激光热裂法切割液晶玻璃边缘崩裂现象研究

发布时间：2018-05-05 23:40

本文选题：激光热裂法切割 + 液晶玻璃　；参考：《浙江工业大学》2016年硕士论文

【摘要】：高透光率玻璃盖板已广泛应用于办公设备、手持电子设备及可穿戴电子设备中。作为显示屏幕的重要保护材料,其材料本身与显示材料的结合程度越来越高,成本也越来越高。由于玻璃制出面积较大,而产品所使用面积较小,因此玻璃盖板需要高效率、低成本、高良率的分割加工方法。在使用激光热裂法切割超薄液晶玻璃基板的过程中,由于切割参数的设置变化或环境因素的影响,其切割边缘有较大概率会出现微裂纹,并且在其后的温度变化作用下逐步扩展并联结,导致玻璃切割边缘崩裂脱落、加工质量低下。根据本文实验观察,切割实验前,玻璃基板材料中不含气穴等缺陷,切割过程中观察到激光头上出现有白色气化物,该白色物为切割过程中玻璃表面气化并由热应力作用下上升并附着在激光头上,冷却后切割边缘表面下有微小气穴形成。基于以上背景,本文的主要工作如下:(1)利用有限元法分析了激光扫描玻璃基板的瞬态热传导,求得其热流密度场,按热弹性平面应力理论及多裂纹扩展理论分析热应力场,根据微裂纹的开裂准则判定裂纹的扩展方向及开裂情况,根据裂纹的分叉准则计算裂纹分叉角的大小。通过该方法分析了对称式切割下,玻璃基板在激光扫描和冷却过程中产生的崩裂微裂纹及崩裂现象的形成机理。(2)本文提出了激光扫描过程的仿真及微裂纹扩展方向的分段迭代算法。观察其微裂纹结构,提出了微裂纹的扩展模型,每一段微裂纹的扩展均按照最大周向应力准则(MTS)预测其扩展方向,并在此基础上拟合下一段裂纹的扩展角度,通过将一条裂纹按扩展顺序分割成多段,模拟整个崩裂裂纹的行程轨迹,判断理论裂纹扩展与实验的偏离程度。(3)针对切割边缘崩裂微裂纹,实验采用了计算机图形学处理方法。在对实验拍摄的图像进行灰度化、二值化、腐蚀算法等处理后获得裂纹图像的像素坐标信息,使用自行设计的裂纹最大宽度及裂纹真实长度提取方法对裂纹图像进行处理。提高了实验数据的处理效率及精度。本文中给出的算例结果表明:微裂纹起始于玻璃边缘的气穴或凹坑圆弧的中点,且在凹坑的弧线中点向玻璃内部扩展,扩展倾斜方向与激光扫描方向相反。微裂纹尾端由于裂尖达到临界应力强度因子而出现分叉,冷却过程中,微裂纹继续扩展而联结,最终导致边缘崩裂。
[Abstract]:High transmittance glass cover has been widely used in office equipment, handheld electronic devices and wearable electronic devices. As an important protection material of display screen, the material itself is more and more combined with display material, and the cost is higher and higher. Because the glass production area is larger and the product area is smaller, the glass cover plate needs high efficiency, low cost and high yield. In the process of cutting ultra-thin liquid crystal glass substrate by laser hot cracking method, due to the change of cutting parameters or the influence of environmental factors, there is a large probability that micro-cracks will appear in the cutting edge. After the temperature change, the glass cutting edge is gradually expanded and connected, resulting in the glass cutting edge crack and fall off, and the processing quality is low. According to the experimental observation in this paper, before the cutting experiment, the glass substrate material does not contain holes and other defects. During the cutting process, white gasification was observed on the laser head. The white material is the glass surface vaporized during the cutting process, rising under thermal stress and attached to the laser head. After cooling, there are tiny air holes formed under the cutting edge surface. Based on the above background, the main work of this paper is as follows: (1) the transient heat conduction of laser-scanned glass substrate is analyzed by finite element method, and the heat flux field is obtained. The thermal stress field is analyzed according to the theory of thermoelastic plane stress and the theory of multi-crack propagation. The crack propagation direction and crack condition are determined according to the crack criterion, and the crack bifurcation angle is calculated according to the crack bifurcation criterion. By using this method, the symmetrical cutting is analyzed. The formation mechanism of crack microcrack and crack phenomenon in laser scanning and cooling of glass substrate. In this paper, the simulation of laser scanning process and the piecewise iterative algorithm for the direction of microcrack propagation are presented. After observing the microcrack structure, a microcrack propagation model is proposed. The propagation direction of each microcrack is predicted according to the maximum circumferential stress criterion (MTS), and the propagation angle of the next crack is fitted on this basis. By dividing a crack into multiple segments according to the sequence of propagation, simulating the whole crack path and judging the degree of deviation between the theoretical crack propagation and the experiment, the computer graphics method is used to deal with the microcrack in the cutting edge crack. The pixel coordinate information of the crack image is obtained by grayscale, binarization and corrosion algorithm, and the crack image is processed by the self-designed method of extracting the maximum crack width and the real crack length. The processing efficiency and accuracy of experimental data are improved. The numerical results show that the microcracks begin at the central point of the hole or concave arc at the edge of the glass and propagate to the glass interior at the midpoint of the arc line of the crater and the direction of the propagation is opposite to the direction of laser scanning. Due to the critical stress intensity factor at the crack tip, the end of the microcrack diverges. During the cooling process, the microcrack continues to expand and join, and finally leads to the edge crack.
【学位授予单位】：浙江工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TQ171.734;TN249

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