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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
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