Collaborative robots, or cobots, have been around for more than 15 years now. They began lending a hand with repetitive welding tasks in fabrication shops several years ago. Cobot use in the welding industry has exploded in those few years, largely due to the ease of programming, versatility and affordability offered by these systems – helping fill the gap between manual welding and traditional robotic weld cells.
The ever-present shortage of skilled labor was made even more severe by the pandemic and recent supply chain struggles; with the problem only becoming more acute it further fuels the fabricator’s need for simple, flexible automation tools.
As with many new technologies, cobot welding systems started out performing the easiest weld tasks – simple welds on repetitive and consistent steel parts, typically with smaller weld wire diameters. But, more recently, cobot welding integrators are enabling a broader range of welding applications through the development of new configurations and technologies on their cobot welding platforms.
These new developments include heavy-duty packages for welding with larger wire diameters (up to 1/16 in. or larger), push-pull packages for welding with aluminum and other soft wires, various deployment options that further boost versatility, and software features such as touch sensing, multi-pass capability and through-the-arc seam tracking. Each of these evolutions allow more types of applications in the fab shop to be tackled – heavy weldments, larger parts, various materials and components where automation-level upstream consistency simply cannot be maintained in production.
Managing inconsistencies
That last challenge – managing production inconsistencies – is a key need for numerous manufacturers, particularly those doing large weldments. Even with upstream improvements (lasers, CNC press brakes, etc.) and better fixturing, inconsistencies still exist in the weld shop.
Vectis Automation’s new ArcPilot arms its Cobot Welding Tool, a system powered by cobots from Universal Robots, with a potent tool to help manage those variations. The new through-the-arc seam tracking is a functionality that enables path correction during live welding by monitoring the welding arc’s electrical characteristics, then using those readings to make cobot path adjustments in microseconds.
This innovation has enabled users to leverage automation on applications that were previously too inconsistent, such as plates that distort while welding and assemblies where slot-and-tab construction isn’t viable or where precision fixturing would not be economical.
Through-the-arc seam tracking works by monitoring the electrical characteristics of the welding arc as it progresses along the weld joint, then making adjustments to the cobot’s programmed path based on an ongoing comparison of those readings. It is primarily used as a tool to maintain weld placement and quality on joints where part-to-part consistency is not possible to achieve via upstream processes and fixturing (e.g., distortion on heavy-plate parts).
Basic law
The ArcPilot seam tracking feature is able to correct both contact-tip-to-work (stickout) distance and steer the cobot to stay in the center of symmetrical joints (fillets, bevels, etc.).
The base principle at work here is Ohm’s Law (voltage = current X resistance). In the MIG welding process, resistance changes inversely to current. So, when the welding current changes, the ArcPilot tracking system is able to detect that and learn something about the resistance (tip-to-work distance). An algorithm then uses that correlation to pilot the cobot correction path in the joint at the proper tip-to-work distance.
This technology can also be used in conjunction with Vectis’ multi-pass software to correctly offset subsequent weld passes using the root pass that was seam-tracked. When combined, this technology combo has enabled significant productivity gains for heavy-weldment fabricators. One customer reported reducing overall welding process time on a repetitive 30-pass heavy weld by more than 80 percent, all while improving quality and consistency. It also allows their skilled welders to shift their focus to the weldments requiring more human finesse.
As cobots become more prolific in the welding and cutting market, new technologies like through-the-arc seam tracking will continue to increase the portfolio of viable applications.
