**1. Introduction**

Titanium and its alloys materials are broadly used in applications like air frame components, medical implants/devices, surgical instruments, ballistic armour, space vehicles/structures, missile components, navy ship components, chemical processing equipment, hydrocarbon refining/processing, hydrometallurgical extraction/electrowinning offshore hydrocarbon production, desalination, brine concentration/evaporation, power generation, automotive, mining, railways and sporting goods. The large variety of application is due to its desirable properties, mainly the relative high strength combined with low density and enhanced corrosion resistance. In terms of biomedical applications, the properties of interest are biocompatibility, corrosion behaviour, mechanical behaviour, process ability and availability [1–5].

In machining of brittle and ductile materials, selection of available tools with different grades is a complex matter. Economics and quality of the machining are dependent on tool wear. Evaluation and measurement of tool wear in micromilling are challenging compared to the conventional machining process. In high-speed micromilling based on the surface finish requirement on the desired work material, tools with smaller diameter, that is, two flute and four flute end mills, are used for superfinishing operation. Two, four and more flute tools having larger tool diameter are used for the roughing operation. Tool wear occurrence in four flutes is lower than two flutes as the cutting and load bearing capacity is higher for four flutes in roughing and super finishing operations. In super finishing, at high spindle speeds for a slotting operation which is single pass cutting, the usage of micro-end mills is limited, maybe two to three slots. Burr formation, cutting forces, surface roughness and acoustic emission signals observation and analysis information provide the tool wear prediction in high-speed micro-end milling. Tool material properties and machining parameters decide the tool wear formation. Tool wear of a different kind takes place in micromilling because of small cutting edge, microstructure variation, difference in work and tool material phases, deformed chips, wrong rake angle tools selection shape and a number of flutes, friction and stress induced [6–9] on the tool.

Komanduri and Reed [10] investigated the cutting performance of carbide grades and new cutting geometry in turning operation of titanium alloys. They observed that prolonged tool life in machining Ti alloys can be obtained at high clearance angle and high negative rake angle. Kitagawa et al. [11] investigated the temperature and wear of cutting tools in high speed machining of Ti-6Al-6V-2Sn and found that temperature plays the major role for tool wear during machining. According to Jawaid et al. [12], CVD-coated tools performed well during face milling of Ti-6Al-4V than PVD tools. They observed nonuniform flank wear pattern on both the tools and found that coating delamination, diffusion, attrition, adhesion wear mechanisms were responsible factors. Liu et al. [13] investigated cutting forces and surface quality in micromilling of TC4 titanium alloy. They found that surface quality of machined surface is prone to the influence of burrs and residual chips. Nouari et al. [14, 15] investigated CVD tools and uncoated tools performance in machining titanium alloy Ti-6242S and they observed almost equal performance of both tools. They observed similar physical phenomenon while machining as mentioned by Jawaid et al. [12]. Rahman et al. [16] presented a review on high-speed machining of titanium alloys especially in turning and milling operations. They discussed the performance of coated and uncoated tungsten carbide tools, polycrystalline diamond (PCD) tools, cubic boron nitride (CBN) tools, and binderless cubic boron nitride (BCBN) tools in terms of cutting forces generation and tool wear. They found that BCBN tools performed well in high-speed machining conditions and traditional tools in moderate cutting speed conditions. Ginta et al. [17] investigated tool wear morphology and chip segmentation in end milling of titanium alloy Ti-6Al-4V using uncoated WC-Co inserts. They also performed modelling and optimization of tool life and surface roughness. They observed abrasion/attrition, plastic deformation and diffusion wear processes. They found that combination of high cutting speed and feed substantially increases the stress near the nose and flank zone, generates high temperature and encourages high wear rate.

Schueler et al. [18] investigated the burr formation mechanisms and surface characteristics in micro-end milling Ti-6Al-4V and Ti-6Al-7Nb titanium alloys. Large areas were machined to observe the microstructure on the surface and the influence on surface quality. Up milling and down milling at the sidewalls were compared. They found that down milling is better than up milling. Arrazola et al. [19] investigated and compared the cutting forces, tool wear and chip geometry in the machining of (α + β) Ti-6Al-4V and near-beta (β) Ti555.3 titanium alloys. They found that adhesive

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*The Comparison of Cutting Tools for High Speed Machining of Ti-6Al-4V ELI Alloy (Grade 23)*

and diffusion wear on cutting tools when machined with both the grades of titanium alloys. Specific feed force and cutting force are higher for Ti555.3 alloy than Ti-6Al-4V alloy. Chip formation observed was segmented with and without adiabatic shear zones in Ti-6Al-4V alloy and narrow adiabatic shear bands for Ti555.3 alloy. Malekian et al. [20] investigated tool wear monitoring in micromilling processes to avoid the failure of tools during the considered machining conditions. Tool edge radius and wear were observed and measured using vision system and as well as gathered sensor signals of acoustic emission, acceleration and force data. These data were interpreted offline using adaptive neuro-fuzzy inference ystem and compared with experimental wear results that were agreeable. Smith et al. [21] investigated surface quality and tool wear in micromilling of Ti-6Al-4V using monocrystalline CVD diamond cutting edges with preferential crystallographic orientation. The analyses of tool wear and workpiece surface quality proved that monocrystalline CVD diamond cutting edges with preferential crystallographic orientation along rake and clearance faces can be successfully utilised for interrupted cutting operations (i.e., micromilling) of alloys which react with diamond, such as those based on titanium. Zhang et al. [22] investigated the cutting forces and tool wear variations during high-speed microend milling of titanium alloy (α + β) Ti-6Al-4V using uncoated cemented tungsten carbide tools. They found that due to adhesion, abrasion and diffusion process, tool wear takes place and cutting force component Fy, in the considered experiment, has a

*DOI: http://dx.doi.org/10.5772/intechopen.80641*

positive relationship with the tool wear propagation.

Ozel et al. [23–25] carried out experimental investigation and finite element simulation with CBN tools and uncoated tools in the micromilling of Ti-6Al-4V. They found that larger the feed rate, the higher the burr formation, surface roughness, temperature generation, cutting forces and tool wear. CBN tools had less tool wear and temperature formation than uncoated tools. Wyen et al. [26] investigated the influence of the cutting-edge radius on surface integrity in slot milling of Ti-6Al-4V with different edge radius tools. As the cutting temperature and kinematics influence the up and down machining processes, they thoroughly researched on cutting edge radius owing to the temperature generation. They found that down milling is better than up milling for surface roughness and burr formation which gradually increase with increasing cutting-edge radius from the measurements of residual stress and compressive stress generation. Durul and Ozel [27] presented review on machining-induced surface integrity in titanium and nickel alloys. They reported detailed performance of the different tools, tool wear behavior, burr formation, surface topography and FEM simulations. Bajpai et al. [28] investigated surface quality and burr formation in HSMEM of Ti-6Al-4V and it was found that as cutting speed, feed rate and depth of cut increased, then smoother surface finish can be achieved. Burr formation is increased due to increment in depth of cut. Hou et al. [29] investigated the influence of cutting speed on tool wear, flank temperature and cutting force in macro-end milling of titanium alloy Ti-6Al-4V using PVD-coated TiN/TiAlN and uncoated tungsten carbide tools. They found that high cutting forces were generated when cutting speed is increased and increment in mean flank temperature for the coated cutting tools, whereas it is almost constant for uncoated tools. At higher cutting speeds, no abrasion and fatigue wear were observed for uncoated tools and in contrast with coated tools. Kim et al. [30] discussed the machining input parameters influence and found that spindle speed and feed rate were the most influencing factors for generating cutting forces and burr formation on Ti-6Al-4V. Pervaiz et al. [31] presented a review on influence of tool materials on machinability of titanium- and nickel-based alloys. Ceramic, PCD, CBN, boronized carbide tools and high pressurised coolant supply show good results for machining. They observed that in experimental studies that high pressurised coolant supply reduces cutting temperature and improves chip

### *The Comparison of Cutting Tools for High Speed Machining of Ti-6Al-4V ELI Alloy (Grade 23) DOI: http://dx.doi.org/10.5772/intechopen.80641*

and diffusion wear on cutting tools when machined with both the grades of titanium alloys. Specific feed force and cutting force are higher for Ti555.3 alloy than Ti-6Al-4V alloy. Chip formation observed was segmented with and without adiabatic shear zones in Ti-6Al-4V alloy and narrow adiabatic shear bands for Ti555.3 alloy. Malekian et al. [20] investigated tool wear monitoring in micromilling processes to avoid the failure of tools during the considered machining conditions. Tool edge radius and wear were observed and measured using vision system and as well as gathered sensor signals of acoustic emission, acceleration and force data. These data were interpreted offline using adaptive neuro-fuzzy inference ystem and compared with experimental wear results that were agreeable. Smith et al. [21] investigated surface quality and tool wear in micromilling of Ti-6Al-4V using monocrystalline CVD diamond cutting edges with preferential crystallographic orientation. The analyses of tool wear and workpiece surface quality proved that monocrystalline CVD diamond cutting edges with preferential crystallographic orientation along rake and clearance faces can be successfully utilised for interrupted cutting operations (i.e., micromilling) of alloys which react with diamond, such as those based on titanium. Zhang et al. [22] investigated the cutting forces and tool wear variations during high-speed microend milling of titanium alloy (α + β) Ti-6Al-4V using uncoated cemented tungsten carbide tools. They found that due to adhesion, abrasion and diffusion process, tool wear takes place and cutting force component Fy, in the considered experiment, has a positive relationship with the tool wear propagation.

Ozel et al. [23–25] carried out experimental investigation and finite element simulation with CBN tools and uncoated tools in the micromilling of Ti-6Al-4V. They found that larger the feed rate, the higher the burr formation, surface roughness, temperature generation, cutting forces and tool wear. CBN tools had less tool wear and temperature formation than uncoated tools. Wyen et al. [26] investigated the influence of the cutting-edge radius on surface integrity in slot milling of Ti-6Al-4V with different edge radius tools. As the cutting temperature and kinematics influence the up and down machining processes, they thoroughly researched on cutting edge radius owing to the temperature generation. They found that down milling is better than up milling for surface roughness and burr formation which gradually increase with increasing cutting-edge radius from the measurements of residual stress and compressive stress generation. Durul and Ozel [27] presented review on machining-induced surface integrity in titanium and nickel alloys. They reported detailed performance of the different tools, tool wear behavior, burr formation, surface topography and FEM simulations. Bajpai et al. [28] investigated surface quality and burr formation in HSMEM of Ti-6Al-4V and it was found that as cutting speed, feed rate and depth of cut increased, then smoother surface finish can be achieved. Burr formation is increased due to increment in depth of cut. Hou et al. [29] investigated the influence of cutting speed on tool wear, flank temperature and cutting force in macro-end milling of titanium alloy Ti-6Al-4V using PVD-coated TiN/TiAlN and uncoated tungsten carbide tools. They found that high cutting forces were generated when cutting speed is increased and increment in mean flank temperature for the coated cutting tools, whereas it is almost constant for uncoated tools. At higher cutting speeds, no abrasion and fatigue wear were observed for uncoated tools and in contrast with coated tools. Kim et al. [30] discussed the machining input parameters influence and found that spindle speed and feed rate were the most influencing factors for generating cutting forces and burr formation on Ti-6Al-4V. Pervaiz et al. [31] presented a review on influence of tool materials on machinability of titanium- and nickel-based alloys. Ceramic, PCD, CBN, boronized carbide tools and high pressurised coolant supply show good results for machining. They observed that in experimental studies that high pressurised coolant supply reduces cutting temperature and improves chip

*Titanium Alloys - Novel Aspects of Their Manufacturing and Processing*

In machining of brittle and ductile materials, selection of available tools with different grades is a complex matter. Economics and quality of the machining are dependent on tool wear. Evaluation and measurement of tool wear in micromilling are challenging compared to the conventional machining process. In high-speed micromilling based on the surface finish requirement on the desired work material, tools with smaller diameter, that is, two flute and four flute end mills, are used for superfinishing operation. Two, four and more flute tools having larger tool diameter are used for the roughing operation. Tool wear occurrence in four flutes is lower than two flutes as the cutting and load bearing capacity is higher for four flutes in roughing and super finishing operations. In super finishing, at high spindle speeds for a slotting operation which is single pass cutting, the usage of micro-end mills is limited, maybe two to three slots. Burr formation, cutting forces, surface roughness and acoustic emission signals observation and analysis information provide the tool wear prediction in high-speed micro-end milling. Tool material properties and machining parameters decide the tool wear formation. Tool wear of a different kind takes place in micromilling because of small cutting edge, microstructure variation, difference in work and tool material phases, deformed chips, wrong rake angle tools selection shape and a number of flutes, friction and stress induced [6–9] on the tool. Komanduri and Reed [10] investigated the cutting performance of carbide grades and new cutting geometry in turning operation of titanium alloys. They observed that prolonged tool life in machining Ti alloys can be obtained at high clearance angle and high negative rake angle. Kitagawa et al. [11] investigated the temperature and wear of cutting tools in high speed machining of Ti-6Al-6V-2Sn and found that temperature plays the major role for tool wear during machining. According to Jawaid et al. [12], CVD-coated tools performed well during face milling of Ti-6Al-4V than PVD tools. They observed nonuniform flank wear pattern on both the tools and found that coating delamination, diffusion, attrition, adhesion wear mechanisms were responsible factors. Liu et al. [13] investigated cutting forces and surface quality in micromilling of TC4 titanium alloy. They found that surface quality of machined surface is prone to the influence of burrs and residual chips. Nouari et al. [14, 15] investigated CVD tools and uncoated tools performance in machining titanium alloy Ti-6242S and they observed almost equal performance of both tools. They observed similar physical phenomenon while machining as mentioned by Jawaid et al. [12]. Rahman et al. [16] presented a review on high-speed machining of titanium alloys especially in turning and milling operations. They discussed the performance of coated and uncoated tungsten carbide tools, polycrystalline diamond (PCD) tools, cubic boron nitride (CBN) tools, and binderless cubic boron nitride (BCBN) tools in terms of cutting forces generation and tool wear. They found that BCBN tools performed well in high-speed machining conditions and traditional tools in moderate cutting speed conditions. Ginta et al. [17] investigated tool wear morphology and chip segmentation in end milling of titanium alloy Ti-6Al-4V using uncoated WC-Co inserts. They also performed modelling and optimization of tool life and surface roughness. They observed abrasion/attrition, plastic deformation and diffusion wear processes. They found that combination of high cutting speed and feed substantially increases the stress near the nose and

flank zone, generates high temperature and encourages high wear rate.

Schueler et al. [18] investigated the burr formation mechanisms and surface characteristics in micro-end milling Ti-6Al-4V and Ti-6Al-7Nb titanium alloys. Large areas were machined to observe the microstructure on the surface and the influence on surface quality. Up milling and down milling at the sidewalls were compared. They found that down milling is better than up milling. Arrazola et al. [19] investigated and compared the cutting forces, tool wear and chip geometry in the machining of (α + β) Ti-6Al-4V and near-beta (β) Ti555.3 titanium alloys. They found that adhesive

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breakability which results in improved tool life. Increase in the pressure of coolant supply also improves tool life. Notch wear was reduced by increasing coolant supply pressure when machining titanium alloys.

Hassanpour et al. [32] investigated the cutting force, microhardness, surface roughness and burr size in micromilling of Ti-6Al-4V using minimum quantity lubrication. They found that cutting speed and feed per tooth significantly affect the surface roughness. Bandapalli et al. [33] have investigated the influence of machining parameters in high-speed micro-end milling of commercially pure titanium Grade 2 and found that cutting forces and surface roughness formation increases at high spindle speed by increasing feed rate and depth of cut. Ghani et al. [34] investigated the wear mechanism of uncoated carbide cutting tool in milling of aluminium metal matrix composite (AlSi/AlN MMC), PVD-coated TiAlN/AlCrN tool in milling of Inconel 718 and uncoated tool in turning of Ti-6Al-4V ELI. They found that tools failed primarily on two main areas of the flank and rake faces for cutting the Inconel 718 and titanium alloy. Wear such as crater, nose wear, abrasion, notching, fracturing and cracking were observed. In machining AlSi/AlN MMC, the tools mainly failed due to the uniform flank wear that was caused by abrasion.

However, research findings related to considered machining parameters in highspeed micro-end milling (HSMEM) of titanium alloys for comparison and evaluation of uncoated, PVD-coated TiAlN and AlTiN tools are inadequate. The purpose of this research work is to evaluate the performance of tools like uncoated and physical vapour deposition (PVD)-coated TiAlN and AlTiN tools in terms of tool wear formation in HSMEM of alpha + beta Ti-6Al-4V ELI titanium alloy (Grade 23). The goal was to improve the quality or productivity of the specific machining process based on empirical experiments using a variety of speeds, feeds and depth of cut. This work is categorised into four sections, first with an introduction. Experimental details were discussed in Section 2. Results and discussion were presented in Sections 3 and 4 and finally Section 5 is presented with conclusions.
