Laser transmission welding of thermoplastics requires both a polymer that is transparent to the laser beam and one that is absorbent. The transparent material is placed on top of the absorbent material and clamped. The diode laser beam penetrates through the transparent layer and heats up the surface of the absorbent material. Energy absorption and thermal conduction causes both the transparent and absorbent materials to melt and after re-solidification, the two parts are reliably joined and as strong as the base material. Nearly all thermoplastics, even fiber reinforced grades, can be laser welded if one of the parts provides sufficient transmission for the laser beam.
Today, a spectrum of laser transmissive dyes is available if the part has a solid color such as black. In addition, absorbing coatings are used for laser welding of two clear or colored translucent part. Complex three-dimensional designs and geometries are easily realized utilizing either contour or quasi-simultaneous laser welding of plastics. Because laser diode welding is a non-contact process with very low thermal and no mechanical impact, it is well-suited to welding hermetically sealed housings that contain electronics or other heat-sensitive components, food packaging and medical applications. The completely emission-free process is hygienic, precise and the weld seam offers the highest visual quality. There is no tool wear or requirement for consumables.