Finite Element Simulation Research On Micro-roll Forming Process

Roll forming is a plastic processing technology in which sheet metal is continuously passed through a rolling mill and transversely bent into the required crosssectional shape.It has the advantages of high forming accuracy and continuous mass production.Micro-forming process is a plastic manufacturing process that produces parts in the sub-millimeter range in at least two directions.The significant increase in market demand for micro-components has greatly promoted the development of microforming technology.In order to achieve high-efficiency continuous production of slender metal parts with small cross-sectional features,researchers have proposed the concept of micro-roll forming process.At present,the research on traditional roll forming has been relatively in-depth,but the systematic research on the complex deformation of materials behavior and the process simulation in micro-roll forming is still blank.To establish a constitutive model suitable for describing the material in micro-roll forming under special loading conditions,and to explore the high-precision and high-efficiency simulation modeling method of micro-roll forming material deformation and spring-back has important application value for micro-roll forming process production.In this paper,SUS316L stainless steel is used as the research material,through uniaxial tensile and plane strain tests,the mechanical properties and the constitutive relationship of the material are obtained,which lays the foundation for the finite element simulation of micro-roll forming.Aiming at the anisotropy of materials and the characteristics of micro-roll forming process,an improved method for solving Hill48 yield criterion parameters is proposed.According to the experimental mechanics model,the Hill48 yield criterion parameters are solved.The micro-bending test and the finite element simulation were carried out.Through comparison,it was found that the test and the simulated forming contour curve were roughly consistent,which showed that the finite element model established based on the Hill48 yield criterion can reasonably describe the bending spring-back and deformation laws of the sheet metal.According to the characteristics of roll forming process,combined with theory and practice,a V-shaped micro-roll forming process was designed.Based on the macro-size empirical parameters,the pre-research of micro-roll forming test was carried out.The test pieces were of poor quality,with defects such as large longitudinal bending,distortion,and edge waves.The micro-roll forming process parameters were optimized based on finite element simulation,and the optimized parameters were obtained from the simulation results without forming defects.According to the optimized parameters,the micro-roll forming test was verified,and the micro-roll forming test pieces with better forming quality were obtained.Through stress and strain analysis,it is concluded that micro-roll forming is a cyclic directional loading-unloading process of plane strain.The simulated cross-section profile is in good agreement with the test profile curve,and the established finite element model can effectively describe the deformation and spring-back of the sheet metal in the micro-roll forming process.In the micro-roll forming process,there are very subtle deformation characteristics,and sometimes there are even only a few crystal grains at the corners.In this case,the analysis based on macro-phenomenology is often less accurate.Therefore,this paper further explores the finite element simulation of crystal plasticity.Based on the basic theory of crystal plasticity finite element(CPFE),a crystal finite element RVE model is established based on the Voronoi diagram method.The material properties are assigned to the model through UMAT subroutine.Through the comparison of crystal plasticity model simulation and experimentation,it is found that the crystal plasticity model can accurately describe the deformation behavior of the material,and the relationship between the macro and microscopic material deformation is established,which lays a solid foundation for the crystal plastic finite element study of the microroll forming process.The foundation also provides a feasible method and idea for the further research.