Old is new in powertrain laser welding

  • 19-Feb-2015 02:03 EST
Comparisons.jpg

The weld at left was done with a CO2 laser, the one on the right with a fiber laser. Notice the better weld quality and lack of discoloration on the CO2-welded part.

Using lasers is often the best choice for welding, especially in precision parts where weight is a premium, such as in powertrain and engine components. Why? Given a proper fit-up, manufacturers can often dispense with filler wires. Lasers easily join dissimilar alloys, allowing for even more lightweighting opportunities. Additionally, a laser’s narrow, high-intensity beam means a low heat-affected zone, reducing heat-induced distortions. Another distinct advantage of laser welding in general is that it is easier for manufacturing engineers to automate than other methods.

Advances in lasers are also making them more attractive. For example, the advent of fiber laser technology got many thinking that older technologies, like the venerable CO2 laser, were on their way out. The fiber laser is smaller and produces light in a 1-micron wavelength. This makes its power easily delivered in a fiber-optic cable compared to the rigid optics required of the 10.6-micron CO2 laser. Fiber lasers have better wall-plug efficiency, typically 25-30% compared to approximately 10-15% with the best CO2 lasers. The 1-micron wavelength of the fiber laser more easily couples with material, improving the energy input into the weld.

However, the fact that fiber lasers are so good at coupling with the material may be a good reason for sticking with CO2 lasers. Spatter is the issue.

“Since the 1-micron wavelength has a much better coupling efficiency with the metal [compared to 10.6-micron wavelengths], it vaporizes the metal in the weld pool even faster and that creates spatter,” explained Chris Dackson, Sales Manager for Rofin-Sinar. These small fragments present particular problems in precise powertrain parts, such as clutches, gears, and carriers. “It’s a quality problem,” he stated. CO2 lasers simply produce welds with less spatter compared with a high power 1-micron beam.

To make CO2 lasers more efficient and cost-competitive, Advanced Nozzles, LLC introduced a new nozzle to reduce the use of the process gas helium, according to Dackson. Rofin uses these nozzles on many of its installations. One of the best ways of increasing efficiency of welding with any laser is to use a process gas.

“A process gas suppresses plasma in CO2 or particle formation in any 1-micron laser. If you do not use a process gas, you lose efficiency but you lose more efficiency with CO2 lasers because of plasma formation,” explained Dackson.

Add to that the fact that helium is one of the more expensive industrial gases, making them even less competitive. “Replacing helium with cheaper argon and CO2 to mitigate plasma formation means CO2 lasers compare more favorably with fiber lasers. This new nozzle device also reduces flow rates, to a combined total of 35 standard cubic feet per hour of CO2 and Ar from 50 to 60 with helium,” he said.

Now with the improved CO2-argon gas welding nozzle, CO2 laser welding compares even more favorably for high-volume applications over fiber lasers, according to Dackson.

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