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Engineering Review: Multi-pass Welding Laser Welding Cobot – Prague, Czech Republic

Field Report: Multi-pass Implementation of Laser Welding Cobot Systems

Location: Industrial Zone, Prague, Czech Republic

Engineer: Lead Welding Specialist

1. Introduction and Objective

This report details the technical deployment and optimization of a 2kW Fiber Laser Welding Cobot at a specialized fabrication facility in Prague, Czech Republic. The primary objective was to transition a critical structural assembly line from manual Gas Tungsten Arc Welding (GTAW) to an automated system capable of high-precision Aluminum Alloy welding. The project focused on multi-pass weld configurations on 10mm and 15mm 6061-T6 aluminum plates, a task traditionally difficult for standard automation due to the high thermal conductivity and reflectivity of the substrate.

The core of this implementation relies on the synergy between advanced Laser Technology and collaborative robotics. Unlike traditional industrial robots, the cobot allows for a smaller footprint in the Prague workshop while providing the sub-millimeter precision required for multi-pass laser transitions. Our focus remained on achieving full penetration while minimizing the Heat Affected Zone (HAZ) and eliminating common porosity issues inherent in aluminum fabrication.

2. The Role of Laser Technology in Aluminum Fabrication

Aluminum presents a unique set of challenges: a high melting point for its oxide layer (approx. 2000°C) versus the base metal (approx. 660°C), and high hydrogen solubility in the molten state. Implementing high-density Laser Technology allows us to bypass many of the limitations found in MIG or TIG. By utilizing a concentrated fiber laser source, we achieve “Keyhole” mode welding, which provides a high depth-to-width ratio.

In the Prague facility, we utilized a continuous wave (CW) fiber laser with a 50-micron feed fiber. The high power density allows for rapid melting and solidification, which effectively “traps” fewer hydrogen bubbles, significantly reducing porosity. Furthermore, the ability to modulate the beam—specifically using a “wobble” function—is essential for Aluminum Alloy welding. The wobble head creates a larger weld pool, which helps in cleaning the oxide layer and bridging gaps that are inevitable in large-scale structural assemblies.

3. Laser Welding Cobot: Integration and Pathing

The Laser Welding Cobot serves as the bridge between human expertise and machine repeatability. In our Prague tests, the cobot was programmed to handle the complex torch angles required for multi-pass V-groove joints. The flexibility of the cobot arm allowed us to maintain a consistent “Push” angle of 10 to 15 degrees, which is critical for directing shielding gas and managing the plasma plume generated by the Laser Technology.

Laser Welding Cobot in Prague, Czech Republic

3.1. Seam Tracking and Repeatability

One of the “lessons learned” during the first week in Prague was the sensitivity of laser optics to part fit-up. While a manual welder can compensate for a 1mm gap variation, a laser beam is unforgiving. We integrated a laser line profile sensor onto the cobot head. This allowed the Laser Welding Cobot to perform a pre-weld scan of the joint, adjusting the trajectory in real-time to ensure the beam remained centered in the groove. This is particularly vital for Aluminum Alloy welding, where even a slight offset results in lack of fusion on one sidewall.

4. Multi-pass Strategy for Thick-Section Aluminum

Welding 15mm aluminum plates required a three-pass strategy. This is where the precision of the Laser Welding Cobot truly outperformed manual labor. Each pass required specific parameter adjustments to manage the cumulative heat build-up in the workpiece.

Pass 1: The Root Pass

The root pass utilized the “Keyhole” capabilities of our Laser Technology. We operated at 100% power (2kW) with a travel speed of 1.2 meters per minute. No filler wire was used for the root to ensure maximum penetration and to avoid “humping” defects. The Laser Welding Cobot maintained a tight 0.1mm focal point at the bottom of the V-groove.

Pass 2: The Fill Pass

For the fill pass, we introduced a cold-wire feeder integrated into the cobot’s control system. Using 1.2mm ER4043 filler wire, we reduced the laser power to 1.8kW and implemented a 2mm circular wobble pattern. This oscillation ensures the filler metal merges seamlessly with the root pass and the sidewalls. Managing the feed rate (set to 3.5 m/min) was crucial to prevent the “freezing” of the wire in the path of the laser.

Pass 3: The Cap Pass

The final pass focused on aesthetics and reinforcement. We widened the wobble to 4mm and increased the travel speed to 1.5 m/min. This lowered the heat input, preventing the 6061-T6 aluminum from over-aging in the HAZ, which would otherwise result in a significant drop in tensile strength. The Laser Welding Cobot‘s ability to maintain a constant standoff distance ensured a uniform ripple pattern equivalent to high-end TIG welding.

5. Technical Challenges and Field Solutions

During the Prague implementation, several site-specific challenges arose that required immediate engineering pivots.

5.1. Back-Reflection Issues

Aluminum Alloy welding is notorious for reflecting laser energy back into the optics, especially when the beam is perpendicular to the plate. We encountered several “Back-Reflection Alarms” that halted the Laser Welding Cobot. The solution was two-fold: we tilted the laser head 10 degrees off-axis and adjusted the Laser Technology software to include a ramp-up/ramp-down power cycle at the start and end of each seam. This prevented the “mirror effect” of the molten pool from damaging the fiber connectors.

5.2. Shielding Gas Dynamics

In the Prague workshop, ambient drafts were disrupting the Argon shield. Unlike MIG, laser welding uses a very narrow gas nozzle. We redesigned the gas delivery to a coaxial setup combined with a trailing “shoe” or “curtain” of Argon. For Aluminum Alloy welding, ensuring less than 50ppm of oxygen in the weld zone is non-negotiable to prevent blackening and oxide inclusions.

6. Synergy and ROI in the Prague Context

The synergy between the Laser Welding Cobot and the underlying Laser Technology has resulted in a 400% increase in throughput compared to manual GTAW. The Prague facility has seen a drastic reduction in post-weld grinding and straightening. Because the laser concentrates energy so tightly, the overall heat input is approximately 30% of that of traditional arc welding. This means the aluminum parts remain dimensionally stable, eliminating the need for expensive jigging and rework.

Furthermore, the “collaborative” nature of the cobot allowed us to train the existing Prague welding staff—who were skeptical of automation—within just three days. The interface allows them to “lead” the robot by the hand to teach points, while the Laser Technology handles the complex physics of the melt pool.

7. Lessons Learned and Best Practices

  1. Cleanliness is Paramount: In Aluminum Alloy welding, the “Prague standard” now includes a mandatory stainless steel wire brush and solvent degrease within 10 minutes of the weld. The laser will not “burn off” contaminants; it will only trap them.
  2. Focus Position is Variable: We found that the focus position should be shifted deeper into the material for the root pass and slightly above the surface for the cap pass. The Laser Welding Cobot must be programmed to adjust the Z-axis height between passes automatically.
  3. Wire Feed Consistency: Aluminum wire is soft and prone to bird-nesting. We switched to a “Push-Pull” feeder system mounted directly on the cobot’s 3rd axis to ensure zero lag in wire delivery during the fill passes.

8. Conclusion

The deployment of the Laser Welding Cobot in Prague marks a significant shift in how high-performance Aluminum Alloy welding is approached in the region. By leveraging the high power density of modern Laser Technology, we have successfully moved beyond the limitations of manual arc welding for thick-section aluminum. The repeatability of the cobot ensures that multi-pass welds are no longer a source of scrap, but a standardized, high-quality output. Future phases will explore the use of Green Laser sources to further improve the coupling efficiency on highly reflective aluminum grades.

Advanced Programming: OLP vs. Teaching-Free System

For large-scale gantry welding, manual "point-to-point" teaching is inefficient. PCL offers two cutting-edge solutions to minimize downtime and maximize precision. Understanding the difference is key to choosing the right automation level for your factory.

SOFTWARE-BASED

Off-line Programming (OLP)

OLP allows engineers to create welding paths in a 3D virtual environment using CAD data (STEP/IGES).

  • Zero Downtime: Program the next job on a PC while the robot is still welding.
  • Collision Detection: Simulates the gantry movement to prevent accidents in a virtual space.
  • Best For: Complex workpieces with high repeat rates and detailed weld joints.
AI & SENSOR BASED

Teaching-Free Welding System

Uses 3D laser scanning or vision sensors to "see" the workpiece and generate paths automatically without any CAD data.

  • Instant Setup: No manual coding or 3D modeling required; just scan and weld.
  • High Flexibility: Ideal for "One-off" parts where every workpiece is slightly different.
  • Real-time Adaptation: Automatically compensates for thermal distortion and fit-up gaps.
  • Best For: Custom fabrication, repairs, and low-volume/high-mix production.
Feature Off-line Programming (OLP) Teaching-Free System
Input Required CAD 3D Models 3D Laser Scanning
Programming Time Minutes to Hours (Off-site) Seconds (On-site)
Ideal Production Mass Production / Batch Work Custom / Single Unit Work
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One thought on “Engineering Review: Multi-pass Welding Laser Welding Cobot – Prague, Czech Republic”

  • Robert Garcia | CTO

    Excellent cut quality on 15mm alloy. The edges are clean and burr-free.

    Reply

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