applications from engine compo- nents all the way down the driveline including transmissions,” said Rick Davis, automotive OEM & powertrain key account manager for Trumpf, Inc. (Plymouth, 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 dis- cussed is laser welding of differential gears. In this process, lasers are replac- ing joining using screw fasteners. The challenge was to weld a housing made of ductile cast iron to a case-hardened ring gear made of specialty alloy steel. Eliminating screws meant eliminat- ing cost and weight—about 1 kg per gear. Other added benefi ts, according to Davis, meant allowing the gear to transmit higher torques while reduc- ing 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 embrittlement 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 materials, it results in a weld that is not as hard or brittle, [eliminating] the need for a fi ller wire,” he said. This required precise positioning of the laser beam, as well as spe- cialized 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 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
By replacing screw fasteners, laser welding automotive powertrain components reduces weight and provides other benefi ts.
Photo courtesy Trumpf
lasers are used in welding, “the 1-μm wavelength has a tendency to get the material very excited 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. A solution that Trumpf is fi nding potentially
attractive for the future is to weld under partial vac- uum. 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.
Lasers Finding Their Place
Noncontact laser welding adds value in small parts as well as large. “Lasers are becoming the
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