Microstamping Of Cylindrical Parts Based On Crystal Plasticity Theory

With the rapid development of precision and lightweight,the demand for micro equipment and products in all walks of life increases,which promotes the progress of micro forming theory and micro manufacturing technology.Microplastic forming has the advantages of high efficiency,high precision and low cost,and is widely used in aerospace,electronic technology,biomedicine and other fields of precision micro parts manufacturing.However,when the precision of the micro parts reaches micron level,the deformation characteristics of the materials are different from the traditional plastic deformation phenomenon,that is,there is "size effect",which leads to the macroscopic plastic forming theory is not applicable to the analysis of micro plastic deformation.Crystal plasticity theory combines dislocation motion at micro scale with plastic formation at macro scale and provides an important method for the study of mechanical behavior of materials at micro scale.In this paper,T2 pure copper foil is used as the research material under the classical crystal plasticity theoretical framework.Through the method of combining numerical simulation and experimental verification,the research on micro-stamping of cylindrical parts in micro scale is carried out.The main research contents are as follows:(1)A new material constitutive subroutine UMAT is defined to realize information interaction with ABAQUS main program;Based on the algorithm principle of Voronoi diagram,Matlab software was used to write programs to generate two-dimensional and threedimensional grain models with required boundary types.The boundary information of the model was extracted into ABAQUS by Python script program,and the material attributes were assigned to complete the establishment of Voronoi polycrystal finite element model.(2)under different process by annealing experiment material with different grain size of the experiment,based on the experiment of grain information,build Voronoi uniaxial tensile crystal plasticity model,the analysis results show that the degree of grain number,grain not neat,cell size,type of grain boundary are a great influence on the precision of the Voronoi models,optimization of the scope of influence factors;The accuracy of Voronoi model is verified by comparing the results of uniaxial tensile test.(3)The crystal plasticity model of T2 pure copper foil Voronoi microstamping was established,and the geometric optimization of grain boundary grid elements was carried out to reduce the stress concentration near the grain boundary.Through the analysis of metal flow trend and deformation in different contact areas in different stages of micro-stamping process,the forming law and forming defects of T2 pure copper foil in micro-stamping process were determined.The size effect of different grain size is studied.The results show that the grain size can cause the size effect of geometry shape and impact pressure curve.(4)The forming rules and defects of cylindrical parts under different die structural parameters were studied by analyzing the influence rules of punching pressure and deformation inhomogeneity in micro-stamping with different die structural parameters,that is,the maximum stress was mainly concentrated in the rounded corner area of the die.Under different die fillet and punch chamfering,the variation curve of punching pressure appears obvious double peaks.When the chamfering radius of the die is 0.2mm,the wall area of the cylinder is too thin,and when the chamfering radius of the die is 0.35 mm,the rounded corner area of the die is folded.When the chamfering radius of the punch is 0.1mm,the cylinder parts are pulled away and the chamfering area of the punch at the bottom occurs failure.When the chamfering radius of the punch is 0.3mm,serious stress concentration occurs in the chamfering area of the punch and the defect of excessively thick cylinder wall edge appears.(5)Micro-stamping experiments were carried out to determine the size effect caused by the grain size in micro-stamping.The top of the cylindrical stamping part is wavy.With the increase of grain size,the lug making phenomenon becomes more obvious,the forming quality of the stamping part becomes worse,and the uneven edge contour increases.The grain size will cause the impact pressure curve and the impact pressure peak size effect.