Precision CMT Laser Welding Cobot – Hamburg, Germany

Field Engineering Report: Implementation of Precision CMT Laser Welding Cobot

Site: Hamburg Industrial Zone, Northern Facility

Date: October 2023

This report summarizes the field deployment and performance validation of the integrated Laser Welding Cobot system at our Hamburg facility. The primary objective was to transition high-volume Carbon Steel welding operations from manual Gas Metal Arc Welding (GMAW) to an automated solution leveraging advanced Laser Technology. The facility’s transition focused on reducing post-weld distortion and increasing throughput for S355 structural components used in maritime applications.

1. System Integration and Configuration

The deployment centered on a 2kW fiber-coupled Laser Welding Cobot. Unlike traditional industrial robots, the cobot’s ability to operate in shared workspaces (within a Class 1 laser enclosure) allowed us to integrate the station into a pre-existing workflow without a massive footprint expansion.

The core of the system is the synergy between the motion control of the cobot arm and the high-density energy of the Laser Technology. In Hamburg, we faced specific challenges regarding the local humidity and its effect on Carbon Steel welding. We implemented a synchronized wire-feed system—specifically Cold Metal Transfer (CMT) logic—to bridge the gaps that often occur in the fit-up of heavy plate carbon steel.

1.1 Beam Delivery and Optics

The Laser Technology employed utilizes a 1070nm wavelength fiber laser. We utilized a wobbling head configuration on the cobot. This is critical for Carbon Steel welding because it allows the operator to oscillate the beam in various patterns (circular, zigzag, or figure-eight). This oscillation compensates for the minor fit-up inconsistencies (up to 0.5mm) typical in large-scale carbon steel fabrication.

2. Practical Application: Carbon Steel Welding Parameters

Carbon Steel welding remains the backbone of our Hamburg operations. However, the high thermal conductivity and potential for hydrogen-induced cracking in S355JR/J2 grades require precise heat control.

2.1 Material Preparation and Fit-up

One of the hard lessons learned during the first week in Hamburg was that Laser Technology is less forgiving than manual MIG. For Carbon Steel welding, the mill scale must be entirely removed. We observed that even minor oxidation layers led to significant porosity when processed by the Laser Welding Cobot.

The following parameters were established for 6mm S355 butt joints:

• Laser Power: 1800W
• Travel Speed: 15mm/s
• Wire Feed Speed (G3Si1): 4.5 m/min
• Shielding Gas: 100% Argon at 20L/min (Experimental phase used Ar/CO2, but 100% Ar provided a cleaner keyhole transition).

2.2 Heat Affected Zone (HAZ) Reduction

The most significant advantage of using the Laser Welding Cobot over traditional methods was the 65% reduction in the Heat Affected Zone. In our Hamburg laboratory tests, we found that the rapid cooling cycle associated with Laser Technology preserved the grain structure of the carbon steel more effectively than the multi-pass GMAW approach. This is vital for components subject to the cyclic loading found in North Sea maritime environments.

3. Synergy Between Cobot Kinematics and Laser Technology

The “Cobot” aspect of the Laser Welding Cobot is not just about safety; it is about the “Lead-Through” programming. In a high-mix environment like our Hamburg shop, we don’t have time for complex G-code re-programming for every minor bracket change.

3.1 Path Repeatability

The Laser Welding Cobot maintains a path repeatability of ±0.03mm. When welding Carbon Steel welding components, this precision ensures that the focal point of the Laser Technology stays exactly at the root of the joint. In manual welding, the torch angle often fluctuates, leading to inconsistent penetration. The cobot eliminates this human variable.

3.2 CMT Integration

The integration of CMT (Cold Metal Transfer) with Laser Technology provided a “cool” filler metal addition. By using the Laser Welding Cobot to manage the arc-less laser melt pool while the CMT-style feeder pulsed the wire, we achieved a bead morphology that required zero post-weld grinding. For Carbon Steel welding, where labor costs in Germany for grinding are prohibitive, this is a massive ROI driver.

4. Lessons Learned and Field Adjustments

During the 30-day trial in Hamburg, several technical hurdles were identified that are common when merging Laser Technology with Carbon Steel welding.

4.1 Gap Bridging and Beam Wobble

Initially, we struggled with “burn-through” on 2mm carbon steel sheets. The intensity of the Laser Technology was too concentrated. By adjusting the Laser Welding Cobot to a 2.5mm wobble width at a 200Hz frequency, we redistributed the energy density. This allowed us to bridge gaps up to 0.8mm, which were previously un-weldable via laser without filler wire.

4.2 Shielding Gas Dynamics

The Hamburg facility is prone to drafts. We found that the standard gas nozzle on the Laser Welding Cobot was insufficient for Carbon Steel welding at high speeds. We had to design a custom trailing shield to maintain an inert atmosphere over the weld pool for an extra 150ms post-weld. This eliminated the “blueing” or oxidation of the S355 surface, ensuring better paint adhesion for the final product.

4.3 Safety and Reflections

While Carbon Steel welding is generally less reflective than aluminum or copper, the 1070nm beam still poses a back-reflection risk during the initial piercing phase. We adjusted the Laser Welding Cobot approach angle to a 5-degree lead to ensure that any back-reflected Laser Technology energy did not damage the laser source or the internal optics.

5. Metallurgical Observations

Cross-sectional analysis of the welds produced in Hamburg showed a deep, narrow “finger” penetration profile typical of keyhole mode welding. In Carbon Steel welding, this can sometimes lead to center-line cracking if the cooling rate is too high. However, by fine-tuning the Laser Welding Cobot‘s ramp-down (crater fill) settings, we successfully managed the thermal exit gradient, eliminating any crater cracks.

The hardness testing across the weld joint showed a peak of 280 HV (Vickers), which is well within the acceptable limits for S355 steel, ensuring the weld isn’t overly brittle. This balance is difficult to achieve without the precise energy input control offered by modern Laser Technology.

6. Conclusion and Future Outlook

The deployment of the Laser Welding Cobot in Hamburg has proven that Laser Technology is no longer just for high-end aerospace or automotive sectors. It is a viable, rugged tool for heavy-duty Carbon Steel welding.

The synergy between the cobot’s ease of use and the laser’s precision has resulted in:

• A 40% reduction in total cycle time per component.
• Near-zero distortion, eliminating the need for hydraulic straightening.
• Significant reduction in consumable costs compared to traditional flux-cored wire.

Moving forward, we recommend the Hamburg team expand the use of the Laser Welding Cobot to include lap joints and fillet welds on the 8mm chassis line. The transition to Laser Technology represents a fundamental shift in our fabrication philosophy, prioritizing “precision at the source” over “correction after the fact.”

Signed,

Senior Welding Engineer
Hamburg Site Inspection Team