chapter 4 milling performance of aisi d2, aisi...

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CHAPTER 4

MILLING PERFORMANCE OF AISI D2, AISI D3, AISI H13

AND AISI P20 TOOL STEELS UNDER CRYOGENIC

COOLING

The milling experiments were carried out on AISI D2 and AISI D3

tool steels with CVD TiN coated tungsten carbide tools, AISI H13 steels with

PVD TiAlN coated carbide tools and AISI P20 steels using uncoated carbide

tools at different speed–feed combinations under dry, wet and cryogenic

machining conditions. The experimental results of cryogenic machining on

the cutting temperature, cutting force, and surface roughness have been

compared with those under dry and conventional coolant (wet) machining

conditions.

4.1 EFFECT OF CRYOGENIC COOLING ON CUTTING

TEMPERATURE

In the metal cutting process, mechanical energy is converted into

heat energy. There are three main sources of generating heat during the

cutting process, (1) Plastic deformation by shearing in the primary shear zone.

(2) Plastic deformation by shearing and friction on the cutting face.

(3) Friction between the chip and the tool on the flank face. All such heat

sources produce the maximum temperature at the chip – tool interface, which

substantially influences the chip formation mode, cutting forces and tool life.

Most of the mechanical energy used to form the chip, which generates high

temperature in the cutting region. The cutting temperature increased with an

increase in the cutting velocity and feed rate for all work-tool combinations.

Higher cutting temperature affects tool wear, dimensional and form accuracy,

70

and surface integrity of the product. The excessive tool wear resulting from

high cutting temperature, would also cause the cutting tool failure due to

mechanical breakage, cutting edge blunting, or plastic deformation.

4.1.1 Effect of Cutting Temperature on Milling of AISI D2 Steel

The variation in the cutting temperature during the milling of

AISI D2 steel with CVD TiN coated tungsten carbide tool of ISO XDHT

090308 - TN450 under dry, wet and LN2 machining is shown in Figure 4.1

(a-c). Table 4.1 shows the percentage reduction in the cutting temperature due

to LN2 machining, compared to dry and wet machining for different

speed-feed combinations in the milling of AISI D2 tool steel. It shows that the

cutting temperature increased with an increase in the cutting speed and feed,

as reported in the earlier work (Sornakumar and Senthilkumar 2008). It was

observed that LN2 cooling reduced the cutting temperature over dry and wet

machining in all cutting conditions.

In the milling of AISI D2 steel with a TiN coated carbide tool,

when no coolant was supplied to the cutting zone (Dry), the cutting

tempertaure at a cutting speed of 125 m/min and feed rate of 0.02 mm/tooth

was 491°C. When an emulsion cutting fluid was supplied to the cutting zone

(Wet), the cutting temperature was 429°C for the simillar cutting conditions.

When the LN2 coolant was supplied into the tool – work interfaces, the cutting

temperature was 293°C for the simillar cutting conditions. It was observed

that the mean reduction in the cutting temperature due to LN2 cooling was

40% over dry machining and 31% over wet machining. The LN2 cooling in

the present method enabled the reduction in the cutting temperature in the

range of 40-48% and 31-40% respectively as compared to dry and wet

machining.

71

(a)

(b)

(c)

Figure 4.1 Cutting temperature variation in the milling of AISI D2

steel at different cutting speeds (a) 75 m/min (b) 100 m/min

(c) 125 m/min.

72

Table 4.1 Reduction in the cutting temperature due to LN2 cooling in

the milling of AISI D2 steel

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Cuttingtemperature(°C) % reduction

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 386 330 198 48.7 402 75 0.015 392 346 210 46.42 39.33 75 0.02 439 380 241 45.1 36.574 100 0.01 398 356 210 47.23 41.015 100 0.015 412 370 232 43.68 37.296 100 0.02 457 411 269 41.13 34.547 125 0.01 451 389 247 45.23 36.58 125 0.015 487 416 274 43.73 34.139 125 0.02 491 429 293 40.32 31.7

4.1.2 Effect of Cutting Temperature on Milling of AISI D3 Steel

The variation in the cutting temperature during the milling of

AISI D3 steel with CVD TiN coated tungsten carbide tool of ISO XDHT

090308- TN450 under dry, wet and LN2 machining is shown in Figure 4.2

(a-c). Table 4.2 shows the percentage reduction in the cutting temperature due

to LN2 machining compared to dry and wet machining for different

speed-feed combinations. In the milling of AISI D3steel using a TiN coated

carbide tool, the cutting temperature at a cutting speed of 125 m/min and feed

rate of 0.02 mm/tooth was 472°C, 346°C and 269°C for dry, wet and LN2

cooling, respectively. The reduction in the cutting temperature due to LN2

cooling was 43% and 22% over dry and wet machining, respectively. In the

milling of AISI D3 steel, LN2 cooling reduces the cutting temperature in the

range of 43-54% and 22-40% compared to dry and wet machining

respectively.

73

(a)

(b)

(c)

Figure 4.2 Cutting temperature variation in the milling of AISI D3


(c) 125 m/min.

74


the milling of AISI D3 steel

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Cutting temperature(°C) % reduction

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 357 271 162 54.62 40.222 75 0.015 388 298 201 48.19 32.553 75 0.02 411 311 216 47.44 30.544 100 0.01 360 284 181 49.72 36.265 100 0.015 399 312 210 47.36 32.696 100 0.02 456 328 247 45.83 24.697 125 0.01 424 316 218 48.58 31.018 125 0.015 452 321 241 46.68 24.929 125 0.02 472 346 269 43 22.25

4.1.3 Effect of Cutting Temperature on Milling of AISI H13 Steel

The reduction in the cutting temperature due to LN2 cooling over

dry and wet machining in the milling of AISI H13 steel with a PVD TiAlN

coated carbide tool is shown in Figure 4.3(a-c). Table 4.3 shows the

percentage reduction in the cutting temperature due to LN2 cooling over dry

and wet machining for different speed-feed combinations. In the milling of

AISI H13 steel with a PVD TiAlN coated carbide tool, the cutting

temperature at a cutting velocity of 125m/min and feed rate of 0.02 mm/tooth

was was 582°C, 396°C and 246°C for dry, wet, and LN2 machining,

respectively. The cutting temperature for LN2 cooling was reduced by 57 %

over the dry machining and 37% over the wet machining. For this work-tool

combination, LN2 cooling reduces the cutting temperature in the range of

57-65% compared to dry machining and 37-51% compared to wet machining.

75

(a)

(b)

(c)

Figure 4.3 Cutting temperature variation in the milling of the

AISI H13 steel at different cutting speeds (a) 75 m/min

(b) 100 m/min (c) 125 m/min.

76


the milling of AISI H13 steel

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Cutting temperature (°C) % reduction

Dry Wet LN2LN2 over

dryLN2 over

wet1 75 0.01 412 289 141 65.77 51.212 75 0.015 441 316 163 63.03 48.413 75 0.02 486 329 190 60.9 42.244 100 0.01 456 337 176 61.4 47.775 100 0.015 492 349 198 59.75 43.266 100 0.02 546 366 224 58.97 38.797 125 0.01 498 343 196 60.64 42.858 125 0.015 532 369 220 58.64 40.379 125 0.02 582 396 246 57.73 37.87

4.1.4 Effect of Cutting Temperature on Milling of AISIP20 Steel

Figure 4.4 (a-c) shows the variation in the cutting temperature

during the milling of the AISI P20 steel with an uncoated tungsten carbide

tool under dry and wet machining conditions. The percentage reduction in the

cutting temperature due to LN2 cooling over dry and wet machining in the

milling of AISI P20 steel is presented in Table 4.4. The cutting temperature at

a cutting speed of 125 m/min and feed rate of 0.02 mm/tooth was 421°C,

402°C and 267°C for dry, wet and LN2 cooling, respectively. When the LN2

was supplied to the tool – chip interfaces, the cutting temperature reduced by

36% and 33% compared to dry and wet machining, respectively. In the

milling of AISI P20 steel with uncoated carbide tools, the cutting temperature

reduced in the range of 36-49% and 33-39% as compared to dry and wet

machining, respectively.

77

(a)

(b)

(c)

Figure 4.4 Cutting temperature variation in the milling of AISI P20


(c) 125 m/min.

78


the milling of AISI P20 steel

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Cuttingtemperature(°C) % reduction

Dry Wet LN2LN2 over

dryLN2 over

wet1 75 0.01 254 213 129 49.21 39.432 75 0.015 357 309 190 46.77 38.513 75 0.02 372 327 210 43.54 35.774 100 0.01 251 220 136 45.81 38.185 100 0.015 366 336 212 42.07 36.96 100 0.02 398 356 236 40.7 33.77 125 0.01 334 309 196 41.31 36.568 125 0.015 399 378 244 38.84 35.449 125 0.02 421 402 267 36.57 33.58

In all the work – tool combinations, a lower temperature was

observed under LN2 machining compared to dry and wet machining. This is

because the temperature of the LN2 is extremly low (-196 C), which is

supplied at tool – chip interface, and it evaporates quickly by absorbing the

heat, resulting in the reduction of the cutting temperature. The rate of heat

removal depends mainly on the convection heat – transfer coefficient and

temperature of the cutting fluid.

In wet machining, the cooling effect is decreased at higher cutting

temperatures because the convection heat – transfer coefficient is reduced as a

result of the boiling of the flood coolants, whereas, in LN2 machining, the

compressed air is passed to the cryogenic container through an inlet pipe and

transferring the fluid to the cutting zone, which further increases the heat

transfer rate, and results in lower cutting temperature compared to dry and

wet machining. It was also observed that LN2 cooling, in its present method

79

of application, enabled a reduction in the cutting temperature in the range of

36 - 65% and 22 - 51% over dry and wet machining, respectively depending

upon the cutting parameters and work – tool combinations. The reduction in

the cutting temperature has a significant influence on the other machinability

indices, such as the cutting force, surface roughness and tool wear.

In the milling of AISI D2 steel, when the cutting speed was

increased from 75 m/min to 100 m/min and 125m/min under a constant feed

rate of 0.02 mm/tooth, the variation in the percentage of reduction in the

cutting temperature, due to LN2 cooling was found to be 3.97% and 2.03%,

and 4.18% and 4.87% compared to dry and wet machining, respectively.

Similarly, when the feed rate was increased from 0.01mm/tooth to

0.015 mm/tooth and 0.02 mm/tooth under a constant cutting speed of

125 m/min, the variation in the percentage of reduction in the cutting

temperature due to LN2 cooling was observed to be 1.5% and 2.37%; and

4.31% and 4.8% compared to dry and wet machining, respectively.

In the milling of the AISI D3 steel, when the cutting speed was



cutting temperature due to LN2 cooling was found to be 1.61% and 5.85%;


Similarly, when the feed rate was increased from 0.01mm/tooth to

0.015 mm/tooth and 0.02 mm/tooth under a constant cutting speed of

125 m/min, the variation in the percentage of reduction in the cutting

temperature due to LN2 cooling was observed to be 1.9% and 6.09%; and

5.58% and 8.76% compared to dry and wet machining, respectively.

In the milling of AISI H13 steel, when the cutting speed was



80



Similarly when the feed rate was increased from 0.01mm/tooth to 0.015

mm/tooth and 0.02 mm/tooth under a constant cutting speed of 125 m/min,

the variation in the percentage reduction in the cutting temperature due to LN2

cooling was found to be 2% and 2.48%; and 3.21% and 4.98% compared to

dry and wet machining, respectively.

In the milling of AISI P20 steel, when the cutting speed was





Similarly, when the feed rate was increased from 0.01mm/tooth to 0.015

mm/tooth and 0.02 mm/tooth under a constant cutting speed of 125 m/min,

the variation in the percentage of reduction in the cutting temperature due to

LN2 cooling was found to be 2.47% and 1.12%; and 4.74% and 5.2%

compared to dry and wet machining, respectively. It was observed that in all

work-tool combinations, the increase in the cutting speed and feed rate

decreased the effect of cryogenic cooling. The effect of cryogenic cooling is

decreased because of an increase in the cutting temperature, thereby changing

the chip – tool contact and heat transfer.

4.2 EFFECT OF CRYOGENIC COOLING ON CUTTING

FORCE (Fx, Fy and Fz)

Cutting forces are one of the important criteria by which the

performance of milling process can be assessed. Since milling is intermittent

cutting process which can lead to undesirable vibrations, resulting in poor

quality of the machined part. Energy consumption in a cutting operation was

associated with friction and cutting forces (Shaw 2005).

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4.2.1 Effect of Cutting Force on Milling of AISI D2 Steel

The comparison of the feed force (Fx), normal force (Fy), and axial

force (Fz) with different speed-feed combinations in the milling of AISI D2

steel under three different machining conditions is shown in Figures 4.5 (a-c),

4.6 (a-c) and 4.7(a-c). The percentage decrease in cutting forces due to LN2

machining over dry and wet machining in the milling of AISI D2 steel is

shown in Tables 4.5, 4.6 and 4.7. It shows that the cutting force decreases

with increasing cutting speeds and increases with increasing feed rates under

all machining conditions. This is due to the fact that as the cutting speed

increases, a higher cutting temperature is generated at the cutting zone,

resulting in the softening of the workpiece and decrease in the shearing area,

causing decrease in the cutting force. The cutting force increased with an

increase in the feed rate due to an increase in the chip load per tooth. The

cutting force decreases with an increasing cutting speed, and increases with an

increasing feed rate, as reported in the earlier work (Thomas and Beauchamp

2003, Kumar and Choudhury 2008).

In the milling of AISI D2 steel, the feed force (Fx), normal force

(Fy), and axial force (Fz) at a cutting speed of 125 m/min and feed rate of

0.02 mm/tooth, was 320 N, 396 N and 371 N for dry machining. When an

emulsion cutting fluid was applied to the cutting zone, the feed force, normal

force and axial force was 290 N, 336 N and 302 N for the similar cutting

conditions. The feed force, normal force and axial force was 229 N, 280 N

and 241 N, when the LN2 coolant was supplied to the cutting zone. In LN2

cooling, the feed force, normal force and axial force decreased by 28.43%,

29.29% and 35.04%; and 21.03%, 16.66% and 20.19% compared to dry and

wet machining respectively. In this work – tool combination, LN2 cooling

decreased the feed force, normal force and axial force in the range of 28-44%,

29-39% and 35-41% compared to dry machining, and 20-29%, 15-31% and

18-25% compared to wet machining respectively.

82

(a)

(b)

(c)

Figure 4.5 Comparison of the feed force in the milling of AISI D2 steel

at different cutting speeds (a) 75m/min (b) 100m/min

(c) 125 m/min

83

(a)

(b)

(c)

Figure 4.6 Comparison of the normal force in the milling of AISI D2

steel at different cutting speeds (a) 75m/min (b) 100 m/min

(c) 125 m/min

84

(a)

(b)

(c)

Figure 4.7 Comparison of the axial force in the milling of AISI D2 steel

at different cutting speeds (a) 75m/min (b) 100m/min

(c) 125 m/min

85

Table 4.5 Feed force in the milling of AISI D2 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Feed force, Fx (N) % decrease

Dry Wet LN2LN2 over

dryLN2

over wet

1 75 0.01 336 266 188 44.04 29.322 75 0.015 412 322 242 41.26 24.843 75 0.02 424 331 251 40.8 24.164 100 0.01 296 236 168 43.24 28.815 100 0.015 362 276 212 41.43 23.186 100 0.02 391 302 240 38.61 20.527 125 0.01 268 211 151 43.65 28.438 125 0.015 291 261 189 35.05 27.589 125 0.02 320 290 229 28.43 21.03

Table 4.6 Normal force in the milling of AISI D2 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Normal force, Fy(N)

% decrease

Dry Wet LN2LN2 over

dryLN2

over wet1 75 0.01 417 371 254 39.08 31.532 75 0.015 439 386 282 35.76 26.943 75 0.02 478 410 316 33.89 22.924 100 0.01 372 316 229 38.44 27.535 100 0.015 402 322 261 35.07 18.946 100 0.02 431 347 293 32.01 15.567 125 0.01 348 306 219 37.06 28.438 125 0.015 362 310 232 35.91 25.169 125 0.02 396 336 280 29.29 16.66

86

Table 4.7 Axial force in the milling of AISI D2 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Axial force, Fz (N) % decrease

Dry Wet LN2

LN2overdry

LN2overwet

1 75 0.01 369 291 217 41.19 25.422 75 0.015 421 353 267 36.57 24.363 75 0.02 438 369 281 35.84 23.844 100 0.01 351 271 210 40.17 22.55 100 0.015 380 298 239 37.1 19.796 100 0.02 408 320 262 35.78 187 125 0.01 312 251 190 39.1 24.38 125 0.015 332 269 209 37.04 22.39 125 0.02 371 302 241 35.04 20.19

4.2.2 Effect of Cutting Force on Milling of AISI D3 Steel

The comparison of the cutting force with different speed-feedcombinations in the milling of AISI D3 steel under three different machiningconditions, is shown in Figures 4.8(a-c), 4.9(a-c) and 4.10(a-c). Tables 4.8,4.9 and 4.10 show the percentage decrease in the cutting forces due to LN2

cooling over dry and wet machining. In the milling of AISI D3 steel, when nocoolant was supplied to the cutting zone, the feed force, normal force andaxial force at a cutting speed of 125 m/min and feed rate of 0.02 mm/toothwere 389 N, 551 N and 562 N, while for the same cutting conditions, the feedforce, normal force and axial force were 356 N, 446 N and 476 N in wetmachining. The feed force, normal force and axial force were 290 N, 283 Nand 343 N in LN2 cooling for the same cutting conditions. The decrease in thefeed, normal and axial forces due to LN2 cooling was 25.44%, 48.63% and38.96%, over dry machining. The feed, normal and axial forces decreased by18.53%, 36.54% and 27.94% in LN2 cooling over wet machining. Inmachining of AISI D3 steel, LN2 cooling decreased the feed force, normalforce and axial force in the range of 25-34%, 39-51% and 38-47%; and18-27%, 22-43% and 27-39% compared to dry and wet machiningrespectively.

87

(a)

(b)

(c)

Figure 4.8 Comparison of the feed force in the milling of AISI D3 steel

at different cutting speeds (a) 75 m/min (b) 100 m/min

(c) 125 m/min

88

(a)

(b)

(c)

Figure 4.9 Comparison of the normal force in the milling of AISI D3

steel at different cutting speeds (a) 75m/min (b) 100 m/min

(c) 125 m/min

89

(a)

(b)

(c)

Figure 4.10 Comparison of the axial force in the milling of AISI D3 steel


(c) 125 m/min

90

Table 4.8 Feed force in the milling of AISI D3 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2LN2

over dryLN2 over

wet1 75 0.01 368 329 240 34.78 27.052 75 0.015 379 338 265 30.07 21.593 75 0.02 426 379 304 28.63 19.784 100 0.01 346 308 229 33.81 25.645 100 0.015 357 326 253 29.13 22.396 100 0.02 412 370 298 27.66 19.457 125 0.01 324 296 223 31.17 24.668 125 0.015 336 311 241 28.27 22.59 125 0.02 389 356 290 25.44 18.53

Table 4.9 Normal force in the milling of AISI D3 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Normal force, Fy(N) % decrease

Dry Wet LN2LN2

over dryLN2 over

wet1 75 0.01 539 469 264 51.02 43.712 75 0.015 567 493 298 47.44 39.553 75 0.02 590 566 359 39.15 36.574 100 0.01 483 429 246 49.06 42.655 100 0.015 521 465 277 46.83 40.436 100 0.02 563 499 309 45.11 38.077 125 0.01 351 253 196 44.15 22.528 125 0.015 449 367 221 50.77 39.789 125 0.02 551 446 283 48.63 36.54

91

Table 4.10 Axial force in the milling of AISI D3 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Axial force, Fz(N) % decrease

Dry Wet LN2LN2 over

dryLN2 over

wet

1 75 0.01 561 481 293 47.77 39.082 75 0.015 583 562 343 41.16 38.963 75 0.02 607 576 362 40.36 37.154 100 0.01 498 446 261 47.59 41.475 100 0.015 530 472 282 46.79 40.256 100 0.02 572 516 353 38.28 31.587 125 0.01 412 365 237 42.47 35.068 125 0.015 459 390 273 40.52 309 125 0.02 562 476 343 38.96 27.94

4.2.3 Effect of Cutting Force on Milling of AISI H13 Steel

The comparison of the cutting force with different speed-feedcombinations in the milling of AISI H13 steel under three different machiningapproaches is shown in Figures 4.11(a-c), 4.12(a-c) and 4.13(a-c). Thepercentage decrease in the cutting forces due to LN2 cooling over dry and wetmachining is shown in Tables 4.11, 4.12 and 4.13. In the milling of AISI H13steel, the feed force and normal force at a cutting speed of 125 m/min andfeed rate of 0.02 mm/tooth were 336 N, 282 N and 256 N; and 381 N, 328 Nand 286 N for dry, wet and LN2 machining, respectively. At the same cuttingconditions, the axial force was 398 N, 346 N and 294 N for dry, wet and LN2

machining, respectively. LN2 cooling decreased the feed force and normalforce by 23.8% and 24.93%; and 9.21% and 12.8 % compared to dry and wetmachining, respectively. The axial force also decreased by 26.13% and15.02% compared to dry and wet machining. In machining of AISI H13 steel,LN2 cooling decreased the feed force, normal force and axial force in therange of 22-27%, 19-25% and 20-27%; and 4-14%, 9-15% and 11-17%compared to dry and wet machining respectively.

92

(a)

(b)

(c)

Figure 4.11 Comparison of the feed force in the milling of AISI H13


(c) 125 m/min

93

(a)

(b)

(c)

Figure 4.12 Comparison of the normal force in the milling of AISI H13


(c) 125 m/min

94

(a)

(b)

(c)

Figure 4.13 Comparison of the axial force in the milling of AISI H13


(c) 125 m/min

95

Table 4.11 Feed force in the milling of AISI H13 steel under three

different machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 290 246 211 27.24 14.222 75 0.015 327 280 242 25.99 13.573 75 0.02 368 300 286 22.28 4.664 100 0.01 279 231 206 26.16 10.825 100 0.015 310 252 231 25.48 8.336 100 0.02 352 290 274 22.15 5.517 125 0.01 272 226 198 27.2 12.388 125 0.015 289 245 219 24.22 10.619 125 0.02 336 282 256 23.8 9.21

Table 4.12 Normal force in the milling of AISI H13 steel under three


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Normal force, Fy (N) % decrease

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 336 303 260 22.61 14.192 75 0.015 342 314 272 20.46 13.373 75 0.02 391 346 314 19.69 9.244 100 0.01 321 286 243 24.29 15.035 100 0.015 338 296 257 23.96 13.176 100 0.02 386 339 301 22.02 11.27 125 0.01 314 269 233 25.79 13.388 125 0.015 328 283 246 25 13.079 125 0.02 381 328 286 24.93 12.8

96

Table 4.13 Axial force in the milling of AISI H13 steel under threedifferent machining conditions

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2overdry

LN2overwet

1 75 0.01 396 359 306 22.72 14.762 75 0.015 413 373 324 21.54 13.133 75 0.02 427 386 341 20.14 11.654 100 0.01 378 332 286 24.33 13.855 100 0.015 406 357 312 23.15 12.66 100 0.02 410 361 316 22.92 12.467 125 0.01 362 318 261 27.9 17.928 125 0.015 381 333 278 27.03 16.519 125 0.02 398 346 294 26.13 15.02

4.2.4 Effect of Cutting Force on Milling of AISI P20 Steel

The comparison of the cutting forces with different speed-feed

combinations in the milling of AISI P20 steel under three different machining

conditions is shown in Figures 4.14(a-c), 4.15(a-c) and 4.16(a-c). Tables 4.14,

4.15 and 4.16 show the percentage decrease in the cutting forces due to LN2

cooling over dry and wet machining. In the milling of AISI P20 steel, when

no coolant was supplied to the cutting zone, the feed force, normal force and

axial force at a cutting speed of 125 m/min and feed rate of 0.02 mm/tooth

were 213 N, 232 N and 230 N, while for the same cutting conditions, the feed

force, normal force and axial force were 187 N, 190 N and 216 N in wet

machining. The feed force, normal force and axial force were 164 N, 175 N

and 191 N in LN2 cooling for the same cutting conditions. The decrease in the

feed force, normal and axial force due to LN2 cooling was 23%, 24.56% and

16.95%, over dry machining.The feed force, normal and axial force decreased

by 12.29%, 7.89% and 11.57% in LN2 cooling over wet machining. In milling

of AISI P20 steel, LN2 cooling decreased the feed force, normal force and

axial force in the range of 23-43%, 22-44% and 16-36%; and 12-23%, 7-39%and 11-28% compared to dry and wet machining respectively.

97

(a)

(b)

(c)

Figure 4.14 Comparison of the feed force in the milling of AISI P20 steel


(c) 125 m/min

98

(a)

(b)

(c)

Figure 4.15 Comparison of the normal force in the milling of AISI P20


(c) 125 m/min

99

(a)

(b)

(c)

Figure 4.16 Comparison of the axial force in the milling of AISI P20


(c) 125 m/min

100

Table 4.14 Feed force in the milling of AISI P20 steel under three


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 246 183 140 43.08 23.492 75 0.015 261 223 193 26.05 13.453 75 0.02 290 249 218 24.82 12.444 100 0.01 189 146 120 36.5 17.85 100 0.015 210 172 149 29.04 13.376 100 0.02 242 198 173 28.51 12.627 125 0.01 172 139 109 36.62 21.588 125 0.015 198 156 136 31.31 12.829 125 0.02 213 187 164 23 12.29

Table 4.15 Normal force in the milling of AISI P20 steel under three


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Normal force, Fy (N) % decrease

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 284 260 158 44.36 39.232 75 0.015 296 268 208 29.72 22.383 75 0.02 312 290 230 26.28 20.684 100 0.01 209 189 139 33.49 26.455 100 0.015 228 202 162 28.94 19.86 100 0.02 253 216 197 22.13 8.797 125 0.01 188 169 129 31.38 23.668 125 0.015 206 184 151 26.69 17.939 125 0.02 232 190 175 24.56 7.89

101

Table 4.16 Axial force in the milling of AISI P20 steel under three


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 346 304 218 36.99 28.28

2 75 0.015 359 310 240 33.14 22.58

3 75 0.02 386 346 281 27.2 18.78

4 100 0.01 231 210 177 23.37 15.71

5 100 0.015 249 228 198 20.48 13.15

6 100 0.02 276 252 223 19.2 11.5

7 125 0.01 193 182 150 22.27 17.58

8 125 0.015 219 204 176 19.63 13.72

9 125 0.02 230 216 191 16.95 11.57

The experimental findings shows that the LN2 cooling produced

lower feed force, normal force and axial force compared to dry and wet

machining. This is because, on applying the LN2 coolant into the cutting zone,

the LN2 evaporates, and a nitrogen cushion is formed between the tool – chip

and tool – work interfaces. This lowers the coefficient of friction and

provides better lubrication between tool – chip and tool – work interfaces.

It is evident from the Figures 4.5(a-c) - 4.16(a-c) that the cutting

forces in LN2 cooling are lower than those under dry and wet machining. The

lower cutting forces obtained under LN2 machining can be attributed to the

increased strength and hardness of the tool material, reduced tool wear, and

adhesion between the tool – chip and tool – workpiece interfaces through the

102

reduction of the cutting temperature. In LN2 cooling, the feed force, normal

force and axial force decreased in the range of 23-44%, 19-51% and 16-47%

compared to dry machining, and 4-29%, 7-43% and 11-39% compared to wet

machining respectively, depending upon the cutting parameters and

work – tool combinations.

Kumar and Choudhury (2008) have reported a reduction in the

cutting force over dry cutting, when cryogenic liquid nitrogen was supplied at

the tool tip using a nozzle, in the machining of stainless steel 202. Wang et al

(2002) have also reported that cryogenic cooling-enhanced machining

reduced the cutting force in the turning of Tantalum with a carbide tool insert

over conventional machining.

Dhar et al (2000c and 2000d) have reported that the application of

liquid nitrogen jets along the main and auxiliary cutting edges substantially

change the chip formation and reduce the cutting forces. Dhar et al (2002)

also reported a substantial reduction in the cutting forces by favorable chip

formation, in the turning of AISI 1040 and AISI 4320 steels with cryogenic

cooling by liquid nitrogen jets.

4.3 EFFECT OF CRYOGENIC COOLING ON SURFACE

ROUGHNESS (Ra)

Surface roughness is one of the important factors for evaluating

workpiece quality of the machined components because the surface roughness

influences the functional characteristics of the workpiece such as

compatibility, fatigue resistance and surface friction. The factors which

influence the surface roughness during the end milling process, include tool

geometry, process parameters and heat generated in machining operation. The

surface quality mainly depends upon the geometry and condition of the

103

auxiliary cutting edge, including a part of the round nose (Dhar and

Kamruzzaman 2007). The surface roughness decreased with an increase in the

cutting velocity, and increased with an increase in the feed rate, as reported in

the earlier work (Sornakumar and Senthilkumar 2008, and Cakir et al 2004).

4.3.1 The Effect of LN2 as a coolant on the Surface roughness (Ra)

while Milling of AISI D2 Steel

Figure 4.17 (a-c) shows the variation in the surface roughness (Ra)

with feed rates at different cutting speeds in the milling of AISI D2 steel

under all machining conditions. The percentage reduction in the surface

roughness (Ra) due to LN2 cooling over dry and wet machining, during the

milling of AISI D2 steel, is shown in Table 4.17. In the milling of AISI D2

steel under dry machining (no coolant) and conventional cooling (wet), the

surface roughness (Ra) value of the workpiece surface at a cutting speed of

125 m/min and feed rate of 0.02 mm/tooth were 5.16 µm and 3.21 µm,

respectively. When the LN2 was supplied into the tool – chip interfaces, the

surface roughness (Ra) value of the workpiece surface was 2.42 µm.

This because of better cooling and lubrication effect provide lower

friction at the tool-chip and tool-wok interfaces. Furthermore, better

lubrication allows the chips to slide more easily over the tool surface. It was

observed that the reduction in the surface roughness due to LN2 cooling was

53.1% and 24.61% over dry and wet machining, respectively. In this

work – tool combination, LN2 cooling reduced the surface roughness in the

range of 52-65% compared to dry machining and 24-43% compared to wet

machining depending upon the cutting parameters.

104

(a)

(b)

(c)

Figure 4.17 Variation in the surface roughness (Ra) with different feed

rates in the milling of AISI D2 steel at different cutting

speeds (a) 75 m/min (b) 100 m/min (c) 125 m/min

105

Table 4.17 Surface roughness (Ra) in the milling of AISI D2 steel under

dry, wet and LN2 machining

S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Surface roughness,Ra (µm) % decrease

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 6.9 4.18 2.36 65.79 43.542 75 0.015 7.12 4.22 2.71 61.93 35.783 75 0.02 7.33 4.48 2.97 59.48 33.74 100 0.01 4.89 2.93 1.69 65.43 42.325 100 0.015 5.43 3.96 2.44 55.06 38.386 100 0.02 5.85 4.3 2.79 52.3 35.117 125 0.01 4.11 2.41 1.6 61.07 33.68 125 0.015 4.9 2.9 2.1 57.14 27.589 125 0.02 5.16 3.21 2.42 53.1 24.61

4.3.2 Effect of Surface roughness (Ra) on Milling of AISI D3 Steel


with feed rates at different cutting speeds in the milling of AISI D3 steel

under three different machining conditions. The percentage reduction in the

surface roughness (Ra) due to LN2 cooling over dry and wet machining during

the milling of AISI D2 steel is shown in Table 4.18. In the milling of AISI D2

steel under dry and wet machining, the surface roughness (Ra) values at a

cutting speed of 125 m/min and feed rate of 0.02 mm/tooth was 4.74 µm and

3.81 µm, respectively. When the LN2 was supplied into the tool – chip

interfaces, the surface roughness (Ra) value of the workpiece surface was

2.46 µm. It was observed that the reduction in the surface roughness due to

LN2 cooling was 48.1% and 35.43% over dry and wet machining,

respectively.

106

(a)

(b)

(c)


rates in the milling of AISI D3 steel at different cutting


107

Table 4.18 Surface roughness (Ra) in the milling of AISI D3 steel under


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 5.6 4.17 2.6 53.57 37.642 75 0.015 5.92 4.54 2.94 50.33 35.243 75 0.02 7.66 5.81 3.9 49.08 32.874 100 0.01 3.6 3.36 2.47 31.38 26.485 100 0.015 3.8 3.49 2.69 29.21 22.926 100 0.02 4.86 4.4 3.51 27.77 20.227 125 0.01 2.78 2.57 1.82 34.53 29.188 125 0.015 3.67 2.92 2.11 42.5 27.739 125 0.02 4.74 3.81 2.46 48.1 35.43

4.3.3 Effect of Surface roughness (Ra) on Milling of AISI H13 Steel


with feed rates at different cutting speeds in the milling of AISI H13 steel



the milling of AISI H13 steel is shown in Table 4.19. In the milling of

AISI H13 steel at cutting speed of 125 m/min and feed rate of 0.02 mm/tooth,

the surface roughness was 3.71 µm and 2.96 µm for dry and wet machining,

respectively. Surface roughness (Ra) was 2.22 µm when liquid nitrogen was

supplied at the cutting zone. The LN2 cooling method reduced the surface

roughness in the range of 40.16% and 25% compared to dry and wet

machining, respectively.

108

(a)

(b)

(c)


rates in the milling of AISI H13 steel at different cutting


109

Table 4.19 Surface roughness (Ra) in the milling of AISI H13 steel under


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)


Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 3.28 2.89 1.93 41.15 33.212 75 0.015 4.08 3.82 2.6 36.27 31.933 75 0.02 4.12 3.88 2.72 33.98 29.894 100 0.01 2.95 2.48 1.71 42.03 31.045 100 0.015 3.18 2.63 1.86 41.5 29.276 100 0.02 3.92 3.21 2.32 40.81 27.727 125 0.01 2.8 2.18 1.56 44.28 28.448 125 0.015 3.06 2.44 1.79 41.5 26.639 125 0.02 3.71 2.96 2.22 40.16 25

4.3.4 Effect of Surface roughness (Ra) on Milling of AISI P20 Steel


with feed rates at different cutting speeds in the milling of AISI P20 steel



the milling of AISI P20 steel is shown in Table 4.20. In the milling of

AISI P20 steel at a cutting speed of 125 m/min and feed rate of 0.02

mm/tooth, the surface roughness was 2.33 µm and 2.19 µm for dry and wet

machining, respectively. When the LN2 was supplied at the cutting zone, the

surface roughness was 1.92 µm. In this LN2 cooling method, the surface

roughness reduced in the range of 17.59% and 12.32% compared to dry and

wet machining respectively.

110

(a)

(b)

(c)


rates in the milling of AISI P20 steel at different cutting


111

Table 4.20 Surface roughness (Ra) in the milling of AISI P20 steel under


S.NoCuttingspeed

(m/min)

Feed rate(mm/tooth)

Surface roughness,Ra (µm)

% decrease

Dry Wet LN2

LN2

overdry

LN2

overwet

1 75 0.01 3.71 3.1 2.31 37.73 25.48

2 75 0.015 3.82 3.22 2.49 34.81 22.67

3 75 0.02 4.14 3.6 2.88 30.43 20

4 100 0.01 2.31 2.24 1.76 23.8 21.42

5 100 0.015 2.44 2.42 1.94 20.49 19.83

6 100 0.02 2.77 2.69 2.3 16.96 14.49

7 125 0.01 2.11 1.98 1.66 21.32 16.16

8 125 0.015 2.23 2.08 1.8 19.28 13.46

9 125 0.02 2.33 2.19 1.92 17.59 12.32

In all the work materials that can be machined, using LN2 cooling

produced a better surface finish compared to that of dry and wet machining

conditions. This can be attributed to the better lubrication action of the liquid

nitrogen, reducing the frictional forces, and hence, the cutting temperature

generated, and ultimately reducing the tool wear, which results in reduced

surface roughness. Further, the decrease in the cutting temperature leads to

less adhesion between the tool – chip and tool – work interface, which is one

of the reasons for the reduction in the surface roughness. The surface

roughness reduced in the range of 16-65% and 12-43% in LN2 cooling, when

compared to dry and wet machining conditions, respectively, depending upon

the cutting parameters and work – tool combinations.

chapter 4 milling performance of aisi d2, aisi...

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