Engineering Review: Multi-pass Welding Laser Welding Cobot – Madrid, Spain

Field Report: Implementing Multi-pass Laser Welding Cobot Systems in Madrid

This report outlines the technical deployment and operational assessment of the 3kW **Laser Welding Cobot** at the Talleres de Acero Madrid (TAM) facility. The primary objective was to replace legacy Gas Metal Arc Welding (GMAW) processes for heavy-duty **Structural Steel welding**, specifically targeting S355JR grade frames used in regional infrastructure projects.

Over the 14-day implementation period, we transitioned from manual deep-groove welding to an automated multi-pass laser strategy. The results indicate a significant reduction in thermal distortion and a 400% increase in travel speed on the root pass, though the process demands far more stringent joint preparation than traditional methods.

The Integration of Laser Technology in Structural Fabrication

The shift to **Laser Technology** in the Madrid workshop was driven by the need to minimize the Heat Affected Zone (HAZ) in thick-section S355JR steel. Traditional GMAW requires massive heat input to achieve full penetration in 12mm to 20mm plates, often leading to longitudinal bowing of the structural members.

By utilizing a high-brightness fiber laser source, we achieved a power density that allows for a “keyhole” welding mode. This ensures deep penetration with minimal volumetric heat input. However, the application of **Laser Technology** in a structural context—where fit-up tolerances are historically loose—required a paradigm shift in our upstream cutting and fit-up departments. We moved from plasma-cut edges to fiber-laser-cut edges to ensure the 0.15mm gap tolerance required for the **Laser Welding Cobot** to function effectively without excessive wire-feed compensation.

The Laser Welding Cobot: Deploying Collaborative Automation

The choice of a **Laser Welding Cobot** over a standard industrial robotic cell was strategic. The Madrid facility has a high-mix, low-volume production schedule. A fixed robotic cell would have been underutilized and too rigid for the varied geometries of structural frames.

The cobot’s 6-axis flexibility allowed us to mount the unit on a heavy-duty magnetic base, enabling “on-the-tool” deployment directly onto the large structural steel workpieces. This mobility is the defining advantage of the **Laser Welding Cobot**. It allows the welder—now acting as a technician—to lead the arm to the joint, record waypoints, and execute a multi-pass program without complex G-code programming.

Technical Deep Dive: Multi-pass Laser Welding on S355JR

The core technical challenge at the Madrid site was the execution of multi-pass welds on 15mm V-groove joints. Single-pass laser welding is typically limited to 6-8mm for a 3kW source. To handle structural thicknesses, we developed a three-pass strategy.

Root Pass Dynamics and Joint Fit-up

The first pass (root) utilized the keyhole mode. We found that for **Structural Steel welding**, a zero-gap configuration is ideal, but a 0.2mm gap can be bridged using a “wobble” (oscillation) pattern of 1.5mm width at 150Hz.

**Lesson Learned:** In the Madrid workshop, ambient temperatures in July can exceed 40°C. We noted that the chiller units for the fiber laser were running at 95% capacity. We had to recalibrate the gas flow (Pure Argon vs. Ar/CO2 mix) because the higher ambient temperatures affected the gas density and, consequently, the shielding effectiveness. We eventually settled on an Argon/CO2 (80/20) mix to stabilize the plasma plume, which is critical when the **Laser Welding Cobot** is operating at high travel speeds.

Fill and Cap Strategy

For the second and third passes (fill and cap), we transitioned from keyhole mode to a conduction-limited welding mode with increased wire feed speed. The **Laser Technology** used here allows for synchronized wire feeding (1.2mm S355 wire).

1. **Second Pass (Fill):** 2.8kW power, 12mm/s travel speed, 3mm wobble width. This pass was designed to fuse the sidewalls of the V-groove.
2. **Third Pass (Cap):** 2.2kW power, 10mm/s travel speed, 5mm wobble width. The goal here was aesthetic consistency and ensuring a slight reinforcement over the base metal.

The synergy between the cobot’s precision and the laser’s concentrated energy resulted in a weld profile that is significantly narrower than a GMAW profile, reducing the total volume of filler metal required by approximately 35%.

Synergistic Gains: Laser Tech meets Robotic Precision

The integration of a **Laser Welding Cobot** into the **Structural Steel welding** workflow provides a level of repeatability that manual labor cannot match in the Madrid heat. Manual welders often suffer from fatigue-induced oscillation variance during long shifts. The cobot maintains a consistent torch angle (crucial for laser reflection management) and a constant “stick-out” distance for the wire feeder.

The **Laser Technology** further enhances this by providing a “cold” start and stop. Unlike arc welding, which leaves a crater, the laser power can be ramped down over a 500ms interval, effectively filling the end-crater and eliminating a common failure point in structural frames.

Field Observations and Lessons Learned

Operating in an active Madrid workshop provided several practical insights that aren’t found in the manufacturer’s manual.

Thermal Management and HAZ Reduction

One of the primary “wins” was the reduction in post-weld straightening. In **Structural Steel welding**, the cost of labor to “torch-straighten” warped beams is often 20% of the total fabrication cost. By using the **Laser Welding Cobot**, the total heat input was reduced by nearly 60% compared to GMAW. We observed a Heat Affected Zone that was 75% narrower. This is vital for S355JR, as it preserves the grain structure and mechanical properties of the base metal near the fusion line.

Safety and Infrastructure in the Madrid Facility

The deployment of **Laser Technology** requires a Class 4 safety environment. We had to install specialized laser-safe curtains (OD7+ rating) around the cobot station. Unlike traditional welding, the specular reflection from a laser can be hazardous at great distances.

**Lesson Learned:** We initially underestimated the importance of fume extraction. Laser welding of structural steel produces a very fine particulate compared to GMAW. We had to upgrade the local extraction system to a HEPA-filtered unit to ensure the air quality in the Madrid shop remained within EU occupational limits.

The Human Element: From Welder to Operator

The transition was initially met with skepticism by the senior welders in Madrid. However, once they saw the **Laser Welding Cobot** handling the repetitive, long-seam welds while they focused on complex tacking and fit-up, the value proposition became clear. The “collaborative” aspect of the cobot is not just a marketing term; it allows the operator to stay close to the weld (with proper PPE) and make real-time adjustments to the wire feed or oscillation width via the pendant.

Conclusion

The implementation of the **Laser Welding Cobot** at the Madrid site has proven that **Laser Technology** is no longer restricted to thin-sheet automotive applications. When applied to **Structural Steel welding**, specifically in a multi-pass configuration, it offers a path toward higher productivity and superior metallurgical outcomes.

The key to success lies not in the laser itself, but in the synergy between the robotic motion control and the upstream preparation. For the Madrid facility, the reduction in consumables and the elimination of post-weld distortion have already offset the initial capital expenditure of the system within the first six months of operation. Future deployments will focus on integrating AI-driven seam tracking to further compensate for the minor fit-up variations inherent in heavy structural fabrication.