【作者】 邵其文；

【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结合了激光熔覆与快速成形(Rapid Prototyping)两大技术的优点,成为了目前先进制造技术的一个重要研究方向。但是目前此项技术中成形所采用送粉方式为单粉管光外侧向送粉和多粉管光外侧向同轴送粉。光外侧向送粉成形有一些不足之处:倾斜侧向输送的粉末一般呈抛物线运动,多粉束汇聚精度低,其运动轨迹受多种因素干扰,任意光轴横截面上的粉末密度分布不均匀,激光束与粉末耦合效应不高,热作用效率低,成形件表面较粗糙,金属粉末利用率一般只有20%~30%。针对上述不足之处,本文采用“光束中空,粉管居中,光内送粉”的方法进行三维成形,对光内送粉工艺进行了部分实验研究。分析了光内正向同轴送粉工艺下的激光束与粉末相互作用过程,以作用区域的整体粉束为研究对象,重点讨论了金属粉末的有效利用率ε。建立粉末有效利用率的计算模型。实验证明,光内送粉的粉末有效利用率在一定条件下随着送粉速率的增大而增大,达到一定程度后便下降;随着扫描速度的增大亦出现如上规律。测试数据证明:光内送粉比传统光外送粉的粉末利用率提高2~3倍。利用自主研制的光内同轴送粉喷头进行了单层和多层堆积实验,找出不同工艺参数与熔覆层质量之间的联系,主要针对激光功率密度、光斑形式、送粉速率和扫描速度等工艺参数变化对成形的影响进行了实验研究。在此基础上进行圆柱空心薄壁件和锥形空心薄壁件的多层堆积实验。实验证明,与侧向单粉路送粉和多粉路光外同轴送粉成形工艺相比,光内送粉装置实现了光、粉、气一体同轴,成形过程稳定可靠,光内送粉喷头的使用性能和工艺性能具有明显的优势,成形件表面光洁度高,侧面无未熔化颗粒,尺寸精度得到很好保证。最后对成形件进行了显微组织分析、硬度测试、残余应力测试,结果证明:成形件显微组织晶粒细小、均匀,致密无缺陷,性能优越。更多还原

【Abstract】 Laser cladding rapid prototyping combines advantages about technology of laser cladding and rapid prototyping, is the research direction of advanced manufacturing technology, but now the type of powder feeding is the lateral powder feeding or coaxial powder feeding outside the laser about this process, there are many disadvantages: such as lateral powder feeding shows itself as parabolic motion of powder, being easily interfered by many external factors, asymmetry of powder in any section, poor coupling of laser and powder reciprocity, coarseness of parts surface, inefficiency of laser and powder thermodynamics reciprocity, difficulty in prototyping high quality parts and only twenty to thirty percent powder catchments efficiency. Aiming at so many disadvantages, this article puts forward a new process of hollow focusing laser, powder tube being medial and inside-laser powder feeding. Combines the existing experiment condition, researches the technology of this new process according experiments.The article discusses the course about laser and alloy powder reciprocity, researches the alloy powder in the area of laser, and discusses its efficiency. Established the model about alloy powder efficiency, according to experiment, the efficiency of the powder increases with the increase of powder cladding speed, at a point, it will fall down. And the same disciplinarian appears with the increase of scanning speed. At last, the powder efficiency is tested about sixty-eight point three percent, higher than that in the process of lateral powder feeding or coaxial powder feeding outside the laser.The article also discusses the key process parameters that are needed in the cylindrical shaped and taper shaped parts experiment, such as laser power density, beam of light mode、powder delivered speed、scanning speed etc. The steel medicinal pinhead is chosen as powder feeding nozzle and nitrogen gas is adopted as the pneumatic drive to feeding powder. Through several monolayer line scanning cladding experiment and multilayer line scanning cladding experiment the multimode laser, the relation between different process parameters and cladding coat quality is obtained. Based on the experiment research, cylindrical shaped and taper shaped parts prototyping experiment is accomplished with the new inside-laser coaxial powder feeding process. In the experiment process, laser power is synchronously controlled by the molten pool temperature collected by infrared temperature measuring apparatus and z axis increment is also modified every time. Experiment results shows that The shaping process of inside-laser coaxial powder feeding overcomes the disadvantages of the former shaping process: realizing the integrative coaxial function of laser, powder and gas, forward and vertical powder feeding inside laser, the shaping process is stable and reliable, the functional and process property of new powder feeding nozzle is superior to the traditional powder feeding nozzle and parts surface quality and dimension precision are improved greatly, compared with the former prototyping process. At last, the article analyses microscopic structure、hardness of shaped metallic parts and remainder stress. The microscopic structure is dense、crystal is thin and has no defects and the hardness of shaped metallic parts enhances greatly.更多还原