【作者】 李春生；

【导师】 石世宏；

【作者基本信息】 苏州大学 ， 机械制造， 2010， 硕士

【摘要】 激光熔覆快速成形就是利用聚焦激光束与同步送入光斑的金属材料耦合进行三维立体成形的技术。目前此项技术中激光聚焦光斑普遍采用实心光斑,送料方式为单料管光外侧向送料或多料管光外包围同轴送料。在这种光源和送料方式下,光斑和熔覆材料的耦合稳定性比较差,造成成形过程不稳定,沉积率极低,冶金质量不高,加工件精度与粗糙度不理想。本文应用了一种新型的中空环形激光聚焦系统,并采用了光内同轴送料熔覆方式。本课题重点对这种中空环形激光束的传输转换、聚焦光斑的能量分布和光料耦合效应进行了研究。运用几何光学,采用光线追迹法,建立了中空环形激光聚焦系统的光束转换聚焦模型,并模拟出了在不同离焦量横截面上聚焦光斑的能量分布。通过研究得出:光束在离焦|z|小于0.727mm时,聚焦光斑叠加为实心光斑,而在其它离焦量的横截面上均为中空环形光斑。中空环形激光聚焦光斑的能量密度呈“双峰形”分布,并推断出中空环形激光在扫描时线宽方向上吸收的光能呈“马鞍形”分布。同时得出了不同离焦量横截面上中空环形光斑的大小和占空比之间的关系。利用中空环形激光光内同轴送料熔覆方式进行了扫描方向性试验,并分别进行光内送粉和光内送丝的单道熔覆以及三维成形试验。试验证明:中空环形光光内同轴送料熔覆实现了光料真正意义上的同轴,光料能够准确的耦合,完全消除了扫描方向性对熔覆质量的影响。中空环形聚焦光斑扫描线宽方向上吸收光能的“马鞍形”分布与实心光斑的“高斯形”分布相比,不仅减小了熔池的能量密度梯度,而且为熔道侧面提供了更多的能量,减小了实心光斑熔覆时边缘能量不足对熔道侧面的影响。对成形件进行分析可知,成形件表面光洁,与基体形成了致密的冶金结合,微观组织晶粒细小、均匀,无杂质、气孔等缺陷。更多还原

【Abstract】 Laser cladding rapid prototyping is a technique which coupling the focused laser beam and the metal materials which enter into the spot simultaneously to Three-Dimensional Prototyping. But now the solid focused laser spot is commonly used in this technology, and the type of material feeding is the lateral material feeding or coaxial material feeding outside the laser. Under this laser spot and material feeding method, the stability of the coupling performance of the laser spot and the cladding material is very poor, which leads to the instability of the prototyping process, the very low metallurgical quality and the nonideal precision and the roughness of the work pieces. This paper uses a new type of hollow circular focusing system and adopted a method of inside-laser coaxial material feeding to clad. Paying heavy stress on the transmission conversion of this hollow circular laser and the coupling between optical and material.Using geometrical optics and ray tracing method, this paper establishes the hollow circular laser beam focusing system conversion model and simulates the energy distribution of the focused spot at different defocusing cross section. According to the research,the conclusiones can be geted as flollowing: when|z| is littler than 0.727mm,the focusing laser is solid spot, but it is hollow circular spot at the other defocusing cross sections. The energy distribution of the hollow circular laser beam is“bimodal-shape”, according to which we can deduce that the energy absorbed at the scan direction of the hollow circular laser is“saddle-shape”. At the same time we can get the relationship between hollow circular laser beam and duty circle at different defocusing cross section.This paper uses the approach of inside-laser coaxial material feeding cladding with the hollow circular laser to do the scanning direction test, and do the inside-laser coaxial power feeding cladding and inside-laser coaxial wired feeding cladding separately.It is proved that:the inside-laser coaxial material feeding cladding can achieve a real coaxial of the laser material,the optical and material can coupe accurately, eliminating completely the impaction of the scanning direction to the cladding quality. Compared with the“Gaussion-shape”of solid spot, the“Saddle-shape”distribution of the energy absorbed at the scan dirction of the hollow circular laser not only reduces the energy density gradient of the pool, but also provides more energy to the melting road side,and reduces the bad impact on melting road side caused by the shortage of the energy of the edge of the solid laser spot.Through anglicizing the prototyping modeling it is concluded that:the prototyping modeling surface is very smooth and form the metallurgical combination with the bade,the microstructures are very small, even,without impurities, porosity and other defects.更多还原