Laser welding which has long been used for the joining of metals is now emerging in the plastics industry. Strong, precise, airtight, watertight welds are easily achieved by welding with lasers.
- sensitive (e.g., contain circuit boards), involve complex geometries, or have strict cleanliness requirements (medical devices).
- Lasers have long been used to weld metals and have made recent inroads in the cutting and marking of plastics. However, laser joining of plastics has been held back until now by a lack of suitable equipment, restrictions on polymers and colors that can be joined, and limited awareness of the technology's potential.
- The striking attribute of laser welding is its ability to create a precise, strong, hermetic (airtight and watertight) weld while minimizing resin degradation, particulate generation, and marring of the part surface around the weld.
- In the U.S., laser welding appears likely to evolve into a joining method for niche applications where it offers cost or performance benefits over proven alternatives like ultrasonic, vibration, and hot-plate welding
- Innovative materials and additives are making it feasible for lasers to weld parts in colors once beyond the technology's reach. Black-to-black and clear-to-clear laser welding are now possible due to new colorant technology. And material suppliers are tweaking existing formulations to improve their transmittance or absorption of laser light.
- Clean, gentle, versatile
- Laser-transmission welding is feasible when two materials that respond quite differently to laser light are used in joining. The method uses near-infrared (NIR) light at wavelengths around 810 to 1064 nm. It passes through one (NIR-transmitting) part and is then absorbed by a second (NIR-absorbing) part while the two parts are clamped together at low pressure. The absorbing material converts NIR to heat and melts at the part interface, while heat is also conducted back into the mating surface of the light-transmitting part to create a welding zone. Joint strength can exceed that of the original materials.
- Laser welding also greatly reduces vibration and thermal stress on parts.
- Laser welding is adept at welding parts with complex (even three-dimensional) contours and reaching areas not accessible using other joining methods.
- Maturation of laser technology in fields as far-flung as defense and medicine is helping to expand its role in plastics joining. Diode and Nd:YAG types of lasers have evolved since the mid-1990s in ways highly favorable to plastics welding. The power of these lasers has increased significantly, even as their cost has declined by around 90% in the last five years. Most plastics have been found to be efficient in transmitting laser light in or near the wavelength bands at which diode (810 to 940 nm) and Nd:YAG (1064 nm) lasers typically operate. (CO2 lasers, however, emit wavelengths readily absorbed by plastics, which risks burning.).
- Diode and Nd:YAG lasers have also proved to be highly versatile when applied to plastics welding. Diode lasers, for instance, can be configured in arrays to create complex line welds. Further, diode light emitters can be combined into stacks to provide the welding power needed for the specific application.
- A faster technique is "simultaneous" welding, in which the laser beam is collimated into a line or curve so it can expose an entire joint at once.
- Despite its speed, simultaneous welding is limited in terms of weld geometry.
- Simultaneous welding is said to be more cost-effective in high volumes.
- High-energy diodes make an incredibly strong weld, which allows them to join dissimilar and hard-to-weld materials, examples being PP and glass-reinforced acetal.
- In response to growing interest in laser welding, leading materials suppliers are investigating how well their materials work in the process.
- Also, clear-to-clear (and often all-translucent and all-white) combinations cannot be laser-joined due to the absence of NIR absorption by either part. That is a drawback in medical, packaging, and consumer products where clarity is required.
- Finally, many mineral-filled compounds are NIR absorbers and generally not viable for laser welding. High levels of glass reinforcement can distort NIR-transmission and impair welding efficiency, but suppliers have generally formulated around that limit.
To read the original article please click:
http://www.ptonline.com/articles/200202fa2.html |
Article Details