Carbon dioxide lasers have been used to make lap welds in thermoplastic films very effectively. However, this laser type is only applicable to welding plastics up to a total of 0.4mm thick in a lap configuration. Welding speeds in excess of 500m/min are feasible, making the process ideal in high volume production, for example, packaging. By careful control of the laser beam profile, it is also possible to make a weld and cut at the same time in an operation called a cut-seal.
Diode, Nd:YAG and fibre lasers can be used to weld transparent to opaque injection moulded or film or sheet plastic components. The infrared laser beam passes through the transparent plastic but is absorbed at the surface of the opaque plastic where it creates the heat to form a weld. The thickness of materials that can be welded in this way is limited only by the transmission properties of the upper material. This may be up to 10mm for semi-crystalline plastics or much more for amorphous types.
Recent developments have enabled two similar clear plastics to be joined rapidly, neatly and with a virtually invisible weld line using the Clearweld® process. Developed by TWI and using diode or Nd:YAG lasers, the new technique works by using an almost colourless dye which absorbs the infrared laser light and converts it into heat to make the weld. The dye is applied to one of the components to be welded, either to the surface by painting or printing, or into the bulk of the plastic. It can also be applied as a thin film inserted in the joint. The new technique can be used to spot or seamweld film, sheet, moulded plastics and fabrics.