Numerical Modeling of a Moving, Oscillating Welding Heat Source

Transcription

1 Numerical Modeling of a Moving, Oscillating Welding Heat Source NSRP Welding Technology Panel 26 August 2014 Matthew F. Sinfield & Charles R. Fisher Code 611 Welding, Processing, & NDE Branch Office: matthew.sinfield@navy.mil

2 Overview Problem Statement: The influence of arc oscillation (i.e., weaving) on local welding thermal cycles is not well understood Research in this area 1 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 1 Quintana, M. A., et al., Weld Metal Toughness Sources of Variation, Proceedings of the 8 th International Pipeline Conference, Calgary, Alberta, Canada, September 27 October 1,

3 Experimental Approach 1. Construct a Welding Heat Source Oscillation Model SYSWELD, a commercially available thermo-mechanical, thermometallurgical welding process finite element software was used Develop and refine a methodology to simulate a mechanized, zigzag 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

4 Heat Source Oscillation Model Development

5 Constrained Cooling Condition Empirical Weldment Cooling Rate Equation 2 for Steel dd dd dd = dd R[(M(T T 0) 2 E )+Q] = Calculated cooling rate at T, F/s R = Jhaveri cooling rate factor T = temperature at which the cooling rate is calculated, F T 0 = preheat/interpass temperature, F E = welding heat input, kj/in M and Q are empirically derived constants Process M Q T T 0 E GMAW-S* Cooling Rate ( F/s) Cooling Rate vs. Thickness GMAW-S at 47 kj/in 2D Cooling Thickness (in.) 3D Cooling * GMAW-S constants were used since ones for FCAW do not exist 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 2 The Effect of Plate Thickness and Radiation on Heat Flow in Welding and Cutting. Jhaveri, Moffatt, and Adams 5

6 Determination of Oscillation Velocities 1. For each weave condition, calculate weave vector velocity (V 1-2, V 3-4, etc.) 2. Convert dwell time into length and apply V 1 = V 2-3, V 4-5 Actual Welding Weave Data 6 Amplitude Frequency Dwell Travel Speed (V 1 ) 22 mm Hz 0.25 sec 2.50 mm/s 5 4 SYSWELD Weave Data 3 v 1 V 1-2 V 2-3 V mm/s 2.50 mm/s mm/s 2 V mm/s 1 6

7 Weld Oscillation Model Construction Single Pass Weld Plate Model Parameters Conditions Material (Base and Weld Metal) A36 Steel Thickness (mm) [in] [1.25] Pre-Heat ( C) 121 Ambient Temp ( C) 20 Element Size (mm 3 ) ~ 1 Weld Pool Size (mm) 6 x 6 Arc Type GMAW* Arc Efficiency 85% * SYSWELD does not have a FCAW process arc type 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 7

8 SYSWELD Heat Source Calibration Stringer Bead Minimum Weave Bead Maximum Weave Bead Parameters a and c 1,2, are calibrated from the observed weld pool Arc (Circle) Weld Pool (Oval) Measurement a,c Weld Type a,c Location 1,c 2 (mm) c 2 (mm) 1 (mm) Stringer Minimum Weave Left Center Right Maximum Weave Left Center Right Goldak s 3D Moving Heat Source Equation q ( x, y, z, t) = e e e ( z ν ( τ t )) 3 x ² 3 y² f Q a² b² 2 c, 2 a b c 1,2 π π 1 ² 8

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 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 a) Pulsed Gas Metal Arc Welding b) Shielded Metal Arc Welding c) Flux-cored Arc Welding 9

10 Oscillation vs. Stringer Weld Models Oscillation Model Stringer Model Pink Area denotes the molten weld pool (~1500 C) 10

11 Heat Source Oscillation Model Validation

12 Parametric Study - Weld Test Conditions Weld Parameters Minimum Amplitude Maximum Amplitude Nominal Stringer Amplitude (mm) N/A Frequency (Hz) N/A Dwell (s) N/A Current (A) Voltage (V) Cross Travel Speed (mm/s) N/A Dwell Travel Speed (mm/s) Cross Heat Input (J/mm) N/A Dwell Heat Input (J/mm) Note: For purposes of this presentation, amplitude is the only oscillation parameter discussed Minimum Amplitude Amplitude: 9.5 mm Maximum Amplitude Amplitude: 17 mm Increase Amplitude: 1. Decreases weld bead height 2. Widens HAZ 3. Decreases HAZ depth 12

13 Oscillation Model Validation Nominal Amplitude Condition Weld Cross-Section of Nominal Amp Condition Hot XZ slice Model cross-section taken during steady-state at center of oscillation path Validation: Weld bead width & depth HAZ width & depth Weld metal shape 5.0 mm 13

14 Heat Source Oscillation Model Results

15 Effect of Oscillation Amplitude Weld Metal Peak Temperature Temperature ( C) Center Node Stringer - Node 1122 MinAmpl - Node 1341 MaxAmpl - Node 1978 Nominal - Node Time (s) Temperature ( C) Edge Node MaxAmpl - Node Nominal - Node MinAmpl - Node Stringer - Node Time (s) Increased Oscillation Amplitude: Edge Node Center Node Lower peak temperatures at the center of the weld Higher peak temperatures at the weld bead edges 15

16 Effect of Oscillation Amplitude Weld Metal Cooling Rate, t 8/5 Temperature ( C) Center Node Stringer - Node 1122 MinAmpl - Node 1341 MaxAmpl - Node 1978 Nominal - Node Inter-critical Temperature Region Temperature ( C) Edge Node MaxAmpl - Node Nominal - Node MinAmpl - Node Stringer - Node 1159 Inter-critical Temperature Region Time (s) Time (s) Edge Node Nominal Center Node Cooling Time from C (s) Model Center Edge Stringer Min. Amplitude Max. Amplitude Nominal

17 Nominal Amplitude Model Thermal Aspect: C Only Effect of Oscillation Amplitude Heat Affect Zone Cooling Rate, t 8/ Nominal - Node Nominal - Node Nominal - Node Temperature ( C) Inter-critical Region Oscillation within HAZ intercritical temperature region confirmed through simulation XZ slice 300 Node #: Time (s) 17

18 Correlation of Microstructure to Oscillation Thermal Cycles

19 Weld Metal Microstructure Comparison Temp. ( C) 1 mm Deep Center Stringer Temp. ( C) Nominal Amplitude Center Node 3mm Deep Center 1 mm Deep Stringer 3 mm Deep Stringer Temperature ( C) mm Nominal 1 mm Deep Center Stringer 1 mm Deep Center Stringer 3 mm Deep Center Time (s) 5.0 mm 1 mm Deep - Nominal Nominal amplitude shows an apparent increase in weld metal grain boundary ferrite and finer dendrite size 19

20 Temp. ( C) Near Fusion Boundary Microstructure Comparison Nominal Amplitude 2 mm Deep Center Node 2 mm Deep - Side New Dendrite Growth 5.0 mm Reheated Weld Metal due to Oscillation Temperature ( C) mm Deep Nominal 3 mm Deep Side Nominal 2 mm Deep Side Nominal 1 mm Deep Center Stringer 3 mm Deep Center Time (s) Coarse Grain HAZ 20

21 Summary 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 t 8/5 weld metal cooling appears unaffected for 3D cooling Welding arc oscillation appears to influence local weld metal microstructure evolution near the fusion boundary 21