Engineering Review: Multi-pass Welding Robotic Arm Welder – Ho Chi Minh City, Vietnam

Field Report: Multi-pass Robotic Arm Welder Implementation – Ho Chi Minh City Industrial Zone

1. Project Overview and Site Conditions

This report details the commissioning and optimization of a 6-axis Robotic Arm Welder system integrated into a heavy machinery production line in Thu Duc, Ho Chi Minh City. The primary objective was to transition from manual Stick (SMAW) and semi-automatic MIG (GMAW) to a fully realized Industrial Automation workflow for thick-section Carbon Steel welding.

The facility operates in a high-humidity tropical environment, typical of Southern Vietnam. During the July-August monsoon window, ambient humidity levels inside the workshop averaged 82%. This environmental factor is critical when discussing Carbon Steel welding, as hydrogen-induced cracking (HIC) becomes a significant risk if material handling and gas shielding are not surgically precise. The deployment focused on 12mm to 25mm ASTM A36 plate configurations, requiring consistent multi-pass fillets and grooves.

2. The Synergy of Industrial Automation and the Robotic Arm Welder

The core of this implementation is not merely the Robotic Arm Welder itself, but its integration into the broader Industrial Automation ecosystem. In the HCMC workshop, we linked the robotic controller to a centralized PLC (Programmable Logic Controller) that manages hydraulic jigs and a two-axis positioner.

2.1. Kinematic Precision vs. Manual Variance

The shift to Industrial Automation allowed us to eliminate the “arc-off” time associated with manual repositioning. By using a coordinated motion profile, the Robotic Arm Welder maintains a constant Torch-to-Work Distance (CTWD). In manual operations, HCMC welders often struggled with heat exhaustion during the long shifts required for heavy Carbon Steel welding, leading to inconsistent travel speeds. The robot maintains a steady 380mm/min travel speed on the root pass, regardless of ambient workshop temperature.

2.2. Data-Driven Interpass Control

Automation enables real-time monitoring of interpass temperatures. For multi-pass Carbon Steel welding, maintaining a temperature between 150°C and 250°C is vital for grain structure. We integrated infrared sensors into the automation loop. If the plate exceeds 250°C, the Robotic Arm Welder enters a “cool-down” cycle, or moves to a different joint on the workpiece, optimizing the duty cycle without risking the Heat Affected Zone (HAZ) integrity.

3. Technical Deep-Dive: Multi-pass Carbon Steel Welding Procedures

Welding thick carbon steel requires a strategic layering approach. We utilized an ER70S-6 solid wire with a 1.2mm diameter, shielded by an 80% Argon / 20% CO2 mix.

3.1. The Root Pass Strategy

The initial pass in a V-groove is the most volatile. We programmed the Robotic Arm Welder to use a short-circuit transfer mode to prevent burn-through on the 2mm root face. Through Industrial Automation, we synchronized the wire feed speed to the arm’s oscillation (weaving). A 2.5mm weave width was established to ensure adequate sidewall fusion, a common failure point in manual carbon steel joints in this facility.

3.2. Fill and Cap Passes

For the subsequent five fill passes, the system switched to spray transfer mode. This is where the Robotic Arm Welder truly outperforms manual labor in a humid HCMC environment. The high current (280A–310A) creates a significant radiant heat load that manual operators find difficult to manage. The robot, however, maintains a consistent 7-degree lead angle, ensuring the puddle stays ahead of the arc to avoid slag inclusions (though we are using solid wire, “cold-lapping” remains a risk on thick Carbon Steel welding).

3.3. Managing Porosity in HCMC Humidity

A major technical hurdle was localized porosity. We discovered that the Industrial Automation gas delivery system was pulling moisture from the ambient air through micro-leaks in the standard plastic hosing. We replaced these with high-density Teflon-lined hoses and implemented a pre-flow of 2.0 seconds. This ensures the Robotic Arm Welder initiates the arc in a completely inert environment, essential for the metallurgy of Carbon Steel welding when the dew point is high.

4. Equipment Configuration and Calibration

The system comprises a FANUC M-20iD/25L arm paired with a Lincoln Electric Power Wave R450 power source. The integration logic is handled via EtherNet/IP.

4.1. TCP Calibration (Tool Center Point)

In Industrial Automation, the TCP is the “truth.” We found that the torch neck was deforming slightly due to the high heat of continuous Carbon Steel welding. We implemented an automated “Bullseye” calibration station. Every 10 cycles, the Robotic Arm Welder checks its TCP. If a deviation >0.5mm is detected, the system auto-corrects or alerts the tech. This is non-negotiable for multi-pass welds where a 1mm offset on the cap pass results in a rejected part.

4.2. Seam Tracking Implementation

Given the thermal expansion of thick carbon steel plates during welding, the joint geometry shifts mid-process. We utilized “Through-Arc Seam Tracking” (TAST). As the Robotic Arm Welder weaves across the joint, the automation system monitors changes in welding current. If the current increases, the robot knows it is getting closer to the side wall and adjusts its path in real-time. This level of Industrial Automation is the only way to achieve X-ray quality welds on 25mm plate consistently.

5. Lessons Learned from the Field

The deployment in Ho Chi Minh City provided several “hard-won” insights that differ from theoretical office modeling.

5.1. Power Grid Stability

The HCMC industrial grid can experience voltage sags during the peak afternoon cooling period (when city-wide AC usage spikes). These sags affect the Robotic Arm Welder‘s arc stability. We had to install a dedicated servo-controlled voltage stabilizer for the Industrial Automation cabinet to prevent “arc outages” during critical Carbon Steel welding passes. Without this, we were seeing intermittent fusion defects in the third pass of our 5-pass schedule.

5.2. Material Cleanliness

While Carbon Steel welding is generally more forgiving than aluminum, the combination of HCMC humidity and salt air (proximity to the Saigon River) leads to rapid surface oxidation. The Robotic Arm Welder cannot “see” rust. We learned that the Industrial Automation workflow must include a mechanized wire-brushing stage or a strict 4-hour window from grinding to welding. If a plate sits overnight in the HCMC humidity, the resulting weld will fail ultrasonic testing (UT) due to subsurface porosity.

5.3. Wire Feed Friction

The distance between the bulk wire drum and the Robotic Arm Welder was initially 5 meters. The high humidity made the wire surface “tacky,” increasing friction in the liners. This led to “bird-nesting” at the drive rolls. Lesson learned: Use a pressurized wire feeder and ceramic liners to ensure the Industrial Automation sequence isn’t interrupted by mechanical feed issues.

6. Results and Conclusion

After four weeks of optimization, the HCMC facility reported a 40% increase in throughput for heavy Carbon Steel welding components. The Robotic Arm Welder achieved a 98.5% first-pass acceptance rate via UT, compared to 76% with manual GMAW.

The success of this project hinges on the understanding that a Robotic Arm Welder is not a standalone solution. It is the centerpiece of an Industrial Automation strategy that must account for local environmental variables, power quality, and material science. For future deployments in the Vietnam market, the focus should remain on hardening the automation against humidity and ensuring the kinematic paths account for the significant thermal deformation inherent in heavy-section carbon steel work.

Report Signed:
Senior Welding Engineer
Field Operations – HCMC Division