Precision Laser Welding of Clear
Thermoplastics Without Additives
The welding of plastics using laser technology enables the rapid, clean result medical device manufacturers
The through-transmission laser welding process (1.0 micron wavelength range) above and the Clear-Joining process (1.5 to 2.0 micron wavelength range) below.
want. However, when welding clear or translucent plastics, additives must be used in order for the bond to
occur. That is, until now. New laser technology enables these types of plastics to be welded without any addi-
tives being used.
Josh Brown, Laser Plastic Welding Sales, LPKF
Laser & Electronics
Laser plastic welding has gained a strong foothold in the medical device industry as a suitable alternative to other types
of plastic welding or bonding. With advantages such as precision, cleanliness, and
repeatability, laser welding is able to take on
assembly tasks that were previously impossible. Until now, welding clear or translucent
plastics has been difficult or costly, requiring
undesirable color combinations or costly
special absorbing additives. But that is all
changing with the advent of higher-wave-length lasers.
Previously, diode lasers in the 1.0-micron
wavelength range were used for bonding
thermoplastics. The laser energy at this
wavelength will pass through any clear or
translucent thermoplastic. In order to achieve
a weld, a lower layer colored or doped with
an absorbing additive had to be used to
absorb the laser light and convert it into heat
energy at the weld interface.
Higher wavelength fiber lasers have
Percent absorption by laser wavelength
opened the doors to new possibilities in
laser welding, namely bonding of clear
thermoplastics. These lasers interact with
thermoplastics differently. At wavelengths
above 1.5 microns (1,500 nanometers), the
laser begins to show inherent absorption in
the clear plastic. Not all of the light transmits; some absorbs into the plastic. This
allows for the creation of heat energy in
virgin thermoplastics with no colorants or
The goal is to then get some of the energy
to transmit while some of the energy absorbs.
Using this method, all layers, whether it is
just two layers or many more, are volumetri-cally heated by the laser energy.
The 1940 nanometer fiber laser is a preferred choice for many applications as it falls
into the Goldilocks zone with an absorption/
transmission ratio of about 30% absorption to
70% transmission, and also works well with
most any thermoplastic.
Clear and translucent plastic are highly
desired by medical device designers for their
clean look, but also often used
out of necessity when visibility
through the device is required.
Higher wavelength lasers pro-
vide an elegant, robust solution
for joining clear plastics, a very
important step for laser plastic
welding as it pertains to the
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