Effect of part thickness, glass fiber and crystallinity on light scattering during laser transmission welding of thermoplastics

• We measure the effect of thickness, resin, and reinforcement on the transmitted laser intensity.
• A wide range of resins, reinforcement and crystallinity levels are examined.
• A novel experimental technique and mathematical analysis are employed.
• Agreement between models and experimented data is excellent.
• Results permit users to predict transmitted laser intensity with a 2 parameter model.

It is important to understand how laser energy scatters within the transparent component in order to predict and optimize the laser transmission welding process. This paper examines the influence of part thickness, glass fiber and crystallinity levels on the distribution of laser light after transmission through amorphous polycarbonate (PC) and semi-crystalline polymers such as polyamide 6 (PA6), polypropylene (PP), and polyethylene (PE). An experimental technique based on laser-scanned lines of progressively increasing power was used to assess the transmitted energy distribution. This distribution was characterized using a two-parameter model that captures scattered and un-scattered components of the laser beam. The results clearly show how the scattering is increased by increasing the numbers of interactions between laser light and phase boundaries either by increasing the particle concentration (i.e., glass fiber level and crystallinity) or increasing part thickness.