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During scanner welding, the scanner optics can be guided over a workpiece in conjunction with a robot. This "flying" movement inspired the term "welding on the fly.”

A Lesson in Lasers for Assembly

While resistance spot welding is the traditional go-to for automotive assembly applications, David Harvilla, manager of product and applications at the Trumpf Inc. (us.trumpf.com) Laser Technology Center, says that of the more than 2,000 disk lasers in the field, in excess of 75% of them are used for welding.

While resistance spot welding is the traditional go-to for automotive assembly applications, David Harvilla, manager of product and applications at the Trumpf Inc. (us.trumpf.com) Laser Technology Center, says that of the more than 2,000 disk lasers in the field, in excess of 75% of them are used for welding. While the European market is leading in the use of laser welding, Timothy Morris, general manager of the tech center, says the U.S. is gaining traction. Here are some benefits of laser welding:
•    Increasing visibility. With laser welding, you can shrink the flange by about half because you no longer have to accommodate electrodes. By using a butt weld, the flange can be eliminated. Consequently, things like narrower A-pillars can be achieved, increasing visibility and accessibility for the driver.
•    Cost and weight reduction. Reducing the number of flanges or eliminating them means less is spent on materials. This also reduces weight.
•    Reliability. Lasers offer a high power density weld process with laser uptimes of > 98%.
•    Stiffness and strength. With spot welding, you have a joint every couple of inches. With a laser, you can strategically place your welds, including going to a continuous welding mode.
•    Maintenance. Laser welding is a non-contact process, so the tip maintenance required for spot welding guns is eliminated.

Scanner Welding
This process uses a scanning optic that Trumpf calls a “programmable focusing optic” (PFO). Rather than having a robot manipulate the beam, the task is performed with mirrors and optics. The scanning optics are quickly reoriented so that they can reach areas of the workpiece without stopping for repositioning. Some of its automotive applications include the welding of trunk and rear panels, doors, seat frames, and IP beams.

Another feature of scanner welding is that it allows engineers to choose the shape of the weld (e.g., C-shaped vs. linear) based on the type of stress that the part will experience. The programmable weld shapes result in optimal joint strength and a reduction in the number of fixtures.

Benefits of Brazing
Morris explains the reasons why brazing is beneficial:
•    Good gap bridgeability.
•    Appearance. Brazing can get rid of the ditch joint where the body side meets the roof. Spot welding requires sealing of the joint and a molded insert. With brazing, these are no longer necessary. This has the potential to save money and changes design aesthetics.
•    High-process velocity. Laser brazing can be performed at 4 to 5 m/min.
•    Low heat input. Brazing can be achieved with 3, 4, or 5 kW of power.

Which Laser is the Right Laser?
Havrilla says this all depends on the application. So Trumpf has a portfolio approach to its offerings:
•    TruPulse solid-state lasers permit short, powerful pulses, so they are ideal for spot and seam welding, as well as for cutting.
•    TruDisk lasers are flexible. They can be used for remote welding, brazing, and for cutting metals where quality and continuous beam power are required.
•    The TruDiode laser is applicable to brazing.
•    CO2 lasers (which he says often get a bad rap for being passé) are used in the welding of transmission components and in the fabrication of airbags when other lasers can’t absorb into the material.

Economics
Like other aspects of lasers, their price has changed in the past few years. Havrilla explains: “Generally speaking, investment costs have come down dramatically in the last six to eight years, and operating costs have also come down. For example, a 4-kW solid-state lamp pumped laser was about $600,000. Today, a 4-kW disk laser is about $250,000, and prices keep coming down.” He adds that the introduction of Trumpf’s next-generation disk laser later in 2012 will further the cost savings for customers. “Improvements continue to be made in laser technology to greatly increase intervals on maintenance, and in some cases altogether eliminate consumable costs, both of which reduce operating costs. These trends have made it more and more affordable for manufacturers to adopt laser technology.”—BC