Key Technical Foundation Of Process Diagnosis And Control For Robotic Plasma Spray Forming

Plasma spray has been applied widely in the high and new technology industries, such as rapid mould, functional coating, solid oxide fuel cell (SOFC) and so on, in view of its short-circuit, rapid and other unique characteristics. However, as a complicated process with the multiple sub-process correlations and the parameter interdependencies, it is a key issue to select the appropriate spraying parameters to fabricate the high-quality coatings meeting with the actual requirements in the control of the manufacturing process. Furthermore, high grade and new demands for the process stability and reproducibility of plasma spray arise. Therefore, systematic researches ranging from developing the control system, monitoring the spraying process, investigating relationships between processing parameter, plasma jet and coating quality, and predicting the resultant coating quality are carried out in this thesis. Relevant results are applied in the SOFC, a new energy resource field, and major research contents are listed as follows.(1) Specially designed MOTOMAN UP20 robot control software was presented based on Ethernet to meet with the requirements of plasma spray. Plasma spray control system was developed based on PC+PLC. Finally, the Open architecture robotic plasma spray forming system was established accompanied with forming process monitoring, on-line adjustment of robot spraying trajectories, real-time control of robot and other functions. The flexibility of the resultant forming system is promoted integrating the two working units, the plasma spray forming and the robot motion control. They are the technical foundation for the development of the professional robotic plasma spray system. A monitoring software SprayMonitor was developed on the basis of OPC (OLE for Process Control) protocol and COM (Component Object Model).(2) An on-line temperature measurement approach for sprayed coatings is presented in this dissertation, which realizes the real-time visual monitoring and dynamic analysis. The influence of robot spray trajectory parameters on coating temperature was experimentally investigated. The analysis of heating effect on substrate by plasma jet and particle flux were carried out under different spray distances and lengths of plasma jet to analyze their characteristics. These conclusions can be used in the formability and quality control of plasma spray.(3) Investigations on the relationship between processing parameter, plasma jet and coating quality were carried out. The morphological feature of plasma jet was first characterized by the aspect ratio, and the clustering analysis was done based on experimental results. The quality of clusters was evaluated by the properties and microstructure of coatings, so the inference rule sets from processing parameters to the optimal quality cluster were produced. Hence, an intelligent control approach of plasma power source was presented.(4) To shift plasma spray to the new field, manufacturing core compontents of SOFC, the liquid feedstock system was designed, and suspension plasma spray (SPS) was used to prepare the dense electrolyte of SOFCs. The porosity of the resultant electrolyte is 1.61%. SEM of the electrolyte coating show that melting state of spray particles was sufficiently promoted during the process of SPS and the tight bonding among the flat layers was also observed. Both the factors are not only favorable to enhance the mechanical strength and density, but also helpful to effectively improve the electrical conductivity of electrolyte.Based on the studies above, the quality diagnosis of plasma jet and the temperature control of sprayed coating were carried out during fabricating core components of SOFC by APS and SPS. Both the spray forming processes were improved and their stability and reproducibility were also upgraded.The contents of this thesis provide a reference for optimal matching of plasma spraying parameters, including plasma power source, robot spray trajectories, powder and suspension feeding and so on. Furthermore, they are also the key technique foundation for the fabrication of the core component of SOFC during the integral spray process by APS and SPS, which contains the porous electrodes but density electrolyte.