Laser makes invisible welds in plastics

Citation

(1999), "Laser makes invisible welds in plastics", Assembly Automation, Vol. 19 No. 3. https://doi.org/10.1108/aa.1999.03319caf.002

Laser makes invisible welds in plastics

Laser makes invisible welds in plastics

Keywords: Lasers, Welding, Plastics

TWI's Advanced Materials and Processes department has recently developed a technique for laser welding plastics, creating a joint almost invisible to the human eye.

Until now a black absorber, most commonly carbon black, or some other visible absorber acted as the medium that heats in the laser to create the weld. However, this new approach enables two similar clear plastics to be joined with no visible weld line. Unlike many other methods, laser welding is carried out without vibration and with the minimum of heat input and is therefore unlikely to damage or distort a component. This method, transmission laser welding, can be used for welds in film, sheet and moulded plastics. Diode or Nd:YAG lasers are usually used in either a "single-shot" or continuous seam welding process. Both methods are very rapid and produce little or no flash.

The novel adaptation to this technique works by using an almost colourless dye, which absorbs the infrared laser light very efficiently, converting the absorbed light energy to heat without significantly absorbing visible light. 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 in a thin film inserted at the joint. The dyes are proprietary, complex molecules, not typically available off-the-shelf (see Figure 2).

Figure 2 Laser welded sample (top) using carbon black absorber beside a sample using the new technique with low visability absorber

The use of infrared dye as the absorber offers the opportunity of producing a low visibility weld between two materials that need to be clear or have a pre-defined colour. Potential applications include finished products where appearance is important. Packaging, fabrics, visual displays and optical products, and automotive components are being considered. LP Frieder III of GENTEX Corp., a leading supplier of this type of absorber, says

These dyes are used in various applications which require absorbing IR light while maintaining visible transmission, a typical example being laser protective eyewear. Using them as a means of generating heat for welding is entirely new. This is a very exciting development in the use of these products and gives a new dimension to the light management capabilities of Filtron® dyes.

The work has been carried out under TWI's Core Research Programme and TWI has applied for a patent for the use of these absorbers in laser welding of plastics.

For more information on this technique and how it may be applied to your business contact Ian Jones at TWI. Tel: +44 (0)1223 891162; Fax: +44 (0)1223 892588; E-mail: iajones@twi.co.uk