【作者】 孙后顺；

【导师】 石世宏；

【作者基本信息】 苏州大学 ， 机械制造及其自动化， 2012， 硕士

【摘要】 激光熔覆成形(Laser Cladding Forming，LCF)技术是激光熔覆技术与快速成形技术的结合，目前已成为先进制造技术的一个重要研究方向。目前LCF技术中成形所采用送粉方式多为光外侧向送粉和光外同轴送粉，这两种送粉方式在使用时出现一些不可忽视的问题，如激光束与粉末耦合性差，金属粉末利用率低等。针对光外侧向送粉和光外同轴送粉的缺点，本课题组开发了一种新型的光内同轴送粉成形工艺，很好地解决了以上问题。本课题对熔覆过程中的能量分配形式和金属粉末堆积方式进行了分析，并针对现有光内同轴送粉喷嘴及调节装置的不足，做出了相应的改进。本课题使用改进后的光内同轴送粉喷嘴及调节装置，研究和总结了激光功率、送粉速度、扫描速度和离焦量等主要工艺参数对送粉熔覆层形貌和成形质量的影响规律，还进行了变宽熔道成形试验。研究发现：(1)当功率较低时，升高激光功率可以增大熔道高度和宽度；当功率偏大时，升高激光功率对熔道高度和宽度影响不大。(2)当送粉速率较小时，增大送粉速率可以增大熔道高度和宽度；当送粉速率较大时，增大送粉速率对熔道高度和宽度影响不大。(3)随着扫描速度的增大，熔覆层的宽度和高度都会减小。其中熔覆层的高度明显减小，而宽度稍有减小。(4)在负离焦状态下，随着离焦量的增大，熔道高度会增大，熔道宽度会减小；在正离焦状态下，随着离焦量的增大，熔道高度会减小，熔道宽度会增大。(5)在保证激光功率P、送粉速率Vf和D×Vs不变的基础上，改变扫描速度和离焦量的配比进行光内送粉激光熔覆试验，最终得到了高度稳定，宽度变化均匀的熔道。本课题以四方形薄壁件为例，使用常规方法进行了非圆滑过渡薄壁件的成形试验。结果发现，试验因四方形薄壁件的拐角出现凸起而无法继续进行，针对这种问题，提出了非圆滑过渡薄壁件成形的自修复效应，并根据该效应从两方面改进了试验方案：(1)使用X,Y轴联动方式扫描代替单一X,Y轴扫描方式；(2)使用负离焦状态代替正离焦状态。试验最终成功得到了四方形薄壁件。改进试验得到的四方形薄壁件表面光滑平整，内部组织致密，晶粒细小，优于铸件和热处理后的普通钢零件的性能，这对今后非圆滑过渡复杂零件的快速成形也具有一定的指导意义。更多还原

【Abstract】 Laser Cladding Forming (LCF) technology, which mixes the advantages of LaserCladding and Rapid Forming technology, has become one of the important researchdirections of advanced manufacturing technology. At present, the main method ofpowder seeding in LCF is outside-beam powder seeding technology, which contains twokinds of classifications called lateral powder feeding and coaxial powder feeding. Thereare many problems arising when the two methods are used, such as the laser beam can’tmatch the metal powder well, the part’s surface is too rough, the utilization efficienciesof energy and powder are very low and so on.According to the shortcomings of lateral outside-beam and coaxial outside-beampowder feeding, our research group has developed a kind of new technology calledcoaxial inside-beam powder feeding, which can solve all the problems above. By seriesof experiments, this paper analyzed the relationship of energy and the relationshipsmetal powder, and summarized the parameters’ influence to the layer’s feature andquanlity (The parameters contain laser power, powder seeding velocity, scanningvelocity, defocusing distance.).At last some cladding experiments were made to aquirethe layers with variable width. The experiment results can be showed as follow:(1)When the laser power is very low, the layer’s height and width become larger with laserpower’s increase.When the laser power is high enough,it has little effect on the layer’sheight and width.(2) When the powder seeding velocity is very low, the layer’s heightand width become larger with the powder seeding velocity’s increase.When the powderseeding velocity is high enough,it has little influence on the layer’s height and width.(3)When the scanning velocity increases, the cladding layer’s height decrease evidently,and it’s width slightly.(4) When the powder seeding nozzle is in the minus defocusingstate, as the defocusing amount increases, the cladding layer’s height increases, and thewidth decreases.When the powder seeding nozzle is in the plus defocusing state, as the defocusing amount increases, the cladding layer’s height decreases, and the widthincreases.Although the coaxial inside-beam powder feeding technology is better than the oldmethods, it has been not yet a mature technology. According to the existing weaknessesof coaxial inside-beam nozzle and the adjusting device in the process of laser cladding,this paper has made some modifications in the design of them.Taking the square thin-walled part’s forming processing for an example, this paperused the conventional LCF technology to manufacture thin-walled part with unsmoothtransition.The results showed that there were steady bulges appeared in the square’scorners, which made the experiment can’t be carried out smoothly. According to thissituation, this paper firstly put forward the auto-repairing theory in the formingexperiment of thin-walled part with unsmooth transition. This paper modificated theexperiment scheme by the auto-repairing theory.According to this theory above,thispaper improved the test scheme from two aspects:(1) Instead the single-axis scanningmode with X, Y linkage scanning mode.(2) Instead the plus defocusing state withminus defocusing state.At last,we got square thin-walled part successfully.The testing and analysis of the part showed that the microstructure was uniformlydistributed, and the part’s hardness was higher than the castings and the ordinary steelparts with heat treatment. This experiment has a certain significance to the formingexperiment of thin-walled part with complex structure in the future.更多还原