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DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Numerical Modeling of a Moving, Oscillating Welding Heat Source
Matthew F. Sinfield & Charles R. Fisher Code 611 – Welding, Processing, & NDE Branch
Office: 301-227-5555
E-mail: [email protected]
NSRP – Welding Technology Panel 26 August 2014
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Overview
Problem Statement: – The influence of arc oscillation (i.e., weaving) on local welding
thermal cycles is not well understood – Research in this area1 suggests weaving can promote the formation
of local brittle zones (LBZ) leading to erratic low temperature impact toughness behavior in high-strength steel weld metals
Objectives: – Develop and validate a moving, oscillating welding heat source
single pass model – Via parametric study, draw a correlation between: weave
parameters (e.g., amplitude, frequency, dwell time), calculated local thermal cycles, and resulting weld metal microstructure
2
1 Quintana, M. A., et al., “Weld Metal Toughness – Sources of Variation,” Proceedings of the 8th International Pipeline Conference, Calgary, Alberta, Canada, September 27 – October 1, 2010.
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Experimental Approach
1. Construct a Welding Heat Source Oscillation Model – SYSWELD, a commercially available thermo-mechanical, thermo-
metallurgical welding process finite element software was used – Develop and refine a methodology to simulate a mechanized, zig-
zag weaving technique in SYSWELD • Note, weaving is not a designed-in software feature
2. Model Validation – Fabricate a series of automated flux-cored arc bead-on-plate
welds using a range of typical shipyard weave parameters (e.g., amplitude, frequency, and dwell time)
– Perform same parametric study using SYSWELD to calculate welding thermal cycles
– Validation: Compare actual fusion zone profile with predicted
3. Correlate Microstructures to Oscillation Thermal Cycles 3
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Heat Source Oscillation Model Development
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
5
05
101520253035404550
0 0.25 0.5 0.75 1 1.25 1.5 1.75
Coo
ling
Rat
e (°
F/s)
Thickness (in.)
Cooling Rate vs. Thickness GMAW-S at 47 kJ/in
2 “The Effect of Plate Thickness and Radiation on Heat Flow in Welding and Cutting”. Jhaveri, Moffatt, and Adams
𝑑𝑑𝑑𝑑
= 𝑅[(𝑀(𝑑−𝑑0)2
𝐸)+Q]
3D Cooling 2D Cooling
𝑑𝑑𝑑𝑑
= Calculated cooling rate at T, °F/s
R = Jhaveri cooling rate factor
T = temperature at which the cooling rate is
calculated, °F
𝑇0= preheat/interpass temperature, °F
E = welding heat input, kJ/in
M and Q are empirically derived constants
Empirical Weldment Cooling Rate Equation2 for Steel
Process M Q T T0 E
GMAW-S* 0.00377 -1.72 1000 250 47
For this analysis, a plate thickness of 1.25-in was selected to ensure 3D cooling to isolate the thermal effects due to arc oscillation
Constrained Cooling Condition
* GMAW-S constants were used since ones for FCAW do not exist
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6 1
2
3
4
5
6
SYSWELD Weave Data V1-2 48.99 mm/s V2-3 2.50 mm/s V3-4 48.99 mm/s V4-5 2.50 mm/s
v1
Actual Welding Weave Data Amplitude 22 mm Frequency 0.714 Hz
Dwell 0.25 sec Travel Speed (V1) 2.50 mm/s
1. For each weave condition, calculate weave vector velocity (V1-2, V3-4, etc.) 2. Convert dwell time into length and apply V1 = V2-3, V4-5
Determination of Oscillation Velocities
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Weld Oscillation Model Construction
Plate
Single Pass Weld
7
Model Parameters Conditions Material (Base and Weld Metal) A36 Steel Thickness (mm) [in] 31.75 [1.25] Pre-Heat (°C) 121 Ambient Temp (°C) 20 Element Size (mm3) ~ 1
Weld Pool Size (mm) 6 x 6 Arc Type GMAW* Arc Efficiency 85%
Oscillation Path Embedded into Weld Mesh
Actual Base Plate Material: A36 Steel Actual Weld Metal: FCAW, Fe-0.07C-0.75Mn-0.60Si-2.5Ni-0.20Cr-0.50Mo-0.05V-0.06Cu
* SYSWELD does not have a FCAW process arc type
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
8
Arc (Circle) Weld Pool (Oval)
Weld Type Measurement Location a ,c1 ,c2 (mm) c2 (mm) a ,c1
(mm) Stringer - 3.0 6.5 3.9
Minimum Weave Left 2.5 6.5 2.5 Center 2.7 5.3 2.6 Right 2.4 5.8 2.5
Maximum Weave Left 2.0 3.4 2.2 Center 3.0 8.6 2.4 Right 3.1 4.9 3.5
( )( )
eeeq ctz
by
ax
tzyx cbaQf
22,1
²3²
²3²
²3
2,1),,,(
36 −⋅−−⋅−⋅−
⋅⋅⋅⋅⋅⋅⋅⋅⋅⋅
=τν
ππ
Stringer Bead Minimum Weave Bead Maximum Weave Bead
Goldak’s 3D Moving Heat Source Equation
Parameters a and c1,2, are “calibrated” from the observed weld pool
SYSWELD Heat Source Calibration
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a) Pulsed Gas Metal Arc Welding b) Shielded Metal Arc Welding c) Flux-cored Arc Welding
9
Navy IR Weld Camera
• Sinfield, M.F., Lueken, D.M, and Setlik, B.J., “Longwave Infrared Imaging of a High-Temperature, High-Intensity Light Source,” Navy Case No. 102,787. USPTO Nonprovisional Patent Application, Filing Date: 19 December 2013.
• Validated technique for viewing variety of arc welding types (below images)
• Noted features: absence of welding fume, clear image of both arc and weld pool, steady image without flicker, and defined weld pool base metal interface
• Carderock’s Technology Transition Office looking for potential commercialization partners for the technology
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Oscillation vs. Stringer Weld Models
10
Stringer Model Oscillation Model
“Pink Area” denotes the molten weld pool (~1500°C)
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Heat Source Oscillation Model Validation
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Parametric Study - Weld Test Conditions
12
Weld Parameters Minimum Amplitude Maximum Amplitude Nominal Stringer Amplitude (mm) 9.5 17 14.3 N/A Frequency (Hz) 0.73 0.73 0.73 N/A Dwell (s) 0.3 0.3 0.3 N/A Current (A) 200.4 195.0 196.6 202.9 Voltage (V) 23.0 22.9 23.0 22.8 Cross Travel Speed (mm/s) 20.5 44.2 37.7 N/A Dwell Travel Speed (mm/s) 2.5 2.5 2.5 2.5 Cross Heat Input (J/mm) 224.9 101.1 119.8 N/A Dwell Heat Input (J/mm) 1841.2 1788.1 1807.0 1848.5
Amplitude: 9.5 mm Amplitude: 17 mm Increase Amplitude: 1. Decreases weld
bead height 2. Widens HAZ 3. Decreases HAZ
depth
Minimum Amplitude Maximum Amplitude
Note: For purposes of this presentation, amplitude is the only oscillation parameter discussed
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Oscillation Model Validation Nominal Amplitude Condition
Hot
XZ slice
Validation: • Weld bead width & depth • HAZ width & depth • Weld metal shape
5.0 mm
13
Model cross-section taken during steady-state at center of oscillation path
Weld Cross-Section of Nominal Amp Condition
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Heat Source Oscillation Model Results
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Effect of Oscillation Amplitude Weld Metal Peak Temperature
15
0
400
800
1200
1600
2000
2400
2800
3200
0 5 10 15 20 25 30 35 40
Tem
pera
ture
(°C
)
Time (s)
Center Node
Stringer - Node 1122MinAmpl - Node 1341MaxAmpl - Node 1978Nominal - Node 17821
0
200
400
600
800
1000
1200
1400
0 5 10 15 20 25 30 35 40
Tem
pera
ture
(°C
)
Time (s)
Edge Node
MaxAmpl - Node 18753Nominal - Node 32599MinAmpl - Node 12723Stringer - Node 1159
Increased Oscillation Amplitude:
• Lower peak temperatures at the center of the weld
• Higher peak temperatures at the weld bead edges
Center Node Edge Node
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
16
Cooling Time from 800-500°C (s)
Model Center Edge Stringer 5.4 6.9
Min. Amplitude 5.6 7.5 Max. Amplitude 5.6 4.1
Nominal 5.9 4.8
400
500
600
700
800
900
14 16 18 20 22 24 26 28
Tem
pera
ture
(°C
)
Time (s)
Center Node Stringer - Node 1122MinAmpl - Node 1341MaxAmpl - Node 1978Nominal - Node 17821
400
500
600
700
800
900
10 12 14 16 18 20 22 24 26
Tem
pera
ture
(°C
)
Time (s)
Edge Node MaxAmpl - Node 18753Nominal - Node 32599MinAmpl - Node 12723Stringer - Node 1159
Inter-critical Temperature
Region
Inter-critical Temperature
Region
Center Node Edge Node
Nominal
Effect of Oscillation Amplitude Weld Metal Cooling Rate, t8/5
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
300
400
500
600
700
800
900
1000
7 8 9 10 11 12 13 14 15 16 17 18
Tem
pera
ture
(°C
)
Time (s)
Nominal - Node 74849
Nominal - Node 80346
Nominal - Node 85843
Nominal Amplitude Model Thermal Aspect: 800-500°C Only
XZ slice
Inter-critical Region
17
80346
Oscillation within HAZ inter-critical temperature region confirmed through simulation
85843
74849 Node #:
Effect of Oscillation Amplitude Heat Affect Zone Cooling Rate, t8/5
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Correlation of Microstructure to Oscillation Thermal Cycles
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
Weld Metal Microstructure Comparison
19
Nominal Amplitude Stringer
5.0 mm
Temp. (°C) Temp. (°C)
5.0 mm
Center Node
0
500
1000
1500
2000
2500
4 6 8 10 12 14 16 18 20
Tem
pera
ture
(°C
)
Time (s)
3mm Deep Center
1 mm Deep Center
Stringer 3 mm Deep
Center
Stringer 1 mm Deep
Center
Nominal 1 mm Deep
Center
1 mm Deep – Stringer
3 mm Deep – Stringer
1 mm Deep - Nominal
Nominal amplitude shows an apparent increase in weld metal grain boundary ferrite and finer dendrite size
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Near Fusion Boundary Microstructure Comparison
20
Nominal Amplitude Temp. (°C)
5.0 mm
0
200
400
600
800
1000
1200
1400
1600
4 6 8 10 12 14 16 18 20
Tem
pera
ture
(°C
)
Time (s)
Nominal 3 mm Deep
Side
Nominal 2 mm Deep
Side
3 mm Deep
Center Node
Stringer 3 mm Deep
Center
Nominal 1 mm Deep
Center
2 mm Deep 2 mm Deep - Side
Coarse Grain HAZ
Reheated Weld Metal due to Oscillation
New Dendrite Growth
DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited.
• An oscillating (i.e., weaving) welding heat source, single pass, finite element model was developed and validated
• Periodic fluctuations in temperature were observed in the oscillation model’s calculated weld metal and HAZ thermal cycles
• The effects of oscillation amplitude on local heating and cooling were examined: Increased amplitude decreases the weld metal peak temperature
at the center of the bead, but increases it at the weld edge
Final t8/5 weld metal cooling appears unaffected for 3D cooling
• Welding arc oscillation appears to influence local weld metal microstructure evolution near the fusion boundary
Summary
21