| As an important soft magnetic alloy and functional material indispensable for electric power,telecommunication and military industry,electrical steel is not only used to make transformer,generator and motor iron cores as well as ballast,relay,magnetic switch and other magnetic conducting elements,but also widely used in medical MRI scanners,high-energy accelerators,new energy vehicles and other fields.In the process of electromagnetic core manufacturing,it is necessary to first cut the wide cold-rolled electrical steel plate into strips of set width through the longitudinal shear of disc cutter,and then further cut into plate strips of set length through the horizontal shear or the strip for punching processing,with the shear processing surface directly as the component part of the product.In the process of shearing,the electrical steel plate will suffer elastic deformation,plastic shear slip and ductile fracture under the action of the cutting edge The serious residual stress near the section will damage the arrangement of the magnetic domain and the section will morphologically deflect and burr.This will decrease the permeability of the sheet metal,lower the lamination coefficient of the iron core,increase the iron loss and even cause damages to electrical equipment due to short circuit.Therefore,it is necessary to study the mechanism and technology of electrical steel shearing,so as to reduce shearing damages,magnetic loss and iron core lossIn this paper,the unique polycrystalline grain structure of electrical steel with the grain diameter up to tens of microns or even several millimeters,the cutting edge damage and burr can be reduced by optimizing the shearing process parameters,improving the sharpening mode of shear knives and adopting proper lubricant,etc.,its specific work details are divided into four aspectsFirstly,aiming at the electrical steel plates with different properties(orientation,non-orientation and grain size difference d),a systematic experiment was carried out to study the effects of the processing parameters(relative lateral clearance c/t,plate thickness,etc.)on the quality of the shear section and the hardening of material machining through horizontal shear.It is found that overall,a better processing effect can be achieved only when the shear clearance is kept appropriate.In general,if the shear clearance is too small,the cutter wears seriously;on the contrary,if the shear clearance is too wide,the section integrity becomes lower,the work hardening tends to be more serious and the shear quality becomes poorer.When the relative shear clearance is 3%-5%,a better shear section can be obtained.The smaller the plate thickness,the more serious the work hardening,and the worse the shear qualitySecondly,we have systematically studied the wear process,wear form and wear mechanism of the crosswise shear in the process of electrical steel shearing,discussed the impact of the tool wear on the shearing quality and force,and found that the oblique shear knife will suffer from non-uniform wear and have a wear belt formed on its side,which will deteriorate the shear quality.In order to reduce tool wear and improve shear quality,we have studied the impact of lubricant types(powder and liquid)on the shear quality and found that the shear effect of MoS2 powder lubricant was better than that of liquid lubricant.In line with the discovery,the tool surface roughness is matched with the lubricating effect and lubrication will optimally improve the machining quality when the tool surface roughness is Ra0.2?m;the direction of tool sharpening texture has an obvious impact on the shear quality and force.When the angle between the sharpening texture and the direction of the tool edge is 45°,it will offer the best shear quality,which provides a useful reference for the tool sharpening process.Thirdly,we have studied the mechanism of shear section formation.Based on the material tensile experiment,the deformation and fracture process of electrical steel are studied under three stress states such as shear,45° tension shear and tension,with the results showing that the stress triaxiality has a decisive impact on the plastic deformation and fracture behavior of the material.High-speed photomicrography was introduced to trace the structure flow of electrical steel plate during shearing;metallographic examination,EBSD,SEM observation of grain surface slip band and other relevant means were used to study the process of grain deformation and cross-section formation during shearing;finite element simulation was adopted to analyze the stress-strain distribution in the shear zone.All such test and characterization methods are helpful to understand the shear mechanism of electrical steel and provide theoretical basis for effective burr reduction.Furthermore,electrical steel samples with different grain sizes(31-360?m)were prepared to study the mechanism of the grain size effect on the characteristics of the shear section,and the results show that electrical steel large in grain size is more prone to shear defects and more difficult machining.The shear knife state,process parameters and material properties codetermine the shear section characteristics of materials.Moreover,the materials large in grain size are prone to defects in shear,so it is necessary to reduce the shear clearance and improve the cutting edge sharpness appropriately.Finally,the transverse and disc slitting shears were reformed and the force measuring instrument Kistler 5073A was used to set up a real-time force measuring platform for shearing process and experimentally study the three-way shear force characteristics and its impact during shearing.Systematical and experimental studies were conducted on the shear force characteristics of the electrical steel plates in different materials(orientation/non-orientation,grain size)and with different thickness(0.23-0.65mm);studies were made on the impacts of the technological parameters(such as shear clearance,plate thickness and pressing force)of the disc cutter longitudinal shear and straight cutter transverse shear on the shear forced;contrastive analysis was completed between the actual measured value and the calculated value via the traditional shear theoretical formula.It is found that the cutting edge size effect will have a significant effect on the shear force and material stress-strain states during shearing if the thickness is small.In addition,a method for identiFying disc shear cutter states based on eigenmode function energy moment and implicit Markov model was proposed to have successfully identified various faults in disc shear cutters,such as tool shutdown,idling and disc cutter radial runout. |
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