Advanced Robotic GMAW Cladding Process Development

Marc A. Purslow1 (V)

Weld cladding of carbon steel with stainless steel alloys is common for components used in commercial and military

ships. While automated gas metal arc welding (GMAW) has been shown to reliably produce clad layers with

adequate flatness, joint fusion, and acceptable levels of dilution, porosity defects have been reported as a significant

issue. Due to the large volumes of weld metal commonly required, commercially available electrodes are preferred

over custom-made products to reduce cost. GMAW uses a continuously-fed electrode in wire form and productivity

requirements demand long arc-on times for these cladding applications, making improved contact-tip-wear an

important consideration as well.

KEY WORDS: Cladding; Porosity; Stainless steel; Plasma-

Jet; Chemistry.

INTRODUCTION

Weld cladding of carbon steel with stainless steel alloys is

common for components used in commercial and military ships.

While automated gas metal arc welding (GMAW) has been

shown to reliably produce clad layers with adequate flatness,

joint fusion, and acceptable levels of dilution, porosity defects

have been reported as a significant issue. Due to the large

volumes of weld metal commonly required, commercially

available electrodes are preferred over custom-made products to

reduce cost. GMAW uses a continuously-fed electrode in wire

form and productivity requirements demand long arc-on times

for these cladding applications, making improved contact-tip-

wear an important consideration as well.

The goals of the project described in this paper were to develop

stainless steel GMAW cladding procedures that minimize

porosity using commercially available ERER308L and

ERER309L electrodes and to maximize arc-on time by

increasing contact tip life.

Pulse Waveform Evaluation and Selection

Weld trials were conducted to evaluate pulsed GMAW

(GMAW-P) and constant voltage GMAW (CV GMAW).

Commercially available GMAW-P waveforms and custom

GMAW-P waveforms developed at EWI were evaluated using

laser diode-illuminated high-speed video with synchronized data

acquisition and radiography (RT). A design of experiment

(DOE) approach was used to evaluate the influence of electrode

diameter, shielding gas, weld mode, travel speed, travel angle,

part inclination, contact-tip-to-work distance (CTWD), and arc

length on porosity formation. Using these data, a prediction

model was created and validation trials were conducted.

Electrode chemistries were analyzed to identify which elements

promote porosity formation. The effect of travel angle and

electrode diameter on dilution was evaluated and contact-tip-life

studies were conducted, comparing CV GMAW to GMAW-P.

Initial welding trials focused on developing and evaluating

GMAW-P waveforms to reduce porosity. Three commercially

available 0.063-in. stainless steel waveforms and one

commercially available 0.045-in. stainless steel waveform were

evaluated. Based on end-user requirements, trials were

conducted using 100% argon and 99.75% argon/0.25% CO2

shielding gasses. The majority of development work conducted

under this project was performed using a ER308L electrode

based on the assumption that porosity mitigation techniques

would also be applicable to ER309L electrodes.

High-speed video revealed a necking phenomenon with poor

droplet transfer, a columnar arc, and a significant weld pool

depression for all waveforms when using 100% argon shielding

gas (Figure 1). A minimum arc length of approximately 0.35 in.

was required to avoid excessive short circuiting and spatter

generation. This arc length resulted in poor wetting and

inconsistent bead width when welding on a carbon steel

substrate; however, wetting improved significantly when

welding on a stainless steel substrate or when welding on

previously deposited stainless steel layers. The addition of

0.25% CO2 to the shielding gas marginally improved droplet

transfer and significantly improved wetting consistency on

carbon-steel substrates.

Figure 1: GMAW-P necking phenomenon

Last name of Lead Author Paper Title in Times New Roman 9 point font 2

Figure 2. Commercially available 0.045 in. stainless steel

electrode pulse waveform

Figure 3. Commercially available 0.063 in. stainless steel

electrode pulse waveform

The use of 100% argon and 99.75% argon/0.25% CO2 shielding

gasses resulted in inconsistent droplet transfer and excessive

short-circuiting with arc lengths below 0.35-in. EWI developed

additional 0.045-in. and 0.063-in. stainless steel electrode

waveforms with higher pulse frequencies to promote more

consistent transfer of smaller droplets with the goal of

transferring a single droplet per pulse. The wire feed speed used

with the 0.045-in. waveform was 360 inches per minute (ipm),

resulting in an average current of 194 amps, and a pulse

frequency of 312 Hz. The wire feed speed used with the 0.063-

in. waveform was 200 inches per minute (ipm), resulting in an

average current of 246 amps and a pulse frequency of 322 Hz.

Current and voltage traces of these waveforms are provided in

Figure 4 and Figure 5.

Figure 4. EWI-developed 0.045 in. stainless steel electrode

pulse waveform

Figure 5. EWI-developed 0.063 in. stainless steel electrode

pulse waveform

The four waveforms described above were used to create 12-

layer weld clad deposits with 100% argon shielding gas and a

CTWD of 3/4-in. A travel speed of 6 ipm was used with a

weave width of 0.75 in. at a frequency of 1.3 oscillations per

minute. An overlap of 3/8 in. resulted in adequate tie-in and a

flat weld clad deposit. Completed weld clad deposits were

evaluated with RT. Both 0.045-in. pulse waveforms resulted in

significant levels of porosity and poor droplet transfer. The

commercially available 0.063-in. pulse waveform resulted in the

fewest number of pores while the EWI-developed 0.063-in.

pulse waveform resulted in the largest number of pores. Both

commercially available pulse waveforms were selected for use

in all subsequent trials.

Diode-laser-illuminated high-speed video was used to observe

the effect of welding mode, CTWD, and arc length on weld pool

depression. Figure 5 and Figure 6 illustrate that when welding

with GMAW-P, a 3/4-in. CTWD produced a deeper weld pool

depression than a 1 1/8 in. CTWD. This is due to the fact that an

increased CTWD results in increased resistive heating of the

electrode, reducing the current required to melt the electrode.

The required pulse frequency decreases as well, resulting in a

less focused arc. These effects reduce both the magnitude and

the footprint of the arc force on the molten weld pool, creating a

shallower weld pool depression. Figure 7 illustrates that the

more conical CV arc results in a larger-diameter weld pool

depression, decreasing the current density “seen” by the molten

weld pool when operating at the same current level. Table 1

quantifies these effects.

Last name of Lead Author Paper Title in Times New Roman 9 point font 3

Figure 5. Weld pool depression with GMAW-P, 0.063-in.

electrode, and a 1 1/8 in. CTWD

Figure 6. Weld pool depression with GMAW-P, 0.063-in.

electrode, and a 3/4-in. CTWD

Figure 7. Weld pool depression with CV GMAW, 0.063-in.

electrode, and a 1 1/8-in. CTWD

Table 1. Resultant pulse frequencies and average currents

for varied CTWDs

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

Design of Experiment Investigation

In preliminary weld trials, stringer beads consistently contained

more porosity than welds made with a weave. Porosity was

typically found at the penetration spike located at the weave

edges, indicating that stringer beads would represent a “worst-

case-scenario” regarding porosity and that methods of reducing

porosity in stringer beads would likely be effective in weave

welds. An additional benefit of eliminating the weave was that

the number of variables was reduced, simplifying the DOE. A

fractional factorial DOE design based on a Hadamard Matrix

was used. A resolution V design was used, allowing the

estimation of the main effects of each variable, as well as the

interactions between variables (1).The DOE required the

selection of two levels for each of the following variables.

Electrode diameter

Shielding gas

Weld mode

Travel speed

Part inclination

Travel Angle

Contact tip to work distance

Arc length

The following levels were selected based on end-user

requirements and/or EWI experience:

Electrode diameter: 0.045-in., 0.063-in.

Shielding gas: Argon, 99.75% Argon + 0.25% CO2

Weld mode: GMAW-P, CV GMAW

Scaling trials were performed to determine the remaining levels.

The primary criterion for level selection was whether a setting

would produce a visually acceptable bead for the majority of

variable combinations. For example, if travel speeds up to 16

ipm produced visually acceptable welds when welding with a

“short” arc length but the maximum achievable travel speed

when welding with a “long” arc length was 12 ipm, then the

upper travel speed level was set at 12 ipm. Since it was

assumed that increased penetration would correspond to

increased porosity, a secondary criterion for parameter selection

was penetration depth. Further, parameters were selected to test

the widest range possible for each variable.

Travel speed levels were selected based on resultant bead shape.

A travel speed of 4 ipm resulted in an excessively large bead

while 16 ipm or greater resulted in inconsistent beads with poor

weld pool-follow for some variable combinations. As a result,

the two levels selected for the DOE were 8 and 12 ipm.

Three part inclination angles were selected for scaling trials; -

10° (welding downhill), 0°, and 10° (welding uphill). Welds

were cross-sectioned to examine the effect on penetration.

Welding with a -10° part inclination resulted in less penetration

and a flatter reinforcement. Welding with a 10° part inclination

resulted in more penetration and a taller, more convex

Last name of Lead Author Paper Title in Times New Roman 9 point font 4

reinforcement (Error! Reference source not found.). The two

levels selected for the DOE were 0° and -10°.

Figure 8. Travel Speed vs. Part Inclination

Three travel angles were selected for scaling trials; -20° (drag),

0°, and 20° (push). Welding at a -10° part inclination with the

torch oriented at a -20° torch angle resulted in less penetration

and a flatter reinforcement. Conversely, it was observed that

welding at a -10° part inclination with the torch oriented at a 20°

resulted in more penetration and a taller, more convex

reinforcement (Figure 9). Based on these observations, the two

levels selected for the DOE were 0° and -20°.

Figure 9. Part Inclination vs. Travel Angle

The CTWD range selected for scaling trials was 5/8 in. to 1 1/2

in. A CTWD greater than 1 1/8 in. resulted in inconsistent

beads and poor arc starts. In both GMAW-P waveforms, arc

length was increased by reducing the background time. At a

CTWD of 5/8-in. the background time was nearly eliminated to

achieve the current level and arc length required to maintain

pulsed-spray transfer and avoid excessive short-circuiting.

Without the ability to further reduce the background time, the

arc length could no longer be increased when welding at this

condition. The minimum CTWD still allowing the use of an arc

length greater than 3/16-in. was 3/4-in. As a result, the two

levels selected for CTWD were 3/4-in. and 1 1/8 in.

The shortest arc length which could be used without significant

short-circuiting was 3/16 in. using GMAW-P, while CV

GMAW required a slightly longer arc length. For GMAW-P

and CV GMAW, the longest arc length which still produced a

consistent bead shape and had acceptable stability was 5/16 in.

The two levels selected for arc length were 3/16 in. and 5/16 in.

The DOE consisted of 48 weld beads. Since CV GMAW using

100% argon shielding gas resulted in poor arc stability and an

inconsistent bead shape, 99.75% argon/0.25% CO2 shielding

gas was used for these welds. A summary of DOE weld trials is

provided in Appendix A. Each bead was examined for porosity

using computed radiography (RT). Porosity was evaluated by

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, and the

number of isolated pores.

Pore size was scaled as follows:

● 0 = no pores

● 1 = pores ≤ 1/64-in.

● 2 = 1/64-in. < pores < 3/64-in. (Under size limit)

● 3 = pores ≤ 3/64-in. (Includes maximum size)

● 4 = pores ≥ 3/64-in. (Rejectable per size limit)

The shade of indications was scaled as follows:

● 0 = no pores

● 1 = light indications

● 2 = light and medium indications

● 3 = medium indications

● 4 = medium and dark indications

● 5 = dark indications

Acceptability per the end-user supplied criteria was scaled as

follows:

● 0 = Minimal to no porosity

● 1 = Below the acceptable level

● 2 = Barely acceptable

● 3 = Above the acceptable level

● 4 = Excessive porosity

A numerical model was created to predict the porosity level

resulting from the input variables investigated in the DOE.

Last name of Lead Author Paper Title in Times New Roman 9 point font 5

CTWD was identified as a significant contributor. Table 2

contains a set of optimized parameters and the predicted level of

porosity when using a 1.125 in. CTWD. Using this parameter

set, the model predicts minimal to no porosity in all categories.

Table 3 contains the same set of parameters with a 0.75-in.

CTWD. The model predicts a 3.7 on the acceptability rating,

medium and dark indications, and a total of 31 pores less than or

equal to 3/16-in.

Table 1. Predicted Porosity Level for 0.125-in. CTWD

Optimized Parameters Model Inputs

Wire Diameter

(in.)

Arc

Length CTWD (in.)

Travel Speed

(ipm)

Travel Angle

(deg.)

Part Inclination

(deg.)

Weld

Mode

Shielding

Gas

0.0625 Long 1.125 12 -20 0 Pulse Ar + CO2

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)

Summary - Porosity Measurements

Table 3. Predicted Porosity Level when Changing CTWD

to 0.75-in. Model Inputs

Wire Diameter

(in.)

Arc

Length CTWD (in.)

Travel Speed

(ipm)

Travel Angle

(deg.)

Part Inclination

(deg.)

Weld

Mode

Shielding

Gas

0.0625 Long 0.072 12 -20 0 Pulse Ar + CO2

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)

Summary - Porosity Measurements

0.72

The model also indicated that using the shorter arc length and/or 100% argon shielding gas could lead to increased porosity formation; however, changing the weld mode to CV would not result in increased porosity. Verification tests were run to validate the prediction model. Error! Reference source not found. provides the settings used for these tests. Table 4. DOE Verification Tests

Verification

Set

Wire

Diameter

(in.)

Arc

Length

(in.)

CTWD

(in)

Travel

Speed

(ipm)

Travel

Angle

(°)

Part

Inclination

(°)

Welding

Mode

Shielding

Gas

Voltage/

Frequency

1 0.0625 Long 1.125 12 -20 0 GMAW-P Ar + CO2 175 Hz

2 0.0625 Long 1.125 12 -20 0 CV-GMAW Ar + CO2 28.6V-29.2V

3 0.0625 Long 0.72 12 -20 0 GMAW-P Ar + CO2 294 Hz

4 0.0625 Long 1.125 12 -20 0 GMAW-P Argon 167 Hz

5 0.0625 Short 1.125 12 -20 0 GMAW-P Argon 159 Hz

RT examination revealed that Sets 1, 2, 4 and 5 were acceptable with minimal porosity. Plate 3 contained excessive porosity in all five welds. Error! Reference source not found. and Error! Reference source not found. illustrate the effect of CTWD on porosity formation, dilution, and penetration, and these results correlate directly to the predictions of the DOE model provided in Error! Reference source not found. and Error! Reference source not found.. A cross section of beads deposited using parameter set 3 is provided in Error! Reference source not found. with visible pores at the bottom of the penetration spike. Contrary to the prediction of the model, changing from 99.75% argon/0.25%CO2 to 100% argon shielding gas did not result in increased porosity. The same was true for welding with the shorter arc length.

Figure 10. Optimized GMAW-P with 1.25 in. CTWD

(predicted acceptability rating: 0)

Figure 11. GMAW-P with 0.72 in. CTWD (predicted

acceptability rating: 3.7)

Figure 12. Porosity at Base of Penetration Spikes when

Welding with a 3/4-in. CTWD

Error! Reference source not found. contains a summary of the

dilution and penetration depth of each verification parameter set.

The following conclusions can be drawn from these data:

Addition of 0.25% CO2 increased penetration and

dilution

Welding in CV mode increased penetration and

dilution

Welding with a shorter CTWD increased penetration

and dilution

The GMAW-P weld with the most penetration

contained the highest level of porosity

Table 5. Dilution and Penetration Depth for DOE

Verification Parameter Sets

Verification Set

CTWD (in.)

Welding Mode

Shielding Gas

Average Dilution

(%)

Average Penetration

(in.)

1 1 1/8 GMAW-P Ar + CO2 32.28 0.136

2 1 1/8 CV-GMAW Ar + CO2 42.27 0.165

3 3/4 GMAW-P Ar + CO2 46.21 0.214

4 1 1/8 GMAW-P Argon 26.77 0.112

5 1 1/8 GMAW-P Argon 25.82 0.106

Six additional weld clad deposits were made using oscillation

transverse to the welding direction, commonly referred to as

“weaving”. A summary of operating parameters, number of

pores, and pass/fail rating is provided in Error! Reference

source not found.. The DOE model predicted that W1, W2, and

Last name of Lead Author Paper Title in Times New Roman 9 point font 6

W6 would have minimal to no porosity, W4 and W5 would

have an acceptable amount of porosity, and W3 would have

porosity far exceeding the acceptance criteria. The results were

consistent with these predictions, aside from W5, which failed

due to the presence of pores exceeding the size limit.

Table 6. Weave-Weld Parameters Weave

Parameter

Set CTWD

Arc

Length Gas

Weld

Mode

Wire

Diameter

Travel

Angle

Part

Inclination

# of Pores

per 100

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

A graph of welding current versus the number of pores per 100

inches of weld for parameter sets W1 through W6 is provided in

Figure 13. This graph illustrates that at a welding current of 300

amps, the weld clad deposit made using CV GMAW had less

than 5% of the number of pores contained in the GMAW-P weld

made at an equal average current. These results indicate that the

level of porosity is not only related to current level, but also to

current density. Distributing the arc force over a greater area

leads to less finger-like penetration and reduces the number of

pores which are driven to the bottom of the penetration spike.

Figure 13. Welding Current vs. Number of Pores

While welds W1 through W6 were made with a 0° travel angle,

welding with a 10 degree push angle using CV GMAW resulted

in decreased oxidation and a wider, more uniform weld bead.

This was true whether welding on a carbon steel base plate or on

top of previously deposited layers. Additional weld clad

deposits were made to evaluate whether CV GMAW would

consistently result in welds with reduced porosity. While all

pores were within the acceptable size limits, the weld clad

deposit made with a 0.045 in. diameter electrode had more

porosity than the two weld clad deposits completed with a

0.0625 in. electrode (Table 7).

Table 7. Results from 3-layer CV Weld clad deposits

TrialCTWD

(in.)

Arc Length

(in.)Gas

Gas Flow

Rate (cfh)

Weld

Mode

Wire Diameter

(in.)

Pores per 100

inches

308L Push BU1 1.125 0.25 Ar + CO2 40 CV 0.0625 4.861

308L Push BU2 1.125 0.25 Ar + CO2 35 CV 0.0625 3.676

308L Push BU3 1.125 0.25 Ar + CO2 35 CV 0.045 8.929

* pores at the starts/stops have been disregarded

A twelve-layer weld clad deposit was created with over 550

linear inches of weld using CV GMAW, a 0.0625-in. electrode,

and a 10-degree push angle. Only two pores were found

resulting in a porosity level of 0.36 pores per 100 inches.

Electrode Chemistry

Material certifications for the five heats of ER308L used in

welding trials were studied to identify whether the levels of

chemical elements could be correlated to porosity formation.

The graph provided in Error! Reference source not found.

depicts the average number of pores per 100 linear inches of

weld for five electrode heats with data points representing

individual weld clad deposits. Data presented is for welds made

only with GMAW-P, since a larger number of samples were

created with GMAW-P than with CV GMAW. This graph

includes weld clad deposits made with different shielding gasses

and power sources. Heat “A” was 0.094-in. in diameter while all

other electrodes were 0.062-in. in diameter. Given the previous

conclusion that porosity level increases with increasing current

density, the low number of pores shown suggests a reduction in

current density with the larger electrode diameter. This is

consistent with previous findings that a lower welding current

density results in reduced porosity.

Figure 14. Average Number of Pores per 100 Linear Inches

of Weld vs. Electrode Heat

By comparing these data to material certifications and electrode

chemistry measurements, it was determined that the level of

chromium present in the electrode significantly influences the

porosity level. This is likely due to the fact that chromium

affects the solid solubility of nitrogen in the weld pool. This is

significant because nitrogen that cannot be absorbed by the weld

pool must escape via degasification before solidification occurs,

or porosity will result. As such, increased levels of chromium

correlate to decreased levels of porosity as shown in Figure 15.

Last name of Lead Author Paper Title in Times New Roman 9 point font 7

Figure 15. ER308L chromium levels

The chemical composition requirements for ER308L call for

19.5% to 22% chromium, while the requirements for ER309L

call for 23% to 25% chromium. Observations of the effect of

increased levels of chromium suggest that ER309L would be

less susceptible to porosity formation than ER308L. Additional

weld clad deposits were created with a solid ER309L electrode

as well as a metal cored ER309L electrode. These results are

included in Figure 16 as a comparison to the results from the

ER308L weld clad deposits. Both ER309L electrodes resulted

in low levels of porosity compared to the majority of ER308L

electrodes. The metal cored ER309L electrode, which had the

lowest current density of all electrodes tested, had the lowest

level of porosity.

Figure 16. Average Number of Pores per Inch vs. Electrode

Heat Including ER309L Weld Clad Deposits

A strong correlation was also found between the level of sulfur

present in electrodes and the level of porosity in the weld clad

deposits. Sulfur is a surface-active element that creates a layer

on the surface of the weld pool which acts as a barrier to

degassing, increasing porosity levels. The levels of sulfur found

in the ER308L electrodes and in corresponding buildups are

provided in Figure 17.

Figure 17. ER308L sulfur levels

Effect of Electrode Diameter and Travel Angle on Dilution

When welding on carbon steel, electrode diameter, travel angle,

and weld mode significantly influenced dilution (Error!

Reference source not found.). The lowest dilution was

achieved when welding with a 0.045-in. diameter electrode at a

20° drag angle; however, more porosity was observed than with

a 0.063-in. electrode. The decreased amount of dilution seen

when welding at a drag angle can be attributed to the welding

arc being located on the molten weld pool. Since this provides

additional material for the welding arc to penetrate, dilution is

reduced.

Figure 18: Effect of Travel Angle and Electrode Diameter on

Dilution

Contact-tip-life Trials

Contact-tip-life studies were conducted to compare GMAW-P to

CV GMAW. The results indicate an improvement in arc

stability and a significant decrease in contact tip wear when

using CV GMAW. Worn contact tips result in variation in the

last point of electrical contact with the electrode, which results

in variation in the arc length and voltage. As a result, voltage

data were recorded and used as a method of monitoring contact

tip wear. Figure 19 shows voltage data for the first half hour of a

Last name of Lead Author Paper Title in Times New Roman 9 point font 8

GMAW-P weld as well as data for the last half hour of a four-

hour-long CV GMAW weld. Contact tip wear when using CV

GMAW was visibly better than when using the baseline

GMAW-P waveform, as shown in Figure 20 and Figure 21.

Figure 19: Voltage data from GMAW-P and CV GMAW

contact-tip-life trials

Figure 2. GMAW-P contact tip wear

Figure 3. CV GMAW contact tip wear

CONCLUSIONS The findings of this project indicate that low porosity levels can

be achieved in ER308L and ER309L clad layers by

manipulating key process parameters and by selecting electrode

heats with ideal levels of chromium and sulfur. These findings

suggest that porosity occurs via two distinct mechanisms.

In the first mechanism, pores are driven to the bottom of the

penetration spike by a forceful arc. This mode is referred to as

“plasma-jet-induced” porosity. Data from welding trials showed

that the current density at the surface of the molten weld pool

has a significant effect on porosity level, and that current density

can be effectively reduced by using CV GMAW with an

extended CTWD. The forceful, columnar arc common to

GMAW-P produced a deep weld pool depression, driving pores

to the bottom of the penetration spike. Welding in CV mode

resulted in a more conical arc shape that reduced the current

density and the severity of the depression in the weld pool.

Welding with an extended CTWD further reduced the current

density as the increased resistive heating experienced by the

electrode decreased the current required to melt the electrode. A

10° (push) travel angle improved wetting and reduced porosity,

but increased dilution compared to a -10° (drag) travel angle.

In the second mechanism, porosity level is a function of

electrode chemistry. Porosity levels were correlated to the

amount of chromium and sulfur in the welding electrode.

Increased levels of chromium correlated to decreased levels of

porosity because chromium increases the solubility of nitrogen

in the weld pool. Electrodes with higher levels of chromium

were able to absorb higher levels of nitrogen, minimizing the

level of degasification required to allow pores to escape the

weld pool before solidification. Decreased levels of sulfur

correlated to decreased levels of porosity because sulfur is a

surface-active element which creates a layer on the weld pool

surface that can act as a barrier to degassing.

In addition to reduction in porosity, contact-tip-life and arc

stability were both significantly improved when using CV

GMAW compared to GMAW-P.

REFERENCES 1. Diamond, William J., Practical Experiment Designs

for Engineers and Scientists, 1981.

Last name of Lead Author Paper Title in Times New Roman 9 point font 9

APPENDIX

DOE

Run #

Electrode

Diameter

(in.)

Arc

Length

(in.)

CTWD

(in.)

Travel

Speed

(ipm)

Travel

Angle

(deg.)

Part

Inclination

(deg.)

Weld ModeShielding

gas

1 0.0625 5/16 0.75 8 0 0 GMAW-P Ar

2 0.0625 5/16 0.75 8 -20 0 GMAW-P Ar + CO2

3 0.0625 5/16 1.125 12 -20 0 GMAW-P Ar

4 0.0625 3/16 1.125 8 0 0 GMAW-P Ar + CO2

5 0.0625 3/16 1.125 8 0 -10 GMAW-P Ar

6 0.0625 5/16 1.125 12 0 0 GMAW-P Ar + CO2

7 0.0625 3/16 1.125 8 -20 -10 GMAW-P Ar + CO2

8 0.0625 5/16 0.75 8 -20 -10 GMAW-P Ar

9 0.0625 5/16 1.125 12 -20 -10 GMAW-P Ar + CO2

10 0.0625 3/16 0.75 12 0 -10 GMAW-P Ar + CO2

11 0.0625 3/16 0.75 12 0 0 GMAW-P Ar

12 0.0625 3/16 0.75 12 -20 -10 GMAW-P Ar

13 0.045 3/16 0.75 8 -20 -10 GMAW-P Ar + CO2

14 0.045 3/16 1.125 12 -20 0 GMAW-P Ar + CO2

15 0.045 3/16 1.125 12 -20 -10 GMAW-P Ar

16 0.045 5/16 1.125 8 0 0 GMAW-P Ar

17 0.045 5/16 0.75 12 -20 -10 GMAW-P Ar + CO2

18 0.045 5/16 0.75 12 0 0 GMAW-P Ar + CO2

19 0.045 5/16 1.125 8 -20 -10 GMAW-P Ar

20 0.045 5/16 0.75 12 0 -10 GMAW-P Ar

21 0.045 3/16 0.75 8 0 0 GMAW-P Ar + CO2

22 0.045 3/16 0.75 8 -20 0 GMAW-P Ar

23 0.045 5/16 1.125 8 0 -10 GMAW-P Ar + CO2

24 0.045 3/16 1.125 12 0 0 GMAW-P Ar

25 0.0625 3/16 0.75 8 0 0 CV-GMAW Ar + CO2

26 0.0625 5/16 1.125 8 0 -10 CV-GMAW Ar + CO2

27 0.0625 3/16 1.125 12 0 -10 CV-GMAW Ar + CO2

28 0.0625 5/16 0.75 12 -20 0 CV-GMAW Ar + CO2

29 0.0625 5/16 0.75 12 0 -10 CV-GMAW Ar + CO2

30 0.0625 3/16 0.75 8 0 -10 CV-GMAW Ar + CO2

31 0.0625 5/16 0.75 12 -20 -10 CV-GMAW Ar + CO2

32 0.0625 5/16 1.125 8 -20 0 CV-GMAW Ar + CO2

33 0.0625 5/16 1.125 8 -20 -10 CV-GMAW Ar + CO2

34 0.0625 3/16 0.75 8 -20 0 CV-GMAW Ar + CO2

35 0.0625 3/16 1.125 12 0 0 CV-GMAW Ar + CO2

36 0.0625 3/16 1.125 12 -20 0 CV-GMAW Ar + CO2

37 0.045 5/16 0.75 8 0 -10 CV-GMAW Ar + CO2

38 0.045 3/16 0.75 12 -20 0 CV-GMAW Ar + CO2

39 0.045 3/16 0.75 12 -20 -10 CV-GMAW Ar + CO2

40 0.045 5/16 1.125 12 0 -10 CV-GMAW Ar + CO2

41 0.045 3/16 0.75 12 0 -10 CV-GMAW Ar + CO2

42 0.045 3/16 1.125 8 -20 0 CV-GMAW Ar + CO2

43 0.045 5/16 1.125 12 0 0 CV-GMAW Ar + CO2

44 0.045 3/16 1.125 8 0 -10 CV-GMAW Ar + CO2

45 0.045 3/16 1.125 8 -20 -10 CV-GMAW Ar + CO2

46 0.045 5/16 0.75 8 0 0 CV-GMAW Ar + CO2

47 0.045 5/16 1.125 12 -20 0 CV-GMAW Ar + CO2

48 0.045 5/16 0.75 8 -20 0 CV-GMAW Ar + CO2