As the Pendulum Tilts - High-Performance Machine & Semi-Auto GMAW/MIG/MAG Pipe Fabrication

The so-called “progress, “time marching on,” is not a straight line, but a pendulum. - Zygmunt Bauman

LJ Welding Automation’s equipment enables the productivity and quality benefits of flat and rolled welding for customers worldwide. The essence of our approach to machine welding is “coordination and sequencing of welding and motion”. We’re continuing our focused pursuit of excellence in machine welding and have a short case study to share - videos below feature an integrated pipe welding cell including an LJ MNP5-700 Manipulator with LJ Tilt Rotate Pendulum Oscillator (TRPO) and LJ P3PS Positioner welding NPS 6 (6.625”[168.28 mm] OD) Schedule 80 (0.432” [10.973 mm] WT) ASTM A106 Grade B (ASME P1 Group 1) steel pipe.

Machine / Mechanized External Open Root Pass

In the above timestamped Cavitar C300 video, a machine / mechanized open root pass is applied using two of EWM’s high-performance waveforms:  

• RootArc is a short-circuit transfer waveform, used here at open root segments.  
• RootArc Pulse is a pulsed spray transfer waveform, used here to ensure fusion and wetting over the feathered tack welds.   

Root Pass Waveforms: RootArc and RootArc Pulse

• Low-spatter, digitally-controlled metal transfer with easy arc starting and superb arc stability.  
• Excellent gap-bridging with effortless control of the weld pool and mastery of gaps. Wide process windows maintain arc stability even at high wire feed speeds or when arc-to-puddle placement is suboptimal (e.g. an unskilled welder “riding the puddle” or “outrunning” it).
• Reduced heat input and spatter compared to CV short-circuit transfer roots, which deliver excess energy(waste heat). The video from the U of Alberta’s CCWJ captured using a ‘Phantom’ high-speed camera clearly shows this: https://www.youtube.com/watch?v=tpXFGpSXONY
• Favorably-convex root formation with reliable sidewall fusion – clearly visible in both root videos. 

This root pass was accomplished using a travel speed between 12.0 – 12.5 ipm travel speed, and a WFS of 272 ipm (a summary of all passes is included later in this article). The process window was maximized by using a circumferential position of 45°, which aligns with recommendations for rolled roots from Lincoln for their comparable STT? process (STT? Pipe Root Pass Weld Process Guide [TE12.014 07/15]: “1:00 – 2:00 with a 10° trailing angle”) and Miller’s recommendations for their comparable RMD? process (Guidelines for Pipe Welding [247250C 2018?08]: “1:30-2 o’clock” with a “5 to 10 degree trailing angle”).

Handheld Semi-Auto External Open Root Pass

While machine / mechanized roots are certainly impressive to watch, our recommendation is to only use this technique when excellent fit-up tolerance is achieved– this is typically when machine-bevelled or high-def plasma bevelling is done on consistent-geometry pipe. 

Note that both pipe/fitting and bevel/prep technique contribute to fit-up variation. Knowing consistent near-perfect fit-up isn’t always achievable, LJ equips this machine with a semi-auto torch to provide a means of reliably applying root passes when fit-up inevitably varies. With 2 tactile buttons on top of the torch handle, semi-auto root passes also benefit from:

• Toggling between EWM’s RootArc and RootArc Pulse based on joint and tack conditions (just like shown in the machine root welding video above). 
• Toggling between Main Program Pa and Reduced Program Pb based on root gap and puddle conditions.   

The adaptations a trained welder naturally and intuitively makes in response to varying fit-up, arc and puddle conditions are further elevated by the use of a variable-speed foot pedal (shown here), which allows the welder to speed up for narrow root gaps or slow down positioner rotation for wide root gaps or when using the Pb reduced program during the root welding operation.

Machine / Mechanized Hot Pass, Fill and Cap

The next timestamped Cavitar C300 video shows a machine welding hot pass, fill and cap. After the hot pass is completed, a quick “Job”/waveform change sequence is initiated, including a short stoppage in workpiece rotation to allow for arc re-ignition. Unfortunately, the initial 16.5 ipm fill travel speed was carried over from NPS 8 pipe parameters and proved too slow for this NPS 6 pipe, leaving a defect at the fill pass start - more about this in the TOFD section below.

Hot Pass Job/Waveform: ForceArc Pulse

A waveform-controlled pulsed spray transfer Job designed for high penetration and high travel speeds. It was selected to help ensure fusion at the root pass toes and consistently achieve hot pass wetting, all while “pushing” the root out (by ~ 1/32” [0.8 mm]) for a consistently convex ID profile. 

• Heat-minimized pulsed arc
• Outstanding wetting with low undercut tendency
• Deep and concentrated penetration profile
• Low spatter, low fume

Fill and Cap Pass Job/Waveform: GMAW Pulse

A waveform-controlled pulsed spray transfer Job providing efficient filling with lowered heat input compared to CV spray. Because both Fill and Cap use the same Job/waveform, the transition from one pass to the next is seamless, with welding workpoint and oscillation changes coordinated together due to the machine’s full integration, coordination and sequencing of welding and motion.

• Heat-minimized pulsed arc
• Low spatter

Time-Of-Flight Diffraction (TOFD) Ultrasonic Inspection

The completed weld was brought to InnoTech Alberta’s facilities at the Devon Research Centre for TOFD scanning, executed in accordance to BS EN ISO 10863 using their Olympus OmniScan MX2 with Jireh STIX 2 Probe Scanner. As was suspected/expected, a significant flaw was found at start of the fill pass.

Lessons learned:

• The process should have been stopped and grinding performed prior to resumption of welding. 
• Next time, we’ll fully optimize welding parameters prior to capturing crystal-clear welding video on a (short term) demo camera for sharing on social media!    

Pipe Welding Cell Components

LJ MNP5-700 Column and Fixed-Boom Manipulator

The fixed-boom design allows unimpeded fit and tack welding operations on the positioner not currently in use with the manipulator.

• With both semi-auto and machine (mechanized) welding capability, you can choose your best approach for your application – workpiece dimensional variation (ovality, seam peaking, flat spots, diameter variance), fit-up variation, pre-tacked assemblies or not, bevelling technique and consistency (machined > plasma > oxy-fuel).
• LJ’s servo-driven Tilt Rotate Pendulum Oscillator (TRPO) provides fast and accurate weaving with minimal vibration and deflection. 
• LJ’s Topflight Tactile Controls are inspired by aircraft cockpit controls design philosophy. The ergonomically-arranged buttons and knobs feature tactile feedback and distinguishable shapes, grouping and sizing to reduce operator error and provide predictable and repeatable motion.
• The touchscreen HMI provides access to comprehensive settings and modes, with the PLC programmed for total integration and control of the welding system, providing true Machine Welding by coordinating and sequencing motion and welding together. This includes automatic positioner RPM assignment for the workpiece diameter entered on the HMI.  
• EWM’s GMAW/MIG/MAG systems including the alpha Q 552 puls MM on the LJ machine above provide superb arc starts and exceptional arc stability (no sense lead required!) with a large library of “all-in” (no-extra-charge) advanced waveforms for a variety of applications and materials. It’s interface allows LJ to fully integrate using fast communication for control and feedback, including fast 5 ms refresh rate on arc parameters (A, V, WFS) making it useful without modification or external instrumentation for through-arc tracking, and designed for safe automation with features like a hard-wired E-Stop. 
• High-pressure high-wattage water cooling, here an EWM Cool 82 with heavy-duty pump, features integrated actuation and flow monitoring, providing effective torch cooling for extended consumables life and reduced maintenance downtime.   
• EWM’s Xnet system provides full Industry 4.0 data capture (see screenshots above). 
• Enviroflex Fume Extractor with custom LJ torch-mounted nozzle for effective source capture. 

Two Positioners (Workpiece Rotation)

• LJ’s positioners including the P3PS and P6PS shown in this cell provide absolutely consistent and integrated rotation even for offset/levered assemblies (within spec).
• Grouping one manipulator with 2 positioners enables high manipulator utilization by reducing wait times for fit and tack welding operations. Some heavy wall applications will also benefit from semi-auto root welding on the positioner not currently in use with the manipulator.  

LJ Welding Automation – State-of-the-Art Machine Welding Equipment – Made in Alberta with World-Class Components.

Acknowledgements

Thank you to Christian Kutschke and Cavitar for the use of their C300 demo unit, and thanks to Sean Watt (shown in TOFD image above) and Randi Smallwood (not shown) at InnoTech Alberta for facilitating this welding camera technology evaluation and hosting me at the Devon Research Centre for the TOFD inspection! Team LJ shown below is (Left to Right) Tony Braun, Mark Armstrong and me, Chris Penniston.