The document describes a two-step finite element simulation of diamond-coated cutting tools. In the first step, a cohesive zone model is used to analyze residual stresses deposited during the coating process. In the second step, a 2D cutting simulation is performed using the residual stresses as initial conditions. The effects of fracture energy, interface strength, deposition temperature, and cutting parameters on coating delamination are investigated. The simulations demonstrate that residual stresses significantly impact coating failure during cutting, and failure is more likely with higher stresses, lower interface strength, or increased uncut chip thickness.

1. IMPLEMENTING A COHESIVE ZONE INTERFACE
IN A DIAMOND-COATED TOOL FOR 2D CUTTING
SIMULATIONS
Feng Qin
Ninggang (George) Shen
Dr. Kevin Chou
11/15/2012
The University of Alabama-Mechanical Engineering 1

2. Outline of the contents
1. Introduction
2. Cohesive zone model
3. Two-step FE model application
4. Simulation results analysis
5. Conclusions
6. Future work
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3. 1. Introduction and research objectives
Diamond cutting tools
• PCD tools and CVD coated tools
Applicable work materials
• High-Si Al alloys, A390
• Metal matrix composite, A359/SiC-20p
• Plastic matrix composite, CFRP
• Automotive
• Aerospace
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4. 1. Introduction and research objectives
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5. 1. Introduction and research objectives
Methodology
• A two-step 2D cutting simulation
• Residual deposition stress analysis (various CZM or process parameters)
• 2D cutting simulation (various cutting parameters)
Objective/Significance
• Couple the effect of coating deposition
• Investigate the effect of CZM or process parameters on coating delamination
• Understand the effect of residual deposition stresses on cutting process
• Demonstrate the feasibility of evaluating coating delamination of a diamond-coated tool
during cutting
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6. 2. Cohesive zone model
σ Cohesive crack tip 1.2
1
σmax 0.8
Tn/σmax
0.6
0.4
0.2
0
δmax 0 0.5 1 1.5
δ
δn
forward wake
Fig. 2 The cohesive zone model for normal traction
Fig. 1 Typical traction-separation response [1]
mode described by Geubelle & Baylor [2].
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7. 2. Cohesive zone model
Nomenclature:
- Interface normal strength
For δn >0
- Interface tangential strength
- Interface characteristic length parameter
- Critical normal and tangential separations
- Non-dimensional normal, tangential and
For δn = 0
total displacement
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8. 3. Two-step FE model application
Coating and substrate geometry
Tool material Abaqus Mesh, BCs and
property CAE interactions
Deposition
Cohesive zone temperature
Abaqus
(material, elem field, BCs, interacti
input file
ents, etc.) ons and output
variables
Coupled thermal-mechanical
simulation for deposition process
Workpiece
Coupled thermal- BCs
geometry,
mechanical (speed), outp
mesh, ALE
simulation for ut variables
and
cutting process and
material
interactions
Coupled thermal-
mechanical simulation New BC for
for workpiece workpiece
withdrawal simulation (displacement load)
Fig. 3 Flowchart of the simulations with cohesive zone residual stress included in a diamond-coated tool.
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9. 3. Two-step FE model application
Coating Cohesive zone
• Geometry
 Edge radius (re) = 50 µm
 Coating thickness (t) = 15 µm
• Mesh Substrate
 Coating: Automatic structural meshing
 Substrate: Free meshing
 Cohesive zone: Manual structural meshing
• Element
 Coating & substrate: CPE4RT
 Cohesive zone: COH2D4
Fig. 4 Tool geometry and configuration
• Analysis: Explicit coupled thermal-displacement for both steps
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10. 3. Two-step FE model application
Tab. 1 The Cohesive Zone Parameters for the Diamond-
Coated WC Tool
Fracture Deposition
σmax τmax
Material # E/GPa G1/GPa energy temperature
/MPa /MPa
(J/m2 ) /˚C
1 5 5 500 100000 100 800
2 4 4 400 100000 80 800
3 5 5 500 100000 100 600
Tab. 2 Material Properties of the WC-Co Substrate [3,4]
E (GPa) ν σ0 (MPa) n σy (GPa)
620 0.24 18036 0.244 5.76
Fig. 5 Cohesive zone failure after deposition.
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11. 3. Two-step FE model application
Tab. 3 Parameters & CZ properties in 2D cutting simulation
Parameters Values
Edge radius, re (μm) 50
Coating thickness, (μm) 15
Chip
flow Cutting speed, v (m/sec) 5
Uncut chip thickness, tc (mm) 0.05, 0.45
Cohesive fracture energy (J/m2) 100
Inflow Interfacial tensile strength, σmax (MPa) 500
Deposition temperature ( C) 600
Outflow
Fig. 6 Configuration of the 2D cutting simulation
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12. 4. Simulation results analysis
Fracture energy effect
(a) (a)
(b) (b)
Fig. 7 σn results of cohesive zone at different fracture energy Fig. 8 σn responses for different interface normal strength
values after deposition at (interface strength 500 MPa): (fracture energy: 100 J/m2): (a) 500 MPa; (b) 400 MPa.
(a) Fracture energy 80 J/m2; (b) Fracture energy 100 J/m2.
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13. 4. Simulation results analysis
Original View Zoom-in View
tc = 5 μm
tc = 45 μm
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14. 4. Simulation results analysis
(a) (b)
Fig. 9 Stress state of tool and workpiece at the beginning of the simulation (a) and during the simulation (b).
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15. 4. Simulation results analysis
(a) (b)
Fig. 10 Initial cohesive zone failure during the cutting: (a) Auto-Fit view; (b) Zoom-in view.
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16. 4. Simulation results analysis
(a) (b)
T-S curve for node 224 and 145
(c) 500 (d)
224
400
Tn -S22 (MPa)
145
300
200
100
0
0 0.0002 0.0004 0.0006
Δn-e22 (mm)
Fig. 11 Zoomed-in view of coating delamination evolution:
(a) Initial cohesive failure after deposition; (b) Steady cohesive failure during cutting;
(c) Final cohesive failure after tool withdrawal;
(d)Traction-separation curve for nodes in an alive and failed element, respectively.
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17. 5. Conclusions
• Interface delamination is the major failure mode for diamond-coated tools.
Due to insufficient adhesion, and induced deposition stresses and thermo-mechanical loads
during machining
• A cohesive zone model is included with deposition stresses in 2D FE simulations
Different cohesive fracture energy values and different interface normal strengths employed
in the cutting simulations
• Significant effect of residual deposition stresses on cohesive zone failure
The higher the stress is, the easier to fail.
• Cohesive interface failure can be predicted for diamond-coated tool with
Incorporated the deposition residual stress as the initial condition in cutting simulation
• Cohesive failure is sensitive to the cutting parameter
The larger the uncut chip thickness is, the easier to fail.
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18. 6. Future work
• Deposition temperature
• Tool geometry
• Cutting parameters
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19. Acknowledgement
Sponsor: NSF, Grant #: 0728228 and 0928627
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20. Q&A
Thank you for your attention!
Any Question?
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21. Reference
[1] Hu, J., Chou, Y. K., & Thompson, R. G. (2008). Cohesive zone effects on coating failure evaluations of diamond-
coated tools. Surface and Coating Technology, 203, 730-735.
[2] Geubelle, P. H., & Baylor, J. S. (1998). Impact-induced delamination of composites: a 2D simulation.
Composites Part B: Engineering, 29 (5), 589-602.
[3] Qin, F. and Chou, Y. K. (2010). 2D Cutting Simulations with a Diamond-coated Tool Including Deposition
Residual Stresses, Transactions of NAMRI/SME, Vol. 38, pp. 1-8.
[4] Dias, A. M. S., Modenesi, P. J., & de Godoy, G. C. (2006). Computer simulation of stress distribution during
Vickers hardness of WC-6Co. Materials Research, Vol. 9, 73-76.
[5] Liu, C., Wu, B., and Zhang, J., 2010, "Numerical Investigation of Residual Stress in Thick Titanium Alloy Plate
Joined with Electron Beam Welding," Metallurgical and Materials Transactions B, 41(5), pp. 1129-1138.
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