In Through Transmission Laser Welding (TTLW) the parts are pre-assembled and clamped together to provide intimate contact between their joining surfaces. The laser beam is delivered to the parts interface through the upper “transparent” part and is absorbed by the lower absorbing part, which converts IR energy into heat. The heat is conducted from the lower absorbing part to the upper part allowing the melt to propagate through the interface and form a bond. Precise positioning and clamping of the assembly is essential, as intimate contact is required for heat transfer between the parts. Carbon black and specially designed absorbers are blended into resin or applied to the surface to enable IR radiation absorption in the lower part of assembly.
The TTLW welding technique is dependent on the presence of an absorbing agent in the lower component, and this limits the process applicability for manufacturing of medical devices, electronics and some consumer goods when a “clear-to-clear” or a “clear-to-colored” assembly is required.
Engineers have successfully overcome this obstacle by integrating a recently developed 2 micron laser, which is readily absorbed by clear polymers and enables highly controlled melting through the thickness of optically clear parts. This drastically improves and simplifies laser welding of clear polymers for the medical device industry