High Speed Turning of Titanium (Ti-6Al-4V) Alloy · High Speed Turning of Titanium (Ti-6Al-4V)...

High Speed Turning

Titanium (Ti-6Al-4V) Alloy

Anil Srivastava, Ph.D. Manager, Manufacturing Technology

TechSolve, Inc., Cincinnati, OH 45237

Outline

• Applications of Titanium Alloys

• Technical Difficulties in Machining Titanium Alloys

• High Speed Turning of Ti-6Al-4V Alloy

• Some Recent Test Results

• Conclusions

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

• 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

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

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

(SFPM)

(in/rev)

DEPTH OF

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

• 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

• 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

Turning of Titanium (Ti-6Al-4V) Alloy

Experimental Set-up for Turning Tests

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)

Turning Test Results

Figure: Effect of Feed Rate on Average Cutting Force

0.025 0.05 0.075 0.1 0.125 0.15

Uncoated

C8 - Nanolayer Coated

C2-SL - Nanolayer Coated

2390 Ultrahard Coated

Variable Edge Prep

Feed Rate (mm/rev)

Cutting Speed - 240 m/min

Figure: Effect of Feed Rate on Average Cutting Force

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)

0.025 0.05 0.075 0.1 0.125 0.15

Uncoated

Variable Edge Prep

Feed Rate (mm/rev)

Figure: Effect of Cutting Speed on Average Cutting Force

100 120 140 160 180 200 220 240

Uncoated

C2-SL - Nanolayer Coated 2390 Ultrahard Coated

Variable Edge Prep

Feed Rate - 0.100 mm/rev

Cutting Speed (m/min)

100 120 140 160 180 200 220 240

Uncoated

Variable Edge Prep

Figure: Effect of Cutting Speed on Average Cutting Force

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

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

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

Uncoated C-8 Nano-layered

C-15 Nano-layered C2-SL Nano-layered

# 2390 Ultrahard

#2391 Ultrahard

#2393 Ultrahard Variable Edge Prep

# 2390 Ultrahard

#2391 Ultrahard

Cutting Speed : 240 m/min,

Feed Rate : 0.075 mm/rev,

Depth of Cut : 1.000 mm

Uncoated C-8 Nanolayered C-15 Nanolayered

# 2390 Ultrahard #2391 Ultrahard #2393 Ultrahard

# 2390 Ultrahard

#2391 Ultrahard

#2393 Ultrahard

# 2390 Ultrahard

#2391 Ultrahard

# 2390 Ultrahard

#2391 Ultrahard

# 2390 Ultrahard

#2391 Ultrahard

C-15 Nanolayered C2-SL Nanolayered

# 2390 Ultrahard

#2391 Ultrahard

Uncoated C-8 Nanolayered

C-15 Nanolayered C2-SL Nanolayered

# 2390 Ultrahard

#2391 Ultrahard

Depth of Cut: 1.00 mm)

Uncoated C-8 Nanolayered

# 2390 Ultrahard

#2391 Ultrahard

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.

Friction at the Tool-Work-Chip Interface

Figure: Effect of Feed Rate on the Coefficient of Friction

(with/without coolant application)

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

Figure: Maximum Tool -Wear v/s Machining Time

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)

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

Cutting Speed - 120 m/min;

Feed Rate - 0.075 mm/rev;

Depth of Cut - 1.000 mm,

Cutting Fluid - Trim Sol (5% vol.)

Magnetic Field Assisted Super-Finishing

Figure: Magnetic Field Assisted Super-Finishing of Carbide Insert

(Courtesy of University of Florida, Gainesville, FL)

Edges of Carbide Inserts Super-Finished

Insert Surface-Finish Measurement

Polished Surface Roughness

Some Recent Turning Test Results

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.

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.

Thank You !

High Speed Turning of Titanium (Ti-6Al-4V) Alloy · High Speed Turning of Titanium (Ti-6Al-4V)...

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