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Fiber Lasers have now matured into exceptionally reliable and stable industrial tools. These Lasers have unique capabilities that enable a wide range of high quality micro-machining processes; of interest here is their ability to produce high quality welds between plastics. Many different methods of plastic welding have been found since the need to join plastic parts became of great importance. Methods like vibration, linear/orbital, ultrasonic, spin, and hot plate welding have been used but Laser welding has been found to be very efficient, precise and time saving. This application insight explores the different types of plastic welding including; transmission, Contour, Simultaneous, Quasi-simultaneous, Globo, and Radial Welding.
How Laser welding of plastic works (IR wavelength):
In this process, the two layers, to be joined, must differ in such a way that the top one allows the infrared light to pass through while the bottom layer absorbs it in order to allow a heating effect to occur. The following picture gives a better illustration of the procedure.
Joe Lovotti l Director of Laser Technologies,
In contour welding, the Laser is guided along a prearranged welding pattern, melting it locally. The welding volume remains comparatively small due to geometric conditions (small sections), and extrusion of the melt is avoided. Relative motion is achieved by moving the component, the Laser, or a combination of both. Contour welding is more suitable when joining the edges of a plastic component to a surface.
Characteristics and application:
Two scanner mirrors deflect the Laser spot and guide it along the welding contour at a very high speed. The joining surface is traversed several times per second, whereby the Laser beam effectively heats and plasticize the entire welding seam at the same time. Part tolerances can be melted off forming a welding bead, as both joining parts are pressed together during the welding process. This type of welding has also been patented by ©bielomatik Leuze.
Globo welding (patented by LEISTER ®) works almost the same way as in contour welding. A Laser beam is focused at a point on the joining plane via an air bearing, frictionless, freely rotating glass sphere. The glass sphere not only focuses – it also serves as a mechanical clamping tool. While the sphere rolls on the component, it applies continuous pressure at a point on the joining plane. This ensures that the Laser beam is only incident at the point at which the contact pressure is also applied.
Images courtesy of LEISTER Process Technologies LEISTER ®
A unique method for bonding cylindrical components, developed by LEISTER ®, whereby a mirror deflects the Laser beam such that it impinges radially on the outside symmetrical surface of the component. The tight fit between the joining parts ensures the clamping pressure required for the welding process. The component remains in a fixed position during the circumferential, continuous welding process.
In this technique, one or more Lasers heat the entire weld area simultaneously. High power diode Lasers are generally used as a result of their compact design. It is very easy to achieve linear welding seams. Almost any beam geometry can be generated by means of special, state-of-the-art beam shaping elements.
With this LEISTER ® patented technique a mask is inserted between the Laser source and the parts to be welded. A curtain or collimated Laser beam is moved across the entire joining area of the parts. The Laser beam is only incident on the components where they are not obscured by the mask. The mask makes it possible to project extremely fine structures in the order of micrometers. Mask welding therefore achieves a very high resolution. The most diverse welding seam structures can be produced with mask welding – for example straight and curved weld lines of different width, as well as two-dimensional structures – all in a single operational step.
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