RESUMO
Undesirable crossing crack defects are prone to occur in the laser processing of glass, but a comprehensive analysis of the crack mechanism is absent. We apply an acoustic emission (AE) monitoring technique in the glass's laser scanning to reveal the crack phenomenon. A two-step experiment (single-line and multi-line scanning) is designed to present the crossing crack's occurrence and growth, and the corresponding AE signals are collected and analyzed in different domains. The time-domain AE feature (root mean square) correlates strongly with the laser ablation intensity in the single-line scanning experiment, and the frequency content of 150 â¼ 200 kHz is extracted as the crack characteristic in the multi-line experiment. The crossing crack growth is proved to be generated by the rapid release of thermal stress in the overlapped heat-affected zone by a brief mechanism discussion. This paper interprets the crack behavior in glass's laser scanning and provides a basis for other monitoring research on laser processing.
RESUMO
Understanding the mechanism of and how to improve the laser processing of polymer films have been important issues since the advent of the procedure. Due to the important role of a photothermal mechanism in the laser ablation of polymer films, especially in transparent polymer films, it is both important and effective to adjust the evolution of heat and temperature in time and space during laser processing by simply adjusting the ambient environment so as to improve and understand the mechanism of this procedure. In this work, studies on the pyrolysis of PET film and on temperature field-assisted ultraviolet nanosecond (UV-ns) pulse laser processing of polyethylene terephthalate (PET) film were performed to investigate the photothermal ablation mechanism and the effects of temperature on laser processing. The results showed that the UV-ns laser processing of PET film was dominated by the photothermal process, in which PET polymer chains decomposed, melted, recomposed and reacted with the ambient gases. The ambient temperature changed the heat transfer and temperature distribution in the laser processing. Low ambient temperature reduced the thermal effect and an increase in ambient temperature improved its efficiency (kerf width: 39.63 µm at -25 °C; 48.30 µm at 0 °C; 45.81 µm at 25 °C; 100.70 µm at 100 °C) but exacerbated the thermal effect.
