Laser Welding of Polymers
Laser welding of plastics is a relatively new process that heats the polymer without physical contact. For most applications, the process involves directing a beam of infrared light at the weld joint by going through one of the parts. This is commonly referred to as through transmission infrared (or laser) welding (TTIR). In this technique, the infrared source, usually a laser, irradiates the joint through one part and the light is absorbed at the surface of the other. While broad band infrared sources can be used, monochromatic lasers allow rapid heating of small regions of the part which enables the parts to be welded rapidly but with very small changes to the part geometry.
Laser welding is one example of an electromagnetic plastic welding process. It does not require physical contact. When radiant energy is directed at a polymer surface, a combination of three things happen to it; some of the light transmits through, some is absorbed, and some is reflected away. For most applications the process involves directing a beam of infrared light at the weld joint through one of the parts. A part that transmits most of the energy does not heat, while an absorbing part will be heated. Since most virgin, organic polymers do not absorb energy at infrared laser wavelengths, dyes and fillers such as carbon black are used to absorb the energy at the weld joint interface. This is commonly referred to as through transmission infrared (or laser) welding (TTIR).
The lasers most commonly used for plastic welding applications include diode lasers and Nd:YAG lasers. They are usually fiber delivered and can be either pulsed or continuous. The wavelengths that these lasers emit fall in the 800nm to 1064nm range. For most applications, the power needed is below 250 watts, making the cost of lasers comparable to other common plastic welding equipment.
Lasers allow energy to be delivered quickly to very small volumes of material. This makes the technique very attractive for welding products with heat sensitive parts in close proximity to the joint. This has proven to be useful in both battery and sensor assembly where the final joint in the device is often formed after sensitive parts are assembled. The heating and cooling rates are also so fast that it is possible to weld small volumes of amorphous engineering resin PEEK rapidly enough to avoid crystallization and the embrittlement that results from it.
Another advantage of laser welding is process flexibility. Since it is a non contact process, only simple part fixturing is necessary. Application of the laser to the joint area can be controlled using a mask or by using a computer to define either the movement of the beam over the sample or the sample under the beam. This is advantageous for short production runs. Since the pressure required for laser welding is low, there is little flash and part geometry is preserved during the process. This means that critical tolerances, such as those in microfluidic device channels can be maintained.
Laser welding is still a relatively new technique compared to other plastic welding processes. The process is currently being used in manufacturing in many industries, and EWI is very active in developing the process for many of our customer’s applications. EWI’s dedicated laser labs are equipped with numerous lasers and workstations available for creating and analyzing plastics welding.
Contact EWI now to learn how we can help you develop an effective laser welding process and bring it into commercial production.
. |
Joining Processes
