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Assessing compatibility: Can your laser weld these two plastics?

Lasers are well suited for high-precision manufacturing

Lasers are well suited for high-precision manufacturing, especially in tasks such as welding small plastic parts (Credit: Hamamatsu)

Plastic welding stands out as an application where lasers outperform alternative methods such as bonding with adhesives, hot press welding, and ultrasonic welding. Laser technology allows for focused beams, resulting in finer and more uniform processing areas. Therefore, lasers are well suited for high-precision manufacturing, especially in tasks such as welding small plastic parts, and substrates with intricate designs such as medical devices and implants. Additionally, lasers contribute to lower material wastage, promoting environmental sustainability. 

Semiconductor near-infrared (NIR) lasers have an energy efficiency of greater than 50% which results in significant energy savings – another eco-friendly advantage of lasers in plastic welding. The high spatial precision of laser processing when coupled with its high speed proves extremely effective for substrates containing heat-sensitive parts. This is attributed to the localised heat which prevents spreading beyond the processing region. Moreover, the manoeuvrability of laser beams, coupled with rapid power control and instantaneous on/off operation, align seamlessly with industry 4.0 standards, further enhancing the efficiency and adaptability of plastic welding processes.

Requirements for two plastics to be successfully laser welded 

Having briefly discussed some of the advantages of lasers in plastic welding applications, we wish to address the common question we hear from customers; “I want to weld plastics A and B, will your laser do the job?” This fundamental question is often the first consideration for those exploring laser plastic welding. Understanding this, we would like to clarify several essential generic requirements for two plastics to be successfully welded by lasers.

Thermoplastics: Laser plastic welding works by melting the plastics, letting the molten plastics fuse and then solidify upon cooling. Therefore, the first requirement for successful laser plastic welding is that the materials involved belong to the category of thermoplastics. This group of plastics includes many common plastics including PA, PP, PET, PBT, PPS, PE, PC, and PMMA.

Compatibility of plastics: The two different thermoplastics should be chemically compatible.

The above two sets of requirements are for the thermal welding of plastics and are not unique to laser welding alone. However, there are specific requirements unique to lasers used for plastic welding.

Pigmented Plastics: For effective plastic welding, one of the plastics should strongly absorb laser wavelengths as it serves as the heating source. Specifically, we refer to NIR lasers, such as those offered by Hamamatsu Photonics1. Most plastics by themselves do not strongly absorb NIR wavelengths but often plastics are mixed with visible pigments for functional or aesthetic purposes. These pigments show strong absorption for NIR wavelengths which works in favour of laser plastic welding.

Access to interface: Laser plastic welding involves pressing two plastic substrates together and heating them at the interface with a laser. When the interface of two plastics to be welded is directly accessible to the laser beam2, no special considerations are necessary. However, often the interface of the plastics to be welded is hidden behind the plastics. In such cases, the laser energy has to reach the interface with minimal attenuation, and this is achieved by focusing the laser at the interface through the less absorbing plastic3. The strongly absorbing plastic on the other side of the interface gets heated first, causing it to melt which in turn melts the less absorbing plastic substrate. The specific combination of plastics and the laser's orientation play a crucial role in achieving effective welding.

Hamamatsu Photonics offers a wide range of fibre coupled NIR lasers for material processing1. We have also developed in-house knowledge of applications4 which we can address with our laser systems. As a result, we developed value-added features such as temperature monitoring, built-in feedback controls, and communication interfaces for easy integration5. Our engineers are continuously testing the compatibility of plastics for laser welding and finding the optimal process parameters to ease the development load on our customers. 



Further information
Find out more information about Hamamatsu Photonics’ range of fibre coupled NIR lasers for material processing.


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Manufacturing, Welding

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