【作者】 王明娣；

【导师】 王珉； 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 针对现有的激光熔覆快速制造过程中偏置侧向送粉和多粉管光外同轴送粉熔覆成形工艺的不足,本文提出了一种“光束中空,粉管居中,光内送粉”的新型激光熔覆快速制造工艺,可应用于金属零件激光熔覆直接制造领域。本文完成的主要工作和取得的成果如下:1.设计了一套基于光内送粉的激光熔覆快速制造系统,该系统将传统的圆锥形聚焦激光束变换为中空的锥形聚焦激光束,将粉末送入中空部分,实现光粉同轴;对所设计的送粉系统开展了性能分析,结果表明,粉末利用率高达60%-75%,比现有的多粉管光外同轴送粉的粉末利用率提高50%以上。2.以作用区域的整体粉末为研究对象,建立了光内同轴送粉成形工艺下的激光束与粉末相互作用的粉末遮光率和粉末颗粒温升简化数学模型,分析了激光利用率;所建立的模型可有效指导送粉喷头的结构优化设计和成形过程仿真。3.详细研究了光内送粉试验关键工艺参数,如光束输出模式、离焦量、激光功率密度、送粉量和扫描速度等对熔覆质量的影响;在多模激光束模式下,探索了不同工艺参数与熔覆层质量的关系,为多层熔覆薄壁墙成形试验打下良好的基础。4.建立了光内送粉激光熔覆快速制造过程中温度场和应力场有限元分析模型,研究了光内送粉熔覆过程中工件的温度分布和应力分布,为控制熔覆层微观质量和预防裂纹产生提供理论指导;设计了一套熔池温度控制系统,可以有效防止热积累,抑制裂纹效果显著。5.在理论分析和实验研究的基础上,开展了光内同轴送粉激光熔覆快速制造的应用基础研究,探索了变方向、变截面、变斑等工艺在金属典型零件中的应用。并结合激光重熔以获得较好的零件表面质量。研究结果表明,利用光内送粉激光熔覆快速制造系统进行金属直接制造,可以提高粉末利用率和成形质量;与原有成形方式相比,成形件显微组织更致密无缺陷,成形过程稳定可靠,表面粗糙度大大降低,无“上粗下细”现象,侧面几乎没有未熔颗粒。更多还原

【Abstract】 For the disadvantages of the lateral powder feeding and multi-lateral coaxial powder feeding process in laser cladding rapid prototyping process, a new process of hollow focusing laser, powder tube being medial and inside-beem powder feeding is put forward, which can be especially apply in laser cladding direct manufacturing.The major work completed and the results obtained are as follows:1.A new system of inside-beam coaxial powder feeding is designed, which can transform the conical focusing laser beam to hollow conical focusing laser beam and powder is delivered to the middle hollow part, and powder is coaxial with the laser. Then the performance of this system is analyzed. The results show that the powder utilization can reach to 60% -75%, which is 50 percent higher than that of the existing coaxial powder.2. Selecting the overall regional powder as the research object, the simplified mathematics model of powder shading efficiency and powder temperature increment model is established, and the power effect efficiency is analyzed also, which is useful for the design and optimization of powder feed nozzle and the simulation of forming process.3. The key process parameters, such as laser power density, beam of light mode and scanning speed etc, are studied in detail. In the multimode laser, the relation between different process parameters and cladding coat quality is found out, which can prepare fully for shaping multilayer parts.4. The finite element analysis model of temperature and stress of the laser cladding rapid manufacturing using inside-beam powder feeding is established, temperature distribution and the stress distribution of the workpiece is researched, which is theoretically useful for controlling the quality of microstructure and to prevent the cracks. Then the pool temperature control system is designed that can prevent heat accumulation effectively and delay cracks remarkably.5. Based on the theoretical analysis and experimental research, the laser cladding rapid manufacturing using inside-beam powder feeding is developed. The applications in the typical metal parts with process of variable direction, variable cross-section and variable spot are studied. Combined with laser re-melting, a better surface quality can be obtained.The results show that if adopting the system of the laser cladding rapid manufacturing using inside-beam powder feeding, the powder utilization and forming quality can be improved; compared with the original mode, there has a dense microstructure and no more defects, the process is more stable and reliable, the surface roughness is reduced greatly, and there is no "the thick top and the thin bottom " phenomenon, and has no melting particles in the side wall.更多还原