Joining Technology LASER TECHNOLOGY [VEHICLE ENGINEERING] [MEDICAL TECHNOLOGY] [PACKAGING] [ELECTRICAL & ELECTRONICS] [CONSTRUCTION] [CONSUMER GOODS] [LEISURE & SPORTS] [OPTICS] Welded from the Ends Advanced Laser Butt Welding for Joining High-Wall and Same-Material Parts Thanks to technical advances which have made implementation easier, laser butt welding which was invented in the 1990s is now about to make the breakthrough. Aside from high-wall parts, it can be used to weld samematerial polymers using precision laser technology. efore now, the most commonly employed laser technique for welding polymers was transmission welding. In this, a laser beam passes through one part to be joined, which is transparent to the wavelength of the laser, into a second part which absorbs the radiation and converts it into heat. This absorption is achieved, e. g., by adding carbon black particles. Heating occurs through total absorption near the surface, whereby the laser energy is transformed into thermal energy. As a result of heat conduction, the transparent part in contact with the absorbing partner softens as well. Advantages and Disadvantages of Laser Transmission Welding The advantages of laser transmission welding lie in low heat input away from the root face. The technique is also virtually vibration-free and is counted as a particle-free type of welding. The welding process does not lead to any additional impurities in the part. It is therefore widely employed in medical technology and in the electronics industry. The most common variant of transmission welding is quasi-simultaneous welding. In this, the laser beam is guided along the welding contour with the aid of scanning mirrors at a high traversing speed of up to 10 m/s. Due to the high speed of the energy source, which is essentially a point source, the mating surface can be traversed several times, being heated in its entirety and plasticized almost simultaneously [1, 2]. The disadvantage of this technique is that the manufacturing process (injection molding) for the two parts to be joined requires separate material and mold hand- Turn2Weld technique: the newly developed welding machine uses one laser per part and swivels the machine tables through 90° toward the laser scanners with the aid of servo motors ling. Furthermore, there are restrictions with regard to the shape of the transparent part and, above all, to the thickness of the polymer material. Depending on the material used, the height of the layer through which the laser beam passes may be a few millimeters only, i.e. not too high. Laser welding has several competitors, e. g. heating tool, infrared and hot gas welding, with which it is possible to weld uniformly colored parts having high-wall lids and shells. However, the disadvantage of these is that the heat radiation cannot be focused sufficiently and they can therefore influence sensitive parts both optically and functionally – usually in a relatively uncontrolled manner. Furthermore, these techniques require a part-specific heating medium (heating tool, IR emitter, hot gas heat exchanger and manifold), and that adds to the tooling costs. » Kunststoffe international 6-7/2019 www.kunststoffe-international.com © Carl Hanser Verlag, Munich. Reproductions, even in extracts, are non permitted without licensing by the publisher.

SPECIAL LASER TECHNOLOGY Joining Technology IA|lasers \ T I Joining © Kunststoffe Fig. 1. Functional principle: in conventional laser butt welding, the aligned parts were heated by means of deflecting mirrors which were positioned between them and had to be returned to the home position prior to joining [1,3] (source: bielomatik) The Authors Christian Class, M.Sc., has been a development engineer at bielomatik Leuze GmbH + Co. KG, Neuffen, Germany, since 2017; [email protected] Matthias Greif, M.Sc., has been a development engineer at bielomatik Leuze since 2017; [email protected]...

Joining Technology LASER TECHNOLOGY susceptibility of the deflecting mirrors to dirt pickup. In certain circumstances, the small distance to the parts to be joined can lead to dirt deposition on the mirror surface. In the worst case, dust particles will be burned by the laser and the mirror will be damaged. All these issues and critical points apply to the technique shown in Figure 1, but they were never properly resolved because the technique failed to make the necessary breakthrough in industry. The pneumatic drives used previously to move the mirror and the part axes were also a weak point....