INNOVATION | JOINING AND ASSEMBLY
the laser-transmitting component. Neither would a white component, where a typical pigment used is titanium dioxide. We can give different colour options in a wide range of polymers including polypropylene, ABS, polycarbonate, PC/ABS blends and more. In collaboration with laser equipment suppliers, we’ve developed analytical techniques that can be used to screen different solutions to find the best one.”
Laser all-clear Just as laser welding requires that one of the two plastics parts must be transparent to laser frequencies so that the light can reach the join and heat it up, so it follows that the process won’t work if both components are laser transparent. Solutions that enable the joining of parts that are both transparent are increasing in number, not only from materials suppliers, but also welding equipment makers. Emerson, which owns welding equipment specialist Branson, recently collaborated with Sono-Tek to develop a new variant of the process. It combines Branson simultaneous through- transmission infrared laser welding technology and an ultrasonic spray deposition technology from Sono-Tek. The Sono-Tek technology deposits a laser- absorbing material in the form of microparticles of a dye or carbon black suspended in a low boiling point liquid. The laser heats up these particles, which in turn heat up the plastic to the point that it softens and so enables bonding under pressure. Spraying is carried out using an ultrasonic horn
Below: Joining automotive taillights with the LPKF PowerWeld 3D 8000 laser system
that atomizes the dye and deposits it in patterns that can be as narrow as 0.5 mm and with thicknesses measured in nanometres. The carrier fluid is flashed before the welding process begins. Hugh McNair, laser applications and systems manager for assembly technologies at Emerson, says that because the spray deposition process is
so precise, the need to precisely focus the laser energy is possibly not as great as when welding plastics that are inherently laser-absorbent, since clear-on-clear welding only occurs where the laser-absorbing dye has been deposited. Branson says the technology is invaluable for medical devices that demand optically clear flow paths, simplifying everything from automated blood cell counts in capillary-sized fluid paths, to providing visual validation to a technician that a micro-dose of a powerful therapy is being properly administered to a patient. The process can also make high-quality transparent lenses, fluid-handling devices and other components for consumer products. The Branson/Sono-Tek development is tied to
the Clearweld process invented back in 1998 by TWI, the UK-based industrial research and development organisation that specializes in materials joining. The Clearweld process is covered by a number of worldwide patents now owned by or licensed to Gentex. Companies buying material from Gentex or from its licensed supplier, Crysta- Lyn Chemical, have rights to use the process. “We have been developing our optically clear to optically clear plastic welding process for over five years,” says Tom Hoover, Senior Medical Business Development Manager, Americas, at Branson Ultrasonics Corp. “There are multiple methods to apply laser absorbing dies, with ultrasonic spray deposition currently being the most accurate. We worked with Gentex, then Crysta-Lyn, to formulate the best absorber particle composition, size and carrier fluid. Part of our development time was for cytotoxicity and biocompatibility approvals. Our technology breakthrough is in terms of the scale and accuracy that we can deliver.”
Expanding capability
Another welding equipment company increasingly involved in laser welding is Dukane, already a worldwide leader in plastics welding. Last year, it bought Blackhawk Technology Group, a laser welding equipment company headquartered in Oregon, US. According to Dukane, Blackhawk is a “systems, services, and contract manufacturer for laser plastic welding,” with a focus on end-to-end service, from basic material tests to full process development and contract manufacturing. Mike Johnston, Dukane President & CEO, says his company’s LaserlinQ technology’s ability to enable welding of clear-to-clear (2-micron) components without the need for additives has grown the demand for its own laser technology. He says customers are now requesting laser technology for 1-micron opaque to coloured weld
36 INJECTION WORLD | May 2020
www.injectionworld.com
IMAGE: LPKF
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