HIGH BRIGHTNESS HYBRID WELDING OF STEEL Paper 106

Brian Victor1, Brad Nagy1, Stan Ream1, Dave Farson2

1 EWI, 1250 Arthur E. Adams Dr., Columbus, OH, 43212, USA

2The Ohio State University, 1246 Arthur Adams Dr., Columbus, OH, 43212, USA

Abstract

Recent advances in solid-state laser technology have improved the return on investment for laser and hybrid welding in deep-penetration applications. In this research, a high-power high-brightness fiber laser was coupled to a pulsed gas metal arc welding (GMAW) system to evaluate hybrid laser-arc welding (HLAW) of carbon steel. The effects of multiple process variables on weld penetration were tested. These variables included shielding gas, beam-to-wire distance (BTWD), laser focal position, and process orientation. High-speed video was used to record welding trials. A custom diode laser illumination system was developed to improve clarity and image quality of the high-speed videos. Additionally, a custom integration package was developed in collaboration with The Lincoln Electric Company and The Ohio State University Welding Engineering program to provide synchronized pulsing of the laser and GMAW systems. Welding trials were conducted with this system to evaluate the benefit of synchronous or asynchronous pulsing of the two welding processes.

Introduction

In recent years the performance of high-power, high-brightness solid-state lasers has rapidly improved. The primary laser technologies influencing this improvement are the fiber laser and disk laser, which share the following characteristics: can be fiber delivered to transmissive optics, have excellent electrical efficiency, can produce excellent beam quality, and can produce higher output power than previous generations of fiber-delivered lasers.

While the performance of disk and fiber laser technologies has progressed, the cost to purchase these technologies has continued to decrease. With the growth in performance and reduction in cost of high-brightness lasers, laser welding is becoming a more attractive option for thick-section welding applications.

Several automated welding processes exist that can be used for welding thick-section steel. Among these are gas metal arc welding (GMAW), submerged arc

welding (SAW), laser welding, and electron beam welding. While the arc welding processes are relatively inexpensive, they generate high heat input and considerable distortion at moderate welding speeds. Electron beam welding can produce deep-penetrating, high depth-to-width ratio welds with low heat input at fast travel speeds, but the equipment is very expensive. High-brightness lasers are approaching the penetration and depth-to-width ratios possible with electron beam welding, but at a lower cost.

Although the power and performance of high-brightness lasers is improving, autogenous laser welding still has some limitations.

The small spot size of the focused laser beam makes it difficult to tolerate gaps in the weld joint.

Undercut and underfill can occur without the addition of filler material.

Hybrid welding, or hybrid laser-arc welding (HLAW), combines laser welding and GMAW into a single welding process. By combining the two processes, the advantages of each process can be realized. Deep penetration and high travel speeds are obtained from the laser welding process, while alloying and filling of the joint are achieved with the GMAW process. Due to the deep penetration possible with the HLAW process, joint preparations requiring less filler metal can be used as compared to conventional arc welding. In addition, HLAW can fuse thick-section joints in a single pass with low heat input, low distortion, and in some cases without the need for backing material.

Although HLAW has some advantages over conventional thick-section welding processes, there are several factors preventing it from being implemented in industrial settings.

Investment costs for a hybrid laser welding system are considerably higher than for an arc welding system.

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Implementing a laser welding system requires increased safety, protection, and operator training.

The gap bridging tolerance for hybrid welding is far less than conventional arc welding processes.

Currently, there is no AWS or ISO standard pertaining to HLAW.

There has only been limited implementation of this process outside of a laboratory environment.

For these reasons, there is limited hybrid welding experience and expertise in manufacturing.

This study evaluated hybrid welding of carbon steel with a 10-kW Yb-fiber laser. Welding trials were conducted to evaluate the effects of beam-to-wire distance (BTWD), focal position, and process orientation (arc-leading vs. laser-leading) on the welding process. Both full- and partial-penetration welds were investigated. Welding trials were also conducted with modulated laser power synchronized to the pulse waveform of the GMAW power supply. High-speed video was used to record the HLAW process. To improve the image quality and clarity of the high-speed videos, a diode laser illumination and filtering system was developed and evaluated.

Objectives

The objective of this project was to develop process knowledge of hybrid welding with high-power, high-brightness lasers by:

Developing a diode illumination system to improve high-speed video quality

Testing the effects of various HLAW parameters on weld profile and penetration

Designing and testing a control system capable of synchronous pulsing of the laser and GMAW power supply

Evaluating the effects of synchronous pulsing on weld profile and penetration.

Experimental Procedure

Partial- and full-penetration HLAW bead-on-plate and square butt trials were conducted on mild carbon steel (AISI 1018) in the flat position (1G). Partial-penetration was selected for certain trials to quantify

changes in penetration. Bead-on-plate was selected for certain trials to eliminate effects from joint gap or mismatch. A 10-kW IPG Yb-fiber laser was coupled to custom EWI focusing optics to deliver the beam to the work-piece (Figures 1 and 2). The laser optics included a 200-m process fiber, 150-mm collimator, and a 250-mm parabolic focusing mirror. A Lincoln Electric Power Wave i400 and LN-10 semi-automatic wire feeder were used for the GMAW portion of the hybrid process. All trials were performed using pulsed GMAW waveforms unless otherwise noted. All welds were shielded with 90%-argon / 10%-CO2 shielding gas delivered through the GMAW torch. Backside shielding was used for certain full penetration welding trials. The GMAW filler wire used for all trials was 0.045-in. ER70S-6. The GMAW torch angle was 30 degrees from the beam axis for all trials.

Figure 1. IPG 10-kW Fiber Laser (right) and 4-Fiber Beam Switch (left)

Figure 2. Custom Laser Welding Optics Built by EWI

Diode Illumination for High-Speed Video

In this research, a 915-nm 100-W CW fiber-delivered diode laser from JDS Uniphase was used for illumination (Figure 3). A Vision Research Phantom high-speed camera with a maximum frame rate of 10,000 fps was used to capture the video.

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Figure 3. Experimental Setup for Diode-Illuminated High-Speed Video Trials

Baseline high-speed videos were taken using only arc illumination. The arc-illuminated trials used a 940-nm interference filter. Using the same GMAW parameters as the arc-illuminated trials, diode laser illumination was tested using a 905-nm laser line filter. The power and spot size of the diode laser were adjusted to improve illumination. To reduce the brightness of the arc and improve image quality with diode illumination, additional filters were tested.

With the optimum filters and laser irradiance selected, the incident diode laser angle with respect to the camera viewing angle was evaluated. The optimum angle of the laser was determined for the side, front, and front-oblique camera views. Each of these camera angles were used to capture different phenomena of the welding process. Once the diode illumination and filtering system was optimized, high-speed video was used to evaluate the effects of various welding process adjustments.

Beam-to-Wire Distance Evaluation

BTWD is the distance between the laser beam axis and the GMAW wire measured at the work surface. Various distances were evaluated to determine the effect on penetration and profile of the welds. All welds for these trials were bead-on-plate made in the partial-penetration mode.

The variables listed in Table 1 were fixed for all BTWD trials. Only the BTWD and process orientation (arc-leading or laser-leading) were varied. Trials were conducted in both the laser-leading and arc-leading orientations for BTWD of 0, 1, 2, 3, 4, 6, 8, 10, and 12 mm. High-speed videos were taken from the side view to evaluate the effects of BTWD. The welds were then cross-sectioned to measure the penetration.

Table 1. Fixed Variables for BTWD Evaluation Wire Feed

Speed Travel Speed

(m/min)

Laser Power (kW)

Spot Size (m) (m/min) (ipm)

CTWD (mm)

2 5 333 8.89 350 16

Arc-Leading vs. Laser-Leading

Two distinct orientations can be used with the HLAW process: arc-leading or laser-leading (Figure 4). In the arc-leading direction the GMAW torch uses a drag angle. In the laser-leading direction the GMAW torch uses a push angle. Both orientations were investigated during the BTWD trials. In both the arc-leading and laser-leading cases, the laser beam was oriented perpendicular to the work. Cross-sections and high-speed videos from the BTWD trials were evaluated to determine the effect of process orientation at different BTWD.

Figure 4. Laser-Leading (Left) and Arc-Leading (Right) Orientations

Process orientation was also evaluated to determine the effect on weld pool mixing. In deep-penetration hybrid welding the composition at the top of the weld is mostly filler metal, while the composition at the root is mostly base metal. To evaluate the effect of process direction on filler metal mixing, hybrid welds were conducted with 0.045-in. ER308 stainless steel filler wire. Full-penetration welds were performed on 9.5-mm steel square butt joints using both process orientations with two BTWD. The welds were then cross-sectioned and etched to determine the level of filler metal mixing for the different conditions. Table 2 lists the parameters used for these trials.

Table 2. Welding Parameters for Filler Metal Mixing Trials

Wire Feed Speed BTWD

(mm) Orientation

Travel Speed

(m/min)

Laser Power (kW) (m/min) (ipm)

2 Arc-Lead 2.3 9 8.89 350 5 Arc-Lead 2.3 9 8.89 350 2 Laser-Lead 2.3 9 8.89 350 5 Laser-Lead 2.3 9 8.89 350

Focal Position Evaluation

For both hybrid welding and autogenous laser welding, other researchers have reported an increase in penetration by moving the focal position of the laser

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above or below the top surface of the plate. The focal position most often reported as optimum by other researchers is 1 to 4 mm below the top surface of the plate. To test the validity of these claims, autogenous and hybrid welds were conducted to evaluate the effect of focal position on penetration.

The variables listed in Table 3 were fixed for all autogenous laser welding focal position trials (partial-penetration, bead-on-plate). Trials were conducted with the laser at focus and 2, 4, 6, 8, and 10 mm above and below the top surface of the plate. These welds were cross-sectioned to evaluate the penetration.

The variables listed in Table 4 were fixed for all hybrid welding focal position trials (partial-penetration, bead-on-plate). Focal position was evaluated for hybrid welding in the laser-leading direction only. The torch position was adjusted to maintain the same contact tip-to-work distance (CTWD) for all trials (Figure 5). Trials were conducted with the laser at focus and 2, 4, 6, 8, and 10 mm above and below the top surface of the plate. The welds were cross-sectioned to evaluate the penetration.

Table 3. Fixed Variables for Autogenous Laser Focal Position Evaluation

Travel Speed (m/min)

Laser Power (kW)

Focusing Optic (mm)

2 5 250

Table 4. Fixed Variables for Hybrid Laser Focal Position Evaluation

Wire Feed Speed Travel Speed

(m/min)

Laser Power (kW)

Focus Optic (mm)

(m/min) (ipm) CTWD (mm)

2 5 250 8.89 350 16

Figure 5. Focal Position Variation and Terminology

Laser-Arc Interaction

To evaluate the effect of laser power on the welding arc, GMAW trials were conducted in constant voltage (CV) mode with and without the laser. Baseline GMA welds were made using four different arc power levels. The trials were then repeated with 5 and 9 kW of laser power added to the welding arc (Table 5). For all trials, the CTWD was set at 16 mm, and the travel speed was 1 m/min. For the hybrid welds, the BTWD was 2 mm.

For each weld, the average arc current and arc voltage was calculated using a data-acquisition system. High-speed video was used to record the welds from the side view. A still shot was taken from each video that showed a representative arc length. The arc length of each weld was measured using the known diameter of the GMAW wire as a reference. The arc length, current, and voltage were then compared to determine if the laser power had an influence on the arc.

Table 5. Welding Variables Evaluated for Laser-Arc Interaction Trials

Wire Feed Speeds

(m/min) (ipm)

Voltage Set Points

(V) 7.62 300 29.0 8.89 350 30.5

10.16 400 32.7 11.43 450 33.6

Full-Penetration Root Evaluation

Full-penetration hybrid welds were performed on 9.5-mm square butt joints to evaluate the formation of root profiles during welding. A backing gas chamber with a clear acrylic window was constructed to enable viewing of the root during welding. Still air, moving air, argon, nitrogen, and helium were tested in the backing gas chamber. High-speed video was used to capture videos of the keyhole and backside weld pool during welding. Laser power and travel speed were also adjusted to evaluate the effects on root profile and spatter.

Laser and GMAW Synchronization

Other researchers have claimed increased penetration and extended process synergy from hybrid welding by coordinated modulation of the laser power with the GMAW arc pulse. To evaluate these claims, a synchronized modulation system was designed to modulate the laser power in phase or out of phase from the frequency of the pulsed GMAW current. In this task, Lincoln Electric and The Ohio State University

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(OSU) Welding Engineering Program collaborated with EWI to develop a synchronized hybrid welding modulation system.

Lincoln Electric developed a custom solution in the i400 GMAW system to produce an output signal to control the laser power. The laser output signal was synchronized to the frequency of the current pulse for any wire feed speed. The phase delay between the laser and arc, the laser peak power, and the laser background power could be adjusted from the i400 controls on the wire feeder. The output signal generated by the i400 was a 0- to 10-V analog signal. This 0- to 10-V signal was wired into the fiber laser to generate an output of 0 to 100% laser power.

With the synchronized modulation system developed, a series of welding trials were designed by OSU to investigate the effects of in-phase and out-of-phase modulation with different BTWD and process orientations. Partial-penetration welds were conducted in the bead-on-plate configuration. The laser power modulation was designed to maintain an average power of 5 kW for comparison to baseline welds completed with 5-kW constant laser power. Figure 6 illustrates the two laser modulation conditions.

Figure 6. Illustration of Modulated Laser Power Conditions, Both with 5-kW Average Power

The parameters listed in Table 6 were fixed for all synchronized laser-GMAW welding trials. Table 7 lists the parameters that were varied. Current, voltage, and laser power were recorded with a data-acquisition system for all welds. High-speed videos were also taken to evaluate the effects of synchronous

modulation. Each weld was then cross-sectioned to measure penetration depth and profile.

Table 6. Fixed Variables for Synchronized Laser-GMAW Trials

Wire Feed Speed Travel

Speed (m/min)

Spot Size (m)

(m/min) (ipm) Pulse

Frequency (Hz)

CTWD (mm)

2 333 8.89 350 190 16

Table 7. Welding Parameters for Synchronized Laser-GMAW Trials

Trial

Orientation

Phase

BTWD (mm)

Peak (kW)

Background (kW)

1 Arc-Lead In 1 8 2 2 Arc-Lead In 4 8 2 3 Arc-Lead In 7 8 2 4 Arc-Lead In 1 6 4 5 Arc-Lead In 4 6 4 6 Arc-Lead In 7 6 4 7 Arc-Lead Out 1 8 2 8 Arc-Lead Out 4 8 2 9 Arc-Lead Out 7 8 2 10 Arc-Lead Out 1 6 4 11 Arc-Lead Out 4 6 4 12 Arc-Lead Out 7 6 4 13 Laser-Lead In 1 8 2 14 Laser-Lead In 4 8 2 15 Laser-Lead In 7 8 2 16 Laser-Lead In 1 6 4 17 Laser-Lead In 4 6 4 18 Laser-Lead In 7 6 4 19 Laser-Lead Out 1 8 2 20 Laser-Lead Out 4 8 2 21 Laser-Lead Out 7 8 2 22 Laser-Lead Out 1 6 4 23 Laser-Lead Out 4 6 4 24 Laser-Lead Out 7 6 4

Results and Discussion

Diode Illumination for High-Speed Video

Typically, high-speed videos of the GMAW process are illuminated by two types of sources: light from an external lamp or light produced by the arc. In the case of external lamp lighting, the source is generally broadband light from a halogen, xenon, or incandescent bulb. The light can be directed at the process from the same direction as the camera or it can backlight the process. Backlighting produces a silhouette of the process to witness droplet detachment, shape, and size. However, since the image is a side-view silhouette, only limited information can be gathered.

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The other source typically used for illuminating high-speed videos of GMAW is light emitted by the welding arc. Because the arc light is generally too bright for the camera, the incoming light must be attenuated by filters, an aperture, or both. When properly attenuated, the arc light can illuminate the wire, droplets, and weld pool. However, due to the broadband spectrum and high intensity of the welding arc, it is difficult to limit the brightness of the central arc column without sacrificing overall image clarity. Producing clear high-speed videos of pulsed GMAW is particularly difficult because of the bright arc at peak current and the low light during the background current.

The solution developed in this program for illuminating high-speed videos was to use a diode laser. Because the diode laser light is monochromatic, filters can be used to attenuate the incoming light allowing only the illumination wavelength to reach the camera. This can enable higher quality video images and better attenuation of the arc than other illumination methods. In addition, the power, spot size, and incident angle of the diode laser light can be adjusted to precisely control the intensity of the illumination area for repeatability.

Other researchers have used diode lasers, both CW and pulsed, of various wavelengths for illumination of high-speed videos. In this research, a 915-nm 100-W CW fiber-delivered diode laser from JDS Uniphase was used. This laser was chosen for portability, air cooling, and ease-of-integration with the existing hybrid welding setup. The 915-nm wavelength was beneficial because the intensity of the arc is relatively low in the infrared region. This enables the arc to be attenuated while not filtering too much of the diode laser light.

Baseline high-speed videos were taken using only arc illumination. Figure 7 is a screen shot from the arc-illuminated high-speed video trials during peak and background current. Using the same GMAW parameters, welds were completed with diode laser illumination and a 905-nm laser line filter.

An additional 905-nm laser line filter was added to further limit arc light, and a 0.2 OD neutral density filter was added to attenuate all wavelengths and reduce spectral glare from laser reflections. Figure 8 is a screen shot from the final diode filtering trial during peak and background current. The optimum laser irradiance with these filters was approximately 20 W/cm2 of CW laser power.

Figure 7. Stills from Arc-Illuminated High-Speed Video, during Peak Current and Background Current

Figure 8. Stills from Diode-Illuminated High-Speed Video, during Peak Current and Background Current

In addition to improving the clarity of viewing the arc welding process, diode illumination enables viewing of the laser keyhole, which is difficult with other illumination techniques. Typically, the laser keyhole is a bright spot on high-speed video; however, by using diode illumination, the depression and shape of the laser keyhole can be seen. In addition to the keyhole shape, diode illumination can enable viewing droplet detachment, wire feed speed, weld pool depressions, and base metal that may not have been possible with other illumination methods of GMAW or HLAW high-speed videos. Figure 9 is a screen shot from a diode-illuminated high-speed video of a hybrid bead-on-plate weld.

Figure 9. Diode-Illuminated High-Speed Video Still

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Beam-to-Wire Distance Evaluation

The welds from the partial-penetration BTWD trials were cross-sectioned and weld penetration was measured. From this data, the BTWD seemed to have little effect on penetration depth. As seen in Figure 10, the arc-leading welds had consistently more penetration than the laser-leading welds, but both process orientations followed the same trend with BTWD.

Hybrid Penetration vs. BTWD

3

4

5

6

7

8

9

0 1 2 3 4 6 8 10 12

BTWD (mm)

Pene

tratio

n (m

m)

Laser Leading Arc Leading

Figure 10. Hybrid Weld Penetration vs. BTWD

BTWD had an effect on the fusion profile. At short BTWD, the weld profile seen in the cross-sections appears as one solidification zone. At longer BTWD, the weld has two distinct solidification zones due to the separation of the processes. At 2-m/min travel speed, the BTWD at which two solidification zones occur appears to be around 5 mm.

Arc-Leading vs. Laser-Leading

From the BTWD trials, arc-leading was shown to have deeper penetration than laser-leading by an average of 0.5 mm for all BTWD. At short BTWD in the arc-leading orientation, the laser beam strikes the part in the arc depression. This can be seen in the high-speed video stills in Figure 11. At long BTWD in the arc-leading condition, the laser strikes the deposited metal (Figure 11); however, penetration is still deeper than the laser-leading condition at the same BTWD (Figure 10). One explanation for the increased penetration may be that the beam is always striking molten metal in the arc-leading condition. In the laser-leading condition, the laser is always striking base metal at any BTWD.

Another notable difference between arc-leading and laser-leading is the profile of the weld reinforcement. Because of the different push/drag GMAW torch

angles in each direction, the convexity of the weld reinforcement is different. Arc-leading produces a narrower, more convex bead. Laser-leading produces a wider, smoother surface profile.

Figure 11. Keyhole Location in Weld Pool for Different Process Orientations

To test the effect of process orientation on filler metal mixing, hybrid trials were conducted with stainless steel filler wire. Stainless steel filler was chosen to contrast the carbon steel base metal after etching the cross-sections. Welds were performed in both the arc-leading and laser-leading directions at two BTWD (Figure 12). In the arc-leading welds, the mixing appears to be similar for both BTWD. In the laser-leading welds, the 2-mm BTWD produced better mixing than both arc-leading cases. However, at the 5-

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mm BTWD, the GMAW pool was far enough behind the laser beam to prevent any mixing. There are clearly two solidification zones Figure 12-d.

Figure 12. Filler Metal Mixing Trials, (a) Arc-Leading, 2-mm BTWD, (b) Arc-Leading, 5-mm BTWD, (c) Laser-Leading, 2-mm BTWD, (d) Laser-Leading, 5-mm BTWD

Most noteworthy from these stainless filler wire mixing trials is that in all cases there was incomplete mixing to the root of the 9.5-mm joint. For this mixing evaluation, only four welds and four cross-sections were made. Additional trials should be conducted to evaluate a larger sample size. A more closely matching filler wire composition is also recommended for further testing.

Focal Position Evaluation

The weld penetration for different focal depths is plotted in Figure 13. The best penetration for both autogenous and hybrid welding was found to be when the laser was focused at the top surface of the plate (focal position of 0 mm). Other researchers have reported the best penetration to occur when the laser focus was moved 1 to 4 mm into the plate (focal position of -1 to -4 mm). This may be due to focal shift of the welding optics. Moving the nominal focus into the plate would compensate for a focal shift.

As seen in Figure 13, hybrid welding produces slightly more penetration than autogenous welding. More interestingly, hybrid welding maintains penetration over a wider range of focal position variations than autogenous welding. The tolerance to focal position variations for autogenous welding appears to be approximately 1 mm above or below the top surface of the plate before penetration starts to decrease. For

hybrid welding, the tolerance appears to be approximately 4 mm above or below the top surface of the plate before penetration starts to decrease.

Penetration vs. Focal Postion

3

4

5

6

7

8

9

-10 -8 -6 -4 -2 0 2 4 6 8 10

Focal Position (mm)

Pen

etra

tion

(mm

)

Autogenous Hybrid

Figure 13. Penetration vs. Focal Position for Autogenous and Hybrid

Laser-Arc Interaction

From the data collected, laser power does not appear to have a significant effect on the arc characteristics. The data acquisition verified that the GMAW power supply in CV mode maintained the arc voltage within less than 1% error regardless of the laser power. For the same arc settings, the average current at 5 and 9 kW was within 3% of the average current at no laser power.

The arc length measurements do not show a clear trend with voltage, laser power, or current. This may be due to the measurement method for arc length. One representative still was taken from each video and measured rather than averaging multiple measurements for each video. In addition, from the side view videos, weld pool depression could not be accounted for in arc length measurements.

Full-Penetration Root Evaluation

With no back-shielding, the exit side of the keyhole was violent. Large spatter globules and vapor or smoke sprayed from the keyhole opening. Most of the spatter traveled away from the plate, but some of the globules were directed toward the backside of the plate. Due to this violent and chaotic spatter transfer, the resulting root profile is irregular as seen on the right of Figure 14-a. A typical discontinuity in hybrid welding is underfill or suck-back on the root that may be caused by spatter loss from the keyhole or keyhole instability. By changing the shielding gas in the backing chamber to helium, the keyhole was much less

a b

c d

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violent and ejected only a fine spray of spatter. With a less violent keyhole and less spatter loss, the root profile produced with helium back-shielding was much smoother as seen in Figure 14-b. The effect of argon, nitrogen, and moving air were also tested on root profile. The performance of each backing gas is listed in order of best to worst: helium, argon, nitrogen, moving air, still air. Performance was determined by material loss and root bead consistency.

Figure 14. Video Still of Keyhole and Weld Root with (a) Still Air and (b) Helium Backing Gas

Laser and GMAW Synchronization

Once the synchronized laser-GMAW system was integrated to the i400 power supply by Lincoln Electric, test welds were completed to verify the phase delay and laser output with data acquisition. Figure 15 is a data-acquisition screen shot from a weld with in-phase laser pulse at the 4- to 6-kW laser power modulation. The top green trace is the measured arc voltage, and the bottom green trace is the measured arc current. The purple trace is the laser output signal overlaid on the current trace to verify phase delay. Figure 16 is a data-acquisition screen shot from a weld with 180-degree out-of-phase laser pulse at the 2- to 8-kW laser power modulation.

With the system output verified, hybrid welding trials were conducted according to Table 7. The welds were completed with the same equipment as for all previous trials. Analysis of the welds and data was completed by OSU.

.

Figure 15. Data Acquisition Trace of In-Phase Laser Modulation

Figure 16. Data Acquisition Trace of Out-of-Phase Laser Modulation

Figure 17 summarizes the laser-leading trials for both in-phase and out-of-phase at three different BTWD. The 4- to 6-kW laser power modulation produced deeper penetration than the 2- to 8-kW modulation. Both modulation amplitudes produced deeper penetration than the 5-kW constant power welds produced in the previous BTWD evaluation trials. This is most likely due to the higher peak laser power. Phase did not appear to have an effect on penetration.

Figure 18 summarizes the arc-leading trials for both in-phase and out-of-phase at three different BTWD. The 4- to 6-kW laser power modulation again produced deeper penetration than the 2- to 8-kW modulation, and both modulation amplitudes produced deeper penetration than 5-kW constant power. Overall, arc-leading produced deeper penetration than laser-leading. Phase did not appear to have an effect on penetration for arc-leading trials.

a

b

Arc Voltage

Arc Current w/ Laser Overlay

Arc Voltage

Arc Current w/ Laser Overlay

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Figure 17. Data Acquisition Trace of Out-of-Phase Laser Modulation

Figure 18. Data Acquisition Trace of Out-of-Phase Laser Modulation

Conclusions

From this research, the following conclusions can be drawn:

(1) Diode illumination can provide excellent high-speed videos of hybrid welding.

(2) BTWD and process orientation directly affect through-thickness filler metal mixing and fusion profile.

(3) The arc-leading orientation generates slightly more penetration than laser-leading.

(4) Hybrid welding has a higher tolerance to focal position variations than autogenous laser welding.

(5) Laser power has no discernable effect on arc characteristics in CV GMAW of steel.

(6) Inert shielding gas on the root side of full-penetration hybrid welds improves the root bead profile and reduces backside spatter.

(7) There is no significant penetration increase due to synchronous or asynchronous pulsing of laser power and GMAW current.

Acknowledgements

EWI acknowledges the contribution of the State of Ohio, Department of Development and Thomas Edison Program, which provided funding in support of Edison Technology and Industry Center Services.

Meet the Authors

Mr. Brian Victor is an Applications Engineer in the Laser Processing group at EWI. His primary areas of expertise include hybrid laser-arc welding, laser welding autogenously and with cold-wire addition, and laser processing of concrete. Mr. Victor received his B.S. and M.S. in Welding Engineering from the Ohio State University.

Mr. Brad Nagy is an Applications Engineer in the Laser Processing group at EWI. His primary areas of expertise include hybrid laser-arc welding, tandem gas metal arc welding, and automated GMAW. Mr. Nagy received his B.S. in Welding Engineering from the Ohio State University.

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