Laser Light Transmission Through Thermoplastics as a Function of Thickness and Laser Incidence Angle: Experimental and Modeling

Abstract

It is important to accurately measure and predict the laser light transmission through unreinforced and reinforced thermoplastics if candidate materials are to be assessed for laser transmission welding (LTW) applications. This paper presents the results of laser transmission measurements through unreinforced polyamide 6 (PA6) and 10% glass fiber reinforced polycarbonate of various thicknesses and corresponding to various laser incidence angles (angle betH'een the incident laser beam and the normal to the transparent part), A novel transmission measurement method, developed by the authors, was employed, A model, utilizing the Fresnel specular suiface reßection conditions as well as accounting for refraction, absorption and reflection of the laser light through the bulk material, was used to predict transmission as a function of thickness and laser incidence angle. Results of transmission tests on both materials showed that, for a given thickness, the transmission decreases as the laser angle of incidence increases, ¡n addition, at any given laser incidence angle, the transmission decreases as the thickness increases. The advantage of the model is that it requires only one experimentally determined constant for a given material. Good agreement existed between the experimentally measured transmission and the model prediction for the range of thicknesses and laser incidence angles studied, [

Effects of thermoforming on the physical and mechanical properties of thermoplastic materials for transparent orthodontic aligners

“…In addition, with a decrease in thickness after thermoforming, the transparency also decreased. This finding is inconsistent with that in a previous study showing an increase in transparency with a decrease in thickness 28. In another study, however, the transparency of thermoplastic plates that deformed from amorphous to crystalline structures decreased according to the temperature, pressure, and working time, while light was scattered by the thermoplastic materials after thermoforming 29.…”

“…This finding is inconsistent with that in a previous study showing an increase in transparency with a decrease in thickness. 28 In another study, however, the transparency of thermoplastic plates that deformed from amorphous to crystalline structures decreased according to the temperature, pressure, and working time, while light was scattered by the thermoplastic materials after thermoforming. 29 Therefore, structural deformation of thermoplastic materials results in decreased transparency.…”

Clinical Performances and Biological Features of Clear Aligners Materials in Orthodontics

“…This finding contrasts with a previous study an increase in transparency with decreased thickness (Azhikannickal et al, 2012).…”

Laser Transmission Welding of Semi-Crystalline Polymers and Their Composites: A Critical Review

“…Studies have shown that the laser light transmitted through the thermoplastics are a function of thickness [ 87 ] and the laser incidence angle. There is a decrease in the transmission rate with an increase in the laser angle of incidence [ 88 ]. Transmission of laser energy in polymer reduces due to an increase of crystallinity and large spherulites [ 89 ].…”