【作者】 彭善飞；

【导师】 石世宏；

【作者基本信息】 苏州大学 ， 机械制造及其自动化， 2008， 硕士

【摘要】 激光熔覆快速成形技术是在激光熔覆技术的基础上,结合快速成形制造的特点发展起来的一种先进制造技术。目前激光熔覆快速成形技术普遍采用的送粉方式为偏置侧向送粉和多粉管光外同轴送粉,激光光斑为圆形光斑,在这种送粉方式下,光斑和粉斑的耦合稳定性比较差,本文采用环形激光光内同轴送粉的方式进行激光熔覆快速成形,重点对光内送粉工艺参数对成形的影响进行了分析研究。通过建立环形激光束与光内同轴送粉粉束相互作用的简化数学模型,以作用区域的粉末为研究对象,重点讨论了环形激光作用效率η。经计算,同一z坐标处的η随送粉量M_p（ g / s）的增大而增大,随粉流速度v₀的增大而减小;送粉量M_p和粉流速度v₀一定时,η随z的增大而增大。分析了环形激光光斑在扫描线宽方向能量的分布情况,与传统的圆形光斑和矩形光斑相比,有利于能量的合理分布和提高激光热作用效应;讨论了环形激光熔覆成形中主要工艺参数,如环形激光功率密度、扫描速度、送粉速率和光斑直径等对成形的影响。利用环形激光光内同轴送粉喷头进行了多模激光束下单道单层、单道多层,离焦和多道搭接熔覆实验和测试。研究了在环形激光作用下激光功率、扫描速度、搭接量、送粉速率、光斑直径等工艺参数对成形尺寸、形貌、显微组织的影响,分析了不同工艺参数与熔覆层质量的关系。结果表明:要获得较好的成形质量,搭接量应大于光斑半径,激光功率、扫描速度和送粉速率存在着最佳匹配值,环形光斑下的正负离焦量可达14 mm,能够在离焦状态下实现较高质量的激光熔覆快速成形。试验证明,与圆形光外同轴送粉成形工艺相比,环形激光束与粉末耦合性好,激光光斑充分包围粉斑,成形件表面光洁度高,侧面无未熔化颗粒;环形激光热作用充分,其显微组织致密无缺陷,熔覆层边界与基体结合情况良好。更多还原

【Abstract】 Laser cladding rapid prototyping bases on laser cladding is an advanced manufacturing technology, which was developed from rapid prototyping(RP). At present, the widely used method of powder feeding is lateral powder feeding and coaxial powder feeding process. This paper aims at studying the laser cladding rapid prototyping parts by annular laser facula and inside-laser coaxial powder feeding device to optimize the laser processing parameters.This paper establishes the simplified mathematics model of laser and powder reciprocity in the inside-laser coaxial powder feeding process and deduces the calculation formula of laser effect efficiency. Through theoretically calculation, at the same coordinate, laser effect efficiency increases with powder feeding quantity rising and powder velocity decreasing. When powder feeding quantity being an invariable numerical value, laser effect efficiency increases with a powder granule’s time increasing in laser, which corresponds to the former study. This paper also analyses the energy distribution of annulus laser facula, the annulus laser facula is much propitious to shaped than traditional circular or rectangular facula; discusses the key process parameters that needed in the thin wall shaped parts experiment, such as laser power density, beam of light mode and scanning speed etc.Through several monolayer line scanning cladding experiment, multilayer line scanning cladding experiment, lines overlapping scanning cladding experiment in the multimode laser, analyzed their microscopic structure、hardness of shaped metallic parts. To obtain the parts with high precision and the excellent quality, the influence of many processing parameters on sizes of cladding coatings, precision and surface quality has been analyzed in detailed. These parameters include: laser power, scanning speed and ratio of overlapped. The results show that for getting the parts with best quality by, the value of overlapping ratios should be greater than that of the spot sizes. And furthermore, the optimum matching of laser power, scanning speed powder delivery speed is necessary, it is impossible to produce the high-grade laser cladding rapid prototyping parts within 14 mm determinate defocusing.The experiment results shows that the coupled performance of laser and powder reciprocity is excellent, the surface of parts is smooth, heat action of annular facula laser is sufficient, compared with the former prototyping process. Ultimately,the article analyses microscopic structure and hardness of shaped metallic parts. The microscopic structure is dense and has no defects and the hardness of shaped metallic parts enhances greatly.更多还原