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CHAPTER 3

EXPERIMENTAL PROCEDURE

The objective of this study is to evaluate the performance of cermet

tools which is subjected to either plain, coated, cryogenically treated. In order

to evaluate these following experimental procedures followed.

3.1 CUTTING TOOL INSERTS

Machining tests were carried out using different cermet cutting

tools on a precision lathe (Venus, Model-SU4) having 18 spindle speeds and

18 table feeds with a maximum speed of 2500 rpm whose specification is

listed in Table 3.1. Cermet cutting tools were used for this study which is

subjected to various conditions and their notations used as described below:

1) Plain cermet without Ti-Al-N coating (UC) and without

Cryogenic treatment (UT) – (UC&UT)

2) Cryogenically treated (T) and uncoated tool (UC) – (UC&T)

3) Ti-Al-N coated cermet (C) without cryogenic treatment (UT)

– (UT&C)

4) Cryogenically treated and subsequently Ti-Al-N coated (T&C)

and

5) Ti-Al-N coated and subsequently cryogenically treated cermet

(C&T).

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Element composition details of cermet cutting tool using XRF is

shown in Figure 3.1. The element composition details and specifications of

the cutting tool inserts are presented in Tables 3.2 and 3.3 respectively. TiC

based cermet (TTI15 grade) cutting tool inserts from WIDIA Inc.with ISO

P-10 grade cermet rhombic flat inserts of ISO specification CNMG12040822

are used for this study. The Machining was performed using WIDAX tool

holder with ISO specification PCLNR 1616 K 12 fitted with one insert. The

image and specification of the cermet insert and tool holder assembly are

shown in Figures 3.2 to 3.4 respectively.

Table 3.1 Lathe specifications

Specifications Dimensions

Model Venus (SU4)

Bed Length 5+1/4’ and 6’

Bed Width 11"

Center Height 9"

Spindle bore 54 mm

Horse power of the motor 3 HP

Number of speeds 18 (45Rpm - 2500 Rpm)

Number of feeds 18 (0.025 mm/rev – 0.99 mm/rev)

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Figure 3.1 Element composition details of cermet cutting tool using XRF

Table 3.2 Element composition details of cermet cutting tool

Elem. Line Mass[%] 2sigma[%] Intensity[cps/mA]

22 Ti K 65.78 25.83 30.46

23 V K 0.11 5.19 0.07

27 Co K 20.75 21.92 9.75

28 Ni K 13.37 19.76 7.13

Table 3.3 Details of cutting tool inserts specifications

Cutting tools

rakeangle

clearanceangle

inclinationangle

plan approach

angle

Includedangle

nose radius

( ) ( ) ( ) ( ) (er) (re)

Parameter -6 6 -6 95 80 0.8 mm

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Figure 3.2 Photo image of the cutting insert used

Figure 3.3 Cermet insert specification details

Figure 3.4 Image of the cutting tool holder assembly

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3.2 CRYOGENIC TREATMENT

The cermet tools are subjected to cryogenic treatment either in

plain condition or with or without Ti-Al-N coating for this study. The

cryogenic treatment cycle is given in Figure 3.5, which consists of following

stages:

(i) a gradual lowering of temperature to -195°C

(ii) holding for 18 h, and

(iii) then subsequently raising temperature back to room

temperature.

The cryogenic treatment was carried out by Cryoking processor,

CRYOKING Inc. Whose specification is given in Table 3.4.

Table 3.4 Specifications of cryogenic processor

Specifications Details

Model Cryoking

Cryogenic temperature range up to -250º C

Maximum Weight of Materials can be treated 500 Kg

Controlling Method (Temperature Control ) PLC based

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04080

120160200240280320360

0 6 12 18 24 30

Time (Hours)

Cryogenic Treatment Schedule

Figure 3.5 Cryogenic treatment cycle

3.3 Ti-Al-N COATING

Tool wear is inherent in machining. There are many steps and

measures taken to reduce the level of tool wear on cutting tools. One of the

steps is applying surface treatment on the base cutting tool material.

A popular method is applying coating onto the base cutting tool material by

the use of PVD method. The TiAlN coating provided on the cermet cutting

tools by Overlooks Balzers Coating India Ltd with the commercial name of

“BALINIT®FUTURA NANO” using INNOVA, a new-generation coating

system.

In arc evaporation (Figure 3.6) an arc is struck between the backing

plate (anode) and the coating material (cathode). The arc moves over the

coating material and evaporates it. Due to the high currents and power

densities employed, the evaporated material is ionised to a high degree

Ascend Soak Descend

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reactive gas and metal ions hit the component surface and are deposited there

as the coating material.

(Courtesy, Oerlikon Balzers Inc.)

Figure 3.6 Arc evaporation process

1. Argon

2. Reactive gas

3. Arc Sources (coating material and backing plate)

4. Components

5. Vacuum pump

Tools are placed in a processing chamber, which is pumped down

to produce a vacuum. The cermet tools are coated with Ti-Al-N whose

specification of the coating is listed in Table 3.5.

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Table 3.5 Properties of BALINIT®FUTURA NANO coating

Properties Units BALINIT® FUTURA NANO

Coating material Ti-Al-N

Micro hardness (HV 0.05) 3300

Coefficient of friction against steel (dry) 0.30 – 0.35

Coating thickness m) 4

Residual compressive stress (GPa) -2.0

Maximum service temperature (°C) 900

Coating temperature (°C) < 500

Coating colour violet-grey

Coating structure Nano - structured

3.4 WORK MATERIALS

The work materials used in these machining studies were AISI

4340 steel (also known as EN 24 steel) and AISI D2 steel (also known as Die

steel) which were hardened to a hardness value of HRC 45 and HRC 50

respectively. The work piece materials used for the machining studies and

their hardness after heat treatment are given in Table 3.6. As per ISO 3685

(1993) the work pieces selected in the present study has the dimensions of 50

mm diameter and 375 mm length, so that L/D ratio should not exceed 10 ,in

order to assure the necessary stiffness of the elastic fixed system

chuck/piece/cutting tool .

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Table 3.6 Work piece materials and their hardness after heat treatment

Sl.No Work piece Material Hardness after heat

treatment 1 AISI 4340 steel HRC 45

2 AISI D2 steel HRC 50

3.4.1 AISI 4340 Steel

AISI 4340 steel is Nickel-Chromium-Molybdenum high tensile

steel. It has good wear resistance and shock resistance and it is characterised

by high strength and toughness. The hardened and tempered AISI 4340 steel

can be further surface hardened by flame or induction hardening and followed

by Nitriding. It is mostly used in industrial sectors for applications requiring

high tensile/yield strength. The typical applications are heavy duty shafts,

gears, axles, spindles, couplings etc. The AISI 4340 steel hardened by heat

treatment of quenching followed by tempering at 845°C and 440°C.

AISI 4340 steel is regarded as readily machinable, and operations

such as turning, milling and drilling etc. can be carried out satisfactorily.

Some of the related specifications of AISI 4340 steel are EN 24, BS 970

817M40, SAE 4340, 40NiCrMo6 etc. The chemical composition of AISI

4340 steel is given in Table 3.7. The microstructure and EDAX analysis of

AISI 4340 steel (HRC 45) are presented in Figure 3.7 and 3.8 respectively.

Figure 3.7 reveals the presence of carbide particles in the Fe matrix.

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Table 3.7 Composition of AISI 4340 steel by weight percentage

Composition C Si Mn Cr Mo Ni

(Wt %) 0.38- 0.43 0.2-0.35 0.65-0.85 0.7 – 0.9 0.2-0.3 1.65-2.0

Figure 3.7 Optical micrograph showing the microstructure of hardened AISI 4340 steel (HRC 45)

Figure 3.8 Electron dispersive X- Ray analysis (EDAX) of AISI 4340 steel

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3.4.2 AISI D2 Steel

AISI D2 is a high-carbon, high-chromium tool steel alloyed with

Molybdenum and Vanadium characterized by high wear resistance, high

compressive strength, good through-hardening properties, high stability in

hardening, and good resistance to tempering reported by Arsecularatne et al

(2006). AISI D2 steel is one of the most widely used steel in the industry. The

chemical composition and EDAX analysis of AISI 4340 steel is given in

Table 3.8 and Figure 3.9 respectively. AISI D2 steel is recommended for tools

requiring very high wear resistance, combined with moderate toughness

(shock-resistance). The AISI D2 steel hardened by heat treatment of

quenching followed by tempering at 1050°C and 530°C respectively.

Table 3.8 Composition of AISI D2 steel by weight percentage

Composition C Fe Mn Si Cr Mo V

(Wt %) 1.4-1.6 rema 0.6 0.6 11-13 0.7 -1.20 1.10

Figure 3.9 Electron dispersive X- Ray analysis (EDAX) of AISI D2 steel

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3.5 EXPERIMENTAL CONDITIONS

Machining studies were conducted on hardened AISI 4340 steel

and AISI D2 steel using the above mentioned cermet cutting tools at different

cutting conditions. Experimental conditions are shown in Table 3.9 and 3.10.

For AISI D2 steel machining, the lower and higher cutting conditions are

considered, because the middle cutting condition may not be significantly

varied. The comparison was carried out in terms of the performance of the

different processed cermet tools while machining AISI 4340 steel and AISI

D2 steel respectively.

Table 3.9 Experimental conditions for AISI 4340 steel

Cutting speed m/min 115, 140, 180

Feed rate mm/rev 0.06,0.08,0.12

Depth of cut mm 0.1,0.15,0.2

Environment Dry

Table 3.10 Experimental conditions for AISI D2 steel

Cutting speed m/min 75, 92, 118

Feed rate mm/rev 0.06,0.12

Depth of cut mm 0.1,0.2

Environment Dry

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3.6 OBSERVATIONS

The main objective of the present study is to evaluate the

performance of different cermet cutting tools on machining AISI 4340 steel

(HRC 45) and AISI D2 steel (HRC 50). The performance of the cermet

cutting tools was evaluated by i) Measurement of flank wear ii) Measurement

of surface roughness on work materials iii) measurement of cutting forces iv)

Microscopic studies on worn out tools and chips of the work materials.

The wear measurements were taken using a Tool Makers Microscope

(Metzer-model METZ 1395) with 30X magnification factor. The machining

time was accurately measured with a stopwatch. The machining was stopped

periodically to measure tool wear and surface roughness of the work

materials. The surface roughness (Ra) values were obtained by moving the

stylus of the surface roughness measuring instrument (TR 200) on the work

material. The specification of surface roughness measuring instrument is

given in Table 3.11.

The cutting force components were measured during turning using

strain gauge type dynamometer with a sensitivity of 1 Newton. The

metallographic microstructure of cutting tool was obtained according to

ASTM B 390-92 (2000). Scanning Electron Microscope (FEI ESEM Quanta

200) was used to study the wear of worn and microstructure of the tool

materials. The electrical resistivity of the cryogenically treated and untreated

types of cutting tool inserts used in this study was measured with a standard

four probe set-up (Four probes Resistivity Instrument, Concord, India) and the

average values of electrical resistivity were evaluated.

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Table 3.11 The specification of surface roughness measuring instrument

Specifications of TR200 Surface Roughness Tester

Model Name TR200 Surface Roughness Tester –TIME make

Roughness Parameters

Ra, Rz, Ry, Rq, Rt, Rp, Rmax, Rm, R3z, S, Sm, Sk, tp

Profiles Measured Primary profile (P), Roughness Profile (R) tp curve (Mr)

Measurement Accuracy < ±10%

Max Tracing Length 17.5mm

Detector Standard model TS100, inductive, Diamond tip radius 5microns

Power Li-Ion Battery Rechargeable

Battery Capacity 1000mAh (>3000measurements)

Charger 220V/110V, 50Hz

Working Temperature 5 to 40 degree C

Dimensions 141mmx56mmx48mm