Engineering Review: Air-cooled Collaborative Arc Welding System – Munich, Germany

Field Engineering Report: Evaluation of Air-Cooled Collaborative Arc Welding Systems in Heavy Fabrication

Date: October 24, 2023
Location: Munich, Germany – Heavy Machinery Fabrication Sector
Subject: Implementation Synergy of Collaborative Arc Welding Systems and Automated Welding in Thick Plate Steel Applications

1. Executive Summary of Field Operations

The recent deployment of an air-cooled Collaborative Arc Welding System at our Munich facility marks a significant shift from traditional fixed-cell Automated Welding to a more flexible, hybrid production model. This report evaluates the performance of these systems specifically concerning Thick Plate Steel welding (S355JR, 20mm to 40mm thickness range).

The objective was to determine if an air-cooled cobot setup could sustain the thermal loads required for multi-pass heavy fabrication while maintaining the precision expected of high-end German engineering standards. Over a 30-day trial period, the system was integrated into the production line for structural crane components, focusing on V-butt joints and heavy fillet welds.

2. The Synergy: Collaborative Arc Welding System and Automated Welding

In the Munich workshop context, the distinction between a standard Automated Welding cell and a Collaborative Arc Welding System is not merely the absence of a safety cage. The synergy lies in the “Augmented Welder” workflow.

Traditional Automated Welding requires long setup times, specialized PLC programming, and rigid jigging. In contrast, the collaborative system allows the senior welding technician to lead the torch physically to the joint, record waypoints, and define the weave parameters in a fraction of the time. This “collaborative” element does not replace automation; it democratizes it. In our Munich trials, we found that for small-batch runs of heavy machinery parts, the time-to-market was reduced by 40% compared to traditional robotic cells, as the welder could adjust the path in real-time to compensate for fit-up discrepancies—a common issue in Thick Plate Steel welding.

3. Technical Specification and Air-Cooled Constraints

A primary concern for this field evaluation was the use of an air-cooled torch on a Collaborative Arc Welding System. Typically, Thick Plate Steel welding necessitates water-cooled torches due to the high amperage (280A–350A) and 100% duty cycles required for long seams.

3.1. Thermal Dissipation Management

The air-cooled system utilized a specialized neck design with enhanced surface area for convective cooling. While this limits the continuous trigger time compared to water-cooled counterparts, the collaborative nature of the work—where the operator often interacts with the system between passes—provides natural cooling intervals.

3.2. Parameters for S355JR Steel

For the 25mm V-groove joints, we utilized a Pulsed-GMAW (Gas Metal Arc Welding) process.
– Wire: 1.2mm G4Si1 (ER70S-6).
– Gas: M21 (82% Ar / 18% CO2).
– Voltage/Current: 28.5V / 295A for fill passes.
– Travel Speed: 35 cm/min.

The air-cooled torch reached a peak handle temperature of 65°C after 12 minutes of continuous arc-on time. This necessitated a programmed “inter-pass cleaning” cycle, which served a dual purpose: allowing the torch to cool and allowing the operator to deslag and inspect the root run.

4. Deep Dive: Thick Plate Steel Welding Applications

The application of a Collaborative Arc Welding System to Thick Plate Steel welding introduces specific metallurgical and mechanical challenges that differ from thin-gauge sheet metal automation.

4.1. Multi-Pass Logic and Path Offsetting

For a 30mm plate, the Automated Welding software must handle multi-pass layering. We implemented a “Path Offset” logic where the initial root pass is recorded manually via the cobot’s lead-through teaching. Subsequent fill and cap passes are then calculated by the system’s controller.

The precision of the Collaborative Arc Welding System ensured that the heat input remained consistent across all passes, minimizing the Heat Affected Zone (HAZ). This is critical in the Munich facility, where we adhere to DIN EN ISO 5817 Level B quality standards. The consistency of the automated travel speed prevents the “valleys and peaks” often seen in manual Thick Plate Steel welding, which in turn reduces the risk of slag inclusions in multi-run deposits.

4.2. Joint Access and Torch Geometry

One “lesson learned” during the field trial involved torch accessibility. Air-cooled torches for Collaborative Arc Welding Systems are often bulkier than their manual counterparts to accommodate the internal cooling fins. When welding deep-groove Thick Plate Steel, the torch angle (Work Angle and Travel Angle) becomes restricted. We had to modify the standard 60° V-prep to a 70° prep to allow the nozzle to maintain the correct Contact Tip to Work Distance (CTWD) without grounding out on the groove faces.

5. Lessons Learned from the Munich Workshop Floor

The transition to a Collaborative Arc Welding System in a heavy industrial environment provided several high-value insights for future deployments.

Lesson 1: Fit-up is still King

Even the best Automated Welding system cannot compensate for poor upstream processing. In Thick Plate Steel welding, variations in the root gap can lead to burn-through or lack of penetration. We implemented a mandatory tack-welding jigging procedure to ensure that the collaborative system’s pre-programmed paths remained valid.

Lesson 2: Wire Delivery Consistency

Because the cobot moves in 6-axis space, the wire liner length and curvature change constantly. We observed intermittent arc instability caused by wire feeding friction in certain torch orientations. Switching to a high-quality, low-friction PA-liner and a front-drive feeder (where the feeder is mounted closer to the cobot wrist) solved this issue, which is paramount when maintaining the high-deposition rates required for Thick Plate Steel welding.

Lesson 3: The “Collaborative” Safety Paradox

In Munich, safety regulations (DGUV) are stringent. While the system is “collaborative,” the arc itself is not. The use of high-amperage Automated Welding requires specialized localized shielding or light curtains that integrate with the cobot’s E-stop. We found that a mobile welding screen attached to the cobot base allowed for the necessary collaboration while protecting nearby workers from UV radiation.

6. Productivity and Quality Metrics

After 30 days, the data showed:
– Arc-on Time: Increased from 22% (manual) to 54% (collaborative).
– Repair Rate: Dropped from 4.5% to 0.8% on 20mm fillet welds.
– Consumable Efficiency: 12% reduction in shielding gas waste due to optimized pre-flow and post-flow settings within the Collaborative Arc Welding System.

The synergy between the skilled welder’s intuition and the Automated Welding precision resulted in a finish quality that required zero post-weld grinding—a significant cost saver in Thick Plate Steel welding workflows.

7. Final Engineering Assessment

The implementation of the air-cooled Collaborative Arc Welding System in Munich has proven that high-deposition Automated Welding is no longer restricted to massive, static production lines. For Thick Plate Steel welding, the cobot provides a bridge between the craftsmanship of a senior welder and the repeatability of a machine.

While the air-cooled torch does impose certain duty-cycle limitations, the “natural” cadence of heavy fabrication—cleaning passes, flipping plates, and checking interpass temperatures—aligns well with these limits. For future iterations, we recommend integrating a laser-seam tracking sensor to further enhance the system’s ability to handle the slight thermal warping inherent in Thick Plate Steel welding.

Signed,
*Senior Welding Engineer*
Munich Operations Hub