Student Evaluation of Mechanical Strength at High Energy Conditions in Micro-joining of Glass by Picosecond Pulsed LaserTuesday (23.06.2020) 10:50 - 11:10 Room 2
In the past several years, ultrashort pulsed laser has been proven to be a powerful and reliable tool for micro-welding of glass. A proper selection of processing parameters such as pulse energy and scanning velocity is essential to achieve high mechanical strength of the weld joint . It was reported that higher pulse energy can be absorbed without cracks by using N.A. 0.65, which results in the stable and efficient formation of molten area . Moreover, high scanning velocity is helpful to conduct welding process for mass production. Therefore, the discussion about high energy conditions of high pulse energy and scanning velocity is necessary. In this study, the mechanical strength created at high energy conditions in micro-joining of glass by picosecond pulsed laser was experimentally evaluated. A picosecond pulsed laser of 1064 nm in wavelength and 12.5 ps in pulse duration was tightly focused at 20 µm below the interface of two glass specimens at 1.0 MHz pulse repetition rate by using objective lenses of numerical apertures 0.45, 0.65 and 0.85. Breaking test was carried out to evaluate the breaking stress of welded glass specimens. In addition, the strength of molten area was evaluated by measuring Young’s modulus. Figure 1 shows the influence of numerical aperture on breaking stress, and the highest breaking stress was obtained by using N.A. 0.65. The relationship between breaking stress and scanning velocity by N.A. 0.65 was shown in Fig. 2, showing that the breaking stress decreased with increasing the scanning velocity. On the other hand, breaking stress increased with increasing the pulse energy from 2.0 μJ (Green plot) to 3.0 μJ (Red plot) at high scanning velocity of 100mm/s, which indicated high energy conditions. The Young’s modulus distribution of molten area by N.A. 0.65 at pulse energy of 2.0 μJ was shown in Fig. 3. The Young’s modulus showed an ununiform distribution, and higher values were concentrated around the top and the center of molten area. However, all average values of Young’s modulus were higher than that of non-laser irradiated glass, and Young’s modulus showed uniform distribution inside molten area at pulse energy of 3.0 μJ, as shown in Fig. 4. This phenomenon proved that it is possible to enhance the mechanical strength of weld joint at high energy conditions of high pulse energy and scanning velocity, when N.A. 0.65 is employed.