Laser Cutting of Functional Materials by Twin Laser Beam and Thermal Stress Analysis

1.激光切割实验表明，当激光方向发生变化时，无论角度如何，裂纹扩展方向都向激光扫描线外延伸。采用最大切向应力理论对裂纹扩展方向进行了有限元预测。分析结果与实验结果吻合较好。根据有限元分析结果，可以通过控制激光扫描方向来控制裂纹扩展方向。但是，激光扫描方向的控制比较复杂，难以预测裂纹的扩展方向。有限元分析结果表明，在裂纹尖端前后平行于激光扫描线的双激光束可以有效地控制裂纹的扩展方向。裂纹扩展方向受两梁强度比和后梁位置的影响。采用棱镜驱动激光束，研制了双激光头。该方法是一种简单易行的获得双激光束的方法。通过在激光头中加入对棱镜位置的控制系统，可以根据有限元分析的结果切割出复杂的形状。采用不带启动缺口的试样研究了裂纹的起裂行为。离焦距离越小，裂纹产生时间越早。有限元分析结果表明，离焦距离较小时，应力分布较陡。裂纹随条件不稳定扩展。

1.According to the laser cutting experiment, crack growth direction was going to out of the laser scanning line when the direction of the laser changed regardless of the angle.2.Crack growth direction was predicted by FEM analysis with the maximum tangential stress theory. Result of the analysis showed good agreement with that of the experiment.3.It could be possible to control crack growth direction by controlling laser scanning direction according to the result of FEM analysis. However, control of laser scanning direction is complicate and it is difficult to predict a crack growth direction.4.Appling a twin laser beam placed forward and following of the crack tip with in parallel to the laser scanning line is effective to control the crack growth direction according to the result of FEM analysis. Crack growth direction could change by the beam intensity ratio between two beams and the position of the following beam.5.Twin laser beam head was developed by using a prism to sprit a laser beam. This method is simple and easy way to obtain twin laser beam. By adding the control system for the position of a prism in the laser head, it could be possible to cut the complicated shape based on the result of FEM analysis.6.Crack initiation behavior was studied by using the specimen without a starter notch. Crack may earlier initiates when the defocusing distance is small.7.Stress distribution was steep in case of defocusing distance is small according to the results of FEM analysis. Crack unstably propagated with the condition.