LASER WELDING
used in any tailor welded product. His company is investigat- ing various alloys and thicknesses. The Ford F-150 with its heavy use of aluminum is catching their attention. “We are in- vestigating 5000, 6000, and 7000 series alloys of aluminum,” he said. The company has proven laser welding using only 5000 series alloys and continues to experiment with other grades and welding processes.
Powertrain Too
In addition to BIW applications, companies are also turn- ing to lasers for powertrain components. “We are seeing lasers used in powertrain welding applications from engine components all the way down the driveline including trans- missions,” said Rick Davis, automotive OEM & powertrain key account manager for Trumpf, Inc. (Plym- outh, MI). As in body structures and closures, saving weight for better fuel economy is driving a search for better methods of joining. One such application Davis discussed is laser welding of differential gears. In this pro- cess, lasers are replacing joining using screw fasteners. The challenge was to weld a hous- ing made of ductile cast iron to a case-hard- ened ring gear made of specialty alloy steel. Eliminating screws meant eliminating cost and weight—about 1 kg per gear. Other added benefi ts, according to Davis, meant allowing the gear to transmit higher torques while re- ducing emitted noise. Trumpf delivered a 4-kW solid-state laser in an automated system, with robotic material handling and a laser cleaning station as well. Weld speeds are about 1.5 m/ min with a penetration of 5 mm. Like in other applications, weld embrittle-
ment from autogenous welds was a challenge. “To counter that we use fi ller wire,” he said. However, studying the process more carefully, they found a clue to creating more effi cient autogenous welds. “If we can precisely control the carbon dilution between the two materi- als, it results in a weld that is not as hard or brittle, [eliminat- ing] the need for a fi ller wire,” he said. This required precise positioning of the laser beam, as well as specialized sensors to guide it. Their integrated system used sensors to measure the gap before welding, penetration depth during welding, and width of the seam after welding. This precise system
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AdvancedManufacturing.org | February 2015
guarantees a ‘ductile’ weld with no fi ller wire, reducing weight even further.
Like in other applications, solid-state lasers are fast becoming the tool of choice in powertrain. However, as seen elsewhere, the older CO2
lasers with their 10.6-μm
wavelengths still have their place. Why? When near-infrared wavelength of solid-state lasers are used in welding, “the 1-μm wavelength has a tendency to get the material very ex- cited and it wants to expel out of the weld zone and splatter,”
Davis said. “While it is a sound weld, manufacturers use CO2 lasers in an effort to avoid potential splatter BBs, especially where gears are involved.” However, many manufacturers would like to adopt solid-state lasers because of their fl exible beam delivery and smaller footprint.
By replacing screw fasteners, laser welding automotive powertrain components reduces weight and provides other benefi ts.
A solution that Trumpf is fi nding potentially attractive for
the future is to weld under partial vacuum. Davis presented results that showed welding under 10 millibar conditions (about 1/100th normal pressure) reduces the brightness of the vapor torch and provides negligible splatter, even with a 1-μm wavelength beam.
Photo courtesy Trumpf
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