Advanced Robotic GMAW Cladding Process Development November 6 th and 7 th, 2013
Introduction Stainless steel cladding is common for carbon steel components used in commercial and military ships Porosity defects have been reported as a significant issue in automated gas metal arc welding (GMAW) Commercially available electrodes are preferred over custom-made products to reduce cost Productivity requirements demand long arc-on times making extended contact-tip-life an important consideration
Objectives Develop stainless-steel GMAW cladding procedures to ─ minimize porosity using commercially available ER308L and ER309L stainless steel electrodes ─ maximize arc-on time by increasing contact tip life.
Approach Majority of development work conducted using ER308L stainless steel electrodes ─ Assumed that porosity mitigation techniques would apply to ER309L stainless steel electrodes Laser-diode illuminated high-speed video ─ GMAW-P ─ Commercially available waveforms ─ EWI-developed waveforms ─ CV GMAW DOE approach to identify critical variables Porosity prediction model DOE validation trials Electrode chemistry analysis Effect of travel angle and electrode diameter on dilution Contact-tip-life trials
Pulse Waveform Evaluation and Selection Four Commercially available GMAW-P stainless steel waveforms ─ Three 0.063-in. waveforms ─ One 0.045-in. waveforms ─ 100% Argon shielding gas ─ Necking with poor droplet transfer ─ Forceful, columnar arc ─ Significant puddle depression ─ 0.35-in. arc length required ─ Shorter arc lengths resulted in excessive shorting and spatter ─ Poor wetting and inconsistent bead width on a carbon steel ─ Improved wetting on subsequent layers ─ 99.75% argon/0.25% CO2 shielding gasses ─ Necking with marginally improved droplet transfer ─ Arc length could be reduced slightly ─ Significantly improved wetting on carbon-steel substrates
Pulse Waveform Evaluation and Selection (cont.) 0.045-in. Waveform One waveform of each diameter selected 0.045-in. stainless steel waveform Wire feed speed: 360 ipm Average current: 202 amps Pulse frequency: 203 Hz 0.063-in. stainless steel waveform Wire feed speed: 200 ipm 0.063-in. Waveform Average current: 221 amps Pulse frequency: 153 Hz
EWI Pulse Waveform Development 0.045-in. Waveform Higher pulse frequencies to improve droplet transfer 0.045-in. stainless steel waveform Wire feed speed: 360 ipm Average current: 194 amps Pulse frequency: 312 Hz (+54%) 0.063-in. stainless steel waveform 0.063-in. Waveform Wire feed speed: 200 ipm Average current: 246 amps Pulse frequency: 322 Hz (+110%)
12-layer Build-ups All four GMAW-P waveforms were used to create 12-layer build-ups ─ Shielding gas: 100% argon ─ CTWD: 3/4-in. ─ Travel speed: 6 ipm ─ Weave width: 0.75-in. ─ Weave frequency: 1.3 oscillations per minute ─ Bead overlap: 3/8-in. Evaluated with radiography (RT) ─ Both 0.045-in. waveforms resulted in significant levels of porosity and poor droplet transfer ─ The commercially available 0.063-in. waveform had the fewest number of pores ─ The EWI-developed 0.063-in. pulse waveform had the largest number of pores ─ The commercially available pulse waveforms were selected for use in all subsequent trials.
Diode-laser-illuminated high-speed video Used to observe the effect of welding mode, CTWD, and arc length on puddle depression CTWD significantly affects the depth of the puddle depression ─ Increasing the CTWD increases the resistive heating of the electrode GMAW- P, 0.75” CTWD, 294 Amps ─ The required current is reduced ─ The required pulse frequency is reduced ─ Results in a less-focused arc with a larger footprint ─ Current density is reduced ─ Puddle depression is more shallow GMAW- P, 1.125” CTWD, 230 Amps
Diode-laser-illuminated high-speed video GMAW CV arc is more conical Results in a larger-diameter puddle depression Decreases the current density “seen” by the molten puddle when operating at the same current level Weld Mode CTWD Pulse Frequency Average Current GMAW-P 1.25 175 230 GMAW-P 0.72 294 294 CV GMAW 1.25 N/A 300 CV GMAW, 1.125” CTWD, 300 Amps
DOE In preliminary trials, stringer beads contained more porosity than welds made with a weave When a weave was used, the majority of porosity was found at the penetration spike located at the dwells Assumptions ─ Stringer beads represent a “worst -case- scenario” regarding porosity ─ Methods of reducing porosity in stringer beads will be effective in weave welds Fractional factorial DOE design based on a Hadamard Matrix A resolution V design, allowing the estimation of the main effects of each variable, as well as the interactions between variables (1) 48 weld beads
DOE Levels Two levels required for each of the eight variables selected for investigation Based on end-user requirements and/or EWI experience: ─ Electrode diameter: 0.045-in., 0.063-in. ─ Shielding gas: 100% Argon, 99.75% Argon + 0.25% CO 2 ─ Weld mode: GMAW-P, CV GMAW Scaling trials were used to select the following levels: ─ Travel speed: 8 ipm, 12 ipm ─ Part inclination: -10° (downhill), 0° ─ Travel Angle: -20° (drag), 0° ─ CTWD: 3/4-in., 1 1/2-in. ─ Arc length: 3/16-in., 5/16-in.
DOE Level Selection Criteria Setting must produce a visually acceptable bead for the majority of variable combinations ─ Example: ─ Travel speeds up to 16 ipm were acceptable with a 3/16-in arc length ─ The maximum travel speed with a 5/16-in. arc length was 12 ipm ─ The upper travel speed level was 12 ipm Less penetration is preferred Parameters selected to test the widest range possible Part Inclination -10° 0° +10° Travel Speed 8 ipm X 36 36 Example
DOE Level Selection Weld beads evaluated with radiography Porosity evaluation criteria ─ Size ─ Shade of indications ─ Acceptability per end-user supplied criteria ─ Total number of pores ─ Number of groups of pores ─ Percent of weld length containing scattered porosity ─ Number of isolated pores Numerical model created to predict porosity level ─ “Acceptability scale” from 0 to 4 ─ 0: no pores ─ 4: porosity far exceeding the acceptable level
Numerical Prediction Model Model predicts CTWD as the most significant variable ─ Verified in validation trials Also predicted that short arc lengths and 100% Argon shielding gas would increase porosity ─ Disproved in validation trials Model Inputs Wire Diameter Arc Travel Speed Travel Angle Part Inclination Weld Shielding (in.) Length CTWD (in.) (ipm) (deg.) (deg.) Mode Gas 0.0625 Long 1.125 12 -20 0 Pulse Ar + CO2 Summary - Porosity Measurements Shade Total # of Pores % Length Scattered Porosity # of Porosity Groupings Single Pores Pore Size Acceptability 0.7 0 0 0.0 1 0.6 0.0 (0-5) (count) (% Length) (count) (count) (0-4) (0-4) Model Inputs Wire Diameter Arc Travel Speed Travel Angle Part Inclination Weld Shielding X (in.) Length CTWD (in.) (ipm) (deg.) (deg.) Mode Gas 0.0625 Long 0.072 0.72 12 -20 0 Pulse Ar + CO2 Summary - Porosity Measurements Shade Total # of Pores % Length Scattered Porosity # of Porosity Groupings Single Pores Pore Size Acceptability 3.5 31 0 1.2 2 2.9 3.7 (0-5) (count) (% Length) (count) (count) (0-4) (0-4)
Validation Trials X
Weaving Validation Trials Six additional weld build-ups made using a weave DOE model predictions ─ W1, W2, and W6 would have minimal to no porosity ─ W4 and W5 would have an acceptable amount of porosity ─ W3 would have porosity far exceeding the acceptance criteria 5 results were consistent with the model predictions W5 failed due to pores exceeding the size limit # of Pores Weave Arc Weld Wire Travel Part per 100 Set CTWD Length Gas Mode Diameter Angle Inclination Inches Pass/Fail? W1 1.125 5/16 Argon+CO2 Pulse 1/16 -20 0 0.00 Pass W2 1.125 3/16 Argon+CO2 Pulse 1/16 -20 0 10.94 Pass W3 0.72 5/16 Argon+CO2 Pulse 1/16 -20 0 65.63 Fail (number) W4 0.72 3/16 Argon+CO2 Pulse 1/16 -20 0 1.56 Pass W5 1.125 5/16 Argon Pulse 1/16 -20 0 15.63 Fail (size) W6 1.125 5/16 Argon+CO2 CV 1/16 -20 0 3.13 Pass
Effect of Current Density At 300 amps, the build-up made using CV GMAW had less than 5% of the number of pores contained in the GMAW-P build-up made at an equal average current Indicates that porosity is not only related to current level, but also to current density
CV GMAW Build-ups Additional build-ups made to evaluate whether CV GMAW would consistently reduce porosity Twelve-layer build-up created using CV GMAW ─ Over 550 inches of linear inches of weld ─ 0.0625-in. electrode ─ 10-degree push angle ─ 1.125-in. CTWD ─ Only two pores were found, both within the size limit ─ 0.36 pores per 100 linear inches of weld
Effect of Electrode Chemistry Five heats of 308L were used in welding trials Material certifications were studied to identify whether chemical elements could be correlated to porosity formation ─ Data presented is of welds made with GMAW-P, since a larger number of samples were created with GMAW-P than with CV GMAW
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