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MACHINING ADVANCED TITANIUM ALLOYS
Advantages of Difficult Ti Alloys
LightweightStrong at elevated temperaturesGamma Ti alloys are burn resistantAttractive to industryAerospaceAuto racing
Titanium AlloysAlpha alloys (Ti, lightly alloyed alloys)
Essentially pure titanium and relatively soft Chip control is a problem
Alpha/Beta alloys (Ti 6Al 4V) Very common More difficult to machine
Beta alloys (Ti 5553, Beta C, Ti 17) More heavily alloyed More difficult to machine due to hardness
Gamma alloys (TiAl) Of great recent interest Very difficult to machine
4Classification of Ti alloys
Ti-5Al-5V-5Mo-3Cr
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Ti 5Al-2.5Sn
α-alloyCharacterized by Satisfactory strength Toughness Creep resistance Weldability
Suitable for cryogenic applications (no ductile-brittle transition)Tensile strength 890MPa (129,000 psi), hardness 34 HRCCannot be heat treated
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Ti-6Al-4V
α+β alloyTypically Good fabricability High room temperature strength Moderate elevated temperature strength
Properties can be controlled by controlling the β phase through heat treatment More than 20% β makes the alloy difficult to weld
Typical tensile strength 950 Mpa (138,000 psi)
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Ti-10V-2Fe-3Al
Near β alloyβ alloys are generally formable and have a high cycle fatigue strengthDeveloped for airframe forging applicationsTypical tensile strength 1310MPa (190,000 psi), hardness 41HRCHeat treatable to very high strengths
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Ti-5Al-5V-5Mo-3Cr
Near β alloyCharacteristics: Low elastic modulus Good hardenability by heat treatment Low heat transfer rate Tensile strength1240 MPa (180,000 psi) Good strength to weight ratio
Ti-48Al-2Nb-2Cr
γ alloyExcellent high temperature propertiesBurn resistantVery low densityTypical tensile strength 1200 Mpa (175,000 psi)
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Photo courtesy of ATI
Opportunities and Challenges of Innovative Alloys
Material Machinability Rating Number of Inserts Required
Typical Al alloy 140 0.7
B1112 100 1
Ductile iron, 4140 50 2
Ti 6Al 4V 35 3
IN 718 15 6.6
Ti 5553 12 8.3
Ti Al 5 20
SP
ECIF
IC P
RO
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MS
Opportunities and Challenges of Beta and Gamma Ti Alloys
Low ductility Surface and sub-surface cracking Surface integrity compromised
Good high temperature strength High stress on cutting Tends to “crush” the cutting edge
Poor thermal conductivity Heat concentrated at cutting edge Tends to promote deformation and
cratering
Ti chemically reactive Cratering Danger of fire (alpha and some beta
alloys)
Photo courtesy of Aspinwall, et. al.University of Birmingham
Difficulties in Machining Titanium
Titanium alloys work harden – Notching
Titanium alloys have high heat capacity, low conductivity – heat concentrated at cutting edge
Deformation Wear Cratering Poor chip control
Titanium has a low modulus of elasticity - Part deflection
Titanium is reactive – built-up edge, cratering and fires
Chip Formation
Opportunities and Challenges of Innovative Alloys
Traditional techniques High pressure coolant High lead angles in turning Micrograin carbide Milling techniques: high feed, trochoidal, and
optimized roughing
Non-traditional techniques Diamond tools Laser assisted machining
Opportunities and Challenges of Innovative Alloys
Beta and Gamma alloys are difficult to machine
Special techniques are often used
No matter what technique is used, tool life is poor
Try to minimize amount of stock to be removed
Try to minimize heat
HIG
H P
RES
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Opportunities and Challenges of Innovative Ti Alloys
High pressure coolant may result in 10 fold improvement in tool life compared to conventional coolant
Flow rate may be more important than pressure
Running at too high pressure generates chips that interrupt coolant flow
A range of high performance tools designed to deliver coolant directly at the insert cutting zone.
Capable of delivering coolant pressures ranging from 15 – 4000 psi (1 to 275 bar)
High Pressure Coolant Systems
Cop
yrig
ht©
Sec
o To
ols
AB
Thin, High Velocity Chip
Small ConcentratedHeat Zone
Conventional Coolant
Cutting data 130 – 200 sfpm
Tool life is typically 20 minutes
Failure mode – typically flank wear
Feature - Long uncontrollable chips
High pressure coolant systems
Titanium 6AL4VLow ‘Thermal Conductivity &
Low Modulus of Elasticity.
Pressurised jet of coolant,directed at the cutting zone
Reduces temperature in cutting zone.Allowing higher cutting speed andlonger tool life.
Coolant pressure deflects chips to break into smaller more manageable pieces.
Pressurised Coolant
High pressure coolant systems
Requirements (checklist):At high pressure consider:
Encapsulation of machine. Exhaust/Ventilation. Filtration of coolant (particles in coolant may “sand blast”
surface) Increased consumption of coolant (+10%). Larger pump means higher volume -> bigger coolant tank. High pressure coolant beam may deform thin-walled
component. High pressure coolant beam can be harmful to hands and
fingers. The higher the pressure the more complex the system.
High pressure coolant systems
Benefits:
Elevated Cutting Data= Increased Productivity
Extended Tool-Life= Cost Reductions= Reduced Programme stops for Insert Indexing
Improved Chip Control= Less Downtime due to Operator Intervention
Improved Surface finish
High pressure coolant systems
Conventionalcoolant
High pressure coolant
Titanium Alloy Ti 6Al-4V (typical values)
Cutting speed +50%Cycle time reduction –50 %Insert consumption – 60 %Excellent chip control, fewer stops (see picture)Efficient coolant deliveryImproved surface finish
High pressure coolant systems
Customer Experience – Ti 6Al 4VConventional Coolant
Cycle time reduction 50% + Carbide consumption -60% + Efficient coolant delivery +++ Chip control +++ Improved surface finish
Conventional
High pressurecoolant
Ti 6Al-4V
Customer experience – blisk turning
Setup 4%
Index INS 10%
Remove Chips 14%
Machining 72%
Total cycle conventional coolant application
18 * index
17 * remove chips
Customer Experience – Ti 6Al 4V
Setup 11%
Index INS 7%
Remove Chips 0%
Machining 82%
5 * index
0 * remove chips
Total cycle for machining with Jetstream ToolingTM
Total time saved 240 min Increased machine usage
Customer Experience – Ti 6Al 4V
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Lead Angles - Taking the LeadMaterial = Inconel 625
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Lead Angles
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Lead AnglesMaterial = Inconel 625
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Some GuidelinesUse low cutting speeds.
Maintain high feed rates.
Temperature is not affected by feed rate as much as by speed, and the highest feed rates consistent with good machining should be used.
Use copious amounts of cutting fluid.
Use sharp tools and replace them at the first sign of wear. Tool failure occurs quickly after a small initial amount of wear.
Never stop feeding while tool and work are in moving contact. Allowing a tool to dwell in moving contact causes work hardening and promotes smearing, galling, seizing and tool breakdown.
DIA
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Titanium machining with PCDGeneral conclusions
Cooling of cutting edge is of outmost importance!Coolant pressure below 70 bar is not enough.Coatings improves tool life.R-style inserts are definitely preferable due to reduced heat concentration in cutting edge. E- and F-style inserts are more suitable in Ti 6-4, while S- and E-style is more suitable for Ti 5-5-5-3.
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RCMW 3, uncoated, vc 150 m/min, f 0.2 mm/rev, ap 0.5 mm, TIC 11 min, Ti 5553
RCMW 3, uncoated, vc 150 m/min, f 0.3 mm/rev, ap 0.5 mm, TIC 7 min, Ti 5553
Two casesDNGA 432E10-L1-K Fine grained PCD
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Vc 130 m/min Vc 170 m/min
Speed of 130 m/min (425 sfpm)EDS analysis
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Speed of 170 m/min (560 sfpm)EDS analysis
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Chemical wearMaterial build-up from
work piece on cutting edge.
Speed of 130 m/min (425 sfpm)
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Light grey areas = residues from work piece materialChemical wearMetal build-up
Speed of 130 m/min (425 sfpm)
11.12.2012 Stefan G Larsson
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Chemical wearNotch wearHeavy flank wearMaterial build-up from
work piece on cutting edge.
Speed of 170 m/min (560 sfpm)
11.12.2012 Stefan G Larsson
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Increased cutting speed results in higher temperatures in cutting zone. This leads to a greater and faster chemical wear of the PCD since Ti is a great carbide former.
Reduction of generated heat in cutting zone is necessary.
Adding of an inert, or near inert, zone between workpiece material and cutting edge could improve tool life.
Conclusions
11.12.2012 Stefan G Larsson
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Titanium machining with coated PCDResults
E10 edge prep.Coarse crater wearBig flank wear
E10 edge prep.More even wearLess flank wear
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RCMW 3, uncoated, vc 150 m/min, f 0.2 mm/rev, ap 0.5 mm, TIC 11 min, Ti 5553
RCMW 3, TiAlN, vc 150 m/min, f 0.2 mm/rev, ap 0.5 mm, TIC 11 min, Ti 5553
Cutting material
Fine grained PCD (2 microns) F - sharp
Coated Uncoated
E10 - hone
Coarse grained PCD (25 microns) F - sharp
Coated Uncoated
E10 - hone
Insert geometry RPMW 43
Ti 5553
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Test strategy
A number of variations in speed, feed, edge preparations, coating or not, and so on, were tested.
The best combination was then chosen to be run as a tool life test.
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Test 1
PCD05 F, uncoated4000 rpm - 502.6
m/min0.07 mm/tooth
Average chip thickness 0.022 mm
0.2 mm DOCConventional millingTIC 30 min
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Test 2
PCD05 F, uncoated4000 rpm - 502.6
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCConventional millingTIC 15 min
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Test 3
PCD05 F, uncoated4000 rpm - 502.6
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 15 min
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Test 4
PCD05 E10, uncoated4000 rpm - 502.6
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 15 min
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Test 5
PCD05 F, coated4000 rpm - 502.6
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 15 min
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Test 6
PCD30M F, uncoated4000 rpm - 502.6
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 15 min
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Test 7
PCD30M F, uncoated4000 rpm - 502.6
m/min0.18 mm/tooth
Average chip thickness 0.055 mm
0.2 mm DOCClimb millingTIC 11.7 min
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Test 8 (Repeat of 7 with the same edge)
PCD30M F, uncoated4000 rpm - 502.6
m/min0.18 mm/tooth
Average chip thickness 0.055 mm
0.2 mm DOCClimb millingTIC 23.4 min
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Test 9
PCD30M F, uncoated4500 rpm – 565.5
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 13.3 min
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Test 10
PCD30M F, coated4500 rpm – 565.5
m/min0.14 mm/tooth
Average chip thickness 0.044 mm
0.2 mm DOCClimb millingTIC 13.3 min
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Test 11
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingRepetition of test 6TIC 15 min
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Test 12 (Repeat of 11 with the same edge)
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingTIC 30 min
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Test 13 (Repeat of 11 with the same edge)
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingTIC 45 min
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Test 14 (Repeat of 11 with the same edge)
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingTIC 60 min
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Test 15 (Repeat of 11 with the same edge)
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingTIC 75 min
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Test 16 (Repeat of 11 with the same edge)
PCD30M F, coated4000 rpm – 502.6
m/min0.14 mm/tooth
Average chip thickness 0.031 mm
0.2 mm DOCClimb millingTIC 90 minNot end of tool life
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Alicona comparisons
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Test 1
Test 2
The same amount of materialremoved, but Test 2 hastwice as high feed as Test 1.
Observe that scales are different!
Alicona comparisons
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Test 3 – Climb milling
Test 2 – Conventional milling
Observe that scales are different!
Alicona measurements
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After test 16: 90 min TIC
Volume loss comparison
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TIC [min]
Test 1 30Test 2 15Test 3 15Test 4 15Test 5 15Test 6 15Test 7-8 23,4
Test 9 13,3Test 10 13,3
Test 11-16 90
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
200000
0
500000
1000000
1500000
2000000
2500000
3000000
3500000
4000000
4500000
Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Test 7-8 Test 9 Test 10 Test 11-16
Volu
me
loss
Volume loss comparison
Volume loss [μm³] Volume loss/time unit [μm³/min]
Volu
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loss
/tim
eun
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Summary
For milling, coarse grained PCD is the best choice.F-style edge prep is preferable.Coating does not have a big effect on tool life, but improves wear detection.
Avergage chip thickness should be 0.03-0.045 mm (0.001 – 0.002”)
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Summary
Stability problems Sensitive to find the right speed/feed combination Long tool solution at the end of the silent bar
Too low lubricant level in emulsionF-style edge prep is much more suitable for this application than first believedNiobium nitride improves tool life and reduces wearCombination of small depth of cut and the standard high pressure coolant inducer is not an optimized solution.
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Surface quality
2016-10-06 Stefan G Larsson
0.000.100.200.300.400.500.600.700.800.90
PCD05 PCD20 PCD30M
Ra after 1.75 minVc 175 m/min (575 sfpm) f 0.40 m/rev (0.016 ipr)
Chip formation
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Chip formation
Friction dependance Coating Grit size
Easier to handle small/short chips
2016-10-06 Stefan G Larsson
Coating
New combination coating for titanium machining
(Ti,Al)N+NbN
Reduces chemical wear
2016-10-06 Stefan G Larsson
Coolant
Most important points in titanium machining regarding coolant Flow rate Flow rate Flow rate Lubrication level Flow rate
2016-10-06 Stefan G Larsson
OP
TIM
IZED
RO
UG
HIN
G
Linear milling:ae = programmed ae
Effective ae
Arc Of Contact principles
ae
Arc of Contact increases as the tool enters a corner.If compensation in feedrate or Ae is not made, the tool will most likely become overloaded. Chatter Poor surface finish Tool breakage Increased build-up Undercut corners
Trochoidal/Hard Milling
R
ae
ά
Where :
R = Radius of tool
ae = radial depth of cut
ά = arccos (R-ae)/R))
The Arc Of Contact principle
Average Chip Thickness = sine(ά) X FPT
Small arc of contact
Big arc of contact
Big A.O.C=
Lower Vc
The Arc Of Contact principle
Optimized Roughing
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“Optimized roughing strategies”“Optimized roughing strategies”
Cutter diameter should be no larger than 70% of the slot width
Infeeds of less than 10% should be used Reduce the arc of contact to limit temperature
development Small radial cutting depth.
Trochoidal Milling
Optimized Roughing Strategies:
Strategies that actively manage all or a combination of the following cutting conditions: radial width of cut arc of contact chip thickness feedrate
Goal of these methods is to maximize MRR while smoothing machine load, increasing tool life, and reducing cycle time
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What NOT to do
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Best Tools: Many flutes
4+ flutes for medium steels, stainless steels, super alloys 2-4 flutes for aluminum alloys and soft steels 5+ flutes for hardened steels, super alloys
High Ap
Depths of cut up to 4XD are easily achieved in stable setups and good tool holders
Select tools with larger core diameters or with dual cores to maximize rigidity
Chip Control Chip splitters or corn cob style tools
Size Tool diameters depend on feature size Most common sizes:
1/2” – 5/8”
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Optimized Roughing Tools
Additional geometrical features
1* Dc
• Chips are split with a length of 1*Dc• Splits are positioned 0.25 * Dc after each other
Tooth 1 Tooth 2 Tooth 3 Tooth 4 Tooth 1
1*Dc0.25*Dc