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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


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.


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


Heat Source Oscillation Model Development


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


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


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


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


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


Oscillation vs. Stringer Weld Models

10

Stringer Model Oscillation Model

“Pink Area” denotes the molten weld pool (~1500°C)


Heat Source Oscillation Model Validation


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


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


Heat Source Oscillation Model Results


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


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


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 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


Correlation of Microstructure to Oscillation Thermal Cycles


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


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


• 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

numerical modeling of a moving, oscillating welding heat ... · numerical modeling of a moving,...

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