher than any other toolany present in this Regardless tested. Another small note that can be made is that due to its geometrical configuration, chip extraction thisthe fact, thegenerated tool generated a fairly satisfactory machined surface quality. of thisoffact, tool a fairly satisfactory machined surface quality. No EDS analysis was made astool thisdid toolnot didshow not show anycollision/adhesion major differences fromprevious previousto the is more easily accomplished, which consequently minimizes ofthe material No EDS analysis was made as this any major differences from the ones edges. tested. Another small notecan thatbecan made that its geometrical configuration, chip ones tested. Another small note that made is SEM thatisdue todue its to geometrical chippresence tool’s cutting This can be confirmed bybethe imagery, showing aconfiguration, relatively low of extraction is more which consequently collision/adhesion of material extraction is more easily accomplished, consequently collision/adhesion of material white specs across the endeasily millaccomplished, surface,which as can be seen in minimizes Tableminimizes 15, where the tool wear can be observed the tool’s cutting Thisbecan be confirmed the imagery, SEM imagery, showing a relatively to thetotool’s cutting edges.edges. This can confirmed by thebySEM showing a relatively low low and the probable causes of that wear are listed, as well as some possible solutions. presence of white themill endsurface, mill surface, be in seen in Table 15, where thewear tool wear presence of white specs specs acrossacross the end as canasbecan seen Table 15, where the tool be observed and the probable that are wear are listed, asas well as some possible solutions. can becan observed and the probable causescauses of thatofwear listed, as well some possible solutions. Table 14. DORMER 2Z AlCrN SEM analysis after 8 cycles of machining. 14. DORMER 2Z AlCrN SEM analysis 8 cycles of machining. Table Table 14. DORMER 2Z AlCrN SEM analysis after 8after cycles of machining.


(a)

(a)

(b)

(b)


21 of 30

Table 14. Cont.

Coatings2016, 2016,6, 6, 51 51 Coatings

21 of 30

Observable Issues Analysis Observable Issues Analysis Observable Issues Analysis

Coatings Coatings 2016, 6,2016, 51 6, 51

Damage Issues Issues Damage

21 of 30

21 of 3021 of 30

Probable Causes Probable Causes

Possible Possible Solutions Solutions Probable Causes Possible Solutions Excessive cutting speed  Lower cutting speed Observable Issues Analysis Observable Issues Analysis Lower cutting speed 21 of 3021 of 30 Excessive cutting speed  • Lower cutting speed Low wear resistance/tool  Select tools with higherSolutions toughness Probable Causes Possible Probable Causes Possible Solutions Select tools with higher Low wear resistance/tool resistance/tool grade  • Select tools with higher toughness grade too soft Observable Issues Analysis Observable Issues Analysis  soft Excessive cutting speed  Lower cutting speed Excessive cutting speed  grade Lower cutting speedgrade too toughness grade too soft grade Feed toowear low   Increase feedwith rate Probable Causes Possible Probable Causes Possible Solutions  rate Low resistance/tool • Select tools withSolutions higher toughness Low wear Select tools higher toughness Feed rateresistance/tool too low Increase feed rate Feed ratecutting toosmall low Lower Increase feed rate Flank angle too  Increase flank angle  Excessive cutting speed  Lower cutting speed Excessive speed  cutting speed too soft grade too soft grade Flankgrade angle too small • grade Increase flank angle Flank angle too small Select Increase flank angle Low wear resistance/tool Select tools with toughness Low wear resistance/tool tools higher toughness  rate Feed rate too low  Increase feed ratehigher Feed too low  Increase feedwith rate

Damage Issues Coatings 6, 51 Coatings 2016, 6,2016, 51 [24] Flank wear

 • Damage Damage Issues Issues •  Damage Damage Issues Issues •   •   Edge Chipping [24]   Unstable machining conditions   Stabilize machining grade toosmall soft grade grade too soft grade  Flank angle too small  Increase flankconditions angle Flank angle too Increase flank angle • Hard/fragile tool class   Select tools withrate tougher  rate Feed rate too lowconditions • Stabilize Increase feed rategeometry Feed too low feed Unstable Increase machining conditions machining Stabilize machining conditions Flank angle too small Increase flank angle Flank angle too small flank angle Hard/fragile tool class Increase tools with tougher geometry  Unstable machining conditions • Select Stabilize machining conditions • Unstable Hard/fragile tool class Select tools with tougher geometry machining conditions  Stabilize machining conditions   

 Hard/fragile tool class  Select toolstougher with tougher geometry Hard/fragile tool class  Select tools with geometry  Unstable machining conditions  Stabilize machining conditions Unstable machining conditions  Stabilize machining conditions Cutting Edges Close Up  Hard/fragile tool class  Select toolstougher with tougher geometry Hard/fragile tool class  Select tools with geometry

(c)

(d)

Note: (a) Top view of end mill by secondary electron imaging (mag. 50×); (b) Top view of end mill by retro diffused electron (c) imaging 500×); (d) (c) (mag. 50×); (c) Cutting edge 1 with VB = 62.50(d)µ m (mag. (d) Cutting edge 2 view with VB = 89.50 µby m (mag. 500×). (c) (d)ofview Note: Topof view of end mill by secondary electron imaging 50×); (b) Top end Note: (a) Top(a) end mill secondary electron imaging (mag. (mag. 50×); (b) Top view endof mill bymill by Notes: (a) Top view of end mill by secondary electron imaging (mag. 50×); (b) Top(d) view of end mill by retro (c) (c) retro diffused electron imaging (mag. 50×); (c) Cutting edge 1VB with VB(d) =(b) 62.50 µview m (mag. 500×); (d)by Note: (a) Top view of end mill by secondary electron imaging (mag. 50×); Top of end mill retro diffused electron imaging (mag. 50×); (c) Cutting edge 1 with = 62.50 µ m (mag. 500×); (d) diffused electron imaging (mag. 502Z ×);AlCrN (c) Cutting edge 1 with VB = 62.50 µm (mag. 500×); (d) Cutting edge 2 Table DORMER SEM analysis after 16 cycles of(b) machining. Note: (a) Top15. of end mill by electron imaging (mag. 50×); Topµof view of end mill by Note: (a) Top view of end mill secondary electron imaging (mag. 50×); Top view mill by Cutting edge 2view with VB µ msecondary (mag. 500×). Cutting 2electron with VB = 500 89.50 µ89.50 m (mag. 500×). retro diffused imaging (mag. 50×); (c) Cutting edge 1 with VB = (b) 62.50 mend (mag. 500×); (d) with VB = edge 89.50 µm (mag. ×=).by retro diffused electron imaging (mag. 50×); with VB = µ62.50 µ m (mag. retro diffused electron imaging (mag.Top 50×); (c) Cutting edge 1edge with1VB = 62.50 m (mag. 500×); 500×); (d) (d) View of (c) EndCutting Mill Cutting edge 2 with VB = 89.50 µ m (mag. 500×). Cutting 2VB with VBDORMER =µ89.50 µm Cutting edgeTable 2edge withTable = 89.50 m2Z(mag. 500×). 15. 2Z(mag. AlCrN SEM analysis after 16 cycles of machining. 15. DORMER AlCrN SEM500×). analysis after 16 cycles of machining.

Table 15. DORMER 2Z AlCrN SEM analysis after 16 cycles of machining. Table 15. DORMER 2Z Top AlCrN SEM analysis 16 cycles of machining. Top View of Endafter Mill of End Mill Table 15. DORMER 2Z View AlCrN SEM analysis after 16 cycles of machining. Table 15. DORMER 2Z AlCrN SEM analysis after 16 cycles of machining.

TopView Viewof ofEnd EndMill Mill Top

(a)

(b)

(a)

(a)

(b)

(b)

(a)

(a)

(b)

(b)

(a)

(b)


22 of 30


Table 15. Cont.



22 of 30

22 of 30

22 of 30

Observable Issues Analysis Observable Issues Analysis Observable Issues Analysis

Coatings 2016, 6,2016, 51 6, 51 Damage Issues Coatings Damage Issues

22 of 3022 of 30 Probable Causes Possible Solutions Probable Causes Possible Solutions Probable Causes Possible Solutions Observable Issues Analysis   Excessive cutting speed  Lower cutting speed Excessive cutting speed  Lower cutting speed Probable cutting Causes speed Solutions • Excessive • Possible Lower cutting speed Observable IssuesIssues Analysis Observable Analysis Low wear resistance/tool Select tools with higher toughness Low wear resistance/tool  •Select tools withwith higher toughness • Excessive cutting speed  Lower cutting speed Low wear resistance/tool grade Select tools higher Damage Issues Probable Causes Possible Solutions Damage Issues  Probable Causes  Possible Solutions grade too soft grade Low wear resistance/tool Select tools with higher toughness grade grade too softtoo soft toughness grade Excessive speed speed  Increase Lower cutting speed speed  rate Excessive  Lower cutting   grade Feed toocutting low cutting feed rate too soft grade Feed rate too low  •Increase feed feed rate rate • Feed rate too low Increase  Flank Low wear resistance/tool  Increase Select tools with higher toughness  Low wear resistance/tool  Select tools with higher toughness  angle too small  flank angle • Feed rateangle too low  Increase feed rate Flank too Increase Flank angle toosmall small  •Increase flankflank angleangle grade grade too soft grade grade too soft  Friction  Increase rake angle to improve  angle too small  Increase flank angle  Flank Friction Increase rake to improve Feed too low  sharpness feed rate  rate Feed rate too low  •Increase Increase feedangle rate angle Oxidation Increase  Friction  Increase rake angle torake improve to  Oxidation sharpness • Friction Notch wear [24]  Flank angle too small  Increase flank angle  Flank angle too small  sharpness  Increase angle improve Hardened or doughy Change depth of flank cut sharpness  Oxidation • material Oxidation Hardened or doughy Increase Change depth ofimprove cut Friction  CVD rake angle to  Friction  •coating Increase rake angle to cut improve Change depth of to wear  Hardened or doughy  Change depth ofimprove cut Hardened or doughy material Oxidation sharpness material  CVD coating to improve wearwear  Oxidation sharpness • CVD coating to improve •  material Negative geometry  PVD coating to improve BUE and  CVD coating to improve wear • Negative geometry Hardened or doughy  flaking Change depth of cut  Hardened or doughy  Change depth of cut of tool • PVD coating to improve BUE Negative geometry  PVD coating to improve BUE and and  Negative geometry  PVD coating to improve BUE and material  flaking CVD coating improve wear wear material  flaking CVD coating improve flaking of to tool oftotool of tool  Unstable machining  Negative geometry PVD to improve BUE and  Negative geometry  coating PVD coating to improve BUE and   Stabilize machining conditions Edge chipping [24] conditions   Unstable machining Unstable machining flaking of tool flaking of tool  Stabilize Select•tools with tougher geometry  machining conditions • Unstable machining conditions Stabilize machining conditions  Stabilize machining conditions  conditions Hard/fragile tool class conditions  Select tools with tougher geometry • Hard/fragile tool class • Select tools with tougher geometry Unstable machining  Unstable machining  Select tools with tougher geometry   Hard/fragile tool class  Stabilize machining conditions  Stabilize machining conditions   Excessive wear tool class Hard/fragile conditions conditions Select tools with geometry  vibrations Select toolstougher with tougher geometry Tool gradewear too hard   Reduce   Excessive Hard/fragile tool class  Hard/fragile tool class Breakage/Fracture [24]  Lack Excessive wear of cutting edge  Reduce Lower feed rate • Tool grade too hard  vibrations Excessive wear  strength Tool grade too wear hard  grade vibrations Excessive wear  cutting Excessive •Reduce vibrations Tool with toughness • Lack edge  Lower feedReduce rate higher Toolofgrade too hard Tool too hard vibrations  ofgrade Tool grade too hard   Tool grade Reduce vibrations Lack of cutting edge Reduce feed rate •Lower Lower feed rate   strength Lack holder rigidity with higher toughness • Lack of cutting edge strength  Lack of cutting edgeClose  Lower feed rate  Lack of cutting edge  Lower feed rate • Tool grade with higher toughness Cutting Edges Up strength Tool grade with higher toughness • Lack of of holder rigidity Lack holder rigidity strength  Tool with higher toughness strength  grade Tool grade with higher toughness  Lack of holder rigidity Cutting Edges Close Up  Lack holder rigidity  of Lack of holder rigidity Cutting CuttingEdges EdgesClose CloseUp Up Cutting EdgesEdges Close Close Up Up Cutting

Flank wear [24] Damage Issues


(c)


(d)

(d) Top view of end mill Note: (a) Top view(c)of end mill by secondary electron imaging (mag. 50×); (b) by retro imaging (mag. 50×); (c) Cutting edge 1 with VB = 881.80 µ m (mag. 220×); Note: (a)diffused Top viewelectron of(c) end mill Top view (c) by secondary electron imaging (mag. 50×); (b)(d) (d) of end mill (d)retro Cutting edge electron 2 with VB = 926.10 µ m (mag. 220×). by diffused imaging (mag. 50×); (c) Cutting edge 1 with VB = 881.80 µ m (mag. 220×); (c)ofview (d) Note: (a) Top(a) view mill bymill secondary electron imaging (mag.50 50×); Top view end mill Note: Top end secondary imaging (mag. 50×); (b) Topof view end by millretro Notes: (a) Top view end end mill by secondary electron imaging (mag. ×); (b) view of endof mill (d) Cutting edge 2of with VB =of926.10 µ mby (mag. 220×). electron electron imaging (mag. 50 ×AlCrN );imaging (c) Cutting edge 1 (c) with VB =1881.80 µm (mag. 220 × );µ(d) Cutting edge 2 by retro diffused electron imaging (mag. 50×); (c) Cutting edge with VB = 881.80 µ m (mag. 220×); by retro diffused electron (mag. 50×); Cutting edge 1 with VB = 881.80 m (mag. 220×); 3.3.5.diffused Chip Analysis for DORMER 2Z and WALTER 3Z AlCrN End Mills Note: (a) Top view of end mill by secondary electron imaging (mag. 50×); (b) Top view of end mill with VB 926.10 µm ×=).926.10 (d)=Cutting edge(mag. 2edge with220 µ m (mag. 220×). 220×). (d) Cutting 2VB with VB = 926.10 µ m (mag.

3.3.5.Chips Chip Analysis forbyDORMER 2Z AlCrN WALTER 3Z AlCrN Mills by retro diffused electron imaging (mag. 50×); (c) Cutting edge 2Z 1End with VB =were 881.80 µ m (mag. 220×); generated mill tools HPTM 3Zand AlCrN and DORMER AlCrN collected after

(d) Cutting edge 2mill withand VB observed =HPTM 926.10 3Z µunder mAlCrN (mag. the 8Chips cycles machining the220×). SEMDORMER microscope. By observing Figure 7,after it is generated bytrials tools and 2Z AlCrN were collected the 8 cycles machining trials and observed under the SEM microscope. By observing Figure 7, it is Chips generated by mill tools HPTM 3Z end AlCrN and AlCrN were collected after after Chips generated by mill2Z tools HPTM 3Zmill AlCrN and3Z DORMER 2Z AlCrN were collected The chips created by the HPMT 3ZAlCrN AlCrN demonstrate a2Z rougher and more irregular 3.3.5. Chip Analysis for DORMER WALTER AlCrN End Mills possible to perceive differences between the chips created byDORMER each tool. Chips generated by mill tools HPTM 3Zand AlCrN and DORMER 2Z AlCrN were collected after the the 8 cycles machining trials and observed under the SEM microscope. By observing Figure 7, it is7, it is the 8 cycles machining trials and observed under the SEM microscope. By observing Figure edge/rim. This created geometry may be explained by the higher rake angle (less sharp)and of this tool, which The chips byand the HPMT 3Z AlCrN end mill demonstrate a rougher more irregular 8 cycles machining trials observed under the SEM microscope. By observing Figure 7, it is after possible Chips generated by mill tools HPTM 3Z AlCrN and DORMER 2Z AlCrN were collected possible to perceive differences between the chips created by each tool. possible to perceive differences between the chips created by each tool. consequently friction loadsby between cutting chips, andofby thetool, additional edge/rim. Thisgenerates geometryhigher may be explained the higher rakeedges angleand (less sharp) this which tothe perceive differences between the chips created each 8 cycles machining trials and observed under the microscope. observing Figure 7, it is Theof chips created by due theby HPMT 3Z AlCrN end by mill demonstrate a That rougher and more irregular The chips created HPMT 3Z AlCrN end milltool. demonstrate aBy rougher and more irregular difficulty chip extraction tothe the increased number ofSEM cutting said, surface consequently generates higher friction loads between cutting edges flutes. and chips, and bythe thechip additional The chips created by the HPMT 3Z AlCrN end mill demonstrate a rougher and more edge/rim. This geometry may be explained by the higher rake angle (less sharp) of this tool, which edge/rim. This geometry may be explained by the higher rake angle (less sharp) of this tool, which possible to perceive differences between the chips created by each tool. (seen in Figure displaysdue greater irregularities, indicating theThat existence of chip larger loads irregular difficulty of chip 8) extraction to thesurface increased number of cutting flutes. said, the surface consequently generates higher friction loads between cutting edges and chips, andsharp) by the additional consequently generates higher friction loads between cutting edges and chips, and by the additional edge/rim. This geometry may be explained by the higher rake angle (less of this tool, which The chips created by the HPMT 3Z AlCrN end mill demonstrate a rougher and more irregular during extraction/ejection. (seen in Figure 8) displays greater surface irregularities, indicating the existence of larger loads difficulty of chip extraction due to the increased number of cutting flutes. That said, the chip surface difficulty of chip extraction due to the increased number of cutting flutes. That said, the chip surface edge/rim. This geometryhigher may be explained the higher rake edges angle (less sharp) and of this which consequently generates friction loadsbybetween cutting and chips, by tool, the additional during extraction/ejection. (seen (seen in Figure 8) displays greater surface irregularities, indicating the existence of larger loads loads in Figure 8) displays greater surface irregularities, indicating the existence larger consequently generates higher between cutting edges and chips, andsaid, byofthe difficulty of chip extraction duefriction to the loads increased number of cutting flutes. That theadditional chip surface during extraction/ejection. during extraction/ejection.

Chips generated by mill HPTM 3ZAlCrN AlCrN and DORMER AlCrN were collected after 3.3.5. Chip Analysis forDORMER DORMER 2Z and WALTER 3Z AlCrN End Mills 3.3.5. Chip Analysis fortools DORMER 2Z and WALTER 3Z2Z AlCrN End Mills 3.3.5. Chip Analysis for 2ZAlCrN AlCrN and WALTER 3Z AlCrN End Mills possible to perceive differences between the chips created by each tool.

difficulty of chip extractiongreater due tosurface the increased number indicating of cutting flutes. That said, the chip surface (seen in Figure 8) displays irregularities, the existence of larger loads during (seen in Figure 8) displays greater surface irregularities, indicating the existence of larger loads extraction/ejection. during extraction/ejection.


23 of 30


23 of 30 23 of 30

(a) (a)

(b) (b)

(c) (c)

(d) (d) Figure 7. Chip SEM analysis; (a) Chip made by HPMT 3Z AlCrN (mag. 50×); (b) Chip created by of Figure 7. Chip SEM analysis: (a) Chip made by HPMT 3Z AlCrN (mag. 50×); (b) Chip created by of Figure 3Z 7. Chip SEM analysis; 3Z AlCrN (mag. 50×); (b)(d) Chip created by by of HPMT AlCrN (mag. 160×);(a) (c) Chip Chip made made by by HPMT DORMER 2Z AlCrN (mag. 50×); Chip created HPMT 3Z3Z AlCrN (mag. 160 ×); (c) Chip made by DORMER 2Z AlCrN AlCrN(mag. (mag.50×); 50×(d) ); (d) Chip created by HPMT AlCrN (mag. 160×); (c) Chip made by DORMER 2Z Chip created by DORMER 2Z AlCrN (mag. 220×). DORMER 2Z AlCrN (mag. 220 × ). DORMER 2Z AlCrN (mag. 220×).

(a) (a)

(b) (b)

Figure 8. SEM analysis of chip made by HPMT 3Z AlCrN during an 8 cycles trial; (a) Overall view of Figure SEM analysis chip madeofbychips HPMT 3Z AlCrN during 8 cycles trial; (a) Overall view of chip (mag. 220×); (b) close up detail crushed surface (mag.an 3750×). Figure 8. 8. SEM analysis ofofchip made by HPMT 3Z AlCrN during an 8 cycles trial: (a) Overall view of chip (mag. 220×); (b) close up detail of chips crushed surface (mag. 3750×). chip (mag. 220×); (b) Close up detail of chips crushed surface (mag. 3750×).

The chips originated by the DORMER 2Z AlCrN end mill demonstrate a cleaner and more The surface chips originated by the 2Z AlCrN end millextraction demonstrate cleaner and loads. more uniform and rim edge. ThisDORMER is mainly due to its facilitated and alower friction uniform surface and rim edge. This is mainly due to its facilitated extraction and lower friction loads.


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The chips originated by the DORMER 2Z AlCrN end mill demonstrate a cleaner and more Coatings 2016, 6, 51 24 of 30 uniform surface and rim edge. This is mainly due to its facilitated extraction and lower friction loads. In In Figure 9, 9, it it is ispossible the machined machinedchip, chip,demonstrating demonstrating a lesser crushed Figure possibletotoobserve observethe the surface surface of of the a lesser crushed surface mainly due to the smaller rank angle (sharper) and spaced out cutting flutes. surface mainly due to the smaller rank angle (sharper) and spaced out cutting flutes.

(a)

(b)

Figure 9. SEM analysis of chip made by DORMER 2Z AlCrN during an 8 cycles trial; (a) Overall view Figure 9. SEM analysis of chip made by DORMER 2Z AlCrN during an 8 cycles trial: (a) Overall view of chip (mag. 200×); (b) Close-up detail of chip crushed surface (mag. 3750×). of chip (mag. 200×); (b) Close-up detail of chip crushed surface (mag. 3750×).

4. Discussion 4. Discussion In this section, a global analysis was done in order to establish which tools demonstrated In thisperformance section, a global was doneresults. in order to establish which tools demonstrated superior superior and analysis what lead to such performance and what lead to such results. Depending on which tool was used and the length of the trial, several different roughness results Depending which was used and the of 8the trial,trials several differentlower roughness results were measuredonon each tool machined surface. Thelength shorter cycles presented roughness were measured on each machined surface. The shorter 8 cycles trials presented lower roughness values, values, as expected. As seen in Figure 10, the tool which produced the lowest surface roughness for as the expected. seenrun in Figure 10,DORMER the tool which produced surface roughness the shorter shorterAs cycle was the 2Z AlCrN end the mill,lowest having, as well, the leastfordifference cycle run was the and DORMER 2Z AlCrN end values. mill, having, as well, the leastuniform difference between radial between radial tangential roughness This indicates a more surface without and tangential roughness values. This indicates a more uniformofsurface without noticeable feed marks. noticeable feed marks. The Rz values were also the smallest all tests, indicating a low variation between surface and valleys, ensures longer partvariation life withbetween continued dimensional The Rz values were peaks also the smallest of which all tests, indicating a low surface peaks and accuracy. valleys, which ensures longer part life with continued dimensional accuracy. The WALTER TiAlN gave slightlyhigher higherroughness roughnessvalues valuesfor forthe the88cycles cycles when when compared compared to The WALTER 4Z4Z TiAlN gave slightly to the previous mentioned tool, however, it returned the most consistent global performance. the previous mentioned tool, however, it returned the most consistent global performance. Regarding theHPMT HPMT3Z 3ZAlCrN AlCrNtool, tool, reasonable reasonable roughness z) values were obtained, Regarding the roughness(including (includingRR z ) values were obtained, being the third best tool for the 8 cycles in terms of machining length. being the third best tool for the 8 cycles in terms of machining length. End millHPMT HPMT4Z 4ZAlCrN AlCrNperformed performed poorly, poorly, returning returning very was End mill very high highvalues. values.This Thisoutcome outcome was somewhat unexpected and, perhaps, may be a consequence of the excessive wear/damage suffered somewhat unexpected and, perhaps, may be a consequence of the excessive wear/damage suffered by by the tool on the account of hardened material phases possibly present in the raw material. A the tool on the account of hardened material phases possibly present in the raw material. A possible possible manufacturing defect may also be speculated as the reason for such a rapid downfall. manufacturing defect may also be speculated as the reason for such a rapid downfall. Figure 10 also shows, in terms of radial roughness, an end mill which negatively stands out Figure 10 also shows, in terms of radial roughness, an end mill which negatively stands out among the rest (HPMT 4Z AlCrN). While all other end mills showed similar Ra results, HPMT 4Z among the rest (HPMT 4Z AlCrN). While all other end mills showed similar R results, HPMT 4Z AlCrN mill revealed higher Ra radial roughness. As previously discussed, this toola suffered damage AlCrN mill higher Ra radial roughness. previously discussed, this of tool damage during therevealed experimental trials, leading to a loss ofAs material and edge sharpness thesuffered cutting flutes. during the experimental leading to anoticeable loss of material andembossments, edge sharpness of thetocutting flutes. This phenomenon may trials, explain the more feed mark leading the larger This phenomenon may explain the more noticeable feed mark embossments, leading to the larger radial Rz and Rmax roughness values. radial RTangential roughness values. z and Rmax roughness values for the 16 cycles trials, shown in Figure 11, clearly demonstrate that Tangential 16 cycles trials, in Figure clearly demonstrate that WALTER 4Z roughness TiAlN and values HPMTfor 4Z the AlCrN obtained theshown best results. The11,remaining tools present WALTER and HPMT 4Z AlCrN obtained the best results. remaining tools present similar 4Z andTiAlN satisfactory tangential Ra values, however, they exhibitThe higher Rz values which leadsimilar to a more irregular tangential surface in terms of peak height and valley depth. and satisfactory Ra values, however, they exhibit higher Rz values which lead to a more irregular surface in terms of peak height and valley depth.

Coatings 2016, 6, 51 Coatings 2016, 6, 51 Coatings 2016, 6, 51

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Figure 10. Roughness values observed on machined surfaces after 8 cycles. Figure Figure10. 10.Roughness Roughnessvalues valuesobserved observedon onmachined machinedsurfaces surfacesafter after 88 cycles. cycles.

Figure Figure11. 11.Roughness Roughnessvalues valuesobserved observedon onmachined machinedsurfaces surfacesafter after16 16 cycles. cycles. Figure 11. Roughness values observed on machined surfaces after 16 cycles.

All tools used in the experimental trials demonstrated similar types of wear, some All tools used used experimental trials demonstrated similar of having wear, having having some All tools inin thethe experimental trials demonstrated similar types types of wear, some suffered suffered more wear than others. In a broad way, it is possible to say that the main issues encountered suffered more wear than others. In a broad way, it is possible to say that the main issues encountered more wear than others. In a broad way, it is possible to say that the main issues encountered were were flank wear, chipping, cracking and breakage of the cutting edges. These issues manifested in were flank wear, chipping, cracking and breakage of the cutting edges. These issues manifested in


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Coatings 2016, 2016, 6, 6, 51 51 Coatings

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flank wear, chipping, cracking and breakage of the cutting edges. These issues manifested in different levels of levels severity. Tools with higher wear demonstrated poorer machined surfaces, while tools that different levels of of severity. severity. Tools with higher wear demonstrated demonstrated poorer machined machined surfaces, while different Tools with higher wear poorer surfaces, while suffered created surfaces noticeable feed marks. tools thatbreakage suffered breakage breakage createdwith surfaces with noticeable noticeable feed marks. marks. tools that suffered created surfaces with feed The depth of cut used for all trials (0.5 mm) was more in tune with aa finishing finishing operation operation rather rather The depth of cut used for all trials (0.5 mm) was more in tune with than a conventional roughing operation. The small material removal rate, aided with cutting fluid, conventional roughing roughing operation. operation. The The small small material material removal removal rate, rate, aided aided with with cutting cutting fluid, fluid, than a conventional allows aa reduction temperatures at Theuse useof ofcutting cuttingfluids fluidsgives gives way way to to aa large allows reduction of of temperatures temperatures at the the tool’s tool’s tip. tip. The The use of cutting fluids gives way to large allows variation of temperature during machining, creating heat cycles which may lead to thermal fatigue. temperature during during machining, machining, creating creating heat heat cycles cycles which which may may lead lead to to thermal thermal fatigue. fatigue. variation of temperature for instance, instance, cutting other encountered encountered This fatigue fatigue may may perhaps perhaps be be the the cause cause of, of, for cutting edge edge fractures fractures or or other This defects. When Whenadding addingthe theinherent inherentvibration vibration(created (createdby bythe the machining machining of of tough tough materials) materials) to defects. When adding the inherent vibration (created by the machining of tough materials) to the the defects. equation, the potential for tool chipping and crack propagation is increased, which then leads to equation, the the potential potential for for tool tool chipping chipping and and crack crack propagation propagation is is increased, increased, which which then then leads leads to aa equation, probability. higher tool tool failure failure probability. probability. higher beseen seenin inFigures Figures12 12and and13. 13.The TheWALTER WALTER A comparison of flank flank wear wear suffered suffered on on each each tool tool can can be be seen in Figures 12 and 13. The WALTER A comparison of 4Z TiAlN is the end mill with the lowest flank wear in the group having, as well, the smallest wear 4Z TiAlN is the end mill with the lowest flank wear in the group having, as well, the smallest wear rest. evolution when when compared compared to to the the rest. evolution

Figure 12. 12. Flank Flank wear (VB) values registered on the edges of of each each end end mill mill for for 88 cycles. cycles. Flankwear wear(VB) (VB)values valuesregistered registeredon onthe theedges Figure

Figure 13. Flank wear (VB) values registered on the edges of each end mill for 16 cycles. Figure Figure13. 13.Flank Flankwear wear(VB) (VB)values valuesregistered registeredon onthe theedges edgesof ofeach eachend endmill millfor for16 16cycles. cycles.


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DORMER 2Z AlCrN came in second in terms of flank wear for the smaller cycle run, however, DORMER 2Z AlCrN came in second in terms of flank wear for the smaller cycle run, however, when compared to the results after 16 machining cycles, it is noticeable that this tool suffered severe when compared to the results after 16 machining cycles, it is noticeable that this tool suffered severe cutting edge wear. As this tool only has two cutting flutes, it is at a disadvantage when compared to cutting edge wear. As this tool only has two cutting flutes, it is at a disadvantage when compared to the others, demanding that each flute do extra work to achieve the same 15 m machining distance. the others, demanding that each flute do extra work to achieve the same 15 m machining distance. HPMT 3Z AlCrN achieved similar low VB values for the initial trial indicating low tool wear, HPMT 3Z AlCrN achieved similar low VB values for the initial trial indicating low tool wear, and demonstrated the second best result after 16 cycles of machining. Although obtaining reasonable and demonstrated the second best result after 16 cycles of machining. Although obtaining reasonable results, a large variation of flank wear between cutting flutes is present. Despite the fact that a low results, a large variation of flank wear between cutting flutes is present. Despite the fact that a low flank wear is present, this tool gave the highest surface roughness of all machined parts, delivering an flank wear is present, this tool gave the highest surface roughness of all machined parts, delivering inferior machined surface finish. an inferior machined surface finish. As stated previously, the HPMT 4Z AlCrN end mill suffered extended wear and damage during As stated previously, the HPMT 4Z AlCrN end mill suffered extended wear and damage during the first trial, exhibiting an overall significant degree of wear. SEM results for the lengthier trial show a the first trial, exhibiting an overall significant degree of wear. SEM results for the lengthier trial show large wear variation between cutting flutes. This variation may support the statement given previously a large wear variation between cutting flutes. This variation may support the statement given which speculates that this tool dealt with different levels of hardness during its machining operation previously which speculates that this tool dealt with different levels of hardness during its machining due to the presence of heterogeneities in the material. operation due to the presence of heterogeneities in the material. Considering Figures 12–15, it is possible to state that the WALTER 4Z TiAlN end mill: Considering Figures 12–15, it is possible to state that the WALTER 4Z TiAlN end mill:

• • •

Showedthe theoverall overallbest bestperformance performanceof ofthe theexperiments; experiments; Showed Gavethe thesecond secondbest/lowest best/lowestradial radialand andtangential tangentialsurface surfaceroughness roughnessresults resultsfor for the the 88 cycles cycles trial trial Gave andthe thebest/lowest best/lowestfor forthe the1616cycles cyclestrial; trial; and Thequality qualityof ofthe themachined machinedsurface surfaceisis maintained maintained independently independentlyof of the the increase increase in in machining machining The distance/workinglife lifeofofthe thetool. tool.This Thiscan canbe beseen seenby bythe theregistered registeredlow lowVB VB values values of of the the cutting cutting distance/working flutesand andby bythe thesmall smallslope slopeof of the the line line that that correlates correlates surface surface roughness roughness between between the the first first and and flutes secondtrials. trials.This Thisslope slopeisisthe thesmallest smallestamong amongall all the the tools tools indicating indicating aa slower slower wear evolution second andconsequently consequentlylonger longertool toollife. life. and

As As can can be be seen seen in in the the previous previous figures, figures, the the coatings coatings are are valid valid essentially essentially during during the the initial initial stage stage of the trials. Posteriorly, it is possible to observe deeply worn cutting edges, displaying of the trials. Posteriorly, it is possible to observe deeply worn cutting edges, displaying coating coating detachment detachment and and requiring requiring the the hard hard metal metal substrate substrate to to work work without without any any of of the the advantages advantages conferred conferred by the coating. Thus, it is important to observe the wear evolution from the 8 cycles by the coating. Thus, it is important to observe the wear evolution from the 8 cyclesto to16 16cycles cyclestrials. trials. The both in in 88 and and 16 The TiAlN TiAlN coating coating displays displays better better results results in in terms terms of of flank flank wear, wear, both 16 cycles cycles trials. trials. All All the the AlCrN coatings demonstrate premature detachment and severe wear, mainly after 16 machining AlCrN coatings demonstrate premature detachment and severe wear, mainly after 16 machining cycles. cycles. it can be that, statedwhen that, machining when machining Stainless a TiAlN coating displays Hence,Hence, it can be stated DuplexDuplex Stainless Steel, aSteel, TiAlN coating displays better better results in terms of machining work than a AlCrN coating. results in terms of machining work than a AlCrN coating.

Figure Figure 14. 14. Radial Radial roughness roughness evolution evolution from from eight eight to to 16 16 cycles cycles of of machining. machining.


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Figure Figure 15. 15. Tangential Tangential roughness roughness evolution from eight to 16 cycles of machining.

Hard Hard metal metal grade grade seems seems to to play play an an important important role role in in wear wear evolution evolution as as some some tools tools showed showed substrate wear and corresponding degradation in terms of flank wear. substrate wear and corresponding degradation in terms of flank wear. The The number number of of flutes flutes is is also also an an important important issue issue to to consider consider because because when when using using the the same same feed feed speed on a tool with less cutting flutes, the number of tool rotations and corresponding impact speed on a tool with less cutting flutes, the number of tool rotations and corresponding impact increase, increase, to a premature cutting edge wear. leading toleading a premature cutting edge wear. The overall best tool (WALTER 4Z TiAlN) a coating composed by titanium aluminium The overall best tool (WALTER 4Z TiAlN) has has a coating composed by titanium aluminium nitride. nitride. This was coating wastoshown to be generally superior in longevity terms of longevity and of This coating shown be generally superior in terms of and quality of quality machined machined surfaces. The aluminium oxide promotes high temperature resistance while the surfaces. The aluminium oxide promotes high temperature resistance while the combination of combination of elements promotes a hard and tough In fact, the general consensus is that elements promotes a hard and tough surface. In fact,surface. the general consensus is that tools that are tools that are properly coated improve longevity and optimize cutting parameters. properly coated improve longevity and optimize cutting parameters. 5. 5. Conclusions Conclusions All All in in all, all, it it is is possible possible to to state state that that end end mills mills with with four four cutting cutting flutes flutes maintained maintained aa better better surface surface roughness, presenting the lowest R a , R z and R max results for the 16 cycles trials. They are an roughness, presenting the lowest Ra , Rz and Rmax results for the 16 cycles trials. They are an appropriate appropriate choice side to perform milling on operations onofthe grade Stainless of DuplexSteel Stainless used in choice to perform millingside operations the grade Duplex used Steel in this study. this study. Nonetheless, the other tested end mills showed interesting results (only slightly worse Nonetheless, the other tested end mills showed interesting results (only slightly worse than the than the four-flute endbeing mills), being more suitable for slotting ormilling down milling operations. In types these four-flute end mills), more suitable for slotting or down operations. In these types of machining operations, having lesser cutting flutes gives the advantage of easily and of machining operations, having lesser cutting flutes gives the advantage of easily and effectively effectively extracting chips from the tooling edges. This ease of extraction avoids potential material extracting chips from the tooling edges. This ease of extraction avoids potential material adhesion adhesion or build up onedges, cuttingphenomena edges, phenomena that worsens when machining materials with or build up on cutting that worsens when machining materials with similar similar compositions as the ones here tested. On the downside, tools with only two or three cutting compositions as the ones here tested. On the downside, tools with only two or three cutting flutes tend flutes tend to have a shorter to the fact that,the to machine the same each to have a shorter working lifeworking owing tolife theowing fact that, to machine same distance, eachdistance, cutting knife cutting knife work has a load higher work load when for example,end to four-flute mills. has a higher when compared, forcompared, example, to four-flute mills. Theend work loadThe per work tooth load per tooth is independent of speed parameters, such as the feed per tooth speed of the machining is independent of speed parameters, such as the feed per tooth speed of the machining center. center. The duplex stainless steel used in the experiments proved to be very harsh on the cutting tools. The duplex steel used inused the experiments to be to very on the cutting tools. Even though thestainless machining distance in the trials isproved considered be harsh relatively short, the tested Even though the machining distance used in the trials is considered to be relatively short, the tested tools suffered extended damage and wear, exemplifying how difficult it is to work and process these tools extended damage and wear, exemplifying how difficult it is to work and process these typessuffered of materials. typesItofseems materials. to have been made clear that WALTER 4Z TiAlN end mill delivered the best results It seems to have made clearofthat WALTER 4Z TiAlN endWorth mill delivered the as best results in in terms of wear and been almost always machined surface quality. mentioning well is that, terms ofof wear and almost always machined surface quality. Worthwith mentioning as well is that,end in in spite suffering large wear, theofsurface quality of parts machined DORMER 2Z AlCrN spite of suffering large wear, the surface quality of parts machined with DORMER 2Z AlCrN end mill revealed very good results, being close to those of the other tools. However, this outcome can be attributed essentially to the quality of the tool substrate, made from a very good hard metal grade.


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mill revealed very good results, being close to those of the other tools. However, this outcome can be attributed essentially to the quality of the tool substrate, made from a very good hard metal grade. Thus, despite the large evolution registered by AlCrN coatings, this work shows that TiAlN is yet more effective in cutting tough materials, such as Duplex Stainless Steel grades, in end mill machining operations. Acknowledgments: Authors would like to thanks to António Pedro Pinho from ARSOPI, S.A., Vitor Almeida from DORMER TOOLS Portugal, Lda. and Fernando Reis from F. REIS, Lda., due to their support and collaboration in this work. The institutions ISEP—School of Engineering, Polytechnic of Porto and INEGI—Instituto de Ciência e Inovação em Engenharia Mecânica e Engenharia Industrial are also acknowledge due to permission to use their facilities and financial support. Author Contributions: Pedro Reis and Francisco Silva conceived and designed the experiments; Pedro Reis performed the experiments; Pedro Reis, Francisco Silva and António Baptista analyzed the data; Ronny Gouveia and Francisco Silva wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.

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Bohler Edelsthal (Austria), W705 Steel Datasheet, W705 DE 01.02 EM-WS. Available online: www.bohler.at/ deutsch/files/downloads/W705.pdf (accessed on 4 July 2016). ISO 6892-1:2016 Metallic Materials—Tensile Testing—Part 1: Method of Test at Room Temperature; International Organization for Standardization: Geneva, Switzerland, 2016. ISO 6506-1:2014 Metallic Materials—Brinell Hardness Test—Part 1: Test Method; International Organization for Standardization: Geneva, Switzerland, 2014. DIN 6350-2:2010-05 Lathe Chucks, Hand-Operated—Centric clamp—Part 1: Cylindrical Mounting Recess; German Institute for Standardization: Berlin, Germany, 2010. DIN 69871-1-1995 AD/B—Tool Shanks with 7/24 Taper for Automatic Tool Exchange—Part 1: Type A, Type AD, Type B and with Data Media; German Institute for Standardization: Berlin, Germany, 1995. ISO 4288:1996 Geometrical Product Specifications (GPS)—Surface Texture: Profile Method—Rules and Procedures for the Assessment of Surface Texture; International Organization for Standardization: Geneva, Switzerland, 1996. Manual Técnico de Usinagem: Torneamento, Fresamento, Furaçãp, Mandrilamento e Sistemas de Fixação; AB Sandvik Coromant: Sandviken, Sweden, 2005; pp. A88–A89. (In Portuguese/Brasil) © 2016 by the authors; licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).