Laser Transmission Welding of Plastics

This technique relies on the different optical properties of the two plastics being joined. The upper layer must be transparent or translucent to the specific laser wavelength (e.g., near-infrared from a diode or Nd:YAG laser), while the lower layer must contain an absorbent additive, often carbon black or specialized dyes, to convert light energy into heat. The process is highly controllable, allowing for precise weld paths defined by the laser’s movement via robotics or scanner optics. The clamping force is critical to ensure good thermal contact and to forge the weld as the interface melts. This method produces aesthetically pleasing welds with no flash or particulate generation, making it ideal for medical and electronic applications where cleanliness is paramount.

Different variations exist, such as contour welding (tracing the path), quasi-simultaneous welding (rapidly scanning the path multiple times), and simultaneous welding (using multiple beams or masks), which offer trade-offs between speed, flexibility, and equipment cost. The success of the weld depends on material compatibility, the concentration of the absorbing additive, laser power, welding speed, and clamping pressure.