摘要
激光熔覆快速成形技术集激光技术、计算机技术、数控技术、传感器技术及材料加工技术于一体,是一门多学科交叉的边缘学科和新兴的先进制造技术。为提高成形件的质量和精度,激光熔覆快速成形对粉体输送技术提出了较高的要求,一方面希望输送过程稳定、均匀、精确可控,另一方面希望尽量提高粉体输送分辨率。
目前的粉体输送方式存在以下一些问题：机械结构比较复杂,磨损严重；粉末利用率不高；可控性普遍不高,通断不可控；粉体输送分辨率较低；粉体广适性差等。因此,研究分辨率高、稳定性好、可控性高、具有粉体广适性并且装置结构简单的粉体输送技术是值得研究的重要课题。
本论文针对粉体脉冲微输送技术进行研究,首先进行理论分析,在此基础上进行大量实验,研究系统参量对脉冲输送微特性的影响规律,最后通过实验结论指导功能梯度材料的制备。取得的成果如下：
以粉体在微喷嘴中形成的微拱为研究对象,得到了微喷嘴内静态微拱形成的两个必要条件,以及粉体在微喷嘴中的流动判据,在此基础上分析了粉体脉冲输送的过程,并定性地得到了粉体质量流量方程。
选取粉体输送率Q与输送稳定性C·V作为粉体脉冲输送微特性的评价指标；构建了粉体脉冲微输送实验系统；得出了电压幅值、驱动频率、微喷嘴内径、输送角度4种系统参量对角形铬粉和角形TC4粉的输送微特性的影响规律；设计了正交试验,得到了各个系统参量对粉体输送率的影响程度大小,并对系统参量进行了优化；以铬粉为例,给出了粉体脉冲微输送中系统参量的确定与选择依据,实验表明了很好的输送效果。结果表明,粉体脉冲微输送系统能够输送流动性差的角形粉体,并且具有分辨率高、稳定性好等良好的输送微特性。
构建了两路粉体脉冲微输送系统,通过实验验证了两种粉体可按一定比例精确稳定输送。在此基础上,制备出了Cu/Cr功能梯度材料、Cu/A1203功能梯度材料,并进行了相应的表征,表明了粉体脉冲微输送系统可以用于制备功能梯度材料。
Laser cladding rapid prototyping is a multidisciplinary frontier subject and an emerging advanced manufacturing technology, which integrates laser technology, computer technology, numerical control technology, sensor technology and material processing technology. To improve the quality and precision of formed parts, higher requirements in laser cladding rapid prototyping are put forward. On the one hand, the process of powder transfer is to be stable, homogeneous and exact controllable, on the other hand, the transfer resolution improved.
The following problems exist in the current powder transfer methods:mechanical structure is complicated and badly worn; powder utilization not high; controllability generally not well, usually uncontrollable; powder transfer resolution lower; the powder adaptability width poor and so on. Therefore, the research of powder transfer technique with high resolution, good stability, high controllability, wide powder adaptability and simple structure is an important topic worthy of study.
This thesis aims to pulse transfer of powder (treated as microfluids) technique researching. Theoretical analysis was made, and then, to study the influencing rules of the system parameters on micro characteristics, lots of experiments were carried out. The experiment results could be used to guide the generation of functional gradient materials. Results obtained are as follows:
Two necessary conditions for the formation of the static micro-arch and the flow criterion of powder were obtained through researching the powder micro-arch in the micro-nozzle, based what the process of powder transfer was analyzed and the powder mass flow equation was got qualitatively.
Powder transfer rate Q and transfer stability C·V was chosen as the evaluation index of micro characteristics; the experiment system of pulse transfer of powder was built; influencing rules of four system parameters which were the voltage amplitude, the driving frequency, the inner diameter of micro-nozzle, and the angel of transfer, on micro characteristics of triangular Cr powder and TC4 powder; an orthogonal experiment was designed and the significant influence of each system parameter on the transfer rate was obtained and these parameters were optimized. Setting Cr powder as the experiment object, the identification and selection basement of the microfluids system parameters was given out. Experiment results indicate that the pulse transfer of powder system can transfer angular powder and has excellent micro characteristics of high transfer resolution and good stability.
A novel pulse transfer of powder system which could separately transfer two kinds of powder on the same time was built; experiment results indicated that two kinds of powder could be stably transferred for a precision mixing proportion. The Cu/Cr and Cu/AI2O3 functional gradient materials were generated and characterized, which indicated that the system could generate functional gradient materials.
引文
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