Scanners Handle High-Power Welding

Greg LaManna, Trumpf Inc

The idea of scanning a laser beam has been around for years. Until recently, though, the concept has been implemented primarily with low-power lasers in equipment such as laser printers and in marking images and text on manufactured components; e.g., integrated circuit chips, computer keyboards and automotive components. In the past few years, researchers at Trumpf Inc. have worked to integrate multikilowatt CO₂ lasers with scanning technology.

The strategy devised uses a focus optic mounted to a linear drive axis to move the focal point in the vertical axis, and two deflection mirrors with cone angles of ±20° to move the focal point in the horizontal plane (see figure).

In remote scanning technology for higher-power CO₂ lasers, such as Trumpf’s TLW60S system, high beam quality and a beam-expanding telescope achieve a focused spot that can produce the necessary energy density to couple with various work materials, even with focal lengths of 1.5 to 2.25 m.

For welding and cutting applications, the focused laser beam’s spot size must be in the range of 500 μm in diameter to achieve the energy density needed for coupling with various materials. Historically, this has been accomplished through the use of reflective or transmissive optics, and focal lengths have been limited to 50 to 400 mm. The goal of this new scanner technology is to increase the work envelope by increasing the focal distance, while introducing a flexible, programmable solution for materials processing.

Because raw beam diameter and beam quality influence the focused spot size, an enlarged raw beam of high quality has been necessary for remote welding. However, advances have continued in laser design in parallel with scanner technology, so this is no longer a concern. The high beam quality factors available with current laser systems, combined with a beam-expanding telescope, achieve the needed focused spot using a focal length of 1.5 to 2.25 m. Resulting 4- to 6-kW laser systems have a work envelope of 800 × 800 × 300 mm (X-Y-Z), and 1.8 to 3.5-kW systems have a work envelope of 1250 × 1250 × 300 mm.

High-power CO₂ laser scanning technology can be used in a wide variety of applications, from cutting textiles to welding coated and uncoated steel. This technique is advantageous because it is noncontact and because it requires less maintenance and less frequent replacement of wear components, such as welding electrode tips. Remote CO₂ scanning technology also typically consumes less floor space than a robotic welding cell with the weld gun attached to a robot that performs sequential welds.

There are other potential benefits to scaling remote welding to higher-power CO₂ lasers. The increased distance between the workpiece and the optics reduces potential contamination of the optics. The large work envelope allows parts to be processed in the scanner’s field of view, which reduces or eliminates workpiece movement during welding and makes flying optics unnecessary.

Point-to-point indexing speeds of the focused laser spot in excess of 700 m per minute are a result of the high dynamics of the motion system: The linear axis is capable of greater than 6-g acceleration and of velocities of more than 200 m/s, and the deflection mirrors move at 12.5 rad/s. These speeds translate into near-zero indexing time and maximum beam-on time.

As an example, scanner welding can be as much as six times faster than sequential resistance spot welding in components with multiple welds. Besides weld time, sequential resistance spot welding requires movement of the electrodes or workpiece and squeeze time for the weld guns. Programming flexibility with remote welding, however, allows optimized weld paths and sequences, decreasing processing times and reportedly producing a better strategy for reducing thermal distortion of the workpiece.

Thus, laser scanner technology provides manufacturers with an added dimension of kilowatt-level CO₂ processing flexibility. When it is implemented on the factory floor, the technology facilitates programmable changeovers and increases the productivity of a cell through high indexing speeds between parts or locations.

Meet the author

Greg LaManna is product manager for CO₂ lasers at Trumpf Inc. in Plymouth Township, Mich.; e-mail: greg.lamanna@us.trumpf.com.