【作者】 谢小柱；

【导师】 李力钧；

【作者基本信息】 湖南大学 ， 机械制造及其自动化， 2006， 博士

【摘要】 激光切割是一种应用最广泛的激光加工技术，其工业应用始于七十年代初。随着激光器件和加工技术的进步，其应用领域逐步扩大到低碳钢、不锈钢等金属和木材、增强塑料、陶瓷、石英，石材等非金属板材的切割，应用规模也不断扩大。本文系统研究了CO₂激光气化切割高吸收率非金属材料的机理及其影响因素，重点分析了切口处前沿和壁面的光线传输和能量吸收过程，建立了中低功率激光切割非金属材料的理论模型，通过分析得出如下主要结论： 1．研制了满足试验要求的PHC—1500折叠式准封离型连续CO₂激光器，输出为稳定的基模线偏振光，配套的光学和机床系统能够很好地保证切割精度。 2．采用量热法试验测定了模切板和有机玻璃对CO₂激光的反射率，结果发现垂直于入射面线偏振光的反射率随入射角的增大而增大。平行于入射面线偏振激光的反射率在较小入射角下（60°以下），反射率较小，且随入射角的增大而缓慢减小；入射角大于60°以后，反射率随入射角的增大而急剧增大。比较理论计算结果，发现两者具有较好的一致性。 3．采用高速摄影的方法拍摄气化切割前沿形状。随着焦点位置下移，切割速度的降低、激光功率增加，切割前沿深度增加，弯曲程度减小。由于材料较厚，切割前沿弯曲，对激光存在多次反射，使得光线朝着深部传输，有利于切割前沿深度的增加。 4．基于试验拍摄的前沿形状和切缝形状，经过理论分析建立了激光气化切割非金属材料的三维能量耦合模型，分析了实际弯曲切割前沿和两壁面对激光的反射传输和能量吸收过程：（1） 前沿和壁面的能量吸收主要都决定于入射光束的前三次入射（即两次反射），前沿本身的多次反射增强前沿底部的功率密度，壁面的多次反射增强前沿中下部位的功率密度。正是由于多次反射的存在，使得整个前沿都有功率密度分布。由于切割速度的影响，激光轴线朝着前沿方向移动；（2） 在前三次入射的总激光功率密度方面，前沿部分s偏振光＞c偏振光＞p偏振光，壁面部分p偏振光＞c偏振光＞s偏振光；而在吸收的总激光功率密度方面，前沿部分p偏振光＞c偏振光＞s偏振光，壁面部分s偏振光＞c偏振光＞p偏振光，三种不同偏振光之间吸收功率密度的差值较之金属还是要小很多。试验采用线偏振激光沿着八个不同方向切割模切板，发现沿着不同方向切割的上、下切缝之间的差值很小，验证了理论分析结果，也就是说偏振性对高吸收率的非金属材料影响不大；（3） 两切口壁面对入射激光有波导作用，入射激光在左右两壁面之间相互反射，朝着切口深部传输，即所更多还原

【Abstract】 Laser cutting is one of the most widely used laser processing technology, and its application in industry dates back to the beginning of 1970s. With the improvement of the laser devices and processing technology, it can also be applied to the cutting of the metals such as mild steel and stainless steel and the nonmetallic materials such as wood, FRP, ceramic, quartz and rock. This paper systematically studies the mechanism of evaporation CO₂ laser cutting high absorptive nonmetallic material and its affecting factors, emphasizes the beam transmission and energy absorption of the cutting front and wall, creates a theoretical model of medium and low power level laser cutting nonmetallic material and draws such conclusions as follows:1. The experiment-required PHC-1500 folded quasi-sealed continuous wave lasers is developed, which outputs stable TEMoo mode polarized beam and the optical and machine system equipped well guarantees the cutting precision.2. The die-board and PMMA reflectivity to CO₂ laser is measured by the calorimetric method. The results indicate that the reflectivity to perpendicular polarized beam will increase with the incident angle’s growing. The reflectivity to parallel polarized beam is small with the incident angle below 60 degree, and will diminish gradually with the growing of the incident angle, when the incident angle reaches above 60 degree, the reflectivity will increase abruptly with the growing of the incident angle. The theoretical results and calculation results show consistency.3. The evaporation cutting front shape is obtained by high speed photography. With focus position downward, the reducing of the cutting speed and the increasing of laser power, the depth of cutting front will increase and the curvature will increase as well. Due to the thick material, the cutting front will bend, which causes multiple reflections, transmits the light toward the deep position and is favorable for increasing the cutting front depth.4. Based on the cutting front and kerf shape photographed in the experiment, a three-dimensional energy coupling model for evaporative laser cutting nonmetallic material is established through theoretical analysis and the reflective transmission and energy absorption of laser against real bended cutting front and both two walls are analyzed: （1） the front and wall’s energy absorption is mainly更多还原