Hello and welcome to
this blog post. Today we discuss laser welding of plastics as an efficient and effective
way of joining plastic parts together.
Overview joining of
plastics
There are three established ways on how to join plastic
parts together: mechanical joining using screws and bosses, adhesive joining
using different types of glues, and welding. Within the welding techniques we
can further distinguish between vibration, ultrasonic, high frequency,
extrusion, hot air, hot plate, and laser using infrared light as energy source.
Let us now focus on the laser welding technique.
Laser welding – 4 key
working principles
Important for the
understanding of how laser welding works are the four key working principles:
1.
Transmissive
upper polymer layer: most thermoplastics transmit near-IR beam and the upper polymer
layer needs to be transparent for wavelengths between 808 nm – 1064 nm. Laser
welding radiation is outside the visible light spectrum of the human eye and
therefore, polymer parts are laser transparent although they are not optically
transparent through our human eye view. For example, you can have a black upper
layer which is transmissive to a 980 nm laser. A minimum transmission rate of
5% is required, however optimal would be 30% and greater.
2.
Absorbing
lower polymer layer: the lower polymer layer is responsible for turning the
remaining laser energy into heat at the surface of the absorbing layer. Additives,
colorants and fillers all play a role for absorption. The most effective and
most economical additive for the absorbing layer is carbon black soot. The amount
is usually between 0.2 and 0.4% by volume and provides excellent absorbing
properties to any thermoplastic.
3.
Contact
between upper and lower layer: excellent contact during the welding process to
ensure proper heat conduction. Contact is accomplished with various methods of
clamping devices or special component designs.
4. Material compatibility: two polymers which are to be joined can, but are not required to, be the same type of thermoplastic. The most critical material factors are melt-temperature, and the surface energy of the plastics. The most common thermoplastics such as PA 6, PA 66, POM, PBT, PC, ABS, PP, TPE and PE are easily weldable.
Advantages and
disadvantages
In the table 1,
advantages and disadvantages of plastic laser welding is shown:
 |
| Advatages and disadvantages of plastic laser welding |
4 process types of
laser plastic welding
Next we discuss the four most commonly used process types
in plastic welding: contour welding, simultaneous welding, quasi-simultaneous
welding, and mask welding.
In contour welding, the laser beam is focused into a point
which moves relative to the component contour. It is suited for large parts and
three dimensional parts.
In simultaneous welding, the entire weld seam is heated at
the same time. This is achieved by using specially designed fiber-optics. The
laser energy is formed into the pattern of the weld seam and is projected onto
the entire seam simultaneously. This process is suitable for high volume runs
that require ultra-low cycle times and little flexibility or variation.
Quasi-simultaneous welding is a combination of contour and
simultaneous welding. In this process, a single, focused laser beam is guided
by galvo-scanning mirrors, which traces the weld path multiple times at very
high speeds. The entire joint line is effectively heated simultaneously.
Mask welding is an inflexible process since for each
contour, a new mask is needed. Allover, it consumes much more laser power than
needed and results in an inefficient process.
Overview joint types
and clamping units
There are several possibilities of joints such as the lap
joint (overlap of the two polymer parts), butt joint (end-on-end of plastic
parts; more difficult to realize), radial joints (in case you weld pipes or cylindrical
cases), and T-joints (also called collapsing rib joint since the inner rib will
be heated and melted which results in a collapse of the rib).
Training video with application
examples
I invite you to check
out my training video on plastic laser welding which provides an introduction
and includes also several welding examples:
Thank you for reading
and #findoutaboutplastics
Greetings,
Herwig
Literature:
[1] https://www.lpkf.com/de/branchen-technologien/laser-kunststoffschweissen/technologie-schweissverfahren
[2] https://www.lpkfusa.com/articles/lq/LPW_GL_Hybrid_Laser_Wedling_Design_Guidelines.pdf
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ReplyDeleteHello Tam, thanks for your feedback - glad to hear that you enjoyed the post! best regards, Herwig
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ReplyDeleteVery informative post about laser welding techniques. Thanks for sharing this post! However, can you weld cast iron to steel?
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