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

Field Report: Implementing Multi-pass 6-Axis Collaborative Welding in Rayong Industrial Zone

1.0 Introduction and Objective

This report outlines the technical deployment and performance evaluation of a **6-Axis Collaborative Welder** integrated into a high-capacity fabrication facility in Rayong, Thailand. The primary objective was the transition from manual heavy-gauge Mild Steel welding to a semi-autonomous system to address two critical issues: inconsistent penetration in multi-pass joints and a localized shortage of high-skill welders capable of maintaining duty cycles in 35°C+ ambient temperatures.

Rayong’s industrial environment presents specific challenges, including high humidity affecting gas shielding and the rapid oxidation of raw mild steel stock. This deployment focused on utilizing **Automated Welding** logic within a collaborative framework to maintain the flexibility of a manual shop while achieving the precision of a hard-tooled robotic cell.

2.0 Technical Configuration and Synergy

The synergy between a 6-Axis Collaborative Welder and the broader concept of Automated Welding is often misunderstood. In this Rayong workshop, “Automated Welding” refers to the pre-programmed execution of weld parameters, while the “6-Axis” component provides the necessary Degrees of Freedom (DoF) to replicate the complex torch manipulations required for multi-pass V-groove joints.

2.1 Hardware Specifications

We utilized a 10kg payload cobot integrated with a high-end synergic GMAW (Gas Metal Arc Welding) power source. The 6-axis configuration is essential here; unlike 3-axis linear gantry systems, the 6-axis arm allows for precise adjustment of the torch’s work angle and travel angle during the oscillation (weaving) required for heavy Mild Steel welding.

2.2 Why Collaborative?

The choice of a collaborative system over a fenced industrial robot was driven by floor space constraints and the need for “human-in-the-loop” intervention. In multi-pass thick-plate welding, the slag removal and interpass cleaning on mild steel are still more efficiently handled by a technician. The cobot allows the operator to clean the bead and inspect the root pass without exiting a light-curtained zone, significantly reducing cycle time.

3.0 Practical Application: Mild Steel Multi-pass Execution

The project focused on 20mm thick A36 Mild Steel plates with a 60-degree V-prep. Manual welding of these joints typically requires 5 to 7 passes.

3.1 Root Pass Dynamics

The root pass is the most critical. We programmed the 6-Axis Collaborative Welder to maintain a consistent 1.5mm arc gap. In manual operations, fatigue often leads to “burn-through” or “lack of fusion” at the root. By leveraging Automated Welding, we maintained a constant travel speed of 250mm/min with a pulsed-spray transfer mode, ensuring deep penetration without excessive heat input.

3.2 The Multi-pass Strategy

For passes 2 through 6, we implemented a “stacking” logic.

• Pass 2-3 (Fill): Employed a horizontal “figure-8” weave pattern. The 6-axis flexibility allowed the torch to maintain a 15-degree lead angle even as the weld pool grew, preventing the arc from “outrunning” the puddle.
• Pass 4-6 (Cap): Focus shifted to aesthetics and toe-line fusion. The automated consistency ensured the cap height did not exceed 3mm, complying with AWS D1.1 standards.

4.0 Environmental Challenges in Rayong

Rayong’s coastal climate is brutal on Mild Steel welding. During the July-August period, we observed significant porosity issues.

4.1 Humidity and Hydrogen

High humidity (often >80%) leads to moisture absorption in the shielding gas lines and on the surface of the mild steel wire. We had to implement heated wire enclosures. The Automated Welding system was recalibrated to include a 2-second pre-flow of shielding gas (Ar/CO2 80/20) to purge the lines, a step often skipped by manual welders in a hurry.

4.2 Thermal Expansion and Workpiece Distortion

Mild steel has a high coefficient of thermal expansion. In a multi-pass scenario, the heat build-up is immense. A 6-axis cobot, while precise, follows a programmed path. If the plate warps 2mm upward due to heat, the robot will maintain its original path, resulting in a crashed torch or poor fusion.
Lesson Learned: We integrated “Touch Sensing” into the automated routine. Before every pass, the robot uses the welding wire to touch the plate at three points to recalibrate the work offset. This is where the synergy between the robot’s sensors and the automated pathing saved the project from high scrap rates.

5.0 Performance Metrics: Manual vs. Automated

Data collected over 30 days in the Rayong facility showed the following:

• Duty Cycle: Manual welders averaged a 25% “arc-on” time due to heat breaks and repositioning. The 6-Axis Collaborative Welder maintained a 65% arc-on time.
• Consumable Efficiency: Automated control of the wire feed speed (WFS) reduced over-welding (excessive reinforcement) by 15%, leading to direct savings in mild steel filler wire.
• Rework Rate: Dropped from 8.2% to 1.1%. Most manual failures were due to interpass slag inclusions—a human error. The robot doesn’t get distracted.

6.0 Lessons Learned from the Field

6.1 The “Black Box” Fallacy

One major mistake we made early in the Rayong deployment was treating the 6-Axis Collaborative Welder as a “set and forget” tool. Automated welding is only as good as the fit-up. If the gap varies by more than 1mm, the program fails. We had to retrain the upstream plasma cutting team to provide tighter tolerances for the mild steel preps. Automation starts at the cutting table, not the welding booth.

6.2 Interpass Temperature Control

In the heat of Thailand, mild steel doesn’t cool down quickly. We initially saw grain growth and reduced toughness in the Heat Affected Zone (HAZ). We had to program “cooling timers” into the automation script. The robot would finish a pass and wait until an infrared sensor confirmed the interpass temperature was below 250°C before commencing the next layer.

6.3 Collaborative Safety is Cultural

In Rayong, the local staff was initially hesitant to work alongside the arm. We found that “teaching” the robot by physically leading it through the path (Lead-Through Programming) helped the operators feel a sense of ownership over the machine. It ceased to be “the robot” and became “the tool.”

7.0 Conclusion

The deployment of the 6-Axis Collaborative Welder for Mild Steel welding in Rayong has proven that Automated Welding is viable even in non-traditional, high-heat environments. The 6-axis versatility is non-negotiable for multi-pass work where torch angles must evolve with the weld buildup.

For future installations, the focus should remain on pre-weld fit-up and environmental controls (humidity/heat). The cobot handles the “skill” of the arc, but the engineer must still handle the “science” of the metallurgy. This project confirms that for heavy-duty mild steel fabrication, the future is not fully autonomous, but collaborative.

Report End.
Prepared by: Senior Welding Engineer, Rayong Site Office.