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In this article, learn more about advanced technology in polymer laser welding.
A range of industries require compact, user-friendly, and sealed plastic parts. The automobile industry, chemical industry, pharmaceutical industry, especially medical institutions, need a large number of these sealed plastic parts.
The increased availability of fiber-coupled laser sources based on high-power diodes has caused plastic welding-based technologies to become commonplace in each of these fields and industries.
The company requires higher throughput and smaller welding details, as well as reduced color sensitivity and clear to clear joints. The latter is usually provided by Monocrom's FLEX series modules, which can operate in the 2 µm to 3 µm area because of the large size. The absorption of most thermoplastics increases.
The company's unique "rectified polarized beam combination" technology allows applications up to 105 W in CW.
Laser plastic welding is a common non-contact technology that can combine multiple customized plastic parts through the interaction of laser radiation. Laser plastic welding is an increasingly popular material processing application, which is constantly evolving to meet changing industrial needs.
Laser plastic welding is most suitable for the use of thermoplastics, such as PA6, PEEK, PMMA, PTFE and TPU. Certain combinations of thermoplastics will exhibit stronger weld strength than others, and it is recommended to check before starting.
Depending on the type and temperature range in question, certain forms of thermoplastics will form a liquid phase before decomposing. You can select a suitable combination according to these temperature windows.
Welding methods can generally be divided into two major programs. These are summarized below.
Figure 1a shows a schematic diagram of standard transmission laser welding. In this example, energy deposition occurs in the lower part due to the total absorption of the incident laser light. The energy absorption is due to the use of different plastics or through the addition of IR (~1 µm) absorbing particles.
Through transmission, laser welding is established between two different plastics or between the same kind of plastic, but when the same kind of plastic is used, the underlying plastic will use infrared absorbing additives or different colors.
Figure 1.a shows a schematic standard for welding by transmission laser, where energy deposition occurs in the lower part due to the total absorption of the incident laser. Energy absorption is caused by the use of different plastics or the addition of IR (~1 µm) absorbent particles.
number. b illustrates the so-called laser welding scheme from transparent to transparent. The phenomenon used here is different because the energy is deposited in the bulk material through the higher inherent absorption of longer wavelength (>2 µm) lasers. This method allows multilayer welding.
In transmission laser welding, energy deposition occurs at the junction of the two parts by completely absorbing the radiation from the lower part (Figure 1a).
Usually a wavelength between 808 nm and 1064 nm is used. The range of 808 nm to 1060 nm can be achieved by using high-power direct diode lasers, while the range of 1030 nm to 1064 nm is generally the emission line of Yb and Nd doped lasers.
Figure 1b shows a clear to clear laser welding scheme. In this scheme, energy is deposited in bulk materials through higher inherent absorption of longer laser wavelengths (>2 µm). This method can be used to promote multilayer welding.
Most thermoplastics exhibit increased intrinsic absorption in the SWIR (>2 µm) light zone, thus allowing a large amount of energy to be deposited. Depending on the plastic to be welded, a 2 µm direct diode-based laser source can provide 20% to 30% higher adsorption than lasers operating near 1 µm.
Since energy deposition occurs inside the bulk material instead of underneath, it is possible to create multilayer joints. These are particularly useful in the manufacture of next-generation microfluidic chips and devices.
This section focuses on transparent joints, where two parts of the same plastic are welded together. Both parts are transparent in the visible light range and have high inherent absorption in the SWIR (>2 µm) region.
The use of colored or white plastic makes this process with standard laser light sources (808 nm to 1060 nm) more challenging, resulting in poor absorption or reflection.
Many important welding parameters must be considered:
The optical power should be around 100 W to 200 W (continuous wave) in order to maintain a reasonable level of throughput during production. The instrument provided by Monocrom has an optical power of 200 W at 940 nm and 980 nm, and an optical power of 105 W at 2 µm and 3 µm.
The source size will determine the "initial" M2 value, which will directly translate into the minimum spot size and/or weld thickness. The 200 µm core is the most commonly used option.
The super-Gaussian strength distribution helps to avoid hot spots inside the weld, thereby improving the overall weld quality. In order to balance the structure and size of the weld, a trade-off must be made.
Laser diode-based solutions always provide a higher total WPE value than other laser systems, making it an ideal solution for polymer welding. Monocrom's FLEX series modules work in the range of 2 µm to 3 µm and can achieve up to 10% WPE.
The setup of the mechanical assembly must be fully planned. The quality of welding can also be improved by using the most suitable beam delivery option; for example, a light guide can be used to make the solder joints even.
Monocrom can provide fiber-coupled modules in the wavelength range between 808 nm and 1060 nm and between 2 µm and 3 µm. All of the company's products are in the form of laser rod-based modules coupled into different fiber cores. These can be equipped with HP-SMA, D80 or QBH connectors.
FLEX I-2000 modules can cover 2 µm – 3 µm wavelengths. These modules can cover any wavelength between 2 µm and 3 µm, while achieving up to 105 W in CW.
It can be adapted to applications that require a specific wavelength (such as 2520 nm), even in situations where other laser technologies (such as optical fiber or solid state) may encounter difficulties. This is due to the unique combination technology of the FLEX I-2000 system-rectified polarized beam combination.
The rectified polarized beam combination is independent of wavelength, which means it can follow the moving gain of the semiconductor laser diode, whether this is caused by the injected current or by the increase or decrease of the pn junction temperature.
This information is derived from materials provided by Monocrom, after review and adaptation.
For more information on this source, please visit Monocrom.
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