Optimization of Laser Deposited Rapid Tooling D. Schwam and Y. Wang Case Western Reserve University NADCA DMC, Chicago – Feb.17, 2010
Download ReportTranscript Optimization of Laser Deposited Rapid Tooling D. Schwam and Y. Wang Case Western Reserve University NADCA DMC, Chicago – Feb.17, 2010
Slide 1
Optimization of Laser Deposited
Rapid Tooling
D. Schwam and Y. Wang
Case Western Reserve University
NADCA DMC, Chicago – Feb.17, 2010
1
Slide 2
Outline
• Objectives-why laser deposit?
• The POM process
• Preliminary thermal fatigue results
• In-plant evaluation of cores at
General Die Casters
• FEA optimization of laser deposited
layer
• Conclusions
2
Slide 3
Objectives – why laser deposit?
• Use of high thermal conductivity alloys in cores and
inserts can accelerate heat extraction, lower surface
temperature reduce soldering and shorten cycle time.
• Copper alloys have good thermal conductivity and are
cost effective candidates for this application.
• However, copper alloys dissolve in molten aluminum.
High temperature and high velocity molten metal flow
exacerbate dissolution.
• A layer of laser deposited H13 over the copper can
prevent dissolution.
3
Slide 4
Washout Damage at the Corners of Cu-Ni-Sn
Thermal Fatigue Specimens
ToughMet 3
ToughMet 2
ToughMet 2
0.5”
ToughMet 2
Copper alloys dissolve in molten aluminum
Slide 5
Metal Mold Material Properties
Product
420 Stainless
H-13 Tool Steel
Moldmax HH
Moldmax XL
Moldmax LH
P-20 Tool Steel
Protherm
Alloy 940
Alloy 18
Alloy 22
Tooling Grade
Aluminum
ToughMet 3
Hardness
(HRC)
50
45-50
40
30
30
30
20
16
B90
35
B88
32
Thermal Charpy V-Notch
Conductivity Impact Stregth
BTU/ft*hr*F
Ft*lb
10
5-10
15
8-14
60
4
35-40
10-15
75
12
17
20-25
145
50
120
30
35
N/A
23
2
90-95
22
30
N/A
Yield
Strength
ksi
200
200
155
100
140
120
90
65
30
55
Tensile
Stregth
ksi
250
250
185
110
170
140
115
96
95
100
Thermal
Expansion
Coefficient
10-6 / F
6.1
7.1
9.7
9.3
9.7
7.1
9.8
9.7
9.0
9.0
75-78
110
75-80
120
12.9
9.1
Slide 6
Rapid Tooling by DMD
Direct Metal Deposition of H13 on Copper - the POM Method
*-Courtesy POM
Slide 7
H13 / H13 sample – as deposited/ finished
H13 / Alloy 940 sample – as deposited/ finished
Slide 8
Slide 9
Evaluation of Laser Deposited Cores
The core is surrounded by molten aluminum and has a record of overheating
and soldering. Extracting heat more efficiently from the core can
lower maximum temperature, prevent soldering and allow shorter cycle times.
9
Slide 10
Typical H13 core with cooling line
10
Slide 11
Composite Core -- H13 Deposited on Cu
H13
Cu
11
Slide 12
Thermal Profile of Cover Half Steel During
Solidification
H-13 Core
Composite Core
At start of a cycle
12
Slide 13
Thermal Profile of Section Through Cover Half at Die Opening
H-13 Core
Composite Core
At 20 seconds
• Temperature of Composite Core is lower.
13
Slide 14
Temperature Advantage of the Copper Core
• Temperature of Composite Core is lower.
14
Slide 15
Creep Failure of in First Composite Core
The core shows creep damage after 250 cycles due to
insufficient stiffness and strength at high temperature.15
Slide 16
Surface Cracks in the H13 Layer
16
Slide 17
Remedial
Approaches
Caves in
Bulges out
The distortion of the
core seems to originate
from insufficient strength
and stiffness at the
operating temperature.
Anviloy and H13 cores
do not suffer from this
problem.
Priority 1 - Increase strength: use core as deposited
w/o tempering (downside-lower toughness).
Priority 2 - Increase thickness of H13 layer(downside
slows down heat transfer).
Slide 18
Optimization of the Laser Deposited H13
• The first core was tempered aggressively. The hardness
of the laser deposited H13 was reduced from 51HRC to
40 HRC to improve toughness. However, this reduced
the strength and caused excessive distortion. The core had
to be removed after 250 shots.
• A new core was made with the laser deposited H13 in
the as-deposited condition (no tempering) at 51HRC.
• This core has been in production at General Die Casters.
So far it has accumulated 5,000 shots.
18
Slide 19
FEA optimization of the H13
laser deposited layer thickness
• The 3D Die Casting model was simplified to a 2D axisymmetric FEA model and analyzed with commercial
FEA software Abaqus.
• The accuracy of 2D Abaqus analysis was verified by
comparing it to a 3D MagmaSoft simulation.
• Cyclic heat transfer and stress analysis was applied to
study the failure mechanism of the composite core.
• Composite cores with different H13 layer thickness and
hardness were compared, to optimize the design.
19
Slide 20
Finite Element Analysis Model
Mold
(H13)
Composite
Core:
Steel
(H13)
Casting
(A389)
Copper
(394)
2D Axi-symmetric model
20
Slide 21
Boundary Conditions
Simulation initial
conditions
Process flow chart:
Preheat (40 sec)
Casting Alloy
A389
Mold Material
H13
Furnace Temperature
Mold close, Metal
Injection and
Solidification (20 sec)
Mold open, Ejection,
air cooling (4 sec)
Spray cooling (3 sec)
Air cooling (13 sec)
New cycle begins, each
cycle takes 40 seconds.
Material plastic
behavior
1350oF
strain rate independent
isotropic hardening
Material stress-strain property definition:
Stress
Tensile
strength
Yield
strength
0
Strain
Elongation
21
Slide 22
Parameters studied
Parameter 1 – H13 hardness / strength:
Label of different Yield strength at room
hardness
temperature (ksi)
UTS at room
temperature (ksi)
HR40
153
183
HR50
239
289
( Ref: Philip D. Harvey, Engineering Properties of Steel, American Society for Metals,
Metal Parks, Ohio, 1982, P457-462.)
Parameter 2 – Thickness of the H13 layer:
Label of different
designs
Thickness of H13 in
composite core
Core050
0.05 in
Core100
0.1 in
Core150
0.15 in
22
Slide 23
Verification of Axi-symmetric FEA Heat Transfer Analysis*
• Maximum
temperature
difference is
smaller than 20oC.
* Abaqus compared to MagmaSoft
23
Slide 24
Thermo-mechanical Analysis for Core100 with H13-HR40
A
B
C
Temperature and
stress fields become
stable after five
cycles.
Edge, 1” from corner
24
Slide 25
Thermo-mechanical Analysis for Core100
Dominant factors
in deformation:
• The thermal gradient
at the surface is a key
factor in deformation
and failure.
I. Thermal gradient
Temperature
II. Thermal expansion
mismatch
Temperature
III. Thermal gradient
Temperature
IV. Thermal expansion
mismatch
Temperature
• Normal stress along
the hoop’direction is
the largest.
B
2
1
3
25
Slide 26
Thermo-mechanical analysis findings
• The temperature and stress fields become stable in
about five cycles.
• The thermal gradient at the surface is the key factor to
deformation and failure.
• Normal stresses in the hoop direction are largest at the
surface , and may cause surface cracks.
• The failure mechanism depends on the maximum stress
and whether it exceeds the material strength at the
operating temperature.
26
Slide 27
Type I Failure Mechanism – Creep
• When strength is low (ex. H13-HR40).
• Buckling occurs due to plastic deformation.
• σyield << σmax ~ UTS
• Improving material strength will
• Plastic deformation accumulates rapidly.
prevent this failure mechanism.
2
1
3
Core100 H13-HR40/
Copper Core after
250 cycles
27
Slide 28
Type II Failure - Low cycle fatigue
• When strength is high (ex.
H13-HR50).
• σyield <σmax < UTS
• Plastic deformation
accumulates slowly.
200
• Radial surface cracks
occur due to low cyclic
fatigue.
• The number of cycles (N)
to failure can be predicted
by an empirical model:
S
N
C
Normal stress (ksi)
150
100
50
ΔS
0
-50
-100
0
10
20
30
40
Time (second)
normal stress along hoop's direction
28
Slide 29
Factors that determine low cycle fatigue life
200
150
Normal stress (ksi)
Fatigue life N
100
Stress variation ΔS
Surface thermal gradient
50
ΔS=σmax-σmin
0
-50
-100
0
10
20
30
40
Time (second)
normal stress along hoop's direction
Temperature
variation ΔT
Detailed analysis
Higher
conductivity for
thinner H13 layer
Not linear
relationship to
H13 thickness
max T2 /
min T1 /
1000
Temperature (oF)
Core thermal
conductivity α
800
600
ΔT2
ΔT1
400
200
0
0
H13 layer
thickness
10
20
30
40
Time (second)
Temperature
29
Slide 30
The Effect of layer thickness on the low
cycle fatigue life of the composite core
Fatigue
life for
typical
H13 Core
The design of composite core with 0.05” thick H13-HR50 layer offers:
•Lower max temperature;
•Longer fatigue life.
30
Slide 31
Summary
• A pre-requisite to prevent premature failure is
sufficient strength to avoid creep .
• A 0.050” thick H13-HR50 layer provides a
good balance of heat transfer and thermal
fatigue resistance:
– Maximizes heat flux, decreasing mold temperature,
and shortening cycle time.
– Reduces the thermal gradient, lowering maximum
stress and extending core life.
31
Optimization of Laser Deposited
Rapid Tooling
D. Schwam and Y. Wang
Case Western Reserve University
NADCA DMC, Chicago – Feb.17, 2010
1
Slide 2
Outline
• Objectives-why laser deposit?
• The POM process
• Preliminary thermal fatigue results
• In-plant evaluation of cores at
General Die Casters
• FEA optimization of laser deposited
layer
• Conclusions
2
Slide 3
Objectives – why laser deposit?
• Use of high thermal conductivity alloys in cores and
inserts can accelerate heat extraction, lower surface
temperature reduce soldering and shorten cycle time.
• Copper alloys have good thermal conductivity and are
cost effective candidates for this application.
• However, copper alloys dissolve in molten aluminum.
High temperature and high velocity molten metal flow
exacerbate dissolution.
• A layer of laser deposited H13 over the copper can
prevent dissolution.
3
Slide 4
Washout Damage at the Corners of Cu-Ni-Sn
Thermal Fatigue Specimens
ToughMet 3
ToughMet 2
ToughMet 2
0.5”
ToughMet 2
Copper alloys dissolve in molten aluminum
Slide 5
Metal Mold Material Properties
Product
420 Stainless
H-13 Tool Steel
Moldmax HH
Moldmax XL
Moldmax LH
P-20 Tool Steel
Protherm
Alloy 940
Alloy 18
Alloy 22
Tooling Grade
Aluminum
ToughMet 3
Hardness
(HRC)
50
45-50
40
30
30
30
20
16
B90
35
B88
32
Thermal Charpy V-Notch
Conductivity Impact Stregth
BTU/ft*hr*F
Ft*lb
10
5-10
15
8-14
60
4
35-40
10-15
75
12
17
20-25
145
50
120
30
35
N/A
23
2
90-95
22
30
N/A
Yield
Strength
ksi
200
200
155
100
140
120
90
65
30
55
Tensile
Stregth
ksi
250
250
185
110
170
140
115
96
95
100
Thermal
Expansion
Coefficient
10-6 / F
6.1
7.1
9.7
9.3
9.7
7.1
9.8
9.7
9.0
9.0
75-78
110
75-80
120
12.9
9.1
Slide 6
Rapid Tooling by DMD
Direct Metal Deposition of H13 on Copper - the POM Method
*-Courtesy POM
Slide 7
H13 / H13 sample – as deposited/ finished
H13 / Alloy 940 sample – as deposited/ finished
Slide 8
Slide 9
Evaluation of Laser Deposited Cores
The core is surrounded by molten aluminum and has a record of overheating
and soldering. Extracting heat more efficiently from the core can
lower maximum temperature, prevent soldering and allow shorter cycle times.
9
Slide 10
Typical H13 core with cooling line
10
Slide 11
Composite Core -- H13 Deposited on Cu
H13
Cu
11
Slide 12
Thermal Profile of Cover Half Steel During
Solidification
H-13 Core
Composite Core
At start of a cycle
12
Slide 13
Thermal Profile of Section Through Cover Half at Die Opening
H-13 Core
Composite Core
At 20 seconds
• Temperature of Composite Core is lower.
13
Slide 14
Temperature Advantage of the Copper Core
• Temperature of Composite Core is lower.
14
Slide 15
Creep Failure of in First Composite Core
The core shows creep damage after 250 cycles due to
insufficient stiffness and strength at high temperature.15
Slide 16
Surface Cracks in the H13 Layer
16
Slide 17
Remedial
Approaches
Caves in
Bulges out
The distortion of the
core seems to originate
from insufficient strength
and stiffness at the
operating temperature.
Anviloy and H13 cores
do not suffer from this
problem.
Priority 1 - Increase strength: use core as deposited
w/o tempering (downside-lower toughness).
Priority 2 - Increase thickness of H13 layer(downside
slows down heat transfer).
Slide 18
Optimization of the Laser Deposited H13
• The first core was tempered aggressively. The hardness
of the laser deposited H13 was reduced from 51HRC to
40 HRC to improve toughness. However, this reduced
the strength and caused excessive distortion. The core had
to be removed after 250 shots.
• A new core was made with the laser deposited H13 in
the as-deposited condition (no tempering) at 51HRC.
• This core has been in production at General Die Casters.
So far it has accumulated 5,000 shots.
18
Slide 19
FEA optimization of the H13
laser deposited layer thickness
• The 3D Die Casting model was simplified to a 2D axisymmetric FEA model and analyzed with commercial
FEA software Abaqus.
• The accuracy of 2D Abaqus analysis was verified by
comparing it to a 3D MagmaSoft simulation.
• Cyclic heat transfer and stress analysis was applied to
study the failure mechanism of the composite core.
• Composite cores with different H13 layer thickness and
hardness were compared, to optimize the design.
19
Slide 20
Finite Element Analysis Model
Mold
(H13)
Composite
Core:
Steel
(H13)
Casting
(A389)
Copper
(394)
2D Axi-symmetric model
20
Slide 21
Boundary Conditions
Simulation initial
conditions
Process flow chart:
Preheat (40 sec)
Casting Alloy
A389
Mold Material
H13
Furnace Temperature
Mold close, Metal
Injection and
Solidification (20 sec)
Mold open, Ejection,
air cooling (4 sec)
Spray cooling (3 sec)
Air cooling (13 sec)
New cycle begins, each
cycle takes 40 seconds.
Material plastic
behavior
1350oF
strain rate independent
isotropic hardening
Material stress-strain property definition:
Stress
Tensile
strength
Yield
strength
0
Strain
Elongation
21
Slide 22
Parameters studied
Parameter 1 – H13 hardness / strength:
Label of different Yield strength at room
hardness
temperature (ksi)
UTS at room
temperature (ksi)
HR40
153
183
HR50
239
289
( Ref: Philip D. Harvey, Engineering Properties of Steel, American Society for Metals,
Metal Parks, Ohio, 1982, P457-462.)
Parameter 2 – Thickness of the H13 layer:
Label of different
designs
Thickness of H13 in
composite core
Core050
0.05 in
Core100
0.1 in
Core150
0.15 in
22
Slide 23
Verification of Axi-symmetric FEA Heat Transfer Analysis*
• Maximum
temperature
difference is
smaller than 20oC.
* Abaqus compared to MagmaSoft
23
Slide 24
Thermo-mechanical Analysis for Core100 with H13-HR40
A
B
C
Temperature and
stress fields become
stable after five
cycles.
Edge, 1” from corner
24
Slide 25
Thermo-mechanical Analysis for Core100
Dominant factors
in deformation:
• The thermal gradient
at the surface is a key
factor in deformation
and failure.
I. Thermal gradient
Temperature
II. Thermal expansion
mismatch
Temperature
III. Thermal gradient
Temperature
IV. Thermal expansion
mismatch
Temperature
• Normal stress along
the hoop’direction is
the largest.
B
2
1
3
25
Slide 26
Thermo-mechanical analysis findings
• The temperature and stress fields become stable in
about five cycles.
• The thermal gradient at the surface is the key factor to
deformation and failure.
• Normal stresses in the hoop direction are largest at the
surface , and may cause surface cracks.
• The failure mechanism depends on the maximum stress
and whether it exceeds the material strength at the
operating temperature.
26
Slide 27
Type I Failure Mechanism – Creep
• When strength is low (ex. H13-HR40).
• Buckling occurs due to plastic deformation.
• σyield << σmax ~ UTS
• Improving material strength will
• Plastic deformation accumulates rapidly.
prevent this failure mechanism.
2
1
3
Core100 H13-HR40/
Copper Core after
250 cycles
27
Slide 28
Type II Failure - Low cycle fatigue
• When strength is high (ex.
H13-HR50).
• σyield <σmax < UTS
• Plastic deformation
accumulates slowly.
200
• Radial surface cracks
occur due to low cyclic
fatigue.
• The number of cycles (N)
to failure can be predicted
by an empirical model:
S
N
C
Normal stress (ksi)
150
100
50
ΔS
0
-50
-100
0
10
20
30
40
Time (second)
normal stress along hoop's direction
28
Slide 29
Factors that determine low cycle fatigue life
200
150
Normal stress (ksi)
Fatigue life N
100
Stress variation ΔS
Surface thermal gradient
50
ΔS=σmax-σmin
0
-50
-100
0
10
20
30
40
Time (second)
normal stress along hoop's direction
Temperature
variation ΔT
Detailed analysis
Higher
conductivity for
thinner H13 layer
Not linear
relationship to
H13 thickness
max T2 /
min T1 /
1000
Temperature (oF)
Core thermal
conductivity α
800
600
ΔT2
ΔT1
400
200
0
0
H13 layer
thickness
10
20
30
40
Time (second)
Temperature
29
Slide 30
The Effect of layer thickness on the low
cycle fatigue life of the composite core
Fatigue
life for
typical
H13 Core
The design of composite core with 0.05” thick H13-HR50 layer offers:
•Lower max temperature;
•Longer fatigue life.
30
Slide 31
Summary
• A pre-requisite to prevent premature failure is
sufficient strength to avoid creep .
• A 0.050” thick H13-HR50 layer provides a
good balance of heat transfer and thermal
fatigue resistance:
– Maximizes heat flux, decreasing mold temperature,
and shortening cycle time.
– Reduces the thermal gradient, lowering maximum
stress and extending core life.
31