High Speed Turning of Titanium (Ti-6Al-4V) Alloy. Anil Srivastava, Ph.D. Manager, Manufacturing Technology TechSolve, Inc., Cincinnati, OH 45237

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1 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 2

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 3

4 Machining Titanium for Economical Production BASIC RULES 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 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. 4 (Courtesy of Supra Alloys, Inc.)

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 costintensive 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,

6 Effect of Cutting Speed and Feed on Tool-Life OPERATION Table: Typical parameters for turning Ti-6Al-4V gas turbine components TOOL MATERIAL CUTTING SPEED (SFPM) FEED (in/rev) DEPTH OF CUT (in) Turn (Rough) C Turn (Finish) C Turn (Finish) C (Courtesy of Supra Alloys, Inc.) Figure: Effect of cutting speed and feed on tool-life when turning Ti-6Al-4V 6

7 Issues with Increasing Productivity and Possibilities 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. 7

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

9 Turning Test Conditions Work Material : Titanium (Ti-6Al-4V) Alloy Bar (2 in diameter) Tool Holder : Type CTGPL 164 Cutting Tool : /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 : (0.050), (0.075), (0.100), (0.125) IPR (mm/rev.) Depth of Cut : (1.000) in (mm) Cutting Fluid : few tests without coolant and few with flooded coolant application (Trim Sol 5% vol.) 9

10 Turning of Titanium (Ti-6Al-4V) Alloy Experimental Set-up for Turning Tests 10

11 Types of Nano-layered and Ultra-hard Coatings 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: HfB 2 coating Figure: High Magnification XTEM Bright Field Image of C2-SL Superlattice Coating. (1 & 2 PVD; 3 is PVD+CVD coating) 11

12 Average Cutting Force (N) Turning Test Results C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Cutting Speed m/min Feed Rate (mm/rev) Figure: Effect of Feed Rate on Average Cutting Force 12

13 Average Cutting Force (N) Average Cutting Force (N) Turning Test Results C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Cutting Speed m/min Cutting Speed m/min Feed Rate (mm/rev) C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated Ultrahard Coated 2391 Ultrahard Coated Ultrahard Coated Variable Edge Prep Feed Rate (mm/rev) 13 Figure: Effect of Feed Rate on Average Cutting Force

14 Average Cutting Force (N) Average Cutting Force (N) Turning Test Results 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 C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Cutting Speed (m/min) Feed Rate mm/rev Cutting Speed (m/min) 14 Figure: Effect of Cutting Speed on Average Cutting Force

15 Average Cutting Force (N) Turning Test Results Feed Rate mm/rev C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Cutting Speed (m/min) 250 Feed Rate mm/rev Average Cutting Force (N) C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated Ultrahard Coated 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Cutting Speed (m/min) 15 Figure: Effect of Cutting Speed on Average Cutting Force

16 Turning Test Results C-8 Nano-layered # 2390 Ultrahard C-15 Nano-layered #2393 Ultrahard Cutting Speed: 240 m/min, Feed Rate: mm/rev, Depth of Cut: mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 16

17 Turning Test Results C-8 Nano-layered # 2390 Ultrahard C-8 Nano-layered # 2390 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard #2393 Ultrahard Variable Edge Prep Cutting Speed : 240 m/min, Feed Rate : mm/rev, Depth of Cut : mm #2393 Ultrahard Variable Edge Prep Cutting Speed: 240 m/min, Feed Rate: mm/rev, Depth of Cut: mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 17

18 Turning Test Results C-8 Nanolayered C-15 Nanolayered C-8 Nano-layered # 2390 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard # 2390 Ultrahard #2391 Ultrahard #2393 Ultrahard #2393 Ultrahard Cutting Speed: 200 m/min, Feed Rate: mm/rev, Depth of Cut: mm Cutting Speed: 200 m/min, Feed Rate: mm/rev, Depth of Cut: mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 18

19 Turning Test Results C-8 Nano-layered # 2390 Ultrahard C-8 Nano-layered # 2390 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard #2393 Ultrahard Variable Edge Prep #2393 Ultrahard Variable Edge Prep Cutting Speed: 200 m/min, Feed Rate: mm/rev, Depth of Cut: mm Cutting Speed: 200 m/min, Feed Rate: mm/rev, Depth of Cut: mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 19

20 Turning Test Results C-8 Nano-layered # 2390 Ultrahard C-8 Nano-layered # 2390 Ultrahard C-15 Nanolayered C2-SL Nanolayered #2391 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard #2393 Ultrahard Variable Edge Prep #2393 Ultrahard Variable Edge Prep Cutting Speed: 120 m/min, Feed Rate: mm/rev, Depth of Cut: mm Cutting Speed: 120 m/min, Feed Rate: mm/rev, Depth of Cut: mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 20

21 Turning Test Results C-8 Nanolayered # 2390 Ultrahard C-8 Nanolayered # 2390 Ultrahard C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard C-15 Nanolayered C2-SL Nanolayered #2391 Ultrahard #2393 Ultrahard Variable Edge Prep Cutting Speed: 120 m/min, Feed Rate: mm/rev, Depth of Cut: mm #2393 Ultrahard Variable Edge Prep Cutting Speed: 120 m/min, Feed Rate: mm/rev, Depth of Cut: 1.00 mm) Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 21

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. 22

23 Friction at the Tool-Work-Chip Interface Figure: Effect of Feed Rate on the Coefficient of Friction (with/without coolant application) 23

24 Turning Test Results Cutting Speed: 100 m/min, Feed-Rate: mm/rev, Depth of Cut: mm, Coolant: (5% vol.) Trim Sol Figure: Maximum Tool-Wear v/s Machining Time 24

25 Maximum Tool Wear (mm) Turning Test Results (K313) Coated C-8 Coated C-15 Coated C2-SL Superfinish Coated C-16 Ultrahard #2390 Ultrahard #2391 Ultrahard 2414 (2393) Coated C-16 Ultrahard # 2391 (K313) Coated C Coated C2 -SL Coated C-15 Ultra-hard # 2414 (2393) 0.1 Ultrahard # 2390 Super-finished Cutting Edge Cutting Time (min) Cutting Speed m/min; Feed Rate mm/rev; Depth of Cut mm, Cutting Fluid - Trim Sol (5% vol.) Figure: Maximum Tool -Wear v/s Machining Time 25

26 Magnetic Field Assisted Super-Finishing Figure: Magnetic Field Assisted Super-Finishing of Carbide Insert (Courtesy of University of Florida, Gainesville, FL) 26

27 27 Edges of Carbide Inserts Super-Finished

28 28 Insert Surface-Finish Measurement

29 29 Polished Surface Roughness

30 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 superfinishing that will provide maximum enhancement in tool-life and productivity while turning Ti-6Al-4V Titanium alloy. 31

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 ultrahard, 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

33 Thank You!?