Engineering Review: Multi-pass Welding 6-Axis Collaborative Welder – Rayong, Thailand

Field Report: Deployment of 6-Axis Collaborative Welder for Multi-pass Heavy Structural Joints

Location: Rayong Industrial Estate, Thailand
Subject: Integration of Automated Welding for Thick Plate Steel Welding (30mm – 50mm)
Lead Engineer: Senior Welding Engineer, Site Operations

1. Introduction and Site Context

The fabrication facility in Rayong currently handles high-volume structural components for offshore energy sectors. The primary bottleneck identified over the last two quarters has been the manual execution of multi-pass welds on thick plate steel welding applications. Manual welders, while skilled, show significant fatigue-induced variance during the 12th to 20th fill passes, leading to inter-pass slag inclusions and inconsistent bead profiles.

To address this, we deployed the 6-Axis Collaborative Welder (Cobot) integrated with a high-deposition GMAW (Gas Metal Arc Welding) power source. The objective was to transition from manual manipulation to automated welding while maintaining the flexibility of a human-centric workshop floor.

2. The Technical Utility of the 6-Axis Collaborative Welder

In the context of thick plate steel welding, a standard 3-axis or 4-axis system is insufficient for the complex torch angles required to ensure proper sidewall fusion in deep V-grooves. The 6-Axis Collaborative Welder provides the necessary degrees of freedom to mimic a human welder’s wrist movement, which is critical during the “weave” pattern of the fill passes.

The 6-axis configuration allows for:

• Torch Re-orientation: Adjusting the work angle and travel angle dynamically as the groove fills.
• Reach and Clearance: Navigating the tight constraints of pre-tacked structural stiffeners.
• Safety: Operating alongside Thai fabrication crews without the need for extensive light curtains or hard fencing, which is vital in the cramped layout of the Rayong facility.

3. Implementing Automated Welding in Multi-pass Scenarios

Automated welding is often misunderstood as a “set and forget” process. In Rayong, where ambient humidity often exceeds 80%, the synergy between the 6-Axis Collaborative Welder and the power source must be calibrated to handle the specific cooling rates of thick plate steel welding.

Multi-pass Strategy and Path Programming

For a 40mm S355JR steel plate with a 60-degree included angle, we programmed a 22-pass sequence. The automated welding logic was divided into three phases:

1. Root and Hot Pass: While the root was performed manually to ensure 100% penetration on variable gaps, the cobot took over for the hot pass to provide a consistent base for the fill passes.
2. Fill Passes: We utilized a “stacked” bead approach. The 6-Axis Collaborative Welder was programmed to shift the Y-axis offset by 3.5mm for each subsequent bead in a layer, ensuring a flat profile and preventing “humping.”
3. Cap Pass: A wide weave was implemented using the cobot’s sixth axis to ensure a smooth transition to the base metal, meeting the stringent aesthetic and structural requirements of the Thai Department of Public Works.

4. Synergy Between Hardware and Environment

The deployment in Rayong presented unique challenges that tested the automated welding system’s resilience. The heat and humidity in Thailand can cause flux-cored wires (FCAW) to pick up moisture if not handled correctly. We synchronized the 6-Axis Collaborative Welder with a specialized wire feeding unit that maintains constant tension, preventing the “bird-nesting” common in humid environments.

The synergy here is found in the cobot’s ability to maintain a consistent Contact Tip to Work Distance (CTWD). In manual thick plate steel welding, as the welder gets hot and tired, the CTWD fluctuates, causing voltage spikes and porosity. The 6-Axis Collaborative Welder maintains a +/- 0.5mm tolerance, which, when paired with the automated welding software, allows for real-time compensation of heat input.

5. Technical Deep Dive: Heat Input and Inter-pass Temperature

One of the critical “lessons learned” during the Rayong field test was the management of inter-pass temperatures. When performing automated welding on thick plate steel welding, the arc-on time is significantly higher than manual welding. This leads to a rapid build-up of heat in the base material.

If the inter-pass temperature exceeds 250°C for S355 steel, the Heat Affected Zone (HAZ) grain structure coarsens, reducing impact toughness. We integrated a thermal sensor into the 6-Axis Collaborative Welder control loop. The automated welding program was scripted to “pause” and signal the operator when the inter-pass temperature exceeded the threshold, resuming only once the plate had cooled to the programmed 150°C.

6. Results and Field Observations

The transition to a 6-Axis Collaborative Welder produced measurable improvements:

• Deposition Rate: We increased the deposition rate from 3.2 kg/hr (manual) to 5.8 kg/hr (automated) by utilizing higher wire feed speeds that a human cannot steadily control.
• Rework Rate: Non-Destructive Testing (UT and RT) showed a reduction in slag inclusions by 85%. The automated welding pathing ensured that each bead overlapped the previous one with mathematical precision.
• Operator Ergonomics: The Rayong welders moved from “holding the torch” to “managing the process.” This shift reduced physical strain and allowed one senior welder to oversee two 6-Axis Collaborative Welders simultaneously.

7. Lessons Learned from the Rayong Workshop

A. Calibration is Non-Negotiable

In the first week, we noticed a drift in the 6-Axis Collaborative Welder‘s zero-point. We traced this to the thermal expansion of the mounting table due to the high-duty cycle of thick plate steel welding.
Lesson: Ensure the cobot base is thermally isolated or recalibrate the TCP (Tool Center Point) every four hours during heavy fill sequences.

B. Shielding Gas Dynamics

Rayong’s coastal location means the workshop is subject to unpredictable drafts. Automated welding sensors can detect arc instability, but they can’t “see” a breeze blowing away the shielding gas.
Lesson: We installed localized wind-screens and increased the gas flow rate by 15% compared to standard lab settings to compensate for the open-air workshop environment.

C. Joint Prep Consistency

The 6-Axis Collaborative Welder is precise, but it lacks the human’s ability to “fill a gap” that wasn’t supposed to be there.
Lesson: Implementing automated welding requires tighter tolerances on upstream processes like plasma cutting and beveling. If the joint preparation is poor, the cobot will faithfully weld a poor joint.

8. Conclusion

The deployment of the 6-Axis Collaborative Welder for thick plate steel welding in Rayong has proven that automated welding is no longer restricted to thin-gauge automotive parts. By leveraging the dexterity of a 6-axis system, we have successfully tackled the rigors of multi-pass heavy fabrication.

The key to success was not just the hardware, but the integration of local environmental considerations—managing Rayong’s humidity and heat—into the programming logic. Moving forward, we recommend the rollout of an additional four units across the Eastern Seaboard facilities to standardize our structural output.

End of Report.