Plastics joining laser

Laser Welding, Chap. 13, Handbook of Plastics Joining, Plastics Design Library, Norwich, NY, 1997. 

Laser welding of plastic parts has been available for the last 30 years. However, only recently have the technology and cost allowed these joining techniques to be considered broadly. Laser welders produce small beams of photons or electrons. The beams are focused onto the work piece. Power density varies from a few to several thousand W/mm, but generally low-power lasers (less than 50 W/mm ) are used for plastic parts. 

In compact-disc (and DVD) manufacturing, the upper face is usually made of an inexpensive polycarbonate or made of a copolycarbonate. The face is covered by a very thin metal layer (usually Al) which reflects diode-laser light. The metallic layer must be protected by a plastic layer (this constitutes the lower face). It is made of polystyrene (or other commodity plastic). The annual production of PC around the world was about 3500 thousand tons in 2007 (5). There are more than ten industries around the world which produce PC. For a long time polycarbonate market needs were satisfied by only two manufacturers, i.e. the GE plastics (an american company renamed SABIC Innovative Plastics in 2007) and Bayer (a German firm). Later other manufacturers have joined them - Dow Chemical, Samyang, Asahi Kasei and Teijin. The most popular PC trade names are LEXAN , CALIBER, SINVETTM, MAKROLONTM. Popular names for PC-PET blends are listed elsewhere (16). 

Lasers have been used primarily for welding polyethylene and polypropylene. Usually, laser welding is applied only to films or thin-walled components. The least powerful beams, around 50 W, with the widest weld spots are used for fear of degrading the polymer substrate. The primary goal in laser welding is to reach a melt temperature where the parts can be joined quickly before the plastic degrades. To avoid material degradation, ac-... 

Laser Transmission Welding (LTW) is a non-contact joining process with no relative part movement, small heat-affected zone, and minimum flash [1, 2, 3, 4], It is a flexible and precise welding process that is increasingly used to join plastic parts. Hi -power diode lasers are the primary choice for LTW because of their high efficiency, compactness and relatively low cost per watt output of photon energy. 

Laser welding of plastics is a suitable complement to established joining processes, and thereby opens up new fields of application. This has been demonstrated by numerous apphcations for small and even for larger components. 

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