The commonly used laser welding progress is called laser transmission welding. The laser beam, after transmission through the upper-layer transparent material, will be absorbed by the lower layer. The laser energy, after being absorbed, will be transformed into heat. Since two layers of materials are forced together, the heat will be conducted to transparent layer from absorbing layer, which would make the two layers of materials melt and connected. At the same time, the internal pressure occurs because of the material’s thermal expansion. The total effort of the internal and external pressure can make sure two layers are firmly welded. For the product lower-layer material does not absorb laser, additive needs to be applied to the lower layer.
Clear Material Laser Welding
Clear polymers required special infrared absorbers which were expensive and difficult to apply. In transparent laser plastic welding, a higher wavelength laser is used, which interacts differently with the plastic than the typical 808nm or 980nm infrared lasers used in through-transmission welding. Some of the laser energy is still transmitted or passed through a clear thermoplastic, but at this higher wavelength, some absorption is seen, volumetrically, through the part - enough volumetric absorption to heat and plasticize the polymer.
It is commonly known that when lasers pass through any medium, some of that laser energy will be absorbed in 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 surfaces at the joint interface and the lower surface. Because the interface of the joint is comprised of two surfaces, most of the absorption in clear-to-clear welding takes place here making it a perfect solution for joining clear thermoplastics without absorber additives.