Thoery And Experiment Study On Stress-strain And Coefficient Of Friction Of Sheet Forming In Meso Scale

As the size decreasing of electronic products recently years, the meso scale parts arewidely used and increasing required in electronic and precise machinery industry. Therefore,the producing technology of meso scale parts turned into the vigorously developingtechnology in manufacturing industry of many countries. But problems in meso scale formingstopped the development of this technology. Firstly, the size effect was observed in manyexperiments but the power of parameter on expressing size effect was not enough and themodel applying, variable assignment, calculating method need to be improved. Secondly, thereason of microscopic level for friction size effect still has’t been found and there is manyvague defination of the model setting up and calculating. Thirdly, the research on meso sheetforming, especially deep drawing still has big blank. In order to improve the meso formingcapacity and micro parts industry, it is urgent to solve these problems.In this paper, manymeso forming reports, especially on stress-strain, friction and meso forming were detaillystudied and many experimens were carried out. The theory research and experiment platformwere set up based on these problems. The stress-strain model based on SAP and frictionmodel based on lubricated area were set up according to the micro morphology of specimens.Compared the model data with experiment, the accuracy of stress-strain and friction model ofsize effect were proved. Finally, the mould of meso scale was developed and micro tube wasdrawed, the quality of micro tube was analysed.Detaily, the following research was carried out in this paper:1. By the analysis and experiment,the stress-strain curver of copper single crystal,coppersingle crystal rod, polycrystalline copper were made out. The simulation and experimentabout the defomation of grain and grain boundary of polycrystalline copper in different grainboundary orientation were carried out. It shows there is obvious stress and stress gradientconcentrate on the grain boundary and periodical distorting exists in vertical grain boundary.The position of holes and cracks in polycrystalline copper with vertical grain boundaryconcentrate on or beside the slipping line. These conclusions will be the base data for the nextchapters.2. The stretching experiment of specimens with different thickness, width, crystal sizewas carried out. It shows that the stress decreased while specimen size decreased and thestress-strain size effect is obviously. The relationship between thickness, width, crystal sizeand size effect was discussed, the parameter SAP was set up. The reason and SAP relatedmodel for size effect of stress-strain were discussed and set up and the scope of k in this model was made out. Finally, according to the experimental data, the proving of this modelwas carried out.3. Based on bend-stretching test theory, the friction test bed was developed and themorphology in different thickness, width, crystal size, lubricating condition were tested. Itshows that the coefficient of friction increased while specimen size decreased and the frictionsize effect is obviously. According to the research and analysis about the present model aboutfriction size effect, a serious defect in this model was found.4. The meso scale friction area morphology preparing test bed was developed and thefriction area morphology was made. The friction area morphology, especially the lubricatedarea was observed. With the image recognization technology, the lubricated area proportionwas calculated and the reason of friction size effect was discussed. It shows that the lubricatedarea proportion decreased while specimen size decreased, which lead to the increasing offriction coefficient. Finally, the model was set up and main parameters in this model werediscussed. After calculating and comparing with a sample, the accuracy of the model wasproved.5. The meso scale deep drawing mould satisfied with the experiment’s aim of this paperwas developed. Afte deep drawing experiment, the height, broke mode and wall thickness ofthe tube were observed. According the conclusions of previous chapters, the factorsinfluncing the height, broke mode and wall thickness of the tube was discussed.Also lots of experiment and research about stess-strain, friction and deep drawing mouldin meso scale foming were carried out and some progresses were obtained, but still there areseveral aspects need to be improved. Firsly, if the stress of transitional layer could besimulated or observed, the accuracy of parameter k will be improved. Secondly, if the mesodeep drawing mould could involed several more processes, more conclusions will be reached.All these aspects should be considered during the next study.