There are four main techniques of laser plastic welding. Each technique or method comes with its own set of advantages and disadvantages. Certain applications can only be completed by one specific method, while other applications have multiple options. Deciding which method to use often comes down to factors such as part geometry, cycle time requirements and process flexibility.
Scanner-based welding is really a hybrid of both contour and simultaneous welding. In this process a single laser beam, guided by high-speed and precision galvo-mirrors, makes multiple passes over the entire joint very quickly. Travel speeds between 70 and 250mm per second are common. Although just a single laser beam is used, the entire joint is heated up at virtually the same time.
The contour welding process involves moving a laser beam along the entire joint pattern, typically only a single pass is made. The laser is often guided by a robotic arm that allows the laser to travel relative to the joint in three-dimensions. This is a critical welding method for large and three-dimensional parts, such as car tail lights.
Radial welding is another very common form of contour welding. A radial welded application is typically cylindrical in shape and takes a slightly different approach. The laser beam, in this case, is in a fixed position and the part to be welded is spun on an axis, allowing laser energy input along the entire circumference of the part of the part.
Simultaneous welding is named as such for the fact that the entire joint is heated simultaneously, unlike contour welding where heating is only taking place where the laser beam is focused at any given time during the cycle. Simultaneous welding does not use a single laser beam, often multiple laser sources are used. The lasers are split, using fibers, and arrayed into the pattern of the joint and the entire weld is flashed at once.
Hybrid welding is essentially another form of contour welding with one major difference, the laser beam is assisted by high-powered halogen lamps. A laser beam is a monochromatic light source, meaning it falls under only a single wavelength (in the case of laser plastic welding often 808 or 980 nanometers). Thermoplastics naturally transmit radiation well at those wavelengths, which is pertinent to the process. The halogen radiation, however, is polychromatic, producing light energy in a wide range of wavelengths. The polychromatic halogen radiation will cause energy absorption in the transmissive upper layer, which assists the laser in heating the plastics.
The larger heat affected zone of the halogen lamp pre-heats the plastic allowing the laser to travel faster while widening the process window during welding. The result is lower cycle times and higher weld strength. Also, because the two parts are being pre-heated by the halogen lamp the parts will anneal during the welding process allowing for better gap bridging, a more natural fit between the two parts and reduced residual part stress. The most common application for hybrid welding is exterior automotive lighting.