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© Fraunhofer IPA
Practical Comparison between the Finite-Element and Mesh-Free Calculation Methods in the
Analysis of Machining Simulations
Fraunhofer Institute for Manufacturing Engineering and Automation IPA
M.Sc. Hector Vazquez Martinez Department of Lightweight Construction Technologies
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Machining processes
Turning
Drilling
Milling
Sawing
Analyzed variables
Cutting forces
Temperature
Stress
Strain
Chip formation
Simulation in the Machining Technology
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Tool development through virtual experimentation
Determination of the relationships between:
cutting and process parameters
stress, strain and temperature development inside the process
Integration of process simulation in the machining technology
Approximation and close analysis of the
high thermo-mechanical loading
conditions inside the process
© Fraunhofer IPA
Department of Lightweight Construction Technologies
High deformation (e)
Effects of strain rate (e)
Effects of temperature (T)
Node separation
Elements deletion
Remeshing
Mesh-free methods
Material separation methods Models of material kf (e, e, T)
Contact and interaction between several bodies
High dynamic (vc > 1 m/s)
High plastic deformation (e > 0.5)
Material separation takes place
Characteristics of machining simulations
Settings for the simulation
Main requirements in the simulation of machining processes
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Alternative numerical methods in LS-Dyna
FEM Finite element method
• Discretization into a
grid of finite elements
• Element based connectivity
• Requires additional separation or fracture formulations
SPH Smoothed particle
hydrodynamics
• Discretization through SPH-particles
• Absence of an interconnected grid
• A smoothing function defines an influence length and interaction strength between particles
• Allows the modeling of solid and fluids
DEM …
EFG Element free Galerkin
• Mesh free principle
• Weak formulation of the method has a higher order
• Mesh supports contact and boundary conditions
• The user interface in LS-Dyna for EFG is not fully implemented
Mesh dependent Mesh free
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Schematic representation of a turning process simulation
Representation of turning processes into 2D-FE-simulations
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Design of a turning process simulation Mechanical 3D-Simulation
1,5 mm
Tool
Calculation methods: FEM / SPH / EFG
Software: LS-Dyna, version 7.1.1
Process : Orthogonal turning
Cutting distance: 0.85 [mm]
Termination time: 0.17 [ms]
Cutting tool
Material: Tungsten carbide (WC)
Element type: rigid shell elements
Number of elements: 16,500
Smallest element size: 3 µm
Work piece
Material: Al7075
Material model: Plastic kinematic (MAT_003)
Rake angle
Clearance angle
7° 6°
Cutting speed vc
Cutting width b
Cutting depth h
300 [m/min]
0.25 [mm]
0.1 [mm]
Process parameters
Cutting radius r
0.01 [mm]
h
0,4 mm
Work piece
vc
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Design of a turning process simulation Simulation parameters
Interface properties
Contact: nodes to surface
Sliding friction coefficient: µ = 0.1
Parameters of the FEM simulations
Element types: tetrahedral volume elements
Number of elements//nodes: 30,000//50,000
Smallest element size: 9 [µm]
Separation: Adaptive remeshing
Parameters of the SPH simulations
Element types: SPH
Number of particles: 40,000
Separation: -none-
Parameters of the EFG simulations
Number of elements//nodes: 30,000//50,000
Smallest element size: 9 [µm]
Separation: Adaptive remeshing
FEM
EFG
SPH
© Fraunhofer IPA
Department of Lightweight Construction Technologies
FEM
Comparison between FEM, EFG and SPH Chip formation
FEM
EFG
SPH
“Stiff” chip formation: the SPH deformation is also dependent on the
smoothing equation of the method
Similar chip formations
All the chip formations are fully dependent on the numerical formulations in each method
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Comparison between FEM, EFG and SPH Strain
SPH
Strain [mm/mm] 6.5 0
FEM
EFG
eMAX = 2.8
eMAX = 3.3
eMAX = 6.5
© Fraunhofer IPA
Department of Lightweight Construction Technologies
SPH
Stress [MPa] 1500 0
FEM
EFG
Comparison between FEM, EFG and SPH Stress
sMAX = 980 [MPa]
sMAX = 1500 [MPa]
sMAX = 1750 [MPa]
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Comparison between FEM, EFG and SPH Cutting force Fx
EFG
Time
Cu
ttin
g f
orc
e F
x
35
0
[N]
25
20
15
10
5
0.05 0 [ms] 0.15
FEM
An increase of the
particles number
may reduce the high
fluctuation
Average force [N]
FEM SPH EFG
26 13 32
SPH
Methods with lowest fluctuations
© Fraunhofer IPA
Department of Lightweight Construction Technologies
03:52
09:45
04:19
00:00
02:00
04:00
06:00
08:00
10:00
FEM EFG SPH
[hours:min]
Comparison between FEM, EFG and SPH Calculation time und memory usage
Co
mp
uta
tio
na
l ti
me
0,0
0,3
0,6
0,9
1,2
1,5
FEM EFG SPH
[GB]
2320 2620
435
0
600
1200
1800
2400
3000
FEM EFG SPH
[MB]
Vo
lum
e o
f d
ata
sto
rag
e
Av
era
ge
RA
M
usa
ge
1.3
0.9
1.4
1.5
0.9
0.6
0.0
0.3
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Comparison between FEM, EFG and SPH Conclusions
Stability # error reports
Manageability # configuration steps and cards
Theoretical precis ion
Field of application
FEM General
applications
EFG Analyses of
deformation (chip formation)
SPH Introductory
process analysis
Good properties
Manageable environment
Rough environment
Lowest calculated
values
Highest time and memory
costs
Numerical error reports take place at the beginning
No need of separation criterion
Formulation equations of higher order
Setup over the k-file Dependency on the smoothing function
© Fraunhofer IPA
Department of Lightweight Construction Technologies
Thank you for your attention!
Fraunhofer Institute for Manufacturing Engineering and Automation IPA Holzgartenstr. 17 | 70174 Stuttgart www.ipa.fraunhofer.de M.Sc.. Hector Vazquez Phone.: 0711 970-1551 Mail : hector.vazquez.martinez@ipa.fraunhofer.de
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