In the past welding clear polymers required special infrared absorbers which were expensive and difficult to apply. The advent of higher wavelenght fiber lasers has all but removed the need for absorbers in most clear-to-clear welding applications.
In transparent laser plastic welding(TLPW) higher wavelength lasers are used, specifically fiber lasers operating at or around 2,000 nanometers (2 micron) wavelenghts. The higher wavelength laser interacts differently with the plastic than the typical 808nm or 980nm infrared lasers used in through-transmission welding. At 2,000nm some of the laser energy is still transmitted or passed through a clear thermoplastic, but at this wavelength some absorption is seen, volumetrically, through the part. Enough volumteric absorption to heat and plasticize the polymer.
It is commonly known that when lasers pass through any lens(or any transmitting medium, plastics in this case) some of that laser energy will be absorbed at the surfaces of the lens. In the case of transparent plastic welding there are four surfaces where absorption will increase: the upper surface, the two surface at the joint interface and the lower surface. Because the interface of the joint is comprised of two surfaces the majority of the absortpion in 2 micron clear-to-clear welding takes place here making it a perfect solution for joining clear thermoplastics without absorber additives.
It is worth noting that special absorbing additives for bonding clear and translucent parts is still a viable welding technique. For more information on this technique please visit our Clearweld page.
TLPW has huge potential in the medical device industry where many devices are not only clear/translucent, but also are required to meet strict FDA guidelines. Adhesives and solvents are the current method of choice for bonding clear thermoplastics, but these are often known to cause contamination or fail regulatory testing. TLPW is clean, precise and requires no additional chemicals or materials.
Laser plastic welding produces very clean welds with minimal to no flash and absolutely no dust-like particulates or scaling. The clean nature of the technology allows it to easily be integrated in to cleanrooms up to ISO Class 5, a factor that certainly sets laser polymer welding apart form other welding technologies.
The only major difference between TLPW and regular through-transmission laser welding is the laser source. This makes it very easy to implement into the already existing modularized LPKF systems designed for both automation and stand-alone production environments.