Engineering Review: Multi-pass Welding Collaborative Arc Welding System – Chennai, India

Field Report: Deployment of Multi-pass Collaborative Arc Welding Systems in Chennai Industrial Zone

1.0 Executive Summary and Site Conditions

This report details the technical deployment and performance evaluation of a Collaborative Arc Welding System (CAWS) integrated into a heavy-scale structural steel welding facility in Sriperumbudur, Chennai. The primary objective was to transition high-volume, multi-pass heavy plate joints from purely manual Gas Metal Arc Welding (GMAW) to a hybrid model utilizing Automated Welding via collaborative robotics (cobots).

The environmental conditions in Chennai—specifically high ambient temperatures (38°C–42°C) and relative humidity often exceeding 75%—presented immediate challenges for equipment duty cycles and shielding gas stability. In the context of structural steel welding for infrastructure components (IS 2062 Grade B), maintaining interpass temperatures while maximizing deposition rates requires a precise balance that manual operators struggle to maintain over an 8-hour shift. The introduction of the Collaborative Arc Welding System was designed to stabilize these variables.

2.0 Technical Infrastructure: The Synergy of Automation and Collaboration

In many traditional “Automated Welding” setups, the system is cordoned off in a light-curtained cell, requiring rigid jigging and perfect part consistency. However, in the Chennai workshop, the structural steel welding assemblies—primarily large-scale box girders and I-beams—exhibit the typical fit-up variances (±2mm to 3mm) inherent in heavy fabrication.

The Collaborative Arc Welding System bridges this gap through a “Lead-Through” teaching method. Unlike traditional industrial robots, the cobot allows the senior welder to physically move the torch to the start and end points of the root pass. This “Collaborative” element ensures that the human’s intuition regarding fit-up and tack weld placement is utilized, while the “Automated Welding” aspect takes over for the actual arc-on time, maintaining a constant travel speed and torch angle that no manual welder can replicate over several meters of weldment.

3.0 Process Specifications for Multi-pass Structural Steel Welding

3.1 Material and Joint Preparation

The workpiece consisted of 25mm to 40mm thick IS 2062 structural steel plates. Joint geometry was specified as a 60° Single-V Butt Joint with a 2mm root face and a 2.5mm root gap. For manual welders, the sheer volume of metal required for a 40mm thickness (requiring 12 to 15 passes) leads to significant fatigue and increased probability of inclusions or lack of fusion in the later filler passes.

3.2 The Multi-pass Programming Logic

The Collaborative Arc Welding System utilized a specialized multi-pass software module. This allowed us to program the root pass, after which the system mathematically calculated the offsets for the subsequent “Hot,” “Filler,” and “Cap” passes.

• Root Pass: Performed using a short-circuit transfer mode to prevent burn-through, with the operator monitoring the melt-back in real-time.
• Filler Passes: The system switched to a spray transfer mode (Ar 80% / CO2 20%) to maximize deposition rates. Here, the Automated Welding capability of the cobot maintained a precise 12mm/s travel speed.
• Capping: The system utilized a weave pattern (3Hz frequency, 4mm amplitude) to ensure consistent toe-blending, reducing the need for post-weld grinding.

4.0 Practical Challenges: Lessons from the Chennai Shop Floor

4.1 Thermal Management and Duty Cycles

One of the hardest lessons learned during the first week in Chennai was the impact of the 40°C ambient temperature on the Collaborative Arc Welding System’s power source. While the cobot itself functioned flawlessly, the torch’s air-cooling system was insufficient for the continuous arc-on time afforded by Automated Welding. We experienced thermal cutout during the 6th filler pass.

Solution: We retrofitted the system with a high-capacity water-cooler for the torch and integrated a thermal sensor into the software logic to pause the cycle if the interpass temperature of the structural steel exceeded 250°C, ensuring grain structure integrity.

4.2 Shielding Gas Turbulence

The workshop’s reliance on high-speed industrial fans for operator comfort created significant turbulence, compromising the shielding gas envelope. In a manual setup, a welder can intuitively adjust their torch angle to compensate for a draft. The Automated Welding system cannot “see” the wind.

Solution: We implemented localized shielding screens and switched from standard gas nozzles to high-performance gas lenses, increasing the laminar flow of the Ar/CO2 mix. This reduced porosity rates from 4% to less than 0.5%.

5.0 Qualitative and Quantitative Outcomes

5.1 Throughput and Efficiency

In structural steel welding, the “Arc-on Time” is the primary metric for productivity. Manual welding in our Chennai facility typically saw a 30% duty cycle due to heat exhaustion and the need for frequent deslagging and repositioning. The Collaborative Arc Welding System increased the arc-on time to 75%. While the travel speed was similar to manual welding, the consistency of the Automated Welding meant zero stops for repositioning along a 3-meter seam.

5.2 Weld Quality and NDT Results

Ultrasonic Testing (UT) of the 25mm joints revealed a significant reduction in “Lack of Inter-run Fusion.” In manual welding, the transition between the end of one electrode/wire segment and the start of the next is a common failure point. The CAWS, using 15kg spools and continuous wire feed, eliminated these restart defects entirely. The bead profile on the capping pass was uniform within ±0.5mm, a level of precision that significantly lowered the stress concentration factors at the toes of the weld.

6.0 The Role of the Senior Welder in the Collaborative Era

A common misconception in the Chennai industrial belt is that Automated Welding replaces the welder. Our field experience proved the opposite. The “Collaborative” nature of the system requires a skilled technician to “tune” the parameters. During the deployment, the senior welder’s role shifted from manual torch manipulation to “Process Controller.”

The welder would observe the arc light and the puddle fluidity—influenced by the day’s humidity and slight variations in the steel’s mill scale—and make real-time micro-adjustments to the wire feed speed via the cobot’s teach pendant. This synergy is the essence of a Collaborative Arc Welding System: the machine provides the steady hand and repeatability, while the human provides the sensory feedback and cognitive correction for environmental variables.

7.0 Metallurgical Considerations for IS 2062 Steel

Structural steel welding in heavy infrastructure requires strict adherence to the Heat Affected Zone (HAZ) properties. High-heat input, common in slow manual welding, can lead to grain coarsening and reduced impact toughness in Chennai’s ambient heat. By utilizing the Collaborative Arc Welding System’s ability to maintain a precise, higher travel speed during filler passes, we successfully lowered the average heat input (kJ/mm) by 15% compared to manual processes. This resulted in a finer grain structure in the HAZ, as confirmed by subsequent hardness testing and micro-structural analysis.

8.0 Conclusion and Recommendations

The integration of a Collaborative Arc Welding System into the Chennai structural steel welding sector is not merely a luxury but a technical necessity for meeting international quality standards (ISO 3834). The synergy between the human welder and Automated Welding technology allows for a level of consistency that overcomes the physical limitations imposed by the local climate.

Recommendations for future deployments:

1. Mandatory Liquid Cooling: For any multi-pass CAWS application in tropical climates, water-cooled torches are non-negotiable to maintain 100% duty cycles.
2. Advanced Sensing: Integrate “Through-Arc Seam Tracking” (TAST) to allow the Automated Welding logic to adjust to the heat-induced warping that occurs in structural steel during the 10th or 11th pass.
3. Operator Upskilling: Shift the training focus from manual dexterity to “Arc Physics and Programming,” ensuring the workforce can troubleshoot the Collaborative Arc Welding System independently.

The success of this Chennai field site demonstrates that when Collaborative systems are deployed with an understanding of local environmental and material constraints, the leap in productivity and metallurgical quality is profound.

Report Filed By:
Senior Welding Engineer
Field Operations – Chennai Division