FEATURE ARTICLE

CWA JOURNAL 2412

EXPERIMENTAL STUDY OF SPINARC™ TECHNOLOGY

Based in Spring, Texas, WeldRevolution markets SpinArc™welding technology to help fabricators and manufacturers in various industrial sectors to increase productivity [1]. On a specially-designed SpinArc™ torch for Gas Metal Arc Welding (GMAW) process, the contact tip and the consumable wire electrode are spin in a conical manner with adjustable rotational spin speeds, spin directions, spin diameters and Contact Tip to Work Distances (CTWD) [1]. According to WeldRevolution, the spinning action allows narrow, deep butt weld joints with little or no edge preparation, improved sidewall fusion and higher welding speeds [1]. In addition, SpinArc™ tech-nology reduces the weld joint preparation time and cost, reduces the volume of fi ller metal needed, and cuts the labour costs by reducing the time required to complete the weld [1].

To observe the above benefi ts of the SpinArc™ technology,an experimental study was conducted. First, to observe the benefi ts of eliminating edge preparation and achieving sidewall fusion using SpinArc™ technology,

¾” (19mm) thick square butt weld joint was qualifi ed in accordance to CSA W47.1 and ASME Section IX codes. Second, a weld produced using SpinArc™ technology was compared against that of a CSA W59 prequalifi ed Submerged Arc Weld (SAW) process. Finally,the effects of the SpinArc™ torch setting parameters on a bead-on-plate weld’s width were investigated using full factorial design of experiments. All welding in this study was conducted in the 1G (fl at groove) position.

EQUIPMENT, MATERIALS AND EXPERIMENTAL SETUP

In this study, the SpinArc™ MA-400 GMAW torch was connected to a Miller PipeWorx 400 welding machine. The torch body was then mounted on Gullco Kat travel carriage. ¾” (19mm) thick ASTM A36 steel bars were selected to mimic heavy fabrication application. To observe the sidewall fusion capability, the ¾” (19mm) thick bar was cut 3” (75mm) wide and 12” (300mm) long and arranged into a narrow gap square groove

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butt joint with a ¼” (6.4mm) root opening. The square groove butt joint was selected as no edge preparation is required. The ¼” (6.4mm) root opening was selected to imitate narrow gap welding, and to minimize the joint cross- sectional area while obtaining sidewall fusion. A ¼” (6.4mm) thick A36 bar was used as backing bar. The SpinArc™ welding assembly is as shown in Figure 1.

In a comparison test, a CSA W59 prequalified weld joint, S2-1, was utilized to produce a weld using the submerged arc welding process [2]. This is a 20º single V-groove joint with a 5 ⁄8” (16mm) root opening (see Figure 2). The backing bar is 3 ⁄8” (10mm) thick. For this weld joint, the root pass was split as mandated by the CSA W59 code [2].

The submerged arc weld was produced using ESAB LAF 631 CC/CV DC power source and ESAB CAB 2200 manipulator. The welding parameters are as summarized in Table 1.

Table 1: SAW parameters used in this study.

WELDING PROCEDURE QUALIFICATION

Initially, several SpinArc™ GMAW welds were attemptedand various parameters were adjusted to achieve a defect-free weld with proper sidewall penetration. The resultant GMAW welding parameters and the SpinArcTM setting are as summarized in Table 2. Because of the narrow square groove joint, the Contact Tip to Work Distance (CTWD) was initially set at 1” (25mm) for the root pass and 5 ⁄8” (16mm) for all subsequences passes. The SpinArc™ torch was set to spin at 750 rpm in the clockwise direction and its spin diameter setting was at 3, which approximately correlates to 3mm (1/8”) diameter of the rotation at the end of the contact tip.

Table 2: SpinArcTM GMAW welding parameters.

Using the above parameters, a SpinArc™ GMAW weld was produced, cross-sectioned, polished, etched and metallurgically photographed. As illustrated in Figure 3, the weld has a flat top and consistent penetration profile to the side walls and the backing bar. The cross-sectional profile of the weld demonstrates the ability of SpinArc™ technology to produce GMAW welds without edge preparation and excellent sidewall fusion in a thick narrow groove joint.

SpinArcTM GMAW assembly.01

CSA W59 S2-1 prequalified SAW weld joint [2].02

Wire & Flux Type EM12K-F7A4 (F49A4)

Wire Size 3/32” (2.4 mm)

Voltage 27 V

Wire Feed Speed 110 ipm (46.5 mm/s)

Welding Speed 27 ipm (11.4 mm/s)

Contact-Tip-To-Work Distance 1” (25.4 mm)

Wire Type ER70S-6 (ER49S-6)

Wire Size 0.045” (1.2 mm)

Shielding Gas 83% ARGON & 17% CO2

Shielding Gas Flowrate 50 cfh (24 ipm)

Voltage 28 V

Wire Feed Speed 325 ipm (138 mm/s)

Welding Speed 24 ipm (10.2 mm/s)

Contact-Tip-to-Work Distance Root pass – 1” (25.4 mm)Fill passes – 5 ⁄8” (16 mm)

Spin Diameter Setting 3

Spin Speed 750 rpm

Spin Direction clockwise

⁄ ” x3”x12” 3 ⁄4” x3”x12”

3 ⁄4” x3”x12” 3 ⁄4” x3”x12” 5/8”

20°

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CWA JOURNAL 2414

The above welding procedure was then qualified according to CSA W59 [2], CSA W47.1 [3], and ASME Section IX [4] codes. As per the requirements of these standards and codes, guided side bend test and transverse reduced section tensile test were performed. For each case, five specimens were produced and tested. The results for CSA W59&W47 codes are summarized in Table 3 and the results for ASME Section IX code are in Table 4.

In both Table 3 and Table 4, the number, the maximum size and the accumulative lengths of all indications (i.e., cracks) are reported. The acceptance criteria for the guided side bend test are that no single indication could be larger than 1 ⁄8” (3.2 mm) with the cumulative length of all indications being no longer than 3 ⁄8” (10 mm). The test specimen has 2, 1 or no crack or indication. All specimens met the acceptance criteria.

For the transverse reduced section tensile tests, CSA standards state that no individual test can be less than 95% of the minimum specified strength, while the averageof all specimens can be no less than the minimum specified tensile strength. ASME code also has the 5% allowance with the minimum specified tensile strength. In both cases, the specified minimum tensile strength is 58 ksi(400 MPa). Clearly, none of the measured tensile strengths is less than the specified value. The lowest measured ultimate tensile strength is 68 ksi (469 MPa) while the overall average of all specimens is approximately71 ksi (490 MPa) which is well above the specified tensile strength.

Based upon these tests results, SpinArcTM technology can be used in GMAW procedures meeting the qualification

Typical cross-sectional profile of a SpinArcTM GMAW weld.03

Specimen Guided Side Bend Test Indications Specimen Ultimate TensileLabel No. of Indications Max. Size Accum. Size Label Strength (ksi)C1 None - - 1C 72C2 2 0.071" 0.083" 2C 70C3 2 0.047" 0.079" 3C 71C4 None - - 4C 70C5 1 0.020" 0.020" 5C 72

Table 3: Guided side bend and transverse reduced section tensile test results for CSA codes.

Table 4: Guided side bend and transverse reduced section tensile test results for ASME code.

Specimen Guided Side Bend Test Indications Specimen Ultimate TensileLabel No. of Indications Max. Size Accum. Size Label Strength (ksi)A1 1 0.037" 0.037" 1A 72A2 1 0.022" 0.022" 2A 73A3 2 0.031" 0.054" 3A 68A4 2 0.025" 0.043" 4A 71A5 2 0.037" 0.048" 5A 74

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requirements of both CSA W59&W47.1 and ASME Section IX. The technology can produce GMAW weld in a thick square groove joint without special edge preparation. Next, the production of a SpinArcTM GMAW weld will be compared to that of a pre-qualified SAW weld joint.

A COMPARISON BETWEEN SPINARCTM AND SUBMERGED ARC WELDS

For a ¾” (19mm) thick steel bar in a butt joint configura-tion, 4 welding passes were needed with the SpinArcTM technology as illustrated in Figure 3. For comparison purposes, a CSA W59 prequalified weld joint, S2-1 [2], was utilized to produce a SAW weld using the welding parameters listed in Table 1. The resultant cross-sectional SAW weld profile is shown in Figure 4.

To produce the weld, SAW process required 13 passes although the number of passes could be further optimized with larger wire diameter. A comparison between the photomicrographs of SpinArcTM and of SAW welds reveals that the SpinArcTM weld has more pronounced columnar solidification grain structure. For each pass, the SpinArcTM weld had smaller width to depth ratio as compared to SAW weld (see Figure 3 and Figure 4).With ¾” (19mm) thick base plates, the SpinArcTM welds solidified at higher cooling rates. Along with ¼” (6.4mm) narrow gap, the high cooling rates promoted the columnar solidification grain structure observed in Figure 3.

The hardness values in the Heat Affected Zone (HAZ), the bay region in the HAZ just beneath the cap weld pass, the weld metal (WM), and the reheated weld metal were measured using a micro Vicker Hardness tester with 1 kg

applied load. From the measurements, the average hardness and 2 standard deviations at each location were calculated and plotted in Figure 5.

From the measurements, the hardness of the HAZ, the bay region HAZ, and the weld metal are statistically similar when comparing the SAW weld and the SpinArcTM weld. The hardness in the reheated weld metal, however, is higher for the SpinArcTM weld than the SAW weld (see the highlighted area of Figure 5). For a multi-pass weld joint, the subsequent welds layers caused grain refinement in the weld metal of the previously deposited weld metal. Since the SAW process had 13 passes, the previous weld metal underwent more heat cycles and thus the hardness is lower than that of the SpinArcTM weld. For time and cost comparison, each weld was assumed as a single pass. As such, the cleaning and the prepa-ration time between passes are not accounted for. The itemized time and cost are summarized in Table 5.

Table 5: Time and cost comparison between SAW and SpinArcTM welds.

The cross-sectional profile of a ¾” (19mm) thick SAW weld using CSA W59 S2-1 prequalified joint.

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The measured average hardness at various locations for both SAW and SpinArcTM welds.

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Wire & Flux Type SAW Weld SpinArcTM Weld

Cross-Sectional Area 0.379 in2 0.188 in2

Welding Wire & Gas/Flux

$3.12 $1.12

Total Arc on Time 6 min 15 sec 4 min 30 sec

Welding Cost $14.30 $8.36

Since the cross-sectional area of SAW is larger than the cross-sectional area of the SpinArcTM weld, more fi ller welding wire and fl ux were used and thus a higher welding consumable cost. Also, the SAW weld had a longer arc on time than the SpinArcTM weld because of its larger cross-sectional area. As a result, in this study, the SpinArcTM weld was signifi cantly less expensive to produce than the SAW weld.

Effects of SpinArcTM Settings on the Bead-On-Plate Weld Width

On the SpinArcTM MA-400 GMAW torch, there are four selectable parameters;the spin dial, CTWD, the spin speed, and spin direction. The spin dial setting controls the diameter of the spin and approximates the diameter of the rotation in millimeters at the end of the contact tip. CTWD is the distance between the work-piece and the contact tip of the torch. The spin speed is the rotational speed and the spin direction is either clockwise or counter-clockwise. In this study, the torch was set to spin clockwise as viewed from the top and along the torch length to the workpiece.

Since the spin dial setting, the CTWD and the spin speed have infl uences on the weld size, these three factors were studied at 2 levels, 5 replicates full factorialdesign of experiments [5]. For each factor, a high value and a low value were selected as listed in Table 6.

Table 6: Parameters of the design of experiments.

The spin dial or diameter setting was set to a high value of 8 and a low value of 1 as these are the limits of the SpinArcTM

MA-400 GMAW torch. The 1” (25 mm) CTWD was used as a high value since this was the farthest distance from the workpiece that adequate shielding gas coverage could still be maintained. The low CTWD was set to 5 ⁄8” (16 mm), a typical distance for GMAW spray transfer.Lastly, the high spin speed was set at 1200 rpm which is the recommended maximum spin speed for a spin dial set-ting of 8. The low spin speed was set to the lowest possible setting of 200 rpm.

With three factors at two possible setting values, there were 8 different possible combinations [5]. For each combination, the experiment was repeated 5 times; i.e., 5 replicate trial runs. To avoid systematic bias during experimentation, the order of the trial runs was completely randomized. For each run, a bead-on-plate weld was produced and the weld width was measured randomly along the weld length.

For the 3 factors at 2 levels full factorial design of experiments, there were poten-tially three individual factor effects, three two-factors interaction effects and one three-factor interaction effects [5]. These effects can theoretically alter the weld width. To separate the signifi cant from non-signifi cant infl uences, a 95% confi dence interval of the effects were calculated and plotted in Figure 6.

From the experimental results, the spin dial setting, the CTWD, the spin speed

CWA JOURNAL 2416

Wire & Flux Type High Value

Low Value

Spin Dial (Diameter) 8 1

CTWD (inch) 1" 5 ⁄8”

Spin Speed (rpm) 1200 200 95% confi dence interval of the effects.06

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and the interaction between the spin dial setting and spin speed have significant influence on the weld width. The larger the spin diameters widen the weld width. Conversely, longer CTWD, higher spin speed or larger interaction value between spin dial setting and spin speed appear to narrow the weld width. Based on these identified significant effects, a linear regression analysiswas performed to yield an analytical equation that predicts the bead-on-plate weld width as a function of the effects. Equation 1 is the result of the linear regression analysis.

W=0.414+0.011A - 0.110B - 5.85x10 - 6 C Equation 1

where W is the weld width (in), A is the numerical spin dial setting on the SpinArcTM MA-400 torch, B is the CTWD (in), and C is the interaction between the spin speed (rpm) and the spin dial setting (i.e., the multiplied value of the spin speed in rpm and spin dial setting). Although it was previously identified as a significant effect from the 95% confidence interval plot, the spin speed appears to be an over fitting factor which has very minimal influence in the analytical model. As a result, it was left out of the final predictive model.

To validate the above predictive model, multiple welds were produced with random spin dial setting, CTWD and spin speed combination. These parameters were set between the high and the low values of Table 6. After welding, each weld width was measured at several locations along the weld. The average weld width and two standard deviations were then calculated. The spin dial setting, CTWD and the spin speed of each weld were then used in Equation 1 to predict the weld width. Both the actual and measured weld widths are plotted in Figure 6. Overall, the model can predict the weld width within two standard deviations of measurements. Of nine test samples, the predictive model is only unsuccessful for one sample. In this case, the predicted value is just lower than the 2 standard deviations.

FINAL REMARKS

In this study, SpinArc™ torch was successfully used to produce cost effective, CSA and ASME qualified welds in a ¾” (19mm) thick steel application with a square-groove butt-joint configuration. The SpinArcTM technology could consistently fuse the sidewall using only a ¼” (6.4mm) gap opening. From the design of experiments, a model was developed and successfully predicted the bead-on-plate weld width based on the spin dial setting, contact tip to work distance and the interaction between spin dial setting and spin speed of the welding torch.

Future work with the SpinArc™ system will explore the tolerance of these narrow joint preparations to variations in fit-up, the ability of the technology to successfully weld multiple-pass groove welds without inter-pass cleaning, boosting weld productivity using larger diameter wires and higher feed-rates, and exploring out-of-position welding applications.

AcknowledgementThe authors would like to acknowledge the invaluable assistances from Abicor Binzel, WeldRevolution, HAI Precision Waterjets, Perfection Inspection, and Cambridge Materials Testing Limited. This study was conducted as a final year engineering technology capstone project and was supported by Conestoga College.

About the AuthorsTyler Rudnicki and Caleb DeVries are both recent graduates of the Manufacturing Engineering Technology – Welding Robotics program at Conestoga College. Mr. Rudnicki has recently accepted a position as the Educational Account Manager for In-House Solutions in Cambridge, ON. Mr. DeVries is currently working as a Joining and Automation Engineer at R&E AutomatedSystems in Macomb County, Michigan. Dr. Tam Nguyen is a Professor at Conestoga College.

References

[1] WeldRevolution, "WeldRevolution," 2017. [Online]. Available: http:// www.weldrevolution.com/. [Accessed July 2017].[2] Canadian Standards Association, CSA W59-13 - Welded Steel Construction (Metal Arc Welding), Mississauga: CSA Group, 2013. [3] Canadian Standards Association, CSA W47.1 - Fusion Welding of Steel Company Certification, Mississauga: CSA Group, 2009. [4] American Society of Mechanical Engineers, ASME Boiler and Pressure Vessel Code - Section IX Welding, Brazing, and Fusing Qualifications, New York: The American Society of Mechanical Engineers, 2013. [5] D. C. Montgomery, G. C. Runger and N. F. Hubele, Engineering Statistics, New York: Wiley, 2011.

The predicted and the measured weld widths along with 2 standard deviations of measured weld widths.

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Tyler Rudnicki, Caleb DeVries and Tam Nguyen Conestoga College

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