In the laser welding of thermoplastics, sometimes referred to as “laser transmission welding” or “through transmission IR welding (TTIr), transparent and absorbent parts are bonded together. The laser beam penetrates the transparent plastic and is converted to heat in the absorbing plastic. Since both parts are pressed together during the welding process, heat is conducted from the absorbent to the transparent plastic, allowing both materials to melt and create a bond. Internal joining pressure also is generated through the local warming and thermal expansion. The internal and external joining pressures ensures a strong weld of both parts.

1. Transparent joining part
2. Absorbent joining part
3. Laser beam
4. Melt zone
5. Weld seam