Study On Cold Welding Sealing In Second Degasification Technology Of Micro Heat Pipe And Equipment

Nowadays, micro heat pipe, using the phase-changing principle to transfer heat from oneend to another efficiently, has been applied to many industries successfully to solve the highheat flux problems. The second degasification sealing process is one of the key processes, forit can affect the degassing and sealing level of micro heat pipes. The study focuses on the coldwelding sealing process during the second degasification process, and its main work is asfollows:The transductive concave-convex structure has been selected to seal the micro heat pipein the second degasification process, because it is simple and compatible with the followingPAW process. Without force-increasing levers, a hydraulic cylinder must be used to produceenough force for sealing.The orthogonal method is applied in the study to research four factors in the coldwelding sealing process for micro heat pipe, including gap width, sealing length, sealingdiameter and sealing velocity. Three levels are selected for each factor. There are twoexperiment targets including sealing strength and the appearance of the sealing end after PAW.The results show that, the NO.2sample has the best appearance after PAW. As for sealingstrength, the factor gap width has the greatest contribution, and followed by sealing length,sealing diameter and sealing velocity. The heat pipe samples are heated until water leaks outfrom the sealing end, and the saturated vapor pressure of water in the leaking temperature istaken for the sealing strength. After the leakage, the samples can still maintain a proper heattransfer performance, which is measured in the experiments. The results show that as timegoes on, the heat transfer performance of the samples decline with different degrees, whichindicates that air can penetrate into the micro heat pipe over time through the sealing end. Themiddle longitudinal section and cross-section of the sealing area are noted as section A andsection B respectively. The hardness distribution on the two sections of several samples aremeasured. It is found that the hardness declines along the direction from convex die toconcave die. As for section A, the material of the middle area is hardest, followed by thebottom area and the top area. As for section B, the material of the middle area is hardest, andthe hardness of the two sides distribute substantially symmetrically.Three3-D FE models of cold welding sealing process with three levels of sealingvelocities are established using Msc.Marc FEM software. In order to guarantee the accuracyof the model, the deformable workpieces in the models are derived directly from the results ofFE analysis of radial forging process. Using thermal-structural coupling solution, the deformation, stress, strain, temperature and the loads of the three models are analyzed. Theresults show that as the sealing velocity increases, the equivalent stress and strain increase, soas the temperature in the sealing area. The equivalent strain declines along the direction fromthe convex die to the concave die, so the degree of work hardening falls along the samedirection, which agrees well with the results of the orthogonal experiments.Based on the results of the experiments and FEM, which includes the optimized processparameters and the loads needed, an automatic equipment for the second degasificationprocess of the micro heat pipe is designed and developed. The equipment meets therequirement of mass production and is applied successfully in Guangdong New IdeaTechnology Co., Ltd.