Effect of glass fiber and crystallinity on light transmission during laser transmission welding of thermoplastics

• We measure the effect of thickness, resin, and reinforcement on laser transmission.
• A wide range of resins, reinforcement and crystallinity levels are examined.
• Results are analysed using a modified Bouguer–Lambert–Beer law.
• Rule of mixtures assesses main contributors to the apparent absorption coefficient.

In order to predict and optimize the contour laser transmission welding (LTW) process, it is important to understand how the laser energy behaves during transmission through the transparent part. In this study, transmission measurements were made on unreinforced and glass-fiber-reinforced amorphous and semi-crystalline thermoplastics at different thicknesses. Using the ratio of transmitted power to laser power, apparent absorption coefficients and apparent reflections were calculated. The results indicate that there is a linear relationship between the glass fiber volume fraction and the apparent absorption coefficient of reinforced polymers; similar effects were also observed for crystallinity. A simple model was developed to estimate apparent absorption coefficient of reinforced polymers as a function of composition.The apparent reflection increased with crystallinity due to increased back scattering. However, for glass-fiber-reinforced polymers, the apparent reflection displayed a more complex behavior.