Abstract
Unlike other joining techniques, laser transmission welding offers unique advantages such as selective and contactless energy deposition. This enables the fabrication of flexible seam geometries at low mechanical and thermal stresses. However, the use of absorbing additives for the lower joining partner such as carbon black is crucial as most polymers are transparent in the spectral range of typical beam sources (800–1100 nm). A novel approach is the application of beam sources emitting radiation within the polymeric intrinsic absorption bands between 1500 and 2000 nm. This enables absorber-free laser welding of transparent polymers for medical or microfluidic applications such as Lab-on-a-Chip devices. The main drawback on the other hand is the large heat affected zone (HAZ) due to the volume absorption which is extending over the entire cross section. A possible way to overcome this disadvantage is a quasi-simultaneous irradiation strategy. It could be proved in the past that the HAZ of polycarbonate (PC) can be reduced in the vertical direction by up to 30% compared with contour welding. Since the effects of light scattering on the absorber-free quasi-simultaneous irradiation strategy are still unknown, the beam propagation was simulated in polypropylene (PP). Based on the results, a thermal simulation of the welding process was carried out using the finite element method (FEM). The simulation model was then evaluated by comparing the results with experimental trials.
Highlights
Since its first industrial introduction in the 1990s, laser transmission welding of plastics has been successfully established in various application areas
In case of PC, this technique contributes to a more favourable and precise energy deposition as the vertical extent of the heat affected zone (HAZ) is reduced by up to 30% compared with contour welding
It could be shown that the highest laser beam absorption was located in the upper joining partner due to the scattering properties of PP
Summary
Since its first industrial introduction in the 1990s, laser transmission welding of plastics has been successfully established in various application areas. This method offers the advantage of a non-contact and highly precise energy deposition. This enables the fabrication of complex and narrow seam geometries which is especially favourable for the encapsulation of sensitive components in the automotive, medical and electronic industry. The disadvantage is the significantly higher price compared with carbon black This has a strong impact especially on the production of high volumetric components. In some areas such as the biotechnology or medical sector, the use of absorbers is inadmissible as the functionality or biocompability of the product may be affected
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