In laser transmission welding of thermoplastics, the laser beam penetrates the upper, transparent joining part and is completely absorbed by the lower, dark surface. The radiation is converted into localised heat and melting takes place. The heat required to melt the transparent joining part is received from the thermal conduction of the absorbing part.
Strong welding of both parts occurs under external compression and the internal joining pressure, arising from local warming and expansion.

Nearly all thermoplastics and elastomers can be welded using laser transmission welding. High welding seam strength in the region of the base material is achieved. Dark plastics, preferably dyed with carbon, are welded with transparent ones. Dark/dark and transparent/transparent combinations are also possible with the aid of special pigments.

The sectional image shows the typical lens-shaped melting zone. The transparent joining part contributes a third and the absorbing part two thirds of the melting volume. Laser transmission welding achieves a precise, optically perfect and strong bond.

Advantages

Non-contacting, flexible welding technique
Minimal thermal stress on the joining parts
Simple welding seam geometry
No release of particles
Vibration-free processing
Optically perfect welding seam
High precision
High strength
No tool wear