Engineering Review: Multi-pass Welding Cobot Welding Machine – Ontario, Canada

Field Evaluation Report: Multi-pass Implementation of Collaborative Robotics in Ontario Heavy Fabrication

1.0 Introduction and Site Context

This report summarizes the field implementation of a Cobot Welding Machine within a heavy structural fabrication environment in Southern Ontario, Canada. The facility primarily handles ASTM A572 Grade 50 structural steel, with a specific focus on Thick Plate Steel welding ranging from 25mm to 50mm (1″ to 2″). The objective was to evaluate the integration of Collaborative Robotics into existing workflows to address the localized shortage of high-pressure CWB (Canadian Welding Bureau) certified welders capable of maintaining consistent quality over long-duration multi-pass sequences.

In the Ontario context, particularly across the Hamilton-Windsor manufacturing corridor, the transition from manual GMAW (Gas Metal Arc Welding) to automated solutions has traditionally been hindered by the high cost of fixed robotic cells and the specialized programming knowledge required. This evaluation focuses on the “Cobot” alternative—specifically how it manages the thermal demands and path offsets required for heavy-section groove welds.

2.0 The Synergy: Cobot Welding Machine and Collaborative Robotics

The term Collaborative Robotics refers to the operational philosophy where the machine and the human operator share a workspace without the need for extensive light curtains or physical fencing (subject to CSA W117.2 safety assessments). In this field application, the Cobot Welding Machine acts as a force multiplier.

The synergy is realized through “Lead-Through Programming.” Unlike traditional industrial robots that require offline programming or complex pendant coding, the Ontario shop floor operators—many with 20+ years of manual experience—can physically move the cobot arm to define the weld path. This allows the welder to apply their intuitive knowledge of “puddle control” and “arc physics” to the robot’s repeatable motion. We observed that the transition time from unboxing to the first arc-on for a multi-pass V-groove was less than six hours.

3.0 Technical Challenges in Thick Plate Steel Welding

3.1 Heat Management and Interpass Temperature

Thick Plate Steel welding introduces significant metallurgical challenges, primarily regarding the Heat Affected Zone (HAZ) and hydrogen-induced cracking. In the Ontario climate, where shop temperatures can fluctuate significantly between seasons, maintaining a minimum preheat of 10°C (50°F) for thinner sections and up to 100°C (212°F) for thicker sections is critical.

The Cobot Welding Machine was programmed with integrated dwell times to ensure interpass temperatures did not exceed 250°C (482°F). Manual welders often rush interpass times to increase throughput, risking grain growth in the HAZ. The cobot, however, executes a programmed cooling delay, ensuring the mechanical properties of the Grade 50 steel remain within the specified CVN (Charpy V-Notch) toughness ranges required by Ontario building codes.

3.2 Multi-Pass Path Offsetting

For a 38mm (1.5″) V-groove, the weld requires approximately 12 to 15 passes depending on the root opening. The primary technical hurdle in Collaborative Robotics for thick plate is “Multipass Software.” We utilized a “floating” coordinate system where the operator defines the root pass, and the software generates the subsequent fill and cap layers using predetermined lateral and vertical offsets.

4.0 Field Observations: Performance and Lessons Learned

4.1 Torch Alignment and Wire Stick-Out

One “lesson learned” during the field trial involved Contact-to-Work Distance (CTWD). In Thick Plate Steel welding, as the groove fills, the CTWD naturally decreases. If the Cobot Welding Machine is not equipped with “Through-Arc Seam Tracking” (TAST), the operator must manually adjust the Z-axis offset every three passes. We found that without TAST, the risk of lack of fusion (LOF) at the sidewalls increased as the arc length shortened.

Recommendation: For Ontario shops specializing in heavy plate, TAST is not an optional feature; it is a technical necessity to compensate for the thermal distortion that inevitably occurs as the 1″ plate “pulls” during the 5th or 6th pass.

4.2 Wire Feed Consistency in Cold Environments

Ontario winters create a specific issue: condensation on wire spools. When the Cobot Welding Machine was positioned near bay doors, we noticed intermittent arc instability. The collaborative arm’s sensitive sensors sometimes interpreted wire-feed “stutter” as a physical collision, triggering an emergency stop.

Lesson Learned: Ensure the use of enclosed wire feeders and heated storage for consumables. Collaborative robots are more sensitive to “micro-collisions” caused by poor wire feeding than traditional, high-torque industrial robots.

5.0 Safety and Regulatory Compliance (CSA W117.2)

In Ontario, the Ministry of Labour and the CWB oversee welding safety. The “collaborative” nature of the Cobot Welding Machine does not exempt the employer from performing a comprehensive Risk Assessment. While the cobot’s force-limiting sensors prevent crushing injuries, they do not protect against UV radiation, weld fumes, or hot spatter.

We implemented a “Zone Control” strategy. While no cages were built, we utilized mobile welding screens and high-vacuum source extraction. The Collaborative Robotics aspect allowed the welder to stand 1.5 meters away, significantly reducing their exposure to hexavalent chromium and manganese fumes, which is a major concern for WSIB (Workplace Safety and Insurance Board) compliance in Ontario.

6.0 Synergy of Man and Machine: The “Operator-Technician”

The most successful implementation occurred when we stopped viewing the Cobot Welding Machine as a replacement and started viewing it as a high-precision tool for Thick Plate Steel welding.

For example, the welder would manually tack the assembly and perform the root pass (the most critical pass for penetration) using a manual GMAW gun. Once the root was cleaned and inspected, the cobot was swung into position to perform the 10+ fill passes. This allowed the human welder to prepare the next assembly while the cobot handled the high-arc-time, repetitive filling. This synergy increased the “Arc-On Time” from a shop average of 25% to nearly 65%.

7.0 Economic Impact for Ontario Fabricators

The ROI calculation for Collaborative Robotics in an Ontario context must account for the high cost of rework. A single failed X-ray on a 2″ thick plate can cost upwards of $3,000 in grinding, re-welding, and re-inspection fees. The Cobot Welding Machine produced a 98% first-pass acceptance rate over a 30-day trial period.

Furthermore, the ability to train an existing Level 1 welder to operate the cobot in a matter of days—rather than hiring a dedicated robotics engineer—drastically lowers the barrier to entry for small-to-mid-sized Ontario shops.

8.0 Conclusion and Engineering Recommendations

The integration of a Cobot Welding Machine into Thick Plate Steel welding workflows is a viable solution for the Ontario heavy fab sector, provided that the limitations of the technology are understood. It is not a “set and forget” system.

Key Recommendations:

• Standardize the WPS: Ensure your Welding Procedure Specifications are specifically qualified for the cobot’s travel speeds, which are often 15-20% faster than manual speeds.
• Invest in TAST: Through-arc seam tracking is essential for multi-pass work on plates exceeding 19mm (3/4″) to account for plate warping.
• Focus on Joint Prep: Automation, even collaborative automation, requires more consistent joint fit-up than manual welding. Invest in CNC plate cutting to ensure the Cobot Welding Machine has a repeatable path.

Final Summary: Collaborative Robotics offers the precision of automation with the flexibility of manual welding. For the Ontario fabricator dealing with heavy sections and a shrinking labor pool, this technology represents the most practical path forward for maintaining CWB-compliant quality while increasing deposition rates.

Report Prepared by: Senior Welding Engineer, Ontario Field Division.