Space-saving and easily integrable Reliable Quality Assurance in Arc Welding During Ongoing Processes

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Leßmüller Lasertechnik GmbH

GGB Heilbronn GmbH

Lessmüller Lasertechnik GmbH is expanding its range of solutions to include automated seam inspection for arc welding. The OCT 250 stand-alone sensor system employs Optical Coherence Tomography (OCT) as a measurement method for continuous seam tracking and real-time seam inspection in automated MAG welding processes.

The advantages for users are clear: OCT methods are significantly more precise than traditional camera technology, the effort for subsequent quality control is substantially reduced, and the user-friendly software allows for the evaluation and documentation of analysis data. This increases productivity and reduces scrap rates measurably.

Arc welding, or MAG welding (Metal Active Gas Welding), is widely used in the metal processing industry, container and vessel construction, machine engineering, and rail vehicle and shipbuilding, as well as in the furniture industry and other sectors. This process enables the joining of thin sheets as well as components with material thicknesses of up to 60 millimetres, and is often employed fully automated and robot-assisted in industrial environments.

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To significantly enhance the productivity of automated MAG welding and to reduce scrap caused by insufficient fusion of the weld joint, the welding process must be precisely controlled. Due to the high demands of robot-guided MAG welding, existing process monitoring systems—using laser projectors and CMOS cameras—are often deemed inadequate. Lessmüller Lasertechnik’s OCT technology now enables efficient quality assurance in arc welding for the first time.

More accuracy, better tracking, and significant time savings

Similar to laser beam welding, the OCT 250 stand-alone welding sensor also facilitates pre-emptive seam tracking and post-inspection during the ongoing MAG welding process. Unlike conventional process monitoring systems using camera technology, the OCT sensor is completely insensitive to light. It operates reliably and with high precision despite the arc, ambient lighting, and reflective welding spatter. This insensitivity allows the measurement lines to be placed much closer to the TCP (Tool Center Point), thereby reducing passive movement paths, i.e., downtime.

The OCT scanner can be directly mounted to a robot-guided welding torch. For process monitoring, the system projects two OCT scan lines near the welding area. The first line, preceding the tool tip, captures the geometry to be welded and measures the gap dimensions if necessary. The second scan line follows behind the burner nozzle (after the arc) and scans the weld bead. In this process, quantitative and qualitative data such as weld bead length, profile, width, area, and throat of the weld bead, convexity and concavity of the seam surface, undercuts and other defects, as well as surface porosities and craters are captured and displayed.

With their proprietary user software, all data for quality assurance of seam tracking and inspection can be comfortably visualized, evaluated, and archived for traceability. The client software can transmit control commands via fieldbus to the machine or robot controller based on the pre-emptive seam tracking, adjusting the robot's programme flow as needed. For example, offsets, welding angles, or a combination of both can be adjusted and tailored to the specific connection type as well as the gap and overlap sizes. The evaluation of the post-inspection permits a comparison with predefined tolerances and can mark components as scrap upon detecting critical errors and even halt the welding process. This eliminates the need for additional subsequent quality controls.

The OCT 250 stand-alone sensor technology provides highly efficient, space-saving, and easily integrable process and quality monitoring for automated MAG welding, with a quick return on investment. Users can avoid production downtimes, ensure high welding quality, and enhance the productivity of their welding processes. Additional control measures can be reduced, saving valuable work time. The reliability and industrial suitability of the system have already been successfully validated in several test applications at research institutes and with Tier 1 automotive suppliers.