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High Speed Turning
of
Titanium (Ti-6Al-4V) Alloy
Anil Srivastava, Ph.D. Manager, Manufacturing Technology
TechSolve, Inc., Cincinnati, OH 45237
2
Outline
• Applications of Titanium Alloys
• Technical Difficulties in Machining Titanium Alloys
• High Speed Turning of Ti-6Al-4V Alloy
• Some Recent Test Results
• Conclusions
3
Application of Titanium Alloys
• Titanium and its alloys are today used in:
– Aerospace
– Medical device
– Food and chemical industries
• Titanium alloys offers:
– High strength-to-weight ratio
– Super corrosion resistance
– Bio-compatibility
• Titanium alloys are difficult-to-machine due to:
– Low thermal conductivity and diffusivity
– High rigidity and low elasticity modulus
– High chemical reactivity at elevated temperatures
– Work hardening characteristics
4
• Use low cutting speeds – a change from 6 to 46 meters per min (20 to
150 sfpm) with carbide tools results in a temperature change from
427°C to 927°C (800°F to 1700°F).
• Use high feed rates – a change from 0.05 to 0.51 mm/rev (0.002 to
0.020 in/rev) results in a temperature increase of only 149°C (300°F).
• Use generous amounts of cutting fluid – coolant carries away heat,
washes away chips, and reduces cutting forces.
• Use sharp tools – replace them at the first sign of wear, or as
determined by production/cost considerations. Complete tool failure
occurs rather quickly after small initial amount of wear takes place.
• Never stop feeding – while a tool and a workpiece are in moving
contact. Permitting a tool to dwell in moving contact causes work
hardening and promotes smearing, galling, seizing, and total tool
breakdown.
Machining Titanium for Economical Production
(Courtesy of Supra Alloys, Inc.)
BASIC RULES
5
Recent News
• Lockheed Martin has obtained government approval to use
‘cryogenic’ titanium machining process in production of the F-35
Lightning II stealth fighter that will improve tool-life by a factor of 10
with appropriate material removal processing speed.
• The Joint Program Office in coordination with the F-35 Fracture
Control Board (FCB) approved the new process for standard
roughing operations, impacting the most time-consuming and cost-
intensive machining processes associated with manufacturing
titanium parts.
• Broadly applied, this new technology could improve affordability and
efficiency in the production of the F-35, which is approximately 25%
titanium by weight.
American Manufacturing, September, 2011
6
Effect of Cutting Speed and Feed on Tool-Life
Figure: Effect of cutting speed and feed on
tool-life when turning Ti-6Al-4V
(Courtesy of Supra Alloys, Inc.)
OPERATION TOOL
MATERIAL
CUTTING
SPEED
(SFPM)
FEED
(in/rev)
DEPTH OF
CUT
(in)
Turn (Rough) C-2 150 0.010 0.250
Turn (Finish) C-2 200 0.006 - 0.008 0.010 - 0.030
Turn (Finish) C-2 300 0.006 - 0.008 0.010 - 0.030
Table: Typical parameters for turning
Ti-6Al-4V gas turbine components
7
• In the past, improvement in cutting-tool performance by the
application of coating technology has been very frustrating.
However, developments of interest include specially designed
turning tools such as micro-edge geometry and new coatings.
• There seems to be great potential in machining of titanium with C-2
carbides when designed with proper geometry.
• Also, very little improvement in productivity has been experienced
by exploring new combinations of machining parameters.
• Data is needed to determine the speeds at which reproducible and
reliable tool life of the order of 5 to 10 min can be obtained, and to
determine whether these conditions improve the economics of
titanium machining.
Issues with Increasing Productivity and Possibilities
High Speed Turning of
Titanium (Ti-6Al-4V) Alloy
9
• Work Material : Titanium (Ti-6Al-4V) Alloy Bar (2 in diameter)
• Tool Holder : Type CTGPL 164
• Cutting Tool : Uncoated/Coated/Micro-edge/Super-finished Edge Geometry Carbide Inserts (TPG 432; Grade – K313)
• Types of Coatings : TiAlN, [C8, C15, C2-SL Nano-Layers], and
[#2390, #2391, #2393, #2414 Ultra-hard]
• Cutting Speeds : 327 (100), 393 (120), 656 (200), 787 (240) SFPM(m/min)
• Feed Rates : 0.002 (0.050), 0.003 (0.075), 0.004 (0.100),
0.005 (0.125) IPR (mm/rev.)
• Depth of Cut : 0.040 (1.000) in (mm)
• Cutting Fluid : few tests without coolant and few with flooded coolant application (Trim Sol – 5% vol.)
Turning Test Conditions
10
Turning of Titanium (Ti-6Al-4V) Alloy
Experimental Set-up for Turning Tests
11
Types of Nano-layered and Ultra-hard Coatings
Figure: High Magnification XTEM Bright Field
Image of C2-SL Superlattice Coating.
Nano-layered Coatings:
1. C-8: TiAlSiCN based coating
2. C-15: CrAlSiN-CrAlSiYN based
coating
3. C2-SL: TiAlN-CrN based coating
(All the three are PVD coatings)
Ultra-hard Coatings:
1. #2390: Multi-layer CrAlN coating
2. #2391: Multi-layer TiAlN coating
3. #2393/#2414: HfB2 coating
(1 & 2 PVD; 3 is PVD+CVD coating)
12
Turning Test Results
Figure: Effect of Feed Rate on Average Cutting Force
0
200
400
600
800
1000
1200
1400
1600
1800
0.025 0.05 0.075 0.1 0.125 0.15
Uncoated
C8 - Nanolayer Coated
C15 - Nanolayer Coated
C2-SL - Nanolayer Coated
2390 Ultrahard Coated
2391 Ultrahard Coated
2393 Ultrahard Coated
Variable Edge Prep
Feed Rate (mm/rev)
Avera
ge C
uttin
g F
orc
e (
N)
Cutting Speed - 240 m/min
13
Turning Test Results
Figure: Effect of Feed Rate on Average Cutting Force
0
50
100
150
200
250
300
350
0.025 0.05 0.075 0.1 0.125 0.15
Uncoated C8 - Nanolayer Coated
C15 - Nanolayer Coated C2-SL - Nanolayer Coated
2390 Ultrahard Coated 2391 Ultrahard Coated
2393 Ultrahard Coated Variable Edge Prep
Feed Rate (mm/rev)
Avera
ge C
uttin
g F
orc
e (
N)
Cutting Speed - 120 m/min
0
200
400
600
800
1000
1200
1400
0.025 0.05 0.075 0.1 0.125 0.15
Uncoated
C8 - Nanolayer Coated
C15 - Nanolayer Coated
C2-SL - Nanolayer Coated
2390 Ultrahard Coated
2391 Ultrahard Coated
2393 Ultrahard Coated
Variable Edge Prep
Feed Rate (mm/rev)
Avera
ge C
uttin
g F
orc
e (
N)
Cutting Speed - 200 m/min
14
Turning Test Results
Figure: Effect of Cutting Speed on Average Cutting Force
0
200
400
600
800
1000
1200
1400
1600
1800
100 120 140 160 180 200 220 240
Uncoated
C8 - Nanolayer Coated
C15 - Nanolayer Coated
C2-SL - Nanolayer Coated 2390 Ultrahard Coated
2391 Ultrahard Coated
2393 Ultrahard Coated
Variable Edge Prep
Feed Rate - 0.100 mm/rev
Cutting Speed (m/min)
Avera
ge C
uttin
g F
orc
e (
N)
0
200
400
600
800
1000
1200
1400
100 120 140 160 180 200 220 240
Uncoated
C8 - Nanolayer Coated
C15 - Nanolayer Coated
C2-SL - Nanolayer Coated
2390 Ultrahard Coated
2391 Ultrahard Coated
2393 Ultrahard Coated
Variable Edge Prep
Feed Rate - 0.125 mm/rev
Cutting Speed (m/min)
Avera
ge C
uttin
g F
orc
e (
N)
15
Turning Test Results
Figure: Effect of Cutting Speed on Average Cutting Force
0
50
100
150
200
250
100 120 140 160 180 200 220 240
Uncoated C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep
Feed Rate - 0.050 mm/rev
Cutting Speed (m/min)
Avera
ge C
utt
ing
Forc
e (
N)
0
200
400
600
800
1000
1200
1400
1600
100 120 140 160 180 200 220 240
Uncoated C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep
Feed Rate - 0.075 mm/rev
Cutting Speed (m/min)
Ave
rage
Cu
ttin
g Fo
rce
(N
)
16
Turning Test Results
Uncoated
C-15 Nano-layered
# 2390 Ultrahard
#2393 Ultrahard
C-8 Nano-layered
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Cutting Speed: 240 m/min,
Feed Rate: 0.100 mm/rev,
Depth of Cut: 1.000 mm
17
Turning Test Results
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed: 240 m/min,
Feed Rate: 0.050 mm/rev,
Depth of Cut: 1.000 mm
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed : 240 m/min,
Feed Rate : 0.075 mm/rev,
Depth of Cut : 1.000 mm
18
Cutting Speed: 200 m/min,
Feed Rate: 0.125 mm/rev,
Depth of Cut: 1.000 mm
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Uncoated C-8 Nanolayered C-15 Nanolayered
# 2390 Ultrahard #2391 Ultrahard #2393 Ultrahard
Turning Test Results
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard
Cutting Speed: 200 m/min,
Feed Rate: 0.100 mm/rev,
Depth of Cut: 1.000 mm
19
Cutting Speed: 200 m/min,
Feed Rate: 0.075 mm/rev,
Depth of Cut: 1.000 mm
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Turning Test Results
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed: 200 m/min,
Feed Rate: 0.050 mm/rev,
Depth of Cut: 1.000 mm
20
Uncoated C-8 Nano-layered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed: 120 m/min,
Feed Rate: 0.100 mm/rev,
Depth of Cut: 1.000 mm
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Uncoated C-8 Nano-layered
C-15 Nanolayered C2-SL Nanolayered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed: 120 m/min,
Feed Rate: 0.125 mm/rev,
Depth of Cut: 1.000 mm
Turning Test Results
21
Uncoated C-8 Nanolayered
C-15 Nanolayered C2-SL Nanolayered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy
Cutting Speed: 120 m/min,
Feed Rate: 0.050 mm/rev,
Depth of Cut: 1.00 mm)
Uncoated C-8 Nanolayered
C-15 Nano-layered C2-SL Nano-layered
# 2390 Ultrahard
#2391 Ultrahard
#2393 Ultrahard Variable Edge Prep
Cutting Speed: 120 m/min,
Feed Rate: 0.075 mm/rev,
Depth of Cut: 1.000 mm
Turning Test Results
22
The Micro Machining Process (MMP)
Figure: The Micro Machining Process (MMP) and Cutting Tool Super Finishing.
The lowest frequency range is the "Form" of the part, and this is what
the designer sees on his CAD screen and is what he is ultimately trying to
manufacture. Layered on top of the Form is the "Waviness", which is
caused by the clearances built into the cutting machine that allow it to move
freely. Layered on top of the Waviness is the "Primary Micro Roughness",
which is normally attributed to the movement of the cutting tool as it
removes material, and is usually similar in shape to the cutting tool
geometry. Finally, layered on top of the Primary Micro Roughness is the
"Secondary Micro Roughness", which results from the roughness on the
surface of the cutting tool that was imparted on it during its manufacturing
process and is now being transferred to the part being cut.
23
Friction at the Tool-Work-Chip Interface
Figure: Effect of Feed Rate on the Coefficient of Friction
(with/without coolant application)
24
Cutting Speed: 100 m/min,
Feed-Rate: 0.075 mm/rev,
Depth of Cut: 1.000 mm,
Coolant: (5% vol.) Trim Sol
Figure: Maximum Tool-Wear v/s Machining Time
Turning Test Results
25
Figure: Maximum Tool -Wear v/s Machining Time
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25 30 35 40 45 50
Uncoated (K313) Coated C-8 Coated C-15 Coated C2-SL Superfinish Coated C-16 Ultrahard #2390 Ultrahard #2391 Ultrahard 2414 (2393)
Cutting Time (min)
Maxim
um
To
ol W
ear
(mm
)
Coated C-16
Ultrahard # 2391
Super-finished Cutting Edge
Coated C- 8
Ultra-hard # 2414 (2393)
Uncoated (K313)
Ultrahard # 2390
Coated C-15
Coated C2 -SL
Turning Test Results
Cutting Speed - 120 m/min;
Feed Rate - 0.075 mm/rev;
Depth of Cut - 1.000 mm,
Cutting Fluid - Trim Sol (5% vol.)
26
Magnetic Field Assisted Super-Finishing
Figure: Magnetic Field Assisted Super-Finishing of Carbide Insert
(Courtesy of University of Florida, Gainesville, FL)
27
Edges of Carbide Inserts Super-Finished
28
Insert Surface-Finish Measurement
29
Polished Surface Roughness
30
Some Recent Turning Test Results
31
Conclusions and Future Work
• Several oblique (3-D) turning tests have been conducted using
uncoated, coated, cutting edge having micro-edge geometry, and
super-finished cutting edge carbide inserts.
• It seems that a few coatings may prove to be a good candidate
for machining of Titanium alloys.
• Super-finished cutting edge inserts show enhanced (~2X) tool life
in comparison to other uncoated and coated inserts.
• Further experiments are being conducted using super-finished
edged cutting tools with the goal of optimizing the level of super-
finishing that will provide maximum enhancement in tool-life and
productivity while turning Ti-6Al-4V Titanium alloy.
32
Acknowledgment
• TechSolve wishes to thank Professor Hitomi,
University of Florida, Gainesville, FL; MicroTek
& UES, Inc., OH; Richter Precision Inc. &
Conicity Technologies, PA for providing ultra-
hard, nano-layered coated, special micro-edge
and super-finished cutting edge prep inserts
used for this study.
• Special thanks to National Science Foundation
(NSF) for supporting this research under the
Award No. 0757954.