Laser Welding Clears Up

Laser welding clear or translucent materials may not work when appearance matters because the weld lines stick out like a sore thumb. Oce Graphic Display Systems, a San Jose, CA-based division of Oce NV, had to confront that exact problem when it revamped the polypropylene inkjet cartridges for its wide-format printing systems. Translucent cartridges make it easier to monitor ink levels. Yet the cartridges in the past required a carbon black additive to absorb the laser energy at the joint interface. Oce recently found a clearer joining solution at Gentex Corp. (www.gentexcorp.com).

Gentex assembles the new cartridges using its ClearWeld process, which creates nearly invisible laser-welded joints in clear or translucent materials. It does so with the help of a proprietary near-infrared-absorbing material. According to Michelle Burrell, a Gentex engineer, a thin layer of this welding aid is applied at the joint interface. "It acts as a focal point for the laser energy," she says. Localized heating of substrates at the joint interface results, producing the weld. Unlike laser welding with carbon black, this absorbing material leaves no noticeable trace. "Carbon black does a good job absorbing laser energy," she adds, "But you can easily see it in the finished part."

Assembling Oce's cartridge, which measures 9.5 x 2.5 x 0.5 inches, involves five different welds to join its injection-molded components. A perimeter weld affixes the lid to a reservoir. Four welds secure outlets that exit the bottom of the reservoir. Gentex applies a laser-absorbing material in joints with a needle-valve liquid dispensing unit. It then welds them with a Coherent Inc. (www.coherentinc.com) 80W, 940 nm diode FAP laser system operating at 55W and a speed of 10 ipm. Clamping pressure of 70 psi holds the assembly together during welding.

The ClearWeld process has other advantages too: For one, there's no rubbing. ClearWeld doesn't involve any friction between mating surfaces, so it avoids problems with polypropylene particulate making its way into the assembled cartridges. "Particulate was a potential problem with ultrasonic welding," Burrell says. For another, ClearWeld limits heating to the weld interface, which heads off risk of part deformation, Burrell adds. Finally, ClearWeld met the strength requirements for this application, such as enduring an internal pressure of 20 psi when the hermetically sealed cartridges undergo leak testing.

The Oce job marks one of the first production applications for the ClearWeld process, which was developed about a year-and-a-half ago. Upcoming applications have been in medical devices, using materials such as acrylic and polycarbonate.