Process Development November 6 th and 7 th, 2013 Introduction - PowerPoint PPT Presentation

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