Chapter 3 Experimental Investigations
3.2 Experimental Results
An importantmachinability index is chip reduction coefficient, ξ (ratio of chip thickness after and before cut). For given tool geometry and cutting conditions, the value of chip reduction coefficient depends upon the nature of chip-tool interaction, chip contact length, curl radius and form of the chips all of which expected to be influenced by high pressure coolant in addition to the level of cutting speeds and feed rates. The thickness of the chips was repeatedly measured by a slide caliper to determine the value of chip reduction coefficient. The variation in value of chip reduction coefficient with change in
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tool configuration, cutting speeds and feed rates as well as machining environment evaluated for Ti-6Al-4Valloy have been plotted and shown in Fig.3.2 and Fig.3.3. The machining chips were collected during all the treatments for studying their shape, colour and nature of interaction with the cutting insert at its rake surface. The results of such categorization of the chips produced at different conditions and environments have been shown in Table-3.3.
70 80 90 100 110 120 130 140 150 160
0.5 0.6 0.7 0.8 0.9 1.0 1.1
Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm
Chip reduction coefficient, ξ
Cutting velocity, m/min Feed rate
0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.2 Variation of ξ with Vc and So in turning Ti-6Al-4V by SNMG insert under dry, cryogenic cooling and high pressure coolant condition
70 80 90 100 110 120 130 140 150 160
0.5 0.6 0.7 0.8 0.9 1.0 1.1
Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm
Chip reduction coefficient, ξ
Cutting velocity, m/min Feed rate
0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.3 Variation of ξ with Vc and So in turning Ti-6Al-4V by SNMM insert under dry, cryogenic cooling and high pressure coolant condition
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Table-3.3 Shape and color of chips produced during turning Ti-6Al-4V by SNMG and SNMM inserts under dry, cryogenic and HPC conditions
Vc
m/min
Env. SNMG 120408 SNMM 120408
0.12 mm/rev. 0.14 mm/rev. 0.16 mm/rev. 0.12 mm/rev. 0.14 mm/rev. 0.16 mm/rev.
shape &color shape &color shape &color shape &color shape &color shape &color
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Dry ▲ metallic ▲ metallic ▲ metallic ▲ metallic ▲ metallic ▲ metallic Cryo ■ metallic ● metallic ● metallic ■ metallic ■ metallic ■ metallic HPC ■ metallic ● metallic ■ metallic ● metallic ● metallic ■ metallic
112
Dry ▲ metallic ▲ metallic ▲ metallic ▲ metallic ▲ metallic ▲ metallic Cryo ● metallic ■ metallic ● metallic ■ metallic ■ metallic ● metallic HPC ■ metallic ■ metallic ■ metallic ■ metallic ■ metallic ■ metallic
156
Dry ● metallic ● metallic ▲ metallic ● metallic ▲ metallic ▲ metallic Cryo ■ metallic ● metallic ■ metallic ■ metallic ■ metallic ● metallic HPC ● metallic ■ metallic ● metallic ■ metallic ■ metallic ● metallic
Chip shape Spiral Tubular Ribbon
Group ■ ● ▲
The optical microscopic views of the polished and etched side surface of the chips obtained during dry, cryogenic and HPC machining of Ti-6Al-4V alloy at a cutting velocity of 112 m/min, feed 0.16 mm/rev and 1.0 mm depth of cut are typically shown in Fig.3.4.
(a) SNMG
200µm 200µm 200µm
(b) SNMM
Dry condition Cryogenic cooling HPC cooling
Fig.3.4 Polished and etched side surface of typical chips produced at Vc=112 m/min and So=0.16 in turning Ti-6Al-4V by (a) SNMG and (b) SNMM insert under dry, cryogenic and HPC conditions
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High production machining associated with high velocity and feed rate inherently generates high heat as well as high cutting zone temperature. The cutting temperature if not controlled properly, cutting tools undergo severe flank wear and notch wear, lose sharpness of the cutting edge by either wearing or become blunt by welded built-up edge and weaken the product quality. In normal cutting condition all such heat sources produce maximum temperature at the chip-tool interface, which substantially influence the chip formation mode; cutting forces, tool life and product quality. High production machining needs to increase the process parameters further for meeting up the growing demand and cost competitiveness. Cutting temperature is increased with the increase in process parameter as well as with the increase in hardness and strength of the work material. Therefore, attempts are made to reduce this detrimental cutting temperature.
In the present work, the average cutting temperature was measured under all the machining conditions undertaken by simple but reliable tool-work thermocouple technique with proper calibration.Fig.3.5 shows the calibration curves obtained for the tool-work pair with tungsten carbide (P30 Grade, Sandvik) as the tool material and the Ti-6Al-4V rod undertaken as the work materials. As titanium undergoes oxidation at around 400oC, the present tool-work thermocouple pair has been calibrated up to 350oC and in this range the temperature and emf relationship is almost linear with a correlation coefficient of around 0.994. The calibration curve for the range of emf’s measured during the turning tests were obtained by extrapolation and the temperatures thus determined are in agreement with previously reported cutting temperatures in machining Ti-6Al-4V [Narutaki and Murakhoshi 1983].
0 2 4 6 8 10 12 14 16 18 20
0 200 400 600 800 1000 1200 1400
Temperature,o C
emf, mV
Work material : Ti-6Al-4V Tool material : Carbide
Fig.3.5 Tool-work thermocouple calibration curve
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The evaluated role of HPC on average chip-tool interface temperature in turning hardened steel at different Vc-So combinations in compare to dry and cryogenic condition have been shown in Fig.3.6 and Fig.3.7.
70 80 90 100 110 120 130 140 150 160
600 700 800 900 1000 1100
1200 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMG 120408 Depth of cut : 1.0 mm
Chip tool interface temperature,o C
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.6 Variation of average cutting zone temperature with Vc and So in turning Ti- 6Al-4V by SNMG insert under dry, cryogenic and HPC conditions
70 80 90 100 110 120 130 140 150 160
600 700 800 900 1000 1100
1200 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm Chip tool interface temperature,o C
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.7 Variation of average cutting zone temperature with Vc and So in turning Ti- 6Al-4V by SNMM insert under dry, cryogenic and HPC conditions
The variation of cutting force components, PX and PZ with that of velocity and feed monitored during turning the Ti-6Al-4V alloy by both SNMG and SNMM under dry,
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cryogenic cooling and HPC conditions have been plotted and shown in Fig.3.8, Fig.3.9, Fig.3.10 and Fig.3.11 respectively.
70 80 90 100 110 120 130 140 150 160
200 300 400 500
600 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMG 120408 Depth of cut : 1.0 mm
Feed force, Px, (N)
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.8 Variation offeed force (Px)with Vc and So in turning Ti-6Al-4V by SNMG insert under dry, cryogenic and HPC conditions
70 80 90 100 110 120 130 140 150 160
200 300 400 500
600 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm
Feed force, Px, (N)
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.9 Variation of feed force (Px)with Vc and So in turning Ti-6Al-4V by SNMM insert under dry, cryogenic and HPC conditions
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70 80 90 100 110 120 130 140 150 160
500 600 700 800
900 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMG 120408 Depth of cut : 1.0 mm
Main cutting force, PZ, (N)
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.10 Variation ofmain cutting force (Pz)with Vc and So in turning Ti-6Al-4V by SNMG insert under dry, cryogenic and HPC conditions
70 80 90 100 110 120 130 140 150 160
500 600 700 800
900 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm
Main cutting force, PZ, (N)
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.11 Variation of main cutting force (Pz)with Vc and So in turning Ti-6Al-4V by SNMM insert under dry, cryogenic and HPC conditions
The growth of principal flank wear, VB with progress of machining recorded while turning Ti-6Al-4V by SNMG and SNMM type inserts at the Vc=112 m/min, So=0.12 mm/rev and t=1.0 mm under dry, cryogenic cooling and high pressure cooling conditions have been shown in Fig.2.12.The growth of average auxiliary flank wear, VS with machining time observed while turning Ti-6Al-4Vby the two different types of inserts under previous conditions and environments have been shown in Fig.2.13.
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0 1 2 3 4 5 6 7 8 9 10
0 50 100 150 200 250 300 350 400
Work material : Ti-6Al-4V Cutting velocity : 112 m/min Feed rate : 0.12 mm/rev Depth of cut : 1.0 mm
Average flank wear, VB, µm
Machining time, min
Environment Dry Cryo HPC
(a) SNMG
0 1 2 3 4 5 6 7 8 9 10
0 50 100 150 200 250 300 350 400
Work material : Ti-6Al-4V Cutting velocity : 112 m/min
Feed rate : 0.12 mm/rev
Depth of cut : 1.0 mm
Average flank wear, VB, µm
Machining time, min
Environment Dry Cryo HPC
(b) SNMM
Fig.3.12 Growth of VB in (a) SNMG and (b) SNMM inserts during turning Ti-6Al-4V under dry, cryogenic and HPC conditions
0 1 2 3 4 5 6 7 8 9 10
0 50 100 150 200 250 300 350 400
Work material : Ti-6Al-4V Cutting velocity : 112 m/min Feed rate : 0.12 mm/rev Depth of cut : 1.0 mm
Auxiliary flank wear, V S, µm
Machining time, min
Environment Dry Cryo HPC
(a) SNMG
0 1 2 3 4 5 6 7 8 9 10
0 50 100 150 200 250 300 350 400
Work material : Ti-6Al-4V Cutting velocity : 112 m/min Feed rate : 0.12 mm/rev Depth of cut : 1.0 mm
Auxiliary flank wear, V S, µm
Machining time, min
Environment Dry Cryo HPC
(b) SNMM
Fig.3.13 Growth of VS in (a) SNMG and (b) SNMM inserts during turning Ti-6Al-4V under dry, cryogenic and HPC conditions
(a) SNMG
(b) SNMM
Dry condition Cryogenic cooling HPC cooling
Fig.3.14 SEM views of the worn out insert (a) SNMG and (b) SNMM after machining Ti-6Al-4V alloy under dry, cryogenicand HPC conditions
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Fig.3.14 shows the scanning electron microscopy (SEM) views of the worn out inserts (SNMG and SNMM) after being used at Vc=112 m/min, So=0.12 mm/rev and t
=1.0 mm for 6 min. under dry and cryogenic cooling conditions.
70 80 90 100 110 120 130 140 150 160
0.50 0.75 1.00 1.25 1.50 1.75
2.00 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMG 120408 Depth of cut : 1.0 mm
Surface roughness, Ra, µm
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.15 Variation of Ra with Vc at different So in turning Ti-6Al-4V by SNMG insert under dry, cryogenic cooling and HPC conditions
70 80 90 100 110 120 130 140 150 160
0.50 0.75 1.00 1.25 1.50 1.75
2.00 Environment
Dry ---
Cryo ...
HPC
Work material : Ti-6Al-4V Cutting tool : SNMM 120408 Depth of cut : 1.0 mm
Surface roughness, Ra, µm
Cutting velocity, m/min
Feed rate 0.12 mm/rev 0.14 mm/rev 0.16 mm/rev
Fig.3.16 Variation of Ra with Vc at different So in turning Ti-6Al-4V by SNMM insert under dry, cryogenic cooling and HPC conditions
Surface roughness has been measured at two stages; one, after a 50 seconds of machining with the sharp tool while recording the cutting temperature and forces and second, with the progress of machining while monitoring growth of tool wear with
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machining time. The surface roughness attained after 50 seconds of machining of Ti-6Al- 4V alloy by the sharp SNMG and SNMM inserts at various Vc−S o combinations under dry, cryogenic cooling and HPC conditions are shown in Fig.3.15 and Fig.3.16 respectively. Fig.3.17 shows the variation of surface roughness observed with progress of machining of Ti-6Al-4V alloy by two types of inserts at a particular set of Vc−S o and t under dry, cryogenic cooling and HPC conditions
0 1 2 3 4 5 6 7 8 9 10
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Work material : Ti-6Al-4V Cutting velocity : 112 m/min Feed rate : 0.12 mm/rev Depth of cut : 1.0 mm
Surface roughness, R a, µm
Machining time, min
Environment Dry Cryo HPC
(a) SNMG
0 1 2 3 4 5 6 7 8 9 10
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Work material : Ti-6Al-4V Cutting velocity : 112 m/min Feed rate : 0.12 mm/rev Depth of cut : 1.0 mm
Surface roughness, R a, µm
Machining time, min
Environment Dry Cryo HPC
(b) SNMM
Fig.3.17 Surface roughness developed with progress in turning Ti-6Al-4V by (a) SNMG and (b) SNMM inserts under dry and cryogenic conditions
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