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What is
laser transmission welding?
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Laser Transmission Welding has been attracting attention
as an alternative method of plastics joining other than hot plate welding,
vibration welding and ultrasonic welding.
Laser transmission welding (LTW) is categorized as a heat
welding method. Similar to hot plate welding, vibration welding and ultrasonic
welding, each of these applications employ heat as a means to join without an
additional adhesive.
However,
in laser transmission welding (LTW), the heat source is different from that in
other methods. A hot
plate (heated metal plate) is used as the heat source in hot plate welding, and
heat from friction is used for melting in vibration welding and ultrasonic wave
welding. In laser transmission welding, however, a plastic part is made to
absorb the laser beam to heat and melt it.
You may
have had the childhood experience of focusing sunlight on a point on a piece of
black paper using a magnifying lens and starting a fire. In laser transmission
welding (LTW), the laser beam serves as the sunlight and the plastic part
serves as paper, and light energy is converted into heat energy.
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We have learned that plastic is welded by means of a laser beam. How are
the plastic parts actually bonded with each other?
The
answer is that bonding is performed by placing a plastic part through which a laser
beam is transmitted (light-transmitting resin part) to a plastic part that
absorbs the laser beam (light-absorbing resin part). First, when a laser beam
is radiated while those two plastic parts are pressed against each other at an
appropriate pressure, the laser beam passes through the light-transmitting
resin part and a portion of the light-absorbing resin part near the border of the
light-transmitting resin part is heated and melted. Then, the heat is also transmitted
to the light-transmitting resin part by heat conduction, and the light-transmitting
resin part is melted and a molten pool is formed. Finally, the light-transmitting
resin part and light-absorbing resin part are bonded with each other.
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- Laser beam To
conduct laser transmission welding (LTW), first of all, the type of laser is important.
The types of laser for resin include fiber laser [wavelength: 1070 nm], YAG (Yttrium-Aluminum-Garnet
crystal) laser [wavelength: 1064 nm] and LD (laser diode) [wavelength: 808,
840, 940 nm]. Generally, by comprehensively judging the beam quality (heat
source), power stability, and cost, an optimum laser is selected. Depending on
the type of plastic, some materials absorb lasers of these wavelengths.
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- Mechanism of laser transmission welding (LTW) |
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