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Experimental study of micro- powder and its application of micro pulses delivered

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Tutor: HouLiYa ZhuLi
School: Nanjing University of Technology and Engineering
Course: Mechanical Manufacturing and Automation
Keywords: laser cladding rapid prototyping,pulse transfer of powder,micro characteristics,
CLC: TB383.3
Type: Master's thesis
Year:  2011
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Abstract:
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.
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