High Speed Turning of 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 2 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 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 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. 4 (Courtesy of Supra Alloys, Inc.) 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 5 Effect of Cutting Speed and Feed on Tool-Life Table: Typical parameters for turning Ti-6Al-4V gas turbine components CUTTING DEPTH OF TOOL FEED OPERATION SPEED CUT MATERIAL (in/rev) (SFPM) (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 (Courtesy of Supra Alloys, Inc.) Figure: Effect of cutting speed and feed on tool-life when turning Ti-6Al-4V 6 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 High Speed Turning of Titanium (Ti-6Al-4V) Alloy Turning Test Conditions • 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.) 9 Turning of Titanium (Ti-6Al-4V) Alloy Experimental Set-up for Turning Tests 10 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 Figure: High Magnification XTEM Bright Field Image of C2-SL Superlattice Coating. 3. #2393/#2414: HfB2 coating (1 & 2 PVD; 3 is PVD+CVD coating) 11 Turning Test Results 1800 Uncoated Cutting Speed - 240 m/min 1600 C8 - Nanolayer Coated C15 - Nanolayer Coated 1400 C2-SL - Nanolayer Coated 1200 2390 Ultrahard Coated 2391 Ultrahard Coated 1000 2393 Ultrahard Coated 800 Variable Edge Prep 600 Average Cutting (N) ForceCutting Average 400 200 0 0.025 0.05 0.075 0.1 0.125 0.15 Feed Rate (mm/rev) Figure: Effect of Feed Rate on Average Cutting Force 12 Turning Test Results 1400 Uncoated Cutting Speed - 200 m/min C8 - Nanolayer Coated 1200 C15 - Nanolayer Coated (N) C2-SL - Nanolayer Coated 1000 2390 Ultrahard Coated 2391 Ultrahard Coated 800 2393 Ultrahard Coated Variable Edge Prep 600 400 Average Cutting ForceCutting Average 200 0 0.025 0.05 0.075 0.1 0.125 0.15 Feed Rate (mm/rev) 350 Cutting Speed - 120 m/min 300 (N) 250 200 150 100 Uncoated C8 - Nanolayer Coated C15 - Nanolayer Coated C2-SL - Nanolayer Coated 50 2390 Ultrahard Coated 2391 Ultrahard Coated Average Cutting ForceCutting Average 2393 Ultrahard Coated Variable Edge Prep 0 0.025 0.05 0.075 0.1 0.125 0.15 Feed Rate (mm/rev) Figure: Effect of Feed Rate on Average Cutting Force 13 Turning Test Results 1400 Uncoated Feed Rate - 0.125 mm/rev C8 - Nanolayer Coated 1200 C15 - Nanolayer Coated C2-SL - Nanolayer Coated (N) 1000 2390 Ultrahard Coated 2391 Ultrahard Coated 800 2393 Ultrahard Coated Variable Edge Prep 600 400 200 Average Cutting ForceCutting Average 0 100 120 140 160 180 200 220 240 Cutting Speed (m/min) 1800 Uncoated 1600 C8 - Nanolayer Coated Feed Rate - 0.100 mm/rev C15 - Nanolayer Coated (N) 1400 C2-SL - Nanolayer Coated 2390 Ultrahard Coated 1200 2391 Ultrahard Coated 1000 2393 Ultrahard Coated Variable Edge Prep 800 600 400 Average Cutting ForceCutting Average 200 0 100 120 140 160 180 200 220 240 Cutting Speed (m/min) Figure: Effect of Cutting Speed on Average Cutting Force 14 Turning Test Results 1600 Feed Rate - 0.075 mm/rev 1400 Uncoated (N) C8 - Nanolayer Coated 1200 C15 - Nanolayer Coated 1000 C2-SL - Nanolayer Coated 2390 Ultrahard Coated 2391 Ultrahard Coated 800 2393 Ultrahard Coated Variable Edge Prep 600 400 200 Average Cutting Force Cutting Average 0 100 120 140 160 180 200 220 240 Cutting Speed (m/min) 250 Feed Rate - 0.050 mm/rev 200 150 Uncoated 100 C8 - Nanolayer Coated C15 - Nanolayer Coated Cutting Force (N) Force Cutting C2-SL - Nanolayer Coated 2390 Ultrahard Coated 50 2391 Ultrahard Coated 2393 Ultrahard Coated Variable Edge Prep Average 0 100 120 140 160 180 200 220 240 Cutting Speed (m/min) Figure: Effect of Cutting Speed on Average Cutting Force 15 Turning Test Results Uncoated C-8 Nano-layered # 2390 Ultrahard C-15 Nano-layered #2393 Ultrahard Cutting Speed: 240 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 16 Turning Test Results Uncoated C-8 Nano-layered # 2390 Ultrahard Uncoated 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 : 240 m/min, Cutting Speed: 240 m/min, Feed Rate : 0.075 mm/rev, Feed Rate: 0.050 mm/rev, Depth of Cut : 1.000 mm Depth of Cut: 1.000 mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 17 Turning Test Results Uncoated C-8 Nano-layered # 2390 Ultrahard Uncoated C-8 Nanolayered C-15 Nanolayered C-15 Nano-layered C2-SL Nano-layered #2391 Ultrahard # 2390 Ultrahard #2391 Ultrahard #2393 Ultrahard #2393 Ultrahard Cutting Speed: 200 m/min, Cutting Speed: 200 m/min, Feed Rate: 0.125 mm/rev, Feed Rate: 0.100 mm/rev, Depth of Cut: 1.000 mm Depth of Cut: 1.000 mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 18 Turning Test Results Uncoated C-8 Nano-layered # 2390 Ultrahard Uncoated 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, Cutting Speed: 200 m/min, Feed Rate: 0.075 mm/rev, Feed Rate: 0.050 mm/rev, Depth of Cut: 1.000 mm Depth of Cut: 1.000 mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 19 Turning Test Results Uncoated C-8 Nano-layered # 2390 Ultrahard Uncoated 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, Cutting Speed: 120 m/min, Feed Rate: 0.125 mm/rev, Feed Rate: 0.100 mm/rev, Depth of Cut: 1.000 mm Depth of Cut: 1.000 mm Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 20 Turning Test Results Uncoated C-8 Nanolayered # 2390 Ultrahard Uncoated C-8 Nanolayered # 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, Cutting Speed: 120 m/min, Feed Rate: 0.075 mm/rev, Feed Rate: 0.050 mm/rev, Depth of Cut: 1.000 mm Depth of Cut: 1.00 mm) Figure: Tool Wear during Machining of Titanium (Ti-6Al-4V) Alloy 21 The Micro Machining Process (MMP) Figure: The Micro Machining Process (MMP) and Cutting Tool Super Finishing.