JSET: Journal of Science & Engineering Technology Vol. 3 Issue 2 (December) 2016 pp. 102 – 105

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WEAR MECHANISM ON PVD COATED CARBIDE IN THREADED MACHINING OF TITANIUM BASED

ALLOY UNDER FLOODED CONDITION.

HAMDAN Siti Hartini1, a, MUHAMMAD M.N. Ajwad2,b and Md SAID Ahmad Yasir3,c

1,2,3 Mechanical & Manufacturing Dept, University Kuala Lumpur MFI, 43650 Bandar Baru Bangi, Selangor, Malaysia asitihartini@unikl.edu.my, anurajwadmuhammad@yahoo.com, cyasir@unikl.edu.my

Abstract— This paper deals with a study on evaluation of wear mechanisms of tungsten carbide tools in thread cutting of Titanium Alloy Ti6Al4V. The experiments were carried out under wet cutting conditions using two types of alloyed carbide tool inserts: the uncoated carbide tool and Physical Vapor Disposition (PVD) coated tool. Tool failure modes and wear mechanisms for both tools were examined at various cutting conditions. The localized flank wear (VB) was found to be the predominant tool wears for both tools coated and uncoated. At VB close to 0.3 mm, a brittle fracture (cracking, flaking and chipping) was noted. Adhesion wear and diffusion wear have been occurred on both type of tool used. Tool wear were examined using optical microscope and the metallographic process .The analysis through S-3400 N Scanning Electron Microscope (SEM) by Hitachi has detected the microstructure defects, such as micro crack, chip on and the tungsten carbide particle loosened and Energy Dispersive X-Ray (EDX) analysis used to proved the presence of diffusion process between tool substrate, and work piece materials

.Keywords— Titanium Alloy Ti6Al4V, Wear Mechanisms, Tungsten Carbide, Thread Cutting, flooded Cutting Condition.

I. INTRODUCTION Titanium alloys are metals which contain a mixture of

titanium and other chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures). Titanium alloys are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures [1].

However, the high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, medical devices, connecting rods on expensive sports cars and some premium sports equipment and consumer electronics [2]. Auto manufacturers Porsche and Ferrari also use titanium alloys in engine components due to its durable properties in these high stress engine environments.

Titanium alloy machining performance can be increased by selecting improved cutting tool materials and coated tools.

Nowadays, most of the carbide cutting tools come with hard coatings deposited on them either by the CVD or PVD technique. PVD coated tools have been found to be better performing compared to their CVD counterparts.

II. METHODOLOGY This experiment has been done using the CNC lathe machine under flooded condition. There are few cutting parameters measured along the machining process as listed in Table 1. All experiments were conducted in under wet cutting in thread cutting condition.

Table 1 Factors and levels used for the tool wear thread cutting experiment

Levels Parameter 1 2 3

A

Cutting Speed

(m/min) 40 50 60

B Dept of

Cut (mm) 0.25 0.35

C Tool type (coated)

D Tool type (uncoated)

III. RESULT AND DISCUSSION The results for the tool wear progression of PVD coated Tungsten Carbide are shown in Table 2. There are six samples of tested on each parameter. The time along machining is also recorded.

Short Term Research Grant (STRG) UniKL/IRPS/str 12096

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Table 2 Tool wear of PVD coated carbide

Table 2 represent the result of flank wear progress PVD coated tungsten carbide differentiate by cutting speed in wet cutting condition. In general cutting Speed is major influence of the rapid tool wear in wet cutting condition

1) Flank Wears Progression of Uncoated Tungsten

Carbide The results for the tool wear progression of PVD coated Tungsten Carbide is shown in Table 3. There is six more sample of testing on each parameter continual from coated tool. The time during cutting process also recorded. Table 3 Tool wear of uncoated Tungsten Carbide

Tool wear Time

Run Designation 1 2 3 4 5 1 7 A1B1D 0.22 0.27 0.30 - - 219 8 A1B2D 0.56 - - - - 87 9 A2B1D 0.20 0.54 - - - 178

10 A2B2D 0.30 - - - - 82 11 A3B1D 0.17 0.24 0.37 - - 232 12 A3B2D 0.34 - - - - 85

Figure 1 : Flank wear progress PVD coated

Coatings are considerably harder, provides more abrasion resistance to the cutting edge and its high temperature resistance enables transfer of maximum part of heat to the chips. Figure 1 shows the effect of using the cutting speed of 60 m/min and depth of cut 0.30 mm, the rapid growth of flank wear land on the of the tool before 173 seconds while when using cutting speed of 50 m/min and depth of cut 0.30 mm the wear land is delayed until 236 seconds and 247 seconds for cutting speed of 40 m/min. Liu & Rahman [4],conluded that the lower was the cutting speed, the longer the duration in which the cutting forces kept unchanged and the longer the tool life. The higher the cutting speed, the faster the cutting forces increased, and the shorter the tool life.

Figure 2 Flank wear progress Uncoated

Meanwhile, figure 2 stated that the tool life, measured in time travelled by the tool, was found to increase with the cutting speed. A long tool life of nearly 232 second was achieved when machining at a cutting speed of 60 m/min and depth of cut 0.30 mm, whereas a tool life of only 219 second was achieved when machining at 40 mm/min and depth of cut 0.30mm but when machining at cutting speed of 50 m/min and depth of cut 0.30 resulted in the failure of the cutting tool achieved 200 second in tool life. In other words, the application of a cutting speed in the range of 40-50 m/min caused the tool life to drastically decrease.

The wet cutting also may shorten the tool life because of the high cutting temperature of the tool edge so the depth of cut 0.35 mm maybe not suitable in dry cutting condition. The generation of heat and ultimate weakening of the cobalt bond were the results of the direct and indirect effects of the cutting force and cutting temperature, which are commonly associated with the machining parameters considered [4].

00.10.20.30.40.50.6

0 100 200 300

Ave.

Fla

nk W

ear

(mm

)

Cutting Time (Sec)

Flank Wear Progress PVD coated Tungsten Carbide

C.S=40,DOC=0.30,C.S=40,DOC=0.35,C.S=50,DOC=0.30,C.S=50,DOC=0.35,C.S=60,DOC=0.30,C.S=60,DOC=0.35,

Too

l wear Time Run Designation 1 2 3 4 5 1

1 A1B1C 0.14 0.23 0.32 - - 247 2 A1B2C 0.35 - - - - 100 3 A2B1C 0.23 0.27 0.31 - - 236 4 A2B2C 0.27 0.42 - - - 169 5 A3B1C 0.21 0.39 - - - 173 6 A3B2C 0.52 - - - - 110

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WEAR MECHANISM The worn-out cutting edges of different cutting tools were examined using an optical microscope to recognize type of tool wear. The performance of a carbide tool not only depends on the type and number of coating layers applied but also on the size of the carbide particles and the number of binders. Information regarding porosity, particle size and tunqsten bond, carbide solid solution and metal binder can be obtained by polishing a sample [4].

Figure 3 (a) Top view of insert at Vc = 50m/min, DOC= 0.35mm, and cutting time = 82 second.

Figure 3 (b). The flank wear on cutting edge of PVD uncoated tungsten carbide insert at Vc = 50m/min, DOC= 0.35mm, and

cutting time = 82 second.

By examining Figure 3(a) and (b) closely, one will notice the existence of a burnt mark near the edge of the flank wear, indicating high temperature cutting process. The burnt mark becomes noticeable at higher cutting speed. It is interesting to mention that at certain point of worn tool, the temperature was significantly high. The cutting speed generated more heat during machining and the high temperature caused high wear rate[5].

2) Failure mode of carbide tool at cutting speed of 50m/min

Figure 4 (a) Failure mode on the uncoated tungsten carbide insert Figures 2 (b) High magnification of cutting tool surface showing loosen particle of tungsten carbide.

From the illustrate Figure 4(a), it is shown that a tungsten carbide particle that was loosened from the binder and chipped from the cutting tool. A cutting edge surface possessing cracks will lead to chipping and brittle fracture[4]. Meanwhile Figure 4 (b), some parts of the worn surface are still covered by molten chip [6].

3) EDX Analysis Result

The tool chip interface at the flank face area located by arrow number 3 of Figure 2 (b) was analyze using Energy Dispersive X-Ray (EDX).The results of EDX analysis are shown in Table 4 analysis of the uncoated tungsten carbide insert when machining at 50 m/min with a depth of cut of 0.35 mm, and cutting time of 82 second. On the wear surface of the cutting tool, a Ti content of 4.45 wt% was detected.

Table 4: EDX analysis of the uncoated tungsten carbide insert.

Element Weight% Atomic%

C K 32.04 72.94

O K 8.52 14.56

Al K 1.35 1.37

Ti K 4.45 2.54

Co K 1.96 0.91

W M 51.68 7.69

Totals 100

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IV. CONCLUSION The results show that the localized flank wear VB on the tool leading cutting edge is the dominant wear determining the tool life of uncoated and PVD-coated tools. The localized flank wear of 0.3 mm is frequently followed by a brittle fracture (cracking, flaking and chipping). Adhesion wear is appeared on uncoated tungsten carbide insert when machining at cutting speed of 50 m/min, depth of cut 0.35 and cutting time of 82 second, due to the mechanical removal of the tool material parts when the adhesive junctions are broken. In addition, Carbide is inherently a brittle material thus; brittle fracture was expected to occur in this study. This failure mode was initiated by the formation of micro cracks. However, catastrophic failure should be avoided to prevent long setup times, which affects manufacturing productivity. To maximize the performance and reduce the wear mechanisms of uncoated and PVD coated carbide tools, flooded cutting machining is the right way. PVD coated carbide tools in compare between PVD coated and uncoated is perform better.

V. ACKNOWLEDGMENT The authors wish to thank Universiti of Kuala Lumpur for their financial support to this work through the Short Term Reseach Grant (STRG) funding number :UniKL/IRPS/str12096 and providing all equipments needed in this study.

VI. REFERENCES

[1] Welsch, Gerhard, Rodney Boyer, and E. W. Collings, eds. Materials properties handbook: titanium alloys. ASM international, 1993. [2] Ramanaa, M. Venkata, K. Srinivasulub, and G. Krishna Mohana Raoc. "Performance Evaluation and Selection of Optimal Parameters in Turning of Ti-6Al-4V Alloy Under Different Cooling Conditions." [3] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide. [4] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [5]Che Haron, C, & Ginting, A. (2006). Performance of alloyed uncoated and CVD-coated carbide tools in dry milling of titanium alloy Ti-6242S.

[6] Gusri Akhyar, I., & Che Hassan, C. H. (2010). Application of Box-Behnken in Turning of Inconel 718 using PVD Carbide Tools under Minimum Quantity Lubrication.

] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide. [3] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide. [3] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide.

ERENCES

[1] Che Haron, C, & Ginting, A. (2006). Performance of alloyed uncoated and CVD-coated carbide tools in dry milling of titanium alloy Ti-6242S. [2] Gusri Akhyar, I., & Che Hassan, C. H. (2010). Application of Box-Behnken in Turning of Inconel 718 using PVD Carbide Tools under Minimum Quantity Lubrication. [3] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool , A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide. [3] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbide.

ERENCES

[1] Che Haron, C, & Ginting, A. (2006). Performance of alloyed uncoated and CVD-coated carbide tools in dry milling of titanium alloy Ti-6242S. [2] Gusri Akhyar, I., & Che Hassan, C. H. (2010). Application of Box-Behnken in Turning of Inconel 718 using PVD Carbide Tools under Minimum Quantity Lubrication wear in ductile cutting of tungsten carbide.

REFERENCES

[1] Che Haron, C, & Ginting, A. (2006). Performance of alloyed uncoated and CVD-coated carbide tools in dry milling of titanium alloy Ti-6242S.

Figure 5 Result of EDX analysis of the uncoated tungsten carbide insert

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[2] Gusri Akhyar, I., & Che Hassan, C. H. (2010). Application of Box-Behnken in Turning of Inconel 718 using PVD Carbide Tools under Minimum Quantity Lubrication.

[3] Jaharah, A., & Che Hassan, C. (2006). Wear Mechanism And Failure Mode of P10 TIN Coated Carbide Tools. [4] Liu, K., & Rahman, M. (2003). CBN tool wear in ductile cutting of tungsten carbid