Meso-Scale Modeling Of Ultra-thin Electrical Steel Blanking And Its Effect On Magenetic Properties

Non-oriented electrical steel,as the core functional materials,mainly determines the energy conversion efficiency of new energy vehicle motor.However,the manufacturing process,especially blanking,will inevitably introduce local plastic deformation,which leads to the magnetic properties degradation of non-oriented electrical steel.For the sake of energy saving,it calls for more attention on the manufacturing process of non-oriented electrical steel.In order to meet the growing demand of motor efficiency,the development trend of non-oriented electrical steel is towards thinner sheet and larger grains.Both the material intrinsic characteristics and processing geometry are down to the meso scale,which results in the occur of so called size effect.The traditional blanking technique parameters will cause more worsening of fracture edge and magnetics properties.Therefore,it is necessary to carry out the study of meso-scaled modeling of blanking ultra-thin non-oriented electrical steel and magnetic properties degradation reduction method.So far,the technical difficulties mainly include:size-effect material constitutive model and grain-size-effect fracture criteria,numerical model of blanking process considering grain size effect,and magnetic properties degradation reduction method in blanking process.This dissertation takes the blanking of ultra-thin non-oriented electrical steels as research objects.The size effect in deformation of material and the magnetic properties degradation mechanism are studied with the methods of mathematic model,experiment,and finite element model(FEM).In the aspect of theoretical model,on the one hand,both the material constitutive model and damage fracture criteria(DFC)are proposed to illustrate size effect.On the other hand,the meso-scaled numerical model of blanking process is establised to analyze the deformation and fracture of material.For the experiment design,the flexible blanking platform of non-oriented electrical steel is developed to study the influence of material intrinsic characteristics and processing geometry.For the application,a FEM assisted method of optimum clearance selection is proposed to provide a guidance for reducing the magnetic properties degradation caused by blanking.Major research work of this dissertation covers the following sections:(1)Size-effect material constitutive modeling and grain size-effect fracture criteria modelingAiming at the size effects of material intrinsic characteristics and processing geometry on the material deformation,based on the surface layer model and CMSG theory,the material constitutive model considering both material intrinsic characteristics and processing geometry size effects is proposed.The series of uniaxial tension tests and 4 point micro-bending tests of non-oriented electrical steel is conducted to identify and verify the model respectively.Meanwhile,based on the porous material theory and surface layer model,Oyane damage fracture criteria(DFC)is modified to illustrate grain size effect phenomenon in the fracture morphology.Three shapes of tension specimens are designed to identify the DFC parameters via DIC system.The modified DFC is well verified and applied in FEM simulation.(2)Grain-size considered numerical modeling of blanking processConsidering the characteristics of grain microstructure and difference of surface and inner grains,the method of Voronoi polygon is adopted.According to the surface layer model,the flow stresses of surface and inner grains can be obtained.Meanwhile,the CMSG theory is introduced.Thus the meso-scaled numerical model of blanking process is developed,differing from the traditional macro-scaled model.Through simulations and analysis,the blanking deformation is explored.The effects of grain size,thickness and clearance on the blanked edge distribution are investigated.The accuracy of model is validated with the blanking experiments.(3)Grain-size considered experimental analysis of blanking processBased on the designed blanking platform,the effects of thickness,grain size,punch-die clearance on blanked edge distribution are investigated via blanking tests.The experiment results show the grain size becomes an important factor in the meso-scaled blanking process.Compared to the macro blanking,the ratio of clearance to grain size is a new indicator guiding the meso-scaled blanking process.(4)Grain-size related magnetic properties degradation reduction method in blanking processIn order to alleviate the degradation of magnetic properties caused by blanking process,varies of magnetism tests are conducted to reveal the mechanism.The magnetism experiment results show that the quality of blanked edge directly determines the degradation level.The larger ratio of clean-cut,the less ratio of fracture,and the less degradation of magnetic properties.In further,according to the calculation of crack propagation and tool geometric angle at the crack initiation moment,the FE assisted method of optimum clearance selection is proposed to be minimize the magnetic properties degradation.Taking c/D as a new indicator,it offers an empirical guidance for industrial lamination manufacturing.In summary,this dissertation has systematically studied the size effects from material intrinsic characteristics and processing geometry on the blanking ultra-thin non-oriented electrical steel process and the mechanism for magnetism degradation caused by blanking process.The achievement of this dissertation provides the guidance for designing the blanking process parameters in industrial lamination manufacturing.