Research overview of Ti-6Al-4V machining project

1. ..:: PMRC
Microstructure Sensitive Constitutive
Modeling For Machining Applications
1 / 12
PI: Dr. Shreyes Melkote
Post-Doc: Dr. Buddhika Jayasena
GRAs: Rui Liu & Patxi Fernandez-Zelaia

2. ..:: PMRC
2 / 12
Outline
• Introduction
• Motivation
• Current Work
• Future Work

3. ..:: PMRC
3 / 12
Introduction
• Machining processes often
follow primary shaping
• Industrial applications
performed at high speeds
– Improved finish
– Decreased cutting forces
– Decreased thermal effects
– Improved production time
• Orthogonal cutting used to study
mechanics of process
– Plane strain
“Large Strain Deformation Field in
Machining” Lee et al. 2006

4. ..:: PMRC
4 / 12
Introduction
• Large imposed strains under
high rate deformation
– upto ~105 s-1, ε=~1-15
– Large temperature rise
• Thermo-mechanical loading
induces microstructural
evolution
“On the Metal Physical
Considerations in the
Machining of Metals”
Ramalingam & Black 1972 “Large strain deformation and ultra-fine grained
material by machining” Swaminathan et al. 2005

5. ..:: PMRC
5 / 12
Introduction
• Significant work performed to
study role of processing
conditions on microstructure
• Continuous DRX grain
refinement mechanism
associated with dislocation cell
formation and LABHAB
transition
“A study of the interactive effects of strain, strain
rate and temperature in severe plastic deformation of
copper” Brown et al. 2009
“Large strain deformation and ultra-fine grained
material by machining” Swaminathan et al. 2005
“Evolution of misorientation
distribution during warm ‘abc’ forging
of commercial-purity titanium”
Mironov et al. 2006

6. ..:: PMRC
6 / 12
Motivation
• Predictive capabilities needed
for design of machining
processes
– Cutting forces, temperature,
surface finish, processing
instabilities, workpiece
mechanical properties, etc..
– Johnson-Cook model typical
• Focus in machining community
has been on dynamics of
process, fixturing, etc..
– Simple/empirical material models
“Modified material constitutive models for serrated chip
formation simulations and experimental validation in
machining of titanium alloy Ti–6Al–4V” Sima and Özel
2010
“Severe plastic deformation (SPD) of titanium at
near-ambient temperature” Shankar et al. 2006

7. ..:: PMRC
7 / 12
Motivation
• Development of physics-based
microstructural sensitive models
improves predictive capabilities
– Greater control of manufacturing
process
– Design tool for engineers
– Improved model confidence and
range of applicability
“A model of continuous dynamic recrystallization”
Gourdet & Montheillet 2006
“A Rate-Sensitive Plasticity-Based Model for Machining
of Face-Centered Cubic Single-Crystals—Part I: Model
Development” Kota et al. 2011

8. ..:: PMRC
[Regazzoni, et al., 1987]
8 / 12
Current Work
Flow Stress
Strengthening due to
Dislocation Forests
σρ
Hall-Petch Equation Taylor’s Equation [Follansbee & Kocks, 1988]
흈흆 = 휶흆푮풃 흆
Strengthening due to
Short Range Barriers
σs
흈풔 = 흈ퟎ ퟏ −
풌푻
품푮풃ퟑ 풍풏
휺 ퟎ
휺
ퟏ
풒
ퟏ
풑
Strengthening due to
Grain Boundaries
σG
흈푮 =
풌푮
푫
Strengthening due to
Viscous Drag
σD
흈푫 =
푴푩
흆풎풃ퟐ 휺
흆 = Δ흆 푫푹푿 + 흆푯&푫푹
Hardening & Dynamic Recovery
풅흆
풅휺
= 푨 흆 − 푩 휺 , 푻 흆
흆푯&푫푹 =
푨
푩
+ 흆ퟎ −
푨
푩
풆−
푩휺
ퟐ
ퟐ
Dynamic Recrystallization
푫 = 푫풇 + 푫ퟎ − 푫풇 풕풂풏풉
휺풓
휺
풖
Δ흆 푫푹푿 = 풌 휺 , 푻
ퟐ
푫ퟎ
−
ퟐ
푫
[Estrin & Mecking, 1984]
• Synopsis of the Unified Model
 Phenomenological microstructure evolution laws

9. ..:: PMRC
9 / 12
Current Work
• Model calibrated using
available data in literature
– Limited to large-strain/low-rate
and low-strain/high-rate
data
– Machining uniquely offers
deformation to large strains
and high rates
Experimental data for CP-Ti: Nemat-Nasser, S.,
et al. (1999)

10. ..:: PMRC
10 / 12
Current Work
• Orthogonal cutting tests on
CP-Ti Gr2 for model
validation
– Force measurement
– Chip morphology
characterization
• Limited Microscopy
– SEM images “featureless”
– Working towards TEM sample
prep

11. ..:: PMRC
11 / 12
Future Work
• Grain size characterization
– Others have successfully used
SEM-OIM techniques for refined
microstructures in CP-Ti
• Hardness measurements
– Validation of model hardening
prediction
• Extension towards α-β Ti-6Al-4V
– Homogenization challenges for
dual phase material
– Additional cutting tests &
microscopy
“Large strain deformation and ultra-fine grained
material by machining” Swaminathan et al. 2005
“Evolution of misorientation
distribution during warm ‘abc’ forging
of commercial-purity titanium”
Mironov et al. 2006

12. ..:: PMRC
12 / 12
Questions?
Questions?