Engineering Review: Deep Penetration Laser Welding Cobot – Manchester, UK

Field Report: Deep Penetration Laser Welding Cobot Integration

Project Overview: Trafford Park Facility, Manchester, UK

This report details the field commissioning and performance evaluation of the newly installed 3kW Fiber Laser Welding Cobot at our Manchester heavy-fabrication facility. The primary objective was to transition our structural Mild Steel welding operations from manual Metal Inert Gas (MIG) to an automated laser process to address throughput bottlenecks and minimize post-weld distortion.

In the Manchester workshop environment, where humidity levels and ambient temperatures fluctuate significantly, the stability of Laser Technology is paramount. We are currently focusing on S355 mild steel plate ranging from 6mm to 10mm in thickness, specifically targeting deep penetration fillets and butt joints that previously required multi-pass MAG (Metal Active Gas) procedures.

1. The Synergy of Laser Technology and Automation

High Power Density and Keyhole Dynamics

The core of this installation is the fiber-delivered laser technology. Unlike conventional arc welding, which relies on surface conduction, the 1070nm wavelength laser provides sufficient power density to achieve “keyhole” mode welding. In this state, the laser vaporizes the mild steel, creating a cavity that allows the beam to deposit energy deep into the root of the joint.

During our Manchester trials, we observed that the laser technology allows for an aspect ratio (depth-to-width) that is unattainable with manual processes. For 8mm Mild Steel welding, we achieved full penetration in a single pass at 1.2 meters per minute. This is roughly four times the travel speed of our previous manual pulse-MIG setups. The reduced heat input—a direct byproduct of the concentrated laser technology—has virtually eliminated the 3mm-5mm bowing we previously encountered on 3-meter longitudinal seams.

The Role of the Laser Welding Cobot

While the laser provides the “bite,” the Laser Welding Cobot provides the “path.” In a busy Manchester shop floor, a traditional industrial robot requires extensive guarding and a fixed footprint that we simply couldn’t afford in the current layout. The cobot’s localized safety scanners and “hand-guiding” teaching mode allowed our senior welders to program complex geometries in under ten minutes.

The synergy here is critical: the Laser Welding Cobot maintains a consistent Stand-Off Distance (SOD) and torch angle (70-80 degrees for fillets), which is humanly impossible to sustain over long durations at the speeds required by laser technology. If the torch angle fluctuates by even 5 degrees, the keyhole can collapse, leading to porosity. The cobot’s precision ensures the focal point remains 1.0mm below the material surface, optimizing the deep penetration characteristics of the laser.

2. Technical Analysis: Mild Steel Welding Performance

Material Preparation and Surface Chemistry

Mild steel welding with lasers is sensitive to surface contaminants. In the Manchester facility, we noticed that “black” hot-rolled steel with heavy mill scale caused significant spatter and compromised the protective window of the laser head. We have now implemented a mandatory mechanical cleaning or fiber-laser cleaning pass on the weld zone.

The chemical composition of the S355 mild steel also plays a role. We found that higher manganese content improved the wetting of the laser puddle, while carbon levels above 0.22% required a slight reduction in cooling rates to prevent martensitic transformation in the Heat Affected Zone (HAZ). By adjusting the Laser Welding Cobot’s travel speed to 15mm/s, we managed to balance the cooling rate and maintain a ductile grain structure in the fusion zone.

Wobble Parameters and Gap Bridging

One of the greatest challenges in Mild Steel welding is the “fit-up.” Lasers have a tiny spot size (0.2mm – 0.6mm), making them intolerant to gaps. To combat this, we utilized the “wobble” function integrated into the laser head. By oscillating the beam in a circular or “figure-8” pattern at 150Hz with a 2.0mm width, the Laser Welding Cobot successfully bridged gaps up to 1.2mm without needing filler wire. This oscillation also helps in degassing the molten pool, which is essential when working with UK-sourced mild steel that may have trace impurities.

3. Lessons Learned from the Manchester Shop Floor

Lesson 1: Environmental Controls and Gas Shielding

The Manchester climate presented an unexpected hurdle: condensation. Early morning shifts saw moisture buildup on the mild steel plates stored in the unheated bay. Moisture is the enemy of laser technology; it dissociates into hydrogen and oxygen in the keyhole, leading to hydrogen-induced cracking.

Correction: We implemented a localized pre-heat using an induction blanket for any plate over 10mm and upgraded our gas delivery system. We switched from a standard 100% Argon shield to an Argon/CO2 (2%) mix. The addition of CO2 stabilizes the arc-like plasma plume generated during deep penetration laser welding, providing a smoother bead profile on mild steel.

Lesson 2: Fixturing and Thermal Expansion

Because the Laser Welding Cobot moves so quickly, the “tack” welds must be significantly smaller than those used in MIG. Heavy tacks act as heat sinks and can deflect the laser beam. We learned to use “laser tacks”—0.5-second bursts from the cobot itself—to secure the parts. Furthermore, because the heat is so localized, the material expands differently. We had to redesign our jigs to allow for “breathing” along the longitudinal axis to prevent the part from lifting off the table and changing the focal position of the laser technology.

Lesson 3: Operator Transition and “The Skill Gap”

The most significant “soft” lesson was the transition of our manual welders. Initially, there was skepticism toward the Laser Welding Cobot. However, once the team saw the reduction in grinding and post-weld straightening (which accounts for 40% of our labor time), adoption increased. The “Senior Engineer” takeaway here is that the cobot doesn’t replace the welder; it replaces the fatigue. The welder’s knowledge of “how steel flows” is still required to set the initial wobble and power parameters.

4. Efficiency Metrics and Output Quality

Throughput Comparison

• Manual MIG: 250mm/min travel speed; 30 minutes post-weld dressing; 2 passes for 8mm fillet.
• Laser Welding Cobot: 1200mm/min travel speed; 0 minutes post-weld dressing; 1 pass for 8mm fillet.

The total cycle time reduction for a standard Manchester-produced support frame was 65%.

Metallurgical Integrity

Cross-sectional macro-etching of the mild steel welding samples showed a highly refined grain structure. The HAZ was measured at 0.8mm, compared to 4.5mm with MIG. Hardness testing across the weld interface remained within the 180-220 HV range, which is well within the acceptable limits for structural S355 steel. The deep penetration achieved by the 3kW laser technology ensured that the root was fully consumed, eliminating the “lack of fusion” defects that often plague manual overhead welds.

5. Safety and Compliance in a Cobot Environment

Deploying a Laser Welding Cobot in a Manchester workshop requires strict adherence to BS EN ISO 11553-1. While the “cobot” is safe for physical interaction, the Class 4 laser is not. We installed a modular, interlocked laser-safe enclosure (active guarding). The cobot’s internal safety logic is synced with the enclosure doors; if a breach occurs, the laser technology undergoes a “hard stop” in under 50 milliseconds. This dual-layer safety approach—mechanical guarding for the radiation and cobot sensors for the movement—is the only way to safely run high-power Mild Steel welding in a collaborative environment.

6. Conclusion and Future Roadmap

The integration of the Laser Welding Cobot at our Manchester site has proven that laser technology is no longer reserved for thin-gauge automotive sheet metal. For heavy-duty Mild Steel welding, the benefits of deep penetration, minimal distortion, and high travel speeds are undeniable.

Moving forward, we plan to integrate a wire-feed system to the cobot to allow for even larger gap bridging and to explore “Dual-Beam” laser technology to further refine the solidification of the weld pool. The data suggests that we will recoup the capital expenditure on this system within 14 months based on labor savings and gas consumption reductions alone. The Manchester facility is now positioned as a lead site for automated laser fabrication within the group.

Signed,
Senior Welding Engineer, Manchester Site