MACHINING ADVANCED TITANIUM ALLOYS - mapyourshow.com · Titanium Alloys Alpha alloys (Ti, lightly alloyed alloys) Essentially pure titanium and relatively soft Chip control is a problem

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

5

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

6

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)

7

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

8

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)

9

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

BLE

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


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


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

SU

RE

CO

OLA

NT

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


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.


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


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


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

31

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

MO

ND

TO

OLS

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.

2016-10-06

34

RCMW 3, uncoated, vc 150 m/min, f 0.2 mm/rev, ap 0.5 mm, TIC 11 min, Ti 5553


Two casesDNGA 432E10-L1-K Fine grained PCD

11.12.2012

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Vc 130 m/min Vc 170 m/min

Speed of 130 m/min (425 sfpm)EDS analysis

11.12.2012

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Speed of 170 m/min (560 sfpm)EDS analysis

11.12.2012

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Chemical wearMaterial build-up from

work piece on cutting edge.

Speed of 130 m/min (425 sfpm)

11.12.2012

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Light grey areas = residues from work piece materialChemical wearMetal build-up


11.12.2012 Stefan G Larsson

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Chemical wearNotch wearHeavy flank wearMaterial build-up from

work piece on cutting edge.



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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


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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

2016-10-06

42


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


m/min0.14 mm/tooth


0.2 mm DOCConventional millingTIC 15 min

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Test 3


m/min0.14 mm/tooth


0.2 mm DOCClimb millingTIC 15 min

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Test 4

PCD05 E10, uncoated4000 rpm - 502.6

m/min0.14 mm/tooth



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Test 5

PCD05 F, coated4000 rpm - 502.6

m/min0.14 mm/tooth



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Test 6

PCD30M F, uncoated4000 rpm - 502.6

m/min0.14 mm/tooth



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Test 7


m/min0.18 mm/tooth


0.2 mm DOCClimb millingTIC 11.7 min

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Test 8 (Repeat of 7 with the same edge)


m/min0.18 mm/tooth



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Test 9

PCD30M F, uncoated4500 rpm – 565.5

m/min0.14 mm/tooth



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Test 10

PCD30M F, coated4500 rpm – 565.5

m/min0.14 mm/tooth



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Test 11


m/min0.14 mm/tooth


0.2 mm DOCClimb millingRepetition of test 6TIC 15 min

55



m/min0.14 mm/tooth



56



m/min0.14 mm/tooth



57



m/min0.14 mm/tooth



58



m/min0.14 mm/tooth



59



m/min0.14 mm/tooth


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

me

loss

/tim

eun

it

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.

2016-10-06

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


Chip formation

Friction dependance Coating Grit size

Easier to handle small/short chips


Coating

New combination coating for titanium machining

(Ti,Al)N+NbN

Reduces chemical wear


Coolant

Most important points in titanium machining regarding coolant Flow rate Flow rate Flow rate Lubrication level Flow rate


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

© 2016-10-06, all rights reserved

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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

MACHINING ADVANCED TITANIUM ALLOYS - mapyourshow.com · Titanium Alloys Alpha alloys (Ti, lightly alloyed alloys) Essentially pure titanium and relatively soft Chip control is a problem

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