Engineering Review: Water-cooled Laser Welding Cobot – Quebec, Canada

Field Engineering Report: Implementation of Water-Cooled Laser Welding Cobot in Quebec Structural Steel Facilities

1.0 Introduction and Site Context

This report details the technical commissioning and performance evaluation of a 2kW water-cooled Laser Welding Cobot system at a medium-scale structural steel fabrication facility in the Centre-du-Québec region. The primary objective was to transition specific high-volume sub-assemblies from traditional Gas Metal Arc Welding (GMAW) to automated Laser Technology to address the acute skilled labor shortage currently impacting the Quebec manufacturing sector.

The facility specializes in Structural Steel welding for commercial infrastructure, primarily utilizing CSA G40.21 44W (ASTM A572 Gr. 50 equivalent) plate and section. The environment presents specific challenges: high ambient temperature fluctuations between winter and summer, and the presence of mill scale and atmospheric moisture typical of the Saint Lawrence Valley.

2.0 Technical Synergy: Laser Technology and the Cobot Platform

The core of the system is the integration of a continuous wave (CW) fiber laser source with a high-precision collaborative robot (cobot). This synergy is critical. Traditional manual laser welding relies on the operator’s steady hand, which often leads to inconsistent travel speeds and varying focal points. In Structural Steel welding, where weld throat consistency is non-negotiable for CWB (Canadian Welding Bureau) compliance, the Laser Welding Cobot provides the necessary mechanical rigidity.

2.1 Beam Delivery and Water-Cooling Logistics

Unlike air-cooled systems, the water-cooled variant was specified due to the high duty cycles required in Quebec’s industrial settings. The chiller unit maintains the laser source and the optical head at a constant 22°C. During the field test, we observed that ambient shop temperatures of 32°C in July did not degrade the beam quality (M² factor), whereas air-cooled units in neighboring bays suffered from thermal lensing and power fluctuations.

The Laser Technology utilized here employs a 50μm transport fiber, which allows for high power density. When paired with the Laser Welding Cobot, we can achieve travel speeds of 1.2 meters per minute on 6mm lap joints, a 4x increase over manual GMAW. However, the cooling circuit requires a 30% glycol mix to prevent freezing during weekend shutdowns in Quebec’s winter months, a lesson learned during the initial pilot phase.

3.0 Practical Application: Structural Steel Welding Parameters

Structural Steel welding with laser sources requires a fundamental shift in joint preparation. Unlike GMAW, where a 2mm gap can be easily bridged with filler wire, Laser Technology is notoriously sensitive to “fit-up.”

3.1 Weld Bead Morphology and Penetration

In our tests on 8mm base plates, the Laser Welding Cobot was programmed with a circular wobble pattern (frequency: 150Hz, width: 2.5mm). This oscillation is vital for Structural Steel welding as it compensates for the tight tolerances required by the laser’s small spot size. The “keyhole” mode of the laser provides deep penetration with a remarkably narrow heat-affected zone (HAZ), which significantly reduces transverse shrinkage and angular distortion—major pain points when fabricating long structural beams.

3.2 Shielding Gas and Plasma Suppression

For the Quebec site, we opted for a 100% Argon shield at 25 L/min. While CO2 mixes are standard in GMAW for Structural Steel welding, they interfere with the Laser Technology by causing plasma plumes that defocus the beam. The cobot’s ability to maintain a consistent 15-degree “push” angle ensured that the gas lens provided laminar flow over the molten pool, preventing the oxidation typical of high-speed laser passes.

4.0 Lessons Learned: Field Observations from the Quebec Shop Floor

4.1 The Myth of “Zero-Gap” in Structural Steel

One of the primary lessons learned is that “perfect” fit-up is impossible in large-scale structural fabrication. To make the Laser Welding Cobot viable, we integrated a wire feeder. The synergy between the Laser Technology and the cold-wire feed allowed us to bridge gaps up to 1.0mm. However, anything exceeding 1.2mm resulted in “burn-through” or “underfill.” The takeaway: downstream automation success is 90% dependent on upstream cutting (plasma/laser) precision.

4.2 Managing Mill Scale

Quebec-sourced structural steel often carries a heavy layer of mill scale (magnetite). Laser Technology reacts poorly to this oxide layer, often resulting in porosity or “spitting” during the weld. We found that a quick abrasive flap-disc pass on the weld zone was mandatory. Attempting to weld through mill scale with the Laser Welding Cobot resulted in a 30% failure rate during ultrasonic testing (UT). After implementing a cleaning protocol, the pass rate moved to 98%.

4.3 Safety and the “Class 4” Reality

The deployment of Laser Technology in an open shop environment is a significant safety hurdle. Unlike GMAW, where a simple welding curtain suffices, the 1070nm wavelength of the fiber laser is invisible and lethal to eyesight. We had to construct a dedicated Class 4 enclosure. In a Quebec shop environment, where space is at a premium, the footprint of the safety cell must be factored into the ROI. The Laser Welding Cobot is “collaborative” regarding force-limiting movement, but the laser beam itself is not.

5.0 Heat-Affected Zone (HAZ) and Material Integrity

In Structural Steel welding, the mechanical properties of the HAZ are critical for seismic load-bearing components. We conducted Charpy V-Notch (CVN) testing on welds produced by the Laser Welding Cobot. The results showed that the concentrated heat input of the Laser Technology resulted in a much finer grain structure compared to the coarse grain structure of GMAW. This improved the toughness of the joint at -20°C, a standard requirement for outdoor infrastructure in Quebec.

6.0 Integration with Hydro-Québec Power Standards

The energy efficiency of the Laser Welding Cobot system is a notable advantage. The wall-plug efficiency of fiber Laser Technology is approximately 30-35%, significantly higher than older CO2 lasers. In the context of Quebec’s industrial electricity rates, the lower kVA requirement per meter of weld provides a marginal but measurable reduction in operational costs over three shifts.

7.0 Conclusion: The Future of the Quebec Workshop

The deployment of the Laser Welding Cobot at the Drummondville site has proven that Laser Technology is no longer restricted to the laboratory or high-end aerospace applications. For Structural Steel welding, it offers a path toward higher productivity and better de-skilling of the welding process. However, the transition requires a “systems thinking” approach: better fit-up, rigorous cleaning, and uncompromising laser safety protocols.

8.0 Summary of Technical Parameters for 6mm G40.21 Steel

• Power: 1800W (CW)
• Travel Speed: 18mm/s
• Wobble Type: Figure-8 (2.0mm width)
• Wire Feed Speed: 1.5 m/min (0.9mm ER70S-6)
• Coolant Temp: 22.5°C
• Gas: Argon (100%) at 20 L/min

The system is now cleared for Phase 2, which involves the integration of a rotary axis to handle cylindrical structural columns. This will further leverage the Laser Welding Cobot‘s ability to maintain constant surface speed on complex geometries.

Report Prepared By: Senior Welding Engineer, Site Services Division
Date: May 2024
Location: Quebec, CA