| Micro stamping technology is a plastic deformation technology of producing at least two dimensions in the dimension of sub millimeter scale(mesoscale),and is become one of the key technologies in the large-scale production of MEMS(Micro Electro Mechanical System,MEMS).With the rapid development of MEMS and its practical application,the demand for micro parts becomes more and more huger,the micro stamping technology has become an important research topic in the field of plastic forming.As the widely used and key processes for high speed precision stamping,micro blanking makes great influence on the follow-up process and product performance,and has become an important research topic in micro stamping.Fracture mechanics,computational mathematics,material science,artificial intelligence,engineering optimization and prediction theory,numerical simulation combining simulation and experimental research methods adopted in this dissertation,from the mesoscale material properties,the blanking process numerical simulation,high speed punching and cutting mechanism,the blanking quality prediction and control and other aspects,which has provided fundamental researches for the application of high speed precision blanking technology of mesoscale sheet.The main work and the results obtained in this dissertation are as follows:(1)The shortcoming of the high speed precision blanking technology for the micro-meso scale plastic forming and its facing problems are reviewed and analyzed systemically.The application prospect of high speed precision blanking technology for mesoscale sheet and its key issue need to be solved urgently are also discussed and summarized.It has been put forward that scheme using both experimental study and theoretical analysis methods to promote the application of the high speed precision blanking technology for mesoscale sheet.(2)Based on uniaxial micro tensile test of mesoscale sheet,the size effect of the mechanical properties is studied.And the constitutive equation coupled feature dimension and grain size of micro sheet metal is established,which provides the reasonable material model for mesoscale sheet forming technology research.(3)By SHTB(Split Hopkinson Tensile Bar,SHTB)test,the dynamic mechanical properties of the material under high strain rate were obtained and the rate dependent constitutive relation was established.Based on the theory of dislocation motion,the microstructure evolution and the variation tendency of the macro mechanical properties of the materials under different strain rates were compared and analyzed,which provide reliable material models and theoretical basis for high speed precision blanking technology.(4)Based on the theory of surface layer,the high speed precision blanking dynamic constitutive model of mesoscale sheet is obtained,in which size effect of material model is considered.According to the DIC(digital image correlation,DIC)based fracture toughness experiment and analysis,the corresponding blanking fracture criterion was established and predicted the ductile damage of thin sheet metal under high speed precision blanking process,.The mesoscale sheet high speed precision blanking was simulated with FEA models which combined the dislocation dynamics theory.And the accuracy of the material model and the reliability of the numerical simulation were verified by the high speed blanking experiments via comparison of blanking force and burnish length.(5)Based on blanking experiments under different speed,the influence of punching speed on the maximum punching force and blanked edge quality were studied by numerical simulation technology,and the temperature distribution of blanked edge was also observed.The morphology,microstructure and properties of blanked edge were characterized and analyzed using SEM,TEM,EBSD,and microhardness meter,.The results show that the adiabatic shear band were generated,accompanied by dynamic recrystallization produced in the local region of the blanked edge under ultra high speed blanking(SPM 1500,SPM 3000),which is due to the high deformation rate and adiabatic temperature rise.(6)A machine learning method based on SVM is proposed for the complex relationship between the mesoscale sheet and the high speed precision blanking process.Using SVM regression analysis to build the precise non-linear regression function model between the process parameters and the blanked edge quality,combining the IPSO algorithm,to optimize the SVM kernel function and get the process parameters and the quantitative relationship between the blanked edge,and to predict the blanked edge quality.The result indicates that IPSO-SVM prediction model is evidently reasonable and valid in the mesoscale sheet high speed precision blanking process optimization and its application in engineering.In order to reveal the deformation mechanics of sheet metal in the strongly coupled thermal-mechanical field generated by the intense in the high speed precision blanking process of micro metal components,the mechanical constitutive relation is studied as the key scientific problem in this dissertation by high strain rate material dynamic mechanical response test and high speed blanking experiment.Based on the analysis of the experimental results and theoretical study,this model is put forward based on the IPSO-VSM algorithm to predict the quality of the blanked edge under high speed blanking.The research results in this dissertation show that the dynamic constitutive model of mesoscale sheet in high speed precision blanking and IPSO-SVM prediction model have the important scientific significance and the clear engineering application prospect.And it gives a good new method for the high speed precision punching process optimization and the blanked edge quality prediction. |
PDF Full Text Request